[Performance of constructed wetland for municipal wastewater tertiary treatment: winter and summer comparison].

ABSTRACT

An improved three-stage vertical flow constructed wetland (CW) was used for tertiary treatment of effluent from two typical Dalian municipal wastewater treatment plants. The experiments were carried out under ambient condition in Dalian for the whole year. Performances of the CW for COD, TN, NH4(+) -N and TP removal in summer (Jun.-Aug.), winter (Nov.-Jan. the second year) and spring (Feb.-Apr.) were compared. In summer, the removal rates of COD, TN, NH4(+) -N and TP reached 88.5%, 76%, 100% and 98%, respectively. While in winter they reached 88%, 85.3%, 86.4% and 97%, respectively. In spring, the removal rates reached 87.7%, 76.7%, 70.3% and 95.5%, respectively. The effluent water quality for summer, winter and spring were COD 2.8, 3.8 and 3.9 mg x L(-1), respectively; TP 0.02, 0.05, and 0.07 mg x L(-1), respectively; TN 6.8, 2.9, and 9.2 mg x L(-1), respectively; NH4(+)-N 0.01, 0.3, and 8.1 mg x L(-1), respectively. Results showed good performance of CW for Dalian municipal wastewater tertiary treatment, especially for COD and TP removal. The effluent COD and TP meet the needs of Environmental Quality Standard for Surface Water (GB 3838-2002) III, whereas the effluent TN and NH4(+)- N meet the needs of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) class I A and B, separately. The pollutant removal loads in summer, winter and spring were as flow COD 4.9, 5.1, and 5.0 g x (m2 x d)(-1); TN 3.4, 3.0, and 5.5 g x (m2 x d)(-1); NH4(+) -N 0.2, 0.6, and 3.7 g x (m2 x d)(-1); TP 0.15, 0.30, and 0.28 g(m2 x d)(-1). It is indicated that no significant influence of seasons on pollutant removal is found by comparing the removal rates as well as pollutant removal loads in different seasons, however, the removal of NH4(+) -N and TN in CW is mainly influenced by influent pollutant loads.