Purification effect of subsurface flow constructed wetland on livestock wastewater

The purpose of this study is to enhance the removal efficiency of pollutants of livestock wastewater in subsurface flow constructed wetlands. Four wetland systems for treating anaerobic digester effluent from swine wastewater were constructed. The internal structure of wetland systems was improved. Gravel and gray bricks were filled as principal media in the wetlands. Two special plants, Bidens frondosa and Rumex dentatus, were cultivated by crop rotation in winter and summer in the wetlands. Processing effects of different wetland systems for swine wastewater were comprehensively studied during the running stage of wetlands. The results indicated that the wetland systems entered a stable period after the start-up for 80 days, and the cultivated plants wetland systems entered a stable period about 10 days in advance than controlled wetland (non-plant system). A significant linear positively relationship was existed between removal efficiency of ammonia nitrogen(NH4+-N), total nitrogen(TN), total phosphorus (TP) and chemical oxygen demand (CODCr) of wastewater and temperature. When HRT was 4 days, and the concentrations of CODCr, NH4+-N, TN, TP in the influent were 520, 110, 120, 10 mg/L respectively, the removal efficiencies of CODCr and TP of wastewater were over 60% and 70%, respectively. Removal efficiencies of NH4+-N, TN of wastewater were 28%-67% and 32%-58%, respectively.The contributions of plants to removal efficiencies of CODCr and TP were around 10% and 4%, respectively. The impact of temperature on plants was important for the removal of nitrogen. The contributions of plants to removal efficiencies of NH4+-N and TN were approximately 13% and 12% in summer. Compared with the subsurface flow constructed wetland, the removal efficiencies of NH4+-N, TN and CODCr improved all over 3% in improved wavy subsurface flow constructed wetland, but the removal efficiency of TP in wetlands has not significant difference(P>0.05). The study could provide a reference for constructing large-scale subsurface flow constructed wetland in livestock wastewater treatment.