Treatment of Highly Concentrated Swine Wastewater and Its Degradation Processes Using Three Matrix Materials

Abstract

The direct discharge of wastewater from pig farms can restrict wetland plant growth meaning that constructed wetlands (CWs) have generally low treatment efficiency. The treatment of farming wastewater using pre-ecological treatment technologies can be used to ensure that effluent concentrations reach the tolerable limits of wetland plants. This study focused on the efficient use of crop straw for reducing the pollution load of swine wastewater. Using field-scale pilot tests, wheat straw, straw, and corn stalk were used as test biological matrix pool fillers to treat the farming wastewater. Continuous intake of wastewater and a hydraulic retention time of 7 days was adopted. When the average concentrations of COD, TN, NH4+-N, NO3--N, and TP in the influent were 1652.83 mg·L-1, 371.31 mg·L-1, 303.51 mg·L-1, 0.67 mg·L-1, and 65.22 mg·L-1, respectively, wheat straw had the greatest removal effect on COD, TN, and TP, achieving a removal rate of 32.1%, 40.9%, and 33.3%, respectively. The removal efficiency of straw on NH4+-N was highest, reaching 43.4%. After 180 days, the lignin, cellulose, and hemicellulose of the three matrix materials were not completely decomposed. The degradation rate of lignin was lower than for cellulose and hemicellulose; the degradation of lignin and cellulose in the straw was fastest; and the degradation hemicellulose in wheat straw was fastest. The results show that wheat straw and straw offer a higher efficiency treatment for swine wastewater than corn stalk, and the suggested replacement cycle period is five months. These results provide initial data to support the application of biological matrix materials in the treatment of swine wastewater.