2020 Volume 18 Issue 4 Pages 238-253
Excess sludge reduction is a central challenge in wastewater treatment, requiring a cost-effective technology. Here, we report the pilot-scale implementation of two Modified Ludzack-Ettinger (MLE) processes with and without a high-pressure jet device (HPJD) as a sludge reduction method based on physically decomposing bacterial cells in activated sludge. The MLE process with an HPJD (MLE-HPJD) bifurcated the activated sludge return lines and directed them to anoxic and oxic tanks; an HPJD was incorporated in the latter. The operation of both processes by continuous municipal wastewater supply for 111 days demonstrated that HPJD application reduced the cumulative waste activated sludge amount by 56.6% without an increase in the effluent suspended solids (SS) concentration. The two MLE processes displayed comparable removal performances for organic carbon and nitrogen, indicating that sludge solubilization by HPJD does not hinder bacterial activity in activated sludge. A combination of the 16S rRNA gene amplicon sequencing and quantitative fluorescence in situ hybridization (FISH) revealed that microbial community compositions were distinct in the two processes. While still effecting excess sludge reduction, HPJD selectively lowered the relative abundance of filamentous bacteria, potentially causing sludge bulking. Further, the relative abundance and cluster structure of ammonia-oxidizing bacteria (AOB) in the MLE-HPJD and MLE processes were comparable, indicating that the application of HPJD did not impair nitrification performance. Monitoring the eukaryote community by microscopy showed that activated sludge in the MLE-HPJD had a much higher abundance of Protomastigida. Therefore, the MLE-HPJD process is an efficient sludge reduction technology that does not compromise organic carbon and nitrogen removal.