A Research On The Anoxic/Aerobic Digestions Of Sludge

The conventional aerobic digestion (CAD) process is considered to be suitable for disposal of the sludge from small scale wastewater plants. The higher power consumption for aeration and the cost of chemical reagent for alkalinity maintenance with CAD prompt a search for an alternative biological approach to stabilizing raw sludge.Anoxic/Aerobic Digestion (A/AD) , by providing periods of cyclic aeration, appears to be one such promising alternative. The purpose of this paper is to research the feasibility and stability of A/AD. The whole experiment is carried out in two parts: static experiment and dynamic experiment. Static experiment which is focused on the feasibility of A/AD was first carried out to study the effects of aerobic manner, sludge initial concentration and temperature on mixed liquor volatile suspended solid (MLVSS) removal, in order to determine the optimum operating parameters. The optimum result of 40. 5% reductions in MLVSS could be achieved at 20d SRT , 12 hours aerobic and 12 hours anoxic cycles, 30°C temperature, and 12.89g/L initial concentration of mixed liquor suspended solid (MLSS). The percent reduction of total nitrogen (TN) in the A/AD can be achieved to 18.5% but was 5.2% in the CAD. A/AD could save 28.6% energy cost compared with CAD, showed great potential in low cost operation.In the dynamic experiment, emphases was put on the stability of A/AD at room temperature (26. 4～28. 1°C) under optimum operation parameters. Result showed that 40.1% of MLVSS and 15.9% of TN could be removed. pH of the sludge mixed liquor maintained at 6.0 steadily through process. The mechanism of A/AD was also discussed in this paper. It is thought that by adopting an intermittent aeration period, pH of the sludge mixed liquor was increased due to denitrification and decreased from nitrification, which helped pH maintain at a steady level and formed a suitable environment for sludge digestion. A/AD made similar effect on MLVSS removal as CAD, while the former can provide alkalinity recovery, energy saving, and nitrogen removal.