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Haag

Keywords: Brittany, non polluter-non pays principle, intensive livestock rearing + ?

This paper presents an overview of the problem implications and policy solutions available for management of nitrogen pollution in the special case of the Brittany region. Firstly, the general situation in respect with water contamination is considered. Then, within the legal context, general and specific regulations are assessed. Then we deal with the agricultural pollution control programme and its implementation in Brittany ; the global cost of the programme is estimated between 12 and 16 billion Francs for the whole France. For Brittany only, this cost is bounded between 2.2 and 2.7 billion Francs. ln the final section of the paper, new perspectives of the policy are reviewed.

Considering the fact that supply facilities frequently exceed the norms, about 3o/o of the French population is served by a water having more than 50 mg of nitrates per liter. Considering Water quality, half of the 200 main French lakes (artificial and natural) are suffering of eutrophication. About 80% of the reservoirs used for public water supplies also have an excess of nutrient salts. Eutrophication is also observed in coastal waters. Lakes and reservoirs are affected by phosphorus mainly originating from municipal sources, as well as from agriculture.

Problems in marine waters are primarily attributed to nitrate from agriculture. For example in the Bay of Brest, it is estimated that 8Oo/o of the influx of nutrient salts originate from agriculture. At the national level the contribution of agriculture to nitrogen pollution is about two-thirds (Etat de L'environnement, 1993).

Even if mineral emissions from agriculture also concern phosphorous and heavy metals, nitrate concentration in groundwater and surface water have received more attention in France. This emphasis is mainly due to the EC Directive relating to the quality of water for human consumption (the Drinking Water Directive). lt is todayîidely agreed that the principal cause of nitrate increase is the change in farming methods. lncreased use of chemical nitrogen fertilizer related to a greater intensity of crop yield per hectare was an important factor.

Nitrate contamination of groundwaters did not take place overnight but over the last four decades as intensive agriculture began to take-off.

The objective of this paper is to present an overview of the problem implications and policy solutions available for management of nitrogen pollution in the special case of the Brittany region. The paper proceeds with five sections. ln the next section the general situation in respect with water contamination is considered . Then, within the legal context general and specific regulations are assessed. The fourth section deals with the agricultural pollution control programme and its implementation in Brittany. ln the final section of the paper, new perspectives of the policy are reviewed.

THE NITRATE CONTAMINATION ISSUE

This section highlights the relationship between nitrate contamination and the modern development of agriculture. Empirical evidence is first discussed at the French national level. ln a second point, the problems arising from intensive livestock are considered through the case of Brittany.

The general problem

The French agriculture has developed dramatically since the 1950s. At the end of the Second World War there was a social determination to be self-sufficient, since the difficulties in feeding the population were in everybody's mind. Consequently, price support and structure measures encouraging farm amalgamation, modernization, irrigation, mechanization and consumption of commercial fertilizers were adopted. There was also much social expenditure providing the farming sector with retirement premiums to modernize the agricultural sector. ln 1994, about only 5% of the French population work in agriculture, whilst this population reached 29% in 1949. Structural changes concerning land use occurred during this period with the transformation of permanent grassland in arable land ( Because arable land refers to land under temporary crops, temporary meadows for mowing or pasture and land temporarily laid fallow or idle, the impact of CAP reform is not clear. There were about 17 million hectares during the 1970s and the 1980s. There are now over 18 million. The high cereal price support had led to plough up pastures since the seventies. Between 1970 and 1990 total permanent grassland decreased by 2.5 million. This decrease was greater between 1990 and 1994 (more than 1 million). The transformation of meadows and pastures used permanently in arable land, and the intensification induced by high prices, led to a steady increase of the use of nitrogen, phosphates and potash (Figure 1). This period is also characterised by the large-scale use of pesticides. ln France, total pesticide use increased from 25,000 to 1 million tonnes in the 1971-1981period. Such intensification had consequences on aquifers and surface waters. The Ministry of'Health decided in 1981 to establish the extent of nitrate pollution. An assessment was made for each "département" with samples taken at public supply boreholes and rivers and reservoirs. This assessment was mainly based on 1gB0 data but it also includes Due to its geological features, Brittany has few aquifers, tertiary basins being the only exception. Underground water represents some 20 percent of the total available drinking water (164,000 m3 per day from 450 boreholes). The 668,000 m3 of surface water per day from 108 draw-off points, are drawn directly from water courses or from larger or smaller reservoirs. ln rural areas underground water accounts for a higher proportion. The quality of these water catchments is very poor, especially in areas where intensive animal rearing is combined with market gardening. For example, in the Finistère (which is one of the four "Départements" of Brittany) 2Oo/o of water catchments are over 100 mg/l of nitrates.

Because of the importance of surface water providing drinkable water and of the intensification of agriculture, Brittany has one of the worst situation in

France. A third of water supply facilities occasionnally exceed 50 mg/l of nitrates. lf physical constraints concerning the volume of water needed for fishes and qualitative constraints concerning the evolution of the nitrate concentration are taken into account there will be a shortage in 2005 ; this will reach22o/o.

THE FRENCH LEGAL CONTEXT

The legal background of pollution associated with agriculture contains both general regulations and more specific ones.

3.1. Water protection Among the general ones, the Water Act of December the 16th of 1964 relates to the management and distribution of water and to the control of water pollution. This act created the qualitative and quantitative management system for the six major French hydrographic networks through advisory basin committees and executive basin agencies (The "Agences Financieres de Bassin", i.e. Water Authorities). Under that act, these agencies determine and define quality targets for watercourses. Quality and flow problems are viewed economically through a system of charges. Pollution discharges are also subject to strict standards.

A key feature of the WaterAct of 1964 was the establishment of a system of charges on water pollutants. This new direction in water policy was in line with the polluter-pays principle but it was restricted to point pollution sources. Charges cover a wide variety of pollutants. They are set through a complex procedure in each Water Authority. Water Authorities also collect the payment of charges whose revenues are then redistributed to the dischargers through the use of grants, soft loans and rewards for abating pollution. Where controlling and monitoring are feasible at low costs, charges are based on individual performance. The Water Act of January the 3rd of 1992 is a more comprehensive act which proposes a balanced management of total water resources. The aim is the protection of the aquatic ecosystems and wetlands, the protection of the quality of surface waters and groundwaters, and a better use of water from an economic point of view. To achieve this balanced management new watershed management schemes were set up.

Specific regu lations

Here we examine specific regulations concerning classified installations and the implementation of the EC Nitrate Directive.

a) Classified installations and intensive rearing

Ïhe Act of July the 1gth of 1976 on classified installations for environmental protection, and its implementation orders supercedes the 1917 Act on hazardous establishments which did not cover intensive rearing activities. An activity coming under this act has to be classified, i.e. listed within a given nomenclature. This applies to livestock rearing installations of a certain size.

According to size there is a reporting regime, i.e. "déclaration" or a permission regime, i.e. "autorisation" (Table 3). The permission regime is more exigent, since the applicant has to provide an impact assessment giving details of the source, nature and magnitude of any disamenities liable to result from the installation concerned. Disamenities include noise, use and discharge of water, the protection of underground waters, and waste disposal. France. The latter explains how to define the vulnerable areas at the regional level.

A task force was set up in each "département" to improve coordination and information. The zoning is based on the average level of nitrate concentration during the past years. Waters for which the level of NO3 is over 50 mg per litre are automatically considered as polluted waters. Consequently the area is classified as "vulnerable". Waters under 25 mg are supposed safe. Special attention is paid to intermediate levels of nitrate concentrations. Time-series are set up in order to define any possible trend in an attempt to foresee any possible problem areas. If the trend indicatesa level of NO3 over 50 mg in 2005, the aquifer or the river is classified as polluted. ln the waters where nitrate concentration reaches 40 mg per litre and where time-series data do not exist, the pollution is considered as apt to occur in the very near future. sources. ln 1982 the water authorities proposed a system of charges per pig according to the number of places available and slurry spreading quality. However this system never entered into application because farmers' unions were against it.

ln June 1991, the French government decided to combat against water pollution caused by nitrates from agricultural sources and to introduce a levy on nitric nitrogen. The aim was a progressive introduction of the polluter-pays principle into agriculture as was already the case for other activities. To achieve this purpose, a special agreement was concluded between the Ministry of Environment and the Ministry of Agriculture on March the 11th of 1992. This agreement includes the various European Directives related to water quality and that concerning the protection of waters against pollution caused by nitrates from agricultural sources.

Even if priority is given to preventive means, especially advice to farmers (more efficient application of fertilizeÏb by more accurate timing or rates of application and a better use of animal waste), the place of economic incentives is important. Subsidies are provided to encourage farmers to reduce their pollution by using methods more compatible with the environment, by preventing water pollution by run-off and the leaching of liquids containing livestock manure and effluents from silage, and by processing manure. We will first review research and extension programmes and we will then consider the charge system and the compliance scheme. The coRPEN has been made responsible for preparing programmes to improve certain agricultural operations in order to reduce the nitrate leaching and nitrate run-off. lt promotes research projects on technical issues and provides advice to farmers. This committee has also elaborated codes of good agricultural practice adapted to local conditions. I

Water effluent charges

The extension of the charge system achieves a process originated in the late sixties. The basic principle to determine the amount of the charge remains the same. At the moment, these charges cover four susbstances, for livestock farming : suspended solids, oxidisable matters, reduced nitrogen, phosphates. ln the future, other substances e.g. heavy metals and some organic toxins would be taken into account. There are three steps in calculating the levy. (i) Emission in physical units are calculated for each pollutant and each category of livestock (dairy cows, pigs, poultry ...). This is based on industry average since technical coefficients are used to transform number of animals into quantity of polluting substances. Then monetary coefficients are used to obtain a gross charge per farm. These coefficients are pollutant specific and do not vary according to the various industries. (ii) Farms are classified according to a number of parameters including manure stôrage facility capacity, sitting of the buildings, run-off from buildings, manure spreading scheme and livestock density. This process leads to I environmental classes which are based on individual performances. The abatement of polluting emissions is then estimated for each farm. This outcome is converted into monetary terms in order to obtain a premium per farm. (iii) Net charge is then obtained, that is to say the difference between gross charge and premium. The charge system and specially the technical coefficients result from negotiations between parties and therefore bear the characteristics of a compromise. lt must be underlined that net charges don't include either suspended solids or phosphates because a 100 percent abatement is assumed forthese two substances. Farmers will finally have to pay net charge if it is lower than 6458 FF (in 1996), which corresponds to 200 population equivalent. This is the monetary equivalent of farmers' rights on the environment.

