Effect of influent COD/SO42− ratios on mesophilic anaerobic reactor biomass populations: physico-chemical and microbiological properties

Abstract

The competitive and syntrophic interactions between different anaerobic bacterial trophic groups in sulphate limited expanded granular sludge bed (EGSB) reactors was investigated. The outcome of competition between the sulphate-reducing, methanogenic and syntrophic populations after development in reactors at varying influent COD/SO4 (2-) ratios was examined in batch activity tests with the inclusion of specific sulphate reducing bacteria (SRB) and methane producing archaea (MPA) inhibitors. SRB species could not out-compete MPA species for acetate at influent COD/SO4 (2-) ratios as low as 2. The SRB were seen to play a more significant role in the conversion of hydrogen but did not become completely dominant. HMPA were responsible for hydrogen utilization at an influent COD/SO4 (2-) ratio of 16, and were still dominant when the ratio was reduced to 4. It was only when the COD/SO4 (2-) ratio was reduced to 2 that the HSRB assumed a more influential role. SRB species were significant in the degradation of propionate at all COD/SO4 (2-) ratios applied. Sludge samples were analysed by scanning electron microscopy (SEM), granule size distribution and fluorescent in situ hybridization (FISH), combined with confocal laser scanning microscopy (CLSM), to monitor any changes in granule morphology under the various COD/SO4 (2-) ratios imposed during the reactor trial. In situ hybridization with domain- and species-specific oligonucleotide probes demonstrated a layered architecture with an outer layer harboring mainly Eubacterial cells and an inner layer dominated by Archaeal species.

Application of molecular techniques to evaluate the methanogenic archaea and anaerobic bacteria in the presence of oxygen with different COD:Sulfate ratios in a UASB reactor

“…O'Reilly and Colleran [38] also observed great diversity in microorganisms of the granular sludge in the inoculum of a UASB ARTICLE IN PRESS reactor used to treat the wastewater from citric acid processing. They observed cocci, microcolonies of Methanosaeta sp., present as rods and filaments, long and thin filaments (possibly Methanobacterium bryantii or M. formicicum) and Methanosarcina-like aggregates in the granule surface.…”

Effect of Sulfate Loading Rate and Organic Loading Rate on Anaerobic Baffled Reactors Used for Treatment of Sanitary Landfill Leachates

“…The theoretical feed COD/SO 4 2-ratio of 0.67 is the critical stoichiometric value required for complete removal of OM by sulfate reduction . At lower COD/SO 4 2-ratios, SRB tends to dominate the reactor microbial community, whereas MPB dominates at higher ratios (De Smul et al, 1999;O'Reilly and Colleran, 2006). In consideration of the thermodynamic properties of sulfate as an electron acceptor, microbial communities dominated by SRB have a higher growth rate that results in increased reactor performance.…”

“…Acetate is poorly consumed at high sulfate loading rates. Propionate is preferentially degraded by BRS, while the butyrate degradation rate is not affected by sulfate concentration (O'Reilly and Colleran, 2006;Bharati and Kumar, 2012). Based on this scenario, the acetate degradation rate is affected by sulfate reduction, provoking its inhibition at low COD/SO 4 2-ratio (Omil et al 1998;Barber and Stuckey, 2000).…”

Release of Extracellular Polymeric Substance and Disintegration of Anaerobic Granular Sludge under Reduced Sulfur Compounds-Rich Conditions

“…A lot of researchers have investigated sulfate-rich wastewater treatment with UASB reactors and pointed out negative aspects of the presence of sulfate such as decrease in methane yield due to competition between methanogen and sulfate-reducing bacteria (SRB) and inhibition by sulfide produced by SRB [17][18][19]. Although most researchers have discussed the oxidized forms of sulfur compounds (sulfate, sulfite, thiosulfate) in input stream of industrial wastewater, however, influent of UASB and EGSB reactors also sometimes contains only reduced sulfur compounds including sulfide, methanethiol, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) instead of the oxidized ones.…”