L. H. Kim

Seasonal nutrient uptake of plant biomass in a constructed wetland treating piggery wastewater effluent.

The surface-flow constructed wetland (CW) located in Nonsan City, South Korea, and constructed as the final stage of a piggery wastewater treatment plant that aims to treat high nutrient content effluent during dry days and stormwater runoff during wet days was monitored from October 2008 to November 2011. This research investigated the seasonal nutrient uptake of plant biomass in the CW and nutrient concentration changes in each treatment region under monsoon and temperate climate conditions. Results showed that the mean total nitrogen removal during summer (June to August) was higher by 13% than in spring (March to May), while total phosphorus removal was higher by 22% in fall (September to November) than in winter (December to February). All plants in the CW reached their maximum biomass coverage and weight in summer and minimum growth in winter. The highest N and P content in plants occurred in September with 583.2 g/m(2) and August with 62.0 g/m(2), respectively. Based on the results, it is recommended that the harvesting of plants should be conducted during the time of the peak nutrient uptake and before the plants release the nutrient content back to the CW. The dependence of nutrient removal efficiency on plants is not so significant. In order to increase the nutrient removal rate by plant uptake, it is suggested that the treatment regions in the CW be covered by plants.

Treatment performance of a constructed wetland during storm and non-storm events in Korea.

The efficiency of a free water surface flow constructed wetland (CW) in treating agricultural discharges from stream was investigated during storm and non-storm events between April and December, 2009. Physico-chemical and water quality constituents were monitored at five sampling locations along the flow path of the CW. The greatest reduction in pollutant concentration was observed after passing the sedimentation zone at approximately 4% fractional distance from the inflow. The inflow hydraulic loading, flow rates and pollutant concentrations were significantly higher and variable during storm events than non-storm (baseflow) condition (p <0.001) that resulted to an increase in the average pollutant removal efficiencies by 10 to 35%. The highest removal percentages were attained for phosphate (51 ± 22%), ammonium (44 ± 21%) and phosphorus (38 ± 19%) while nitrate was least effectively retained by the system with only 25 ± 17% removal during non-storm events. The efficiency of the system was most favorable when the temperature was above 15 °C (i.e., almost year-round except the winter months) and during storm events. Overall, the outflow water quality was better than the inflow water quality signifying the potential of the constructed wetland as a treatment system and capability of improving the stream water quality.

Treatment of suspended solids and heavy metals from urban stormwater runoff by a tree box filter

Particulates, inorganic and toxic constituents are the most common pollutants associated with urban stormwater runoff. Heavy metals such as chromium, nickel, copper, zinc, cadmium and lead are found to be in high concentration on paved roads or parking lots due to vehicle emissions. In order to control the rapid increase of pollutant loads in stormwater runoff, the Korean Ministry of Environment proposed the utilization of low impact developments. One of these was the application of tree box filters that act as a bioretention treatment system which executes filtration and sorption processes. In this study, a tree box filter located adjacent to an impervious parking lot was developed to treat suspended solids and heavy metal concentrations from urban stormwater runoff. In total, 11 storm events were monitored from July 2010 to August 2012. The results showed that the tree box filter was highly effective in removing particulates (up to 95%) and heavy metals (at least 70%) from the urban stormwater runoff. Furthermore, the tree box filter was capable of reducing the volume runoff by 40% at a hydraulic loading rate of 1 m/day and below.

Diffuse pollutant unit loads of various transportation landuses

ABSTRACT A four-year monitoring study was conducted to determine the diffuse pollutant unit loads for the six representative transportation landuses (i.e., highway, parking lot, bridge, service area and toll gate) in urban areas in Korea. Pollutant event mean concentrations (EMCs) were calculated from 123 storm events at eleven sites and the average annual rainfall and runoff coefficients were determined to estimate the unit loads using the National Institute of Environmental Research (NIER) method. Apparent differences in the unit load values existed among landuses as explained by the high variability of EMCs for different rainfall events. The study has found that runoff from bridges and highways contained the highest loadings of TSS and COD while service areas are the primary sources of nutrients and metals. The results of this study could be used by the Ministry of Environment (MOE) to separate the unit loads of transportation landuses from the urban area category in the current unit load system. The v...

Investigation of stormwater runoff strength in an agricultural area, Korea

ABSTRACT To manage and control the nonpoint source (NPS) pollution and to improve the water quality of impaired streams, rivers and lakes, practices including constructed wetlands, permeable pavement, swales and others are being attempted in the world. Before applying these techniques, an analysis of stormwater runoff characteristics should be understood due to the complexity in estimating system design factors for best management practices (BMPs). This study investigates the stormwater discharge from an agricultural area in Korea. Based on this investigation, pollutant and flow coefficient of variation (PFCoV) values were developed in an attempt to explain the stormwater runoff in the agricultural area. Four field studies categorized by rainfall type were then employed to assess the PFCoV values. The results show that the physical meaning of PFCoV values indicates the variation of NPS pollutants during a storm event. As such, this simple and meaningful result can be applied to a wide range of stormwater ...

