Piero Gilento

Giovanni Pesce

Gourguen Davtian

Pierre-Marie Blanc

Khaled Al-Bashaireh

Apolline Vernet

Maen Omoush

Effects of Earthquakes on the Development of the Construction Techniques in a Rural Community in Northern Jordan between the Byzantine and the Mamluk Periods Effetti dei terremoti sullo sviluppo delle tecniche costruttive in una comunità rurale nel nord della Giordania tra il periodo bizantino e quello mamelucco

Keywords: TRANSMISSION, BASALT, ḤAWRĀN, TECHNOLOGY Riassunto TRASMISSIONE, BASALTO, ḤAWRĀN, TECNOLOGIA

The Near East is a highly seismic area characterised by a sequence of catastrophic events that strongly influenced the history of the whole region. Between antiquity and the Middle Ages this region was hit by a series of extremely violent earthquakes recorded both, in the written and in the material sources. The former are of particular importance for the urban contexts since are rich in details and more comprehensive. The latter are essential in rural contexts often characterised by a lack of valid references useful to understand how these events have impacted on villages. This contribution aims at identifying the effects of catastrophic events that affected the site of Umm as-Surab (northern Jordan), by analysing the traces left on its architecture and ground. Furthermore, the paper aims to highlight the solutions used by the local population to overcome the immediate effects of these events on the buildings and, in the long term, to limit the effects of further similar catastrophes. To achieve these objectives, the research approach is based on a longue durée vision that takes into consideration a wide chronological time frame, from the Byzantine period to the beginning of the Mamluk sultanate (4th-13th centuries AD). The good conservation condition of the village allows analysing the changes induced over time to the buildings, using the approach of the Buildings Archaeology. At the same time, the analysis of construction cycles gives the opportunity to better understand some of the phenomena that underlay the development of the building techniques. Our observations on the architecture are enriched with data from a stratigraphic excavation, laboratory analyses, and dating of mortars and plasters. Overall, from this study emerges a picture which, although characterised by the slow transmission of empirical knowledge, demonstrates how small technical changes can lead to important and lasting innovations.

Introduction

The eastern Mediterranean regions have an extremely rich seismic history with disastrous events that have occurred over centuries. In this paper we reflect on how these natural events could have influenced the construction history of the village of Umm as-Surab (today, northern Jordan) through the study of its building techniques. We will focus on the analysis of supporting systems (arches) and masonry techniques. Data from buildings will be complemented with data derived from archaeological excavation and archaeometric analysis of mortars and plasters. The analysis of construction techniques allows recording technological changes that can sometimes be explained only through radical events in the history of a place. These may be due to changes in the social, political and economic organization, or due to natural events. If the first three can be investigated through specific sources, such as the written or materials ones (such as pottery), the natural events, such as earthquakes, are more challenging to investigate since it is difficult to identify their traces and, therefore, to analyse their effects. In fact, although written sources can describe earthquakes and their effects on people and buildings, it is difficult to relate these events to specific evidence, because earthquakes can produce different effects depending on the places where they occur, their intensity, extension, and the construction culture of the area affected. For this reason, attention must be paid to the analysis of the material data available and its results always need to be cross-checked with results from different sources. This paper suggests the idea that an earthquake can cause changes in construction culture that can only be understood by analysing their production cycle. This entails dealing with aspects of the construction that includes the acquisition or development of new technical procedures (e.g. those related to stone quarrying), tools, as well as the development or acquisition of new geometric and mathematical knowledge (e.g. the knowledge necessary to produce squared-off blocks for arches), and the knowledge related to the physic-chemical characteristics of materials (e.g. for the production of mortars). The development of procedures, tools and knowledge is based on continuous testing that requires time and that eventually leads to the development of a new culture (the so-called 'local seismic culture'). In such a context, an earthquake can be the cause of the abandonment of a site or the beginning of new experiences for the community that decides to remain on it. In both cases, social effects of earthquakes can be recorded in the architecture although its traces may be more or less visible depending on the relevance of the changes that can be limited or not easily detectable. It is also interesting to understand how the most ancient building solutions can be maintained after earthquakes because considered effective. Similarly it is interesting to understand how these solutions can be improved or replaced. The time frame for such kind of research can only be long, since this is the only way to understand complex phenomena such as technological and typological changes in construction techniques. Because of this, this research extends from the Byzantine period to the beginning of the Mamluk sultanate. Furthermore, within such a context, written sources and information on the material culture are more abundant, which allows using better qualitatively and quantitatively data to draw at solid conclusions.

Earthquakes in the eastern Mediterranean region from antiquity to the Middle Ages: an overview

The seismic history of the eastern Mediterranean consists of numerous earthquakes documented thanks to written sources and material traces present in both, archaeological contexts and geological deposits. The comparison of these data has already led to the production of a reliable list of historical earthquakes with their epicentres, magnitude and intensity.1 However, research constantly produces new data that improve and enrich these lists. Below we present a series of seismic events that occurred between 3rd-4th century AD and 14th century AD whose effects were recorded in an area between present-day Syria and Jordan. Therefore, these events can be contextualise within the ongoing research at Umm as-Surab. Earthquakes have repeatedly been responsible for the destruction of some important urban centres in Palestine and Arabia, such as Petra (AD 363 and AD 551) or Jerash (AD 749). As for the documented earthquakes between Palestine and Arabia, according to the study carried out by K.W. Russell, and a more recent study by N. Ambraseys that re-discusses the dating and identification and classification criteria of the ancient earthquakes that occurred in the Mediterranean and the Near East, there is the possibility of identifying, through reliable documentary sources, approximately ten destructive seismic events between 2nd and 8th centuries AD. The most extensive and disastrous seem to have been those of AD 551 and 749. The event of AD 363 seems to have been equally disastrous but in a relatively limited area. 2 Information related to it describe two earthquakes that occurred six hours apart and caused the destruction of 22 cities between Syria and Palestine, and the loss of a large number of human lives. 3 The earthquake of 9th July 551 (intensity of X on the Mercalli-Cancani-Sieberg scale, hereafter MCS), probably with its epicentre on the Lebanese coast, caused disasters over 100km from the coast, damaging numerous cities and villages. 4 The 8th century AD is a period of intense seismic activity. A significant series of earthquakes affected the entire area of the Eastern Mediterranean. The earthquake of 18th January 749 is a powerful event that struck Palestine with an intensity of IX-X on the MCS, of which we have information from different Arab, Byzantine and Syriac sources. Its dating was debated for a long time (i.e. if occurred in 746 or 749), and, after several studies, researchers agreed on the 749. 5 Its effects were felt in a huge area ranging from Egypt to Turkey and from the eastern coasts of the Mediterranean Sea to the shores of the Euphrates. For the Middle Ages, two important seismic sequences have recently been defined in detail and studied: the sequence of AD 1138-39 and the sequence of AD 1156 and 1159 which affected Syria, south-eastern Turkey and northern Lebanon. 6 Two other highly intense earthquakes that affected the eastern Mediterranean, and in particular the area of interest of this research, are those of AD 1182 and 1202. The first had Bosra and southern Syria as its epicentre with an intensity of IX on the MCS, while the second is a much larger earthquake (X on the MCS), the effects of which have been recorded from Iraq to Sicily, with the most significant damages are located between the Lebanese coast and centralsouthern Syria. The list of earthquakes between the 13th and 15th centuries AD encompasses many more events but the analysis of their epicentres, intensities and magnitudes do not allow inferring that their effects have significantly affected the area of interest of this study.

Research context

The site of Umm as-Surab is located in northern Jordan, Mafraq governorate, at only two kilometres from the Syrian borders (Figure 1). This area is characterised by a basalt plateau that from northern Jordan extends in larger part towards current Syrian territories and it is also named Ḥawrān. During the Roman period it was part of the province of Arabia, subsequently part of the Diocesis Orientis and then of the al-Urdunn district after the Islamic conquest. Historic and social events, combined with the use of basalt, have created the conditions for the good conservation of the village's ancient habitat. The basalt is a strong and durable building material, characterised by an extremely high density (approx. 2800kg/m 3 ). Its characteristics require some level of complexity for both, the extraction and transport of blocks. Its transformation in building material is also related to the availability and use of 4 Russell 1985: 44-46;Ambraseys 2009: 199-203. 5 Guidoboni, Comastri and Traina 1999: 366. 6 Guidoboni, Bernardini and Comastri 2004: 105-127. cutting and finishing tools with high dynamic hardness, and on the artisans' ability to use them. Despite all these technical restrictions, basalt has been used in the region as a building material since at least the Bronze Age.7 This historical and geographical context made possible the preservation of numerous standing ancient structures, in some cases even exceeding 5m in height. This makes Umm as-Surab an optimal working area for investigating the traditional construction practices used to limit the effects of earthquakes. The site covers a surface of about 17ha. and has been divided into 29 Topographic Units (TU) comprising four churches, some likely public buildings, and 26 housing blocks. The most well-preserved building of the site is the church of Sts. Sergius and Bacchus that has been the object of three main international research projects8 and restorations activities by the Department of Antiquities of Jordan. The church is a building composed of threenaves and, on the north side of it, lies a monastic complex. An inscription on the lintel of the church main door (no longer in situ) dates its foundation to the AD 489, but various occupation phases are documented for the building. In particular, above the ruins of the room built to the north of the semi-circular apse was erected a 9m high tower that was used as a minaret when the building was probably re-used as a mosque. The whole site was subject to a surface survey, and two archaeological excavation (years 2018 and 2019) were carried out in the so-called AREA A, located in the south-eastern sector. The latter activities have brought to light a stratigraphic sequence that spans from the Late-Roman period (3rd-4th century AD) to the late Umayyad-early Abbasid period (8th-9th century AD), to the re-occupation of the area that occurred from the beginning of the 13th century AD to the 15th century AD.

