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International audience; The rapid development of anaerobic digestion brought with it the problem of biomass resources and supply. Marine biomass is emerging as an advantageous substrate. Such macroalgae as Palmaria palmata are promising substrates for anaerobic digestion as they possess a high methane potential (308 +/- 9 mL gvs(-1)). The aim of this paper was to study the efficiency of the anaerobic digestion of P. palmata after a range of thermal and chemical pretreatment. The anaerobic digestion of raw and pretreated macroalgae was carried out in batch mesophilic biomethane potential tests (BMP). Thermal (between 20 and 200 degrees C) and thermo-chemical (addition of NaOH and HCl) pretreatment were performed on P. palmata. Thermal pretreatments at 20, 70, 85 and 120 degrees C and acid or soda pretreatments at 160 degrees C had no significant effect on P. palmata's methane potential. After high temperature pretreatment (180-200 degrees C), the BMP decreased with the temperature which can be explained by the formation of refractory compounds in the liquid fraction. In contrast, the addition of 0.04 gNaOH gTS(-1) at 20 degrees C led to a release of proteins and induced an increase in the BMP from 308 +/- 9 mL gvs(-1) (untreated) to 365 +/- 9 mL gvs(-1). Thus, P. palmata can be used advantageously as a substrate for anaerobic digestion and its methane production enhanced by the addition of NaOH. (C) 2013 Elsevier B.V. All rights reserved.

Mesophilic anaerobic digestion is a treatment that is widely applied for sewage sludge management but has several disadvantages such as low methane yield, poor biodegradability and nutrient imbalance. In this paper, we propose orange peel waste as an easily biodegradable co-substrate to improve the viability of the process. Sewage sludge and orange peel waste were mixed at a proportion of 70:30 (wet weight), respectively. The stability was maintained within correct parameters throughout the process, while the methane yield coefficient and biodegradability were 165 L/kg volatile solids (VS) (0°C, 1 atm) and 76% (VS), respectively. The organic loading rate (OLR) increased from 0.4 to 1.6 kg VS/m3 d. Nevertheless, the OLR and methane production rate decreased at the highest loads, suggesting the occurrence of an inhibition phenomenon.

The high salinity and fat contents of kitchen waste (KW) inhibits the effect of two-phase anaerobic digestion system. This research introduces fruit-vegetable waste (FVW) to alleviate the inhibition effect caused by salinity and fat concentrations, and tries to achieve an optimal addition ratio of FVW, an optimal hydraulic remain time (HRT) of acidogenic-phase reactor and methanogenic-phase reactor. A two-phase anaerobic digestion (AD) system was developed to co-dispose KW and FVW. Four sets of experiments were run with different mass proportions between KW and FVW (25-75, 50-50, 75-25, and 100-0% m/m). Considering the biodegradation rate and the acidification degree, the system with 25% KW had the best performance during the acidogenic phase. When the system was run with 50% KW, it not only had the best stability performance but also had a bigger capacity to treat KW than the system with 25% KW. The system with 50% KW was the best ratio in this two-phase AD system. Co-digestion of KW and FVW by two-phase AD is feasible. The addition of FVW can reduce the inhibition effect caused by salinity and fat concentrations, reduce the HRT, and lead to a higher degree of acidification.

Pig waste (PW) and paper sludge (PS) possess complementary properties that can be combined for successful anaerobic digestion. Biochemical methane potential (BMP) tests revealed that a PW:PS 3:1 (v/v) ratio had the highest normalized CH(4)-COD removal (54%), while PS had the lowest value (11%) and PW had 44%. Batch BMP tests revealed a significant decrease in lag times for methane production in the order of PW:PS 1:3 (14 days)

The application of anaerobic co-digestion of food waste with sewage sludge, although well established in many European countries, is still in its infancy in the UK. This process has many benefits to offer, with a successful application often associated with increased renewable energy potential, outweighing constraints associated with the variability of food waste and its handling requirements prior to co-digestion. With both regulations and water infrastructures designed and constructed on the basis of linear views and sectorial requirements and conditions and technologies from the past in many parts of the world, in the UK, sewage sludge and food waste digestion operations are also under very different regulatory and management regimes. With sustainability requiring that we do not address single issues in isolation, but through a systems approach that delivers integrated solutions, co-digestion of food waste with sewage sludge could become such a solution. If carefully applied, co-digestion can deliver beneficial synergies for the water industry and authorities responsible for food waste management. The collaboration of all relevant stakeholders and regulators to support changes to current regulatory frameworks to enable this, is proposed as the way forward, particularly as their complexity has been identified as the major hurdle to the implementation of co-digestion in the UK.

