축산농가 인근 강우유출수 처리습지의 장기운영에 따른 수질변화 및 처리성능 변동 특성

Variation of Water Quality and Treatment Performance during Long-term Operation of the Stormwater Wetland in the Vicinity of Livestock Farm

Water quality data acquired from 80 monitoring cases for last 9 years were analyzed to identify characteristics of variation on the treatment performance at the stormwater wetland. The surrounding areas of the wetland were mainly used for livestock pen and mechanic factories paved with permeable materials. Annual precipitation was in the range of 96 and 131 days with the highest values observed in 2014. Daily precipitation which was recorded less than 30 mm was 97 times, accounting for 85%, and 251 days as the annual interevent time. Suspended solids (SS) concentrations on an annual basis were increased for the first 3 years after wetland was constructed and then maintained its trend at some degrees. The concentrations of COD and TOC were also demonstrated similar patterns to the case of SS till 2011, and then decreased. As for TN, TP, the concentration of N and P in dissolved phases were increased which was not the case for the particulate phase showing decreasing pattern, and this finding could be attributed to the loading activities of livestock waste waters. Results of water quality variation caused by precipitation size were turned out that analyzed constituents were increased in the range below 60 mm but decreased above 60 mm except phosphorous, which could be explained by the flushing effect. Treatment performance during interevent period to deal with SS, COD, TN and TP on an annual basis was turned out with values of 31.9(± 26.3)%, 16.4(± 8.3)%, 33.8(± 20.6)% and 34.1(± 23.4)%. It was observed that annual performance was varied depending on the interevent period, precipitation size and input loads. In addition, it is critical to understand that the treatment performance was decreased as amounts of nutrient loadings were increased, which was also caused by the expansion of livestock pens and limited storage capacity from increased deposition of sediment. In order to improve treatment performance of wetland, it is worthwhile of noticing two points: 1) increasing storage capacity by maintaining dredging facilities properly and 2) reducing input loads with an aid of strict regulations. Also, an alternative strategy to improve treatment capacity could be wetland expansion.