On-site wastewater treatment systems (OWTS) are primarily monitored using physiochemical factors, including chemical oxygen demand (COD) and residual total suspended solids (TSS), which are indirect measures of the microbial action during the anaerobic digestion process. Changes in anaerobic digester microbial communities can alter the digester performance, but this information cannot be directly obtained from traditional physicochemical indicators. The potential of metagenomic DNA sequencing as a tool for taxonomic and functional profiling of microbial communities was examined in both common conventional and plug flow-type anaerobic digesters (single-pass and recirculating). Compared to conventional digesters, plug flow-type digesters had higher relative levels of sulfate-reducing bacteria (Desulfovibrio spp.) and hydrogenotrophic methanogens (Methanospirillum spp.). In contrast, recirculating anaerobic digesters were enriched with denitrifier bacteria and hydrogenotrophic methanogens, and both were significantly correlated with physicochemical factors such as COD and TSS. Stratification of microbial communities was observed along the digester treatment process according to hydrolytic, acidogenic, acetogenic, and methanogenic subgroups. These results indicate that the high-throughput DNA sequencing may be useful as a monitoring tool to characterize the changes in bacterial communities and the functional profile due to differences in digester design in on-site systems.

Several modifications of the roll-tube method have made it simpler for routine use in the isolation and growth of anaerobic bacteria. These include use of a check valve for the production of prereduced anaerobically sterilized media; a Salvarsan tube under oxygen-free gas pressure for the dispensing of molten prereduced anaerobically sterilized agar medium; a Kelly infusion bottle with a graduated pipette side arm (also under gas pressure) for quantitative delivery of fluid prereduced anaerobically sterilized media; and screw-capped prescription bottles for the cultivation of anaerobes. Colonies of Bacteroides melaninogenicus were easily identified and counted by this method. Other anaerobic bacteria have also been cultivated successfully.

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