The performance of a constructed wetland (CW) and wastewater stabilisation pond (WSP) system for sewage reclamation and paddy rice irrigation in a decentralised rural area was examined using a feasibility study. The CW was satisfactory for sewage treatment, with good removal efficiency even in the winter period, but the effluent concentration was relatively high in the winter period owing to the high influent concentration. The CW effluent was further treated in a WSP and the WSP effluent was considered safe for crop irrigation with respect to sewage-borne pathogens. Reclaimed water irrigation did not adversely affect the yield of rice; on the contrary, it resulted in an approximately 50% greater yield than in controls. The chemical characteristics of the soil did not change significantly during the experimental period of irrigation with reclaimed water. In the winter, CW effluent could be stored and treated in a WSP until the spring; the water could then be discharged or reused for supplemental irrigation during the typical Korean spring drought. Overall, sewage treatment and agronomic reuse using a CW-WSP system could be a practical integrated sewage management measure for protecting receiving water bodies and overcoming water shortages in decentralised rural areas.
A water quality model applicable to rice paddies was developed using field data from 1999-2002. Use of the Dirac delta function efficiently explained the nutrient-concentration characteristics of ponded water. The model results agreed reasonably well with the observed data. The ponded-water quality was influenced primarily by fertilization; nutrient concentration was especially high during early cultivation periods. Reducing surface drainage during the fertilization period may substantially reduce nonpoint source loading from paddies. Increased weir heights and shallow irrigation methods were evaluated by the model as practical methods for reducing nutrient loading from paddies. These methods were effective in reducing surface drainage and are suggested as "best management practices" (BMPs) if applied based on site-specific paddy conditions.
This study was conducted to assess the applicability of green roofs as a low impact development (LID) technology to reduce storm water runoff volume and nonpoint source pollutants. Specifically, the water cycle effects and pollutant removal efficiency through six monitoring results were analyzed. Based on the results, the green roof system achieved an average runoff discharge rate of 72% for storage, exhibiting a rainfall outflow reduction rate of about six times greater than that of the ordinary concrete rooftop. The average reduction efficiency of pollutants was 77%, 43%, 74%, 57%, and 43% for TSS, BOD, TOC, TN, and TP, respectively. In addition, the reduction efficiencies for heavy metals, including Cu and Zn, and isomers such as n-H were all greater than 72%. However, this removal efficiency was highly dependent on rainfall, which was observed specifically for nutrients, including TN and TP, which showed a negative removal for a 40 mm rainfall. Therefore, it seems to be better when the green roof system was installed with LID technologies such as infiltration trenches, rain gardens, infiltration planters, and other infiltration facilities.
Due to urbanization and increase in impervious area, changes in natural water circulation system have become a cause of groundwater recharge reduction, streamflow depletion and other hydrological problems. Therefore, this study developed the infiltration planter techniques applied in an LID facility treating roof stormwater runoff such as, performance of small decentralized retention and infiltration through the reproduction of natural water circulation system and use of landscape for cleaning water. Assessment of an infiltration planter was performed through rainfall monitoring to analyze the water balance and pollutant removal efficiency. Hydrologic assessment of an infiltration planter, showed a delay in time of effluent for roof runoff for about 3 hours and on average, 79% of facilities had a runoff reduction through retention and infiltration. Based on the analysis, pollutant removal efficiency generated in the catchment area showed an average of 97% for the particulate matter, 94% for the organic matter and 86-96% and 92-93% for the nutrients and heavy metals were treated, respectively. Comparative results with other LID facilities were made. For this study, facilities compared the SA/CA to high pollutant removal efficiency for the determination to of the effectiveness of the facility when applied in an urban area.
A study was performed to examine the effects of reclaimed-water irrigation on microorganism concentration in the ponded-water of paddy rice plots. Several treatments were used and each one was triplicated to evaluate the change of indicator microorganisms (total coliforms (TC), faecal coliforms (FC), and E. coli) concentrations in 2003 and 2004 growing seasons. Their concentrations increased significantly after irrigation, but decreased by approximately 45% in 24 h. It implies that agricultural activities such as ploughing and fertilising need to be practiced one or two days after irrigation, considering health risks. Treatments with UV-disinfected water irrigation, demonstrated significantly lower concentrations than others, including control plots where natural water was irrigated. The monitoring result from actual paddy rice fields and experimental paddy plots showed that concentrations of indicator microorganisms ranged from 10(2) to 10(5) MPN/100 mL. The field scale water reuse research project is in progress and national guidelines for reclaimed-water irrigation are under preparation in Korea. A comprehensive assessment of existing agricultural practices and a thorough monitoring in the fields as well as treatment plots are recommended to make national guidelines more representative.
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