Évaluation des taux d’accumulation et de production de boue dans des bassins de stabilisation sous climat méditerranéen : étude de cas en Tunisie

Les taux d’accumulation, la distribution spatiale ainsi que les caractéristiques chimiques des sédiments ont été étudiés dans une installation de lagunage composée d’un bassin anaérobie, un bassin facultatif et deux bassins de maturation pour le traitement des eaux usées en Tunisie.Le taux d’accumulation ainsi que la distribution des boues au sein de chaque bassin ont été déterminés par mesure directe de l’épaisseur des sédiments correspondants sur 90 à 105 points (selon un maillage de 11 mètres). En tenant compte du volume total de boue déterminé sur les quatre bassins, le taux d’accumulation de sédiments est de 0,029 m3•EH‑1•an‑1 correspondant à un taux d’accumulation de 4,14 kg MS•EH‑1•an‑1. La distribution des boues est loin d’être homogène; les épaisseurs de sédiments les plus importantes sont enregistrées aux entrées et sorties des bassins. L’étude de la variabilité horizontale des caractéristiques des sédiments a été réalisée en considérant deux sites (entrée et sortie) du bassin facultatif (BI) au niveau desquels cinq réplicats de carottes ont été prélevés. Par contre, l’étude de la variation verticale a été réalisée sur des carottes de sédiments qui, après prélèvement, ont été sectionnées en tronçons. Des paramètres chimiques tels que : carbone total (CT), azote total (NT), phosphore total (PT), matières sèches (MS) et matières volatiles (MV) ont été mesurés sur ces échantillons. Les résultats obtenus ont montré que la teneur en matières sèches dans la couche la plus profonde est supérieure à celle dans la couche de surface. Par contre, les teneurs en CT, NT, PT, MV diminuent en fonction de la profondeur.This project studied a stabilization pond system in Tunisia composed of four ponds (one anaerobic, one facultative and two maturation) under a Mediterranean climate. The objectives of this work were to determine the sludge characteristics and to study sediment accumulation and spatial distribution in the various ponds. This work was carried out in a pilot-scale stabilization pond system treating domestic wastewater for 282 person-equivalents (PE). The anaerobic pond was 96 m3 in volume, 3.25 m in depth. The facultative and two maturation ponds were respectively 180, 164 and 147 m3 in volume with mean organic loading rates of 7.6, 4.1 and 3.3 kg BOD5•d‑1 respectively. The characteristics of the influent and effluent (including: suspended solids (SS); volatile suspended solids (VSS); chemical oxygen demand (COD) and biochemical oxygen demand (BOD)) were determined twice-monthly during two months of year 2005. A database of previous studies was used to determine the characteristics of the influent and effluent corresponding to the period 1998-2005.The sludge accumulation rates and distribution were determined by measuring the thickness of the sludge layer at 90 to 105 locations throughout each pond. Considering the total volume of sludge determined for the four ponds, the sediment accumulation rate was 0.029 m3 per person-equivalent per year, corresponding to an accumulation of 4.14 kg dry matter per person-equivalent per year. In the three ponds, the distribution of sludge is uneven, with greater accumulation near the inlet. To study the horizontal variation in the sludge characteristics, two samples with five replicates were collected in the inlet and in the outlet of the facultative pond, whereas, for the vertical variation, sludge cores were collected, then sectioned into slices. Several parameters such as total carbon (CT), total nitrogen (NT), total phosphorus (PT), dry matter (DM) and volatile matter (VM) were measured on these sub-samples. The results show that (DM) content in the deepest layer is higher than that near the surface, whereas CT, NT, PT, VM decrease with depth

Enhancement of rhizocompetence in pathogenic bacteria removal of a constructed wetland system

Preprin

Local climate change assessment at five pilot sites in the Mediterranean region

The objective of this study is to provide an overview of local climate change over the Mediterranean (MED) area under the scope of the InTheMED project, EU funded in the framework of the PRIMA programme. Future precipitation and temperature projections are assessed until the end of this century for five different pilot sites, located in the MED region. To this end, the outputs of 17 Regional Climate Models under the RCP4.5 and RCP8.5 scenarios are used. For each pilot site, the raw climate model data were downscaled at each monitoring station location and bias-corrected on the basis of observations recorded in a 30-year historical period. The changes in the annual precipitation are heterogeneous across the five pilot sites: a negligible variation is expected for some areas and a decrease of up to 30% for others. On the contrary, a significant increase in temperature is expected for all sites, confirming the ongoing warming in the MED region

Efficiency of a coagulation/flocculation–membrane filtration hybrid process for the treatment of vegetable oil refinery wastewater for safe reuse and recovery

International audienc

Adopting Sustainable Water Management Solutions under Social and Climate Change in Med Region: Cases from Palestine and Tunisia

The Southern Mediterranean region and particularly Middle East and North Africa (MENA) region are probably one of those regions that face serious social, economic, environmental and political challenges. Among the most critical challenges are the increasing water scarcity and,thus, demand, resulting mainly from climate change and rapid population growth. Based on United Nations’ estimates in 2006, the population of the region will reach about 255 million inhabitants in 2025, out of which 179 million people will be living in urban centers in this region. The current paper summarizes the main findings of the socioeconomic survey conducted with the aim to collect baseline socio-economic information to be used in selecting the appropriate sustainable water management (SWM) solutions that can be implemented in various settlement typologies in the region, selected in the view of the main results of this survey. Data have shown that both, simple and advanced solutions (such as tools for regulating the water flow, shower diffusers, WC “Water Saving”, wastewater and greywater treatment and reuse systems, rainwater harvesting at household level, etc.), respond sufficiently to the multiple and different needs of the settlement typologies in the region and help them to improve their adaptive capacity toward any potential changes (especially climate and demographic ones)

