Influence de la température sur la méthanisation de boues primaires d’épuration

The influence of temperature and organic load on the anaerobic digestion of primary sludge was studied in the range of 28-60°C with organic loads ranging from 2 to 8.5gCOD.L-1.j-1. The work was carried out from a mesophilic inoculum with prior adaptation. The incubation was conducted in 10-L perfectly mixed thermo-regulated digesters which were fed fed daily. Results showed that the daily production of methane was more influenced by the load than by temperature. The performances obtained at 28°, 37° and 49°C were found similar but slightly reduced at 55°C. The digester operated at 60°C with the highest load quickly led to acid inhibition resulting in a drastic drop of methane production. The rise in temperature lead to an accumulation of ammonium NH4+ in the digesters as well as soluble COD (measured after filtration to 0.45 microns). These variations suggested a change in the balance of biodegradation pathway. The effect of temperature on the acceleration of hydrolysis / acidogenesis phases was more acute than on the acetogenic and methanogenic phases, thereby leading to the accumulation of intermediate metabolites.L’influence de la température et de la charge organique sur la méthanisation des boues primaires de station d’épuration a été étudiée dans la plage de 28 à 60°C pour une charge organique allant de 2 à 8.5gDCO.L-1.j-1. Les travaux ont été réalisés à partir d’un inoculum mésophile, préalablement adapté. L’incubation des boues a été conduite dans des digesteurs thermostatés parfaitement agités de 10L alimentés quotidiennement. Les résultats révèlent que la production journalière de méthane est davantage influencée par la charge que par la température. Les performances épuratoires obtenues à 28°, 37° et 49°C s’avèrent similaires. Elles sont légèrement moins bonnes à 55°C, et le digesteur opéré à 60°C avec la charge la plus élevée a rapidement conduit à une inhibition acide avec arrêt de production de méthane. L’élévation de température conduit à une accumulation d’ammonium NH4+ dans les digesteurs, ainsi que de la DCO soluble (après filtration à 0,45µm). Ces variations suggèrent une modification des équilibres de biodégradation. L’effet de la température sur d’accélération des phases hydrolyse / acidogenèse s’avère plus accentué que sur les phases d’acétogenèse et de méthanisation, conduisant ainsi à l’accumulation de métabolites intermédiaires

New insights into the key microbial phylotypes of anaerobic sludge digesters under different operational conditions

Analyses on bacterial, archaeal communities at family level and methane-production metabolism were conducted in thirteen full-scale and pilot-scale anaerobic sludge digesters. These digesters were operated at different conditions regarding solids concentration, sludge retention time, organic loading rate and feedstock composition, seeking to optimize digester capacity. Correlations between process parameters and identified microbial phylotypes were evaluated based on relative abundance of these phylotypes determined by Quantitative PCR and 16S rDNA amplicon sequencing. Results showed that, Total Solids concentration (TS), among the evaluated operational parameters, demonstrated the most positive correlation with chemical parameters (including NH3 and VFAs) and significant impact on the abundance of key microbial phylotypes regardless of other factors. Digesters were grouped into 'Higher-TS' with higher stress (TS > 44 g/L, NH3 > 90 mg/L, VFAs > 300 mg/L) and 'Lower-TS' under easier status (TS <= 44 g/L, NH3 < 120 mg/L, VFAs < 525 mg/L) in this study. We identified the key microbial phylotypes, i.e. the most abundant and discriminating populations, in 'Higher-TS' digesters with high biogas production rate, which were the class Clostridia, the family Methanosarcinaceae and the order Methanobacteriales. Thermoanaerobacteraceae and Syntrophomonadaceae were identified as key families of Clostridia. Methane was produced both from acetoclastic and hydrogenotrophic methanogenesis. By contrast, in 'Higher-TS' digesters with low biogas production rate, the classes Alpha-, Beta- and Gamma-proteobacteria were detected in higher percentages, of which Rhodobacteraceae, Comamonadaceae and Xanthomonadaceae were the most abundant families respectively, and Methanomicrobiales was the prevailing methanogen order. Consistently, hydrogenotrophic pathway was predominant for methanogenesis, indicating existence of syntrophic acetate oxidation in such 'high-stress', low biogas production rate digesters. These microbial phylotypes were therefore considered to be associated to 'Higher-TS' operation. In 'Lower-TS' digesters, the abundance of the class Delta-proteobacteria, the families Anaerolineaceae, Rikenellaceae, Candidatus Cloacamonas and Methanosaetaceae was obviously higher compared with those in 'Higher-TS' digesters, which were thus considered to be marker phylotypes of easy status. The influence of TS and NH3 on the microbiome should be considered when a 'TS-increasing' strategy is applied to increase digester capacity