Achieving one-stage sludge reduction by adding Chironomid larvae in wastewater treatment systems

•One-stage system for pollutant removal and sludge reduction was achieved by adding CL.•CL decreased the VSS/SS ratio and SVI to improve the sludge characteristics.•The competition between CL and nitrifying bacteria on DO could induce the nitritation.

Although worm predation is effective for excess sludge reduction, it usually needs large land facility and high operational cost. In this study, Chironomid larvae (CL), a novel microfauna for sludge treatment was applied to a one-stage sludge reduction system (sequencing batch reactor, SBR). The results showed that adding CL induced the sludge reduction, and the sludge production rate was 31% lower than that in the control. Low volatile suspended solids/suspended solids (VSS/SS) ratio (0.77) and sludge volume index (70 mL/g) were achieved. Moreover, adding CL did not deteriorate the contaminant removal (organic carbon and nitrogen), and the competition between CL and nitrifying bacteria for oxygen was beneficial for nitritation.