Research On Rural Domestic Wastewater Treatment By Constructed Wetlands And Operation Optimization

Currently, rural domestic wastewater is becoming the major sources of water environment pollution in our country. It's important for energy conservation and emission reduction, water environment safety and peoples health & quality of life whether it has been treated efficiently and economically or not. As a wastewater treatment technology with both low construction & operation cost and good efficiency to remove contamination, constructed wetlands have been paid much more attention by environment protection workers. However, with the strigency of discharge standards, it's very important to combine constructed wetlands with other treatment units, such as anaerobic tank, pretreatment tank, and so on.According to the situation of a rural region, the engineering design and construction study aimed at practice application were conducted. The processing technology with capacity of 30t/d was composed of a septic tank, an anaerobic tank, a pretreatment tank and secondary subsurface flow constructed wetlands. Moreover, the dynamic variations of pollution indicators in inflow/effluent during the regulation for the startup were investigated. It found that the constructed wetlands could efficiently remove COD and NH4+-N in the early stage of the regulation for the startup, which probably resulted from the adsorption by the constructed wetlands. Then the removal rates of COD and NH4+-N would be decreased until the wetlands plants grew well. And the COD and NH4+-N in effluents could meet the requirement of discharge standards. On the contray, the filtration effect of SS in the early stage was lower than that of in the later stage. Same as COD and NH4+-N, the adsorption efficiency of TP in the early stage was higher, then the TP in effluents would be higher, but which could stably meet the requirement of discharge standards.Secondly, the operation conditions of constructed wetlands treated domestic wastewater in different seasons have been evaluated. The contrast detectation results of the treatment effect in summer and winter indicated that the temperature had a big effect on removal of COD and NH4+-N. The COD in effluents could meet the requirement of discharge and design standards in winter and summer, in summer COD and NH4+-N average removal rates were 88.86% and 69.65%. Yet it was an additional problem for NH4+-N to be satisfied with discharge standards at the same temperature.Thirdly, some problems occurred in winter and the corresponding optimization & regulation technologies had been studied. The average COD in effluents was 38.2mg/L by regulating the water line of the constructed wetlands. And the mean value of removal rates was higher 7.1% than that of the control. As for NH4+-N, the average of which in effluents was 15.7mg/L. The mean value of removal rates was higher 11.2% than that of the control. The comparative results of sequencing batch and continuous flow operations showed that the removal rates of the sequencing batch system on COD and NH4+-N had increased 2.1% and 12.3%, respectively, than those of the continuous system. Of all the best was the bioaugmentation to degrade NH4+-N.The engineering experiments verified that the constructed wetlands treated rural domestic wastewater had an economic advantage. But the operation and management in winter should be the focus. The removal rates on contaminations could be increased by regulating & optimizating.