Research Methodology

The observations reported in this paper on the buildings of Umm as-Surab are the product of an extensive autoptic analysis of all of the structures described using the methods of Buildings Archaeology (i.e. the application of theoretical principles of archaeological stratigraphy to the study of still-standing buildings). Stratigraphy thus becomes an analytical methodology that can give useful information and help delineate the history of a building. In most of the cases, buildings were also recorded through a digital photogrammetric survey for generating a three-dimensional model with geometrically corrected photographs (orthophotos). The model was verified and its accuracy was assessed during various stages of data acquisition through direct measurements of some portions of the buildings. The detailed description of all features of each masonry type was based on the observations carried out on areas of 2x2m of masonry. The section and core of a wall were also described where possible. Analysis of the arches also included consideration on the deformations caused by the numerous stresses (some of them due to earthquakes). The survey of these building systems was therefore performed in such a way that both the current state of a structure and the geometric reconstruction of its likely original shape could be visualised. For some pillars, precise measurements of the full height could not be obtained due to the considerable amount of material filling the rooms. All the arches were documented photographically except for one located in the western sector of the site (TU10), which was beyond reach due to the collapse of the entrance. Furthermore, archaeometric analyses were performed on samples of mortars and plasters9 taken from stratigraphicallydefined pieces of wall, and initial dates were obtained by the application of the 14 C method to charcoal fragments from both, the mortar and plaster. These results were complemented by the 14 C results from charcoal samples from excavated strata.

Effects of earthquakes on the construction techniques at Umm as-Surab

The stratigraphic analysis of the still-standing structures of Umm as-Surab allowed us to identify and define massive phases of reconstruction. Collapse interfaces and particular deformations of the walls were identified, such as bulging phenomena or the dislocation of the ashlars (Figure 2). These have been classified as possible effects caused by earthquakes. To try to better define these phenomena, we focused on the study of arches and walls, which we present in detail below, and then we discuss the results achieved by crossing them with the data from the archaeological excavation of AREA A and from archaeometric analyses on mortars and plasters.

Arches

In the past centuries, the main support system for the roofs at Umm as-Surab was the arch. Our extensive survey allowed documenting a total of 67 intact arches 10 organised in three groups and subdivided into seven main types related to four main shapes: semi-circular (round), surbased, pointed, and funicular (catenary) (Figure 3). The intense seismic history of the region is clearly readable on these structures which, in Umm as-Surab as well as in the rest of the Ḥawrān, have been reconstructed using older piers and capitals: the only parts of the structure that did not collapse during the paroxysmal event. In the Byzantine period, the semicircular arch was used in the main room of houses, that is a relatively high (between 2.50 and 3.00m) and wide room of about 4.50x5.50m. Almost certainly this room was used as a living and reception space in the Byzantine period and probably it maintained the same function in other periods with only small changes. Evidence of Byzantine arches have been recorded for a total of 26 architectural elements. Currently only three of them are still standing: two inside houses and one inside the presbytery of the church of Sts. Sergius and Bacchus. Of the three, only the latter is in a good state of conservation thanks to the use of very well cut and laid ashlars. These are likely to have allowed for a good resistance to movements. The other two, on the other hand, show some deformations that could be due to both, the loads of the roofs and (probably) to earthquakes, which may have also caused the collapse of all the other arches of the village. The fact that the arches were reconstructed is clearly proved by the fact that the reused voussoirs are not aligned with the central axis of the piers, and by the fact that are not well re-positioned either without further reworking or with some reworking. Unfortunately, it is currently impossible to accurately date the reconstructions of the arches since no archaeological excavations have yet been conducted inside the houses. In any case, from the stratigraphic analysis of the walls and the typology of the arches, it is possible to suggest that some of these may be of medieval origin, while others may have been 10 From this quantity must be subtracted nine arches which were certainly rebuilt between 1918 and 1978. These two chronological end points were derived from the analysis of two aerial images of the site of Umm as-Surab. The 1918 photograph, made by the German Air Force, clearly shows that several buildings did not exist or had collapsed roofs. The 1978 photograph, on the contrary, taken by the Spanish Air Force, clearly demonstrates the presence of new structures and, in other cases, the reconstruction of roofs. Thus, the analysis of the photographs provided an extremely important source of information for determining several modern building phases of the village that are otherwise difficult to detect and document.

The authors wish to thank Bernard Lucke for kindly arranging consultation of the 1918 photograph, as well as the Packard Institute, which owns it. We also wish to thank Antonio Almagro for making available the photographic archive of the Spanish archaeological mission in Jordan, which includes the 1978 photograph, currently housed in the Escuela de Estudios Árabes (CSIC) in Granada.

reconstructed at the end of the Ottoman occupation of the region. Others again might be reconstructed in recent years. Currently, the only dating that it is possible to link to the construction of arches and that can be related to seismic events, are those of the northern courtyard of the church of Sts. Sergius and Bacchus.

In this case, the dating at the second half of the 13th century (1241-96: probability of 95%)11 of a fragment of charcoal embedded in the plaster that covers the walls and the arches of a cistern in the courtyard provides a terminus ante quem for their dating. In addition to this chronological information, the cistern also contains extremely important typological information. The arches supporting the cistern roof have, in fact, two different geometric shapes: catenary (or funicular) and pointed. These shapes, although existing in the region, are extremely rare in rural contexts. Besides, they are quite different from those in the architectural lexicon of the Byzantine era, whereas seems to be more common to the construction culture of the Early and Middle Islamic periods. The second 14 C dating, obtained from a piece of charcoal found in the bedding mortar of the joints of a door in the courtyard of the church, has approximately the same dating as the one seen before (i.e. the second half of the 13th century) confirming the existence of an important building site in this period.

Walls

Six groups of wall techniques, comprising 14 types, were identified in Umm as-Surab and some parallels have been found in other villages of the region (Figure 4). GROUP I: Walls with large polygonal stone blocks collected or extracted from the surface of the basalt rock, laid with the use of wedges and arranged in irregular layers. GROUP II: Walls with large and small split or slightly rough-hewn blocks arranged in irregular layers. GROUP III: Walls with rough-hewn and reworked rectangular elements, arranged in regular layers and containing irregularly-arranged headers in section. GROUP IV: Walls with squared-off and 'L'-shaped blocks. GROUP V: Walls with rectangular elements arranged in regular layers alternated with regular layers of headers. GROUP VI: Walls made with elements recovered from other buildings and reworked, distributed in horizontal and quasi-horizontal layers; the section has headers arranged in regular layers or positioned irregularly.

In this contribution we will focus on the wall types in GROUPS IV, V and VI which correspond to the historical period considered in the research. The types of GROUPS IV and V were built during the Byzantine period and are characterised by the fact that all the elements come from quarries and have specific installation systems, such as L-shaped elements (GROUP IV), and by the presence in the section of headers arranged in ordered layers (GROUP V). The headers have particular features: the visible short end of the blocks is worked (rough-hewn or smoothed) and has standard dimensions of about 0.60m, which is also the width of the section. These are masonry types put in place by highly specialised craftsmen with specific technical knowledge and availability of cutting tools and stone processing that allow their realization. If both of these construction solutions give greater stability to the masonry, the first seems to be a stone cutting system that has a mainly decorative purpose. The use of headers, on the other hand, has an important static role because it allows the two faces of the walls to remain connected despite the stresses caused by earthquakes.

