Olivier Thomas

Benoit Roig

Mineral constituents

Keywords: Suspended matters, metals, oils grease, color

FIGURE 6.2 Main nitrogen forms in water.

the oxygen demand, resulting in the formation of final stable products as nitrate, and are toxic for fishes in rivers. Oxidized forms are one of the main eutrophication factors with phosphorous compounds and can also be toxic to human beings, through tap water. Nitrate can be chemically reduced in nitrite, which is responsible for the lack of oxygenation of cells, more particularly for babies (methemoglobinemia).

.

, UV procedures are also standardized and largely implemented in online or field-portable instruments mainly for nitrate monitoring TABLE 6.1 Selection of standard methods for nitrate determination in water. Method Principle Range Observations/interference 4500-NO 3 2 B UV spectrophotometry 0.2À11 mg L 21 NO 3 2 Organic matter and colloids interference 4500-NO 3 2 C Second-derivative UV 0.5À2.5 mg L 21 NO 3 2 Pathlength 10 mm screening method

Introduction

After considering the UVÀvisible applications for several organic compounds and related aggregate parameters, this section shows that some inorganic constituents can also be studied either directly or indirectly with a UVÀvisible detection. Fig. 6.1 presents the different species studied, present under ionic forms in water and wastewater. Among the different mineral constituents potentially dissolved in water, several groups can be considered with regard to their environmental interest and nature:

• The major minerals coming from the geochemical history of water include cations (Na 1 ,K 1 ,Ca 21 , and Mg 21 ) and anions HCO 2 3 ; SO 22 4 ; CI 2 ; NO 2 3 ÀÁ : These constituents are generally present in all water with concentration from 1 milligram per liter to several grams per liter (seawater). Notice that all these ions have a natural origin, except nitrate.

• The nonmetallic minerals, associated with water pollution, are N, P, S (except sulfate) compounds. The nature and concentration of these constituents is highly dependent on the origin of the pollution (urban, agriculture, industries, etc.) and its importance and type (chronic or accidental). The concentrations corresponding are obviously variable but can reach several hundred milligrams per liter. • The metallic constituents are from natural origin (ore) or more frequently associated with an anthropogenic pollution. Among them, toxic and heavy metals including hexavalent chromium, cadmium, and mercury must be monitored.

Almost all these ions can be determined with a colorimetric method [START_REF] Rice | Standard Methods for the Examination of Water and Wastewater[END_REF].

Inorganic nonmetallic constituents

In a recent paper, Birkmann et al. [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF] studied the UV spectroscopic properties of principal inorganic ionic species in natural waters in the wavelength range of 195 to 280 nm. All absorbing species were identified and the corresponding molar absorptivities were determined experimentally. No cations were found to influence the UV spectrum. Relatively high molar absorptivities were observed for iodide, bromide, and nitrate.

Actually, N and P compounds are the most important inorganic nonmetallic constituents with regard to their environmental effects such as eutrophication of water bodies (lakes and rivers). Some of them are directly considered as nutrients (nitrate or phosphate), while others are nutrient precursors (ammonia, organic nitrogen, and organic phosphorous). Other constituents must also be considered, such as S compounds, mainly, because of specific environmental odor or toxicity concerns.

N compounds

Among water quality parameters, nitrogen is probably the most known and monitored, particularly under is more stable form nitrate. N is present in water in reduced form (organic and ammonium nitrogen) and oxidized form (nitrites and nitrates). The evolution of the N compounds depends on physicochemical and biological mechanisms occurring in natural water or all along treatment processes (Fig. 6.2).

The presence of the reduced N compounds in surface water is due to natural organic matter decomposition and, in urbanized area, to discharges coming from raw wastewater or from biological wastewater treatment plants for the ammoniacal form. These reduced compounds increase in water and wastewater. Ion chromatography or capillary electrophoresis can also be used for nitrate determination. In their review, Azmi et al. [START_REF] Azmi | Techniques in advancing the capabilities of various nitrate detection methods: a review[END_REF] proposed some membrane techniques for the improvement of the capabilities of various nitrate detection methods. A recent review [START_REF] Singh | A review on spectroscopic methods for determination of nitrite and nitrate in environmental samples[END_REF] on spectroscopic methods for the determination of nitrite and nitrate in environmental samples concluded that spectroscopic methods were successful if water sample contains little or no organic matter. Another work on recent progress in sensing nitrate, nitrite, phosphate, and ammonium in aquatic environment [START_REF] Mahmud | Recent progress in sensing nitrate, nitrite, phosphate, and ammonium in aquatic environment[END_REF] recommended that direct nitrate detection is beneficial and can be achieved by a UV spectrophotometric-based sensor. For other forms of nitrogen (ammonia or organic nitrogen), CFA, FIA, and SIA as well as other methods based on the Kjeldahl method can be considered [7À9]. For total Kjeldahl nitrogen (TKN), including organic and ammoniacal nitrogen, the reference procedure [START_REF] Usepa | METHOD 1683 Specific Oxygen Uptake Rate in Biosolids Draft[END_REF] needs mineralization and distillation steps and the use of a final colorimetric or titrimetric determination. In this context, an alternative approach using UV spectrophotometry, either directly or after some simple treatment steps for the final detection, was proposed.

General procedure

This simple methodology, called UV/UV method, was designed for the quick determination of the different forms of nitrogen in water, nitrite, nitrate, ammonium, and TKN [START_REF] Roig | Simple UV/UV-visible method for nitrogen and phosphorus measurement in wastewater[END_REF]. The general procedure is based on several steps (Fig. 6.3) but includes a UV determination of the oxidized forms and one or two UV photooxidation step(s) for the FIGURE 6.3 General UV/UV procedure for N compound determination [START_REF] Roig | Simple UV/UV-visible method for nitrogen and phosphorus measurement in wastewater[END_REF]. mineralization of the reduced forms. Phosphorus determination is also possible with this method. Neither filtration nor acidification of the sample is needed.

First of all, the oxidized forms of inorganic nitrogen (nitrate, nitrite) are detected by direct UV spectrophotometry (way A). Second, the sample is photooxidized with a photo-digester (way B), in the presence of an alkaline oxidant solution (potassium peroxodisulfate buffered to pH 9). Under the influence of UV radiation (in this case, a simple lowpressure mercury lamp emitting at 254 nm), the global nitrogen is converted into nitrate. Then, TKN can be calculated from the difference between the concentration of global nitrogen and the one of the oxidized forms previously determined.

In the third part of the general procedure (way C), the sample is photooxidized in the presence of an acidic oxidant solution (pH 2 with sulfuric acid 20%). In these conditions, only organic nitrogen is converted into nitrate. The difference between the concentration of TKN previously calculated and that of organic nitrogen leads to the calculation of ammonium nitrogen concentration.

Thus all nitrogen forms (N ox ,N org ,N H 1 4 ; and TKN) present in water and wastewater can be rapidly and simply determined by UV spectrophotometry.

Nitrate measurement

The determination of nitrate is certainly the most important application of UV spectrophotometry for water quality monitoring. The reason is that t h es p e c t r ao fn i t r a t es o l u t i o n sa r ev ery characteristic between 200 and 400 nm in function of the concentration (Fig. 6.4). Nitrate ion is rather sensitive to UV absorption with a half Gaussian shape for low concentration (between 0.5 and 15 mg NO3-L 21 without dilution for 10 mm pathlength). When the concentration increases, an absorption peak appears around 3 1 0n mf r o m0 . 2gN O 3 -L 21 , without dilution for 10 mm pathlength. In between, no particular shape exists, except the saturation wall for short wavelengths. This typical response is exploited for nitrate determination with different wavelength ranges in function of the expected concentration. Actually, Simeon et al. [START_REF] Simeon | Existence of two forms of nitrate ion in dilute aqueous solutions. Thermodynamic parameters of interconversion[END_REF] reported the existence of two forms of nitrate ions in relatively concentrated solutions (around 5 g L 21 ), with a very slight difference in their UV spectra. They also showed that depending on the associated cation, nitrate ion associated as ion pairs can give different UV response at high salt concentrations for transition-metal ions compared to that of nontransition cations. That could be a consequence of different types of cationÀanion interactions [START_REF] Gvozdić | Association of nitrate ion with metal cations in aqueous solution: a UV-vis spectrometric and factor-analytical study[END_REF].

A lot of works have been published for more than 50 years on the use of UV spectrophotometry for nitrate determination in water, with more than 35,000 papers since 2017 (Google Scholar database). The proposed methods can be classified according to the exploitation method used, among those presented in Chapter 2:

• The earlier methods are based on simple absorptiometry at one or two wavelength(s) [14À17]. Generally, the use of one absorbance value between 205 and 220 nm, compensated by another one between 250 and 300 nm, is proposed. For example, a screening method based on the measurement of absorbance at 220 nm was standardized [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF],wit ha correction for dissolved organic matter from a second measurement at 275 nm. For high concentrations of nitrate (in the case of industrial application), a simple absorptiometric method can be envisaged at 310 nm. • The second group focuses on the interest of the calculation of the second derivative or its estimation with a three-wavelengths measurement, around 220À225 nm [18À21]. A standardized method using second derivative was also proposed [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF]. These methods are less sensitive to interferences than the first group (supposing that the slope of the UV spectrum of interferences is constant) and can be run on most UV sensors and lab spectrophotometers. • Other efficient methods exploit the entire UV spectrum between 200 and 350 nm [22À25], through multiwavelengths procedures. They are based either on partial least squares (PLS) algorithm [START_REF] Langergraber | A multivariate calibration procedure for UV/VIS spectrometric quantification of organic matter and nitrate in wastewater[END_REF] or on the semideterministic deconvolution procedure or UVSD (UV spectral deconvolution) method [START_REF] Thomas | UV spectral deconvolution: a valuable tool for waste water quality determination[END_REF] described in Chapter 2. These methods give excellent and very rapid results compared to classical analysis, such as colorimetry, but need a specific software for data processing.

