The formation of granules of the activated sludge in aerobic conditions

Abstract

The dynamics of granules formation after incubation of activated sludge with aeration in urban wastewater and wastewater of dair y production was monitored in laboratory. The prepared sludge mixture was incubated on Enviromental Shaker-Incubator ES-20 with the operating frequency of 140 rpm. The pH value was maintained in the range of 6.8–8.5, at temperature 20, 25 and 30°C. The detachable-filling up the mode of incubation that provided alternation of load and of sludge starva-tion was selected. For the purpose of selecting the largest and the most compact flakes and preservation of formed granules, the sedimentation time of activated sludge between feedings was 7 min. Based on the distribution of microorganisms by the main indicator groups, low level of development of the original activated sl udge was noted. Up to 80% of microor ganisms in the activated sludge were testate amoebae. Changes in number and species composition of activated sludge biocenosis in the process of granules formation were tracked. Significant decrease in the number of testate amoebae and obvious increase in proportion of peritrichous ciliates (up to 34% after incubation in municipal wastewater and up to 61% in wastewater of dairy production) was observed. The selected recharge mode was chosen: 1 time per every 4 days for municipal wastewater and 1 time per 10 days for wastewater of dairy production. This provided great er stability of the activated sludge volume after set-tling. The difference in sludge sedimentation character istics, after incubation at different temperatures was marked. With the increase in temperature of incubation, the rate of silt deposition increased and the final volume of sludge after a 7-minute settling reduced. In activated sludge incubated in wastewater of dairy production the granules were found after 70 days, and their size ranged from 1.5 to 4.0 mm. In samples with urban wastewater, the granules formation started on the 80th day, and their size did not exceed 1.5 mm.