[Treatment effect of constructed wetlands on organic matter in wastewater from pig farm].

Using plant species Vetiveria zizanioides and Cyperus alternifolius respectively, two constructed wetlands (CWS) with size of 1.0 m x 0.5 m x 0.8 m were established. The purifying function and its change pattern with season, influent concentration and hydraulic retention time (HRT) of the constructed wetlands on the organic matters in wastewater from a pig farm were studied throughout four seasons in the year. The results showed that the two CWS had very stable effects on the removal of COD and BOD, while the organic matters in wastewater changed. The removal rate of COD and BOD was 70% and 80% respectively by HRT 1-2 d in spring. The removal rate of COD reached 90% with the influent of COD 1000-1400 mg.L-1 in summer. The removal rate of COD and BOD was 50-60% and 50% respectively by HRT 1-2 d in autumn. The removal rate of COD reached 70% with the influent of COD 1003 mg.L-1 in winter. There was no significant difference between two CWS in the removal of COD, BOD and SS. The rule of contaminants decreased with the HRT in CWS followed exponential function: Yt = Y0.exp(-kt). The relation between the concentration of contaminants in influent (x) and outflow (y) at the same HRT followed linear relation: y = a + bx.