Feasibility study of a constructed wetland for sewage treatment in a Korean rural community.

A pilot study was performed to examine the feasibility of using a constructed wetland system for treatment of sewage in a Korean rural community. The treatment system was a subsurface flow wetland with a loading rate and hydraulic residence time of 6.3 cm/day and 3.5 days, respectively. The wetland system was highly effective in treating the sewage; median removal efficiencies of BOD5 (biological oxygen demand) and TSS (total suspended solids) were about 70.0%, with median effluent concentrations of 24 and 13 mg/L, respectively, for these constituents. However, BOD5 and TSS did often exceed the effluent water quality standards of 20 mg/L. Removal of TN (total nitrogen) and TP (total phosphorus) was relatively less effective and median effluent concentrations were approximately 81 and 8 mg/L, respectively. The treatment system did not experience any clogging or accumulation of organic and inorganic solids during the study, and during winter a substantial amount of removal of BOD5 and TSS continued to occur. Overall, the constructed wetland was judged to be an effective sewage treatment system, but not sufficient by itself to attain regional water quality standards. Therefore, treatment of rural sewage by a wetland system should be followed by another process such as use of the effluent for irrigation of agricultural crops (e.g., rice).

Feasibility study of treated sewage irrigation on paddy rice culture.

A feasibility study was performed to examine the agronomic application of the treated sewage on paddy rice culture through field experiment. The domestic sewage was treated using a constructed wetland system, a subsurface flow type consisting of sand and macrophyte. The effluent of the wetland system was diluted to maintain the total nitrogen concentration below 25 mg/L and was used as irrigation water. Addition of the treated sewage to the irrigation water showed no adverse effect on the paddy rice culture; in fact some enhancement was noticed in both growth and yield. Irrigation with the treated sewage after the concentration was adjusted accompanied by conventional fertilization showed a better result, with the yield exceeding that of the control where clean water was used, thus suggesting that reuse of the treated sewage as supplemental irrigation water could be a feasible and practical alternative. For a full-scale application, however, further study is recommended on the specific guideline for controlling the major water quality components in the treated sewage.