The charge system was planned to be gradually enforced, with the following calendar:

for those rearing installations classified before January the 1st of 1991 charges will be paid from January thê 1st of 1993.

for those rearing installations classified during '1992 charges will be paid from January the 1st of 1994.

I

for the whole animal husbandry and crops the charges will be paid from January the 1st of 1995.

For each category subsidies will be given during the year before the levies are charged to help the farmers to meet the standards required. This system was criticised from a theoretical point of view because the regulatory mechanisms to control non point source pollutants are more intricate to implement than those concerning point source pollutants. There are different cost structures for the acquisition of information and informational asymmetries between polluters and regulators can be found. From a political point of view, French farmers protest against the proposed calendar and also against the principle of taxation itself. The farmers'unions argue that agriculture is a special case because of the particular circumstances of the farming economy, of agricultural pollution and agricultural policy. Concerning the levies on intensive animal rearing, pig producers argue that the tax is unfair because mineral fertilizers are not taxed. From an economic point of view the large increase in European pig production has caused prices of pork to fall sharply from around 150 Ecu/100 kg in the summer of 1992to 125 ECU by mid-October before sinking to arounà 1OO ECU in April 1993. Given the continuing increase in pig production foreseen in the EC, there seems to be little prospect of prices increasing over the coming months. So their financial position has deteriorated and they refuse to accept any extra cost.

All these elements led the former government to delay the application of the taxation system. Finally, the biggest farms entered the scheme in 199s. The process is expected to be achieved within a five-year period. Moreover in order to reduce the effect of the charge system on farm income, there is a transitory period during which eligible farmers will only support a fraction of the total amount. For example, in 1995 eligible farmers will have to pay 40 percent of the total, in 2OOO, 76 percent. This process is expected to be achieved in 2003 when farmers will pay the total amount of the charge.

Compliance scâeme

All the required information i.n calculating charges are provided by an environmental audit. This is a compulsory assessment of the farm in terms of its environmental impact. The statement is named DEXEL (diagnostic environnement de I'exploitation d'élevage i.e. environmental audit of the livestock farm). This statement includes two main sections : (i) a detailed description of polluting emission flows with emphasis on building sitting, storage facilities for manure, run-off, leaching and infiltration.

(ii) an assessment of agricultural practices whose main outcome is. a nitrogen balance both on the plot and the farm level. This focuses on the sources of nitrogen surplus. This statement is used to start a negotiation between each eligible farmer and the basin agency. The objective is to achieve individual agreements whose prescriptions deal with the improvement of farm buildings and the promotion of better farming practices. When investments are agreed on, they are subsidized by the state, by regional and departmental authorities (30% of the amount) and by the basin agency (also 3oo/o of the amount). lt must be emphasized that, in addition to the section on building improvements, any contract includes precise prescriptions on farming practices. There are financial and technical commitments involving a classification of the farm in a better environmental class leading to a reduction in the charge amount. Thus before contracting with the agency, every eligible farmer has to trade-off between the extracosts of compliance and the benefits in terms of charge payment. ln return for the conformity of buildings, until 1998, the State and Waters Agencies pay the fee the farmers should pay for pollution. From an environmental point of view, the attribution of a perception threshold can be analysed as a property right of the nature for breeders. At the production level Qo, it corresponds to an alteration of nature equivalent to area [SAB] on Figure 2. ln fact, the social marginal cost C," is equal to the sum of the private marginal cost C'.o with the monetary evaluation of the social damage (positively counted) and amenities (negatively counted). Thus, the attribution of a perception threshold can be justified as a remuneration of eventual positive externalities coming from certain regions or production systems (area at left of S). ln fact, the calculated fee underestimates the social damage valorisation. lf there was no perception threshold, the amount to pay would be equal to [SCD] at the level of competitive supply Q". Let us suppose now that the social damage valorisation is approximated by the social cost of the agricultural pollution control programme, which is higher than the perception threshold. This valorisation implies a decreasing of the damage and the two curves C." and C,no come closer. lf the polluter-pays principle (PPP) is strictly applied, the C'o curve comes closer the C," one and the supply level is Q" lower than Q". on the contrary, the public aid associated to the non polluter-non pays principle (NPNPP) gives a supply level between Q" and Q". The equilibrium level will be all the closer to Q" as the agricultural pollution control programme can induce productivity savings making C'no fall. Figure 1 shows a continuity of situations, but in reality there are very different technologies. ln practice, the two curves Cn.o and C'n" don't always become equal because the agricultural pollution control programme doesn't resolve all the environmental problems. That's why certain breeders will have to pay the fee, for example because of wrong spreading practices. Otherwise, if the state arbitration takes care of the appropriateness between the damage and its internalisation cost, the private arbitration is made between the farmers' financial participation for the agricultural pollution control programme and the fee reduction or productivity savings induced.

From a sample of 500 farms in the "Great West" of France (most of them are integrable in 1994 or'1995), the economy department of INRA-Rennes studied the cost of the environmental programme. The agricultural pollution control programme cost divided by the number of UGB (that is to say 73 kg of nitrogen produced by year) varies with the technical orientation of the farm. Table 4 below indicates this unitary cost calculated with the available data for 1994 and 1995.

Table 4 Cost of the agricultural pollution control programme in 1994-95 for each farm technical orientation This table points out differences between costs varying from 1 to 3. They can be explained by the act on classified installations : the application was stricter for soilless breedings, especially for storage capacities. Thus, bovine breeders still have works to make. The first econometric estimations allow us to see the effect of a 5o/o increase of the animal production level (bovine or soilless) on the cost of the agriculture pollution control programme (Table 5). The negative sign for the soilless breedings with a bad initial environmental situation is the effect of the act on classified installations : the cost for the agriculture pollution control programme only is in reality a supplementary cost, decreasing with the breeding size. So, concerning the renovation works which are to be made, soilless breedings out of a structural excess area are favoured. Requirements in relation with nuisance emission are stricter in areas where spreading possibilities are insufficient. However, in each case, an increase of the production level enjoy economies of scale for renovation work cost. Whatever the production, the marginal production increase will be cheaper (in term of renovation work cost) for breedings having a quite good initial environmental situation.

The study of factors explaining the unitary cost of the programme allows us to calculate a global cost of the agricultural pollution control programme. Thus, we statistically have three types of effects :

. a size one because of economies of scale, in particular for storage buildings.

For the next years, the unitary cost should increase : with a base 100 in 1994-95, we should obtain 138 in 1990, 140 in 1997 and 150 in 1ggg.

an initial environmental situation one. The cost is all the more important as the initial situation is bad. To calculate the cost in the next years, we have to make hypotheses about the number of farms with a bad initial class of animal waste salvage (17.5o/o for soilless breedings and 4so/o for the other onesestimated from the actual sample) a a a spreading surface one : the smaller it is, the higher the cost. To extrapolate the results, we suppose that the next integrable breedings have a spreading surface proportionally equal to that of currently integrable farms.

Knowing the number of integrable farms for each year of the programme, and the number of UGB it represents, we can calculate the global cost of the programme corrected by the effects announced above. Making some hypotheses, the global cost of the programme is estimated between 12 and 16 billion Francs for the whole France. For the only Brittany, this cost is bounded between 2.2 and 2.7 billion Francs. The cost for Brittany represents around 18o/o of the total amount for the national programme. ln fact, this rate is higher in the first years of the programme because of the regional cattle population : it's estimated around 40olo

for 1994 and 1995. We must finally notice uncertainties about the number of integrable farms and the quantity of pollution they represent, which must be underestimated. That's why we can suppose the real cost is in the upper part of margins. The estimation is so-doubled in comparison with the 7 billion Francs estimated at the beginning of the programme.

CONCLUSION

The new policy implemented in the livestock sector relies on the same basic principles which have steered water policy for three decades. Enforcing charges on polluting emissions from livestock farms is a straighforward application of the polluter-pays principle. This could give farmers a good incentive to reduce emissions. But in contrast with other industries there is a huge number of farmers thus establishing environmental audits and agreeing on individual contracts. lt is potentially very costly for the public budget. Transaction and administrative costs could represent a significant proportion of total expenditures. Moreover control and monetary issues received little attention. Future development of the policy will depend on future compromises between public authorities and farmer representatives. The present balance between farmers and public interest benefits farmers. But things could change in response to different political and environmental pressures. The crucial issue will be the benefits (market and non- market) of this programme for society. Great attention will be devoted to the evolution of freshswater nitrate content and of coastal waters eutrophication. These are the key parameters for the general public.

The agricultural pollution control programme stake is very important if we consider the degradation of water quality in some regions or its cost. The first interrogation. is about the efficiency of the programme. ln structural excess areas, where spreading surfaces are insufficient, the successful outcome of the programme depends on animal waste treatment installations with an acceptable cost. But, for now, those installations aren't absolutely technically efficient and their cost is high. Moreover, it can induce a concentration of farms because of economies of scale in individual or collective treatment installations. This risk is all the more important as those processes allow a decrease of the necessary spreading surface.

Finally, for breeders who do not comply with the classified instailation regime, because of an overproduction of more than the 25o/o of the strength of herd authorised, the renovation works financing agreement allows a regularization of their situation. Thus, the community confirms illegal practices of such farmers.

Tl'rere is here an equity problem if we think of the farmers who had made renovation works before and without any aid.

Figure 1 .

 1 Figure 1. Consumption of commercial fertilizers (Nitrogen, Phosphate, Potash) 1970-1992

  AGRICULTURAL POLLUTION CONTROL PROGRAMME Since 1975 there has been a clear legal basis to levy charges on non-point

4. 1 .

