Biogas is a bioenergy produced from organic or all types of biological degradable wastes and could make it possible to limit energy dependence. Sludge is the best alternative substrate for biogas production at a community-level biogas plant. The literature shows that co-digestion can increase the efficiency of sludge anaerobic digestion. This research, thus, focused on (i) determining the conditions of optimal biogas production in the co-digestion of primary sludge (PS) and bovine dung (BD), (ii) evaluating the impact of leachate from organic waste and cellulose on biogas production. Primary sludge was collected in Bacau town wastewater treatment plant in Romania. The sampling of municipal solid waste was carried out in Ouagadougou pre-collect centers (Burkina Faso). Batch tests were conducted in glass bottles through anaerobic digestion (1 L). The following parameters were monitored during the digestion process: pH, volatile fatty acid (VFA), volatile solids (VS) and biogas production. Primary sludge, bovine dung and leachate showed 50.51%, 72.41% and 70.48% of volatile solids content, respectively. Sludge showed good stability, unlike the other two substrates, such as bovine dung and leachate, with VFA to alkalinity ratio 0.54. Leachate from organic waste had high values of VFA to alkalinity ratio > 3600. Co-digestion could make it possible to raise the levels of organic matter and improve microbial growth and the stability of anaerobic biomass. The best biogas production yield of 152.43 mL/g VS was obtained with a combination of 30% bovine dung and 70% primary sludge at 45 °C, with a 21.57% reduction in organic matter. An improvement in biogas productivity was effective with the addition of leachate, which could be used as an additive element during anaerobic digestion.

La gestion des déchets municipaux est devenue une préoccupation majeure dans les pays en développement, due au manque de politique et de stratégie adaptées. L’étude réalisée a porté sur la valorisation biotechnologique de la fraction biodégradable des déchets au Burkina Faso. Une analyse physico-chimique des déchets échantillonnés dans trois (3) centres de précollecte de déchets municipaux de Ouagadougou a été réalisée. L’influence du type d’inoculum (eaux usées, bouse bovine, flux de broyat de termites et une mixture de ces 3 inocula) et de la charge en substrat (déchets organiques) a été évaluée au cours d’essais de fermentation méthanique. Les résultats obtenus ont montré que les déchets organiques municipaux constituent un substrat de prédilection pour la méthanisation avec un ratio C/N de 31,65. Les essais de fermentation ont permis de noter que la bouse bovine comme inoculum avec une charge en déchets municipaux de 2% donnait la meilleure production de biométhane (297,65 l CH₄ / Kg MSV). Il ressort de cette étude que les déchets municipaux peuvent être traités par la voie de la biométhanisation car présentant un potentiel de bioconversion intéressant. © 2015 International Formulae Group. All rights reserved. Mots clés: Déchets organiques, digestion anaérobie, biométhane, environnement, Burkina Faso English Title: Optimization of biomethane production from municipal solid organic wastes English Abstract Municipal solid organic wastes management became a major preoccupation. The achieved study focuses the biotechnological valorization of the biodegradable fraction of solid organic wastes in Burkina Faso. Physicochemical characterization analysis of solid wastes sampled in 03 Ouagadougou’s centers of municipal wastes deposits was achieved. The influence of inoculum source (wastewater, bovine dung, termites’ homogenate and mixture) and substrate concentration (municipal solid waste) were evaluated during biomethane production tests. Results showed that organic fraction of solid wastes represent a source of predilection for methanization with 31.65 C/N cow. Fermentation tests showed that bovine dung used as inoculum in 2% of municipal solid waste gave the highest rate of biomethane production (297.65 l CH₄ / Kg vs). The results demonstrate that municipal wastes can be valorized by biomethanization way because presenting interesting bioconversion potential. © 2015 International Formulae Group. All rights reserved. Keywords: Organic wastes, anaerobic digestion, biomethane, environment, Burkina Faso

