Occurrence and activity of Archaea in aerated activated sludge wastewater treatment plants

Abstract

The occurrence, distribution and activity of archaeal populations within two aerated, activated sludge wastewater treatment systems, one treating domestic waste and the second treating mixed domestic and industrial wastewater, were investigated by denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified ribosomal RNA gene fragments and process measurements. In the plant receiving mixed industrial and domestic waste the archaeal populations found in the mixed liquor were very similar to those in the influent sewage, though a small number of DGGE bands specific to the mixed liquor were identified. In contrast, the activated sludge treating principally domestic waste harboured distinct archaeal populations associated with the mixed liquor that were not prevalent in the influent sewage. We deduce that the Archaea in the plant treating mixed wastewater were derived principally from the influent, whereas those in the plant treating solely domestic waste were actively growing in the treatment plant. Archaeal 16S rRNA gene sequences related to the Methanosarcinales, Methanomicrobiales and the Methanobacteriales were detected. Methanogenesis was measured in activated sludge samples incubated under oxic and anoxic conditions, demonstrating that the methanogens present in both activated sludge plants were active only in anoxic incubations. The relatively low rates of methanogenesis measured indicated that, although active, the methanogens play a minor role in carbon turnover in activated sludge.

Identification and quantification of microbial populations in activated sludge and anaerobic digestion processes

“…However, large numbers of methanogenic organisms have been found in various activated sludge treatment plants [68,69]. Specifically, the same methanogenic orders (methanomicrobiales and methanobacterales) found in the present work have been found in low dissolved oxygen level (0.5 -0.8 mg/l) activated sludge processes by other authors [22].…”

“…However, large numbers of methanogenic organisms have been found in various activated sludge treatment plants [68,69]. Specifically, the same methanogenic orders (methanomicrobiales and methanobacterales) found in the present work have been found in low dissolved oxygen level (0.5 -0.8 mg/l) activated sludge processes by other authors [22].However, the methanogenic archaea found in the samples was probably due, as mentioned above, to sludge from the anaerobic digester being pumped back into the primary clarifier. It has been reported that methanogens in aerated sludges may simply be able to survive high oxygen levels but are inactive until reducing conditions are established [22].…”

“…It has been reported that methanogens in aerated sludges may simply be able to survive high oxygen levels but are inactive until reducing conditions are established [22]. A decrease of approximately 60% in methanogenic archaea levels was observed between the anaerobic digester and the aerobic reactor.…”

“…They have, however, been successfully isolated in anaerobic digesters. These organisms, characterized by their slow growth rate, are assumed to be strictly anaerobic [20] but some studies [21,22] concluded that methanogenic archaea can be detected in anoxic or aerobic microhabitats within floccules in activated sludge [23,24]. The role played by methanogenic archaea in these processes has not been studied thoroughly [22].…”

“…These organisms, characterized by their slow growth rate, are assumed to be strictly anaerobic [20] but some studies [21,22] concluded that methanogenic archaea can be detected in anoxic or aerobic microhabitats within floccules in activated sludge [23,24]. The role played by methanogenic archaea in these processes has not been studied thoroughly [22].Considering the above mentioned phenotypes and the importance of studying them all within the microbial population, the aim of this study is to identify and quantify the main bacteria and archaea (phenotypes) involved in wastewater treatment, both in an activated sludge process and in an anaerobic digester in a full-scale WWTP. …”