| With the prompt developing of society and economy, and the continuous increasing of the amount of sewage, serious problems of environmental pollution in the countryside have been caused. Considering the high cost of construction and operation, the traditional wastewater treatment is not suitable in the rural area. Therefore, a new dispersive sewage management technology is necessary to be developed in the village. We developed the hybrid ecosystem technology to deal with the sewage in the rural area, based on the actual condition in the countryside for dispersive wastewater. The system is composed of anaerobic regulating-pool, complex soil filling system and free water surface constructed wetland. The pollution removal effect of the system was monitored, in order to improve the technology in the practical application. The mechanism of nitrogen removal was also studied in the laboratory due to its relatively lower efficiency compared to removal of COD and TP through the complex soil filling system.In Xin Mi city, the plant operation indicated the following points. (1)Anaerobic regulating-pool is essential structure. Not only it played a role to uniform water quality and balance quantity of waste flow, but also had an obvious removal effect of different pollutants. Because of its underground design, the regulating-pool was less affected by temperature changes in summer and winter, the regulating-pool average removal rates of CODcr, TN, NH4+-N and TP reached 53.96%,41.55%,42.19%, 48.75% and 50.90%,43.10%,42.93%,51.51%, respectively.(2) The complex soil filling system(CSF) was built under the ground so that it was less affected by the factors of external environment. Consequently, the removal efficiency of pollutants was fine and stable. The pH value of the sewage was discharged into the CSF was between 7.50～7.80 in each season. The water temperature was between 25.40℃～28.30℃and 12.00℃～14.60℃in summer and winter, respectively. The CSF average removal rates of CODcr, TN, NH4+-N and TP were 63.54%,49.57%,55.46%, 85.33% and 72.72%,46.19%,53.57% and 73.92% in summer and winter, respectively.(3) The treatment effect of free water surface system was influenced by external factors so that the removal rates of CODcr and TP reached over 40% in each season, but the removal rates of TN and NH4+-N were decreased significantly in winter due to the lower temperature in winter. (4) The treatment efficiency of pollutants of the hybrid ecosystem was quite good. The removal rates of CODcr and TP were above 90%, and the TN and NH4+-N removal rates were above 70% and 80% respectively. Overall, the concentrations of pollutants can steadily meet the requirement of wastewater discharge (GB18918-2002).In order to study nitrogen removal mechanism of CSF system, we also did experiment with simulation devices to analysis three different conditions. The results demonstrated that the system had the best removal effect of nitrogen due to a perfect effect of nitrification and de-nitrification when set the saturation line at 40 cm. The removal rates of NH4+-N and NO3--N were above 40%. When set the saturation line at 0cm,the de-nitrification reactions were not sufficient relative to nitration reactions so that NO3--N in the effluent is higher. When set the saturation line at 60cm, the nitration reactions were not sufficient relative to de-nitrification because of the deficiency of oxygen in the system, and the NH4+-N and NO3-N removal rates were 31.58% and 75.01%, respectively. |
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