This study investigated agronomic characteristics of digestates from cashew nut shell and cow dung anaerobic digestion. General characteristics and agronomic value of digestates were determined using standard methods. Gaseous emissions (biogas, CH₄, CO₂) were evaluated. Microbiological quality of digestates was evaluated, as well as phytotoxicity on maize, okra, tomato and lettuce seeds. Higher conductivity indicated a greater potential for salinity to affect germination and plant growth. High C/N ratio and degree of humification greater than 0.7 are indicative of immature digestate. Total nitrogen, organic nitrogen and phosphorus contents in g/Kg were 11.26, 0.49 and 5.35 for cashew shell digestate and 18.15, 17.12 and 0.16 for cow dung digestate, respectively. Potassium content was 0.32 and 0.98 g K/Kg in cashew shell and boving dung digestate, respectively. Mineral nitrogen content of cashew nut shell digestate was 0.19 g NH₄⁺/kg, 1.28 g NO₂⁻/kg, and 0.0016 g NO₃⁻/kg. These characteristics showed amending and fertilizing effect of digestates. Physical parameters indicate digestate can improve soil structure. Both digestates are significant source of greenhouse gas. Microbiological analysis revealed spore-forming bacteria and coliforms, with proportions that are acceptable for spreading. Germination test on okra, tomato and lettuce seeds indicated high phytotoxicity. Maize showed significant results for seed germination, root elongation, germination index and germination speed with values of 100, 100, 118.63 and 67.21% respectively. The study indicates that digestates present root growth-promoting properties that can be advantageous for plant development. Digestates could be improved by an integrated system in which digestates are composted downstream of anaerobic digestion.

The aim of this work is to contribute to the agronomic utilization of digestate from the anaerobic treatment of faecal sludge at the Office National de l’Eau et de l’Assainissement (ONEA) Kossodo plant in Burkina Faso. Digestates were sampled and dried in the laboratory (25±2 °C). Physico-chemical and microbiological parameters were determined using standard methods. The degree of maturity of the digestate was determined using respirometry and humification tests. The effects of digestate on plants and on environment were studied using phytotoxicity, emergence, growth tests and microbiological analysis. The results revealed a pH of 8.54, electrical conductivity of 7300 µS/cm, 25.42% dry matter, 83.31% organic matter, and 489.8 g/kg total organic carbon. The C/N ratio was 9.7 and the NO3/NH4 ratio was 23.34, indicating mature compost despite other indicators suggesting that the digestate was only partially stabilized. Nutrient contents were 50.48 g/kg total nitrogen, 0.02 g/kg total phosphorus, and 4.72 g/kg total potassium. Water-soluble minerals included 1.97 g/kg ammonium, 45.99 g/kg nitrate, 0.02 g/kg nitrite, 0.35 g/kg phosphate, and 5.90 g/kg sulfate. Phytotoxicity tests showed that cabbage seeds had a germination rate of 89% with digestate filtrate compared to 100% in the control, while tomato seeds had a 100% germination rate with digestate filtrate. The germination indices were 137.58 for tomato and 82.10 for cabbage. Tests on tomato plant growth showed significant effects on biomass, height, leaf number, and branch number, with the 50% digestate proportion demonstrating the highest values. Microbiological analysis detected total aerobic flora at 4.75E+07 CFU/g, yeasts and molds at 7.77E+04 CFU/g, and coliforms at various levels, with potential pathogens such as S. aureus and Salmonella sp. reaching 6.14E+04 and 2.65E+06 CFU/g respectively. The presence of these pathogens suggests a need for further treatment of digestate to ensure safety before field application.

Anaerobic digestion’s contribution to sustainable development is well established. It is a sustainable production process that enables energy to be saved and produced and efficient pollution control processes to be implemented, thereby contributing to the sustainable development of our societies. Optimizing biogas yields from the anaerobic digestion of municipal organic waste is crucial for maximum energy recovery and has become an important topic of interest. Substrate particle size is a key process parameter in biogas production and precedes other pretreatment methods for most organic materials. This study aims to evaluate the impact of particle size and incubation period on biomethane production from municipal solid waste. Sampling of municipal solid waste was carried out in waste pre-collection in the city of Ouagadougou, Burkina Faso. Waste characterization showed lignocellulolytic green waste (grass, dead leaves), waste composed of fruit and leafy vegetables and leftover food waste. TableCurve 3D v4.0 software was used to develop an optimal mathematical model to correlate particle size and biomethane productivity to describe optimal production parameters. Particle sizes ranging from 2000 to 63 µm high biogas production values, specifically 385.33 and 201.25 L·kg⁻¹ of MSV. PCA analysis clearly showed a high correlation between particle size and biogas production, with optimum production recorded for size 250 µm with a biomethane production value of 187.53 L·kg⁻¹ of MSV. The average relative errors and RMSE for CH₄ content were improved by 24.31% and 44.97%, respectively. The data calculated with the developed mathematical model and the existing experimental data were compared and permutated to validate the model. This work enabled the identification of a mathematical model that describes the correlations between the input parameters of an experiment and the monitored parameters, as well as the definition of the particle size that allows for the optimal production of biomethane.