Effects of Mn2+ on sewage purification efficiency of two constructed wetland plants in winter.

Hydroponic experiment was conducted by using Cyperus alternifolius and Hymenocallis americana plants in order to study the effects of Mn2+ stress on sewage purification efficiency of constructed wetland plants in winter for providing the basis on the remediation of sewage polluted by heavy metals. The results indicated that at low Mn2+ concentration (0-50 mg/L), the removal rate of CODcr in sewage by both kinds of plants was higher, while under high concentration (250mg/L), the purification efficiency of Cyperus alternifolius on CODcr decreased significanthy, and showed negative value of CODcr. The purification efficiency of two kinds of plants on TP in sewage were good and stable when treated at early stage, while the purification efficiency decreased significanthy when treated during late stage. At Mn2+ concentration of 50mg/L, the purification efficiency on NH3-N in sewage by the two plants was good at both stages, while the removal rate of NH3-N in sewage decreased suddenly at Mn2+ concentration of 250mg/L, and that of Cyperus alternifolius showed negative value at early stage and Hymenocallis americana showed negative value at both stages. Therefore, Cyperus alternifolius and Hymenocallis Americana were suitable for treating the sewage with lower than 50mg/L Mn2+ concentration.