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This study was conducted to identify the characteristics of non-point pollutants discharge in a small agricultural watershed during farming season. for this purpose, the Neoungchon watershed in Goesangun was selected as a typical agricultural area. Runoff and water quality data in the stream, the domestic sewage and the precipitation of the watershed were analyzed periodically from June 1 to November 6 in 2004 and pollutant loads were estimated. As a result the mean concentrations of BOD, SS, TN and TP in the stream were 3.0, 76.7, 8.7, 0.16 mg/L in rainy season and 2.4, 10.0, 3.5, 0.11 mg/L in dry season respectively. Daily discharge of non-point pollutant occurred above of 95% in rainy period. Measured pollutant loads in the watershed were of T-N and of T-P, within the range of other research results. Effluent loads based on guideline of total pollutant to stream management of MOE (Ministry of Environment) were less than delivery loads since the guideline could not reflect the agricultural practices, geomorphic and meteorological characteristics in an agricultural watershed.

A prototype surface flow constructed wetland was built in the upstream area of reclaimed tidal lands to improve the water quality of Lake Sihwa by treating severely polluted stream water. In this study, a tracer test using rhodamine-WT was performed to investigate the flow characteristics and to quantify the observed hydraulic residence time (HRT) for a high-lying cell in the Banwol wetland of the Sihwa constructed wetland. The tracer test indicated that even if flow was mainly observed in the open water area of the Banwol wetland, water flowed continuously in the vegetative area and there was no dead zone. The calculated HRT (51.3 hrs), calculated by dividing the wetland volume by the wetland inflow, exceeded the observed HRT (38.7 hrs), since the short-circuiting of flux resulting from irregular topography and vegetation was not reflected in the calculated HRT. The exit tracer concentration curves were reproduced well by both the plug flow with dispersion and tanks-in-series models, indicating that the performance of the Banwol wetland can be estimated accurately using these models.

The Shihwa constructed wetland was established for the treatment of severely polluted water from Banwoul, Donghwa and Samhwa streams. This study was focused on investigating dynamics of phytoplankton communities in open waters and periphytic algae on reed (Phragmites communis) planting area at 5 stations from October 2001 to July 2002. The concentration of T-N and T-P of inlet stations from the streams were decreased by flowed through the wetland. However, the TN/TP ratios at all stations were shown as a little over 16 indicating that the T-P will play some role as a limitation factor. Phytoplankton communities were identified as a total 413 taxa which were composed of 375 species, 21 varieties, 2 forma and 15 unidentified species. Standing crops of phytoplankton communities and chlorophyll-a concentrations ranged from and respectively, and showed the decreasing tendency after flowing through the wetland at almost all stations. Dominant species were 14 taxa at all stations which were Euglena oblonga and Synura spinosa etc. Periphytic algae on the reed were a total 329 taxa which were composed of 295 species, 13 varieties, 3 forma and 17 unidentified species. The species numbers were recorded in order of Chlorophyceae-Bascillariophyceae-Cyanophyceae-Euglenophyceae-Chrysophyceae. The relative abundance (%) was showed a seasonal variation from Cyanophyceae to Bascillariophyceae and to Chlorophyceae. Chlorophyll-a concentrations, ie. the biomass of periphytic algae were ranged from . Dominant species were 16 taxa which were Lyngbya angusta of Cyanophyceae in the early investigation, and were changed to Stigeoclonium lubricum of Chlorophyceae, and Nitzschia plea of Bacillariophyceae etc. in the late. Species number, standing crops and chlorophyll-a concentrations of phytoplankton and perphytic algae were shown higher values at the inlet stations than the stations after flowing through the wetland.

The objective of this study was to know the qualities of soil and shallow groundwater in plastic film house fields around Central Part of Korea. The study was conducted at 11 sites in Suweon, Hwasung, Pyungtaek, Yongin and Chuncheon through May to August in 1999. Soil textures of plastic films house were mainly sandy loam or loam. Electric conductivity and organic matter content of surface soils mostly exceeded the critical levels for crop production. Average concentration of in the sha]low groundwater was 19.1 mg/L, and it reached almost the limiting level of agricultural groundwater quality (20 mg/L). Moreover about 36% of survey sites exceeded the limiting level of agricultural groundwater quality. Sulfate concentrations also at some sites exceeded agricultural groundwater quality limit level (50 mg/L). Nitrate-N, one of the most important factors in the groundwater quality, had positive correlations with other ions in foundwater.