An example of the comparison of a second-derivative UV method, with a standard one (NF EN ISO13395) using CFA and colorimetry at 543 nm, is given in Fig. 6.5 [START_REF] Simal | Second derivative ultraviolet spectroscopy ond sulfamic acid method for determination of nitrates in water[END_REF]. The validation was carried out on 580 freshwater samples. The adjustment between the measured concentration of nitrate and the estimated values [by second-derivative absorbance (SDA) at 226 nm] gave a coefficient of determination R 2 greater than 0.99, without filtration of samples.

Nitrite measurement

As for nitrate, nitrite concentration can be measured by FIA or SIA [START_REF] Trojanowicz | Recent advances in flow injection analysis[END_REF][START_REF] Šraj | Analytical challenges and advantages of using flow-based methodologies for ammonia determination in estuarine and marine waters[END_REF]. Concerning its UV absorption characteristics, nitrite ion also presents a specific absorption in the far UV region of spectrum, slightly different from the one of nitrate (Fig. 6.6). A first peak appears, as for nitrate, at 210 nm for relatively low concentrations (actually, rather high with respect to regulation limits). This first peak is shown from concentrations greater than 0.5 mg NO 2 2 L 21 for a 10 mm pathlength. A second peak appears at 355 nm when concentration increases from 0.2 g NO 2 2 L 21 , without dilution for a 10 mm pathlength, as for nitrate. However, contrary to the nitrate spectrum, a shoulder at 280À300 nm accompanies the second peak. This difference can be used for the analysis of nitrate and nitrite in mixture. Actually, as nitrite is very unstable and is easily oxidized into nitrate, its concentration in water is often very low. Thus UV spectrophotometry seems to be useful, for example, for industrial applications where nitrite concentration may be higher than 0.5 mg NO 2 2 L 21 (in agrofood industry wastewater, for example). Based on the spectra characteristics of nitrite solutions (Fig. 6.6), the expected figures of the UV method are a measuring range of 1 to 30 mg NO 2 2 L 21 with a detection limit of 1 mg NO 2 2 L 21 .

Total Kjeldahl nitrogen measurement

Concerning the determination of nitrogenous organic compounds, several methods are available often coupled with phosphorous organic compounds [START_REF] Worsfold | Characterisation and quantification of organic phosphorus and organic nitrogen components in aquatic systems: a review[END_REF], but the measurement of the TKN remains the main procedures. Several methods using UV radiation for the mineralization of samples have been proposed in order to simplify the reference Kjeldahl procedure [START_REF] Lin | Simultaneous determination of total dissolved nitrogen and total dissolved phosphorus in natural waters with an on-line UV and thermal digestion[END_REF]. These methods generally require a classical low-pressure mercury lamp emitting at 254 nm. The use of the far UV radiation of the Hg lamp (185 nm) is made possible by using transparent Suprasil quartz and leads to the improvement of the photodegradation process as compared to the Kjeldahl method (5 to 10 hours for Kjeldahl method; 2 to 3 hours for direct UV). The use of a strong oxidant with a far UV radiation leads to the drastic decrease of the reaction time (5 to 10 minutes) [START_REF] Roig | Measurement of dissolved total nitrogen in wastewater by UV photooxidation with peroxodisulphate[END_REF]. The reaction can be followed by UV spectrophotometry (Fig. 6.7) with the disappearance of UV spectra of initial compounds and the appearance of that of final compound (nitrite and nitrate). The quantification is possible with the semideterministic approach (Chapter 3) by using two sets of reference spectra for the restitution of spectra acquired during the photodegradation. The first basis is the one defined for the estimation of aggregated parameters (see Chapter 5) in water and wastewater. The second basis is simpler as it can include only nitrate and nitrite spectra.

For TKN determination, the photooxidation is carried out in the presence of an oxidant solution (potassium peroxodisulfate K 2 S 2 O 8 buffered to pH 9). In this case, both organic and inorganic nitrogen compounds are converted into nitrate. The concentration of TKN is equal to the difference between nitrate measured after photooxidation ([NOX] f ), and nitrate measured before ([NOX] i ):

TKN ½ 5 NOX ½ f À NOX ½ i
The procedure was first applied on model compounds. Table 6.2 displays the results of the determination of the nitrogen concentration of various N-containing compounds. The conversion into nitrate from all compounds is quantitative, whatever the concentration, and the conversion times are very short, around 5 minutes of irradiation time [START_REF] Roig | Measurement of dissolved total nitrogen in wastewater by UV photooxidation with peroxodisulphate[END_REF].

The conversion into nitrate is possible under UV irradiation without the presence of chemical oxidant, with an increase of the reaction time (around 2 hours).

The validation of the procedure has been carried out from the UV/UV estimation of TKN concentration of 80 samples of urban and industrial wastewater. TKN standard method was used as reference method, and the results are shown in Fig. 6.8. A good adjustment can be observed between the results for a wide concentration range. From few mg N L 21 to several hundred mg N L 21 , the comparison between the two methods is good, as well as the precision.

Thus the UV/UV method can be used as an alternative way for the reference TKN method.

Ammonium measurement

Ammonium determination is usually carried out with CFA, FIA, or SIA [START_REF] Šraj | Analytical challenges and advantages of using flow-based methodologies for ammonia determination in estuarine and marine waters[END_REF][START_REF] Almeida | A membraneless gas-diffusion unit -multisyringe flow injection spectrophotometric method for ammonium determination in untreated environmental samples[END_REF]. With the UV/UV procedure two steps of photooxidation are needed [START_REF] Roig | Alternative method for the measurement of ammonium nitrogen in wastewater[END_REF]. The first one allows the measurement of TKN as shown above. Then, a second one is carried out in the presence of an oxidant solution (potassium peroxodisulfate K 2 S 2 O 8 ), without buffer. In these particular conditions (acidic medium), only organic nitrogen compounds are converted into nitrate, as will be explained afterward.

The concentration of ammonium can be calculated by the difference between the TKN-estimated concentration ([TKN]) and the one of organic nitrogen ([N ORG ]), taking into account an eventual dilution. The relation is the following, where all concentrations must obviously be expressed in the same unit (mg N L 21 ): A validation was carried out for 80 industrial wastewater samples analyzed with both a standard method (capillary electrophoresis) and the UV/UV one (Fig. 6.9). A good adjustment can be observed between the results for a wide concentration range (1À100 mg N L 21 ) and the detection limit is 1.2 mg NH 4 1 L 21 , confirming that this method is only suitable for high ammonium concentrations.

½NH 1 4 5 ½TKN 2 ½N ORG
The presented UV/UV method allows the simple and reliable determination of all nitrogen forms by using the same technique. Moreover, the total reaction time is rather short as a maximum of 40 minutes is required for all measurements (Table 6.3).

Some comments can be made concerning the process, and more precisely the impact of the pH on the photodegradation results. Actually, the photooxidation of nitrogenous organic compounds leads to the cleavage of CÀN bond resulting in the formation of ammonium radical FIGURE 6.9 Comparison of ammonium determination for industrial wastewater (reference method is capillary electrophoresis). TABLE 6.3 Time analysis (in minutes) for the determination of nitrogen forms.

NO x N org N global TKN NH 1 4 Photooxidation no 10À15 10À15 no no Measurement 1 1 1 no no Exploitation 1 (dec) 1 (dec) 1 (dec) 1 (cal) 1 (cal) Total 2 10À15 10À15 1 1
Note: dec, deconvolution; cal, calculation. TKN, total Kjeldahl nitrogen.

NH 1 4 [START_REF] Low | Formation of nitrate and ammonium ions in titanium dioxide mediated photocatalytic degradation of organic compounds containing nitrogen atoms[END_REF]. A hydrolysis step follows this reaction in order to obtain first ammoniacal nitrogen and second the final oxidized forms of nitrogen, that is, nitrite and nitrate.

Moreover, the pH value allows the specific reactivity of organic and i n o r g a n i cn i t r o g e n .T h ep He f f e c tc a nb es t u d i e df r o mt h ec o m p a r i s o no f the photooxidation of urea (as organic nitrogen) and ammonium chloride (as inorganic nitrogen). It appears that the conversion of urea is weakly modified by the pH and varies between 80% and 95%, whatever the pH value, whereas the conversion yield from the ammonium nitrogen is very weak in acidic medium and becomes quantitative for basic conditions [START_REF] Lowry | A rapid automated system for the analysis of dissolved total organic nitrogen compounds in lake waters[END_REF].

T h ep r e s e n c ei nw a s t e w a t e ro fs e v e r al organic (solvent) and inorganic (carbonates) compounds may interfere with the photooxidation because they are scavengers, inhibiting the action of oxidant radicals. Their action can decrease the conversion yield to 50% in function of the concentration [START_REF] Worsfold | Characterisation and quantification of organic phosphorus and organic nitrogen components in aquatic systems: a review[END_REF].

