Flocs vs granules : differentiation by fractal dimension

High rate anaerobic wastewater treatment systems usually give rise to biomass structured in different types of aggregates, depending on prevalent environmental conditions. Although highly dependent on wastewater characteristics, granules are generally formed and found in UASB reactors, whereas flocs are mainly found in fixed bed reactors. Different structures usually have different shapes and surface roughness. The aim of this work is to provide a contribution to the differentiation of those kinds of aggregates. A numerical parameter, the fractal dimension, was used to quantify the surface roughness. The fractal dimension, of two families of particles, was measured by two methods: (i) a box counting method; (ii) a method based on an area-size relationship. In both cases, the differences were highly statistically significant. Using the box counting method, for each of the 54 particles of each family, the average fractal dimension was 1.90 ± 0.02 for flocs and 1.95 ± 0.01 for granules (±99% confidence interval). The log-log plot of area vs longest size was linear and the calculated fractal dimensions from this plot were 1.84 ± 0.13 and 2.14 ± 0.08 (±99% confidence interval) for flocs and granules, respectively. Fractal dimension was proven to be a suitable parameter to quantify and differentiate surface roughness of different microbial aggregates present in high rate anaerobic digesters.União Europeia. Comissão - Human Capital and Mobility programme

Evolution de l'exploitation des eaux souterraines dans le périmètre irrigué du Tadla

International audienceLe périmètre irrigué du Tadla est passé par deux grandes périodes quant à l'évolution de la disponibilité des ressources en eaux. Cette évolution peut être attribuée aux changements intervenus dans la disponibilité de l'eau de surface (diminution des précipitations) et une évolution de la demande en eau (intensification culturale, assolements). La première période s'étale depuis la date d'équipement du périmètre jusqu'à la fin des années 70 et a été caractérisée par une abondance de la ressource en eau de surface et un faible recours aux ressources souterraines. En conséquence des remontées excessives de la nappe phréatique ont été observées entraînant des problèmes d'engorgement des sols. La deuxième période de l'évolution du périmètre irrigué du Tadla a commencé avec la sécheresse qu'a connue le Maroc entre 1981 et 1984. Le problème de pénurie d'eau devient structurel et l'eau d'irrigation n'est plus distribuée à la demande mais au tour d'eau avec des restrictions de plus en plus fréquentes notamment en été. Le recours à la ressource en eau souterraine des nappes phréatiques (généralement de mauvaise qualité) s'est fait de plus en plus ressenti et on a dénombré environ 9000 puits de pompage creusés dans le périmètre entre 1981 et 1985. Ce nombre avoisine les 10000 puits et forages actuellement. Deux changements, intervenus pendant les dernières années, méritent d'être soulignés : d'un côté la mise en place du barrage Mohamed El Hansali sur l'Oued Oum Er Rbia a permis d'améliorer la qualité des eaux d'irrigation du périmètre de Béni Amir (dilution des eaux de l'Oum Er Rbia sur l'ensemble de l'année). De l'autre coté, et face aux rabattements excessifs des nappes phréatiques, les agriculteurs ont commencé à prélever dans les nappes captives profonde (éocène notamment). Se posent alors des questions sur la durabilité de l'exploitation de cette nappe et des solutions devraient être trouvées pour assurer une gestion rationnelle et équitable de cette ressource

A new method to study interactions between biomass and packing material in anaerobic filters

A new anaerobic, random-packed, fixed-bed reactor, where the fixed bed matrix is distributed between up to 36 independent mini-bioreactors, has been developed to investigate biomass-support interactions in anaerobic filters. Glass, Plexiglas and polyvinyl chloride (PVC) of three sizes all gave similar results though entrapped biomass was maximal at 3 g/L of matrix void volume for the smallest size and a maximum of 1 g adhered biomass per m2 was obtained for the largest size. In a second run, by periodically removing 3 mini-bioreactors, potential specific methanogenic activities against individual substrates were determined along the time and a continuous growth of the adhered biomass was observed, achieving a maximum of 40% of the total biomass.Comunidade Europeia - Human Capital and Mobility grant

Quantitative image analysis for the characterization of microbial aggregates in biological wastewater treatment : a review

Quantitative image analysis techniques have gained an undeniable role in several fields of research during the last decade. In the field of biological wastewater treatment (WWT) processes, several computer applications have been developed for monitoring microbial entities, either as individual cells or in different types of aggregates. New descriptors have been defined that are more reliable, objective, and useful than the subjective and time-consuming parameters classically used to monitor biological WWT processes. Examples of this application include the objective prediction of filamentous bulking, known to be one of the most problematic phenomena occurring in activated sludge technology. It also demonstrated its usefulness in classifying protozoa and metazoa populations. In high-rate anaerobic processes, based on granular sludge, aggregation times and fragmentation phenomena could be detected during critical events, e.g., toxic and organic overloads. Currently, the major efforts and needs are in the development of quantitative image analysis techniques focusing on its application coupled with stained samples, either by classical or fluorescent-based techniques. The use of quantitative morphological parameters in process control and online applications is also being investigated. This work reviews the major advances of quantitative image analysis applied to biological WWT processes.The authors acknowledge the financial support to the project PTDC/EBB-EBI/103147/2008 and the grant SFRH/BPD/48962/2008 provided by Fundacao para a Ciencia e Tecnologia (Portugal)