Yves Membrez’s research while affiliated with Lem Sa Switzerland and other places

The purpose of the study is to evaluate, from an environmental viewpoint, the influence of the centralization of the methanization installations which are needed to eliminate the organic waste produced by the population of a given region. Four scenarios of methanization organization are studied for the canton of Vaud, Switzerland (pop. 600,000) in the domains of waste collection, transport, treatment and use for agriculture. The method used is the « ecopoint method », where « ecofactors » are established, which take into account the current impact on the environment, and the critical value of this impact that would cause environ mental perturbation. L'étude est destinée à évaluer, du point de vue de l'environnement, l'influence de la centralisation des installations de méthanisation nécessaires à la digestion des déchets organiques produits par les habitants d'une région. Quatre scénarios d'organisation du traitement sont étudiés sur un canton suisse (Vaud, 600 000 habitants) dans les domaines de la collecte des déchets, de leur transport, de leur méthanisation et de leur valorisation agricole. La méthode employée est celle dite des « écopoints » qui établit des « écofacteurs » tenant compte de la charge actuelle de l'environnement et de la charge critique qui le perturberait.

A process based on partial nitrification and recirculation into the anaerobic digester was studied to remove nitrogen from digested manure and thus reduce enhanced gaseous ammonia emissions due to on-farm biogas production. An anaerobic reactor representing an anaerobic manure digester was fed with a nitrite solution and digested manure liquor. Nitrite was efficiently removed from the influent and ammonium formation was observed first. Ammonium was subsequently eliminated up to a maximum of 90% of the influent concentration, indicating anaerobic ammonium oxidation activity. This activity, however, decreased again and was lost at the end of the 4-month operation period. In a 1.5 L aerobic CSTR that was fed with digested manure liquor, ammonium was efficiently removed from the influent. Nitrite and nitrate formation was observed but mass balances indicated significant N-removal. Accumulation of suspended solids was observed at the end of the experiment suggesting presence of oxygen-free environments. In a second test in a 15 L CSTR where suspended solids sedimentation could be avoided, low N-removal rates were observed in the absence of biofilm carrier elements whereas high N-removal rates were achieved in their presence. A simple one-stage process based on immobilized biomass could therefore be installed downstream of agricultural anaerobic digesters in order to mitigate undesirable gaseous ammonia emissions.

Our work focuses on the promotion and introduction of the biogas technology as innovating solution to manage organic waste and also as a clean and renewable energy. In this article we present the digestible substrate potential in the form of its biogas energy content present in the three regions along the Mediterranean coastline of Morocco, namely de regions of Oriental, Hoceima-Taza-Taounat and Tanger-Tétouan. The organic waste identified are solid manure from animal keeping, the residues of crop growing, industrial organic waste, household organic waste and slaughterhouse waste. The biomass potential from the Oriental region, including the provinces of Oujda, Berkane, Nador, Jerada and Taourirt is about 4.8 million tons a year of which the manure part represents 78 %. This biomass potential can generate theoretically 0,090 Mtep per year of energy in the form of biogas. The biomass potential from the Hoceima- Taza-Taounat region is about 7.8 million tons a year of which 75 % manure, corresponding at 0,130 Mtep of energy per year issued from the biogas produced during the digestion process. The potential in the region of Tanger-Tétouan is about 6.7 million tons a year (81 % manure) representing 0,110 Mtep of biogas energy per year.

Le traitement biologique de l’ammoniac par le procédé classique de nitrification / dénitrification se heurte à deux problèmes majeurs : le coût et la complexité. Ce projet a développé un concept intégré de production de biogaz et d’élimination biologique de l’ammoniac contenu dans le lisier en tirant parti des nouvelles recherches dans ce domaine afin de limiter les besoins d’aération, la consommation d’une source externe de carbone et de simplifier l’exploitation. Une étude expérimentale, menée sur l’effluent de l’installation de biogaz de la famille Martin à Puidoux, a été réalisée au Laboratoire de Biotechnologie Environnementale de l'EPFL et a montré que : (i) Le processus de nitritation est obtenu avec cet effluent dans un réacteur aérobie. (ii) Le processus de dénitritation est aussi obtenu dans le réacteur aérobie en utilisant un support mobile fixant la biomasse. Les rendements obtenus sont très élevés : 90% de l’ammonium est transformé et 80% est éliminé sous forme de N2. (iii) Le processus ANAMMOX peut également être obtenu, mais est instable et n’est donc pas recommandé. L’énorme avantage de cette nouvelle méthode est que l’ensemble des réactions se déroulent dans un seul réacteur, sans modifier le fonctionnement du digesteur. Le bilan d’azote montre que, si la totalité de l’effluent est traité dans le réacteur aérobie, l’élimination de l’azote total initial dans la configuration retenue est de 50%. L’élimination d’une partie seulement de l’azote peut être obtenue en ne traitant qu’une partie de l’effluent. Au niveau du bilan énergétique, le concept n’a pas d’incidence sur la production de biogaz. Un dimensionnement du réacteur aérobie a été proposé en fonction du débit journalier d’entrée et du temps de résidence hydraulique. Le volume utile du réacteur de nitritation / dénitritation devrait être de 30 m3 pour un digesteur de 400 m3. Le dimensionnement du système d’aération en vraie grandeur ne peut pas être défini précisément à partir de la présente étude, ni la consommation énergétique associée. La construction d’une installation pilote / démonstration permettrait de répondre à ces points.

