Effect of chironomid larvae on sludge reduction and activated sludge settling performance

A batch of tests were carried out to investigate the effect of chironomid larvae on sludge reduction and activated sludge settling performance. The results indicated that chironomid larvae improved the activated sludge settlement in 2 h. The Chironomid larvae reduced the settlement of activated sludge after they were inoculated in 15 min, then they had little effect on activated sludge settling performance from 15 to 90 min. Finally, the chironomid larvae improved sludge settlement obviously within the next 30 min. The chironomid larvae were added for 2 h with the sludge volume of 36 %, which was lower than the sludge volume of 42 % without chironomid larvae. After 24 h predation of chironomid larvae, the sludge concentration had a reduction of 12 %, the sludge concentration (MLSS) reduced from 1474 mg/L to 1222 mg/L with the MLVSS reduced from 1299 mg/L to 1075 mg/L correspondingly, while the ratio of MLVSS and MLSS maintained at 87-88 %. The sludge reduction rates with the predation of chironomid larvae were 2.31 g-MLSS/g-chironomid larvae (dry weight) · d and 1.75 g-MLVSS/g-chironomid larvae (dry weight) · d respectively.