Sludge drying reed beds for septage treatment: towards design and operation recommendations

International audienceWith decentralized treatment system development, a new concern emerges: the future of the septage. The aim of this paper is to assess the feasibility of septage treatment by SDRB, and to compare its efficiencies to those of activated sludge treatment in same conditions. The study took place on ten 2m² pilot-scales SDRB. Different designs and operation conditions have been tested on sludge treatment efficiency and will be presented as: (i) the top filtration layer (sand or compost), (ii) the load (from 30 to 50 kgSS/m-2/y). After one year and half commissioning period, we focus on the results obtained at nominal loads presenting: sludge characteristic, filtration efficiency, percolate quality and sludge deposit behaviour. Although results show better filtration efficiency for activated sludge (98.4%) than for septage (87.5%), the feasibility of septage treatment with drying reed bed has been demonstrated. Sludge accumulation is about 7.9 cm/y, when fed at 50 kgSS/m-2/y, and dry matter content of the sludge can reach 70% in summer period. The paper will present sludge characteristics, system efficiency, to finish on design and operation condition recommendations for SDRB treating septage

Treatment of septage in sludge drying reed beds: a case study on pilot-scale beds

International audienceFrench legislation requires, the control of private on-site sanitation systems by local authorities. This will result in a large increase of the quantity of sludge from septic tanks to be treated. Nevertheless, large wastewater treatment plants are not systematically able to treat this sludge because they may have reached their nominal load or they are not so numerous in rural zone to avoid too long transportation. The study concerns both, the feasibility of sludge reed beds devoted to the treatment of septage and the assessment of a simultaneous treatment with aerated sludge. The experiments have been carried out on eight pilot-scale drying reed beds (2m²) planted with Phragmites australis. Two filtration layers of either vegetal compost or sand were tested. The study is focused on the commissioning period (first vegetative year) with a loading rate of 30 kgSS.m-2.yr-1. According to these operational conditions, dewatering efficiencies reached approx. 30% DM during summer but less than 20%DM in winter for each filtration layer and sludge. High removal efficiencies, with an average of 96%, 92% and 89% for SS, COD and TKN respectively, were achieved with septage whereas they were lower for the mixture of aerated sludge and septage. The dewaterability of septage and its filtration behaviour were assessed by several parameters (Capillary Suction Time, bound water) which may be some interesting tools for an optimised loading strategy

Sludge drying reed beds : full and pilot scale study for activated sludge treatment

International audienceSludge drying reed beds have been used for dewatering and mineralization of sludge since the beginning of the 90's, but their insufficient performances in terms of Dry Matter [DM] content and mineralization of the sludge have made necessary new studies. Therefore, 8 pilots of 2m² each and a full-scale plant (13 000 p.e , 8 beds of 470m² in operation for 4 years) have been monitored to examine the influence of the sludge loading rate, the sludge quality and the loading frequency on the dewatering and mineralization efficiencies. Two filtration layers (vegetal compost or sand) and two loading rhythms were tested on pilots which were fed at a loading rate of 25 kgDM.m-2.yr-1 during the first year of operation (commissioning period). Hydraulic behaviour (infiltration rate, outflow), O2 and CO2 relative concentrations in the filtration media, redox potential, pollutants removal and dry matter content were assessed during all the study. The rheological quality of the extracted sludge from full scale beds were assessed and showed that it mechanical behaviour exceed those of sludge of comparable dry matter content, making its spreading easier Therefore, these sludge could easily claim the status of solid and stabilized sludge according to the French regulation. Design and management recommendations (number of beds, loading rates, feeding/rest period) gained from the experiments results are suggested

Treatment wetlands

Treatment Wetlands is the seventh volume in the Biological Wastewater Treatment series, which gives a state-of-the-art presentation of the science and technology of sewage treatment. The major variants of wetland systems are covered in this volume, namely: (i) horizontal flow wetlands; (ii) vertical flow wetlands; (iii) French vertical flow wetlands; (iv) intensified wetlands; (v) free water surface wetlands; (vi) other applications of treatment wetlands. The book presents in a clear and didactic way the main concepts, working principles, expected performance, design criteria, design examples, construction aspects and operational guidelines. The book has been written by an international team of top experts in the field of treatment wetlands.Postprint (published version

