Sludge reduction by a high-pressure jet device in an MLE process: performances and the microbial community

The potential of installation of a high-pressure jet device (HPJD) to reduce excess activated sludge production was investigated by tow pilot-scale MLE (Modified Ludzack-Ettinger) reactor operation with or without HPJD for 111 days. The application of an HPJD in the system reduced wasted activated sludge by 65%, compared to the control without increase in effluent suspended solid (SS) concentration. This result means that one of the major challenges that HPJD increasing SS concentration has been solved. The two MLE processes displayed comparable removal performances of organic carbon, nitrogen and phosphate, indicating that sludge solubilization by an HPJD did not undermine bacterial activity in activated sludge. The MiSeq sequencing and FISH analysis for prokaryote revealed that microbial community compositions in the two systems were distinct, resulting from the HPJD treatment. It reduced filamentous bacteria and increased bacteria that use cell secretion organisms by the HPJD. The install of HPJD increased the number of eukaryotes in the system was confirmed by microscopic observation. It is suggested that it is preying on dispersed microbes by HPJD and contributes to sludge reduction.