 1 Research and extensionSince 1984 the French Government has set out the Standing Committee for the Study of Nitrate Pollution (Comité d'Orientation pour la Réduction de la Pollution des Eaux par les Nitrates et les phosphates provenant des activités agricoles i.e. CORPEN).

Fiqure

Table

  1

Table 1 .

 1 Evolution of arable land and permanent grassland (1,000 ha)

in rural areas where intensive agriculture is dominant. This suggests that there has been an improvement in the quality of the water distributed. ln fact, this improvement does not correspond to a decrease in nitrate concentration in raw water. lt is rather due to the blending of high nitrate supplies with low nitrate sources, the use

  available data for 1979 and 1981. The same inventory was carried out in 1988 and 1993. ln Table2the situation in 1980 is compared to the situation in 1988 and 1993. The distribution of inhabitants according to the quality of drinking water supplied (mean annual nitrate concentration) is also given. The number of persons exposed to high nitrate concentrations has decreased. The supplies where nitrate concentration exceeded 50 mg tend to be located of water of new aquifers, or the treating of water by chemical or biological way to remove nitrates. lt is clearly demonstrated by the increase of the number of water supply facilities in which nitrate concentration exceeds 50 mg/l once a year.

Table 2

 2 Eaux destinées à la consommation humaine-Ministère des Affaires Sociales-Direction Générale de la Santé-Déc 1993 2.2. Intensive livestock rearing and water contamination ïhe development of intensive livestock rearing and its concentration in particular regions has created another important source of nitrogen pollution : that from animal waste. The main part of organic nitrogen is deposited directly on grassland by grazing animals. This poses a lesser problem than high concentrations of organic nitrogen found where there is a high animal density, namely pigs and poultry. ln France, Brittany is the region where intensive animal husbandry is the most important. ln 1994, pig production in Brittany represented 51.2 o/o of the French one. This proportion is lower for poultry. Total chickens, turkeys and guinea fowls represented 30.4 o/o of the French total. For eggs, this proportion is 28.6 %. The total agricultural output for Brittany represents 12o/o of the French total, although the agricultural area accounts for only 5 % of the corresponding French total. The comparison between these two figures (12 o/o of the output and 5 % of the area) gives an indication of environmental problems in Brittany.

	. water Supply Facilities (wsF) and population served with a nitrate
		concentration over 50 mg/l
			1 981		1 988		1993
		WSF	population	WSF	pooulation	WSF	population
	average concentration over 50 mq/l	584	1 160 000	707	860 000	689	720 000
	exceeding Q0 mg/l once a year	1 010	2 180 000	1 074	1 700 000	1 308	5 100 000
							4

Source :

Table 3 .

 3 Legal regime for classified livestock rearing installations according to species and size b) The EC Nitrate Directive and its implementation Ïhree administrative circulars were elaborated by the French authorities, in March 1992, June 1992 and November 1992 to implement the Nitrate Directive in

Table 5 -

 5 Effect of a 50,6 increase of the animal.production level on the cost of the agricultural pollution conkol

	212	69	77	22	81	33
	770	2540	2130	630	1550	1380
			programme


K Latouche
email: latouche@roazhon.inra.fr

Farm animal welfare: French perception through Contingent Valuation Method

This paper deals with French concerns about Farm Animal Welfare (FAW) and their Willingness To Pay (WTP) to support FAW improvement. To elicit respondents''WTP, Contingent Valuation Method (CVM) was used, whereas this method is still criticised. The WTP to support FAW improvement in different production systems is expressed as an increase of the market price of four different products: one kilo of escalope of veal, one kilo of white ham, a dozen eggs and one kilo of beef (steak cut from the ribs). This survey, interviewing 1009 persons, shows that French people are very concerned about FAW. Some production systems have clearly been classified as unacceptable. French producers and public decision makers will have to take these results into account. They are in fact a good indicator of French public opinion and assess the perceifed benefits of farm animal welfare policies. Four econometric models aiming at determining the main variables which explain the WTP elicited to support improvement of animal welfare are proposed. They show that people who feel concerned with farm animal welfare express a greater WTP than the others for improvement in welfare of veal but express the same WTP for the welfare of hens, porks and oxen as the others.

Introduction

Farm Animal Welfare (FAW) has become a major policy issue in European Union in recent years. The United Kingdom has played a key role in promoting cause of animal welfare and it continues to be strengthened, by scientific advice of FAW council and by FAW interest groups lobbying [START_REF] Bennett | People's willingness to pay for farm animal welfare[END_REF]. Facing consumer pressure and growing concern in North European countries, for example by a growing demand for free-range animal products (Winter & al, 1998), legislation has been one of the main responses to this growing concern. ln 1992, the FAW issue was under the treaty of European Union in a declaration on the protection of animals binding on all EU Member States (Council of the European Communities and Commission of the European Communities,1992).

Today, Member States have to implement European directives (86lI13lCEE for hens, 9I/63O/CEE for pigs, and 97l2lCEE for veal). But to assess FAW policy, as for any policy, costs and benefits have to be valued. This paper deals with benefits of FAW issues. Because the benefits have OOCUl\]lEliTATIOl\l ÉCOIIONII RUMLE REl\ll.lES I r ililt ilil ilil lllll lllll lllll llll llll i(004654)l( the characteristics of non-market goods, it is necessary to use specific methods such as Contingent Valuation Method. As Bennett has stated (Bennett, L996), this method can be applied to evaluate benefits of the Animal Welfare issue by estimating how much respondents would be prepared to pay for it.

Whereas this method seems to be the most adjusted to the good considered here, two main types of criticisms are still available.

Firstly, FAW can be valued by respondents as a use value or a non-use value (or existence value). If respondents consider that improvement of FAW also improves the quality of livestock products (that is to say as a use value), then the commodity to be valued is well defined and the CVM is reliable (Lazo & a:,92). But if respondents accept to pay to buy an ethical or moral satisfaction, the commodity to be valued is no more well defined or centred and the choice of the vehicle of payment remains a problem. One of the main problem in valuing FAW issues is that they can be considered as improving livestock products quality and improving moral satisfaction of the respondents. The survey used to study this subject must then take into account these two aspects of FAW issues.

Secondly, the main assumption of CVM is that responses to CV questionnaires may be interpreted as an expression of respondents preferences. However, after the BSE crisis beef was still bought in large part in supermarkets at a cheap price, whereas people interviewed in a CV survey reveal a high willingness to pay to get safer beef (Latouche & al, 1998). In fact, results to CV surveys compared to actual behaviour seem in most cases paradoxical. These situations show that public motivations rather than private ones are involved (Blamey & al,1995). People answer to CV surveys as voters instead of consumers because of a great ethical concern. Over the quality impact on livestock products that can be valued by respondents, the improvement of FAW can also improve a moral satisfaction. Then respondents may answer CV surveys as citizens. Hence, their willingness to pay reflect what they think to be a reasonable decision by the government (Johansson-Senman, 1998).

Even if those responses are considered as biased by CVM detractors, governments and public decision-makers have to take these responses which prove ethical motivations about animal welfare issues into account.

Method

A sample of 1054 persons was interviewed during summer 1998. 1009 questionnaires were completed and usable out of the 1054 administered. The questionnaire considered four main types of information.

The first part deals with concerns about FAW. Opened-questions are asked to determine the knowledge of people about the current ways farm animal are bred. Respondents have also to state the breeding conditions which seem unacceptable to them.

Then an hypothetical scenario is presented to them. It aims at eliciting their WTP to support an improvement in FAV/. The way of improving it is an increase of crates used for veal, pigs and hens. The vehicle of payment used in this survey is an increase of the livestock products prices to compensate the increase in producers' costs. The livestock products considered are: one Kg of escalope of veal, a dozen eggs, one Kg of white ham and one Kg of beef (steak cut from the ribs). The currents prices of these products are given.

Respondents are then asked about their livestock product consumption habits. Especially, the frequency of consumption of different products are stated.

The last type of information asked is related to the socio-economic variables of respondents'

Results

Out of the 1009 respondents , 52.2 Vo were women. The distribution of the respondents according to their age is homogeneous. People over 65 years old represent 20Vo of the respondents and constitute the most important class of age. 58.6 Vo of the respondents are married, and 52.8 7o have no child at home. Among the sample, 50.2 To of respondents have employment. Most of respondents who are unemployed are either retired (47 .4 Vo) or housekeeper (23.9 7o).

As for the level of education, according to the International Standard Classification of Education of UNESCO, 14.8 Vo of rcspondents have a diploma coresponding to compulsory education, 24.3 7o to lower secondary education, 10 7o to upper secondary education and39,4 Vo to higher education. 9.8 Vo have no diploma. Most of respondents (58.5 7o ) have got pets.

Concerns about Farm animal welfare

The first part of the survey reveals a gfeat concern of respondents for farm animal welfare. 81 Vo of the respondents havealready heard that farm animals may be mistreated or suffer during the production process (breeding, transporting and slaughtering) . Most of them heard about it on TV news (73.5 Vo) or on other TV broadcast (31, Vo). Around 73 Vo of respondents feel concerned for breeding, transporting and slaughtering processes of livestock. The most worrying query is breeding process for 42.7 7o of respondents, transporting process for 32.17o and slaughtering for 17.l7o. Only 8 .2Vo of respondents do not worry for any of these three queries.

Open questions have then been asked to determine respondents' opinions about current agricultural processes. Respondents still remain very concerned by the BSE crisis. 26.17o of respondents state that farm animals being badly fed is an unacceptable situation. In fact, they condemn the process leading to feed cows with animal meals. Other unacceptable agricultural practices involve the use of battery for 21.8 7o of respondents, confinement for 20.4 Vo and ensive processes for 19.2 Vo.

At last, respondents were asked to state how either acceptable or unacceptable they consider specific aspects of livestock production systems to be. For 57 7o of tespondents battery egg production where hens are kept in small cages is very unacceptable. For 66 Vo veal production with calves kept in confine crates is very unacceptable. Only 14.5 Vo and 9 Vo rcspectively consider these systems as acceptable (either relatively or completely).