A model for a 1000 kW class solid oxide fuel cell (SOFC) system running on biogas from a sewage sludge digestion plant was implemented in a process flow scheme using external steam reforming. The model stack consisted of planar anode supported cells operated at 800 degreesC displaying state-of- the-art electrochemical performance (0.15 W/cm(2) at 80% fuel utilisation). Real annual data from an existing sewage plant were used as input to the model. From the input of 43 m(3)/h biogas (63% CH4), equivalent to 269 kW (higher heating value, HHV), the SOFC stack was calculated to deliver 131 kW,l electricity (48.7%) using a steam-to-carbon ratio of 0.5. This would allow the sewage site to more than cover its own electrical needs, hence to depollute the waste stream at negative energy cost. In its current exploitation using a low efficient gas engine (130 M), the site is only approximate to50% self- sufficient. Special attention was given to the thermal balance of the stack. The stack developed heat (143 kW) could be balanced by endothermal reforming (78 kW) and by cathode excess air lambda (=3), allowing a temperature difference between stack inlet and outlet of 200 K. The case was compared to other fuel scenarios. Steam-added biogas behaves basically identically to steam-reformed methane. For partial oxidation of biogas or pure hydrogen feeding, electrical efficiency drops to under 43% while needs to be raised to 4.5 to maintain the 200 K thermal gradient over the stack.

This study reports on the combination of solid oxide fuel cell (SOFC) generators fueled with biogas as renewable energy source, recoverable from wastes but at present underexploited. From a mobilisable near-future potential in the European Union (EU-15) of 17 million tonnes oil equivalent (Mtoe), under 15% appears to be converted today into useful heat and power (2 Mtoe).SOFCs could improve and promote the exploitation of biogas on manifold generation sites as small combined heat and power (5–50 kWel), especially for farm and sewage installations, raising the electrical conversion efficiency on such reduced and variable power level. Larger module packs of the high temperature ceramic converter would also be capable of operating on contaminated fuel of low heating value (less than 40% that of natural gas) which can emanate from landfill sites (MW-size). Landfill gas delivers 80% of current world biogas production.This document compiles and estimates biogas data on actual production and future potential and presents the thermodynamics of the biogas reforming and electrochemical conversion processes. A case study is reported of the energy balance of a small SOFC co-generator operated with agricultural biogas, the largest potential source.

Biogas production transforms organic matter into methane, carbon dioxide and ammonia (NH3). The aim of this study was reducing NH3 emissions from liquid effluents of agricultural anaerobic digesters. An alternative to classic nitrification-denitrification was tested: partial nitrification of the ammonium-rich effluent and its recycling into the digester for nitrite conversion into dinitrogen gas (N2) via denitrification or anaerobic ammonium oxidation (Anammox). Two laboratory-scale bioreactors were set-up to this effect. In the first reactor, short residence time and oxygen-limited conditions were guaranteed. The second was filled with digested manure simulating the final stage of a plug-flow anaerobic digester. The feed was artificially amended with nitrtite (NO2-), simulating the effluent of the first reactor. Ammonium (NH4+) removal efficiencies higher than 80% were reached in the aerobic reactor, producing a NO2--rich effluent. However, mass balance showed a large percentage of “nitrogen losses”. This can either be explained by denitrification or Anammox occurring in anoxic zones inside the reactor or by aerobic denitrification, an interesting but not yet fully understood process. The anaerobic reactor removed about 90% of nitrite fed and during a certain period also approximately 80% of ammonium was degraded. Using FISH analysis, Anammox bacteria were identified in the microbial community of this reactor.