Over the last years anaerobic digestion has been successfully established as technology to treat organic wastes. The perspective of turning, through a low-cost process, organic wastes into biogas, a source of renewable energy and profit, has certainly increased the interest around this technology and has required several studies aimed to develop methods that could improve the performance as well as the efficiency of this process. The present work reviews the most interesting results achieved through such studies, mainly focusing on the following three aspects: (1) the analysis of the organic substrates typically co-digested to exploit their complementary characteristics; (2) the need of pre-treating the substrates before their digestion in order to change their physical and/or chemical characteristics; (3) the usefulness of mathematical models simulating the anaerobic co-digestion process. In particular these studies have demonstrated that combining different organic wastes results in a substrate better balanced and assorted in terms of nutrients, pre-treatments make organic solids more accessible and degradable to microorganisms, whereas mathematical models are extremely useful to predict the co-digestion process performance and therefore can be successfully used to choose the best substrates to mix as well as the most suitable pre-treatments to be applied. © 2012 Springer Science+Business Media B.V.

This paper deals with an experimental study aimed at assessing the effect of mixing different organic wastes on the anaerobic digestion process. Livestock manure and organic solid wastes have been taken into account as substrates to verify if their mixing gives rise to higher methane production rates and lower risk of process failure. Bio-methane potential (BMP) tests have been conducted using the following substrates: buffalo manure (BM), poultry manure (PM), organic fraction of the municipal solid waste (OFMSW), greengrocery waste (GW) and two different mixtures composed of BM and OFMSW. Mixing BM with OFMSW resulted in 12% and 30% higher methane volumes after 30 and 15 days from the test start, respectively. Experimental data have been also used to calibrate and validate a mathematical model previously proposed by the authors, showing its capability to reproduce the synergistic effect on methane production promoted by co-digesting BM and OFSMW. © 2012 Taylor and Francis.

Attempt was made to investigate the effect of co-digestion on biogas production using cow slurry and maize cob. Cow slurry and maize cobs were co-digested at ratios 3:1, 1:1 and 1:3 respectively using the percentage volatile solid of each substrate. The investigation was carried out in a laboratory scale (batch experiment). The digester was fed with the calculated amount of cow slurry-maize cob mixtures. Co-digestion of cow slurry with maize cobs at the selected ratios has biogas yields of 0.453, 0.417 and 0.429m3/kgoDM respectively while the methane yields were 0.334, 0.323 and 0.323m3CH4/kgoDM respectively at mesophilic temperature (37oC). From the fresh mass of the substrate, biogas yields of 0.053, 0.065 and 0.100 m3/kgFM were obtained at mesophilic temperatures for cow slurry-maize cob ratios of 3:1, 1:1 and 1:3 respectively while the methane yields from the fresh mass for the same ratios were 0.039, 0.050 and 0.076 CH4/kgFM respectively. Co-digestion of cow slurry with maize stalk was found to have methane concentrations of more than 70% in each case. In all, it can be concluded that co-digestion of cow slurry with maize cob has a notable positive effect on biogas production.