Willingness to pay to support improvement of farm animal welfore An hypothetical scenario is presented to respondents. It proposes improvements in production systems by increasing the size of crates and cages , for veal, hens and pigs. But these improvements also increase production costs. Around 80 Vo of respondents state that they would support products from such production systems. People refusing to support them state that the increase in costs has not to be paid by consumers (24.2 7o) or thatthe taste of such products will not be changed (I5 Vo).

Questions about willingness to pay (WTP) to support improvement in FAW have a high rate of acceptability. Around 80 7o of respondents agree to pay higher prices for livestock products coming from production systems improving FAW.

For one Kg of escalope of veal at FF 80. initially, the mean WTP is FF 17.8 higher, which represents 22Vo of the initial price. Only 5 7o of respondents refuse to pay and state a null WTP.

For one Kg of White ham at FF 60 initially, the mean WTP is FF 19.6 higher and represents 33 Vo of the initial price. 13 7o of respondents state a null WTP. The rate of acceptability is lower than for veal.

The same happens for a dozen eggs. The initial price is FF 15 higher. The mean WTP reaches FF 16.9, with a very high standard deviation. It represents II2Vo of the initial price, which is very important. But respondents with a null WTP represent 16 7o of respondents.

For one Kg of steak cut from ribs whose initial price is FF 80, the mean WTP is FF 16.9 higher. It represents 2I Vo of the initial price. It is the lowest percentage increase. Around 13 Vo of respondents state a null WTP for this product.

For all these WTP questions, respondents provided a statement of reasoning for their responses. People highly concerned about FAV/ in the first part of the survey are those who reveal a high WTP. These results are particularly consistent for improvement in veal production system. There is a higher degree of consistence then for the other products.

Explanatory factors of the WTP An econometric model is proposed to explain the value elicited by respondents to support improvements in the veal breeding process to take welfare into account. This model deals with WTP to support an increase in the size of veal crates, because of a higher degree of consistence of responses than for other products.

The model used is a tobit model.

For one Kg of escalope of veal, four main variables have a key role. The occupation level of the respondent's wife or husband has an impact on the level of the WTP stated by the respondent' This is the only socio-economic variable which is significant. Three other significant variables appear; they are opinion variables. Respondents who feel concerned with FAW accept to pay higher prices. In the same way respondents "not really" accepting veals in crates accept to pay a lower price than respondents who do not accept such a breeding process. The last opinion variable playing a significant role is the affirmation "modern breeding has lots of disadvantage for animals".

Respondents agreeing this statement accept to pay higher prices. These variables, except the variable "feel concerned with FAW", appear to be significant in the choice of the WTP revealed for all the products concerned in this study.

'We can state the influence of the WTP revealed for the escalope of veal in the WTP revealed for ham, eggs and steak. It means that respondents consider the first WTP they reveal as a guide or a scale for the other WTP they have to reveal.

An other variable appear in the other models. It appears that women accept to pay higher prices for one kilo of white ham and one dozen eggs. It is also interesting to note the role of the political party of the respondent in the level of prices accepted for one kilo of white ham, one dozen eggs and one kilo steak cut from the ribs.

Conclusion

The main issue that can be drawn here is that French people seem to be very concerned with FAW. This survey aims at assessing the perceived benefits of farm animal welfare policies. French government and public decision makers have to take these results into account, whatever the joint products to FAW improvements are (a better quality of products or a moral satisfaction of giving or warm glow effect). Whereas the scenario used in this survey was not very detailed and did not explain the good to value, people accepted this scenario and provided a WTP to support an improvement of FAW.

Of course it cannot be stated that people eliciting a high WTP in this survey would effectively buy products from production systems respecting FAW at a higher price. We do not know if respondents have answered as citizens or as consumers. This question will have to be solved in following surveys, especially using focus groups, and hence a more detailed scenario. This could also permit to differentiate the use value with the non-use one in the value that consumers attribute to FAW.

A detailed scenario for each product considered in this first survey could lead to a differentiation in the revealed WTP. The WTP revealed would not be a function of the first WTP revealed in a global survey. Such a survey is now led in France. The results for laying hens will be available in September. The same survey is to be led for veals, and porks. Arendonk ,preciation to taly),


Bérangère Farges
email: berangere.farges@polytech.univ-bpclermont.fr

Céline Laroche

Jean-François Cornet

Claude-Gilles Dussap

Spectral Kinetic Modeling and Long-term Behavior Assessment of Arthrospira platensis Growth in Photobioreactor under Red (620 nm) Light Illumination

Keywords:

The ability to cultivate the cyanobacterium Arhtrospira platensis in artificially lightened photobioreactors using high energetic efficiency (quasi-monochromatic) red LED was investigated. In order to reach the same maximal productivities as with the polychromatic lightening control conditions (red + blue, P/2e -= 1.275), the need to work with an optimal range of wavelength around 620 nm was first established on batch and continuous cultures. The long-term physiological and kinetic behavior was then verified in a continuous photobioreactor illuminated only with red (620 nm) LED, showing that the maximum productivities can be maintained over 30 residence times with only minor changes in the pigment content of the cells corresponding to a well-known adaptation mechanism of the photosystems, but without any effect on growth and stoichiometry. For both poly and monochromatic incident light inputs, a predictive spectral knowledge model was proposed and validated for the first time, allowing the calculation of the kinetics and stoichiometry observed in any photobioreactor cultivating A. platensis, or other cyanobacteria if the parameters were updated. It is shown that the photon flux (with a specified wavelength) must be used instead of light energy flux as a relevant control variable for the growth. The experimental and theoretical results obtained in this study demonstrate that it is possible to save the energy consumed by the lightening device of photobioreactors using red LED, the spectral range of which is defined according to the action spectrum of photosynthesis. This appears to be crucial information for applications in which the energy must be rationalized, as it is the case for life support systems in closed environments like a permanent spatial base or a submarine.

1-INTRODUCTION AND OBJECTIVES

The use of artificially lightening controlled photobioreactors (PBR) seems a very promising technology if the production of high valuable compounds from photosynthetic micro-organisms is to be envisaged. PBR are also of major interest as main operation in biological life support systems. Such complex artificial ecosystems as the MELiSSA project of ESA (http://www.esa.int/SPECIALS/Melissa/) aim at recycling CO 2 gas, liquid and solid wastes produced by a crew in water, food and oxygen inside a thermodynamically closed system (a lunar or Martian base for example). In these systems, the two critical points are the size (or mass) of unit operations and their energy consumption. This is also the case if a previous sub-system and small scale demonstrator is envisaged for a flight onboard the International Space Station such as the Biorat project [START_REF] Hermans | Preliminary evaluation of Biological Life Support in space environment[END_REF], in which the atmosphere revitalization of a consumer compartment (two mice) is ensured by a fully controlled PBR artificially lightened. In order to minimize in all cases the electrical power consumption of the PBR, the artificial light sources have to be optimized. This can be done by seeking light sources having the best energetic yield for radiation emission or more rigorously, taking into account that photosynthesis is a photonic process, with the best quantum yield. It is well known indeed that water photolysis and charge separation processes at photosystem II (PS II) require a photon of 680 nm maximum wavelength (a minimum energy corresponding to a gap of 1.8 eV). Consequently, a non-negligible part of all the visible photons of shorter wavelength energy is dissipated as heat while photons of longer wavelength cannot participate in charge separation process, their energy being also released as heat. As a consequence, one of the most powerful light sources is likely to be LED (using a wavelength as close as possible to 680 nm) with today a good quantum yield among all the possible existing technologies (and likely to increase significantly in the future decade). This advantage, which makes it possible to save electrical energy and to avoid problems of heat rejection control is counterbalanced by the necessity to operate with quasi-monochromatic light, but the use of LED requires the knowledge of its long-term effect on any photosynthetic cultivation in PBR.

If the effects of monochromatic light on short-term kinetics of O 2 evolution have been indeed investigated for a long time, both on eukaryotic microalgae and on cyanobacteria leading to the so-called action spectrum for photosynthesis (strongly different for these two kinds of micro-organisms), the physiological, kinetic and stoichiometric effects of long-term cultivation in continuous PBR are not well documented today. Despite a large amount of qualitative work on the effect of using monochromatic light sources for photosynthetic micro-organisms cultivation (2-7), very few quantitative results have been obtained on cyanobacteria except for the work of Wang et al. [START_REF] Wang | Effects of using light-emitting diodes on the cultivation of Spirulina platensis[END_REF], who has only considered batch cultivations in Erlenmeyer flasks. There is then an important need for studying both the kinetic and related stoichiometric aspects of the well-defined quasi monochromatic light inputs on controlled PBR, first in batch conditions and finally on long-term continuous cultures, enabling us to confirm the potential interest of this approach.

The aim of this paper is first to determine the best quasi-monochromatic wavelength compatible with the objectives of reaching the highest biomass and O 2 productivities (related by the photosynthetic quotient, i.e. the global stoichiometry) together with the lowest energy consumption, and secondly to establish and prove that it is possible to envisage a long-term cultivation in a controlled PBR operating in continuous mode. For this purpose, a theoretical investigation of the problem is first led and a predictive knowledge mathematical model for growth in PBR is developed. This model is based on the previous work of the authors [START_REF] Cornet | Kinetics and energetics of photosynthetic micro-organisms in photobioreactors. Application to Spirulina growth[END_REF][START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF][START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF] and enables coupling a fully-predictive light transfer description in the PBR with a knowledge formulation of photosynthetic kinetic rates and stoichiometry from the definition of a quantum yield. This approach, previously established for polychromatic (white) light illumination of the PBR (like all the models of the specialized literature), is generalized for monochromatic illumination leading to a fully-spectral mathematical model (including spectral kinetics coupling) which is formulated in this paper for the first time. In this study, the cyanobacterium Arthrospira platensis was chosen for its high potential interest for the atmosphere regeneration objective for life support systems with high pH of cultivation favoring a good CO 2 mass transfer and a low CO 2 content in the crew compartment. The result of the theoretical model, based on the action spectrum of photosynthesis for Arthrospira has demonstrated that working with red LED around 620 nm of wavelength enables us to obtain the same biomass productivity as polychromatic white light. For this reason, in a first experimental section, a red (620 nm) LED panel of high quantum efficiency has been built and its ability to reach (at the same incident photon flux density on the PBR) the same kinetic productivity in batch and continuous cultures as a control polychromatic (red + blue) LED panel was validated. Furthermore, in a second experimental section, the long term (30 residence times) cultivation in continuous PBR using the red (620 nm) LED panel was investigated and performed at a higher incident photon flux density. In both cases, the results obtained were compared with the theoretical predictive model independently developed in this work. Because this model establishes a theoretical link between the stoichiometry observed, the P/2e -ratio for photosynthesis and the quantum yield (i.e. the kinetic aspects) with the radiant light transfer (the physical limitation by light) and the spectral quality of light, special attention has also been paid on the possible physiological regulation mechanisms of the photosynthetic apparatus which might result and the main photosynthetic pigment contents have been assessed during the long-term continuous experiment.

