Efficacy of a high-pressure jet device for excess sludge reduction in a conventional activated sludge process: Pilot-scale demonstration

Abstract

Application of a high-pressure jet device (HPJD) is promising for the reduction of excess activated sludge from aeration tanks in wastewater treatment plants. Nevertheless, proving the feasibility of an HPJD installed in the return line of a conventional activated sludge (CAS) process remains a challenge. We investigated differences in two pilot-scale CAS processes with or without an HPJD to demonstrate its influence on waste excess sludge reduction and wastewater treatment during operation for 108days. The application of the HPJD (designated CAS-HPJD) reduced waste activated sludge by 65% compared with the standard CAS. Despite a slight increase in suspended solids concentration from the CAS-HPJD effluent, the total amount of excess sludge from CAS-HPJD was 23% lower than that of CAS. These two CAS processes exhibited comparable performances in the removal of organic carbon, ammonium and phosphate, indicating that sludge solubilization by the HPJD did not undermine microbial activities in activated sludge. In addition, the HPJD allowed oxygenation of the aerobic tank because of intensive mixing and subsequently produced fine bubbles, resulting in a reduction in the air flow rate of 35%. High-throughput Illumina sequencing of prokaryote 16S rRNA genes and Sanger-sequencing of cloned eukaryote 18S rRNA genes revealed that microbial community compositions in the two systems were distinct and were related to the HPJD treatment.