P compounds

Two reviews about phosphorus determination in natural waters were published recently [START_REF] Worsfold | Determination of phosphorus in natural waters: A historical review[END_REF][START_REF] Du | detection of phosphorus species in water: technology and strategies[END_REF]. Considering the role of excess phosphorus in eutrophication and algae blooms, the monitoring of dissolved phosphorus in water and wastewater is important. The main analytical methods for the determination of phosphorus are spectrophotometric ones with the formation of a phosphomolybdate complex. The phosphorus compounds in water and wastewater concern not only some organic forms (natural or anthropic) but also orthophosphate ion and acid hydrolyzable phosphate (condensed phosphate) (Fig. 6.10).

Standard methods [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF] used for the determination of total phosphorus include several procedures. Orthophosphates PO 32 4 and associated forms ÀÁ are determined by colorimetry, ion chromatography, or spectrophotometry (UVÀvisible). Acid hydrolysis allows the transformation of polyphosphates in orthophosphates, which are measured by one of the mentioned methods. Finally, a chemical digestion, followed by the determination of resulting species PO 32

4

ÀÁ

allows the measurement of organic phosphorus forms. Procedures are time-consuming (more than 5 hours) and require strong conditions (acidic medium, high temperature, and catalyst).

Some improvements have been proposed, such as the use of photooxidation as an alternative to chemical digestion, as it has been successfully used for similar applications [START_REF] Worsfold | Determination of phosphorus in natural waters: A historical review[END_REF][START_REF] Nagul | The use of on-line UV photoreduction in the flow analysis determination of dissolved reactive phosphate in natural waters[END_REF][START_REF] Thomas | Wastewater quality monitoring[END_REF] particularly for flow analysis. In order to minimize the photooxidation time, the UV light source (high-, medium-, or low-pressure mercury lamp) can be associated with oxidants (hydrogen peroxide or potassium peroxodisulfate). Generally, the converted forms (orthophosphates) are determined by off-line analysis but can also be measured by CFA, FIA, or SIA.

In this section, a simple procedure, based on the use of a UV photooxidation module (previously described) and a UVÀvisible measurement, is presented [START_REF] Pouly | An alternative method for the measurement of mineral sulphide in wastewater[END_REF]. Another procedure, based on the use of the alternative vanadomolybdophosphoric acid method with a UV-LED detection at 380 nm can also be envisaged [START_REF] Bowden | The determination of phosphorus in a microfluidic manifold demonstrating long-term reagent lifetime and chemical stability utilising a colorimetric method[END_REF].

General procedure

As previously mentioned, phosphorus compounds are commonly classified into orthophosphates PO 32 4

ÀÁ

; acid-hydrolyzable (condensed) phosphates, and organic phosphates. It must be noticed that acidhydrolyzable phosphates (as pyrophosphates) are negligible in sewage [START_REF] Jolley | Rapid method for separating and quantifying orthophosphate and polyphosphates: application to sewage samples[END_REF]. The general procedure illustrated in Fig. 6.11 includes two main steps: an indirect UVÀvisible measurement for PO 32

4

ÀÁ

and a FIGURE 6.11 Speciation of phosphorus in wastewater.

photooxidation step followed by a UVÀvisible measurement for global phosphorus determination (P GL ). First, orthophosphates are determined by the spectrophotometric measurement of the phosphomolybdate complex (formed with addition of ammonium molybdate 40 g L 21 ) using the spectrum deconvolution method (Chapter 3).

Then, an oxidant solution (40 g L 21 potassium peroxodisulfate K 2 S 2 O 8 ) is added to the sample for the photoconversion (15-minute irradiation times) of the organic phosphorus forms into orthophosphates. Orthophosphates are then determined by UVÀvisible spectrophotometry.

The procedure allows the measurement of orthophosphate PO 32 4 ÀÁ and global phosphorus (P GL ). The determination of the sum of organic and hydrolyzable phosphorus P ORG 1 P hyd 5 P GL 2 PO 32 4 ÀÁ is then possible.

Orthophosphates

The measurement of orthophosphates is generally assumed thanks to the phosphomolybdate complex formation produced and detected in a flow analysis system (CFA, FIA, or SIA). For UV determination, the deconvolution procedure [START_REF] Thomas | UV spectral deconvolution: a valuable tool for waste water quality determination[END_REF] can be used with a basis of reference spectra corresponding to the molybdate solution (2.4 g L 21 ) and to the phosphomolybdate complex obtained from 10 mg L 21 of orthophosphate. Notice that in this case the use of a simple multicomponent procedure may be sufficient. The quantification is carried out between 380 and 450 nm. The orthophosphate concentration is given by the product of the phosphomolybdate complex coefficient by the concentration of the corresponding reference spectrum. Fig. 6.12 shows the comparison between the orthophosphate concentration estimated by deconvolution and the concentration measured by ascorbic FIGURE 6.12 UV estimation of orthophosphate concentration [START_REF] Almeida | A membraneless gas-diffusion unit -multisyringe flow injection spectrophotometric method for ammonium determination in untreated environmental samples[END_REF]. acid colorimetry as a reference method. The UV-estimated concentrations are in good agreement with the expected ones and then can be used as an alternative to the standardized method. Even if the characteristics of the method are interesting with a detection limit of 10 µgPO 4 L 21 ,t h i sm u s tb e lowered up to 5 µgPO 4 L 21 for trace analysis. Classical methods based on flow analysis techniques are more adapted in this case.

Total phosphorus

As orthophosphates, total phosphorus is generally determined by flow analysis (CFA, FIA, or SIA). Inductively coupled plasma with optical emission spectroscopy (ICP-OES) can also be used for detection if concentrations are sufficiently high [START_REF] Worsfold | Determination of phosphorus in natural waters: A historical review[END_REF] as well as atomic absorption spectroscopy (AAS). The determination of total phosphorus needs a photooxidation step in the presence of an oxidant (potassium peroxodisulfate, for example) allowing the transformation of all phosphorus forms into orthophosphates that are complex (with a molybdate solution) when they are formed [START_REF] Pouly | An alternative method for the measurement of mineral sulphide in wastewater[END_REF].

Phosphorus forms

À!

hv=S 2 O 22 8 =Molybdate
PO 32 4 Table 6.4 displays the results for the determination of the orthophosphate concentration from the photooxidation of various P-containing compounds. The molybdate solution (1.5 mL) is introduced into the reactor in order to follow the phosphomolybdate complex formation. The conversion yields are quantitative using irradiation time no longer than 15 minutes.

The UV/UVÀvisible method was applied for the determination of total phosphorus from raw effluents. The results were compared with those obtained by atomic absorption spectrometry (AAS) as the reference method (Fig. 6.13) and the comparison showed a good correlation (R 2 5 0.979). The detection limit was 0.05 mg P L 21 for a range of 0.05 to 10 mg P L 21 .

The UV/UV system was described as an efficient method for the measurement of phosphorus in wastewater. According to the experimental conditions of photooxidation or UV measurement, it is possible to evaluate the major part of phosphorus forms (oxidized, organics, inorganics, and hydrolyzable) and total phosphorus.

Finally, a recent method for the simultaneous determination of total dissolved nitrogen and total dissolved phosphorus in natural waters with an online UV and thermal digestion was proposed [START_REF] Lin | Simultaneous determination of total dissolved nitrogen and total dissolved phosphorus in natural waters with an on-line UV and thermal digestion[END_REF].

S compounds

Sulfur occurs in wastewater in various forms. Most of the time, anoxic conditions in urban sewer lead to the production of hydrogen sulfide, but the presence of sulfur compounds is more often related to industrial discharges, mainly from refineries or petrochemical plants.

Some petroleum contains elemental sulfur, which can occur as hydrogen sulfide (H 2 S) and carbonyl sulfide (COS). Sulfur is also present in a wide range of hydrocarbons, largely as mercaptans, organic sulfides, and thiophene derivatives [START_REF] Connell | Basic Conepts of Environmental Chemistry[END_REF]. Sulfur compounds tend to be concentrated in the higher boiling fractions of petroleum, are generally corrosive to metals, and may poison various catalysts. Stripping water is responsible for the presence of sulfide and mercaptans into crude oil refinery wastewater.

Sulfide under dissolved H 2 S form is toxic for fish and other aquatic organisms and can be responsible for the decrease of wastewater treatment plants' efficiency. Therefore its concentration needs to be controlled, especially in wastewater from crude oil refineries.

Inorganic sulfur compounds are numerous and can be classified, as for nitrogen, between reduced and oxidized forms. Table 6.5 lists these compounds and their main origin areas, when they are found in water or wastewater.

The reduced forms of sulfur are also called total sulfides, as they are all associated with the acido-basic equilibrium of hydrogen sulfide (at 25 C): pKa H 2 S=HS À ÀÁ 5 7:05 pKa HS À =S 2À ÀÁ 5 12:92

Considering the pKa values, the predominant form is the bisulfide ion (HS 2 ), since the molecular form of hydrogen sulfide (H 2 S) is volatile. This observation is true if the pH value of water or wastewater is about 7.

The corresponding UV spectra, the shape of which depends on the pH value, are shown in Fig. 6.14. An important peak can be noted at 231 nm, related to the presence of hydrogen sulfide and corresponding to the bathochromic shift between the two forms of first acidity (notice that the spectrum of acidic solutions are much less absorbing because of the hypochromic effect and volatility of hydrogen sulfide).