2-MATERIALS AND METHODS

2.2-Lighting source

The objectives of this work being to demonstrate that it is possible to cultivate cyanobacteria (mainly A. platensis) using monochromatic light (in the range 620-630 nm, see modelling part 3 and the spectral efficiency curve) with the same efficiency as polychromatic white light, we assembled two different LED panels. The first one was conceived as a control panel using polychromatic blue and red LED (the green radiation being poorly absorbed by photosynthetic pigments), in order to rigorously match the photosystem functioning. For this purpose, we chose red and blue LED with the same quantum yields (see Table 1 and Appendix), the number of each type being adjusted to obtain a P/2e -ratio of roughly 1.3 (see Table 2, stoichiometric equation of part 3 and Appendix) corresponding to the mean observed stoichiometry for incident photon flux densities considered in this study. The second one was clearly conceived as an assay panel, using high efficiency red LED in the correct range of wavelength (see modelling part 3 and the spectral efficiency curve) with a peak emission at 626 nm (see Table 1). For the same electrical power consumption, these LED have been demonstrated (see Appendix) to have a quantum yield 4 times higher than the previous one, delivering therefore an incident photon flux density four times higher (see Table 2) or saving a factor four in electrical power consumption for the same photon flux density. The two LED panels (180 mm height × 105 mm width) were built in the same manner, using 180 LED mounted with 10 mm between them. The maximal incident photon flux densities q ∩ (in µmol.m -2 .s -1 ) delivered by the two panels were determined by averaging 24 points of measurement on the surface and using a LI-COR quantum sensor (LI-190 SA). The results are summarized in Table 2 and show, as theoretically calculated (see Appendix), that the high efficiency red LED panel reaches a 4-times higher photon flux density for the same electrical power than the control panel. Conversely, in order to obtain the same incident photon flux densities for the previous experiments this panel was used with a 25% electrical power consumption, delivering then 33 µmol.m -2 .s -1 for the two panels.

2.3-Experimental device

A scheme and a picture of the experimental device are presented in Figure 1. Experiments in batch were performed using two identical 600 mL working volume rectangular photobioreactors with different LED panels in parallel. The first panel corresponding to polychromatic (red + blue) light served as control panel and a second panel with high efficiency monochromatic red LED, corresponding to the main purpose of this work, was also assembled and used. A black plate was placed between the two LED panels in order to avoid interferences between the polychromatic and the monochromatic light. In order to maintain an optimal temperature of 36°C in the PBR, a temperature sensor was used as external control for a heating bath, with water circulation in heating jackets. The distance between LED and PBR was fixed at 10 cm, due to magnetic stirring devices used to mix cultures homogeneously (see Figure 1b). The cultures were aerated with ~2% CO 2 enriched air for pH = 9.5 control, supplied to the PBR using 2 mass flow controllers for gas mixing. In order to prevent liquid losses, peltier condensers were used.

For experiments in continuous, the same experimental device supplemented with a peristaltic pump was used. Two flexible tubes, one for the input and one for the output have been fitted inside this circular pump in order to obtain equal input and output flows.

During the experiments, samples were taken twice a day and pH, OD 750nm , dry mass and pigment content were analysed.

2.4-Experimental methods

Biomass determination

The biomass concentration was determined turbidimetrically at 750 nm (spectrophotometer SAFAS, MC2) using a conversion factor for dry weight and confirmed by dry weight measurements (filters are dried in an oven at 110°C during 24 hours).

Pigment assay

Pigment assay has been performed by measuring optical density at 620, 678, and 750 nm after sonication (to break A. platensis trichomes). Using correlations and correction factors previously established [START_REF] Cornet | Etude cinétique et énergétique d'un photobioréacteur. Etablissement d'un modèle structuré[END_REF][START_REF] Marty | Etude et modélisation du comportement de Spirulina platensis en photobioréacteur en condition de limitation par la lumière et le carbone[END_REF], it was possible to quantify (in g.L -1 ) chlorophyll a and phycocyanin pigments as follows:

[chl a] = 1.04× 10 -2 A 678 -4.09× 10 -3 A 620

[phyc] = 0.297 A 620 -0.076 A 678 in witch A 620 = OD 620 -0.93 OD 750 and A 678 = OD 678 -0.89 OD 750

Action spectrum determination

The A. platensis action spectrum, corresponding to the measurement of O 2 evolution rate for a given monochromatic incident radiation was performed using an ultra-fast Haxo-Blinks type O 2 electrode, associated to a (xenon lamp) light source mounted with a monochromator in series [START_REF] Cornet | Etude cinétique et énergétique d'un photobioréacteur. Etablissement d'un modèle structuré[END_REF].

3-SPECTRAL KINETIC KNOWLEDGE MODEL FOR Arthrospira platensis GROWTH

The best way to achieve a structured knowledge model of photobioreactors which had been previously

established by the authors [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF], requires a precise formulation of the photon transport in a PBR of a given geometry and boundary conditions, and then the coupling between the so-called local volumetric rate of the radiant energy absorbed (LVREA) and the local kinetic rates from the knowledge of energetic and quantum yields. Finally, the complete model is obtained by averaging rates over the illuminated volume of the reactor and including them in the well-known elemental (dry weight) biomass balance to give the evolution equation for any considered component, if a stoichiometric equation is used. The extension of this approach, initially developed in the photosynthetically active radiation (PAR) domain [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF][START_REF] Cornet | Simulation, design and model based predictive control of photobioreactors[END_REF]) to a spectral model, requires first to have a predictive method in calculating the spectral radiative properties of any micro-organism in order to solve accurately the spectral radiative transfer equation (RTE). Secondly, it requires knowing the effect of using a narrow wavelength bandwidth on kinetic rates, i.e. the so-called action spectrum for photosynthesis.

3.1-Spectral Light Transfer Model

Some of the authors have already demonstrated how it was possible to obtain the spectral radiative properties of Chlamydomonas reinhardtii by a predictive mean, using an original method enabling first the calculation of the spectral optical properties of photosynthetic micro-organisms (the complex refractive index) by convolution, from data banks of in vivo absorption spectrum of pigments [START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF]. In this paper, the same approach has been used for Arthrospira platensis, but the considered spectral radiative properties (mass absorption Ea λ and mass scattering Es λ coefficients with the phase function p λ ) have been calculated from the predictive Lorenz-Mie theory, considering A. platensis as a long circular cylinder [START_REF] Bohren | Absorption and scattering of light by small particles[END_REF] randomly oriented (i.e. averaging over all the incident directions of light), and the anomalous diffraction approximation of Van de Hulst [START_REF] Van De Hulst | Light scattering by small particles[END_REF]. Finally, the RTE is solved in rectangular PBR illuminated on one side, using a one-dimensional approximation and a normal quasi-collimated two-flux generalized model, taking into account the reflection at the rear (thickness L) by the water-glass interface (say r λ = 0.01 from the geometrical optics calculation). In this case, the irradiance profile is given by [START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF]:

[ ] [ ] ) exp( ) 1 ( ) exp( ) 1 ( ) exp( ) 1 ( ) exp( ) 1 ( ) exp( ) exp( ) 1 ( ) exp( ) 1 ( ) exp( ) exp( ) 1 ( ) exp( ) 1 ( ) ( 2 2 2 2 , L r L r L L z L r L z L L r q z G λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ λ δ α δ α δ α δ α δ δ α δ α δ δ α δ α - - + - - - - - + - - - + + - - - - + = ∩ [1]
in which we have introduced the linear scattering modulus:

λ λ λ λ Es b Ea Ea 2 + = λ α [2]
and the extinction coefficient related to the dry biomass concentration C X by:

) Es b (Ea Ea C δ λ λ λ λ X λ 2 + = [3]
In these two definitions, the back-scattered fraction b λ characterizing the phase function is calculated as:

 ′ = π π λ λ θ θ θ θ 2 sin ) , ( 2
1 d p b [4]
Clearly, the set of equations [START_REF] Hermans | Preliminary evaluation of Biological Life Support in space environment[END_REF][START_REF] Lönneborg | Acclimation processes in the light-harvesting system of the cyanobacterium Anacystis nidulans following a light shift from white to red light[END_REF][START_REF] Matthijs | Application of light-emitting diodes in bioreactors: flashing light effects and energy economy in algal culture (Chlorella pyrenoidosa)[END_REF][START_REF] Bolychevtseva | A new type of adaptation of the cyanobacterium Spirulina platensis to illumination conditions[END_REF] is entirely predictive, and avoid using models of representation [START_REF] Yun | Attenuation of monochromatic and polychromatic lights in Chlorella vulgaris suspensions[END_REF][START_REF] Yun | Kinetic modeling of the light-dependent photosynthetic activity of the green microalga Chlorella vulgaris[END_REF] in the light transfer description. At this stage, it should be emphasized that the previous irradiance G and incident flux density q ∩ must be defined as photonic quantities (in µmol.m -2 .s -1 ), making it possible to formulate the kinetic coupling solely in terms of quantum yield.