220 p. La obtención de energía es un factor clave para el desarrollo de la actividad humana. La digestión anaerobia aplicada a residuos orgánicos es una opción adecuada de gestión y valorización económica gracias al aprovechamiento del biogás producido y a la estabilización del residuo. Sin embargo, este proceso fermentativo suele estar dificultado por diversos factores relativos a la naturaleza del substrato, como pueden ser el balance de nutrientes, el pH o la presencia de tóxicos e inhibidores. La inclusión de un co-substrato puede ser una opción valida para conseguir un substrato-mezcla adecuado al proceso.Este trabajo está enfocado a la gestión de los residuos ganaderos (ovino, vacuno y porcino), considerando residuos de la industria alimentaria (peladura de patata y patata frita) y bioenergética (glicerina) como posibles co-substratos

At Tekniska Verken in Linköping AB (TVAB) there is a long time experience of handling and producing biogas from large volumes of slaughterhouse waste. Experiences from research and development and plant operations have lead to the implementation of several process improving technological/biological solutions. We can in this paper describe how the improvements have had several positive effects on the process, including energy savings, better odor control, higher gas quality, increased organic loading rates and higher biogas production with maintained process stability. In addition, it is described how much of the process stability in anaerobic digestion of slaughter house waste relates to the plant operation, which allow the microbiological consortia to adapt to the substrate. Since digestion of proteinaceous substrates like slaughterhouse waste lead to high ammonia loads, special requirements in ammonia tolerance are placed on the microbiota of the anaerobic digestion. Biochemical assays revealed that the main route for methane production proceed through syntrophic acetate oxidation, which require longer retention times than methane production by acetoclastic methanogens. Thus, the long retention time of the plant, accomplished by a low dilution of the substrate, is a vital component of the process stability when treating high protein substrates like slaughterhouse waste.

Several wastes from agro-industrial activities were mixed in different ratios to evaluate the co-digestion process. Methane yield YCH4, specific methanogenic activity (SMA) and a kinetic parameter (k0) were determined. A second feeding was also performed to examine the recovery of bacterial activity after exhaustion. Mixture ratios of 1:1:1:1 and 1:3:4:0.5 (w/w) showed the best performance, with YCH4 of 664; 582 NmL CH4/gVSsubstrate, as well as SMA of 0.12; 0.13 gCODNmLCH4/gVSinoculum/d, respectively, during the digestion of the first feed. It was possible to relate synergetic effects with enhancement in YCH4 by up to 43%, compared with values calculated from YCH4 of the individual substrates. All batches started up the biogas production after an exhaustion period, when a second feed was added. However, long lag phases (up to 21 days) were observed due to stressed conditions caused by the substrate limitation prior to the second feed.

This study aims to investigate the feasibility of using seaweed stranded on the beaches as a co‐substrate in the anaerobic digestion of pig slurry. The biochemical methane potential of Ulva sp. was measured and tests for co‐digestion with pig slurry were carried out in a pilot laboratory project. The methanogenic potential of this seaweed was low compared to other co‐substrates potentially available for use by farmers: 148 Nm3CH4.t‐1 volatile solids or 19 Nm3 CH4.t‐1 of crude product. Used as a co‐substrate, it did not appear their use caused any notable disruption in the process of digestion. The amount of hydrogen sulphide found in a biogas is an important consideration. At equilibrium, the biogas produced had a content of 3.5% H2S for a substrate mixture of pig manure / Ulva sp. (48/52%), making it unsuitable for energy recovery without treatment. As a comparison, the content of biogas during digestion of pig manure alone was around 0.2%. The high concentrations of dissolved sulphide in the digesta would be problematic for its agronomic use because the dissolved sulphides would be converted to hydrogen sulphide gas during land application (spreading). Lastly, this study showed that green seaweed was rich in organic nitrogen, which was partially mineralised in ammonium, and this would impact the land application (spreading) plan implemented by the farmer., Cette étude avait pour objectifs principaux d'étudier la faisabilité d'utiliser les ulves échouées sur les plages comme co-substrat dans les unités de méthanisation agricoles. Le potentiel méthanogène maximal des ulves a été mesuré et des essais de co-digestion avec du lisier de porcs ont été réalisés sur des pilotes de laboratoire. Le potentiel méthanogène des ulves est faible comparativement à d'autres co-substrats utilisables par la filière : 148 NlCH4.kg-1de matières volatiles, soit 19 NlCH4.kg.-1 de produit brut. De plus, les algues d'échouage ont une teneur en matières minérales importantes ce qui limitent les apports dans les réacteurs infiniment mélangés. Leur utilisation en tant que co-substrat ne semble pas occasionner de perturbations notoires sur le procédé, aucune inhibition n'a pue être mise en évidence. La quantité d'hydrogène sulfuré retrouvé dans le biogaz est très importante. Ainsi, _a l'équilibre des réacteurs, le biogaz produit présentait une teneur de 3.5% d'H2S pour un mélange lisier de porc/ulves (48/52%), le rendant inutilisable pour une valorisation énergétique sans traitement. A titre de comparaison, la teneur en biogaz lors de la digestion d'un lisier de porcs seul est de l'ordre de 0.2%. Les fortes concentrations de sulfures dissous dans les digestats sont problématiques quant à sa valorisation agronomique car ils sont transférés vers la phase gazeuse sous la forme d'hydrogène sulfuré au moment de l'épandage. Enfin cette étude met en évidence que les algues vertes sont riches en azote organique étant, pour partie, minéralisé sous sa forme ammoniacale impactant le plan d'épandage mis en place par l'exploitant agricole.