In fact, the wall portions that use this construction technique are those more frequently preserved in the village. The masonry techniques described in Group VI appear to be the result of the transmission of technical knowledge that, after a long period of use and experimentation, was absorbed into the local building knowledge, probably because of its great stability. One of the greatest differences between Groups V and VI is the height of the courses: in Group VI it is slightly reduced compared to Group V because of the reworking of the surfaces of individual elements before being relaid. Similarly, the corners demonstrate persistence of the types documented in the previous groups, re-using solutions in which headers and stretchers alternate regularly, contributing to the creation of a particularly solid and stable masonries at the corner of the building. clues for dating this wall techniques to the Islamic period. It is possible to assume that the earthquake of AD 749 could have caused an important break in the building history of the village, further increased by the subsequent political and cultural changes. A new moment of building vitality seems to affect Umm as-Surab in the mid of the 13th century AD, which can be considered as a terminus post quem for most of the types of Group VI. Analysis of these masonry types reveals a radical technological change, compared to the types of Groups IV and V, characterised by much more common practice of the reuse. The five types (i.e. 10, 11, 12, 13 and 14) of Group VI, in fact, show only reused elements organised in slightly irregular layers with reduced height compared to Groups IV and V. For Group VI it is possible to suppose a labour organisation divided into discrete building project sites concentrated in several parts of the village, especially in the central and eastern parts. This group is no longer based on the presence of specialised craftsmen, but on the presence of good shapers and masons capable to recover the abundant old material and build dwellings with different spatial organisation compared to the Byzantine period, where long and narrow spaces appear to predominate.

Archaeological Excavation

In the 2018 and 2019, archaeological excavations were carried out in Umm as-Surab. These activities took place in the south-eastern part of the site and involved a large area of about 25m 2 that extends between two housing units: the TU29.1 and TU24. Although the excavations

have not yet been completed, the stratigraphic sequence defined so far thanks to a preliminary analysis of the pottery,12 has allowed identifying four main periods of occupation: Late Roman-Byzantine; Umayyad; Postearthquake (749) -early Abbasid and Mamluk. Among the main layers unearthed during the excavation, one of the most evident is a vast collapse of basalt stones coming from the wall that still limit the excavation area to the north and that it is the southern perimetral wall of the house 29.1. The analysis of this wall has revealed a collapse interface that marks the boundary between two typologically and technically different masonry techniques. The type of collapse interface and the related layer of stones documented in the excavation leave little doubt about the cause of their formation which is due to an earthquake (Figure 5). By crossreferencing the data from the archaeological excavation and the analysis of the wall it is possible to suggest that the earthquake occurred in medieval times. The collapse of the stones lays in fact on a stratigraphic unit (SU 1469) which has returned pottery from the Mamluk period (c. 13th-14th AD). In turn, the collapse of the stones is covered by a level (SU 1460) whose material culture belongs to the same chronological framework. This suggest that sometime after the seismic event, the area was reoccupied. However, despite the fact that the list of medieval earthquakes that struck in the eastern Mediterranean is quite rich, the dating of the event that could have cause the collapse of the wall is still problematic. Two earthquakes that closely affected the area of this research with an intensity greater than VII of the Mercalli scale are known: that of 1182 (I: VII), which is documented nearby Bosra and its effects could have also affected Umm as-Surab (only 12km away), and the earthquake of 1202 (I: IX, M: 7.6), which is remembered by old sources as one of the most destructive earthquakes of the Middle Ages in the Eastern Mediterranean. However, the dating of these two earthquakes differs from the material culture found in the excavated level (SU 1469) just below the collapse.

The collapse of the wall should therefore be attributed to a later event for which it is currently impossible to provide more reliable information. In fact, in the list of earthquakes that occurred in Syria, between the 13th and 14th century AD, it emerges a sequence of numerous seismic events including those of AD 1303, 1339, 1344 and 1404. 13 However, from the analysis of the geographical location, intensity and magnitude it seems that none of them could have been the cause of the collapse of the perimeter wall of house 29.1. In this regard, the research will have to continue to try to better understand which seismic event can be linked to the material traces found in the wall stratigraphy and in the archaeological excavation. An important fact that emerges from the reading of these data is certainly that relating to the change in the masonry construction technique on the southern perimeter wall of the TU29.1 that has already been discussed in the previous paragraph.

Construction materials and Archaeometry

Although basalt plays a prominent role in Ḥawrān built environment, analysis of the architecture demonstrated that different materials were used at different time.

Therefore, the study of these materials can improve our understanding of the production cycle of different masonries and suggests the presence (or absence) of specific knowledge and skills and, consequently, of specific craftsmen. For example, in Umm as-Surab the core of a wall usually filled with a mortar containing basalt chips, but in the Roman and Byzantine times core mortars also contained earth and ceramic fragments, glass and stone flakes probably intended to make the cores more compact. Chemical and physical analyses of mortars and plasters have provided indicators for the production technology used in different periods.

Results demonstrated that mortars were exclusively made of lime in the Byzantine period, whereas in the Islamic period mortars were based on a mixture of lime and gypsum. 14 Mortar analysis has also facilitated identification and extraction of charcoal fragments originally mixed (intentionally or unintentionally) into the mortars whose radiocarbon dating has provided some of the first absolute chronologies for the whole site (see above) that are of fundamental importance in such context where chronological indicators are extremely difficult to find. Although in smaller quantities, mortars were used also in the joints of walls and arches, and its abundant use in certain types of arches has been demonstrated not only between the voussoirs but also to bind the elements laid above the arch extrados. Therefore, the mortar can be used to discriminate groups of construction systems. Another very common practice in Ḥawrān is the pointing of the mortar joints, probably to prevent the leakage of mortars from the core of the wall. Such a practical function may have been accompanied by an aesthetic value as well, suggested by the arrangement of small basalt fragments either at the juncture between vertical and horizontal seams or along the entire line of a joint. Depending on the stone shape and organization, mortars may not be essential to the stability of the walls in Ḥawrān (e.g. when walls are made of perfectly squared-off blocks with very thin mortar joints), however studying these materials and their physic-chemical characteristics is essential for the study of the craftsmanship that produced them and that, in turn, can highlight changes in the building culture, potentially sprout even by the effects of 14 Gilento, Pesce and Pesce 2019.

earthquakes.

Use and improvement of anti-seismic technical solutions

One main point emerges from the study of earthquakes and construction techniques at Umm as-Surab. It concerns the long-term use and improvement of specific technical solutions, such as the use of headers and wall-corners. The use of prismatic elements with length perpendicular to the face of the wall that can join its two side (i.e. headers) is evidence of the attention paid by the builders to deploy solutions that can greatly improve the stability of the walls. This detail was certainly already in use in the Hellenistic and Roman times in the region, especially in important structures, and it spread as a common practice also in the Byzantine period. This research has shown that even in the medieval period the headers continue to be a common solution in the masonry techniques which, on the other hand, are characterised by less refined faces compared to the Byzantine period (due to the practice of the reuse of the stones). Further evidence of the continuous use of construction techniques is in the wall-corners. Sometimes the corners are the only preserved parts of historic structures, demonstrating their particular resilience. In Umm as-Surab the functionality and resistance of the corners were exploited, for example, to build (probably in the 13th-14th centuries AD) the tower on the remains of the church of Sts. Sergius and Bacchus. Although the stone blocks used in the tower are all re-employed, the corners are well connected, making the whole structure extremely stable and demonstrating the particular attention paid in the construction of the building. In this specific case, the stability of the tower is also improved by the construction of the stairs that develops around a central axis forming a sort of quadrangular-based pillar connected to the tower perimeter wall, making the structure even more stable. A third technical solution that could have been used for anti-seismic purposes in the region, is a particular type of anchoring solution of the blocks that allows a stronger connection: the creation of a so-called mortise and tenon join. According to the literature, this is a widespread system especially used in prestige architecture of the Roman and Byzantine eras. 15 This could be positioned in specific points of the structures as well as in the façades and the upper and lower sections of high-rise buildings, such as the tower of the house XVII at Umm al-Jimāl (Figure 6). According to the literature and field surveys, no traces of such a technical solution have been found dated to the medieval period. This lack of evidence could demonstrate the loss of some construction traditions due to technical, cultural and economic factors. According to Jean-Claude Bessac, the oldest examples of use of this reinforcement technique in the territories of present-day Syria were identified in the walls of Sharah. Here, this technique evolved even further with the creation of a double hook blocks such as those used in Shahba, dated to the 3rd century AD and then spread throughout the Byzantine period (well documented always in Sharah on the Byzantine tower and in Bosra in the church of Sts. Sergius, Bacchus and Leontius, dated to the beginning of the 6th century). The use of double hook mortice and tenon locking systems would have been particularly effective with the use of basalt, which can more easily withstand the tensile forces caused by earthquakes (compared to other stone types) and, in fact, this solution is unknown in limestone constructions of the Near East. From a chronological point of view, another observation made by Bessac,16 concerns the spread of this technical solution from the 2nd century and its systematization in the Byzantine period, almost certainly caused by a strong seismic activity. In fact, such a technique entails a considerably lengthily production (with high costs) that can only be justified by its effectiveness in solving specific problems. This entails the fact that there must have been a specific reason for using it (and for having developed it over four centuries). Unfortunately, traces of this solution were lost at the end of Antiquity. The mortise and tenon technique is also cited as an antiseismic device by Arce, who indicates the example in the tower of the XVII house of Umm al-Jimāl 17 and by Clauss-Balty, that records it in the tower added to 15 Arce 1996; Bessac 2010. 16 Bessac 2010: 419. 17 Arce 1996: 44-45. Kafr Shams' house 1.18

