Operation Optimization And Biofilm Characteristics Of Denitrification MBBR

Moving bed biofilm reactor(MBBR) is a new type of biological wastewater treatment technology, which has the advantages of high efficiency, small occupation and flexible operation. Meanwhile, it is very suitable for the upgrading and reconstruction of the existing technology. The wastewater treatment plant(WWTP) faced the problems of poor total nitrogen(TN) removal under low temperature and lack of carbon source. In this study, the optimum conditions of anoxic biofilm formation process and regular pattern of suspended carriers were studied. In addition, the denitrification capacity of anoxic biofilm at low temperature and low strength carbon source was investigated. Moreover, in order to promote the application of anoxic MBBR, the bioactivity reactivation process under different storage strategies were evaluated. The main research contents and results are as follows:(1) Aerobic biofilm can be obtained by the method of rapid sludge discharge in 20 days, and the anoxic biofilm can be acquired in the following three weeks. The biomass and EPS contents in the individual suspended carriers were both higher than those in compound culture mode, indicating that it is favor of cultivating suspended carriers individually. EPS in anoxic biofilm is dominated by TB-EPS, and the 3D-EEM showed two fluorescent substances(protein and humic acid) are in TB-EPS, respectively.(2) The denitrification capability increased due to the addition of suspended carriers in the activated sludge system at low temperature and low strength carbon source. At 7, 15, 20 and 25℃,the denitrification rates of MBBR sysrem with 20% suspended carriers filling rate increased by 42.9%、31.1%、21.4% and 10.5%, respectively. The effect of temperature on the kinetic parameters of the MBBR system can be quantitatively expressed as Vmax(T)=0.36×1.05(T-15). Furthermore, the respective nitrate removal efficiencies in MBBR system improved by 145.8%, 81.5%, 16.3% and 6.1% when C/N were at the values of 1, 2, 3 and 6.(3) The addition of suspended carriers can promote the denitrification rate in the activated sludge system in a certain period, however, the biomass, EPS contents and denitrification property all decreased along with the operation of MBBR, and the denitrification rate after 40 days operation was only 35%, compared with the start-up period of MBBR. Proteobacteria and Bacteroidetes phylum are the main microbial community, and the dominant species were Dechloromonas in the genus level. In addition, the reduction of Dechloromonas abundance might lead to the poor total nitrogen removal efficiency.(4) After long-term storage, the biofilm can be recovered in 3 weeks, which can effectively reduce the start-up period of anoxic MBBR. In addition, the carriers storage at 4℃ possessed better recovery performance and lower power consumption than those of normal temperature(20~25 ℃) and-25℃storage conditions, which was more suitable for the long-term storage of suspended carriers.