Waste water treatment plant sludge methanization has been used for many years to reduce their volume and to produce a biogas used as an energy source. Certain waste water treatment plants, treating effluent from tourist areas, must deal with significant seasonal fluctuations and hence the digesters are under-used for a significant part of the year. During these periods, it is therefore advantageous to be able to supplement digester feed with other substrates available locally. This article reports an example of digestion (laboratory scale) of waste water treatment plant sludge alongside fat waste from agribusinesses. It is interesting to note that the authors obtained very favourable performance levels in the presence of 40% of the fat (expressed in COD), without observing any significant inhibition in the presence of continuous fermentation methanization, and this with a residence time > 20 days without prior hydrolysis. This strategy, which incorporates co-substrates from a territorial source serves to improve the profitability of sludge methanization-related investments, not only in tourist areas, but also for small-scale waste water treatment plants (René Moletta, Moletta Méthanisation)., La méthanisation des boues de stations d'épuration est appliquée depuis de très nombreuses années pour diminuer leurs volumes et produire un biogaz qui est utilisé comme source d'énergie. Certaines stations d'épuration qui traitent des effluents issus de zones touristiques, doivent faire face à des fluctuations saisonnières importantes et donc les digesteurs sont souvent sous-alimentés une grande partie de l'année. Pendant ces périodes, il est donc particulièrement intéressant de chercher à compléter les alimentations du digesteur par d'autres substrats présents sur le territoire. Cet article rapporte un exemple de digestion de boues (au stade laboratoire) de stations d'épuration avec des graisses issues de flottation d'industries agroalimentaires. Il est intéressant de noter que les auteurs obtiennent des performances très intéressantes lors de la présence de 40 % des graisses (exprimée en DCO) sans observer d'inhibition notable lors de la mise en oeuvre de la méthanisation en fermentation continue, et ceci avec des temps de résidence > 20 jours et sans hydrolyse préalable. Cette stratégie qui incorpore des co-substrats issus d'un gisement territorial permet une meilleure rentabilisation des investissements liés à la méthanisation des boues non seulement dans des zones touristiques mais aussi pour les petites stations d'épuration (René Moletta, Moletta Méthanisation).