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).

The feasibility of an absorbent biofilter system was examined for rural wastewater treatment in Korea. Hydraulic loading rates varied from 50 to 250 cm/day. Effluent of the septic tank was fed into the absorbent biofilter, and small ventilation fan was provided to supply air at the rate of 250 L/min to aerate the biofilter. The biofilter system demonstrated high removal rates for BOD5 and TSS at the loading rate of 150 cm/day, generally meeting the Korean effluent water quality standard of 20 mg/L applicable to both. The nutrient removal was less satisfactory than the results of BOD5 and TSS, but it was within the expected range of biological treatment processes. Considering the abnormally high influent concentration of nutrients during the experiment, better performance results could have been obtained if ordinary domestic wastewater was used. The treatment efficiency decreased during low temperature period in winter, thus enhancement of the system applicable to all seasonal temperature ranges i...

This study focused on estimating a methane (CH4) inventory and developing mitigation options in South Korea, and was performed jointly in an integrated national research program on CH4 from rice fields conducted by three National Agricultural Research Institutes, under the Rural Development Administration during 1993-1997. Methane emissions were measured by a closed chamber method, in rice plots at three locations (Suwon, Iksan, and Milyang) with the single rice cropping system. All experimental data from 5 years of study were summarized and used for calculating nation-wide CH4 emissions. Temperature, soil type, cultural practices, water management, organic matter management, and cultivar selection significantly affected the fluctuations of CH4 emissions. The two most promising mitigation options for reducing emissions were altered water management, in particular mid-season aeration by short-term drainage, and improved organic matter management, by promotion of aerobic degradation through composing or soil incorporation. Annual total CH4 emission in Korea changed from 410Gg in 1990 to 339Gg in 2000, due mainly to a decrease in the cultivated area of paddy rice. If we convert annual CH4 emission to Global Warming Potential as CO2 equivalent, it amounts to 7.1 M CO2 t yr(-1) of greenhouse gas emitted to the atmosphere in 2000 from the rice fields in Korea, which is just 5.3% of the annual CO2 emission from the industry and energy sector. More importantly, the balance between CO2 uptake by photosynthesis and CO2 emission is positive (a net sink), so that rice culture actually has net benefits for the global atmospheric carbon issue. Further reductions in emission amounts, by following recommendations in this article, could make these benefits even greater.

A bench-scale absorbent biofilter system combined with a conventional anoxic process was investigated in regard to its feasibility for removing organic as well as nutrient materials from small community wastewater in Korea. A polyurethane biofilter medium with high porosity and a large surface area were used for the aerobic system. Part of treated wastewater was recirculated into the anoxic process to promote removal rate of nutrients. At three different ratios of recirculation, the BOD and SS of treated wastewater satisfied standard regulations for a small wastewater treatment facility (10 mg/l) during the overall experimental period. The system reduced the concentration of BOD from approximately 130 mg/l to 6.1 (removal rate of 95.2%) and 1.7 mg/l (removal rate of 98.7%). These results correspond to recirculation ratios of 1 and 2, respectively. A further increase of the recirculation ratio did not significantly improve the removal rate or further reduce effluent BOD concentration. Nutrients such as nitrogen and phosphorus also were removed effectively, with maximum removal rates of 65.3 and 84.1% for nitrogen and phosphorus, respectively. The recirculation ratio for optimum nitrogen removal was 2, while the removal of phosphorus continued to increase across the entire range of recirculation ratios tested. With a recirculation ratio of 2, the total phosphorous removal rate increased dramatically as initial ammonium concentration increased, while nitrogen removal was not affected in this manner. During the experimental period of 2 years, the system was quite stable, requiring the minimum amount of maintenance and a relatively low cost compared to other utility expenses. Based on the experimental data, the proposed anoxic-biofilter aerobic recirculation system might be used as a new alternative technology for wastewater treatment in small communities in Korea.

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.