Discussion

The cases discussed above (walls, arches and mortars) clearly demonstrate that there has been a clear change in the production cycle between the Byzantine and medieval periods. However, this change did not influence the choice of technical solutions (corners and headers) that become essential components of the constructive culture of the region: the effect of a continuous adaptation to natural events and environmental needs and the technical success of these solutions in the long term. The mortises and tenons technique, on the other hand, could be a case in which an anti-seismic solution has either, not been incorporated into the local building culture, or lost because of the loss of the necessary technical skills, knowledge or craftsmen. The rebuilding phases after an earthquake can be a moment to introduce new architectural forms, materials and solutions that mark a discontinuity in the construction tradition of the local culture. The arches of the cistern in the monastery of the church of Sts. Sergius and Bacchus could be considered as an example of this typological and technical discontinuity in Umm as-Surab. The cistern was in fact built at the end of the 5th century AD together with the monastery and it is possible to hypothesize that the arches that supported its roof in this phase were semi-circular, following the practices and construction forms of the time. A disastrous earthquake could have caused their destruction, which then gave rise to the need for a reconstruction of the arches for a new use of the cistern, whose plastering dates back to the second half of the 13th century (see above). Two destructive earthquakes can be associated with the collapse of the arches of the cistern: that of 749 and that of 1202. Currently, there is no data suggesting a date or the another. In any case, one of the two events created the opportunity to build new arches, typologically and technically very different from the previous ones. The new arches were built by specialised masons who had the technical and geometrical knowledge necessary, probably acquired in other areas of the region (Bosra?). This introduction of new craftsmanship was, perhaps, sponsored by the new political and social élite (the Mamluks) that had the necessary economic resources and interests to promote a broad project of improving water infrastructure and territorial reorganisation. The rise of the Mamluk sultanate in the mid of the 13th century could, therefore, have created the conditions for external elements to bring innovations that have entered the constructive culture of the village, as demonstrated by the presence of other catenary or pointed arches in the site which completely replaced the semi-circular ones from the Byzantine period (likely almost all of them collapsed due to one or more seismic events). These changes are also found in the mortars studied in Umm as-Surab, showing important technological innovations, such as the use of gypsum, found in a sample of mortar used in a construction phase subsequent to the Byzantine period and technologically very different from it.

Conclusion

Earthquakes occur in specific areas of the Earth that are also unique social and cultural contexts. Earthquakes can trigger changes in various aspects of the communities experiencing such paroxysmal events, although these are not sufficient and require the contemporary actions of other forces pushing for changes already present in nuce in a community. These changes can also be found in construction techniques and become part of a much longer and more complex evolutionary process that can only be appreciated by looking at a longer time perspective. This is what we have tried to demonstrate in Umm as-Surab, where the daily life of a small community can be intertwined with big natural, social and cultural events leaving their traces and effects on its common practices, including those related to the constructions. The local seismic culture developed in Umm as-Surab is the result of a long adaptation to the limits imposed by the construction materials which, for example, did not allow the use of lighter materials for roofing (e.g. timber). Despite this, the continuous experiments, and the timely external influences, have led to the development and use of technical solutions which, while not capable to completely prevent the collapse of the structures, have been able to, at least, mitigate the damage. The result of this long adaptation and evolution of the construction techniques is represented by the chronotypological table of the masonry techniques of Umm as-Surab which demonstrates how the most recent techniques have almost always incorporated past experiences, adapting them to the historical, economic and social context of the time. This does not mean that in the construction history of Umm as-Surab there has been only continuity, but on the contrary, there are also important technical-formal breaks that led to innovations.

Figure 1

 1 Figure 1. A: Location of Umm as-Surab (by Stefano Anastasio); B: Plan of Umm as-Surab (by Piero Gilento and Gourguen Davtian).

Figure 2

 2 Figure 2. A: Collapse interface of the southern perimeter wall of TU 29.1; B: Bulging of a wall in TU28. C: Voussoirs that have been reset on the piers of an older arch (photos by Piero Gilento).

Figure 3 .

 3 Figure 3. A: Semicircular arch in TU29.1 (Byzantine period); B: Pointed arch; C: Funicular arch. Both are located in the cistern of the church of Sts. Sergius and Bacchus and have the terminus ante quem for their construction at the mid of the 13th century (photos and drawings by Piero Gilento).

Figure 4 .

 4 Figure 4. Chrono-typological table of the masonry techniques of Umm as-Surab (by Piero Gilento).

  The types described in this group can be attributed to specialised masons, almost certainly local despite the presence of labour from nearby villages cannot be excluded. The analysed types in fact demonstrate technical characteristics that can be attributed only to expert artisans who have the related knowledge and skills. Several chronological indicators allow to narrow the chronology of these masonry types. Type 10 was used in the western façade of the tower of the church of St. George at Samah as-Sarhan and it is dated after AD 624. Type 13, instead, was used in the reconstruction of the southern edge-wall of TU29.1, in the south-eastern area of the village. The archaeological excavation conducted immediately behind the structure revealed the collapse levels of a wall whose first phase can be dated by stratigraphy and typological comparison to the late Roman/early Byzantine period. The data from the archaeological excavation suggests that the wall collapsed during the Mamluk sultanate (see below for more data). The reconstruction of the wall (i.e. Type 13) is therefore later than this date. The stratigraphy and the typology confirm a similar chronology for the remaining types, which belong to the reconstruction phases of religious or domestic structures. Type 11 was widely employed in the reconstruction of the walls of the so-called 'Two Arches Church'; Type 12, instead, comes from the blocking of the apse of the church of St. George at Samah as-Sarhan and could be contemporary to Type 10. Finally, Type 14 was used in the western elevation of the tower rebuilt on the collapsed portion of the apse of the church of Sts. Sergius and Bacchus at Umm as-Surab. All these types have important building phases in the Islamic era. The most reliable chronological indicator for this group is currently the stratigraphy, that provides the first chronological

Figure 5 .

 5 Figure 5. A: Southern perimeter wall of TU 29.1. In red is marked the collapse interface (photo by Piero Gilento); B: Orthophoto of the archaeological excavation with the collapse layer marked in red (elaboration by Gourguen Davtian); C: Particular of the collapse layer (photo by the Yarmouk University).

Figure 6 .

 6 Figure 6. A: Section wall with headers, Umm as-Surab; B: Still-standing corner, Umm al-Jimāl; C: Lower part of the tower of house XVII at Umm al-Jimāl: mortise and tenon technique (photos by Piero Gilento).

[START_REF] Russell | The Earthquake Chronology of Palestine and Northwest Arabia from the 2nd through the Mid-8th Century A[END_REF][START_REF] Guidoboni | Catalogue of ancient earthquakes in the Mediterranean area up to the 10th century[END_REF][START_REF] Sbeinati | The historical earthquakes of Syria: an analysis of large and moderate earthquakes from 1365 BC to 1900 AD[END_REF]

2005: 347-435; Ambraseys 2009. 2 Russell 1980: 47-64. 3 Ambraseys 2009: 148-151.

Braemer, Échallier and Taraqji 2004.

[START_REF] King | Byzantine and Islamic sites in Northern and Eastern Jordan[END_REF][START_REF] Parenti | Building Archaeology in Jordan. Preliminary Report on the 2009-2011 Surveys at Umm as-Surab[END_REF][START_REF] Gilento | Risultati storico-costruttivi dall'analisi archeologica degli elevati[END_REF][START_REF] Gilento | Ancient architecture in the village of Umm al-Surab, northern Jordan. Construction process and building techniques, a case study[END_REF]

The mortars were studied by Giovanni Pesce and Cecilia Pesce of Northumbria University, Newcastle, in the framework of a collaboration during the EU -Horizon 2020 funded project ACTECH (P.I. Piero Gilento).

The dating was performed by the CNA-Centro Nacional de Aceleradores of the University of Seville. The authors wish to thank its director Francisco Javier Santos Arévalo for the collaboration.

This research, still in progress, has been carried out by Dr. Raffaella Pappalardo, whom the authors thank for her contribution.

Sbeinati, Darawchech and Mouty 2005: 347-435.

Clauss-Balty 2008: 54.

Acknowledgements

This text is the result of an international and interdisciplinary research project that has seen the participation and funding of various institutions: EU Commission -Horizon 2020 for funding the ACTECH project, Paris 1 Panthéon Sorbonne, CNRS, the Yarmouk University, the Ifpo-French Institute for the Near East and the DoA-Department of Antiquities of Jordan.