(trad auto)The main objective of the work carried out during this thesis was to study a management system for livestock manure (pig slurry) from production to anaerobic digestion treatment for hydrogen sulphide production. Hydrogen sulphide is a smelly gas that is produced during anaerobic effluent management. This gas, present in high concentrations in confined spaces, can be dangerous or even fatal. The first part of this thesis work focused mainly on the impact of pig diets on the amount of sulphur in manure. The sulphur load provided by each of the ingredients in the formulation was analyzed. Ingredients from agro-industrial processing have a high mineral sulphur load, but cereals, the main ingredients, have limited contents. The retention and excretion of sulphur ingested by animals (pigs) was evaluated by an in-vivo study. The sulphur absorbed by animals is poorly retained, beyond nutritional requirements, it is excreted mainly in the form of sulphates, by the urinary tract. In addition to this first study, the dynamics of sulphates in manure was evaluated by an anaerobic storage simulation reproducing normal animal manure storage conditions. Under these conditions, we show that the sulphates are consumed and that hydrogen sulphide is produced, which is either transferred to the gas phase or stored in the liquid phase. This consumption is directly dependent on the presence or absence of volatile fatty acids contained in the manure. The dissimilative reduction of sulphates by sufatoreducing microorganisms appears to be the main route of transformation of sulphates under anaerobic effluent storage conditions. The second part of this thesis work is devoted to the fate of sulphur in agricultural methanisation units where the production of hydrogen sulphide is dependent on digested co-substrate mixtures. In this context, the management of substrates entering methanisation units is important because it must respect the dimensioning of the biogas treatment system (biocatalytic desulphurisation) before its use. An inventory of the different substrates that can be used by methanisation units on the farm has therefore been carried out. The total sulphur contents and methanogenic potentials for each of these substrates were determined and a sulphur potential (maximum concentration of hydrogen sulphide in the biogas for a given substrate) was defined. Thanks to these data, a C/S ratio could be defined, which made it possible to classify the different substrates as to their potential to produce hydrogen sulfide. On the basis of this inventory, some co-substrates are distinguished by a higher potential to produce hydrogen sulphide, in particular stranding algae and some agro-industrial waste. The green stranding algae, a substrate with a low C/S ratio, were tested on anaerobic digestion pilots in co-digestion with pig slurry. For these algae, the low biogas production potential coupled with the high hydrogen sulphide content of the biogas measured with our tests severely limits the interest of their use in on-farm methanisation processes.; Le travail réalisé au cours de cette thèse avait pour objectif principal d'étudier une filière de gestion des effluents d'élevage (lisier de porcs) depuis leur production, jusqu'à leur traitement par digestion anaérobie vis-à-vis de la production d'hydrogène sulfuré. L'hydrogène sulfuré est un gaz malodorant qui est produit au cours de la gestion anaérobie des effluents. Ce gaz présent à forte concentration dans les espaces confinés peut être dangereux voire mortel. La première partie de ce travail de thèse s'est principalement intéressée à l'impact des régimes alimentaires des porcs sur la quantité de soufre présente dans les déjections. La charge en soufre apportée par chacun des ingrédients qui composent la formulation a été analysée. Les ingrédients issus des transformations agro-industrielles ont une charge en soufre minérale importante, cependant les céréales, ingrédients principaux, présentent des teneurs limitées. La rétention et l'excrétion du soufre ingéré par les animaux (porcs) ont été évaluées par une étude in-vivo. Le soufre absorbé par les animaux est faiblement retenu, au-delà des besoins nutritionnels, il est excrété principalement sous la forme de sulfates, par la voie urinaire. En complément à cette première étude, la dynamique des sulfates dans le lisier a été évaluée par une simulation de stockage anaérobie reproduisant les conditions normales de stockage des déjections animales. Dans ces conditions, nous montrons que les sulfates sont consommés et que du sulfure d'hydrogène est produit, lequel est, soit transféré vers la phase gazeuse, soit stocké dans la phase liquide. Cette consommation est directement dépendante de la présence ou non d'acides gras volatils contenus dans le lisier. La réduction dissimilatrice des sulfates par des micro-organismes sufato-réducteurs semble être la principale voie de transformation des sulfates dans les conditions de stockage anaérobie des effluents. La deuxième partie de ce travail de thèse est consacrée au devenir du soufre dans les unités de méthanisation agricoles où la production d'hydrogène sulfuré est sous la dépendance des mélanges de co-substrats digérés. Dans ce contexte, la gestion des substrats entrant dans les unités de méthanisation est importante car elle doit respecter le dimensionnement du système de traitement du biogaz (désulfurisation biocatalytique) avant son utilisation. Un inventaire des différents substrats utilisables par les unités de méthanisation à la ferme a donc été réalisé. Les teneurs en soufre total ainsi que les potentiels méthanogènes pour chacun de ces substrats ont été déterminés et un potentiel sulfurogène (concentration maximale d'hydrogène sulfuré du biogaz pour un substrat donné) a été défini. Grâce à ces données, un ratio C/S a pu être défini, lequel a permis de classer les différents substrats quant à leur potentialité à produire de l'hydrogène sulfuré. Sur la base de cet inventaire, certains co-substrats se distinguent par une potentialité à produire de l'hydrogène sulfuré plus élevée, notamment les algues d'échouage et certains déchets agro-industriels. Les algues vertes d'échouage, substrat à faible ratio C/S, ont été testées sur des pilotes de digestion anaérobie en co-digestion avec des lisiers de porcs. Pour ces algues, le faible potentiel de production de biogaz couplé aux fortes teneurs en hydrogène sulfuré du biogaz mesuré avec nos essais limite fortement l'intérêt de leur utilisation dans les filières de méthanisation à la ferme.

