The ratio of filamentous and flocculating microbiota of activated sludge for effective biological wastewater treatment

The ability of filamentous forms of microorganisms isolated from biocenoses of urban and industrial wastewater treatment plants to form filamentous structures and interact with activated sludge flocs when co-cultivated with it at aerobic, microaerobic and anaerobic conditions and at different volume ratios of activated sludge: filamentous bacteria suspensions was studied. The ratio of filamentous and flocculating microbiota for effective biological wastewater treatment has been established. It was found that the joint cultivation of activated sludge and isolates M7, M9 and M26 in microaerobic conditions contributes to the formation of dense and compact floc of activated sludge, the mixing intensity is sufficient to provide dissolved oxygen to the heterotrophic microbiota of sludge, but does not lead to the destruction of floc. When cultivating a mixture of activated sludge and M42 bacteria under aerobic conditions, the formation of the most compact floc was noted, which may be due to the activity of bacteria of this isolate, which were massively embedded in floc, but did not violate its structure. Bacteria of isolate A33 did not affect the structure of floc at any ratios and aeration conditions, but were found in large quantities in mixed culture. Under anaerobic conditions, in the presence of M26 and A12 bacteria, at a ratios of activated sludge : filamentous bacteria equal to 1:1, 3:1, the structure of floc is disrupted, which can lead to a decrease in its sedimentation ability. In addition, in the presence of isolate A12 in the sludge mixture, a large number of non-floc bacterial filaments of small length are observed in the culture liquid, which leads to a significant increase in the concentration of suspended solids in the settled liquid. The established facts should be taken into account when operating treatment facilities at the risk of mass development of filamentous bacteria isolates M26 and A12 and prevent the formation of dead zones in bioreactors.