Upper Limit of Residual Chlorine in Reclaimed Wastewater

Chlorination as a disinfectant of tertiary treatment is the most common form in municipal wastewater treatment plants in China. Excess residual chlorine in reclaimed wastewater is harmful to growth of lawn grass. However, upper limit of residual chlorine aimed at reclaimed wastewater reuse for urban green land irrigation has not been promulgated. Lab-scale potted experiments of seedling tall fescue (Festuca arundinacea Schreb.)(TF) and Kentucky bluegrass (Poa pratensis L.)(KBG) were performed to evaluate the effects of residual chlorine in reclaimed wastewater on these two kinds of lawn grass. The results showed that: relative aboveground biomass, photosynthetic rate and total chlorophll (Tchl) concentration reduced to great extent with increasing of residual chlorine. The activity of catalase (CAT) of TF went up under low concentrations and decreased under higher ones, which was different from the decline trend of the same index of KBG. Considered growth of the two kinds of turf grass and disinfectant of reclaimed water, the upper limits of residual chlorine in reclaimed water for landscape irrigation should be equal to 1.0 mg/L for TF and 0.8 mg/L for KBG.