Biomedical subjects

Chun G Yoon

Publications and source records attributed to Chun G Yoon.

4 recordsLinked to original sources

PubMed2006

Estimating the microbial risk of E. coli in reclaimed wastewater irrigation on paddy field.

Microbial risk was quantified to assess human health risk as a result of exposure to E. coli in reclaimed wastewater irrigation. Monitoring data on E. coli were collected from pond water in paddy rice plots during the growing season. Five treatments were used and each was triplicated to evaluate the changes in E. coli concentrations in experiments performed in 2003 and 2004. The Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion among farmers and neighboring children. A Monte Carlo simulation (10,000 trials) was conducted to estimate the risk associated with uncertainty. In this study, risk values ranged from 10(-4) to 10(-8). UV-disinfected irrigation water showed a lower risk value than others, and its level was within the range of the actual paddy rice field with surface water. Agricultural activity was thought to be safer after 1-2 days, when the paddy field was irrigated with reclaimed wastewater. Also, children were found to have a greater risk of infection with E. coli. This paper should be viewed as a first step in the application of quantitative microbial risk assessment of wastewater reuse in paddy rice culture.

Agriculture↗

PubMed2004

Feasibility study of UV disinfection for agricultural reuse of secondary level effluent in Korea.

A pilot study was performed to examine the feasibility of UV disinfection for agricultural reuse of reclaimed water. The effluent from the bio-filter of a 16-unit apartment was used as input to the flow-through type UV disinfection system, with average suspended solid (SS) and biological oxygen demand (BOD) concentrations of 3.4 and 5.9 mg/L, respectively, and a mean level of total coliforms in the range of 1.5 x 10(4) MPN/100 mL. UV disinfection was found to be effective, in that it reduced mean concentration of indicator microorganisms (total coliform [TC], fecal coliform [FC], and E. coli) to less than 100 MPN/ 100 mL within 60s exposure using 17, 25, and 40 W lamps. The microorganisms often exceeded 200 MPN/100 mL with 17 and 25W lamps, but were completely removed with 40W lamp in one cylindrical chamber. Disinfection with two chambers in series demonstrated complete removal for all the experiments. About 30 mW x s/cm2 was thought to be adequate for the disinfection of secondary effluent to keep the suggested bacterial standards of 100 MPN FC/100 mL for agricultural reuse. Water quality effect on the UV efficiency was not apparent within the experimental conditions. Statistical analysis showed that the removal rates of TC, FC, and E. coli did not significantly vary with turbidity, dissolved organic matter (DOM), or SS concentrations (p = 0.05). Photo-reactivation problems after UV disinfection might be a lesser concern in agricultural reuse than for other uses, due to exposure of water to solar radiation and resulting inactivation. Overall, UV disinfection of effluent from secondary level wastewater treatment plants in Korea was thought to be an effective and feasible alternative for agricultural reuse, and thus it is strongly recommended.

Agriculture↗

PubMed2004

Seasonal performance of constructed wetland and winter storage pond for sewage treatment in Korea.

A pilot study was performed from July 1998 to December 2002 to examine the feasibility of a constructed wetland system for sewage treatment in small communities of Korea. To maintain treatment performance during the winter period, an intermittent-discharge pond was connected to the wetland; its effects were evaluated from December 2001 to April 2003. The subsurface flow (SSF) wetland was satisfactory for treating sewage with good removal efficiency even during the winter period. The wetland effluent concentrations of BOD5 and TSS were often higher in winter than in the growing season, but this was explained by the higher loading rates, rather than lower removal efficiency. The relatively poor-quality wetland effluent was further polished during winter in the pond. The upper layer of the pond water column became remarkably clear immediately after ice melt. Overall, the wetland system was found to be adequate for treating sewage with stable removal efficiency, and the intermittent-discharge pond was found to be effective for further polishing if necessary. Therefore, a wetland and subsequent pond system is recommended as a practical alternative for treating sewage in small communities in Korea, and partial discharge of pond water in March is suggested.

Ecosystem↗

PubMed2004

Model development for nutrient loading estimates from paddy rice fields in Korea.

A field experiment was performed to evaluate water and nutrient balances in paddy rice culture operations during 2001-2002. The water balance analysis indicated that about half (50-60%) of the total outflow was lost by surface drainage, with the remainder occurring by evapotranspiration (490-530 mm). The surface drainage from paddy fields was mainly caused by rainfall and forced-drainage, and in particular, the runoff during early rice culture periods depends more on the forced-drainage due to fertilization practices. Most of the total phosphorus (T-P) inflow was supplied by fertilization at transplanting, while the total nitrogen (T-N) inflow was supplied by the three fertilizations, precipitation. and from the upper paddy field, which comprised 13-33% of the total inflow. Although most of the nutrient outflow was attributed to plant uptake. nutrient loss by surface drainage was substantial, comprising 20% for T-N and 10% for T-P. Water and nutrient balances indicate that reduction of surface drainage from paddy rice fields is imperative for nonpoint source pollution control. The simplified computer model, PADDIMOD, was developed to simulate water and nutrient (T-N and T-P) behavior in the paddy rice field. The model predicts daily ponded water depth, surface drainage, and nutrient concentrations. It was formulated with a few equations and simplified assumptions, but its application and a model fitness test indicated that the simulation results reasonably matched the observed data. It is a simple and convenient planning model that could be used to evaluate BMPs of paddy rice fields alone or in combination with other complex watershed models. Application of the PADDIMOD to other paddy rice fields with different agricultural environments might require further calibration and validation.

Agriculture↗