3.2-Coupling Spectral Light Transfer and Local Kinetic Rates

As explained elsewhere [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF], the local coupling demands to know the LVREA deriving from the previous irradiance profile (eq. 1):

) ( ) ( z G C Ea z X λ λ λ = A [5]
and indeed the conversion efficiency of this absorbed photons rate. From first principles analysis of excitation energy transfer in antenna and of the so-called Z-scheme for photosynthesis, it is possible to introduce a local energetic yield of conversion, depending on the local wavelength-averaged irradiance (dissipative part of the photonic energy as a non-linear phenomenon):

G K K M + = ρ ρ [6]
and a conservative mole quantum yield for the Z-scheme φ ′ which is only P/2e -dependent (10). If an overall structured stoichiometry is postulated, the associated Z-scheme stoichiometry for photosynthesis leads easily to the following definition for φ ′ (see Figure 2):

) e 2 / 1 ( 2 1 , - - + = ′ + P X H NADPH υ φ [7]
As long as polychromatic radiation was used, this formula does not depend on the spectral nature of the photons (λ), but only on the stoichiometry for the produced biomass which is affected only by the averaged radiation field [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF]. For reasonably low incident light fluxes (lower than 150 µmol.m -2 .s -1 ), the following structured stoichiometry has been proposed for A. platensis (9):

+ + + + + →  + + + + + NADP 2.
+   →  + +   →  + + + ATP COF J J [9]
Obviously, in this case, the mean value of the P/2e -ratio is:

275 . 1 e 2 / = = - COF ATP J J P [10]
leading from (eq. 7, 9) to φ ′ = 7.9×10 -8 mol X / µmol hν . Because mass growth rates are rather considered, the mass quantum yield φ is easily derived from the corresponding C-molar mass for A. platensis M X = 23.7× 10 -3 kg X .mol X -1 , giving:

φ φ ′ = X M
= 1.85× 10 -9 kg X / µmol hν . [START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF] In the same way, the local yield ρ is weakly dependent on the wavelength and may be considered as constant over the PAR. Its maximum value ρ M = 0.8 for a quasi-collimated field has been calculated elsewhere [START_REF] Cornet | Procédés limités par le transfert de rayonnement en milieu hétérogène. Etude des couplages cinétiques et énergétiques dans les photobioréacteurs par une approche thermodynamique[END_REF], and the half saturation constant K = 90 µmol.m -2 .s -1 has been validated for A. platensis over a wide range of operating conditions and reactor geometries [START_REF] Cornet | Kinetics and energetics of photosynthetic micro-organisms in photobioreactors. Application to Spirulina growth[END_REF][START_REF] Cornet | Simulation, design and model based predictive control of photobioreactors[END_REF][START_REF] Cornet | A structured model for simulations of cultures of the cyanobacterium Spirulina platensis in photobioreactors -I. Coupling between light transfer and growth kinetics[END_REF][START_REF] Cornet | A simplified monodimensional approach for modelling coupling between radiant light transfer and growth kinetics in photobioreactors[END_REF]. Finally, using a polychromatic irradiation (i.e. visible light) for the PBR leads to the following local kinetic rates (with the help of eq. 5 and 6) for biomass concentration [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF][START_REF] Cornet | Simulation, design and model based predictive control of photobioreactors[END_REF]:

X M M X C G K G Ea K G K K r + = + = φ ρ φ ρ A [12]
Of course, in this equation, Ea, G and A are mean spectral quantities on the visible spectrum which can be obtained rigorously by averaging spectral LVREA [START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF], or working directly with averaged radiative properties if one accepts the corresponding lack of accuracy [START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF].

Nevertheless, using quasi-monochromatic light for the cultivation of photosynthetic micro-organisms leads to different kinetic behaviors depending on how the functioning of the two photosystems in series is affected. For eukaryotic micro-organisms, the action spectrum ranges between 400 and 680 nm with the same efficiency for photosynthesis whatever the wavelength in the interval; then it is well known that it is possible to use red LED (for example) with the same efficiency as white light (3). Conversely, for cyanobacteria like A. platensis, the PSII antennas are mainly constituted of phycocyanins and allophycocyanins (phycobilins) absorbing at their maximum around 620 nm, whereas the PSI is mainly constituted by chlorophylls (absorbing at 440 and 680 nm, see Figure 2). Chlorophyll a 440 and 678 nm If quasi-monochromatic light is used, only red photons can efficiently perform water photolysis at PSII. On the contrary, blue photons cannot be trapped easily by PSII, but only by PSI, leading to a poor efficiency of photosynthesis in this case, resulting from the fact that the two photosystems have to work in series. If only red photons are used, a well-established compensation phenomenon exists [START_REF] Bennett | Regulation of photosynthesis by reversible phosphorylation of the light-harvesting chlorophyll a/b protein[END_REF][START_REF] Allen | Correlation of membrane protein phosphorylation with excitation energy distribution in the cyanobacterium Synechococcus 6301[END_REF][START_REF] Allen | A general model for regulation of photosynthetic unit function by protein phosphorylation[END_REF], enabling the redistribution of the electrons flux to the PSI with a high efficiency and equilibrating the P/2e -ratio. These phenomena are evidenced on the so-called action spectrum of photosynthesis, obtained from the measurement of O 2 evolution rates using monochromatic light [START_REF] Cornet | Etude cinétique et énergétique d'un photobioréacteur. Etablissement d'un modèle structuré[END_REF][START_REF] Haxo | Photosynthetic action spectra of marine algal[END_REF]. Such experiment is depicted in Figure 3 for A. platensis. This action spectrum enables the introduction of the spectral information in the kinetic coupling by defining a spectral efficiency e λ (Figure 3) reaching its maximum value of 1 (as in polychromatic white light) in the range 618-626 nm (with less than 1% deviation). This figure clearly demonstrates that it is necessary to choose LED in this range (around 620 nm) in order to cultivate cyanobacteria (particularly A. platensis) with the same efficiency as with polychromatic visible light. Actually, using LED as lightening source is never really monochromatic and all the spectral quantities need to be averaged on a small bandwidth (usually 20 nm) as follows (the final accuracy is not affected in this case taking into account the narrow bandwidth of the considered spectrum):

Mn 2+ H 2 O X ATP Q A Q B ADP + Pi 2e - Plastoquinone Cytochrome f/b6 Cytochrome C 553 e - ½ O 2 2 h v 2 h v 2 H + + NADPH, H + + 0 -0.8 + 0.8 E' 0 (V)
( ) λ λ ∆ λ λ λ λ λ λ λ ∆ λ ∆ λ ∆ λ ∆ d e b Es Ea e b Es Ea  = max min , , , 1 , , , [13]
( ) λ λ λ λ λ d q G q G  ∩ ∩ = max min , , , [14]
The values of the radiative properties for the wavelength bandwidth considered in this study and calculated as explained above are summarized in Table 3 (respectively for 470, 626, and 640 nm ± 2σ = ± 10 nm). Introducing then these definitions in equation [START_REF] Cogne | Uptake of macrominerals and trace elements by the cyanobacterium Spirulina platensis (Arthrospira platensis PCC 8005) under photoautotrophic conditions: culture medium optimization[END_REF], together with the knowledge of the spectral efficiency e λ (Fig. 3), leads to a generalization of the kinetic coupling for spectral applications as:

X M X C G K G Ea K e r + = λ ∆ λ ∆
φ ρ [START_REF] Marty | Etude et modélisation du comportement de Spirulina platensis en photobioréacteur en condition de limitation par la lumière et le carbone[END_REF] in which the averaged irradiance G and the averaged incident light flux q ∩ are always defined by mean of equation [START_REF] Haxo | Photosynthetic action spectra of marine algal[END_REF].

3.3-Mean Spatial Kinetic Rates and Evolution Equations for the PBR

As already explained in previous papers [START_REF] Cornet | Kinetics and energetics of photosynthetic micro-organisms in photobioreactors. Application to Spirulina growth[END_REF][START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF][START_REF] Cornet | Simulation, design and model based predictive control of photobioreactors[END_REF][START_REF] Cornet | A structured model for simulations of cultures of the cyanobacterium Spirulina platensis in photobioreactors -I. Coupling between light transfer and growth kinetics[END_REF][START_REF] Cornet | A simplified monodimensional approach for modelling coupling between radiant light transfer and growth kinetics in photobioreactors[END_REF], the average volumetric biomass growth rate in the PBR is then obtained by averaging local rates onto the active metabolic and illuminated volume fraction in the reactor (assuming that the dark part of the PBR has no metabolic contribution as it is the case for cyanobacteria having their respiratory electron transfer chain inhibited by light). If this fraction γ is defined as the part of the volume (V l ) in which the irradiance is higher than the value of the compensation point for photosynthesis, the global productivity is calculated and further simplified, taking into account the one-dimensional geometrical simplification:

dz r L dV r V r l l L X l V X l X   = = > < 0 1 1 γ γ [16]
In case of kinetic regime functioning, photons are in excess in the reactor, γ = 1 and L l = L, leading to an integration over the entire volume of the PBR. The evolution equation for the biomass concentration is then easily established, applying a mass balance on the perfectly mixed homogeneous PBR and introducing the hydraulic residence time τ, giving:

τ X X X C r dt dC - > =< [17]
and in continuous and steady state operation:

τ > < = X X r C [18]
These balances, associated to the stoichiometric equation [START_REF] Wang | Effects of using light-emitting diodes on the cultivation of Spirulina platensis[END_REF], completed the spectral knowledge model, as a powerful tool in PBR analysis, simulation, sizing and model based predictive control [START_REF] Cornet | Modeling stability of photoheterotrophic continuous cultures in photobioreactors[END_REF][START_REF] Cornet | Simulation, design and model based predictive control of photobioreactors[END_REF].

4-RESULTS AND DISCUSSION

As explained in the introduction, the objective of this work was to prove the feasibility of a long term cultivation of A. platensis, using high energetic efficiency red LED (instead of white or any polychromatic radiation with lower efficiency) with the same kinetic performance as for visible light.

The preceding mathematical modeling section clearly established that it was theoretically possible from the knowledge of the spectral action spectrum efficiency (Figure 3), taking LED with a main range of emission between 618 and 626 nm, leading to our choice of both the control and the red LED panels (see Materials and Methods section and Appendix). Nevertheless, and before discussing the experimental results obtained in this work, it is interesting to compare the previous mathematical model with the data available in the literature.

