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

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.

[Sorption-desorption of phosphate in wastewater by hydrous iron oxide].

FeCl3 was used t o prepare hydrous iron oxide (HIO) as a n absorbent for phosphate (P) sorption and desorption study. The results showed that as pH decreased, the sorption capacity of HIO increased, and the sorption kinetics followed the second-order model, and the sorption isotherm could be fitted by the Langmuir equation. A 50 g/L NaOH solution was used for desorption of P from HIO, and the desorption rate could be reached over 98% . No relation was found between desorption rate and adsorption capacity. Based on above results, HIO was applied to adsorption of P from supernatant of sludge thickener, and after desorption, more than 90% of P was recovered. According to the results obtained, an effective system for P removal and recovery from municipal wastewater was suggested, which includes the following processes: adsorption, desorption, regeneration of HIO, and of recovery of P from P-rich desorption solution.