Author Contributions

The text was conceived and written by Piero Gilento whereas Giovanni Pesce reviewed it. The other authors have contributed in various capacities through the field research and the discussion of the results: Gourguen Davtian-GIS and GPS survey; Pierre-Marie Blancarchaeological excavation and pottery studies; Khaled al Bashaireh-archaeological excavation and pottery archaeometric studies; Apolline Vernet-archaeological excavation; Maen Omoush-archaeological excavation and pottery studies.


Claire Gerente
email: claire.gerente@emn.fr

Yves Andres
email: yves.andres@emn.fr

Gordon Mckay
email: kemckayg@ust.hk

C Gérente

Y Andrès

P Le Cloirec
email: pierre.le-cloirec@ensc-rennes.fr

Removal of arsenic(V) onto chitosan: From sorption mechanism explanation to dynamic water treatment process

teaching and research institutions in France or abroad, or from public or private research centers.

Removal of arsenic(V) onto chitosan: From sorption mechanism explanation to dynamic water treatment process

Introduction

Arsenic contamination in natural waters is a world wide problem and due to its established toxicity and its presence in overcrowded areas [START_REF] Jain | Arsenic: occurrence, toxicity and speciation techniques[END_REF][START_REF] Hossain | Arsenic contamination in Bangladesh-an overview[END_REF], the guideline concentration limit value recommended by WHO in drinking waters has been 10 gL -1 since 1993. The European Union, USA, Canada, Japan, and Vietnam have accepted this value in their regulatory systems, but other countries (Bangladesh, Bolivia, India, etc.) still operate at present to the 50 gL -1 standard [START_REF] Sengupta | Arsenic in subsurface water: its chemistry and removal by engineered processes[END_REF][START_REF] Nguyen | Specific treatment technologies for removing arsenic from water[END_REF]. Arsenic is introduced in water through natural and anthropogenic sources: release from mineral ores, probably due to long term geochemical changes [START_REF] Hossain | Arsenic contamination in Bangladesh-an overview[END_REF][START_REF] Sengupta | Arsenic in subsurface water: its chemistry and removal by engineered processes[END_REF], and from various industrial effluents like metallurgical industries, ceramic industries, dye and pesticides manufacturing industries and wood preservatives. Two predominant species found in natural waters are inorganic forms of arsenic namely, arsenate As(V) and arsenite As(III) and their presence depends on the pH and redox conditions. As(V) which is the thermodynamically stable form, is found in oxic surface waters, rivers and lakes [START_REF] Smedley | A review of the source, behaviour and distribution of arsenic in natural waters[END_REF]. It is also reminded that it presents three pK a (2.2, 7 and 11.6): it means in most of natural waters, arsenic V is mainly within the H 2 AsO 4

-form (at 3 < pH < 6) or associated with HAsO 4 2-form (at 6.5 < pH < 7.5). After pH 8, HAsO 4

2-is the predominant species. Different technologies based on sorption mechanisms have been reported in literature in order to remove arsenic from industrial effluents or natural waters and include sorption/precipitation on iron and aluminum by-products [START_REF] Meng | Treatment of arsenic in Bangladesh well water using a household co-precipitation and filtration system[END_REF][START_REF] Singh | Equilibrium, kinetics and thermodynamic studies for adsorption of As(III) on activated alumina[END_REF][START_REF] Zhang | Arsenic removal from contaminated water by natural iron ores[END_REF]. Other adsorbents have also been investigated like carbonaceous adsorbents [START_REF] Pattanayak | A parametric evaluation of the removal of As(V) and As(III) by carbon-based adsorbents[END_REF][START_REF] Daus | Sorption materials for arsenic removal from water: a comparative study[END_REF], low-cost mineral materials [START_REF] Elizalde-Gonzalez | Sorption on natural solids for arsenic removal[END_REF] and biosorbents [START_REF] Ghimire | Adsorptive separation of arsenate and arsenite anions from aqueous medium by using orange waste[END_REF][START_REF] Loukidou | Removal of As(V) from wastewaters by chemically modified fungal biomass[END_REF]. These last ones can be compared as wastes, coming from food or seafood industries. Ion exchange has also been performed for As(V) removal, with strong base anion exchange resins like protonated amine functions or quaternary amines [START_REF] Dambies | Immobilized N-methyl-d-glucamine as an arsenate-selective resin[END_REF][START_REF] Henry | Preparation and characterization of a new class of polymeric ligand exchangers for selective removal of trace contaminants from water[END_REF][START_REF] Kim | Modeling a novel ion exchange process for arsenic and nitrate removal[END_REF]. Among the biosorbents, chitosan and its derivatives are obtained from the deacetylation of chitin, the major component of the crustacean shells. It has been widely used for the removal of metals from waters [START_REF] Gérente | Application of chitosan for the removal of metals from wastewaters by adsorption-mechanisms and models review[END_REF] and has also shown efficiency to adsorb arsenate ions [START_REF] Dambies | Arsenic(V) sorption on molybdate-impregnated chitosan beads[END_REF][START_REF] Gérente | Interactions of natural aminated polymers with different species of arsenic at low concentrations: application in water treatment[END_REF] or similar anions like perrhenate [START_REF] Kim | Removal of dissolved rhenium by sorption onto organic polymers: study of rhenium as an analogue of radioactive technetium[END_REF].

Preliminary results conducted with low concentrations (C < 500 gL -1 ) of arsenate indicated that the adsorption reaction was fast and followed a pseudo first order model [START_REF] Gérente | Interactions of natural aminated polymers with different species of arsenic at low concentrations: application in water treatment[END_REF]. The authors also showed that the sorption mechanism was an ion exchange reaction. The aim of this study is firstly to clarify the sorption mechanism with an extension of the arsenate concentration in batch reactor. Two approaches are proposed: the use of different models like Freundlich, Langmuir, Redlich-Peterson and Tempkin to describe the sorption isotherm and the investigation of the pH effect in synthetic and natural waters. In order to complete The breakthrough curves are obtained in deionised and natural spring waters and they are simulated by a mass balance model. These data confirm the potential use of chitosan for the removal of arsenic from contaminated waters.

Methods

Chemicals and apparatus

The chitosan, an amino-polysaccharide, was provided by France-Chitine (La Ciotat-France) and raw flakes have been ground and sieved for a size range between 0.25 and 0.35 mm. It has been characterised [START_REF] Andres | Antibacterial effects of chitosan powder: mechanisms of action[END_REF] and the main properties are summarized in Table 1. All chemical reagents were of analytical grade and the arsenic concentrations were measured by a Perkin Elmer graphite furnace atomic absorption spectrometer (GF-AAS AAnalyst 600). Each determination was realised in 3 replicates, the quantification limit was assessed to 4 gL -1 and the average error estimated to ±6%. Polyethylene bottles were used after an acid washing and it was verified that no arsenic adsorption occurred on the inner walls.

Batch adsorption experiments and modelling

Adsorption isotherms have been performed with initial concentrations of arsenic(V) ranging between 25 and 2000 gL -1 ,a chitosan ratio of 0.5 g L -1 , temperatures selected from 4 to 40 • C and the optimal contact time fixed at 2.5 h [START_REF] Gérente | Interactions of natural aminated polymers with different species of arsenic at low concentrations: application in water treatment[END_REF]. The pH was not adjusted but it was monitored: initial and final pHs were in the same range between 5.6 and 6.2. Hydrochloric acid was added to solutions to decrease the pH when it was necessary. A spring water with a low mineral content and spiked with arsenic was also used in order to simulate the arsenate removal in a natural water (Table 2).

Different adsorption models have been tested based on an argued selection [START_REF] Gérente | Application of chitosan for the removal of metals from wastewaters by adsorption-mechanisms and models review[END_REF]. In the following equations, C e and q e are equilibrium data expressed in gL -1 and gg -1 , respectively. Their parameters were obtained by nonlinear regressive method using nonlinear form, excepted for the Redlich-Peterson model for which a procedure minimising the distance between the experimental data points and the theoretical model predictions was used (Excell solver). The earliest known sorption isotherm equation, called Freundlich model [START_REF] Freundlich | Over the adsorption in solution[END_REF] can be applied to nonideal sorption on heterogeneous surfaces as well as multilayer sorption and is expressed by the following equation:

q e = K F C n F e (1)
where K F and n F are the Freundlich parameters. The Freundlich isotherm has been derived by assuming an exponentially decaying sorption site energy distribution. It has been criticised for lacking a fundamental thermodynamic basis since it does not reduce to Henry's law at low concentrations, but for the special case of n F = 1, it does become Henry's law. In a recent review [START_REF] Gérente | Application of chitosan for the removal of metals from wastewaters by adsorption-mechanisms and models review[END_REF], over 20 chitosan-metal systems have been analysed using the Freundlich isotherm. These have mostly been carried as comparisons with the results of Langmuir analyses and in most cases the fits of the model results were less accurate than those of the Langmuir.

