A 4-YEAR MASS-BALANCE FOR A NATURAL WETLAND SYSTEM RECEIVING DOMESTICWASTE-WATER

In order to clarify the natural purification potential of a natural we tland having free-flowing water, we performed a four-year study on suc h a wetland system which had been receiving for 12 years the domestic wastewater discharged from a residential area comprised of 45 househol ds. The wetland's removal rate of organic matter throughout the four y ears ranged from 80% for COD to 95% for BOD, whereas the corresponding nitrogen removal rate was comparatively lower. Results indicate that NH4-N release from the bottom sediment and repression of nitrification are the main factors responsible for the wetland's low removal rate o f nitrogen during winter, The wetland purification performance even in winter was determined as follows (g m(-2) d(-1)): 2.2 BOD, 0.81 COD, 1.1 TOC, 0.10 T-N, and 0.023 T-P.