Influencing Factors Investigation of On-Site Rural Domestic Wastewater Treatment with Water Hyacinth in Shanghai

Using water hyacinth to treat the domestic wastewater, on-site, from dispersed farmhouses in Shanghai rural area, the relevant influencing factors that are temperature, hydraulic retention time (HRT), water depth (h) and water hyacinth density (WHD), were investigated. The influence of temperature was that water hyacinth had different growth rate in different seasons, which lead to varied pollution abatement ratio in this method. The results showed, when HRT was 60d, the removal efficiency of COD, TN, NH₄ ⁺-N and TP was 81.3%, 96.9%, 98.7% and 97.5% respectively; when HRT was adjusted to 30 d, the removal efficiency of those indexes had a decrease of 8.3,13.1, 16.0, and 1.5; the decrease became 0, 13.8, 9.7 and 11.4 when HRT was reduced from 30 d to 20 d. Three h, 0.4 m, 0.8 m and 1.2 m, were studied, and the results showed that the removal efficiency of COD and TP decreased first then increased, with the rise of h, but the removal efficiency of TN and NH₄ ⁺-N always decreased. As TN and NH₄ ⁺-N were concerned, when HRT was 30 d or 20 d, the change of WHD did not have much influence on them; but the removal efficiency was increased with the increase of WHD when HRT was 15 d. It was also concluded that among HRT and WHD, performance of this method showed higher sensitivity to HRT.