Treatment Wetlands

Overview of Treatment Wetlands; Fundamentals of Treatment Wetlands; Horizontal Flow Wetlands; Vertical Flow Wetlands; French Vertical Flow Wetlands; Intensified and Modified Wetlands; Free Water Surface Wetlands; Other Applications; Additional Aspects

Traitement des eaux résiduaires de temps sec et temps de pluie en réseau unitaire par filtres plantés de roseaux

Les filtres plantés de roseaux à écoulement vertical (FPR-V) pour le traitement des eaux usées domestiques sont relativement bien développés en France et permettent de réaliser un traitement poussé de la matière carbonée et la nitrification. La robustesse de cette filière réside également dans sa capacité à accepter des surcharges hydrauliques en temps de pluie. Cependant ces limites d acceptation hydraulique ne sont pas bien définies et demandent à être optimisées. La conception des FPR-V pour accepter des surcharges hydrauliques est un travail complexe car le contexte local affecte fortement les débits d eau entrants dans la station lors d un événement pluvieux. Dans de tels cas, la conception de filtres demande l utilisation de modèles dynamiques. Ces modèles s appuient le plus souvent sur une approche mécanistique et sont à l'origine conçus et utilisés pour la recherche. Cependant, si ces modèles sont des outils puissants pour décrire en détail la dynamique du FPR-V, ils sont généralement trop complexes à manipuler pour des utilisateurs non experts. Choisir entre une description détaillée et une manipulation facile dépendra des objectifs de modélisation. Quand des objectifs de dimensionnement global sont visés par les concepteurs, l'utilisation de modèles simplifiés semble une bonne alternative. Les modèles simplifiés sont faciles à utiliser pour la conception de FPR-V mais ils sont peu nombreux. Cependant ils sont adaptés à des configurations spécifiques liées au traitement des surverses de déversoirs d orage, ce qui n est pas le cas pour les FPR-V traitant des eaux usées domestiques. En effet, pour ce type de FPR-V les vitesses d infiltration du système varient considérablement. En conséquence, ce travail de thèse a pour objectif de développer un modèle hydraulique simplifié des FPR-V qui permettra de guider les concepteurs dans le processus d adaptation des FPR-V pour traiter les eaux usées domestiques des périodes de temps sec et de temps de pluie. Le modèle simplifié permet de relier (i) l hydraulique du filtre, en simulant le temps de noyage à la surface, et (ii) les performances biologiques, en établissant des alertes de dysfonctionnement , basées sur l'évaluation des performances épuratoires et sur les variations des formes azotées à la sortie du filtre mesurées en continu. Les alertes de dysfonctionnement représentent la charge hydraulique maximale qu'un filtre peut accepter sans compromettre son activité biologique. Le modèle simplifié a été utilisé pour la modélisation hydraulique du FPR-V à long terme (i) pour analyser l impact du contexte local et la conception du filtre dans l acceptation de surcharges hydrauliques. Grâce à cet analyse, (ii) on peut proposer les dimensionnements de FPR-V qui arrivent à mieux gérer l acceptation des surcharges hydrauliques.French vertical-flow constructed wetlands (VFCW) directly treating raw wastewater are known to perform well on for SS, COD and nitrification. They are also known to robustly cope with hydraulic overloads during rainfall events. Although numerous systems have been installed in areas equipped with a combined sewer, the limits of stormwater acceptance remain ill-defined and need to be improved. Looking at the various VFCW designs and usages reported in the literature, it is difficult to draw any consensus on their hydraulic limits. Consequently, designing VFCW to accept hydraulic overloads is a complex task, as local context strongly impacts inlet flows produced during rainfall events. Dynamic models appear a requisite for filter design in such cases. Numerical CW models have essentially focused on horizontal flow, with few attempting to study VFCW dynamics which are more commonly tackled via mechanistic models. Although mechanistic models are powerful tools for describing processes within the VFCW, they are generally too complicated to be readily used by designers. The choice between detailed description and easy handling will depend on the modelling aims. If the aim is a global design tool, simplified models offer a good alternative. However, the simplified models geared to studying VFCW dynamics are extremely reduced. They are easy-handling for design and well-adapted to specific purposes (combined sewer overflow -CSO- treatment) but not necessarily to VFCW treating combined sewer wastewater, where long-term infiltration rates vary significantly. Consequently, this PhD thesis work focused on developing a simplified hydraulic model of VFCW to guide designers through the process of adapting VFCW systems to treat domestic wastewater in both dry and rain events. The simplified model makes it possible to link (i) hydraulics, by simulation of ponding time variations, (ii) biological performances, by establishing dysfunction alerts based on treatment performance assessment and variations in online N forms effluent from the young VFCW. These dysfunction alerts plot the maximal hydraulic load that a filter can accept without compromising its biological activity. The simplified model was used to model long-term hydraulics in the VFCW (i) to analyze the impact of local context and filter design on hydraulic overload acceptance (using dysfunction alerts and bypass discharges) and (ii) to propose VFCW designs for accepting hydraulic overload in different contexts. The modelling demonstrates that VFCW can limit days with bypass discharges to less than 20 times per year without jeopardizing filter performances. Moreover, the most problematic scenario on stormwater treatment remains a watershed with high imperviousness coefficient and low slope under a Bretagne-type climate, demonstrating that the filter is more sensitive to periodicity and duration than to intensity of rainfall events.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Sixteen-Year Monitoring of Particulate Matter Exposure in the Parisian Subway: Data Inventory and Compilation in a Database

