Unpowered Anaerobic Reactor For Domestic Sewage Treatment In Small Railway Station

Currently, the domestic wastewater in most small railway station had not been treated effectively and discharged directly into nearby rivers, depression, etc. It brings undesirable impact on surrounding environment and residents living along the stations. It needs to be treated properly to reach the discharge standards or reuse standards. So, it is necessary to design suitable unpowered, small volume and easy-operation wastewater treatment facilities, aiming for the in-situ treatment and reuse, for the small railway station.The anaerobic treatment system was designed to meet the above objectives. Based on preliminary comparison of packing materials and investigation of biofilm culturing, circular suspended packing and mesh sponge packing were selected for further experiments. In the next stage, during the operation process of reactors in three states in succession, namely aerobic, anoxic and anaerobic states, investigation is carried out to seek for the influencing factors(HRT, pulse intensity and frequency). Then, the effluent from the anaerobic treatment is discharged into an artificial wetland for advanced treatment.Results showed that,(1) Aerobic pre-biofilm-culture could promote the startup process of anaerobic bioreactor biofilm-culture and packing density had an effect on removal of pollutants, which were obtained and indicated in the test of biofilm-culture by different specifications of the suspended packing and sponge packing in aerobic and anaerobic conditions. In following study, anaerobic bioreactors was packed with round suspended packing and mesh sponge packing to startup and biofilm-culture process was achieved in three successive stages(aerobic, anoxic and anaerobic).(2) When treating domestic wastewater, the pulse-feed pattern was adopted in anaerobic biofilm reactor, in which way, the uniformity of water distribution and stability of removal efficiency could also be ensured. HRT, pulse intensity and pulse frequency had great effects on the removal of pollutants. When HRT was set as 24 hr, with the pulse intensity and frequency of the suspended packing reactor standing at 0.108 L/min and 16 times/d, and those of sponge packing reactor at 0.0722 L/m and 20 times/d, respectively, the COD removal reached its maximum value. In this situation, the COD removal in pulse suspended packing reactor, pulse sponge packing reactor and successive sponge packing reactor were 83.0%, 84.0% and 80.3%, respectively. COD concentration of the effluent was about 100 mg/L. In all experimental conditions, TN removal efficiencies were below 20.0%. Among the three reactors, the best COD removal occurred in the pulse sponge packing reactor. Results also indicated that a better biodegradability of effluent was obtained in three reactors, with the ratio of BOD5 to COD(B/C) rising from about 0.30 to over 0.60.(3) Under the optimal operation parameters, the quality of effluent in the pulse anaerobic biofilm reactors were stable, and the main indicators of water quality reached the level III of “Chinese Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant” referring to GB 18918-2002. After the advanced treatment in constructed wetland, water quality mostly reached the level I-B, the final effluent could be discharged directly into neighboring groundwater and rivers or reused for agricultural irrigation.