From an analytical point of view, total sulfide includes dissolved H 2 S and bisulfide ion HS 2 , which are in equilibrium with hydrogen ions. For pH values of wastewater, the S 22 form is generally negligible, less than 1% of the dissolved sulfide under pH 10. Sulfide can be determined in different media, using various techniques [START_REF] Lawrence | Analytical strategies for the detection of sulfide: a review[END_REF][START_REF] Ferrer | Analytical methodologies for reliable sulfide determinations in aqueous matrices exploiting flow-based approaches[END_REF], including flow analysis systems (FIA and SIA). Three main methods are commonly used for the determination of sulfide in solution:

1. the colorimetric method, with methylene blue, based on the reaction of sulfide, ferric chloride and dimethyl-p-phenylenediamine to produce methylene blue, which absorbs at 664 nm [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF]; 2. the iodometric method based on the oxidation of sulfide by iodine in acidic solution followed by a back titration with sodium thiosulfate solution; 3. the potentiometric method using a selective silver electrode. Fig. 6.15 shows UV spectra of refinery wastewater containing mineral sulfide (with corresponding dissolved organic carbon (DOC) around 1000 mg C L 21 ). The value of samples' pH is around 9. The characteristic peak of bisulfide ion appears clearly on the UV spectra (231 nm), despite the matrix sample. The intensity of the UV band is related to the concentration of sulfide.

The use of a UV spectrophotometric procedure can also be proposed as an alternative method for the determination of inorganic sulfide in water and wastewater. A first method, based on the use of a multiwavelengths procedure, has been proposed for natural water [START_REF] Guenther | Determination of total sulfide and iodide in natural water, Moss Landing[END_REF]. The interferences are modeled from an exponential function and the simultaneous determination of total sulfide and iodide is possible. A second method integrates the semideterministic deconvolution procedure or UVSD method [START_REF] Thomas | UV spectral deconvolution: a valuable tool for waste water quality determination[END_REF][START_REF] Pouly | An alternative method for the measurement of mineral sulphide in wastewater[END_REF].T h e potentiometric method will be chosen as reference for the validation of this last procedure. The UV quantification is carried out by deconvolution (see Chapter 3) between 205 and 320 nm. Raw samples were diluted four times to prevent the UV signal saturation for a 10-mm quartz cell. Sulfide concentration is given by the product of the contribution coefficient of sulfide reference spectrum (replacing nitrate in the previous set) and the corresponding concentration, affected by the dilution factor. About 40 wastewater samples from refineries were used for the validation of the UV method [START_REF] Pouly | An alternative method for the measurement of mineral sulphide in wastewater[END_REF]. Fig. 6.16 shows a good linear adjustment between the measured concentration by the potentiometric method and UV determination of sulfide. The characteristics of the UV method (without dilution) are a concentration range between 0.5 and 15 mg S L 21 and a detection limit of 0.5 mg S L 21 . Some compounds absorbing close to 231 nm sometimes present in raw wastewater samples can interfere with sulfide spectra. Several compounds, for example, p-chlorophenol (absorption at 227 nm), anionic surfactant, RBS commercial product (absorption at 223 nm), and 1-propanthiol (absorption at 239 nm), were tested, and the results show low interference values to the studied compounds [START_REF] Pouly | An alternative method for the measurement of mineral sulphide in wastewater[END_REF]. The error of restitution by deconvolution was 5% at maximum with the highest interference associated with anionic surfactant (leading to an error of 4.3%).

The UV method has been described as a simple and reliable procedure for the determination of sulfide in wastewater. Compared with some reference methods, it is less sensitive but do not need any sample preparation (pretreatment, filtration, etc.) and is unaffected by interferences (salinity, suspended matter, organics compounds, etc.).

Recently, two UV-based methods were proposed. The first one [START_REF] Dupraz | Fast determination of the main reduced sulfur species in aquatic systems by a direct and second-derivative spectrophotometric method[END_REF] is a fast determination of the main reduced sulfur species (sulfides, sulfites, and thiosulfates) in aquatic systems by a direct and second-derivative spectrophotometric method, based on the comparison of SDA spectra of the same sample at different pH (9.2, 4.7, and 1.0) and selected absorption wavelengths (250 and 278 nm). The second method is a field method for the determination of trace levels of sulfite in natural waters [START_REF] Leng | A simple field method for the determination of sulfite in natural waters: based on automated dispersive liquid-liquid microextraction coupled with ultraviolet-visible spectrophotometry[END_REF],b a s e do n automated dispersive liquidÀliquid microextraction (DLLME) coupled with ultravioletÀvisible spectrophotometry. The automated DLLME system was designed around a single syringe pump coupled with a multiposition valve. The method allows the precise determination of trace levels of sulfite with a detection limit of 1 µgL 21 .

Concerning the determination of sulfate ion, there exist several standard methods [START_REF] Baird | Standard Methods for the Examination of Water and Wastewater: 4500 Sulfate, American Public Health association[END_REF], such as the ion chromatographic method, capillary ion electrophoresis (for low concentrations), and gravimetric methods for concentration above 10 mg L 21 . Moreover, two procedures used a final optical detection, one based on turbidimetry after precipitation with Baryum chloride (measurement of the absorbance at 420 nm) and the other based on the automated methylthymol blue method (final detection at 460 nm).

Simple colorimetric reactions are not available for sulfate analysis and sulfate ion does not absorb in the UVÀvisible range. However, a recent spectrophotometric method was proposed by Salem and Draz [START_REF] Salem | Synthesis and application of silver nanorods for the colorimetric detection of sulfate in water[END_REF] thanks to the synthesis of PEG-25 stabilized silver nanorods used as sensing probes for the colorimetric determination of sulfate from the decrease of the peak around 460 nm.

Cl compounds

Chlorine compounds are potentially numerous, as sulfur ones, with several oxidation states. Nevertheless, there is a great difference between the two elements, because all oxidized forms of chlorine compounds are generally unstable in solution contrary to sulfate ion. Some of them, for example, chlorine itself (Cl 2 ), hypochlorite ion (ClO 2 ), and chlorine dioxide (ClO 2 ), are used as oxidant agents for tap water production or swimming pool treatment.

Chloride

Chloride ion is one of the major inorganic anions in water and wastewater because it is the more stable form of chlorine in solution. Chloride concentration is very variable and can be high not only in seawater. It is used for domestic purpose, but rather often for industrial processes. In some applications, the resulting concentration in wastewater can be important and greater than 1 g L 21 (food and chemical industry, for example).

Fig. 6.17 presents several spectra of industrial water containing chloride as compared to seawater. In all cases, the shape of chloride signal can be observed, characterized by a very high increase of absorbance values below 210À220 nm, always convex, in contrast to nitrate. The difference between industrial cooling water UV spectra and seawater spectrum is that the first ones show a residual diffused absorption for wavelengths greater than 220 nm due to the presence of organic matter at a higher concentration than in seawater.

Several methods can be used for the determination of chloride in water [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF]. The argentometric and mercuric nitrate methods are based on the titration of chlorine in the presence of an indicator. Experimental procedures are easy, but many substances may interfere with the results. There are also other methods such as potentiometry, capillary electrophoresis and other automated colorimetric methods implemented in flow analysis systems (CFA, FIA, or SIA). Taking into account its UV absorption signal, chloride concentration can be quickly estimated by UV for high concentrations (above 500 mg L 21 ). The semideterministic method (Chapter 3) used for UV spectra exploitation can be applied by integrating the spectrum of a chloride solution on the basis of reference spectra. The concentration is then calculated by multiplying the corresponding chloride concentration with the contribution coefficient of the chloride spectrum.

For a wavelength window between 200 and 320 nm, the method can be applied for a concentration range of 0.5À6gL 21 with a detection limit of 0.5 g L 21 . A comparison between this UV procedure and the reference potentiometric method has been carried out on 110 industrial samples. Fig. 6.18 shows the quality of the adjustment between the two sets of results.

Hypochlorite

Chlorine may also be found in water under the hypochlorite ion form, which is a strong oxidant used for water and housing disinfection. It is used for tap water production as well as for swimming pool water treatment or, in some cases, for the oxidation of odorous compounds. This product (commonly found as "Eau de Javel" or bleach solution) also has a persistent disinfecting action as long as hypochlorite remains in the solution. The residual concentration must thus be sufficient, but not in large excess, because of the formation of organohalogeno compounds such as chloramines, which are responsible for eye irritations and can even be toxic.

The presence of hypochlorite ion can easily be monitored by UV spectrophotometry for relatively high concentrations, because its UV spectrum presents, contrary to the one of chloride ion, an important Gaussian-like peak centered on 290 nm. Applications for oxidation process control using hypochlorite, gaseous chlorine, or chlorine dioxide are thus possible using UV spectrophotometry. The spectrum exploitation is possible with the semideterministic method (by including the corresponding reference spectrum, as previously) but a simpler absorptiometric procedure can be used at 290 nm, if interferences (organic compounds, suspended solids, etc.) are negligible. Fig. 6. [START_REF] Crumpton | Nitrate and organic N analysis with 2nd-derivative spectroscopy[END_REF] shows some examples of samples of swimming pool and deodorization water. A comparison has been carried out between the concentration obtained by UV spectrophotometry, either simple absorptiometry at 290 nm or with the semideterministic approach. Fig. 6.20 shows the right adjustment for the results for 10 samples of real water with standard additions of hypochlorite.