Aqueous synthesis and enhanced photocatalytic activity of ZnO/Fe2O3 heterostructures

International audienceWe report a facile synthesis of ZnO/Fe2O3 heterostructures based on the hydrolysis of FeCl3 in the presence of ZnO nanoparticles. The material structure, composition, and its optical properties have been examined by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance UV-visible spectroscopy. Results obtained show that 2.9 nm-sized Fe2O3 nanoparticles produced assemble with ZnO to form ZnO/Fe2O3 heterostructures. We have evaluated the photodegradation performances of ZnO/Fe2O3 materials using salicylic acid under UV-light. ZnO/Fe2O3 heterostructures exhibited enhanced photocatalytic capabilities than commercial ZnO due to the effective electron/hole separation at the interfaces of ZnO/Fe2O3 allowing the enhanced hydroxyl and superoxide radicals production from the heterostructure

Environmental Risk Assessment of Water Resources in Arid and Semi-arid Lands Using Bioassays Systems

Abstract: Control of effluents has traditionally been regulated using methods with unspecified responses and measuring global parameters, such as the chemical oxygen demand (COD) or Biological Oxygen Demand (BOD). Moreover, information about biological effects is unknown. Thus, the introduction of in vitro assays using mammalian cells to investigate the presence of environmental contaminants is more than needed. At first, physicochemical parameters of municipal wastewater samples from Tunisia were estimated. On a further step, in vitro bioassays systems were applied intending to find out the biological effects of these samples on mammalian cells. Results using the E-screen assay reveal that the wastewater samples induced estrogenic activity at different concentrations in 6 days incubation period. Besides, the same samples were able to generate stress response on animal cells. These findings correlate with the physicochemical parameters data and thus evaluate the efficiency of treatment system to remove such toxic compounds

Porous Mn-doped ZnO nanoparticles for enhanced solar and visible light photocatalysis

International audiencePorous Mn-doped ZnO (ZnO:Mn) nanoparticles with an average diameter of ca. 21 nm were prepared by a simple and cheap solvothermal process involving no templates, post-synthetic annealing or etching. The particles produced were characterized by XRD, Raman spectroscopy, SEM, TEM, XPS, diffuse reflectance spectroscopy and BET surface area measurements and the effects of Mn2+-doping on the structural, optical and photocatalytic properties of ZnO particles were investigated. The particles doped with 3 mol% Mn2+ were found to exhibit the highest catalytic activity toward the photodegradation of the Orange II dye under solar light irradiation. Our results demonstrate that Mn2+-doping shifts the optical absorption to the visible region, increases the specific surface area of the photocatalyst and reduces the recombination of electron-hole pairs. The influence of various operational parameters (amount of catalyst, concentration of dye and pH) on the photodegradation and the photocatalytic mechanism were studied. Finally, we demonstrated that the ZnO:Mn photocatalyst is stable and can be easily recycled up to ten times without any significant decrease in photocatalytic activity

Evaluation of the impact of climate change on the shallow aquifer of Grombalia (Tunisia)

Climate change presents a serious problem for water resources (WR) and the shallow aquifers are strongly affected. This type of WR presents fundamental importance in certain regions, due to their accessibility and sometimes, for their quality, it is preferred to surface water sources, often polluted. It is also, affected by overexploitation problems, which contribute to the destruction of the sustainability of the aquifer system. This study considers the Grombalia aquifer in Tunisia which has suffered from climate change’s impact in recent years due to water resources scarcity. Aim of the present research is to evaluate the impact of climate change on this aquifer that is one of the pilot sites in the European project InTheMed. First, a collection of historical temperature, precipitation and groundwater level data in the period 1976-2020 was carried out. Then, starting from the few available geological cross sections, a two-dimensional numerical model of the aquifer was developed in MODFLOW. The groundwater numerical model reproduces the whole basin, from the recharge area to the outlet in the Mediterranean Sea. The area is characterized by agricultural intensive activities and high-water demand. For this reason, the model required a calibration of hydraulic parameters, recharge and pumping rate. After the calibration, the numerical model was able to estimate the groundwater flow across the entire watershed of Grombalia aquifer. To evaluate the impact of climate change on the future groundwater availability, the model was driven using future precipitation and temperature projections. The water abstractions were assumed to remain unchanged in the future and equal to the condition of existing wells at 2020. To describe the future climate, 17 combinations of Regional Climate Models (RCM) and General Circulation Models (GCMs), developed within the EURO-CORDEX initiative, were used. The simulations were performed for the period 2006-2100, and according to the RCP4.5 and RCP8.5 scenarios. Before their use, the climate projections were downscaled and bias corrected with reference to the historical temperature and precipitation data. The results are evaluated in terms of local variations of the groundwater level and their uncertainty is expressed with reference to the variability of the 17 RCM-GCM combinations. Acknowledgments This work was developed under the scope of the InTheMED project. InTheMED is part of the PRIMA program supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No 1923