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Surface and ground water in rural areas where there is a lack infrastructure of sewage is exposed to a risk of bacteriological contamination. Combined constructed wetland (CW) systems appear to be the most feasible solution in preventing bacteriological contamination of waters in these areas. In this study, a pilot-scale combined CW system was designed to remove coliform source pollution in surface water. The system comprised a vertical, non-vegetated CW (Stage I), a horizontal-subsurface flow bed vegetated with Iris (Stage II), and a vertical-subsurface flow bed vegetated with Phragmites (Stage III) connected in series. Coliform bacteria counts (cfu/100 mL) were made in the input and output of all stages under different hydraulic and loading conditions. The average inflow coliform bacteria in stages I, II and III were 4.26, 3.51, and 2.07 for fecal coliforms (FC) and 5.15, 4.38 and 3.05 cfu/100 mL for total coliforms (TC), respectively. The system was capable of significantly reducing FC and TC in septic wastewater effluent. The second stage removed approximately 95%, with higher elimination than in stage II and III. The average overall reductions of fecal and total coliforms were approximately 99%. No seasonal effects on the average removals were observed. Average removal efficiencies were affected by hydraulic residence time (HRT) and input bacteria counts. TUKEY-HSD tests demonstrated that there were statistically significant differences between stages in coliform removal. The results of this study demonstrated that removal efficiency of the system may enhanced due to a longer HRT when singlestage systems are connected in series.

With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasaköy biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.

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