For a wavelength window between 220 and 325 nm or a single wavelength at 290 nm if no interferences are present, the method can be applied for a concentration range of 0 to 400 mgCLO 2 L 21 with a detection limit of 5 mg L 21 . Using a 100-mm pathlength, this last can be lowered to 0.5 mg L 21 , a value acceptable for some regulation applications.

Organochlorine compounds

The use of UV spectrophotometry for the estimation of monochloramine in water distribution systems was recently reported [START_REF] Sung | Technical note: using UV-vis spectrophotometry to estimate nitrite plus nitrate and monochloramine[END_REF], coupled with the determination of nitrate and nitrite. A model based on the absorbance values measured at 220, 245, 280, and 320 nm gave an estimate of monochloramine concentration. Implemented in an online UVÀvisible spectrophotometer, this method was applied to a given water distribution system and further experiments are needed to check the interest of the method on other sites, regarding potential interferences with organic matter and pH.

Finally, the monitoring of total organochlorine compounds (TOX) during chlorination was proposed from the decrease of the absorbance value at 272 nm [START_REF] Korshin | The decrease of UV absorbance as an indicator of TOX formation[END_REF]. This approach is detailed in Chapter 10.

Metallic constituents

The constant evolution of water quality standards implies the development of faster and cheaper analytical procedures. These are more particularly adapted for online measurement, for the frequent analysis of metallic constituents or for the estimation of global parameters. The cheapest and simplest methods for the determination of metallic constituents are colorimetric ones, which are less precise and selective than instrumental reference methods such as graphite furnace (GF)-AAS or ICP-OES. Other instrumental techniques based on electrochemical principles are also proposed for water quality monitoring, but they are relatively expensive, sensitive to interferences, and, thus, rather inappropriate for wastewater monitoring.

The improvement of UVÀvisible spectrophotometers has led to a renewal in the colorimetric procedures, actually absorptiometric, with the possibility of simultaneous metallic compound determination after selective complexation. Based on the reaction between a ligand and some metallic elements, these complexometric procedures use absorptiometry for final detection generally through flow analysis systems (CFA, FIA, or SIA).

Before considering some of these complexometric procedures with final UVÀvisible detection, designed for the simultaneous determination of metallic constituents, a more simple approach must be considered. In the case of UVÀvisible absorption for some metallic constituents without any reagent, it is interesting to check the feasibility of a direct absorptiometric measurement. This is studied in the first part with the determination of chromium in water and wastewater.

Chromium (direct measurement)

Hexavalent chromium

Chromium VI is one of the metallic contaminants often encountered in industrial wastewater, particularly for metal processing activities such as electroplating, for example. Because of its toxicity, its maximum concentration allowed in treated wastewater must generally be 50 µgL 21 before being discharged into a receiving medium.

There exist several analytical methods for chromium VI determination, often very complex [START_REF] Rao | Determination of chromium in natural waters: a review[END_REF][START_REF] Ahmad | Trace determination of Cr(III) and Cr(VI) species in water samples via dispersive liquidliquid microextraction and microvolume UVÀVis spectrometry. Thermodynamics, speciation study[END_REF]. One of the most simple and widespread methods is the former diphenylcarbazide colorimetric one. Its detection limit is about 1 µgL 21 , but the procedure is time-consuming.

Another type of method is based on the spectrophotometric properties of Cr (VI), sometimes used as standard solution [START_REF] Burgess | Standard in Absorption Spectrometry[END_REF]. Moreover, the spectrophotometric determination of Cr (VI) is well known in the field of water examination, as it can be used for alternative measurement of chemical oxygen demand (COD) [START_REF] Thomas | La mesure de la demande chimique en oxyg{e `}ne dans les milieux faiblement pollu{e ´}s[END_REF] (see Chapter 5). Two other UVÀvisible spectrophotometric methods have been proposed. The first one [START_REF] Oumedjbeur | Rapid determination of chromium (6) in natural waters[END_REF], designed for natural water, uses the peak height measurement at 372 nm, for a basified sample (pH . 9). The peak height is calculated from the absorbance values at three wavelengths (310, 372, and 480 nm), taking into account a very simple third-degree polynomial interference signal.

The second UVÀvisible spectrophotometric method [START_REF]a f f r e c h o u x ,U l t r aviolet multiwavelength absorptiometry (UVMA) for the examination of natural waters and wastewaters Part III. Determination of chromium VI[END_REF] was proposed for natural and urban wastewaters with a more general mathematical compensation of interferences. Both UVÀvisible spectrophotometric methods are rapid and simple with a detection limit of around 5 µgL 21 for a 50-mm optical pathlength. Unfortunately, they cannot be applied for industrial wastewater survey, as the presence of specific compounds cannot be modeled by the mathematical tools used for the removal of interferences.

The application of the semideterministic approach, described in Chapter 3 and applied before in this chapter, can be used for the determination of hexavalent chromium. Exceptionally, the optical pathlength is 50 mm for this application because of the regulation compliance constraint. Contrary to the previous determination (nitrate, sulfide, hypochlorite, etc.), this application must take into account the pKa value (about 5.8) of the dichromate in equilibrium with the chromate form:

Cr 2 O 22 7 1 3H 2 O$2CrO 22 4 1 2H 3 O 1
As the pH of industrial wastewater must be around the pKa value (before neutralization), both chromate and dichromate spectra must be chosen in the basis of reference spectra, taking into account the influence of pH on chromium VI speciation (Fig. 6.21). The two first reference spectra correspond to chromium VI solutions of pH 3.5 and 9.5, respectively. Fig. 6.22 shows real spectra from industrial wastewater and natural sample containing hexavalent chromium at different concentrations.

The spectra of Fig. 6.21 show two absorption peaks in the UV region, depending on pH, and a slight residual absorbance in the visible one. Bathochromic and hyperchromic effects can be noticed between the acidic and basic media. The resulting visible color in the sample containing hexavalent chromium for neutral pH is orange.

A comparison between the diphenylcarbazide and UVÀvisible method for Cr (VI) determination was carried out for more than 50 samples of different origins (44 industrial wastewaters, 8 urban wastewaters, and 4 natural waters), the concentration of which varied between 0 and almost 1 mg L 21 . Fig. 6. [START_REF]a f f r e c h o u x ,U l t r aviolet multiwavelength absorptiometry (UVMA) for the examination of natural waters and wastewaters Part III. Determination of chromium VI[END_REF] shows some examples of the sample spectra. The results of the comparison are shown in Fig. 6.23, and the adjustment is quite good. For a wavelengths window between 300 and 450 nm, the method can be applied for a concentration range of 5 to 1000 µgCr L 21 with a detection limit of 5 µgL 21 .

As the method is designed for industrial applications, the interference of some metallic compounds must be checked. Indeed, different ions, such as copper (II), iron (III), lead (II), and mercury (II), for example, potentially existing in electroplating wastewater, may interfere with the determination of Cr (VI). Except in the presence of Fe 31 , the measurement of Cr (VI) gives an error generally lower than 3% for 0.5 mg L 21 of metallic ion, and for greater concentrations (up to 10 mg L 21 ), the error is negligible for Cu 21 , and lower than 15% for the other ions [START_REF] Gomez | Simultaneous spectrophotometric determination of calcium and magnesium in water[END_REF].

The reason why Fe 31 interferes is shown in Fig. 6.24. Even for a concentration of 1 mg L 21 ,F e 31 , which is the most probable form of dissolved iron in water which absorbs around 300 nm in acidic medium. In this case, the quadratic error of the deconvolution is too high. An increase of the pH value up to 9 (with some drops of NaOH 1M, for example) leads to the precipitation of the hydroxide form, the spectrum of which is very close to the reference of suspended solids. With this simple pretreatment, the error in Cr (VI) determination between the diphenylcarbazide and the UVÀvisible methods becomes lower than 2.5%.

Trivalent chromium

Trivalent chromium (Cr 31 ion) is not as toxic as the hexavalent form and can be directly detected by visible spectrophotometry, its UV absorption being nonspecific. The UVÀvisible spectra of the trivalent form shows a great difference with the one of the hexavalent forms. At pH 1 and 5, two peaks of absorbance are noted at 433 and 600 nm, with very close absorbance values and giving a green color to the solution.

The main application of the optical properties of Cr 31 ion is the final colorimetric determination of COD with the measurement of absorbance at 600 nm, maximum of absorbance in acidic medium (see Chapter 5). As a consequence, the direct spectrophotometric determination of Cr 31 ion in water and wastewater is limited to highly concentrated samples. Some methods for the indirect determination of Cr 31 ion in water or wastewater are proposed in the following section.

Metallic constituents determination by complexometry

Several procedures for the simultaneous determination of metallic constituents have been proposed at least for 25 years (Table 6.6). These analytical methods published since the 1990s show the evolution of the nature of the reagents and the spectrophotometric detection method. The majority of methods was implemented in flow analysis systems (CFA, FIA, or SIA), but the lack of substantial validation on real samples explains why these methods are actually not used for water or wastewater monitoring, for which reference methods such as ICP-OES are preferred. All methods are based on the main complexometric reaction between a reagent (ligand) and some metallic elements, after a liquidÀliquid or solid-phase extraction step if needed, and the resulting signal is exploited in order to determine the corresponding concentrations. The exploitation methods are different according to the methods, based on simple absorptiometry, derivative spectrophotometry, spectral deconvolution, or chemometrics methods (namely PLS). The choice of the different reagents (complexant, buffer, etc.) is obviously dependant on the metallic ion to be determined, but also on their optical properties (principally in the visible region). Several complexant mixtures are proposed in Table 6.6.