The anaerobic treatment of sewage sludges (primary and secondary) mixed to concentrated soluble wastes (olive mill effluents, cheese whey and landfill leacheate) in conventional once-through and anaerobic contact digesters, has been investigated in laboratory scale reactors. Experimental results indicate that it is possible to increase appreciably (100 %) the volumetric loading rate of sludge digesters (anaerobic contact) by addition of soluble substrates and keep stable operating conditions. The proposed treatment is economically very attractive if the load due to high strength wastewaters is of the same magnitude as the sludge load, as it does not require additional reactor volume.

National audience; Co-digestion de boues d’épuration et de déchets organiques d’origine périurbaine

National audience; La méthanisation est un procédé actuellement en pleine expansion en France, notamment du fait de ses avantages environnementaux (réduction des émissions de gaz à effet de serre, production d’énergie renouvelable...). Ce procédé permet, sous l’action d’une succession de transformations microbiologiques complexes (hydrolyse, acidogenèse, acétogenèse et méthanogenèse), de minéraliser une partie de la matière organique en biogaz composé majoritairement de méthane (CH4) et de dioxide de carbone (CO2). Il est surtout mis en oeuvre en milieu liquide et dans des réacteurs themo-régulés à 35-40°C. En méthanisation agricole, les substrats issus de l’exploitation (effluents d’élevage, ensilage...) peuvent être supplémentés avec des déchets provenant de l’industrie agro-alimentaire ou des collectivités. Le biogaz produit est valorisé par des moteurs de cogénération permettant de produire de l’électricité et de la chaleur. Les modèles de développement de la méthanisation sont différents à travers l’Europe avec notamment : - le modèle Allemand développé à l’échelle de la ferme et basé sur la co-digestion d’effluents d’élevage et d’ensilage de maïs ; - le modèle Danois avec des unités centralisées permettant la co-digestion des effluents d’élevage, des déchets industriels et des collectivités. En France, la filière est encore en cours de développement mais les modèles semblent se situer à mi-chemin entre ces deux modèles emblématiques.

Co-digestion of press water from organic municipal wastes and of homogenized food residues with defibered kitchen wastes (food waste) as the main substrate was examined to improve biogas production. Although the biowaste digester was operated already at high organic loading (OLR) of 12.3 kg COD m −3 d −1 during the week, addition of co-substrates not only increased biogas production rates but also improved total biogas production. By feeding the two co-substrates up to 20 kg COD m −3 d −1 gas production followed the increasing OLR linearly. When the OLR was further increased with food waste, not more gas than for 20 kg COD m −3 d −1 OLR was obtained, indicating the maximum metabolic capabilities of the microbes. During weekends (no biowaste available) food waste could substitute for biowaste to maintain biogas production. Addition of press water or food waste to biowaste co-digestion resulted in more buffer capacity, allowing very high loadings without pH control.

Anaerobic co-digestion of animal manure with complex organic substrates can improve the economic viability of farm treatment processes. Co-digestion is a method that increases the buffering capacity of substrate mixtures and adds essential nutrients that can substantially improve methane yields. However, despite the benefits of co-digestion, the overall impact that additional materials have on manure-only fermentation processes is not known.

