Study Of Purification Of Nitrogen And Phosphorus In Farmdrainage By Natural Wetland

Farmdraihage has been one of the most serious sources of water environment pollution in Zhalong Wetland. The influence of Influent ammonia Concentration and hydraulic retention time on the purification efficiency for nitrogen and pHospHorus by the wetland was studied in this study. The soil and reeds samples were collected from Zhalong Wetland ,The samples were measured and analyzed by laboratory incubation experiment. results indicated that effect of different influent NH₄⁺-N ratio on the removal efficiency of nitrogen and pHospHorus were investigated in surface-flow constructed wetlands. The results showed that the nitrogen and pHospHorus removal was non-ideal when the influent concentration is too high or too low. When the influence concentration of NH₄⁺-N was 2, 4, 6, 8, 10 and 12 mg/L , the average removal rate of total N was 41.4%, 44.6%, 48.2%, 33.6m%, 29.6%and 31.6%, and the average removal rate of PO4-pconrespondingly was 42.5%, 68.4%, 77.8%, 49.4%, 67.0% and 55.0% respectively. While the influence concentration of NH₄⁺-N was 6 mg/L , the nitrogen and pHospHorus removal rate reach the highest level. Meanwhile the retention time was investigated and nitrogen and pHospHorus removal rate increased as the time passing. The best removal efficiency expressed when the treating time was 6⁹ days. Thus, The control of the influent NH₄⁺-N ratio and the retention time is an effective measure to improve purification effect of nitrogen and pHopHrus by wetlands.The removal efficiency of nitrogen and pHospHorus were different when the influnet pH was 6.5,7.0,7.5,8.0,8.5 and 9.0. That explained pH had significant influence on purification efficiency of wetlands .when the influent pH value was 6.5, 7.0, 7.5, 8.0, 8.5 and 9.0, the average removal rate of the ttal N was 45.7%,492%,59.0%,73.9% and 67.3%,and the average removal rate of pHospHorus was 32.1%,31.4%,31.4%,39.2%,62.0%,45.5% and 39.1%,the result showed that nitrogen and pHospHorus removal effect is better when the pH value was alkalescent and removal effect is worse when the pH value was weakly acidic ,the best pH value around 8.0. But removal effect of nitrogen was better than pHospHorus. pH value had significant on pHopHorus efficiency.With remowal increasing as HRT increasing ,but regardless of alkalescent or weakly acidic ,the pH value are close around 8.0 with the HRT increaning.This shows that the wetland system has a buffering effect on the water. Water level also had significant on wetland`s purification efficieny .when water level was :5cm,10cm,15cm,20cm and 25cm, the average removal rate of total N was 58.5%, 71.3%, 65.5%, 51.5% and 43.8%, and the average removal rate of PO4-P was 49.3%, 51.2%, 69.8%, 60.5% and 46.3%. While the water level was 10cm, the nitrogen reach the highest and pHospHorus removal rate reach the highest level when the water was 15cm. The result showed that water level was 10¹5cm is better for nitrogen and pHospHorus removal of wetland.