Concerning the choice of the metallic constituents, the majority of studies deal with the main metallic contaminants in water and wastewater, but some other elements found at ultratrace level are also considered (e.g., Co, Pd, and Ru).

As an example, a complexometric method for the simultaneous determination of Cu, Fe, and Hg in water and wastewater is presented more in details [START_REF] C O U L O M B | d a ,O .T h o m a s, Fast and simultaneous complexometric determination of copper (II), iron (II) and mercury (II) in natural waters and effluents using a robust UV-visible spectral deconvolution[END_REF]. The complexant solution is based on the use of dithizone (diphenyl-1,5-thiocarbazone) widely used for metal analysis up to the seventies [START_REF] Budesinsky | Stability constants of some metal dithizonates[END_REF][START_REF] Irving | The analytical application of dithizone[END_REF]. The dithizone solution is mixed with EDTA employed as masking agent, BHA (butylhydroxyanisol), glycine, ethanol, and distilled water.

Taking into account the possible metallic hydroxide precipitation and the potential presence of natural complexes (with humic substances in natural waters, or with specific compounds in industrial wastewater) [START_REF] Moore | Heavy Metals in Natural Waters[END_REF], the working pH is fixed at about 2.8, with a glycine solution for the stabilization of the dithizone spectrum. Notice that the glycine and its eventual metallic complexes are almost transparent in the UV region and do not change the general shape of the spectra of the final mixture [START_REF] Theraulaz | Me ´thodes Complexometriques Rapides de Dosage Des Me ´taux Dans Les Eaux Par Spectrophotome ´trie UV-Visible[END_REF]. Similarly, EDTA (in all the wavelength range) and BHA (transparent above 310 nm), alone or complexed, do not interfere with the UV signal except for copper and iron complexes, responsible for a great absorbance in the UV region.

The quantification of the metallic constituents studied [Cu (II), Hg (II), and Fe (II)] is carried out by the spectral semideterministic method or by any multicomponent procedure (see Chapter 3). The choice of the wavelength range depends on the studied element and on the corresponding basis of reference spectra. Moreover, the optical pathlength is either 10 or 50 mm for high or low concentration, respectively, with two reactive solution concentrations [START_REF] Theraulaz | Me ´thodes Complexometriques Rapides de Dosage Des Me ´taux Dans Les Eaux Par Spectrophotome ´trie UV-Visible[END_REF].

The UVÀvisible spectra of the metallic complexes constitute the basis of reference spectra used for the calculation of Cu (II), Hg (II), and Fe (II) concentrations. Fig. 6.25 shows these reference spectra (completed by a blank of the reagent) and also shows that the UV region is of poor interest for the purpose, taking into account the optical properties of the chosen reagents. Each of these spectra corresponds to a given concentration of a metallic constituent, which serve for the final concentration calculation of a sample. This value is dependant on several parameters, among which the concentration of the studied metal, related to the stoichiometric equilibrium (with dithizone) and the dilution rate of the sample in the sampleÀreagent mixture. The metallic constituent concentration of an unknown sample corresponds to the product of this value by the contribution coefficient related to the corresponding dithizonate spectrum in the linear combination.

For natural waters and/or effluent applications, some interference may occur with the presence of natural or anthropogenic chelating agents. For example, humic substances can compete with dithizone for metallic constituent complexation in natural waters [START_REF] Buffle | Complexation Reactions in Aquatic Systems: An Analytical Approach[END_REF]. In this case, the degradation of organometallic complexes must be effective before the analytical determination. A photodegradation step, with a simple device as the one already proposed in this chapter for the determination of N and P compounds, can be used for the purpose. However, contrary to the previous procedure using an oxidative reagent, the decomplexation can be carried out without the reagent [START_REF] Ghasemi | Surfactant-mediated complex formation for determination of traces amounts of zinc, cadmium, and lead with 4-(2-thiazolylazo) resorcinol and chemometric methods[END_REF].

The characteristics of the method for high-and low-concentration mixtures are presented in Table 6.7. The precision values are calculated for the middle of their respective range, and the sensitivities correspond to the smallest concentration difference data that can be obtained, depending both on the spectrophotometer resolution (10 23 a.u.) and on the precision for the calculation of the contribution coefficient values. The detection limit values are three times the standard deviation of the blank.

Several experiments were carried out on samples of natural waters and industrial wastewaters (12 for Cu, 9 for Hg, and 14 for Fe), with standard additions for some samples [START_REF] Gomez | Simultaneous spectrophotometric determination of metal ions with 4-(pyridyl-2-azo) resorcinol (PAR)[END_REF]. The analysis of the samples was performed both by a reference method (GF-AAS for copper and iron, cold vapor-AAS for Hg) and by the proposed spectrophotometric method. Fig. 6.26 shows the comparison results between the two methods for each metallic constituent. The correlation coefficients of the related regression lines are satisfactory and greater than 0.95 for the three studied metallic constituents, and the intercept values are very small compared to the concentration ranges. Finally, despite the interest of this spectrophotometric approach, performance analytical techniques, such as ICP-OES or ICP-MS depending on the matrix, described as standard methods [START_REF] Birkmann | UV spectroscopic properties of principal inorganic ionic species in natural waters[END_REF], are more adapted for water and wastewater quality monitoring.

FIGURE 6 . 1

 61 FIGURE 6.1 Mineral constituents studies in this section (dark box) and in the library (pale box).

FIGURE 6 . 4

 64 FIGURE 6.4 UV spectra of nitrate solutions.

FIGURE 6 . 5

 65 FIGURE 6.5 Relation between measured and estimated (from SDA226) NO 3 concentrations for 580 freshwater samples[START_REF] Simal | Second derivative ultraviolet spectroscopy ond sulfamic acid method for determination of nitrates in water[END_REF].

FIGURE 6 . 6

 66 FIGURE 6.6 UV spectra of nitrite solutions.

FIGURE 6 . 7

 67 FIGURE 6.7 Initial and final spectrum during photodegradation of an urban wastewater sample.

a

  Concentration between 5 and 50 mg N/L, pH 9. b 5 min irradiation time.

FIGURE 6 . 8

 68 FIGURE 6.8 TKN measurement comparison between the Kjeldahl and the UV/UV methods[START_REF] Roig | Measurement of dissolved total nitrogen in wastewater by UV photooxidation with peroxodisulphate[END_REF]. TKN, total Kjeldahl nitrogen.

FIGURE 6 .

 6 FIGURE 6.10 Phosphorus forms in water.

a

  Concentration between 1 and 10 mg L 21 . b 10À15 min irradiation time.

FIGURE 6 .

 6 FIGURE 6.13 Comparison of total phosphorus measurement by the atomic absorption and UV/UVÀvisible methods.

FIGURE 6 .

 6 FIGURE 6.14 UV spectra of a sulfide solution (HS 2 10 mg L 21 ).

FIGURE 6 .

 6 FIGURE 6.15 Refinery wastewater UV spectra (dilution 25), with sulfide (88, 39, 23, and 45 mg S L 21 , respectively).

FIGURE 6 . 16

 616 FIGURE 6.16 Validation of sulfide UV determination.

FIGURE 6 .

 6 FIGURE 6.17 UV spectra of cooling and seawater (dilution 5). Chloride concentrations are between 15 and 22 g L 21 .

FIGURE 6 .

 6 FIGURE 6.18 Comparison of UV estimation of chloride in industrial water with the potentiometric method.

FIGURE 6 .

 6 FIGURE 6.19 UV spectra of water (swimming pool and deodorization) containing hypochlorite.

FIGURE 6 .

 6 FIGURE 6.20 Hypochlorite detection by absorptiometry (A) or by semideterministic method (B).

FIGURE 6 . 21

 621 FIGURE 6.21 Absorption spectra of a K 2 Cr 2 O 7 solution (1 mg L 21 of Cr, pathlength 50 mm) for different pH.

FIGURE 6 .

 6 FIGURE 6.22 UVÀvisible spectra of wastewater containing hexavalent chromium.

FIGURE 6 .

 6 FIGURE 6.23 Comparison of the diphenylcarbazide and UVÀvisible method for Cr (VI) determination, for water and wastewater samples (pathlength 50 mm).

FIGURE 6 .

 6 FIGURE 6.24 Absorption spectra (pathlength 50 mm) of synthetic solutions containing 1mgL 21 of iron [a-pH 3, b-pH 9, and c-pH 9 and addition of Cr (VI)].

FIGURE 6 .

 6 FIGURE 6.25 Reference spectra basis for the computation of Cu (II), Hg (II), and Fe (II) concentrations for the high-concentration mixture (10 mm cell pathlength) (SR1: Cu (II)dithizonate, SR2: blank of the reagent, SR3: Hg (II)-dithizonate, and SR4: Fe (II)-EDTA complex)[START_REF] Gomez | Simultaneous spectrophotometric determination of calcium and magnesium in water[END_REF].

FIGURE 6 . 26

 626 FIGURE 6.26 Comparison between the UVÀvisible spectrophotometric method and the corresponding reference methods for (A) copper, (B) mercury, and (C) iron determination, with or without standard additions of metals in sample.