Langmuir [START_REF] Langmuir | The constitution and fundamental properties of solids and liquids[END_REF] developed a theoretical equilibrium isotherm relating the amount of gas sorbed on a surface to the pressure of the gas. The Langmuir model is probably the best known and most widely applied sorption isotherm. It has produced good agreement with a wide variety of experimental data and may be represented as follows:

q e = q m b L C e 1 + b L C e (2)
where b L is the equilibrium constant of the reaction (L g -1 ) and q m (gg -1 ) the maximum adsorption capacity. One can readily deduce that at low sorbate concentrations, C e = 0, it effectively reduces a linear isotherm and thus follows Henry's law. Alternatively, at high sorbate concentrations, it predicts a constant -monolayer -sorption capacity also called saturation capacity, defined by q m which provides one of the most useful and widely parameters in literature for comparing adsorbent capacities [START_REF] Gérente | Application of chitosan for the removal of metals from wastewaters by adsorption-mechanisms and models review[END_REF].

A combinaison of Langmuir and Freundlich equations has been proposed by Redlich and Peterson [START_REF] Redlich | A useful adsorption isotherm[END_REF]. It can be described as follows:

q e = K RP C e 1 + a RP C e b RP (3)
where K RP (L g -1 ), a RP (L g -1 ) and b RP are the constants. At high concentrations, it is similar to the Freundlich model and at low concentrations to the Langmuir one. Because of its dual features the application of the Redlich-Peterson isotherm to certain systems has been very successful [START_REF] Gérente | Application of chitosan for the removal of metals from wastewaters by adsorption-mechanisms and models review[END_REF].

Finally, to take into account the effect of the temperature, the Tempkin model [25] has been tested. It assumes that the fall in the heat of sorption is linear due to adsorbate interactions and the adsorption is characterised by an uniform distribution of binding energies until a maximum. The Tempkin isotherm has generally been applied in the following form:

q e = RT z ln(k T C e ) ( 4
)
where z is the adsorption energy (J mol -1 ) and k T the equilibrium constant (L mol -1 )o r( Lg -1 ). In this study, these two equilibrium constants (b L and k T ) are especially interesting because they could be introduced in the van't Hoff equation (Eq. ( 5)) in order to determine the thermodynamic parameters ( H, S and G)of the biosorption reaction. The parameters are useful to describe the adsorption reaction:

G = H -T S=-RT ln K (5)

Dynamic process and modelling

The dynamic process, provided by Polymem (Toulouse, France) is represented schematically in Fig. 1. It involves a continuous stirred tank reactor (CSTR) coupled with a microfiltration immersed-membrane unit. In a previous study [START_REF] Reddad | Cadmium and lead adsorption by a natural polysaccharide in MF membrane reactor: experimental analysis and modelling[END_REF], a membrane reactor used for biosorption had been already developed with an external tubular ceramic membrane and a centrifuge pump. But due to the high transmembrane pressure, the low membrane surface and the poor flowrate, a new process was performed. Originally it was provided for a biological wastewater treatment unit, which implied an agitation by air bubbling, but this kind of agitation was shown sufficient for this study since the chitosan presented a low density (Table 1). The CSTR was fed with a solution containing 350 gL -1 of arsenate, the reactor volume (V) is adjusted to 15 L and the outlet flow rate (Q) set at 10 L h -1 using a peristaltic pump. As a function of time, this flow rate was found to be stable. The volume of the CSTR was maintained constant during all the experiment by a level control that regulated the inlet of the polluted water. The amount of chitosan (X) was similar to that used in the batch reactor (0.5 g L -1 ) and the temperature range was 22-24 • C. After the adsorption step in the CSTR, the separation between the solution and the particles was performed by filtration in an external immersed-membrane unit. This module was made using 350 hollow organic fibers, with a cutoff of 0.2 m and a surface area of 0.2 m 2 . The retentate flux was returned to the CSTR and the arsenic concentration was followed in the permeate in order to obtain the experimental breakthrough. The pH and the T were not controlled but continuously monitored. From the mass balance equation in the CSTR (Eq. ( 6)), a model has been developed for the prediction of the breakthrough curves of arsenic in the permeate:

V dC dt = Q (C 0 -C) = dq dt XV (6)
or in other terms:

dC dt = Q (C 0 -C) V (1 + X(dq/dC)) (7)
with, V is the volume of the reactor (L); C is the concentration of arsenate in the permeate (gL -1 ); C 0 is the initial concentration of arsenate in the polluted wastewater (gL -1 ); q is the fixation capacity on chitosan (gg -1 ); Q is the flow rate (L min -1 ); X is the concentration of chitosan (g L -1 ); t is the time (min). The assumptions were the following: the reaction of arsenate ions onto chitosan flakes was not the limiting step of the fixation due to fast kinetics, and the equilibrium state was reached in the reactor at each time. An adsorption model could be used to describe the term dq/dC. All other parameters being constant except C, Eq. ( 7) was used to predict the breakthrough curves and to compare them with the experimental points.

Results and discussion

Batch adsorption studies

Isotherm curves have been plotted as a function of the temperature (Fig. 2) and the different adsorption models described in Section 2.2 were tested. An example using the Langmuir equation is given in Fig. 2. A comparison of the distribution coefficient indicates that the Langmuir model seems to be the best to describe the experimental data. Maximum fixation capacities, deduced from the equation, are slightly overestimated compared to the experimental ones. However, the variation shows that at higher temperatures, the capacities decrease. The q m values range between 373 gg -1 at 40 • C and 739 gg -1 at 4 • C. The second parameter b L , the equilibrium constant of the adsorption reaction, follows the same progression: from 0.041 L g -1 at 40 • C to 0.0128 L g -1 at 4 • C. Some studies found in the literature present q m values for other adsorbents but few of them have been realised in similar experimental conditions. It can be noted that Zhang et al. [START_REF] Zhang | Arsenic removal from contaminated water by natural iron ores[END_REF] have found a q m value of 400 g of As(V) g -1 at pH 5 and 20 • C onto an hematite sorbent. Dambies et al. [START_REF] Dambies | Arsenic(V) sorption on molybdate-impregnated chitosan beads[END_REF] transformed chitosan into a molybdateimpregnated chitosan and evaluated higher capacities, between 92.9 and 128 at pH 3 and 20 • C, but expressed in g of As(V) per g of molybdate. Other sorption results [START_REF] Pattanayak | A parametric evaluation of the removal of As(V) and As(III) by carbon-based adsorbents[END_REF][START_REF] Daus | Sorption materials for arsenic removal from water: a comparative study[END_REF][START_REF] Elizalde-Gonzalez | Sorption on natural solids for arsenic removal[END_REF][START_REF] Ghimire | Adsorptive separation of arsenate and arsenite anions from aqueous medium by using orange waste[END_REF][START_REF] Loukidou | Removal of As(V) from wastewaters by chemically modified fungal biomass[END_REF][START_REF] Dambies | Immobilized N-methyl-d-glucamine as an arsenate-selective resin[END_REF] cannot be easily compared for different reasons. The capacities are frequently presented in % removal, but this expression takes inadequately into account the idea of equilibrium data and saturation layer. The experimental conditions can be often very different: for example, initial concentrations are close to 400 mg As(V) L -1 in [START_REF] Loukidou | Removal of As(V) from wastewaters by chemically modified fungal biomass[END_REF] which is also far away from a water treatment application. And sometimes, adsorbents are strongly modified by chemical reactions, increasing consequently their cost. Regarding all these parameters, the q m values obtained in this study seem enough relevant to continue the investigation. The Tempkin model also defines an

G (kJ mol -1 ) H (kJ mol -1 ) S (J mol -1 K -1 ) R 2 G (kJ mol -1 ) H (kJ mol -1 ) S (J mol -1 K -1 )

pH effect

To complete the batch study, isotherms have been conducted in deionised water, at initial pH close to 5 and compared with the previous data obtained at pH 6 (Fig. 3). It has to be noted that final pH values are in the same range as the initial ones indicating that the speciation of both arsenic and chitosan should not really change during the fixation. The dashed lines correspond to the Langmuir model and the parameters are presented in Table 5. The fixation of arsenate is enhanced when initial pH value is reduced to 5. Regarding the pK a of the amine function (6.6 in Table 1) and the value of the zeta potential (22 mV at pH 6 and 68 mV at pH 4 in Table 1), the surface of chitosan is more and more protonated and positively charged as the pH decreases and the attraction of anionic species is then favored. So the arsenic sorption capacities are significantly higher. The shapes of the isotherms are quite similar and a plateau is experimentally reached: this implies that experimental points are similar to the q m values of Langmuir equation, respectively, 730 gg -1 at pH 6 and 1370 gg -1 at pH 5 (Table 5). This pH effect is also observed in natural water presented in the next section.

