Inhong Song

Application of microbial risk assessment to the development of standards for enteric pathogens in water used to irrigate fresh produce.

Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 x 10(-5) most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 x 10(3) Salmonella per 100 ml and 9.9 x 10(-3) HAV per 100 ml.

Effect of relative humidity on preharvest survival of bacterial and viral pathogens on the surface of cantaloupe, lettuce, and bell peppers.

The purpose of this study was to compare the effects of humidity on the preharvest survival of microbial pathogens on cantaloupe, lettuce, and bell peppers. An additional goal was to evaluate Clostridium perfringens as an indicator of fecal contamination on produce. The microorganisms used in this study included Escherichia coli, E. coli O157:H7, Shigella sonnei, Salmonella enterica subsp. enterica, Clostridium perfringens, hepatitis A virus (HAV), feline calicivirus (FCV), and coliphage PRD1. The study took place in a controlled environment chamber that allowed for the control of temperature (18 to 26 degrees C) and relative humidity. Survival rates under high (mean, 85.7 to 90.3%) and low (mean, 45.1 to 48.4%) relative humidity were compared. The surfaces of the edible portion of each plant were inoculated with the study microorganisms. Samples were collected throughout 2 weeks. More microorganisms survived significantly longer (P < 0.05) on cantaloupe than on lettuce and bell peppers. The type of produce on which each organism experienced the highest inactivation rate tended to change with relative humidity. The survival of microorganisms on produce surfaces was not uniformly affected by relative humidity. Of the studied microorganisms, HAV, PRD1, and C. perfringens were found to have the lowest inactivation rates, whereas FCV and E. coli ATCC 25922 tended to become inactivated most rapidly. C. perfringens generally survived longer than all other bacteria and FCV in all experiments. This trend suggests that C. perfringens may be an acceptable indicator of bacterial contamination and survival in various environments and on different types of crops.

Surface Drainage Simulation Model for Irrigation Districts Composed of Paddy and Protected Cultivation

The objectives of this study were to develop a hydrologic simulation model to estimate surface drainage for irrigation districts consisting of paddy and protected cultivation, and to evaluate the applicability of the developed model. The model consists of three sub-models; agricultural supply, paddy block drainage, and protected cultivation runoff. The model simulates daily total drainage as the sum of paddy field drainage, irrigation canal drainage, and protected cultivation runoff at the outlets of the irrigation districts. The agricultural supply sub-model was formulated considering crop water requirement for growing seasons and agricultural water management loss. Agricultural supply was calculated for use as input data for the paddy block sub-model. The paddy block drainage sub-model simulates paddy field drainage based on water balance, and irrigation canal drainage as a fraction of agricultural supply. Protected cultivation runoff is calculated based on NRCS (Natural Resources Conservation Service) curve number method. The Idong reservoir irrigation district was selected for surface drainage monitoring and model verification. The parameters of model were calibrated using a trial and error technique, and validated with the measured data from the study site. The model can be a useful tool to estimate surface drainage for irrigated districts consisting of paddy and protected cultivation.

Comparing Farming Methods in Pollutant runoff loads from Paddy Fields using the CREAMS-PADDY Model

BACKGROUND: For Non-Point Source(NPS) loads reduction, pollutant loads need to be quantified for major farming methods. The objective of this study was to evaluate impacts of farming methods on NPS pollutant loads from a paddy rice field during the growing season. METHODS AND RESULTS: The height of drainage outlet, amount of fertilizer, irrigation water quality were considered as farming factors for scenarios development. The control was derived from conventional farming methods and four different scenarios were developed based combination of farming factors. A field scale model, CREAMS-PADDY(Chemicals, Runoff, and Erosion from Agricultural Management Systems for PADDY), was used to calculate pollutant nutrient loads. The data collected from an experimental plot located downstream of the Idong reservoir were used for model calibration and validation. The simulation results agreed well with observed values during the calibration and validation periods. The calibrated model was used to evaluate farming scenarios in terms of NPS loads. Pollutant loads for T-N, T-P were reduced by 5 ∼62%, 8∼37% with increasing the height of drainage outlet from 100 mm of 100 mm, respectively. When amount of fertilizer was changed from standard to conventional, T-N, T-P pollutant loads were reduced by 0∼22%, 0∼ 24%. Irrigation water quality below water criteria Ⅳ of reservoir increased T-N of 9∼65%, T-P of 9∼47% in comparison with conventional. CONCLUSION(S): The results indicated that applying increased the height of drainage after midsummer drainage, standard fertilization level during non-rainy seasons, irrigation water quality below water criteria Ⅳ of reservoir were effective farming methods to reduce NPS pollutant loads from paddy in Korea.

Experimental Verification of Incomplete Solute Mixing in a Pressurized Pipe Network with Multiple Cross Junctions

Water quality models based on accurate mixing data at cross junctions are important for estimating concentrations of chemical species in municipal water distribution systems. Recent studies indicate that the instantaneous complete (thus “perfect”) mixing assumption potentially can result in an erroneous prediction of water quality. The present study examines the updated “incomplete” solute mixing model at cross junctions in a network having multiple cross junctions. The model performance in predicting solute transport was evaluated through a series of tracer experiments in a pressurized 5×5 network with 9 cross junctions. The perfect mixing model consistently overestimated solute dilution at cross junctions and predicted evenly distributed solute concentration throughout the network. In contrast, the incomplete mixing model demonstrated uneven distribution patterns with a distinct solute plume, and the corresponding results were significantly more accurate than those based on the perfect mixing assumption...