TABLE 6 . 2

 62 Percentage of conversion into nitrate from N compounds.

TABLE 6 . 4

 64 Conversion yields obtained from organic phosphorus compounds.

TABLE 6 . 5

 65 Main sulfur species related to water and wastewater.

	Sulfur species	Formula	Origin or use
	Sulfide ion	S 22	Industrial
	Bisulfide ion	HS 2	Industrial/OM reductive degradation
	Hydrogen sulfide	H 2 S	OM reductive degradation (gas)
	Thiosulfate ion	S 2 O 22 3	Chemical reagent (titration)
	Tetrathionate ion	S 2 O 22 5	Industrial
	Sulfate ion	SO 22 4	OM oxidative degradation
	Peroxodisulfate ion	S 2 O 22

TABLE 6 . 6

 66 Complexometric procedures for the determination of metallic constituents.

		Complexant/
	Metallic constituents	reagent	Exploitation method	References
	Ca, Mg	PAR	Multicomponent analysis	[52]
	Cu, Co	MEDTA	Derivative	[53,55]
		5-BSAT	spectrophotometry PLS
	Cd, Co, Cu, Pb, Mn,	PAR	Multiple linear regression	[56]
	Ni, Zn
	Hg	Dithizone	Peak valley (480À585 nm)	[57]
	Hg	Specific	460 nm	[58]
		chemosensor
	Co, Cu, Pb, Mn, Ni,	PAR	First-, second-, and third-	[59]
	Zn, Fe		derivative spectrophotometry
	Cu, Fe	Bathocuproin/	Second-derivative	[60]
		LLE	spectrophotometry
	Cr, Cu	MEDTA	Derivative	[61]
			spectrophotometry
	Cu, Pd	Oxazolidine	Spectrum and first-order	[62]
			derivative spectrophotometry
	Fe, Ag, Mn	Rhodamin B	Kalman filter	[63]
	Ni, Co, Cu, Fe	PAR	Derivative	[64]
			spectrophotometry
	Fe, Ru	Diphenyl	Second-derivative	[65]
		phenantholin	spectrophotometry
	Cu, Fe, Hg	Dithizon, EDTA,	Deconvolution	[66]
		BHA
	Cu, Zn	Zincon	PLS	[67]
	Cu, Ni, Co, Zn	Zincon	PLS	[68,69]
		Nitroso-R salt	Kalman filter
	Al, Fe	Hematoxylin	PLS	[70,71]
		Chrome Azurol/	Measurement at 620 nm
		SPE
	U, Th, Zr	Arseno III/SPE	PLS	[72]
	Zn, Cd, Pb	TAR	PLS	[73]
	Cd, Zn, Co	Br-PADAP	PLS	[74]
	Pb, Cu, Ni	MEDTA	Multiwavelength and	[75]
			derivative measurement
				(Continued)

TABLE 6 .

 6 6 (Continued)

		Complexant/
	Metallic constituents	reagent	Exploitation method	References
	Cu, Pd	Mesoporous	Measurement at 425 (Cu)	[76]
		adsorbent	and 407 nm (Pd)
	Fe	2,4,6-tripyridyl-s-	Led spectrophotometer	[77]
		triazine	(600 nm)
	Se	Composite	Measurement at 430 nm	[78]
		adsorbent
	Cu, Ni, Co	SPE	PLS	[79]
	Co	Composite	Measurement at 420 nm	[80]
		adsorbent
	Ni, Mn, Zn, Ag, Cd,	Thiols, urease,	Linear discriminant analysis	[81]
	Fe, Hg, Cu, Sn, Co, Pb	bromothymol
		blue

LLE, liquidÀliquid extraction; PLS, partial least squares; SPE, solid-phase extraction.

TABLE 6 . 7

 67 Characteristics of the proposed method.

			Working range	Detection limit
		Wavelength (nm)	(µg.L 21 )	(µg.L 21 )	Precision (%)
	Copper	300À650	0À30	3	3.0
			0À600	100	5.6
	Mercury	300À650	0À100	2	3.2
			0À5000	80	5.0
	Iron	300À650	0À1500	45	0.5
			0À12,500	1200	0.4

Chemical reagent (digestion)OM, organic matter.


Koichi Takeuchi

Kyo Kageura

Teruo Koyama
email: t_koyama@nii.ac.jp

Béatrice Daille

Laurent Romary
email: ‡‡laurent.romary@loria.fr

Beatrice Daille
email: ‡beatrice.daille@irin.univ-nantes.fr

Acabit システムに適用し用語抽出実験を行った

Pattern Based Term Extraction Using ACABIT System

Keywords: Term extraction, Pattern based, Morphological patterns, Termhood 文法パターンに基づく用語抽出モデルの構築

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In this article, we proposea pattern based term extraction model and show experimental results that it produces.

The difficulty of term extraction is how to evaluate "termhood'' for inputted word sequences. Since the role of term is to denote one special concept in some domain, termhood should be evaluated according tothe following two aspects: the first one is the strength of unity for componentwords as a term, and the other one is the domain specialty of the word. Most of the previous (see [START_REF] Kageura | [END_REF]) approaches take the latter approach and focuse on the development of evaluation methods of domain specialty based on the statistics of words in documents. However, the former evaluation approach, that is, unity as a term is very important because the development of the approach is directly related to the mechanisms of creation of a new concept by composing words.

Recentl,y some term extraction works have focused on the unity of words. [START_REF] Nakagawa | Automatic term recognition based on statistics of compound nouns[END_REF] proposed a statistical method to evaluate the unity of words based on the strength of the connection between constituent words for Japanese terms. [START_REF] Jacquemin | Connectionist, Statistical and Symbolic Approaches to Learning for Natural Language Processing[END_REF] introduced the idea of term variants assuming complex terms must be derived from the basic terms because unity of term must be kept between basic term and its variants. He developed a pattern based extraction model for complex terms in English and French. Yoshikane el al. (2003) applied Jacquemin's approach to Japanese terms. Extending this approach, [START_REF] Daille | Study and Implementation of Combined Techniques for Automatic Extraction of Terminology, The Balancing Act, Combining Symbolic and Statistical Application to Language[END_REF] proposed morpho-syntactic pattern based model (implemented in a system called ACABIT) to extract basic terms and term variants for French without basic term list.

In this paper, we propose a pattern based term extraction model for Japanese applying Daille's approach.

It must be suitable to Japanese term extraction because most of Japanese terms form compound nouns then morpho-syntactic variation of pattern would be limited.

The aim of this research is to identify the difference of mechanisms of creating new concepts as terms between

French and Japanese by comparing morpho-syntactic patterns.

In the following sections, after presenting an overview of extraction systems and grammatical patterns for Japanese terms, we show some experimental results.

Approach

ACABIT

In the ACABIT system all complex terms are regarded as derivations from basic two word terms, the system tries to ACABIT is basically designed for the extraction of

French terms, but it can be applied to other languages by changing the POS-tagger and the morpho-syntactic patterns.

Overview of Japanese ACABIT

We construct a Japanese term extraction model applying ACABIT. As a POS-tagger, we selected ChaSen (Matsumoto et al. (1996)) that is a morphological analyzer for Japanese. It has about 100,000 word entries in the dictionary and 40 kinds of shallow syntactic tags as

POSes. The morpho-syntactic patterns in Japanese ACABIT system are constructed based on the POS set of ChaSen.

Morphological patterns

In our Japanese term extraction model, we also assume that all complex terms would be derived from basic terms that compose compound nouns or noun phrases. In the following, after we show morphological patterns of basic words for Japanese terms, we show the patterns of complex terms derived from them.

Patterns for basic terms

In Japanese, a morphological head of intra-compounds or phrase is a final word. We design patterns for basic terms enough to be compound noun or noun phrase according to morphological characteristics.

Noun-Noun:

This basic combination of compounds is the most popular one, but there is some specialty of Japanese. In this pattern, "Noun" does not mean only nominal noun, but also deverbal noun and deadjectival noun. Deverbal noun1 acts basically as noun in sentence as itself but it can be a verb followed by the auxiliary verb suru, that is, it has both the characteristics of a noun and a verb. Similarly, a deadjectival noun acts as a noun in a sentence when onits own, but it can be an adjective followed by na inflection. Both deverbal nouns and deadjectival nouns are able to come to head as well as modifier position as nominal noun. Because of the existence of these two special nouns, long complex compounds often appear in Japanese sentence.

Taking for example, is an adjectival noun followed by adeverbal noun.

In the following explanation, noun normally means nominal noun, deverbal noun and adjectival noun. Comparing with English, suffix ka corresponds to two suffixes -ize and -ion.

Prefix-Noun

Noun-SuffixStem-Noun:

There is a special suffix that is very frequent and derives stem of adjectival noun from modifier noun. The pattern of basic term consists of three words.

tetsuduki teki chishiki procedure -al knowledge (procedural knowledge)

Comparing with the translation in English, the function of the suffix teki is to make an adjectival modifier become a noun in the compound.

Vinf-Noun:

Vinf denotes a verb with inflection except deverbal noun. 2 The inflection type depends on the meaning of the term. The example of passive voice is as follows:

toji-ta hairetsu The "suffixstem" that derives stem of adjectival noun does not compose this form. As a whole, this multiword forms the middle between compound noun and phrase.