4.1-Comments of some results in the literature

Only very few quantitative results (with well-documented PBR characteristics and accurate incident quantum light flux calibration) exist for monochromatic light cultivation of A. platensis (or other cyanobacteria) in the literature. We can already discuss further the results of Wang et al. [START_REF] Wang | Effects of using light-emitting diodes on the cultivation of Spirulina platensis[END_REF], who studied, the effects of different LED on kinetics of Spirulina platensis in flasks. Considering that their more accurate results were obtained at high light intensity for the LED (3000 µmol.m -2 .s -1 ) and assuming that they worked in physical limitation by light (linear biomass concentration time course; constant growth rate), it is possible to calculate the best observed productivity (a control), and then the relative productivity for other wavelength sources, matching closely the definition of the spectral efficiency e λ (Figure 3 and eq. 15). Fortunately, their higher productivity was observed for a red LED emitting in the range 620-645 nm corresponding roughly to the highest value of the spectral efficiency ( λ ∆ e = 1) we have introduced (Figure 3). In the same way, calculating their values of λ ∆ e for green LED (515-540 nm) and blue LED (460-475 nm) relative to the productivity with red LED (control), we get respectively 0.25 ± 0.04 and 0.08 ± 0.01, whereas our theoretical results (Figure 3) for λ ∆ e would lead to 0.22 and 0.074. This preliminary analysis shows that our theoretical definition of the spectral efficiency tallies with the experimental results of Wang et al. [START_REF] Wang | Effects of using light-emitting diodes on the cultivation of Spirulina platensis[END_REF]. On the contrary, the agreement was not correct for yellow LED (587-595 nm) giving roughly the same value of λ ∆ e as the green LED for experimental productivity, whereas our theoretical value would be closer to 0.75. This surprising discrepancy could result in some experimental details that have not been reported in their paper like for example a slight difference in the incident intensity or in the flask geometry; this could also explain the slightly lower productivity observed for white light (the control) in comparison to the red LED productivity (apparently not possible from a theoretical point of view).

In any case, it clearly appears that a complete validation of the spectral efficiency curve on kinetic growth rates (eq. 15-17) would require further investigations in fully controlled PBR and many different spectral incident light inputs, but this remains out of the scope of this paper.

4.2-Short-term comparison between control LED panel and high efficiency red LED panel (validation of the knowledge model)

The previous theoretical analysis and mathematical modeling evidence that cultivating A. platensis in two identical PBR with the same incident photon flux density q ∩ , using a polychromatic control (red + blue, P/2e -= 1.275) LED panel or a high efficiency monochromatic red LED panel (with

λ ∆ e = 1)
should lead to the same kinetic growth rates, if operating in physical limitation by light (all the incident photons absorbed). Consequently, a first experiment was carried out in batch conditions, taking the incident photon flux density at q ∩ = 33 µmol.m -2 .s -1 (the maximum value for the control LED panel, see Table 2 and Appendix) for the two PBR, and with a concentration inoculum sufficiently high to obtain the physical limitation by light as confirmed by the predictive light transfer model (eq. 1-4). As expected, the resulting biomass concentration time course observed in Figure 4 appears as linear, the slope being the average biomass productivity [START_REF] Cornet | A structured model for simulations of cultures of the cyanobacterium Spirulina platensis in photobioreactors -I. Coupling between light transfer and growth kinetics[END_REF]. The results depicted in Figure 4 correspond to twofold repeated independent experiments in the two PBR, leading respectively to a mean productivity of

3 10 ) 3 . 0 2 . 3 ( - × ± = > < X r g.L -1 .h -1 for the control LED panel and 3 10 ) 4 . 0 3 . 3 ( - × ± = > < X r g.L -1 .h -1 for
the red LED panel, demonstrating that, as foreseen, there is no significant kinetic difference between the two kinds of LED panel, and confirming then qualitatively the previous reasoning. (corresponding to 25% of the maximum output for this later as explained in appendix); comparison between the completely predictive model and the experimental results. The corresponding residence time was 272 hours. Besides, these results were also confirmed in continuous cultivation conditions, using again the same incident photon flux density q ∩ = 33 µmol.m -2 .s -1 for the two LED panels and the same hydraulic residence time τ = 272 hours for the two PBR. The experimental data are reported in Figure 5 and compared to the theoretical value of outlet biomass concentration given by the model (eq. 1-15 and 18).

They still demonstrated that first, there is no significant difference between the control LED panel and the red one, and second that they are very close to the theoretical knowledge model calculations.

These results clearly confirm the point of interest in using high efficiency red LED panel for the cultivation of cyanobacteria in PBR, since the same productivity was obtained as with the polychromatic control LED panel but saving a factor 4 for the electrical power consumption in this case (see appendix for detailed calculations). This is clearly a crucial point if the availability in electrical power is strongly constrained as it is the case onboard the International Space Station for experiments testing the microgravity effects.

4.3-Long-term validation using the high efficiency red LED panel and pigment content modifications

Finally, in order to verify the long term behavior of A. platensis cultures in PBR illuminated with high efficiency red LED panel, a continuous culture was maintained over 3500 hours (5 months), this choice corresponding to the future duration of an experiment onboard the International Space Station. The high efficiency panel (red LED) was used at its nominal electrical power, delivering an incident photon flux density q ∩ = 135 µmol.m -2 .s -1 (see Table 2 and appendix) and the residence time in the PBR was decreased to τ = 62.5 hours. The experimental data obtained which are summarized in Figure 6 show again a very good agreement with the model calculation (continuous line) leading to a mean productivity in this case

2 10 1 . 1 - × = > < X r g.L -1 .h -1 i.e.
to a theoretical output biomass concentration (eq. 18) C X = 0.7 g/L. This confirms again the predictive character and the structure of the developed knowledge model with an incident light flux four times higher. Besides, these results also demonstrate that there was no kinetic deviation in the PBR driving a long term cultivation corresponding to 30 residence times for the complete experiment.

In addition, the long-time red light cultivation effect on the pigment contents of the cells was investigated. The results are reported in Table 4, in comparison with the pigment contents also obtained for the (red + blue) control LED panel and the well-known contents obtained for white light [START_REF] Cornet | Kinetics and energetics of photosynthetic micro-organisms in photobioreactors. Application to Spirulina growth[END_REF]. As shown, using polychromatic (red + blue) control LED panel does not modify the pigment contents observed for true white light as previously expected, whereas the use of monochromatic red LED panel resulted in a two-fold decrease of the phycocyanin content.

Table 4. Mean pigment contents (% DM) obtained for long-time continuous cultivation of A. platensis in PBR using different spectral incident light sources and for incident photon flux densities q ∩ lower than 150 µmol.m -2 .s -1 .

White light or any polychromatic light (red + blue) polychromatic control LED panel

High efficiency red LED panel

Chlorophyll a content 0.8 ± 0.1 % 0.8 ± 0.1 % 0.8 ± 0.1 % Phycocyanin content 16 ± 1 % 16 ± 1 % 7.5 ± 0.5 % These results were also confirmed by the visible light absorption spectra obtained for the two kinds of LED panels as shown in Figure 7. These spectra were normalized at 750 nm to take into account a possible effect of the biomass concentration on the turbidity of the sample. A possible explanation of these pigment content changes could come from in the well-known compensation mechanism of the electron fluxes in the two photosystems already mentioned in the modeling section and explaining the action spectrum for cyanobacteria. The redirection of the electron flux to the PSI from the mainly excited PSII (red light at 620 nm) seems also responsible in a physiological regulation mechanism decreasing the efficiency of photon capture in the antennas of the PSII (the phycobilins). Conversely, the chlorophyll content, rather representative of the number of reaction centers for photosynthesis, remains constant in all spectral illumination conditions.

It must be pointed out at this stage that this physiological regulation mechanism had likely no significant effect on the mean global stoichiometry in the PBR (mainly on the photosynthetic quotient

> < > < = 2 2 CO O P r r Q
) because as demonstrated by the mathematical knowledge model (eq. 8-11), the stoichiometry of the produced biomass, the mean P/2e -ratio and the kinetics (the mean growth rates) are directly interrelated, a modification of any one of these variables affecting obligatorily the other. in standard conditions (red + blue control LED panel) after long-term continuous exposure to red (620 nm) light. The corresponding residence time of cells in the continuous PBR was 272 hours and the incident photon flux density q ∩ = 33 µmol.m -2 .s -1 . The initial values of pigment content are obtained from continuous culture with red LED, q ∩ = 135 µmol.m -2 .s -1 and τ = 62.5 h.

At the end of the previous experiment, the cells culture conditions were changed, applying on the reactor again a (red + blue) control LED panel with an incident photon flux density q ∩ = 33 µmol.m -2 .s -1 and a dilution rate corresponding to a hydraulic residence time of 272h, enabling us to study the conditions for pigment content recovery. As depicted in Figure 8, the total recovery in pigment content for phycocyanin takes about 850 hours. This time finally corresponds to three residence times in the reactor which is a well-known characteristic time for most of the continuous processes.

5-CONCLUSIONS

In this paper, the possibility of saving significant electrical energy power consumption in artificially lightened PBR was demonstrated, using a high efficiency red (620 nm) LED panel instead of classical white sources or any other polychromatic sources. The choice of the most efficient quasimonochromatic wavelength range (618-626 nm) for Arthrospira platensis was theoretically established from the action spectrum of photosynthesis, and it has been proved experimentally that the resulting biomass productivity < r X > was as high as that obtained with a polychromatic (red + blue) control LED panel, especially designed to match the P/2e -ratio of A. platensis at low incident photon flux densities (less than 150 µmol.m -2 .s -1 ). The comparison was first led in two identical PBR lightened with the same low incident photon flux density (33 µmol.m -2 .s -1 ) for the two LED panels (control and assay) and operating in batch and then in continuous mode. The long term behavior of the continuous cultivation of A. platensis was investigated at a higher incident photon flux density (135 µmol.m -2 .s -1 ) delivered by the high efficiency red (620 nm) LED panel, with the same energy consumption. The results demonstrated the possibility of obtaining high and stable biomass productivities (over 30 residence times, i.e. 3500 hours) with only minor physiological modifications as the decrease in phycocyanin content in the cells, corresponding to a well-known electron fluxes equilibration mechanism in the Z-scheme for photosynthesis.

