Preliminary Studies On The Mechanism And Process Of Sludge Reduction Induced By Aquatic Worms

With the wide application of biological treatment technology in sewage treatment plants, large amounts of waste sludge are produced. Moreover, the cost of excess sludge disposal becomes higher. So the treatment and disposal of excess sludge has become a growing challenge. As one of ecological approaches, reduction of excess sludge through predation of micro faunal, an emerging technology, has been paid more and more attention since it requires a little energy and brings no second pollution.Based on above reasons, this paper, taking common Limnodrilus hoffmeisteri in Southern China as the research object, investigated the influencing factors of sludge reduction induced by aquatic worms after researching its Basic Characteristics. The results show that the growth rate of aquatic worms and the sludge reduction rate were much higher under the adhesion condition than the free. Taking dissolved oxygen (DO), pH, Temperature(T) as the influencing factors, multivariate Synergistic experiments were performed based on single factor experiments. The optimum condition was obtained as DO 3 mg/L, pH 6.5 and T 22.5℃。Under optimum conditions the effect of sludge reduction was investigated, the results shows that the maximum sludge reduction rate was 39.71%, the feeding ability of aquatic worms was 0.258 g TSS/d·g L. hoffmeisteri.Mineralization caused by predation of the aquatic worms will lead to the concentration of increasing pollutants. So, kinetic characteristics of absorption and elimination process of C, N, P in aquatic worms were investigated in a semi-static system in the lab. Kinetic parameters were obtained form the two-compartment model by nonlinear curve fitting, including absorption rate constant (K1), elimination rate constant (K2). Results show that absorption rate constant (K1) was slightly greater than elimination rate constant (K2), which suggested that a small amount of C, N, P absorbed by aquatic worms were used for their own growth, and most of them were excreted through feces. The elimination ability order of aquatic worms in terms of the three pollutants is TN> TP> TOC, shows that during sludge mineralization an increase of phosphorus, nitrogen, carbon in effluent does not seem avoidable. Therein, the release amount of nitrogen is the largest and phosphorus takes the second place, and carbon the smallest. It was found that the data was fitted to the two-compartment model, and good agreement was found using the goodness-of-fit test.Based on above studies, a two stage process was developed, in which the first stage favors the growth and accumulation of predators in the biological filter media to reduced sludge and the second operates as SBR to fully remove the pollutants, while the excess sludge generated by SBR returned to the first stage. After six-month's stable operation, the results shows that the habitat of contact tank is suitable for aquatic worms. When the quality of aquatic worms per unit volume reached 15g/L, the food chain was formed and balanced, which composed of "pollutants (organic compounds in wastewater, aquatic worms carcass, excrement etc.)-microorganism (activated sludge)-aquatic worms-pollutants" Aquatic worms can reduce sludge by predation, and the sludge reduction rate was 39.6%. The removal rate of COD, NH4+-N, TN, TP were respectively above 90%,80%,70%,90%, with the process of synchronous degradation of sludge and wastewater. The experiment proved that the process could achieve both sludge reduction and pollutants removal and the effluent from the two stage process could meet the discharge standard.