Adsorption in natural water

In order to validate the fixation of arsenate onto chitosan in a natural medium, a spring water has been used (Fig. 3). As its natural pH was 7.3, it needed to be lowered for the adsorption study and the initial value was adjusted to 5.5 and 4. It is obvious that the presence of other ions induces a decrease in the Table 5 Langmuir parameters obtained from adsorption isotherms of H2AsO4 -in natural and deionised waters, at 20 • C with different initial pH. Redlich-Peterson parameters are given in natural spring water at pH i 4 (curve not shown).

Langmuir model

Redlich-Peterson model experimental fixation capacities for C e less than 1000-1300 gL -1 . But the shape of the isotherm curves is different and at concentrations higher than 1300 gL -1 , the capacities increase and exceed those obtained in deionised water. Regarding the concentration of the different anions (SO 4 2-, HCO 3 -,C l -and NO 3 -) in this spring water (Table 2), the affinity of the chitosan amine function seems higher for the arsenate at C e > 1300 gL -1 . The Langmuir model correctly describes the experimental points (R 2 = 0.993 at pH 5.5 and 0.999 at pH 4) even if the saturation is not reached. Consequently the maximum capacities deduced from Langmuir model are overestimated in comparison with experimental data. The b L values obtained in the spring water are 10 times less than in deionised water and this may be due to the natural environment. In acidic conditions (addition of HCl until pH 4), the capacities are enhanced: q m = 1180 gg -1 at pH 5.5 and 4020 gg -1 at pH 4. This confirms the observations made in Section 3.2.

qm (gg -1 ) bL (L g -1 ) R 2 KRP (L g -1 ) aRP (L g -
The batch adsorption results and the properties of the chitosan (data shown in Table 1) lead to propose a sorption mechanism. To enhance the arsenate retention, the amine function of the chitosan needs to be protonated, that means that the pH of the solution has to be higher than the pK a (pK a = 6.6 in Table 1). This surface protonation is fast as the biopolymer is not porous (S BET = 3.1 m 2 g -1 ), is confirmed by an increase of the surface charge by zeta potential measurements and concerns an high amount of amine functions (2.5 mmol g -1 and 70% of deacetylation degree) regarding the arsenate concentration. Then, an electrostatic attraction occurs between arsenate ions and the amine function. From pH 6.6, more the pH decreases, more the majority form is H 2 AsO 4 and more the attraction is favored. In different conditions, H 2 AsO 4 ions can be released by ion exchange depending on the nature and the concentration of other anions [START_REF] Gérente | Interactions of natural aminated polymers with different species of arsenic at low concentrations: application in water treatment[END_REF]. The following equilibriums clearly illustrates the sorption mechanism:

R -NH 2 + HCl ⇔ R -NH + 3 , Cl - R -NH + 3 , Cl -+ NaH 2 AsO 4 ⇔ R -NH + 3 , H 2 AsO - 4 + NaCl
Nevertheless, the limits are the following: the chitosan solubility happened at pH < 3.5-4, and at pH > 6.6, the amine function becomes more and more deprotoned so the arsenate electrostatic attraction weakens. It is the reason why no more experiments have been conducted beyond this pH range. These results are consistent with a previously paper [START_REF] Gérente | Interactions of natural aminated polymers with different species of arsenic at low concentrations: application in water treatment[END_REF] indicating that no fixation occurred with arsenite (neutral species) and with chitin (similar biopolymer with no amine function).

Dynamic results and breakthrough modelling

The feasibility of the selected semi-dynamic process including a CSTR and an immersed-membrane separation (Fig. 1), is evaluated by following the concentration of arsenate in the permeate in function of time. This breakthrough curve is described by a model based on a mass balance equation (Eq. ( 1)) and previously performed for another biosorption treatment [START_REF] Reddad | Cadmium and lead adsorption by a natural polysaccharide in MF membrane reactor: experimental analysis and modelling[END_REF]. A blank test without chitosan (i.e. X = 0 in Eq. ( 7)) was also performed to check that no competing adsorption occurred through the whole pilot and the obtained curve was clearly different from the sorption curve with chitosan (data not shown). Then, the feasibility of the process has been tested for two cases: deionised water and acidified spring water with an initial concentration of arsenate of 350 gL -1 and a chitosan amount of 0.5 g L -1 (Fig. 4a andb). In Fig. 4a, during the first 180 min, the modelled curve with the Langmuir equation describes the experimental points very well. After this time, a

, V = 15.3 L, Q =10.2Lh -1 , X =0.5gL -1 and T =21 • C.
nonunderstandable shift is observed and the experimental performances show higher capacities than the model predicted values. The use of the Redlich-Peterson equation allows a good description of experimental points over the whole curve. This kind of empirical model does not bring some new data about the sorption mechanism, but finds an interesting application in the modelling of breakthrough curves. The same experiment has been conducted with natural water: the spring water was previously spiked with 360 gL -1 of arsenate and acidified to pH 4.15 (Fig. 4b). The modelled curve established with the Redlich-Peterson equation also gives a better description of the experimental points indicating that the breakthrough modelling could be used as a predictive tool. However, at 300 min, a fouling of the membrane, probably due to the colloidal fraction of this natural water prevented us from confirming this trend over the whole curve. An optimisation of this process is therefore needed, and regular retro-washings of the membrane unit could improve the membrane behaviour. Nevertheless, these experiments have shown that such a semi-dynamic process can be interesting for the removal of arsenate ions by sorption on chitosan, and that the prediction of breakthrough curves is possible by a relatively simple model.

Conclusions

This work has showed that chitosan, a biopolymer extracted from the wastes of the seafood industries, could be potentially used for the removal of arsenate from natural waters. The sorption mechanism proposed for the fixation of arsenate ions onto chitosan, could be described by the following steps: (i) the increase of amine protonation and zeta potential by a decrease of the pH, at the surface of the chitosan, (ii) the fixation by electrostatic attraction between a positive surface charge located on the amine function and the anionic form H 2 AsO 4 -, the effect of ionic strength being important, (iii) a great influence of T, with negative values of G and H indicating that the biosorption reaction is thermodynamically spontaneous and exothermic. This biopolymer has been used in a semi-dynamic treatment process. The performances have been evaluated through the experimental breakthrough curves and a model based on a mass balance equation, has given a good description of these data and could be considered as a predictive tool.

Fig. 1 .

 1 Fig. 1. Scheme of the experimental pilot: a continuous stirred tank reactor (CSTR) coupled with a microfiltration immersed-membrane unit (LC = level control).

Fig. 2 .

 2 Fig. 2. Adsorption isotherms of H2AsO4 -on chitosan flakes at different temperatures and modelled by the Langmuir equation.

Fig. 3 .

 3 Fig. 3. Adsorption isotherms of H2AsO4 -on chitosan flakes obtained in natural and deionised waters, at 20 • C with different initial pH, and modelled by the Langmuir equation.

Fig. 4 .

 4 Fig. 4. Experimental and modelled breakthrough curves for two conditions: (a) in deionised water (pH 5.8), C0 = 346.3 gL -1 , V = 15.3 L, Q =10Lh -1 , X =0.5gL -1 and T =24 • C and (b) in acidified spring water (pH 4.15), C0 = 356.7 gL -1 , V = 15.3 L, Q =10.2Lh -1 , X =0.5gL -1 and T =21 • C.

Table 1

 1 Main properties of chitosan[START_REF] Andres | Antibacterial effects of chitosan powder: mechanisms of action[END_REF].

	pKa	6.6 ± 0.2
	Ash content (%)	0.05
	Amine concentration (mmol g -1 )	2.5
	BET surface (m 2 g -1 )	3.1 ± 0.1
	Apparent density (kg m -3 )	330
	Degree of deacetylation (%)	70 ± 10
	Zeta potential (mV)	≥ 0atpH≤ 7
		=22mVatpH6and =68mVatpH4
	these batch results, a feasibility study is conducted to propose
	a continuous reactor for arsenate removal. Classically fixed bed
	columns are often considered but it has been chosen to test an
	original membrane process. It consists in a continuous stirred
	tank reactor coupled with a microfiltration immersed-membrane.

