Characterization of lighted upflow anaerobic sludge blanket (LUASB) method under sulfate-rich conditions

Shedding light on biogas: phototrophic biofilms in anaerobic digesters hold potential for improved biogas production

An anaerobic methylotrophic methanogenic enrichment culture, with sustained metabolic characteristics, including that of methanation for over a decade, was the choice of the present study on interspecies interactions. Growth and methanation by the enrichment were suppressed in the presence of antibiotics, and no methanogen grown on methanol could be isolated using stringent techniques. The present study confirmed syntrophic metabolic interactions in this enrichment with the isolation of a strain ofPseudomonas sp. The organism had characteristic metabolic versatility in metabolizing a variety of substrates including alcohols, aliphatic acids, amino acids, and sugars. Anaerobic growth was favoured with nitrate in the growth medium. Cells grown anaerobically with methanol, revealed maximal nitrate reductase activity. Constitutive oxidative activity of the membrane system emerged from the high-specific oxygen uptake and nitrate reductase activities of the aerobically and anerobically grown cells respectively. Cells grown anaerobically on various alcohols effectively oxidized methanol in the presence of flavins, cofactor FAD and the methanogenic cofactor F420, suggesting a constitutive alcohol oxidizing capacity. In cells grown anaerobically on methanol, the rate of methanol oxidation with F420 was three times that of FAD. Efficient utilization of alcohols in the presence of F420 is a novel feature of the present study. The results suggest that utilization of methanol by the mixed culture would involve metabolic interactions between thePseudomonas sp. and the methanogen(s). Methylotrophic, methanogenic partnership involving an aerobe is a novel feature hitherto unreported among anaerobic syntrophic associations and is of ecological significance.

Metabolic characteristics of an aerobe isolated from a methylotrophic methanogenic enrichment culture.

Phototrophic bacterial cells in the effluent from a lighted upflow anaerobic sludge blanket reactor supplied with a medium containing 142 mg S (as SO42−) l−1 accumulated a 6.8% w/w oleic acid content in cells and 19 mg cell-bound oleic acid l−1 in the effluent. Pure cultures of Rhodopseudomonas palustris and Blastochloris sulfoviridis isolated from the effluent also accumulated 5.1 and 6.4% w/w oleic acid contents in cells, respectively. The oleic acid content in the cells recovered from the LUASB reactor effluent was related to the phototrophic bacterial population in the LUASB reactor. The inverse relationship was observed in the LUASB reactor between phototrophic bacterial growth and sulfate concentration in the influent.

Phototrophic bacterial production of oleic acid in an illuminated upflow anaerobic sludge blanket reactor

Removal of 3-chlorobenzoate using an upflow anaerobic sludge blanket reactor under light conditions

Enrichment of methanogenic cultures on methanol from the microbial population in the anaerobic digesters operated on agricultural wastes revealed a high rate of biomethanation efficiency. Routine maintenance of this enrichment in a minimal basal medium at room temperature resulted in maximal growth in 40–50 d, and indicated pigment production toward the end of the growth phase. The cultures grown in three different media, with different substrates under light and dark conditions, were analyzed for protein, pigment, and gaseous products, and morphological studies were carried out by light, phase-contrast, fluorescence, and electron microscopy. In different media with methanol as substrate, growth and pigment production were maximal for the light-grown cells, decreasing in the order: phototrophic (PS(m)) > mineral > basal medium. Methanation and phototrophic growth were inversely correlated under lightgrown conditions. In contrast, growth in the dark was predominently methanogenic in the decreasing order: mineral > basal > PS (m). Among other growth conditions tested, utilization of phototrophic substrates under light and dark conditions indicated the following:

1.

Basal and mineral media were supportive of methanogenic growth under both light and dark conditions, although methane yields under light-grown conditions were low;




2.

Among the different substrates tested, methanol-grown cells gave the highest methane yield in the dark and;




3.

Phototrophic growth in PS medium with succinate, malate, and pyruvate was better than that with methanol.

C. M. Vargheese

Papers

Methanogenesis mediated by methylotrophic mixed culture