Overcapacities of anaerobic digesters at municipal WWTPs are frequently used for the treatment of organic wastes in order to increase the biogas production. However, “co-digestion” of organic wastes leads to additional nitrogen loading and to additional loads of non-biodegradable COD. The effects of (co-) digestion of organic wastes from agro-industries (slaughterhouses, dairies and leather industry) on the wastewater cycle have been evaluated in full-scale investigations at Leoben WWTP with a capacity of 90,000 pe where the methane production was increased from 700 to more than 1,700 Nm3 CH4 per day. For this evaluation, mass balances for COD and nitrogen have been applied to estimate the fluxes of these substances. Application of this method is described in detail. As the additional loadings, it was found that related to methane production less nitrogen is released from the organic wastes than from the waste sludge. While the ammonia nitrogen load in the effluent from sludge digestion was about 100 g NH4-N per Nm3 of CH4 produced, in the effluent from the digestion of organic wastes only 70 g NH4-N/Nm3 CH4 were found. The decrease in the COD removal efficiency after digestion of the organic wastes started was not regarded as significant enough to be seen as a consequence of the treatment of external substrate.

The results of 2 years experiments on thermophilic single and two-phase anaerobic co-digestion process on activated sludge and agro-wastes are presented. Solid agro-waste (mainly fruit and vegetable residuals from markets) and waste activated sludge were used as substrates. A pilot scale CSTR of 200 l working volume was used for single phase test, while an 0.8 m3 digester was added to study two-phase experiments. Treating only wasted sludge, the initial organic loading rate (OLR) was 0.7kgTVS/m3 d; then it was increased up to 2, 4 and 6 kgTVS/m3 d by OFMSW addition. Following OFMSW increase in the feed, it was found out the increase of GPR from 0.12 to 3.12 m3/m3 d and SGP from 0.16 to 0.51 m3/kgTVS in single phase. The stability of the process was showed also in the most critical operative conditions. Two phase experiments didn't show important differences to the single phase test in the range of OLRs studied up to now (up to 4 kgTVS/m3 d), clearly showing that these are not critical conditions for the process, that can be carried out in single phase in all the range studied. Considering the option of retrofitting the anaerobic digesters of the existing sludge line in WWTPs, the obtained data give important indications about process feasibility.

The purpose of this study was to increase biogas production using co-digestion concept. Vinasse Waste (VW) containing high COD and low total Nitrogen content was mixtured with Tofu Liquid Waste (TLW) containing low COD and high total Nitrogen. Substrates were varied with volume ratio of VW:TLW of 100:0, 20:80, 0:100. Total volume of substrates was 250 mL. Anaerobic digesters were operated at room temperatur. After fermentation, biogas total volume of variables of 100:0, 20:80, 0:100 was 88.5; 125.5; 41.5 mL. Initial pH for all variables was 7.0. At the end of fermentation, pH substrates became 3.9; 5.1; 6.8 for variables of 100:0, 20:80, 0:100 respectively.

Solid waste generation from tanning industry is inevitable and is a major concern from an environmental pollution point of view. Co-digestion of tannery solid wastes is an attractive environmental-friendly option which contributes to decreasing the greenhouse gas emissions according to the Kyoto protocol. In the present study, the reactors were operated in semi-continuous mode with volatile solids (VS) input of 38, 45, 53, 60, 68, and 145 g in 6 feeds to evaluate the effect of multiple feeds on co-digestion process. At the VS load of 68 g, biogas generation per gram of VSadded was 470 mL. At this VS load, maximum % of volatile fatty acids (VFAs) reduction was observed, and hence the VS load of 68 g was found to be optimum from the various VS loads investigated in the present study. The ratio of VFA/alkalinity was in the range of 0.206–0.714, and stable conditions prevailed during co-digestion of tannery wastes. This optimization of organic loading rate and performance evaluation data is useful for full-scale implementation of co-digestion process in the tannery sector for management of solid waste.

The status of the recent developments in anaerobic digestion of solid waste (ADSW) is outlined on the basis of a selection of papers presented at the 4th International Symposium on ADSW 2005.

