Research On The Hydroponic Vegetables System For Tail Water Of Rural Sewage Treatment And The Utilization Of Nitrogen And Phosphorus

Based on the low level of organic matter and the high concentration of nitrogen and phosphorus in sewage tail water, the different kinds of combined process of the hydroponic vegetables system and the constructed wetland were used for the utilization of nitrogen and phosphorus. Characteristics and pollutant removal mechanisms of the process was investigated, and parameters were optimized for achieving the maximize utilization efficiency of nitrogen and phosphorus was achieved. Moreover, the safety of water spinach and cress was evaluated. The results were as follows:(1) With hydraulic load or water depth increasing, organic matter, nitrogen and phosphorus removal rates of four kinds of process continued to reduce. To ensure the maximum the utilization of nitrogen and phosphorus and the effluent meet the first standard of GB18918-2002, the hydraulic load of the hydroponic vegetables system and the combined process of the hydroponic vegetables system and the constructed wetland should be 0.2 m3/(m2-d) and 0.3 m3/(m2-d), respectively.(2) When a quarter of the way to harvest was used for water spinach in the hydroponic vegetables system, the stability of the sewage treatment effect could be guaranteed, in addition, compared to that with the whole harvest way and the half way to harvest, the yield of water spinach was increased by 1.3 times and 1.1 times, respectively.(3)Removal mechanisms of different forms of nitrogen and phosphorus in hydroponic vegetables system were analyzed quantitatively. The results were as follows:contributions of water spinach absorption, nitrification and ammonia volatilization to NH4+-N removal were 37.62%,58.86% and 3.52%, contributions of water spinach absorption and denitrification to NOx--N removal were 56.33% and 43.67%, contributions of water spinach absorption, denitrification, ammonia volatilization to TN removal were 47.68～59.52%、39.43～51.34 and 1%, contributions of water spinach absorption, other ways to TP removal were 58.38～77.48% and 22.51～41.62%. Thus, water spinach absorption is the main way for the removal of different forms nitrogen and phosphorus in the hydroponic vegetables system.(4) Tail water of rural sewage was measured according to the standards for irrigation water quality; the content of Hg and petroleum were over the limit value of the standards for irrigation water quality sometime, the other indexes were all kept to the standards. In addition, the safety of water spinach and cress was evaluated, the content of Pb and petroleum in water spinach were over the limit value of the standard some time, and other indexs were kept to the standard.In summary, when the combined process of the hydroponic vegetables system and the constructed wetland were used for Tail water of rural sewage treatment, simultaneous efficient sewage treatment and utilization of nitrogen and phosphorus could be achieved.