Table 2

 2 Average composition of a commercial natural spring water.

		Ca 2+	Mg 2+	Na +	K +	Cl -	NO3 -	HCO3 -	SO4 2-	pH
	Concentration (mg L -1 )	4.1	1.7	2.7	0.9	0.9	0.8	25.8	1.1	7.3

Table 3

 3 Adsorption isotherms data.

	T ( • C)	Langmuir qe =	qm b L Ce 1+b L Ce		Freundlich qe = KF C n F e		Tempkin qe = RT z ln(kT Ce)	Redlich-Peterson qe =	K RP Ce 1+a RP C b RP e
		qm (gg -1 )	bL (L g -1 )	R 2	KF	nF	R 2	kT (L g -1 )	R 2	KRP (L g -1 )	aRP (L g -1 )	bRP
	4	739	0.0128	0.991	98.7	0.287	0.934	0.2256	0.981	8.02	0.00694	1.06
	10	709	0.0117	0.999	83.3	0.303	0.956	0.1668	0.991	8.72	0.01399	0.98
	20	730	0.0046	0.997	46.2	0.366	0.969	0.0801	0.985	3.39	0.00463	1.00
	30	535	0.0047	0.983	20.6	0.463	0.953	0.0467	0.985	1.87	0.00040	1.32
	40	373	0.0041	0.951	11.1	0.497	0.925	0.0601	0.980	1.29	0.00092	1.19
	Table 4
	Thermodynamic parameters of the adsorption isotherms.
	T ( • C)	From Langmuir model					From Tempkin model

  equilibrium constant k T as a function of the temperature. All the Tempkin curves obtained with experimental data also show good distribution coefficients (Table3) and ranged between 0.980 and 0.991. The van't Hoff plots, ln K versus 1/T in Kelvin, have been analysed using these two equilibrium constants and the extrapolated parameters are presented in Table4. The thermodynamic parameters have given similar results for the two cases. Negative values of G and H mean that the biosorption reaction is thermodynamically spontaneous and exothermic. This is in good agreement with the experimental capacities of chitosan deduced by the Langmuir equation, which decrease with an increase in T. Entropy values ( S) are quite low in all cases and their discussion is often limited. Finally, two empirical models widely used in literature(Freundlich and Redlich-Peterson) are also investigated in this study. The Redlich-Peterson isotherm is a combination of the Langmuir and Freundlich. Depending on the b RP value, the equation of Redlich-Peterson is equal to Langmuir equation if b RP = 1 and to Henry's law if b RP = 0. Experimentally, even though the Freundlich model has given good fits and Redlich-Peterson good convergence, their major interest is mathematical, since their constants do not really have a physical significance, that is, the equations are empirical. From 4 to 40 • C, the b RP values from Redlich-Peterson equation approach unity confirming that arsenate ions adsorption onto chitosan follows the Langmuir model, characterised for each temperature by an equilibrium constant b L and a maximum fixation capacity q m . Concerning the Freundlich parameters, all n F values are less to 1 which indicates a favorable adsorption but the distribution coefficients, not higher than Langmuir ones, are acceptable. Even though this model brings few data about the fixation mechanism, it often describes experimental adsorption data well and may be used for the prediction of breakthrough curves in dynamic process modeling.

									R 2
	4	-31.7				-39.9
	10	-32.2				-38.0
	20	-31.1	-25.0	23.9	0.914	-38.0	-30.4	27.5	0.923
	30	-32.1				-38.4
	40	-32.9				-38.3

  1 ) bRP

	Spring water
	pH i 5.5	1180	0.00075	0.993	-	-	-
	pH i 4	4020	0.00046	0.999	2.138	0	0.731
	Deionised water
	pH i close to 6	730	0.0046	0.997
	pH i close to 5	1370	0.0130	0.981


Ferdinand Dhombres

Pierre-Yves Vandenbussche

Ana Rath

Marc Hanauer

Annie Olry

Bruno Urbero

Rémy Choquet

Jean Charlet

OntoOrpha : an ontology to support edition and audit of rare diseases knowledge in Orphanet

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

OntoOrpha : an ontology to support edition and audit of rare diseases knowledge in Orphanet

Ferdinand Dhombres 1,2,3,4 , Pierre-Yves Vandenbussche 1,2 , Ana Rath 2 , Marc Hanauer 2 , Annie Olry 2 , Bruno Urbero 2,5 , Rémy Choquet 1,2 , and Jean Charlet 1,2,4

1 Inserm UMRS 872 éq.20, Paris, France 2 Inserm SC11, Orphanet, Paris, France 3 Sorbonne Universitiés, UPMC, Paris, France 4 Service de Gynécologie-Obstétrique et Centre de Diagnostic Prénatal de l'Est Parisien, Hôpital Armand Trousseau, AP-HP, Paris, France 5 Mondeca, Paris, France 6 Inserm DSI -DR Langedoc-Roussillon, Montpellier, France 7 AP-HP -Assistance Publique, Hôpitaux de Paris, Paris, France {ferdinand.dhombres, jean.charlet}@inserm.fr Abstract. Orphanet is the reference information portal on rare diseases and orphan drugs, for healthcare professionals and for general audience. After ten years of evolution, current Orphanet tools cannot support efficiently the edition, update and data sharing processes of a constantly growing rare diseases knowledge. In order to improve the edition workflow, we conduct research to build and use a rare diseases knowledge base in an Ontology-based architecture that complies with the W3C standards of the semantic web : OWL, RDF, SparQL and Skos. Our ontology design approach is based on both domain expertise (in rare diseases and in knowledge engineering) and knowledge extraction from our relational database. The current version of OntoOrpha comprises over 11,000 classes and 190,000 annotations organized under a Rare Diseases Core Ontology.

In comparison with current Orphanet edition tools, our preliminary experiments are consistent with : (1) better visualization of the knowledge base (2) improved classification edition procedures (3) improved annotation edition procedures (4) valid semantic validation procedures.

Background

Orphanet is the reference information portal on rare diseases and orphan drugs, for healthcare professionals and for general audience. This unit is led by a European consortium of around 40 countries, coordinated by the French team which is responsible for the infrastructure of Orphanet, management tools, quality control, rare disease inventory, classifications and production of the encyclopaedia.

After ten years of evolution, current Orphanet tools cannot support efficiently the edition, update and data sharing processes of a constantly growing rare diseases knowledge (6000 rares diseases with annotations and more than a hundred of overlapping classifications).

Methods

In order to improve the edition workflow, we conduct research to build and use a rare diseases knowledge base in an Ontology-based architecture. This architecture complies with the W3C standards of the semantic web : OWL, RDF, SparQL and Skos.

Our ontology design methodolgy is multidisciplinary as it involves both domain expertise in rare diseases and in knowledge engineering. Our methodology also involes automatic knowledge extraction from Orphanet relational database. The current version of OntoOrpha comprises over 11,000 classes, 72,000 sub-ClassOf axioms (with a high level of polyparentality) and 190,000 annotations, organized under a Rare Diseases Core Ontology (fig. 1). This core ontology was designed as meta-model for the domain ; this level of model was mandatory to provide appropriate representation of the whole disease inventory extracted from the database as classes, and to represent the classifications as classes as well. Domain and range of relationships between classifications, disorders (disease, malformative syndrome,...), groups of disorders (by anatomical system, by physiopathological mechanism,...), subtypes (clinical subtypes, etiological subtypes), clinical signs and genes are therefore represented in the core ontology. Moreover, we take into account that this meta-model should provide all the primitive for validation rules description.

Results

Beside current achritecture, a new experimental architecture is provided by the project to support edition workflow (fig. 2). At the first step of the workflow extraction from the database, building of the ontology and uploading it in a triplestore are performed. This extract-transform-load (ETL) step is automated. The generation process of the ontology is threefold :

1. generation of the header of the final RDF file (including ontology metadata, classes and object properties of the core ontology), 2. generation of the body parts by extraction/transformation of the data (URI construction, skos:prefLabels/altLabels/definition including the management of 6 languages, owl:Restriction,...) 3. merging those parts to produce an XML/RDF file that will be upload in the triple store. The second step is consistent with expert edition of the ontology (Classes, ObjectProperty, Annotations) and rule-based procedures implemented with iterative SparQL queries on the triplestore (for validation, classification generation, audit report generation). The final step is the relational data base update with an ETL process from the triplestore.

In comparison with current Orphanet edition tools, our preliminary experiments are consistent with :

(1) better visualization of the knowledge base : a global view of the hierarchies is provided in the ontology editor during the edition process (Class hierarchy view, Existential tree view, Outline tree view and OntoGraf view in Protégé),

(2) improved classification edition procedures : the experts edit the ontology itself and the rare diseases classifications are automatically generated, using stable SparQL queries,

(3) improved annotation edition procedures : we use a lexicalisation plugin for Protégé developped in our unit that is Skos compliant and supportive for multilingual edition of labels, synonyms and abstracts, (4) semantic validation procedures : both in the ontology editor (a priori validation by the build-in reasoner) and in the triplestore (validation and audit by reasoner and SparQL queries).

Fig. 1 .

 1 Fig. 1. Rare Diseases Core Ontology (view of OntoOrpha, version 2011-06-08).

Fig. 2 .

 2 Fig. 2. Rare Diseases Knowledge edition workflow (research architecture).