Nutrients release and phosphorus distribution during oligochaetes predation on activated sludge

Release of nitrogen and phosphorus into effluent of activated sludge process was reported in the recent researches of sludge reduction induced by oligochaetes. In this study, batch test and radioisotope 32P tracer test were therefore carried out to further investigate nutrients release and phosphorus distribution among supernatant, sludge and worm during predation of oligochaetes on sludge. Results showed that more nutrients release into supernatant occurred in the tests of worms with sterilized sludge than that of worms with activated sludge, and release of nitrogen and phosphorus was few in the tests of worms with activated sludge. Statistical analysis showed that no factor was significantly correlated with phosphorus concentration in the supernatant, but time and worm were only two factors significantly affecting total nitrogen (TN) concentration in the supernatant in the test of worms with activated sludge. Through test of radioisotope 32P tracer, 32P mainly distributed in activated sludge and supernatant, and more release of 32P into the supernatant occurred in the test of sludge with worms. After 24 h, 32P concentration of supernatant in the test of sludge with worms was 9% higher than that in the test of sludge without worms, and 32P concentration of worm increased by 2.7%. Additionally, the release rate of phosphorus into supernatant caused by worm's predation on activated sludge was 0.1211 mgTP/gWorm (wet weight) h.