Study On The Model For Symbiotic System Of Aquatic Worms With Microorganism And Its Validation

The treatment and disposal of excess sludge has become a rising challenge for wastewater treatment plants (WWTPs) in China. Being energy-saving and low-carbon, the potential of using aquatic worms on sludge ruduction has attached more and more attention. The symbiotic minitype ecological system formed by wastewater, microorganism (bacteria, fungus) and minitype animal (aquatic worms), which has sludge reduction and wastewater treatment effect, is called symbiotic system of aquatic worms and microorganism.Therefore, in this thesis, we chosed aquatic worms as a research object. The model for symbiotic system of aquatic worms with microorganism was developed based on the fully coupled activated sludge model (FCASM3) and the growth kinetics of aquatic worms feeding on activated sludge. The principal conclusions were obtained as follows.1. The growth kinetics of aquatic worms was investigated from juvenile to decline phase for 18 weeks by cultivating with activated sludge in batch test. Results showed that the growth of aquatic worms well fit the Gauss curve for cultivating 18 weeks. The maximum specific growth rate of aquatic wormsμmax=0.41d-1 and the maximum growth yield of aquatic worms Yw/s=0.32. The relationship between the specific growth rate of aquatic worms with dissolved oxygen and sludge concentration meet the Monod equation. The sludge concentration had greater effect on the growth kinetics of aquatic worms, aquatic worms can live in the environment with low dissolved oxygen. Aquatic worms can get a rapid growth rate when the sludge concentration was 4000-6000mg/L2.The nutrient released by aquatic worms was investigated in this research, feeding on activated sludge, sterilized sludge and distilled water respectively. Results showed that the nutrient released by aquatic worms were NH4+-N and PO43--P mainly. The NH4+-N released rates were 0.060 and 0.051mg NH4+-N/g Worms·d-1 respectively, feeding with activated sludge and sterilized sludge. The PO43--P released rates were 0.029 and 0.023 mgPO43--P/g Worms·d-1 respectively, feeding with activated sludge and sterilized sludge. 3. According to the interaction mechanism between aquatic worms and microorganism in the symbiotic system. The model of symbiotic system of aquatic worms with microorganism was developed based on the fully coupled activated sludge model (FCASM3) and the growth kinetics of aquatic worms feeding on activated sludge.4. The model of symbiotic system of aquatic worms with microorganism was established for the novel oxidation ditch in WWTP. The validation of this new model was completed based on the results of influent component measurement and respirometric experiments. The dynamic simulation results indicated that it could simulate biological carbon and nitrogen removal processes accurately, but the description of phosphorus removal deviated from measurement due to the low phosphorus level in the influent. Compare with the black-box model, the accuracy of the model of symbiotic system microorganism was higher. Moreover, the model of symbiotic system sloved the problem of NO3-N which has not been sloved by the black-box model.