Le calculateur DIGES est un outil d'aide à la décision, destiné aux agents des délégations régionales de l'Ademe afin de les aider à mieux appréhender le bilan effet de serre des projets de digestion et de co-digestion anaérobie, existants ou émergeants dans leur région. Les enjeux en terme d'effet de serre de ces projets sont liés d'une part au mode de traitement des déchets et d'autre part aux substitutions énergétiques. Ainsi, pour évaluer le bilan « effet de serre » de ce type d'installation, on considère : -les quantités de gaz à effet de serre (N2O et CH4) émises par la filière de digestion anaérobie ; -les quantités de gaz à effet de serre qui auraient été émises par une filière de référence pour le traitement des déchets; -les quantités de gaz à effet de serre qui auraient été émises par une filière de référence pour la production d'énergie. Le calculateur DIGES permet de calculer le bilan des émissions de GES pour des installations traitant de un à sept déchets en mélange. Il est possible de réaliser le calcul à partir de données par défaut, déterminées par rapport à des situations moyennes, ou à partir de données spécifiques aux installations, intégrées par l'utilisateur. Le calculateur est accompagné d'un guide de l'utilisateur et d'un guide de l'administrateur qui indiquent comment utiliser et mettre à jour DIGES. Le guide méthodologique présente quant à lui la méthode de calcul du bilan « effet de serre » et précise les choix faits en matière de déchets à sélectionner, de composition et de facteurs d'émission.

Co-digestion of various wastes has been shown to improve the digestibility of the materials and biogas yield. Batchwise digestion of sisal pulp and fish waste was studied both with the wastes separately and with mixtures in various proportions. While the highest methane yields from sisal pulp and fish waste alone were 0.32 and 0.39 m(3) CH4/kg volatile solids (VS), respectively, at total solid (TS) of 5%. co-digestion with 33% of fish waste and 67% of sisal pulp representing 16.6% of TS gave a methane yield of 0.62 m(3) CH4/kg VS added. This is an increase of 59-94% in the methane yield as compared to that obtained from the digestion of pure fractions at 5% TS. (C) 2004 Elsevier Ltd. All rights reserved.

The anaerobic co-digestion of high strength industrial wastewaters in centralised plants receiving effluents from various local small scale industries is considered to be superior than individual small scale treatment plants. An approach is proposed to systematically tackle co-digestion problems, with respect to both biological and engineering models. In a steady-state mathematical model presented, the effect of combining wastewaters in mixtures, based on major component groups ( i.e. lipids, hydrocarbons and proteins), is systematically accounted for. The model is then solved via a non-linear optimisation program (NLP) which results in the determination of an optimal design of the necessary reactors and their respective layout, by balancing the natural trade-offs between reactor and post-treatment costs (due to high pollutants emissions). The preparation of appropriate mixtures is the major parameter controlled. The applicability and potential of the model are demonstrated with a small example.

This paper deals with the comparison of the co‐digestion performances of two digesters treating organic fractions of municipal solid wastes (MSW) and primary and secondary sewage sludges mixed at various ratios between 0 to 100% TS basis. The organic fractions treated differ in their collection procedures, which influence the chemical characteristics of the substrates and then the process performance. These differences and their influence on the anaerobic digestion process are emphasized throughout the paper so as to assist public sector managers in their choise of treatment method from the harvesting procedure to the final disposal technology of MSW.

The paper gives information on the behaviour of a digester operating under semi-dry thermophilic conditions when algae are co-digested together with the organic fraction of municipal solid waste (OFMSW) at different ratios. These results are compared with those obtained digesting OFMSW alone at similar operative conditions. 25-30 % is the contribution that this approach can give to the disposal of harvested algae from the lagoon of Venice. Since after anaerobic digestion a bio-oxidative step is needed for agricultural utilization of digested sludge, this process has been studied and the performance of this step reported using the OFMSW as bulking agent.

The effect of co-digesting sludge with bio-waste was investigated using an experimental apparatus set for reproducing the operating conditions of a full-scale digester in an existing wastewater treatment plant of 90,000 PE (population equivalent). An increase in the organic loading rate from 1.46 kgVS/m3 day to 2.1 kgVS/m3 day obtained by introducing 40 kg of biowaste per m3 of sludge in the digester caused an increase in the specific methane generation from 90 NL/kgVS to 435 NL/kgVS. These results were used to assess the energetic potential of digesters in eight existing wastewater treatment plants operating in an Italian province with 28,000 PE to 90,000 PE. Results showed that these facilities were able to co-digest globally about 2900 tonnes per year of bio-waste and to generate about 3400 MWh/year of electricity.