Additionally, a predictive kinetic and stoichiometric spectral knowledge model was established in the paper for the first time, introducing the spectral efficiency e λ in coupling kinetics with the volumetric light absorption rate. The resulting simulations were proved to be in very good agreement with the experimental data, both for classical polychromatic irradiation but also when using the monochromatic red LED panel conceived on its theoretical basis. Because all the parameters of the model can be calculated by a predictive mean (optical and radiative properties, quantum yield), its structure appears as very general and it could be used for any other micro-organism as long as the action spectrum for photosynthesis and a structured stoichiometry is known. It must be emphasized that the proposed model clearly established the link between global stoichiometry, P/2e -ratio (thermodynamics of photosynthesis), and the quantum yield responsible for the kinetic aspects for biomass, substrates and products. Conversely, the fact that the productivities appeared insensitive to the spectral nature of light when using the optimal red range of wavelength for A. platensis (618-626 nm) implies that the quantum yield was conserved in this case and then, that the P/2e -and the global stoichiometry are also conserved. Thus, even if the photosynthetic quotient was not determined experimentally in this work, it can be concluded that it is not likely to be affected when using optimal red light, enabling the calculation of the O 2 regenerating performances of any PBR if the air revitalization in closed life support systems was envisaged.

NOMENCLATURE

A

Local volumetric rate of radiant energy absorbed [µmol.s -1 .m First, the conversion factor is easily derived from the knowledge of the spectral energetic emission spectrum of the source w λ (W rad .m -1 which is formally the radiant power transported by photons of wavelength λ) and from its conversion into photonic unit spectrum λ w′ (µmol photon.s -1 .m -1 which is formally the flow rate of photons of wavelength λ). The radiant light power is given by: and is characteristic of the emission spectrum of any given source.

If we assume a solar spectrum or a typical white fluorescent lamp with a color temperature around 5500 K, this average wavelength is roughly 550 nm leading to the well-known conversion factor in the PAR (photosynthetically active radiation) with Ξ = 4.6 µmol photon.s -1 per radiant watt.

Secondly, the energetic yield η is calculated by introducing the photometry units used by the manufacturers of artificial light sources. Generally, the key technical data available is the luminous efficiency E elec (in lumens per electrical watt). In order to define the energetic yield η (radiant watt per electrical watt) it is then convenient to define the radiant efficiency E lum in lumens per radiant watt. This quantity is also determined from the knowledge of the energetic emission spectrum of the source w λ , considering the CIE normalized photopic response of human eye CIE p λ (see Figure A1) and the definition of the candela SI unit, from: On the contrary, for LED, the former quantity E elec is generally not directly available from manufacturers, but may be calculated from basic data as luminous intensity I (in Candela), angle of emission θ, and nominal electrical power consumption W elec by: -Blue LED (Toyoda Gosei E1L51-3B0A, 470 nm): η = 0.057 radiant watt per electrical watt -Γ = 0.22 µmol photon per second and per electrical watt.

-Red LED (Fairchild MV8014, 640 nm): η = 0.041 radiant watt per electrical watt -Γ = 0.22 µmol photon per second per electrical watt. This result explains why these LED were chosen to give the same quantum yield Γ, enabling to simply obtain the target value for the ratio P/2e -= 1.275 just by building a panel with 1.275 blue LED for 1 red LED. Such a control panel delivers for its nominal electrical power an incident light flux q ∩ = 33

  Figure 1. a) Scheme of the experimental device for rectangular PBR (600 mL working volume) experiments with LED panels.

Figure 2 .

 2 Figure 2. Typical Z-scheme of photosynthesis for cyanobacteria (from 9)

Figure 3 .

 3 Figure 3. Determination of the spectral efficiency e λ for A. platensis from the experimental action spectrum of photosynthesis in the PAR measured with Haxo-Blinks electrode (13, 14).

Table 3 .

 3 Main radiative properties versus the considered wavelength bandwidth for the LED of the study, as predictive data for light transfer model calculation and obtained from the method developed by Pottier et al.[START_REF] Pottier | A fully predictive model for one-dimensional light attenuation by Chlamydomonas reinhardtii in a torus photobioreactor[END_REF], for the optical properties assessment. These values were obtained applying the Lorenz-Mie theory with the anomalous diffraction approximation, assimilating Arthrospira platensis to a long circular cylinder randomly oriented.

  blue) control LED panel high efficiency red LED panel model presented in the paper

Figure 4 .Figure 5 .

 45 Figure 4. Time course of Arthrospira platensis dry mass concentration for batch cultivation in two identical rectangular PBR illuminated on one side (L = 0.04 m), with a control LED panel and a high

Figure 6 .

 6 Figure 6. Arthrospira platensis output dry mass concentration versus time for a long-term continuous cultivation in rectangular PBR illuminated on one side (L = 0.04 m) and using a high efficiency LED

Figure 7 .

 7 Figure 7. Absorption spectra obtained from A. platensis samples being cultivated with (red + blue) control LED panel and high efficiency red (620 nm) panel. The spectra are normalized from the turbidity of the sample (dielectric behavior of cells) between 750 and 800 nm.

Figure 8 .

 8 Figure 8. Time course recovery of phycocyanin pigment content during the cultivation (for A. platensis)

φΩ

  Mass quantum yield for the Z-scheme of photosynthesis [kg X .µmol hν -1 ] φ ′ Mole quantum yield for the Z-scheme of photosynthesis [mol X .µmol hν -1 ] Solid angle [rad] Subscripts ∩ Relative to hemispherical incident radiation onto the photobioreactor λ Relative to a spectral quantity for the wavelength λ ∆λ Relative to a narrow interval of wavelength min Minimum value for the spectral range of wavelength max Maximum value for the spectral range of wavelength and Quantum Yields of LED Generally speaking, the energetic yield of a light source η (W rad / W elec ) is defined as the ratio of the radiant light power output over the electrical power input. It can be easily converted into in quantum yield Γ (µmol photon per second and per electrical watt) when the conversion factor Ξ (µmol photon per second and per radiant watt) of the source is known.

λ

  photon W W = Ξ

Figure A1 .

 A1 Figure A1. Normalized and standard CIE photopic curve CIE p λ . The maximum value ( CIE p λ = 1) is

  of the energetic yield with equation (4), and then the quantum yield, applying:Choice of the LED Panels CompositionFirst the control panel of LED has been defined in such a way that the two photosystems of Arthrospira be excited in series in the red domain (PSII) and in the blue domain (PSI) with a P/2e -= 1.275 ratio corresponding to the established stoichiometry for low incident light fluxes used in this study (see the modeling part in the text). The green light has been removed from the control panel because of its poor absorption by pigments in the PBR. From the technical data on the blue and red LED used (see the Materials and Methods part), and combining their emission spectrum with equations (A1-A6), the following energetic and quantum yields are calculated leading to:

2.1-Organism and culture medium

  and 1 mL per Liter of medium of trace elements solution (g.L -1 ) : MnCl 2 , 4 H 2 O 0.23; ZnSO 4 , 7 H 2 O 0.11; CuSO 4 , 5 H 2 O 0.03. The final pH of the medium was adjusted at 9.5.

	The cyanobacterium A. platensis PCC 8005 (Institut Pasteur, Paris, France) was axenically grown in
	Zarrouk medium, modified by Cogne et al. (12), as follow : (g.L -1 ) : NaCl 1.0; CaCl 2 0.03; K 2 SO 4 1.0;
	MgSO

4 , 7 H 2 O 0.2; K 2 HPO 4 0.5; NaNO 3 2.5, NaHCO 3 10.5; Na 2 CO 3 7.6; EDTA 0.08; FeSO 4 , 7 H 2 O 0.01

Table 1 .

 1 Electrical and optical characteristics of the 3 different LED used in the experiments.

	Condition T A = 25°C -I F = 20mA
		Agilent	Toyoda Gosei	Fairchild
		HLMP-EG08-WZ000	E1L51-3B0A	MV8014
		Red LED	Blue LED	Red LED
	Luminous intensity (mcd) 16000	1800	1500
	Intensity (mA)	20	20	20
	Typical voltage (V)	1.9	3.4	2.1
	Peak wavelength (nm)	626	470	640
	Viewing angle (°)	8	15	12

Table 2 .

 2 Maximal incident photon flux density for the two LED panels used in this study. The

	polychromatic control panel is conceived with a P/2e -= 1.275 blue LED for one red LED.

LED Wavelength (nm) Maximal incident photon flux density (µmol.m -2 .s -1 )

	High efficiency red LED panel	Red	626	135
		Red	640	14.5
	Polychromatic control (red + blue) LED panel	Blue	470	18.5 (= 14.5 × 1.275)
		Total	470 and 640	33

ACKNOWLEDGMENT

This work was supported by the European Space Agency (ESA/ESTEC) through the Biorat project.

The authors also thank Pascal Lafon for his technical assistance.

µmol hν .m -2 .s -1 (corresponding effectively to 18.5 µmol hν .m -2 .s -1 for blue LED and 14.5 µmol hν .m -2 .s -1 for red LED as it should be).

Secondly, the high efficiency red panel has been conceived to work in the optimal range of wavelength defined from the spectral efficiency λ ∆ e ≅ 1 (see Figure 3 in text). The same calculations of yields as previously done for these LED lead to:

-High efficiency red LED (Agilent HLMP-EG08-WZ000, 626 nm: η = 0.171 radiant watt per electrical watt -Γ = 0.90 µmol photon per second and per electrical watt. Such a high efficiency panel delivers, for the same nominal electrical power as the control panel, an incident light flux q ∩ = 135 µmol hν .m -2 .s -1 . This experimental value, together with the previous value of the control panel, clearly validates the theoretical approach in the first part of this appendix, considering the yields of LED calculation. They verify indeed: