Yannick Fayolle

Pierre Buffière

Paul Moretti

Jean-Pierre Canler

Sylvie Gillot

Modelling Oxygen Transfer in Moving-Bed Biofilm Reactors Using Dimensional Analysis

Introduction

Optimization of oxygen supply in wastewater treatment processes is needed in order to limit the energy expenditure of wastewater treatment plants (WWTP) and to guarantee the treatment efficiency. To this aim, models based on dimensional analysis [START_REF] Capela | Transfer number in fine bubble diffused aeration systems[END_REF][START_REF] Gillot | Predicting oxygen transfer of fine bubble aeration systems -Model issued from dimensional analysis[END_REF] or computational fluid dynamics (CFD) [START_REF] Fayolle | Oxygen transfer prediction in aeration tanks using CFD[END_REF] were developed to predict oxygen transfer efficiencies of classical fine bubble aeration systems. New treatment processes based on coarse bubble aeration system coupled with fluidized biomedias, which provide a large internal area for bacterial growth (Moving Bed Biofilm Reactors -MBBR and Integrated Fixed-Film Activated Sludge -IFAS), are now competitive and are often proposed for WWTP upgrading and new building. In these new systems, the oxygen transfer performance in the presence of biomedia is not well established [START_REF] Rosso | Oxygen transfer and uptake, nutrient removal, and energy footprint of parallel full-scale IFAS and activated sludge processes[END_REF] and models adjustment are needed for process optimization. The aim of this study is to provide models issued from dimensional analysis linking oxygenation performances in clean water to design and operating parameters for inverse fluidized bed reactors.

Material and methods

Models are developed using a database of 77 oxygen transfer performances on two rectangular semi-industrial scale pilots (the characteristics of the pilots are described in Table 1). The flexibility of these experimental devices enables to study the impact of most design and operating parameters such as reactor dimensions (surface, liquid height), characteristics of the aeration system (fine / coarse bubble diffusion, number and location of aerators), air flow rate and biomedia filling ratio (from 0 to 60% in volume). For each configuration, the oxygen transfer performances were determined in clean water according to the normalized non-steady state method [START_REF]Wastewater treatment plants -Part 15: Measurements of the oxygen transfer in clean water in aeration tanks of activated sludge plants[END_REF].

Table 1. Characteristics of the two semi-industrial scale pilots and operating conditions

Results

In this abstract, results are presented only for reactor 1. Results obtained on reactor 2 will be developed in the full version of the manuscript.

Exploiting the database allows to highlight the impact of major parameters on the oxygen transfer performances:

 Without biomedia, the oxygen transfer coefficient (kLa20) was mainly controlled by the superficial gas velocity and the installed aeration system (Figure 1), due to the bubble size and the resulting liquid flows. A linear correlation between kLa20 and UG is obtained, such as observed on full-scale plants [START_REF] Gillot | Predicting oxygen transfer of fine bubble aeration systems -Model issued from dimensional analysis[END_REF].

Figure 1. Oxygen transfer coefficient as a function of the superficial gas velocity for fine bubble (FB) and coarse bubble (GB) aeration for different configurations of reactor 1

 An increase in the biomedia filling ratio leaded to an increase in kLa20 for coarse bubble aeration (Figure 2). This increase could be linked to a decrease in the mean bubble diameter and an increase in the gas/liquid contact time due to biomedia volume occupation. Preliminary results on reactor 2 showed that the oxygen transfer performance of fine bubble aeration systems were less impacted by the biomedia filling ratio in comparison than in coarse bubble aeration. A model was developed on the basis of a dimensional analysis. The transfer number (NT) is related to the Reynolds number (𝑅𝑒 = 𝑈 𝐺 .ℎ  ), the ratio between the total perforated area of the diffusers (Sp) and the total area of the reactor (S) and the biomedia fill ratio (TRB).

  T 1 S Sp Re 1,19.10 g U a k N 0,51 - RB 0,88 0,13 - 1/3 2 G L T                  3 -  (Eq. 1)
Where: kLa is the oxygen transfer coefficient (s -1 ), UG the superficial gas velocity (m.s -1 ),  the liquid cinematic viscosity (m 2 .s -1 ), h the diffuser submergence (m) and g the standard gravity (m.s -2 ) This model is made independent of the aeration system characteristics (fine/coarse bubble) and enables to predict the transfer number with an average accuracy of 6%. 0.0E+00

Conclusions

The development of models in order to optimize the oxygen transfer performances in inverse fluidized bed reactors commonly used in wastewater treatment is needed. To this aim, a database of 77 oxygen transfer measurements was built on two semi-industrial scale reactors. Exploiting this database for reactor 1 points out the impact of design and operating parameters on oxygen transfer performances. A model, based on dimensional analysis, is also build, allowing to predict the transfer number with a accuracy of 6%. Additional results on reactor 2 will be included in the full version of the manuscript.

  = maximum liquid height / Vmax = maximum volume of liquid / UG = superficial air velocity / FB = fine bubble aeration / CD = coarse bubble aeration

Figure 2 .

 2 Figure 2. Oxygen transfer coefficient as a function of the superficial gas velocity and the biomedia fill ratio (Reactor 1 -Configuration 7 -V = 0.93 m 3 )

Modeled versus experimental transfer numbers for fine / coarse bubble aeration without/with biomedia

		7.0E-03
		6.0E-03
		5.0E-03
	(s -1 )	4.0E-03
	k L a 20	3.0E-03
		2.0E-03				Filling Ratio
		1.0E-03				0%	20%
						40%	50%
		0.0E+00	1.0E-03	2.0E-03	3.0E-03	4.0E-03	5.0E-03	6.0E-03
					U G (m s -1 )
	Figure 3.


R Cresson
email: cresson@supagro.inra.fr

S Pommier

F Béline

T Bouchez

C Bougrier
email: claire.bougrier@veolia.com

P Buffière

A Pauss

P Pouech

S Preys
email: spreys@ondalys.fr

T Ribeiro

M Rouez

M Torrijos
email: torrijos@supagro.inra.fr

Results from a French Inter-laboratory Campaign on the Biological Methane Potential of Solid Substrates

Keywords: BMP, methanogenic potential, inter-laboratory study

A French inter-laboratory campaign on BMP assessment was realised in two phases: free protocol at first, then harmonized protocol. Results show good intra-laboratory repeatability and reproducibility, but in spite of an attempt in the harmonization of practices, the inter-laboratory reproducibility could not be improved and ranges in the magnitude of 20% RSD.

INTRODUCTION

The determination of the methanogenic potential of substrates, also known as BMP (Biological Methane Potential) is a central and essential parameter for any anaerobic processes. Actually it is used for the technical and economic analysis of a project, for the design of treatment and recovery facilities and for the evaluation of the process performance. It is also a key indicator of the stability of solid wastes stored in landfills. While some publications mention methodologies for the determination of the methanogenic potential, the methods are often very different, especially for solid and heterogeneous substrates. This variability in analytical methods directly results from the lack of standardized protocol or adapted normative reference. It raises many questions about the quality of the results and limits their interpretation. Some attempts for the standardization of the BMP protocols have been proposed. In particular, the expert working group on anaerobic digestion (Anaerobic Digestion Specialist Group) of the International Water Association (IWA) has initiated a task group entitled "Task Group for the Harmonization of Anaerobic Biodegradation, Activity and Inhibition Assays". It resulted in the publication of a protocol for solid waste BMP determination [START_REF] Angelidaki | Defining the biomethane potential (BMP) of solid organic wastes and energy crops: a proposed protocol for batch assays[END_REF]. This protocol relies on previous publications that had already attempted to make recommendations based on the analysis of the involved processes [START_REF] Owens | Biochemical Methane Potential of Municipal Solid-Waste (MSW) Components[END_REF][START_REF] Angelidaki | Assessment of the anaerobic biodegradability of macropollutants[END_REF][START_REF] Hansen | Method for determination of methane potentials of solid organic waste[END_REF][START_REF] Rozzi | Methods of assessing microbial activity and inhibition under anaerobic conditions: a literature review[END_REF], or on the application to very specific problems such as the substrate/inoculum ratio [START_REF] Fernandez | Effect of inoculum-substrate ratio on the start-up of solid waste anaerobic digesters[END_REF]. However no further action has so far been proposed after this work and the task group recommendations are still only partially followed by the laboratories. As a consequence, the reliability of BMP measurements is in question. This was illustrated by recent inter-laboratory studies. The first one was reported by [START_REF] Raposo | Biochemical methane potential (BMP) of solid organic substrates: evaluation of anaerobic biodegradability using data from an international interlaboratory study[END_REF] and evaluated the results from 19 laboratories worldwide on simple model substrates (starch, cellulose, gelatine and mung beans). The second one was an Italian campaign reported by Proqueddu et al. (2013) and involved 19 laboratories which evaluated the BMP of freeze-dried samples of cheese whey, silage maize and biowaste. The findings of these studies support a wide dispersion of results with both a high number of outliers and poor reproducibility relative standard deviation.

The aim of the proposed French inter-laboratory campaign was to evaluate the current protocols used in the country for BMP evaluation and to establish their harmonization.

EXPERIMENTAL Organization of the inter-laboratory study

Eleven French laboratories participated in this campaign. The study involved two experimental phases. For each of them, three samples were sent to each participating laboratory, which achieved 6 methanogenic potential measurements for each sample. During the first experimental phase each partner completed the methanogenic potential measurements according to its own protocol. During the second phase each partner made new measurements according to the common protocol defined after analysing the results of the first phase. For each of the experimental phases, the laboratories performed 2 sets of measurements in triplicates, the second set started at least 4 weeks after the first one. The purpose of these repetitions was to evaluate both the inter-laboratory reproducibility and the intra-laboratory reproducibility of the BMP measurement.

Substrates

A sample of the substrates presented in Table 1 was sent to each laboratory. For the first phase, substrates SA, SA' (same substrate but dried and shredded) and SB were studied. For the second phase, substrates SA', SB and SC were studied.

BMP Protocols

For the first phase, participants applied their own typical BMP measuring protocol with the sole obligation to run the tests in two series of triplicates and to include blank samples. The identified factors differing from one laboratory to another were: the main method (manual or automated via AMPTS apparatus), the gas volume measurement technique, the mixing regime, the substrate/inoculum ratio (S/X), the pH buffer addition, the mineral medium complementation and the level of endogenous methane production.

For the second phase, which came after the analysis of results of the first phase, participants were asked to satisfy the following rules: use of a common mineral medium, use of 3 g/L NaHCO3 as pH buffer and set the volatile solid substrate/inoculum ratio to 0.5.

Statistical Analysis

Calculations of the Relative Standard Deviation (RSD) for repeatability and reproducibility were performed according to the metrological NF ISO 5725-1.The influence of the protocol factors was assessed by ANOVA.

RESULTS

First phase: free protocol

The first phase of the campaign was carried out in 2013. The dispersion of the obtained BMP values is synthetized in Table 2. For each laboratory, both repeatability among triplicates and reproducibility between two sets of tests were satisfactory. Nevertheless, the inter-laboratory reproducibility was quite poor, with a RSD around 20% whatever the substrate. ANOVA analysis did not show clear influence of the identified protocol factors, except for the mineral medium implementation which was found to raise the BMP value. For other factors like the assessment method (manual/automated), the S/X ratio and the buffer addition, the influence on the BMP value was found to be substrate-dependant. The solid substrate preparation before BMP assessment (fresh or freeze-dried) had no significant effect on the results.

Second phase: harmonized protocol

After the first phase, discussions between the participants led to the proposal of a harmonized protocol with unified practices for the following factors: S/X ratio, pH buffer and mineral complementation (as described in the EXPERIMENTAL section). The subsequent second phase of the campaign was carried out in 2014 on substrates SA' and SB (same as for the first phase), as well as on a new lipid substrate (SC). As shown in Table 3, despite the proposed harmonization, the inter-laboratory reproducibility was not improved.

Efforts will now be made for the definition of a posteriori validation criterions related to the inoculum activity.

Table 1 .

 1 Composition of the substrates used in the inter-laboratory campaign.

	Substrate	Composition (%w.b)	TS (%)	VS (%TS)	% VS in mixture
		Potato	40%	20%	99%	27%
		Grain maize	20%	27%	99%	18%
	SA	Beef	30%	27%	95%	26%
		Wheat straw	10%	90%	93%	29%
		total	100%	30%	95%	100%
	SA'	Idem SA	100%	97%	95%	100%
	SB	Wheat Straw	100%	92%	93%	100%
	SC	Mayonnaise	100%	75%	99%	100%

Table 2 .

 2 Synthesis for the first phase of the French inter-laboratory campaign.

	BMP (NmLCH4/gVS)	SA	SA'	SB	SC
	Mean	425	403	267	-
	Median	422	407	267	-
	Min	289	250	175	-
	Max	629	481	370	-
	Intra-laboratory repeatability RSD	7%	4%	6%	-
	Intra-laboratory reproducibility RSD	9%	6%	8%	-
	Inter-laboratory reproducibility RSD	20%	17%	20%	-

Table 3 .

 3 Synthesis for the second phase of the French inter-laboratory campaign.

	BMP (NmLCH4/gVS)	SA	SA'	SB	SC
	Mean	-	405	277	848
	Median	-	408	282	828
	Min	-	260	195	660
	Max	-	525	370	1026
	Intra-laboratory repeatability RSD	-	4%	4%	4%
	Intra-laboratory reproducibility RSD	-	5%	7%	5%
	Inter-laboratory reproducibility RSD	-	19%	21%	13%

ACKNOWLEDGEMENTS

This French inter-laboratory campaign was supported by ADEME.


published or not. The documents may come

Introduction to the Special Issue in Geopolitics titled Bordering the Middle East Introduction Daniel Meier (Editor) In the Middle East, like everywhere else, borders are recognized as state containers and embodied sovereignty. The rise of the jihadist organization of the Islamic State (IS) taking large swaths of land across the Iraqi-Syrian borderlands and threatening surroundings States like Lebanon, Turkey or Libya affected the entire nation state system in the MENA region. It follows that some analysts rose the scenario of a general breakdown of "colonial lines" in reference to the Anglo-French agreement of Sykes-Picot (1916) that divided the Middle East. But seven years after the beginning of the Syrian uprising and thirteen years after the transformation of Iraq into a federal state, one can notice the permanence of the nation state borders on the one hand. On the other hand, the Middle East, like no other region in the world, seems to face such a challenge to the state border system with the lasting internal fragmentations in Syria, Yemen, Libya, Iraq. In reaction to this threat, governments express fear and try to protect their State sovereignty from outsiders of all sorts -be they foreign workers, illegal immigrants or terrorists -through a border walling process [START_REF] Vallet | The (Re)building of the Wall in International Relations[END_REF] as seen with Saudi Arabia, UAE, Tunisia, Morocco, Turkey or Israel. Erections of sophisticated and costly fences at State borders transformed the regional landscape and are raising issues of State's sovereignty and regime's legitimacy; they are also highlighting the existence of local communities (religious, ethnic or tribal) that are largely straddling across the international borders, defining alternative boundaries of belonging. It may thus reshape the meaning of the border as seen in the north of Syria with the emergence of the Kurdish autonomous region of Rojava and its links with the Kurdish Workers Party (PKK) in Turkey triggering Turkish military operations. In other words, questioning borders in the Middle East in the context of the post Arab uprisings unveil the importance of history in national trajectories (Kienle & Skida, 2015;[START_REF] Adham | Back to the Future. The Arab uprisings and the State (re)formation in the Arab World[END_REF], the necessity of a reflection on their mobility in addressing new transnational actors like the Islamic State (IS) (Stern & Bergen, 2014) as well as the transformation of the state and the militarization of its elites in some cases [START_REF] Stacher | Fragmenting states, new regimes. Militarized state violence and transition in the Middle East[END_REF].

Borders act as mental perceptions and have political meanings [START_REF] Jean-Luc | Introduction: logiques de marquages: murs, disputes frontalières[END_REF]. Conceived as human shaped political technology and as a process in constant change due to social interactions, the lens on borders can highlight multiple aspects of the current crisis affecting the region. Focusing on borders in their materiality as well as their symbolic dimensions -their representations or boundaries -may help reappraising the region's own history, the local/national specificities as well as regional/global constraints affecting borderlands and those who cross borders. The current proposal for a Special Issue is preoccupied with two questions: how do borders influence actors' identity building? And how do identity politics at local or national level re/define borders and boundaries?

These two questions appear interlinked when focusing on individual cases. The special issue thus presents six case studies and is a result of several meetings, conferences and scientific debates the author had the chance to have with each paper givers the last three years. All papers provide insights on State-community relationships through the lens of border issues in the Machreq and the Gulf areas thanks to different disciplinary approaches. Through IS territorialisation, Jordanian Bedouins, Kuwait's national identity representations, Israel's Lebanese residents, Oman's construction of political sovereignty and representations of Gulf and Middle Eastern borders, authors highlight multi-scalar processes of identity building and representations through the bordering of the national, tribal or religious group. To define the Self, the materiality of the border plays a key role in the building of the Other. It appears clearly that there is a dialectic relationship between identity and borders when focusing on borderlands' issue: the latter tend to show the interdependency of the two notions.

The nation state system in the Middle East: questioning borders

As seen above, border issues in the Middle East link the territoriality and the sovereignty of the State, the building of a national identity and the type of legitimacy States promote. The literature related to border issues is therefore often linked to these concepts and up until recently, it was rather rare to read studies primarily focusing on borders in the Middle East. In this region, Statebased analyses were often trapped within the realm of cultural readings -mainly referring to the original Islamic State of the community of believers (ummah) -, thus seeing religious belonging, tribal groups and kinship as key explanatory factors in the portrait of a "quasi tribal State" [START_REF] Gellner | Tribalism and State in the Middle East[END_REF]. The breakdown of the Ottoman Empire and the strong influence of the French and British powers in the region then spread the nation-state model over the former Ottoman territories dividing lands into sovereign states, most of them under foreign Mandates [START_REF] Georges | L'Europe et l'Orient. De la balkanisation à la libanisation[END_REF]. In Islam sovereignty (siyada) is largely a non-territorial notion that refers above all to the human community [START_REF] George | Territory, State and Nation in the Middle East and North Africa[END_REF]. Additionally, during centuries the Ottoman Empire dealt with its various population thanks to the system of millet a non-territorial system of sectarian and religious governance. Both rendered quite difficult the identification of local population to the nation-state system. The Mandates of the League of Nations granted to France and Great Britain in 1920 fostered the penetration of the western territorial sovereignty state system and secured the foundations of the implementation of this model in the Middle East through elites production and the political control of the new states. Local populations struggled against these new externally imposed state borders for years after the 1920 San Remo conference. The only endogenous local borders in the region was the Ottoman-Persia border and only the Kingdom of Saudi Arabia and Turkey succeeded to negotiate their borders with European powers. But in the meantime, they both imposed new borders to other groups in borderland regions (Kurds, Alawites, Shi'ites, Houthis).

The importation of theories of nationalism in the region led to a contradiction between a nonterritorial Arab nationalism that encompass all Arab states because of its reliance on ethnic belonging [START_REF] Khalid | La dimension absente du nationalisme arabe: le territoire[END_REF] and the State fragmentation of the Middle East resulting from the western Mandates' order. The new State system challenged the region as the nationhood in its western meaning was trapped between two poles: the infra-national belongings like the communitarian or tribal links, and the supra-national belongings, namely the umma and pan-Arabism [START_REF] Dieckhoff Alain | Nationalismes en mutation en Méditerranée orientale[END_REF]. Therefore, States' legitimacy in the Middle East oscillated between the "khaldunian" model -which rests on the leadership of the group of solidarity, the 'asabiyat -and the Islamic model, both perceived as authoritarian. These regimes accommodated the mandate's legacy; a state territoriality upon which they tried to build a national group-feeling. Pan-Arabism laid the foundations of few exceptions -like the short-lived United Arab Republic between Syrian andEgypt (1958-1961) which failure tended to undermine the pan-Arab ideology. While political Islam took over with a narrative that mobilised actors throughout the region and setting up Islamic networks, none of the Islamic republics or regimes rose any territorial claims beyond their state borders. In other words, state territoriality and its "national" borders have been ratified by all the political actors in the region and therefore went through a process of legitimization. Nowadays spectrum of borders in the Middle East oscillated between unmarked ones to highly fenced demarcations. Recent conflicts and regional turmoil tended to push for clearer demarcations and like in Israel, Turkey or Saudi Arabia, large projects of fencing the entire borderlines tend to highlight another critical link between national identity, territorial control and political regime trying to secure their authority over borderlands [START_REF] Daniel | Penser les frontières au Moyen-Orient et au Sahel : enjeux et concepts[END_REF].

Borders and borderlands have a critical impact on the formation of States and nations and in the process of their change (Donnan & Wilson, 1998). It is clear in the case of Jordan, defined as the "kingdom border" through the lens of political sociology (Bocco & Chatelard, 2001) or in the historical perspective [START_REF] Rogan | Frontiers of the State in Late Ottoman Empire: Transjordan, 1850-1921[END_REF]. Borders transformed local communities' way of living, they changed tribal groups representations and sometimes succeeded to enforce a national belonging over the infra/supra national affiliations. Thus, the incorporation of the tribal world or communitarian groups within the State produced several adaptations to the political system but at the same time sectarian or tribal groups influenced Middle Eastern States. It appeared quite obviously with the Syrian Alawite regime that subverted the Baath party for its own profit (Belhadj, 2016) or with Saddam Hussein's tribe Al-Bu Nasir that took the lead in Iraq in the 1960s [START_REF] Eric | Memories of State: politics, history, and collective identity in modern Iraq[END_REF]. Kurds, Palestinians or Jews, as well as other minorities, like the Druzes or the Shi'ites, fought for autonomy over regions or borderlands. This has strongly impacted the shaping of states in the Middle East, for instance in Israel/Palestine [START_REF] Cédric | Palestinians and Israelis in the Shadows of the Wall. Spaces of Separation and Occupation[END_REF] in the North of Iraq with the Kurds (Bengio, 2012) or in Yemen with the Houthis (Brehony, 2013).

Broader multidisciplinary analyses of border issues in the Middle East emerged in the 2000s and tended to focus more on symbolic boundaries between nations, sects and the state's borders. In his seminal book on boundary making, Migdal (2004) focused on the nation and state's capacity in shaping identities in several contexts around the world. He highlighted the key role of the state in framing categories, shaping group identities as well as its capacity to include/exclude. Brandell (2006) drew on some of these elements while focusing on the territorialisation of the nation-state system in the MENA region through a multifaceted portrayal of border life that tended to underline the importance of perception of the borders in their impact on actors life. Other general publications focused on Middle East power relations in the post-2001 context (Bocco & Meier, 2005), on the key role of state building in fixing borders (Atzili, 2012), on contentious borders in a changing environment (Del Sarto, 2017) or on historical approaches of territorial disputes in the region [START_REF] Jörum | Beyond Syria's borders: a history of territorial disputes in the Middle East[END_REF]. For ten years, monographs on Arab states in varied disciplines of social sciences provided insightful knowledge on local and national borders [START_REF] Balanche | La région alaouite et le pouvoir syrien[END_REF]Madawi, 2008;[START_REF] Natali | The Kurdish Quasi-State. Development and Dependency in the Post-Gulf War Iraq[END_REF][START_REF] Noel | Yemen Divided: The Story of a Failed State in South Arabia[END_REF]Abdelkhah, 2012;[START_REF] Daniel | Shaping Lebanon's Borderlands. Armed Resistance and International interventions in South Lebanon[END_REF]. They all stress the importance of contextualized approaches while illuminating the border as a process of human production as well as a component of actors' group definition and actions.

Theoretical tools

In order to propose a more systematized approach to border issues in the Middle East, it may be worth turning to thematic research labelled as "border studies". This field of research was initially focused on the US-Mexico border and spread worldwide as a consequence of the fall of the Berlin wall, globalization and the securitization processes on the rise since the 9/11. Recent works on African or Asian borders illustrate quite well this recent process1 . Border studies did not really penetrate the Middle East, although geographers dealing with border issues in this region did open up their analysis to several concepts stemming from other disciplines (Schofield, 1993). This special issue intends to bring together Middle Eastern scholars in anthropology, sociology or political science through border studies' conceptual tools. Authors of this special issue share the same understanding of borders as processes and not simply as material taken-for-granted facts. This vision of the border as a social construct stemmed from the 2000s "spatial turn" which overcame the territorial and weberian paradigm -which reduced the border to a line of sovereignty, a state container -and open the doors to alternative topologies (borderlands, networked borders, bordercapes, borderities) and a socio-cultural perspective including discursive practices and social perceptions of borders (Parker & al., 2009).

New approaches to border studies emphasise the interest in deepening and widening the scope of analysis by focusing on borderlands and on processes to understand several dimensions of border spaces [START_REF] Gabriel | Bordering and Ordering the Twenty-first Century. Understanding Borders[END_REF]. Since the 1990s, a wide range of specialists of borders in political science, geography and anthropology have emphasized the links between borders as processes and identity building [START_REF] Ansi | Territories, Boundaries and Consciousness: The Changing Geographies of the Finnish-Russian Border[END_REF]Albert & alii, 2001;[START_REF] Van Houtum Henk | Bordering, Ordering and Othering[END_REF]Arbaret-Schulz & al., 2004;Prokkola, 2010). The link between space and territory with the production of identity became a key component of further development. In addition, the importance of representation on borders has been underlined and tends to complexify the understanding of the nature of borders as well as their social production. Following the "spatial turn", the idea of borders as mobile entities appeared more clearly the moment technologies of identity control tended to spread border checkpoints before and beyond the traditional border line -what Bigo called "pixellisation" [START_REF] Didier | The Transformation of the European Border Controls[END_REF]. The paradoxical nature of globalization that emerged is revealed by its capacity to ease border crossing for certain types of border crossers (citizens of rich countries and elites) while making it harder for others (migrants from the global south, refugees). The significance of such development at the scale of Europe but also worldwide thanks to cooperation in the security sector links identity with control through the mediation of the territory (through its political ordering and border regime).

Seen as a principle of organization of social relations (Popescu, 2012: 76) the notion of 'bordering' captures the changing face of borders, implies the study of the social space of the borderland, its process and context, and involves all types of actors, institutions as well as companies, individuals and all social groups involved in the conduct of "borderwork" [START_REF] Chris | Towards a Multiperspectival Study of Borders[END_REF]. Bordering is a means of ordering (Albert & al., 2001) and also of othering: as Henk Van Houtum & Ton Van Naerssen (2002: 134) suggest, "making others through a territorial fixing of order is intrinsically connected to our present image of borders". The three processes of bordering/ordering/othering thus appear clearly linked to the space/identity relationship: while the bordering process refers to the definition of and sovereignty over a defined space, the ordering process primarily deals with identity building and the power over it, as the group needs values, symbols and a sense of belonging. For its part, the process of othering is a facet of the collective identity building that is related to a specific territory and refers to the building of the figure of the foreigner, the neighbour, the Other. The idea of border as a process helps to de-construct some aspects of the border. Among them, researchers in border studies raised the question of the actors that are taking part in bordering.

Drawing on this intuition, the theoretical framework of borderscape (Rajaram & Grundy-Warr, 2007;Brambilla, 2014) underlines alternative bordering that refugees or artists as well as political groups (Meier, 2015) can perform through practices and everyday action that tend to redefine the meaning of the border. Another recent development linked to the border as a process refers to the management of the border understood as governmentality. Amilhat-Szary and Giraud (2015) described it as "borderities", another way to develop the idea of mobile borders as well as to leave behind the tautological relationship between State, territory and borders.

In the literature on borders, there usually are three main types of border along which the bordering process is taking place: borderlines, borderlands and networked borders [START_REF] Gabriel | Bordering and Ordering the Twenty-first Century. Understanding Borders[END_REF]. Borderlines refer to the physical delimitations on the ground -not always as visible as they look on a map. Their persistence is observable through their vitality as 26,000 km of new borders have emerged in the last two decades and, since 9/11 a physical reinforcement in walling/fencing has occurred [START_REF] Alexander | Theorizing Borders in a 'Bordereless World': Globalization, Territory and Identity[END_REF]Jones, 2009). This first type of border is usually investigated through the state immigration/security policy at the border, regarding the relationships between the two states the border separates, through the walling and fencing industry and of course through the impact of borderlines on local communities.

Borderlands are less easily noticeable as there are no clear signs to identify them but their landscapes as well as their social relations set them apart from the rest of the territory of the state. Randy Widdis (2005:154) defines the borderland as "a physical, ideological, and geographical construct, a region of intersection that is sensitive to internal and external forces that both integrate and differentiate communities and eras on both sides of the boundary line". This underlines their relationship with the border making process, a more or less violent one, which has often left claims unresolved (Rumley & Minghi, 1991). They can be studied by focusing on ethnic minorities or relegated communities at the periphery of the state or through cross border exchanges and solidarity among groups located in contiguous states, based on political, social or religious affiliation. Borderlands offer a vantage point for confrontation with "others" and clearly refer to identity shaping for the group boundaries [START_REF] Ansi | Territories, Boundaries and Consciousness: The Changing Geographies of the Finnish-Russian Border[END_REF][START_REF] Daniel | B)ordering South of Lebanon: Hizbullah's identity building strategy[END_REF].

Borders perceived as networks capture the spatial nature of these border-making developments through the label "networked borders" (Walter, 2004;[START_REF] Chris | Introduction: Theorizing Borders[END_REF] describing the dispersion of borders throughout societies and re-creating a network form spanning over several states. People and goods are checked and scrutinized before they reach the state border and after they enter the territory, the border becoming embedded in the flow (Sassen 2006). In sum, networked borders appeared to characterize a comprehensive border regime of movement control [START_REF] William | Mapping Schengenland: Denaturalizing the Border[END_REF] linking dispersal of the physical border line with technologies of surveillance before and beyond the border line [START_REF] Balibar | Politics and the Other Scene[END_REF]. Among the hotspots where they can be observed are the refugee camps, 'in-between places' where people's status is purposefully kept undetermined. Due to the development of networked borders, the border crossing experience has changed: as it has multiplied away from the official state borders, categories like race, class, ethnicity, religion, etc. have become more important factors affecting groups in different ways.

In sum, nowadays conceptualization in border studies clearly emphasizes the connexion between territory, identity and sovereignty [START_REF] Van Houtum | Human blacklisting: the global apartheid of the EU's external border regime[END_REF]. Following this conceptual link, this Special issue intends to shed a light on several spaces and places in the changing Middle East thanks to some of these conceptual tools. Representations of space and the others are key elements shaping the first four papers. George Joffé opens the volume with an in-depth reflection on the territorialisation of the so-called Caliphate of the Islamic State, showing, among other things, that this project stems from centuries of resentment toward European behaviour in the Middle East incarnated by IS Jihadists perception of the Sykes-Picot Agreement (1916). Valeria Ruggiu's paper is addressing the deep-rooted issue of identity building through the figure of the Other in Jordan, namely the continuous construction of tribal East Bankers identity towards the Palestinian West Bankers. Margins of the Kuwaiti national territory are at the heart of Claire Beaugrand's paper on Bedouin identity claims. Her inquiry explores the territorialisation of the othering process Bedouin faced in a state where the Kuwaiti identity has been historically defined in reference to the city walls, thus excluding the desert borderlands. Adoram Schneidleder's paper studies the process of identity building in Israel of Lebanese migrants from Jabal 'Amil. His work focuses on the level of interiorisation of former workers and former militiamen of the South Lebanese Army; both raise visions of the now separated borderland area of Galilee-Jabal 'Amil depending on their place of residence in Israel.

The last two papers are dealing slightly more with the materiality of border delimitation/separation and its effect on identities and perceptions. Thus, the recently separated twin city, the al 'Ain -Buraymi oasis town between United Arab Emirates and Oman is studied by Marc Valeri. Despite the culture and history shared by the two States in this oasis, the author shows the process of separation as it epitomizes the evolution of the States' bilateral relationships and a hardening of the national identity boundaries. Finally, Richard Schofield deals with various examples of Northern Gulf borderline disputes on the ground and in the sea and highlights that, far from the various representation we have of border issues in this region, there is no real specificities in Middle Eastern borderlands.

See for instance the African borderland research programme leaded by Paul Nugent or the institutionalization of the border issues in Asia with the Asia Borderlands Research Network.