Post-treatment and reuse of tertiary treated wastewater by constructed wetlands

¸ Three pilot-scale constructed wetland (CW) units were built in an area near to Pasaköy Advanced Biological Wastewater Treatment Plant (PWWTP) in Istanbul in 2002. The aim of this study was to evaluate the effectiveness of constructed wetland systems in the removal of organic matter from tertiary effluents and the potential factors effecting removal. The first pilot system is a gravel-substrate horizontal-subsurface flow (H-SSF) wetland (7.5 × 20 m) planted with Cyperus. The second is a without substrate and surface flow (SF) wetland system (7.5 × 20 m) with Cyperus. The third is a four serial-connected free water surface flow (FWS) wetland system (each 6.5 × 8 m) planted with Lemna. Pilot systems were operated for a period of 3 years. The hydraulic loading rate varied between 4.8 and 15.6 m3 d−1. The average removal efficiencies were higher in summer periods. The average removal values at H-SSF, FWS and SF systems were 80%, 65% and 72% for SS; 65%, 64% and 62% for BOD5; 50%, 45% and 47% for COD; 29%, 34% and 37% for TOC, respectively. The average overall removal of fecal coliform and total coliform were 94% (with an average effluent 140 cfu/100 mL for fecal coliform and 1240 cfu/100 mL for total coliform). Removal efficiencies were affected rather by hydraulic residence time (HRT) and mass loading rates (MLR). Statistical analysis (ANOVA) showed that there was significant difference between temperatures and loading rates (MLR and HRT) and removal efficiencies. TUKEY-HSD tests demonstrated that there was not statistically significant difference between configurations in BOD5, COD and TOC removal. The results of this study demonstrated that constructed wetlands had a potential for BOD5, COD and coliform removal and the treatment and reuse of tertiary effluents.

This study demonstrated the effects of temperature, mass loading rates and HLRs on the performances of constructed wetlands. Removal efficiencies are significantly affected by seasonal changes. There were not found significant differences between the winter and summer periods for coliforms. H-SSF systems had lower performance in the TOC removal (29%) while it had higher performance in the SS (80%), BOD5 (65%) and COD (50%) removals. H-SSF wetland system was performed better for removing SS, BOD5 and COD than FWS and SF wetland systems. The relationships between loading rate and removal rate were obviously linear. The linear correlations between loading and removal rate were strong for BOD5, but weak for COD and TOC. The relationships between HRTs and the average removal efficiencies were logarithmic for all wetland systems. The linear correlations between HRTs and the average removals were weak, but better for coliforms when compared to other. Statistical analysis data showed that there was a significant difference between temperatures and loading rates-removal efficiencies except relationships between loading rates and its removal efficiencies. On the other hand, significant differences were not found among the systems in average removal efficiencies. The results of this study indicated that constructed wetlands had a potential for SS, BOD5, COD and coliform removal and treatment of tertiary treated wastewater.