Bioréacteur à membranes immergées pour le traitement des eaux résiduaires urbaines : spécificités physico-chimiques du milieu biologique et colmatage

Cette étude s’attache à décrire et analyser les interactions liant les spécificités du milieu biologique d’un bioréacteur à membranes immergées (BAMI) et les phénomènes de colmatage. Le BAMI a été comparé avec un procédé à boues activées, tous deux alimentés avec la même eau résiduaire urbaine. Les performances d’épuration des deux procédés sont comparées dans les mêmes conditions opératoires et à différents âges de boues (10 à 110 jours). L’influence de la séparation membranaire et de l’âge des boues sur les caractéristiques des surnageants (polymères solubles, DCO) et des flocs (diamètre, dimension fractale, exopolymères liés, indice de boue, turbidité) a été soulignée. Les productions de boues des deux systèmes ont également été calculées et confrontées à celles prédites par différents modèles. Par ailleurs, les principaux mécanismes impliqués dans le colmatage à court terme et long terme ont été étudiés. Enfin, le rôle spécifique des protéines et polysaccharides du surnageant des boues dans la structuration du dépôt de filtration a été mis en évidence.\u

The political ecology of human-wildlife conflict: Producing wilderness, insecurity, and displacement in the Limpopo National Park

Like conservation-induced displacement, human-wildlife conflict (HWC) has potentially negative implications for communities in and around protected areas. While the ways in which displacement emerges from the creation of 'wilderness' conservation landscapes are well documented, how the production of 'wilderness' articulates with intensifications in HWC remains under examined both empirically and conceptually. Using a political-ecological approach, I analyse increases of HWC in Mozambique's Limpopo National Park (LNP) and the subsequent losses of fields and livestock, as well as forms of physical displacement suffered by resident communities. While intensifications of encounters between wildlife on the one hand and people and livestock on the other result in part from increases in wildlife populations, I argue that HWC and the ways in which it constitutes and contributes to various forms of displacement results more centrally from changing relations between wildlife and people and the power and authority to manage conflict between them. Both of these contributing factors, moreover, are the consequence of practices that aim to transform the LNP into a wilderness landscape of conservation and tourism. HWC and its negative impacts are thus not natural phenomena, but are the result of political decisions to create a particular type of conservation landscape

Greenhouse Gas and Ammonia Emissions from Different Stages of Liquid Manure Management Chains: Abatement Options and Emission Interactions

Farm livestock manure is an important source of ammonia and greenhouse gases. Concerns over the environmental impact of emissions from manure management have resulted in research efforts focusing on emission abatement. However, questions regarding the successful abatement of manure-related emissions remain. This study uses a meta-analytical approach comprising 89 peer-reviewed studies to quantify emission reduction potentials of abatement options for liquid manure management chains from cattle and pigs. Analyses of emission reductions highlight the importance of accounting for interactions between emissions. Only three out of the eight abatement options considered (frequent removal of manure, anaerobic digesters, and manure acidification) reduced ammonia (3-60%), nitrous oxide (21-55%), and methane (29-74%) emissions simultaneously, whereas in all other cases, tradeoffs were identified. The results demonstrate that a shift from single-stage emission abatement options towards a wholechain perspective is vital in reducing overall emissions along the manure management chain. The study also identifies some key elements like proper clustering, reporting of influencing factors, and explicitly describing assumptions associated with abatement options that can reduce variability in emission reduction estimates. Prioritization of abatement options according to their functioning can help to determine low-risk emission reduction options, specifically options that alter manure characteristics (e.g., reduced protein diets, anaerobic digestion, or slurry acidification). These insights supported by comprehensive emission measurement studies can help improve the effectiveness of emission abatement and harmonize strategies aimed at reducing air pollution and climate change simultaneously

Present-day development of gully-channel sinuosity by carbon dioxide gas supported flows on Mars

Martian gullies have been widely studied, but their formation mechanism is still under debate. Their channels generally trend straight downslope, but some display sinuosity. Seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity. Here, we perform a detailed analysis of a gully on a dune within Matara Crater (49.5°S; 34.9°E) where development of channel sinuosity has taken place over 5 martian years (MY29-33) of observation. This study was performed using HiRISE images, HiRISE elevation data, spectroscopic CRISM data and a 1D GCM for surface temperature modelling. The morphological evolution of the gully suggests a significant seasonal contribution of fluid. Each year we observed material collapse and accumulation in the alcove, followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron. Over one martian year, the debris apron propagated by almost 140 m from an initial length of 800 m. These transport events occur in the middle of winter when CO2 frost is still present and are contemporaneous with the beginning of the defrosting. We propose that the activity and the sinuosity development in the gully could be explained by: 1) a flow composed of sand and CO2 gas, producing morphologies similar to those in hyper-concentrated flows on Earth and 2) contribution of material from alternating of the alcove source location

Impact of granular filtration on ultrafiltration membrane performance as pre-treatment to seawater desalination in presence of algal blooms

To mitigate fouling of the ultrafiltration (UF) membrane and improve permeate quality, we coupled granular filters (GF) with UF membrane as a pre-treatment for reconstituted seawater in the presence of algal bloom. Mono and bilayer granular filtrations were led at a mean velocity of 10 m h−1 over a 7-hour period. Both GF gave the same algal cell retention rate (∼63%) after 7 hours of filtration. Turbidity reduction rate was 50% for the monolayer filter and 75% for the bilayer filter. Resulting organic matter removal rate was 10% for the monolayer filter and 35% for the bilayer filter. Dissolved organic carbon removal was low (20%) with the bilayer filter and non-existent with the monolayer filter. GF-coupled UF reduced humic acids in the permeate (20%) compared with UF alone. Peak pressure of 3 bars was reached at the end of 30 minutes of UF in both direct UF or UF after monolayer GF. The filtrate from the bilayer GF enables UF over a longer period (7 hours)