Effects of oligochaete reactor on treating the discharged excess sludge

A new worm-reactor, consisting of free-swimming and sessile worm growing sections, was developed to be habitat for worm stable growth. Two bench worm reactors were used to treat the discharged excess sludge, and comparison experiments were carried out to investigate the sludge reduction with oligochaetes. Tubificidae was selected and inoculated in the start-up phase of Reactor 1 operation, and Reactor 2 was as the control. Tubificidae was present in Reactor 1 throughout the operation period after its inoculation, and mainly attached on the carriers and aggregated on the bottom of the worm-reactor. Free-swimming worms such as Aeolosoma, Aulophorus and Nais were found in both reactors since the 35 th day. Microscopic investigation showed that these free-swimming worms naturally produced in the pilot activated sludge system and then came into worm reactors along with the discharged excess sludge. Results clearly showed that the average sludge reduction in Reactor 1 was 57%, much higher than that in the control, but the presence of Tubificidae was much better than free-swimming worms for sludge reduction. The characteristics of sludge settling was improved by presence of both Tubificidae and free-swimming worms. High ammonia nitrogen concentration in influent was toxic to worms, and then limited worm growth. The growth of oligochaetes growth had little impact on the nitrification process, but resulted in somewhat release of nitrogen and phosphorus into effluent.