[Annual Nitrogen Removal Efficiency and Change in Abundance of Nitrogen Cycling Microorganisms in Swine Wastewater Treated by Crop Straw Materials].

Based on previous research, using straw material to treat swine wastewater can effectively reduce the concentration of nitrogen (N); however, the annual N-removal efficiency and change in the abundance of N-cycling functional genes remain unclear. In this study, four treatments (wheat straw, rice straw, corn stalk, and CK) were set up, with the aim of studying the annual N-removal efficiency and change in the abundance of functional genes. Our results showed that:① the total nitrogen (TN) removal and NH4+-N removal efficiency were the best in the first six months and were significantly reduced in the following six months. In addition, the TN removal and NH4+-N efficiency in straw and wheat straw were better than those in corn straw. The TN-removal efficiency in straw and wheat straw were 32.81%±11.34% and 32.99%±9.60%, respectively. The NH4+-N removal efficiency in straw and wheat straw were 35.3%±13.23% and 34.97%±12.00%, respectively. ② The abundance of N-cycling functional genes significantly increased by the addition of straw materials, compared with that of the CK (P<0.05). The average abundances of nirK, nirS, and hzsB were 6.45×109 copies·L-1, 6.18×109 copies·L-1, and 2.31×109 copies·L-1, respectively. The average abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were 6.12×1010 copies·L-1 and 4.93×109 copies·L-1, respectively. The average hzsB gene abundance was 2.31×109 copies·L-1. The average abundance of 16S rRNA in the treatment was 8.90×1010 copies·L-1. The abundances of hzsB and nirS genes in the straw and wheat straw were higher than those in the other treatment, indicating that the activities of anaerobic ammonia oxidation and denitrifying microorganisms were significantly increased by the addition of straw and wheat straw (P<0.05). In addition, the abundance of AOA and AOB genes were increased in wheat straw, suggesting that wheat straw could promote nitrification. The results provided data supporting the molecular mechanism of nitrogen removal in swine wastewater treatment with straw materials.

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

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.