The regularly reported associations between particulate matter (PM) exposure, and morbidity and mortality due to respiratory, cardiovascular, cancer, and metabolic diseases have led to the reduction in recommended outdoor PM10 and PM2.5 exposure limits. However, indoor PM10 and PM2.5 concentrations in subway systems in many cities are often higher than outdoor concentrations. The effects of these exposures on subway workers and passengers are not well known, mainly because of the challenges in exposure assessment and the lack of longitudinal studies combining comprehensive exposure and health surveillance. To fulfill this gap, we made an inventory of the PM measurement campaigns conducted in the Parisian subway since 2004. We identified 5856 PM2.5 and 18,148 PM10 results from both personal and stationary air sample measurements that we centralized in a database along with contextual information of each measurement. This database has extensive coverage of the subway network and will enable descriptive and analytical studies of indoor PM exposure in the Parisian subway and its potential effects on human health

Identification of Biofilm-Associated Cluster (bac) in Pseudomonas aeruginosa Involved in Biofilm Formation and Virulence

Biofilms are prevalent in diseases caused by Pseudomonas aeruginosa, an opportunistic and nosocomial pathogen. By a proteomic approach, we previously identified a hypothetical protein of P. aeruginosa (coded by the gene pA3731) that was accumulated by biofilm cells. We report here that a ΔpA3731 mutant is highly biofilm-defective as compared with the wild-type strain. Using a mouse model of lung infection, we show that the mutation also induces a defect in bacterial growth during the acute phase of infection and an attenuation of the virulence. The pA3731 gene is found to control positively the ability to swarm and to produce extracellular rhamnolipids, and belongs to a cluster of 4 genes (pA3729–pA3732) not previously described in P. aeruginosa. Though the protein PA3731 has a predicted secondary structure similar to that of the Phage Shock Protein, some obvious differences are observed compared to already described psp systems, e.g., this unknown cluster is monocistronic and no homology is found between the other proteins constituting this locus and psp proteins. As E. coli PspA, the amount of the protein PA3731 is enlarged by an osmotic shock, however, not affected by a heat shock. We consequently named this locus bac for biofilm-associated cluster

Le groupe de travail EPNAC

En France, les procédés de traitement des eaux usées des petites et moyennes collectivités sont en constante évolution et leur diversité augmente fortement. Constitué à l'initiative d'Irstea, le groupe de travail EPNAC a pour objectif de mutualiser et de diffuser une information technique et cohérente sur ces procédés auprès des acteurs de l'assainissement