Study On Effects Of Ammonia Nitrogen On The Treatment Of Leachate From MSW Incineration Plant By EGSB+ A/O~2MBBR Combined Process

Incineration and power generation has been widely applied as an effective way of municipal solid waste (MSW) disposal method in China. It is a way to realize reduction, harmlessness and resource utilization of the MSW. However, an appreciable amount of fresh leachate can be generated during the stage of fresh waste kept in storage bunkers before incineration. The fresh leachate was composed of various compositions such as refractory compound, organics, NH4+-N and toxicity, etc. Currently, "Anaerobic+Aerobic" combination biological treatment process was mainly used to treat the leachate. While high concentrations of NH4+-N can present poisonous to microorganism, reducing the processing efficiency. A lab-scale "EGSB+A/O2MBBR" combination process was used to study the inhibitory effects of high NH4+-N concentrations on the treatment of fresh leachate.The inhibitory effects of high NH4+-N concentrations on the treatment of the leachate by an expanded granular sludge bed (EGSB) reactor were studied. The influent COD concentration was maintained at 17,760 mg/L. When the influent NH4+-N concentration was stepwise increased from 500 to 1,000 mg/L, the COD removal efficiency decreased from 97% to 45% and the CH4 yield rate declined from 0.270 to 0.110 LSTP/h without any rebounding during 30 days of operation. Meanwhile, effluent VFAs concentrations increased to around 70 mmol/L and EPS production incrseased. It suggests that methanogens was inhibited by high NH4+-N concentrations. The inhibiton threshold of NH4+-N concentrations on the treatment of the leachate was around 1,000 mg/L. When the influent NH4+-N concentration was decreased to 200 mg/L, the COD removal efficiency and CH4 yield rate almost returned to the initial level. High-throughput sequencing results showed no obvious changes in microbial communities in the sludge. The dominant archae was still Methanobacterium. The Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes remained the dominant position in eubacterium. The survival of most microorganisms was not affected by a high NH4+-N concentration. The COD removal efficiency and CH4 yield rate decreased with high NH4+-N concentrations due to the decreased bioactivities in the sludge.An anoxic/two-stage aerobic moving bed biofilm reactor (A/O2MBBR) was used to treat the anaerobic effluent of EGSB reactor with higher NH4+-N concentrations. The inhibitory effect of high NH4+-N concentrations on nitrification process was investigated. When the influent NH4+-N concentration was lower than 600 mg/L, the NH4+-N, COD and TN removal efficiency were about 99%, 80% and 80% respectively. When the influent NH4+-N concentration was increased to 700 mg/L, NH4+-N removal efficiency and TN removal efficiency both decreased to about 50%. It was obvious that nitrobacteria were inhibited by the high NH4+-N concentrations. When the influent NH4+-N concentration decreased to 500 mg/L, NH4+-N removal efficiency and TN removal efficiency rebounded to around 90% and 70%. The inhibitory effect of NH4+-N concentration was reversible. The results of DGGE showed that, the dominant bacteria was still Pseudomonas, Bacteroidetes and Thauera in anoxia MBBR, which have strong resistance to high concentrations of NH4+-N. While in the two-stage aerobic MBBR, the Nitrosomonas, Flavobacterium and Flavobacterium were in the dominant position. There were no significant changes in the microorganism structure. The NH4+-N removal efficiency decreased due to the declined bioactivities of microognism.