Effects of temperature and moisture on coliphage PRD-1 survival in soil

The goal of this study was to quantitatively assess the effects of temperature and soil moisture on the survival of coliphage PRD-1 in soil. PRD-1 was added to sandy loam soil at five different soil moisture levels. The soil seeded with PRD-1 was packed into sterile polyethylene jars and exposed to eight different temperatures in an oven. Samples were collected over 14 to 25 days depending on the temperature. The inactivation rate of PRD-1 increased linearly with increased temperature. The inactivation rate gradually decreased when the soil moisture level decreased from 20.9 to 8.9%. However, the inactivation rate increased when the soil moisture content reached 5.1%, suggesting the existence of an optimal soil moisture condition for PRD-1 survival. It is also possible that there is a threshold soil moisture level below which the inactivation of PRD-1 suddenly increases. Marked reductions in recoveries were observed as the soil moisture approached or fell below 5.0% as a result of evaporation. The increased inactivation of PRD-1 due to strong association with soil particles may have caused rapid reductions in recoveries. The evaporation process appeared to affect PRD-1 survival substantially at higher temperatures whereas little effect was observed at lower temperatures. A model developed from this study predicted PRD-1 survival in subsurface soil in field conditions with an average error of 11.0%.

Bias Correction of RCP-based Future Extreme Precipitation using a Quantile Mapping Method ; for 20-Weather Stations of South Korea

The objective of this study was to correct the bias of the Representative Concentration Pathways (RCP)-based future precipitation data using a quantile mapping method. This method was adopted to correct extreme values because it was designed to adjust simulated data using probability distribution function. The Generalized Extreme Value (GEV) distribution was used to fit distribution for precipitation data obtained from the Korea Meteorological Administration (KMA). The resolutions of precipitation data was 12.5 km in space and 3-hour in time. As the results of bias correction over the past 30 years (1976~2005), the annual precipitation was increased 16.3 % overall. And the results for 90 years (divided into 2011~2040, 2041~2070, 2071~2100) were that the future annual precipitation were increased 8.8 %, 9.6 %, 11.3 % respectively. It also had stronger correction effects on high value than low value. It was concluded that a quantile mapping appeared a good method of correcting extreme value.

NITROGEN LOSS DURING SOLAR DRYING OF BIOSOLIDS

ABSTRACT Solar drying has been used extensively to dewater biosolids for ease of transportation and to a lesser degree to reduce pathogens prior to land application. The nitrogen in biosolids makes them a relatively inexpensive but valuable source of fertilizer. In this study, nitrogen loss from tilled and untilled biosolids was investigated during the solar drying process. Samples of aerobically and anaerobically digested biosolids during three solar drying experiments were analyzed for their nitrate (NO3 −) and ammonium (NH4 +) ions concentrations. Nitrogen losses varied depending on the solar drying season and tillage. Although not directly measured, the majority of nitrogen loss occurred through ammonia volatilization; organic nitrogen content (organic N) remained relatively stable for each sample, nitrate concentrations for the majority of samples remained below detectable levels and the decline of ammonium‐nitrogen (NH4 +‐N) generally followed the trend of moisture loss in the biosolids.

Analysis of Nutrient Load Balance in the Reservoir Irrigated Paddy Block

The objective of this study was to investigate the nutrient load balance in the reservoir irrigated paddy block during growing seasons. Idong reservoir irrigation paddy block of 10.3 ha in size was selected to collect hydrologic and water quality data. Irrigation, canal flows, and paddy field drainage were measured using a water level gauge, while water samples were collected and analysed for water quality. The water balance analysis showed that 81 % and 75 % of total outflow were through paddy and irrigation canal drainage during 2011 and 2012, respectively. The water quality of paddy field drainage varied greatly depending on rice cultivation stage ranging from 0.05 to 24.55 mg/L and from 0.01 to 0.76 mg/L for T-N and T-P, correspondently. Paddy field drainage loads during May through June account for 64 % and 76 % in 2012 and 2013, while 82 % and 81 % for T-P in 2011 and 2012, respectively. The Pearson correlation analysis showed that rainfall was significantly correlated with nutrient loads during July through August due to runoff, and irrigation was related with nutrient loads of drainage during some period of July through September due to irrigation return flow. This study results showed characteristics of inflow and outflow nutrient loads from plentiful irrigated paddy block.

Simulation of Agricultural Water Supply Considering Yearly Variation of Irrigation Efficiency

The objective of this study was to evaluate simulation of agricultural water supply considering yearly variation of irrigation efficiency. The water supply data of the Idong reservoir from 2001 through 2009 was collected and used for this study. Total 6 parameters including irrigation efficiency (Es), drainage outlet height, and infiltration, were used for sensitivity analysis, calibration, and validation. Among the parameters, the Es appeared to be the most sensitivity parameter. The Es was calibrated on a yearly basis considering sensitivity and time-varying characteristic, while other parameters were set to fixed values. The statistics of percent bias (PBLAS), Nash-Sutcliffe efficiency (NSE), and root means square error to the standard deviation of measured data (RSR) for a monthly step were 2.7%, 0.93, and 0.26 for the calibration, and 3.9%, 0.89, and 0.32 for the validation, correspondently. The results showed a good agreement with the observations. This implies that the modeling only with appropriate parameter values, apart from modeling approaches, can simulate the real supply operation reasonably well. However, the simulations with uncalibrated parameters from previous studies produced poor results. Thus, it is important to use calibrated values, and especially, we suggest the Es`s yearly calibration for simulating agricultural water supply.