The Combined Treatment Processes Of Domestic Sewage Mixed With Landfill Leachate And Fecal Sewage

With the rapid development of modern cities, urban garbage and fecal sewage has become a big concern,The landfill leachate and fecal sewage are resulting in significant pollutions to the environments. These two types of sewage have high concentrations of nitrogen and organic matters, and the influent quality and quantity are high changable. There were many problems when each of them was treated separately, such as difficulty to treat with proper technologies, high costs for above-mentioned investment and operation management. It is a good option to treat the three kind of sewage with combination so that the fecal sewage and landfill leachate can be easily treated to meet the discharging standards of China by using the effect of cushion and dilution.However, the combined treatment will bring about serious impact on the impulse loading to the sewage treatment plant, it may lead to unsatisfactory of nitrogen removal, biochemical system instability, high sludge production rate, and the effluent water quality. These phenomena were discovered in Datansa Sewage Treatment Plant which had the capacity of 550000 m³/d to treat sewage waste water.Therefore, we designed an A²/O bio-reactor in pilot scale to perform in-site tests for studying the optimal volumetric ratio of landfill leachate, fecal and domestic sewage, the operational parameters and optimal working conditions in the A2/O process. The variation of treatment efficiencies by adding suspended carriers in the oxygen tank are also investigated and discussed.The domestic sewage was mixed with landfill leachate and fecal sewage respectively. The affective factors of nitrogen and organic matters removal through single factor experiment and orthogonal test were conducted. The results showed that HRT had significant effects on nitrogen removal and on COD removal in both case of influent sewage. DO had a remarkable effect on NH4+-N removal in the influent mixture of domestic sewage with leachate.R had a remarkable effect on TN removal in the influent mixture of the domestic sewage with fecal. Moreover, r had a remarkable effect on TN removal to the latter wastewater. Leachate and domestic sewage synchronous processing at the optimal operating conditions(HRT11h,DO3 mg/L,R80%,r200%), the average removal efficiencies of COD,NH₄⁺-N and TN were 77.4%,97.2% and 62.4%,respectively. In case of fecal sewage and domestic sewage synchronous processing at the optimal operating conditions(HRT9h,DO3mg/L,R80%,r200%), the average removal efficiencies of COD,NH₄⁺-N and TN were 88.0%,97.1% and 69.9%, respectively. In case of leachate, fecal and domestic sewage synchronous processing at the optimal operating conditions(HRT11h,DO3mg/L,R80%,r200%), the average removal efficiencies of COD,NH₄⁺-N and TN were 87.7%,97.3% and 64.6%,respectively. The effluent concentrations of COD,NH₄⁺-N and TN in different mixed sewages could meet the discharging limits required by China Discharge Standard of pollutants for municipal wastewater treatment plant.The A²/O -biofilm process was conducted by adding suspended carriers to the oxygen tank of previous A²/O reactor. The objective was to solve the various disadvantage causing by the high organic loading of fecal sewage and landfill leachate as well as the contradiction of SRT between the denitrification and the phosphorus removal in A2/O process. The fuction and the effects of these two carriers were investigated , the optimal ratio and the operation parameters with the addition of the carriers were obtained. The influence of HRT on simultaneous denitrification and the phosphorus removal, the mixed-liquid return ratio and sludge return ratio were experimentally tested to solve the contradiction between the denitrification and the phosphorus removal.The results demonstrated that the dosage of suspended three-dimensional hollow cylindrical biological carrier in the aerobic tank was better than that dosed by lightweight porous ceramic in comparison with the effective operation. The bio-film was formed after 20 days of aeration performance. The optimal volumetric ratio of the carriers was 20%, the optimal volumetric ratio for carriers between the oxygen tank 1 and the oxygen tank 2 was 1:3. The system had a better removal efficiencies of nitrogen and phosphours in the case of the HRT was 5h, the mixed-liquid return ratio was 120% and the sludge return ratio was 60%. It can relieve the contradiction between the denitrification and the phosphorus removal under the condition of the sludge retention time to be 6 days. The system had high and stable removal efficiencies, the average concentrations of COD, NH₄⁺-N, TN, TP in the effluent were 36.22 mg/L, 0.3mg/L, 12.9 mg/L, and 0.35 mg/L, respectively. The main water quality achieved in the effluent can meet the level A dischaging limits of the China discharging standard (GB18918-2002).By using the molecular biological methods, 16S rDNA, the morphology and diversity of microbial community in the A²/O-biofilm system were studied, the results obtained from the experiments showed that abundant microorganisms communities and many bacteria species performing for the nitrogen removal and the degradation of of alkanes were found in the system. The species of various microorganisms in aerobic zone 2 was more abundant than those in the first three zones of the bioreactor. As a result, the dosage of suspended filler into the aerobic zone 2 could change and improve the structure and function of the microbial communities in the system with better biodegradation of organic matters and biological nitrogen removal in the system being achieved.