The role of sulfate reduction in methanogenic digestion of municipal sewage sludge.

Abstract

Relationship between methanogenesis and sulfate reduction in anaerobic digestion of municipal sewage sludge was investigated. The density of methanogenic bacteria in the sludge was estimated to be at the order of 104-106 cells/ml. The density of sulfate reducing bacteria was at the order of 105 colony forming units/ml, while the concentration of sulfate in the sludge was low (< 0.2 mM). Addition of sulfate to the sludge markedly enhanced sulfate reduction without significantly affecting methanogenesis. In the sludge supplemented with sulfate, both methanogenesis and sulfate reduction were significantly enhanced upon the addition of H2. In the presence of exogenous H2, inhibition of methanogenesis or that of sulfate reduction resulted in enhancement of sulfate reduction or that of methanogenesis, respectively. The addition of acetate markedly enhanced methanogenesis but did not affect sulfate reduction, and the addition of propionate markedly enhanced both methanogenesis and sulfate reduction. Degradation of propionate essentially depended on sulfate reduction, and acetate accumulated in response to the propionate degradation when methanogenesis was inhibited. In conclusion, in the sludge, acetate was used only in methanogenesis, and H2 was used in both methanogenesis and sulfate reduction. Sulfate reduction degraded propionate to acetate and enhanced electron flow to methanogenesis.Methanogenesis and sulfate reduction are terminal steps in the anaerobic degradation of organic matter. These reactions are known to compete with each other for electron donors, i.e., H2 and acetate, in various environments. In the presence of sulfate at available levels, sulfate reduction generally dominates over methanogenesis due to kinetic and thermodynamic properties (1,5,6,9,10). Beside this, an inhibitory effect of sulfide, the end-product of sulfate reduction, on anaerobic biogas production is known. Thus, sulfate reduction is generally thought

Physiological properties of a sulfate-reducing bacterium isolated from municipal sewage sludge and its possible role as a syntrophic acidogen in the ecosystem.

“…As reported previously (20), sulfate-reducing bacteria in the sewage sludge were generally enumerated at the levels of 105 colony forming units (CFU)/ml with H2 or lactate as the electron donor, and methanogenic bacteria at the levels of 106 CFU/ml with acetate as the substrate or 104 CFU/ml with H2 as the substrate. Bacteria morphologically resembling to the isolates were found in almost all black colonies formed on roll tubes of the enumeration medium with H2 or lactate as the electron donor, when 104 or 105 dilutions of the sewage sludge were inoculated to the roll tubes (data not shown).…”

“…As reported previously (15,(17)(18)(19)(20), however, sulfate reduction does not apparently compete with methanogenesis in nutritionally rich environments such as the anaerobic digester slurry of municipal sewage sludge or cattle waste, even when sulfate reduction was markedly enhanced by adding sulfate to the slurry. Sulfatereducing bacteria can be generally enumerated at relatively high densities (>i0 5 cells/ml) in such environments even practically devoid of sulfate (18,20).…”

“…Sulfatereducing bacteria can be generally enumerated at relatively high densities (>i0 5 cells/ml) in such environments even practically devoid of sulfate (18,20). Besides, it is known that some strains of sulfate-reducing bacteria can grow as the syntrophic degrader of lactate and ethanol (2,4,5), or propanediols and glycerol (9) in coculture with the hydrogenotrophic methanogen in the absence of oxidized sulfur compounds.…”

Efeitos das relações DQO/'SO IND.4 POT.-2' e das variações progressivas da concentração de sulfatos no desempenho de reator anaeróbio horizontal de leito fixo (RAHLF)

“…Segundo BORREGO et al (1997), é por esta razão que, sob altas concentrações de acetato e baixas concentrações de sulfato (cerca de 100 e 1 mM, respectivamente), não haverá competição entre microrganismos metanogênicos (MM) e microrganismos redutores de sulfato (MRS), de tal forma que a redução de sulfatos até mesmo causa o direcionamento do fluxo de transferência de elétrons através da metanogênese, mediante a degradação microbiana de ácidos voláteis (UEKI & UEKI, 1990;UEKI et al, 1992). Também YODA et al (1987), previamente reportaram acerca de baixas produções de metano em concentrações de 10 a 20 mM de sulfato, sendo que os MM competiam com os MRS sob uma concentração em torno de 300 mM de acetato.…”

“…É interessante notar que as reações efetuadas pelos MRS são independentes da pressão parcial do H 2 . Deste modo, a atividade destes microrganismos pode estimular a degradação do propionato (MCCARTNEY & OLESZKIEWICZ, 1991;PARKIN et al, 1990;QATIBI et al, 1990;HARADA et al, 1994;COLLERAN et al, 1995), ao passo que a adição de propionato poderá também incrementar a redução de sulfato (UEKI et al, 1988(UEKI et al, , 1992 (MULDER, 1984;RINZEMA et al, 1986;HARADA et al, 1994, UBEROI & BHATTACHARYA, 1995OMIL et al, 1996). Este fato corrobora com os fundamentos do processo, de modo que as BRSH obtém mais energia do consumo de hidrogênio molecular e tem uma maior afinidade ao substrato, velocidade de crescimento, e rendimento celular, do que os microrganismos metanogênicos hidrogenotróficos (MMH), segundo OUDE ELFERINK et al (1994) e COLLERAN et al (1995).…”