Study On Treatment Of Domestic Wastewater With Higher Plants

Water pollution is a main factor causing shortage of water supply. As a new, cheap and ecological sound technology, phytoremediation of polluted water attracts many scientists all over the world. In this paper, Canna generalis Bailey, Colocasia esculenta L., Cyperus alternifolius L. and Canna warscewiezii A. Dietr were used to study the function of getting rid of pollutants in the water body. All the experiments were carried out in outdoor natural condition. The study included two stages. The first stage was using ecological floating bed technology, and the second was using combined system that included ecological floating bed technology and a small constructed wetland. The results were summarized as follows: 1. Under outdoor natural condition, Canna generalis Bailey, Colocasia antiquorum Schott and Cyperus alternifolius L. grew up well in wastewater. The static experiment investigated these three kinds of plant had good abilities to get rid of pollutants in wastewater; Canna and Cyperus had priority to get rid of chemical oxygen demand (COD) and biological oxygen demand (BOD), while Canna and Colocasia had priority to get rid of ammonium (NH3–N), total nitrogen (TN), total phosphorus (TP) and suspended solids (SS). With hydraulic retention time increasing, the pollutants concentrations were decreasing. The experiment also investigated decontamination ability was related to how the plants grow up. Result of statistics analysis showed that the rule of decontamination followed exponential function Yt =Y₀*e^-kt, where t denoted hydraulic retention time(HRT). 2. Dynamic experiment was operated under a condition of continuous water input. The tanks wastewater flowed through were listed as follows, buffer tank, Canna-tank, Colocasia-tank, Cyperus-tank and a small constructed wetland. Dynamic experiments included three stages according with different influent: (1)When the influent with COD_cr 63～81mg/L, NH₃–N15～24 mg/L, TN 17～24 mg/L, TP 1.4～2.2mg/L, in this combined system, the removal rate of CODcr, NH₃–N, TN and TP was 85%, 95%, 94% and 100% respectively. And in the Canna-tank, it was 70%, 57%, 50%, and 78% respectively; in the whole floating bed system, it was 78%, 93%, 68% and TP97% respectively. (2)When the influent with COD_cr 136～176 mg/L, NH₃–N27～32mg/L, TN 28～33 mg/L, TP 1.8～2.2mg/L, in this combined system, the removal rate of COD_cr, NH3–N, TN and TP was 94%, 99%, 85% and 100% respectively. In the Canna-tank, it was 55%, 50%, 45% and 72% respectively. In the floating bed system, it was 82%, 94%, 72% and 97% respectively. (3)When the influent with CODcr245～300mg/L, NH3–N40～50mg/L, TN 42～53 mg/L,TP 2.8～3.3mg/L, in this combined system, the removal rate of CODcr, NH3–N, TN and TP was 95%, 93%, 89% and 100% respectively. And in the Canna-tank, it was 61%, 45%, 23% and 75% respectively. In the floating bed system, it was 84%, 74%, 67% and 97% respectively. All above, this combined system utilized a series of tanks to treat wastewater with the cooperation between vegetation and a variety of other organisms. This technology had good abilities to get rid of CODcr, BOD5, SS, NH3–N, TN and TP in wastewater. The research has not only explored the phytoremediation theory and technology of sewage treatment, but also gived us a new way of thinking and technical support of ecological sewage treatment. The technology would be positive for water pollution control and the water quality improvement of small towns in the future.