AInf-Noun:

AInf means an adjective with inflection except deadjectival noun. 3 An example is as follows.

fuka-i chishiki deep-INF knowledge (deep knowledge)

Adj-SuffixNominalize-Noun:

There is a suffix that derives noun from adjectives that is the same as previous pattern.

naga-sa zokusei length attribute (length attribute)

In patterns 7 and 8, inflection '-i' and suffix '-sa' can connect to all adjectives, for example fuka-i (deep) and fuka-sa (depth). If we now compare with English, the Japanese suffix '-sa' seems to be one inflection type of adjective. This grammar set comes from ChaSen as well as standard school grammar in Japanese, but this kind of gap would be regarded through comparing morphemes with a foreign language.

The above is the complete set of patterns for basic terms. From a syntactical view of composition, the patterns from 1 to 4 and 8 form compound nouns, while the patterns from 5 is phrase and 6 and 7 are middle. We have to take care of these type differences because there exist some limitations of composing term variants from these basic terms depending on the differences (see the next section).

Patterns for complex terms

Complex terms may form a compound noun or a phrase that is derived form basic terms. Because of specialty of Japanese words, composition types of compounds are limited according to the characteristics of word types: the one is "imported word" (IW) that originates in foreign language and the other is "word originating in traditional Japanese" (WJ). In compounding, there is a tendency to connect only the same types of words, especially, words in IW group can make long compound nouns with less difficulty, while WJ does not. We show this phenomenon in the following section. Besides the types of phrasal patterns as terms are also limited because most of terms form compound nouns (see Section 3). This is very different from English or French.

Compound nouns

Element+: terms form compounds. Theoretically there is no limitation of connection, but practically we set the limitation of maximum length as 9.

Element

Limited patterns of term variants

The basic terms that contain WJ also form compound nouns or phrases, however, variation patterns of the basic terms are limited. This limitation comes from termhood because there is a preference to select compounds or some short phrasal expressions much more than syntactic long phrase so that one term expresses one static concept. In Theoretically, all compound nouns and noun phrases can be applied to this phrasal pattern. Besides this A of B phrase can be extended recursively as A of B of C.

However we only permit the pattern of "A no (of) B" as variants for complex terms because the meaning of relation no is ambiguous and then we hesitate about using long sequence like "A no B no C" as a term.

How to apply patterns

We implement Japanese morphological patterns into ACABIT system. The important point how to apply them is order of patterns. We take the strategy to apply them from longer patterns so that system does not decompose long sequence term into short ones.

Experiment and results

We have two types of experiments in order to evaluate performance of Japanese ACABIT system. The fist evaluation is about the coverage of morphological patterns we elaborated. We input technical terms to ACABIT and check the rate of acceptability. The second is to evaluate term extraction performance. Since we do not have the all term set to some domain, we can only evaluate precision of our ACABIT. In order to do this experiment, we use the set of abstracts and author's keys that are distributed by NII for term extraction competition [START_REF] Kageura | [END_REF].

Coverage experiment

We prepare three kinds of technical terms: 1) technical term dictionary of information processing (ipdic) (Aiiso 1996), 2) term dictionary in computer domain (comdic) (Nichigai 1998) and 3) author's keywords in artificial intelligent domain [START_REF] Kageura | [END_REF].

All terms are analyzed using ChaSen so that all terms are decomposed into basic word with POS. 4 After this process, we evaluate statistical characteristics of terms about: number of one word terms and number of phrasal terms. 1, the share of one word term is not a little, that is, over than 10 % for every source. In our approach,

ACABIT does not extract one word terms because we assume that all terms consist of more than one word. The rates are upper bound of extraction. While phrasal terms are very few for every source, so our morphological patterns would be work well.

Table 2 shows the results of coverage performance of Japanese ACABIT.

Discussion

From the experimental results of Section 3.1 and 3.2, we found that our morpho-syntactic patterns have good coverage for technical terms. However precision of term extraction is poor because we only apply simple log likely hood evaluation of ACABIT, at the moment. We will be able to improve the precision rates by applying more sophisticated statistical approach to evaluate the unity of intra-term structure as [START_REF] Nakagawa | Automatic term recognition based on statistics of compound nouns[END_REF].

Comparing with foreign language such as English and

French, Japanese terms prefer to form compound noun while English and French prefer to form phrase about complex terms. In Japanese term extraction, we have to discriminate terms from general words on compound nouns while in European language on phrasal expressions.

Conclusion

We proposed pattern based term extraction method and show the experimental results. We try to extract terms using termhood, especially, focusing on the unity of intra-term structure by morpho-syntactic patterns. From the experimental results, our constructed patterns work well for coverage of terms but precision is not so grate.

That problem is not the issue of this paper because that is a problem how to evaluate specialty of words in some domain. Comparing morphological patterns in English and French, we clarify the difference of composing level for terms: most of Japanese terms form compound noun while English and French terms form phrasal patterns.

  patterns. The grammatical patterns are described based on POSes. The input of ACABIT is a POS-tagged text that is annotated by POS-tagger at the preprocessing stage(see Fig.1). From apractical point of view, the morpho-syntactic patterns should thus be designed according to the POS set of preprocessor. The output of the ACABIT system is a list of basic terms and term variants. Terms extracted by grammatical patterns are evaluated by log likelyhood that denotes the strength of connection between words. The outputs are convenient for the application of a deeper analysis because the relations between derived terms and basic terms are designated in the term lists.

Fig.

  Fig. Overview of ACABIT system.

  is made of a nominal noun and a deverbal noun, and anzen taisaku safe(-ty) measure (measure of safety)

6 .

 6 close-ed array (closed array).The inflection ta denotes the passive voice of the root verb toji (close). The example of active voice is as follows: VInf-Suffix: Nominal suffix as pattern 3 can also take inflected verb that is except deverbal noun. Example is as follows.

:

  Noun-Noun, Prefix-Noun, Noun-Suffix, Number-Suffix, Number and Symbol. Here Number means a character sequence of numbers, and Symbol is that of symbols. The pattern Element+ denotes continuing more than one Element that forms compound nouns. This long compound noun is a special characteristic of basic terms in Element that consists of IWs. Adding basic terms of Noun-Noun, Prefix-Noun and Noun-Suffix, Number-Suffix, Number and Symbol are involved as Element. These tree types usually need another element to be terms, therefore they are Element but not basic term patterns. The example of "Number Suffix Noun" is as follows:

"

  the following, we will show the limited patterns of terms variants for basic terms containing WJ and examples. two cases, nouns at the modifier position of Vinf are argument of the root verb (ex. Kyoshi (Supervisor) is an argument of ar-i (exist).).Next case is complex term variants consists of IWs. Noun*" denotes 0 or more than 1 word of Noun is going to continue. The example is the case of Prefix-Noun-Suffix. Of course Prefix-Noun-Noun-Suffix case has already been taken into account at Element+ pattern.

Table 1

 1

		Statistics of input terms
		ipdic (%)	comdic (%)	jsai (%)
	One word	2207/16275	4480/38785	658/4206
	term	(13.6)	(11.6)	(15.6)
	Phrasal	409/16275	2366/38785	231/4206
	term	(2.5)	(6.1)	(5.5)
	From Table

Table 2

 2

	Coverage of Japanese ACABIT
	ipdic (%)	comdic (%)	jsai (%)
	coverage 4080/16275	10623/38785	3056/4206
	(74.9)	(72.6)	(72.7)
	Our ACABIT works well although the upper bound of this
	experiment is about from 86 to 89 % for these terms. The
	error types are categorized into three: a) variety of term,
	For example, nyuuton (Newton) in nyutonn hou (Newton
	method) is annotated proper noun in ChaSen. This is
	correct analysis for general purpose while proper noun
	would not be a term. There is a possibility to make some
	patterns based on suffixes such as "ProperN Suffix
	(method)", but it cannot cover another variety such as
	"Microsoft network".
	b) ChaSen makes annotation errors on ambiguous words
	that are, for example, douki that is deverbal noun is miss
	annotated as adverbial noun. This problem relates lack of
	study of Japanese adverbial words.
	c) ACABIT system makes errors because of lack of
	patterns. Most of them are phrasal expression but are

b) error of annotation of ChaSen, and c) lack of pattern of ACABIT. We explain them as follows.

a) Most errors occur on terms that contain proper nouns. lexicalized such as 1 no hosuu (one's complement). We cannot make a pattern like Number-of-Noun to accept this

It is the same thing that called sahen-verb in Yoshikane et al. (2003).

These kinds of verb originated in traditional Japanese, while deverbal noun in China. They called kango and wago, respectively (see Section 2.3.2)

This adjective originated in traditional Japanese words that is called wago (see Section 2.3.2).

Basic performance of morphological analyzer Chasen is over than 95%.

This is the rate such as recall but not recall, exactly because we do not know the correct all terms in this domain.

because the pattern usually means phrase.

Term extraction

Japanese ACABIT is applied to abstract texts in artificial intelligence domain in order to show term extraction performance of ACABIT. Assuming atuthor's key words are correct terms for the texts, we evaluate the performance of ACABIT by comparing extracted terms with author's key.

Table 3 shows the statistics of author's key. According to the table, 68.7% keys are involved in abstract text and 20.1% of them are one-word keys, then 2308 words are the upper bound keys to be extracted. Table 4 shows the results of term extraction comparing with author's key. words. 5 We evaluate precision, correct rate to all author's key and correct rate to upper bound of author's key.