Ji-Hong Jeon

Model Development for Nutrient Loading Estimates from Paddy Rice Fields in Korea

Abstract 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.

Feasibility Study of UV Disinfection for Agricultural Reuse of Secondary Level Effluent in Korea

Abstract 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 × 104 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 60 s exposure using 17, 25, and 40 W lamps. The microorganisms often exceeded 200 MPN/100 mL with 17 and 25 W lamps, but were completely removed with 40 W lamp in one cylindrical chamber. Disinfection with two chambers in series demonstrated complete removal for all the experiments. About 30 mW·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.

HSPF-Paddy Development for Simulating Pollutant Loadings from Paddy Fields

The Hydrological Simulation Program - FORTRAN (HSPF) was modified to simulate nonpoint pollutant loadings from paddy fields using a field experimental data collected during 2001-2002. The concept of a `dike height` was added in a modified HSPF code, named HSPF-Paddy, to consider the function of retaining water by a weir at the field outlet. The effect of fertilization on the variances of nutrients on the soil surface and shallow soil layer was described mathematically with a Dirac delta function (or first-order kinetics). As confirmed through model verification, the HSPF-Paddy modifications were shown to represent the function of retaining water, varied ponded water, and surface runoff by forced drain during both rainy and non-rainy seasons and reasonably predicted the water balance and nutrients behavior in paddy fields. It is a distributed watershed model which, with the paddy modifications, can now simulate nonpoint pollutant loadings where paddy fields are dominant, and it can be used to evaluate the effects of paddy fields on the water quality at a basin scale, and assess the impacts of proposed BMPs applied to paddy fields.