System design and treatment efficiency of a surface flow constructed wetland receiving runoff impacted stream water

This study reported the efficiency of a free water surface flow constructed wetland (CW) system that receives runoff impacted stream water from a forested and agricultural watershed. Investigations were conducted to examine the potential effect of hydraulic fluctuations on the CW as a result of storm events and the changes in water quality along the flow path of the CW. Based on the results, the incoming pollutant concentrations were increased during storm events and greater at the near end of the storm than at the initial time of storm. A similar trend was observed to the concentrations exiting the CW due to the wetland being a relatively small percentage of the watershed (<0.1%) that allowed delays in runoff time during storm events. The concentrations of most pollutants were significantly reduced (p < 0.05) except for nitrate (p = 0.5). Overall, this study suggests that the design of the system could feasibly function for the retention of most pollutants during storm events as the actual water quality of the outflow was significantly better by 21-71% than the inflow and the levels of pollutants were reduced to appreciable levels.

Development of a horizontal subsurface flow modular constructed wetland for urban runoff treatment

Constructed wetlands (CWs) are well recognized as having low construction and maintenance cost and low energy requirement. However, CW design has been mainly based on rule-of-thumb approaches. In this study, the efficiency of a modular horizontal subsurface flow (HSSF) CW using four different design schemes was investigated. Based on the results, the four systems have attained more than 90% removal of total suspended solids and more than 50% removal efficiency for total phosphorus, PO(4)-P and Zn. The planted system achieved higher pollutant removal rates than the unplanted system. In terms of media, bottom ash was more effective than woodchip in reducing the pollutants. Considering the flow length, optimum removal efficiency was achieved after passing the sedimentation tank and vertical media layer; with respect to depth, more pollutants were removed in the upper sand layer than in the lower gravel layer. This study recommended a surface area of 0.25 to 0.8% of catchment area for planted CW and 0.26 to 0.9% for unplanted CW using the 7.5 to 10 mm design rainfall.

Phosphorus mass balance in a surface flow constructed wetland receiving piggery wastewater effluent

This research was conducted to investigate the phosphorus forms present in water, soil and sediment and to estimate the phosphorus mass balance in a surface flow constructed wetland (CW). Water quality and sediment samples were collected from each cell along the hydrologic path in the CW from October 2008 to December 2010. At the same time, three dominant plant species (e.g. common reed and cattails) were observed through the measurement of the weight, height and phosphorus content. Based on the results, the orthophosphate constituted 24-34% of total phosphorus in water for each cell. The overall average phosphorus removal efficiency of the CW was approximately 38%. The average inflow and outflow phosphorus loads during the monitoring period were 1,167 kg/yr and 408 kg/yr, respectively. The average phosphorus retention rate was 65%, was mainly contributed by the settling of TP into the bottom sediments (30%). The phosphorus uptake of plants was less than 1%. The estimated phosphorus mass balance was effective in predicting the phosphorus retention and release in the CW treating wastewater. Continuous monitoring is underway to support further assessment of the CW system and design.

Particle removal properties of stormwater runoff with a lab-scale vortex separator

ABSTRACT A lab-scale vortex separator, based on a swirling motion to remove settleable particles, was used to remove suspended solids in urban stormwater runoff. However, the treatment is limited to the removal of large settleable particles. The synthesized stormwater runoff was made with tap water and the addition of road sediment. The vortex separator has internal components designed to enhance vortex separation by minimizing the turbulence, increasing the efficiency, and preventing captured pollutants from washout. As the flow continues to spiral down around the inlet baffle, a low energy vortex motion directs settleable particles into the protected sediment storage zone. Advanced vortex separation provided an extendable and stabilized flow path while protecting the captured pollutants for a wide range of flow rates. The range of the inflow rate was 30–115 l/m, and the size of the influent particles varied from 75 to 200 μm. Overall removal efficiencies of 51.8% for SS, 26.6% for COD, 70.5% for TP, and...

Comparison of the treatment performance of hybrid constructed wetlands treating stormwater runoff

This study was conducted to compare the treatment performance of two hybrid constructed wetlands (CWs) in treating stormwater runoff. The hybrid CWs were composed of a combination of free water surface (FWS) and horizontal subsurface flow (HSSF) CWs. Based on the results, strong correlation exists between potential runoff impacts and stormwater characteristics; however, the low correlations also suggest that not only the monitored parameters contribute to stormwater event mean concentrations (EMC) of pollutants, but other factors should also be considered as well. In the hydraulic and treatment performance of the hybrid CWs, a small surface area to catchment area (SA/CA) ratio, receiving a high concentration of influent EMC, will find it hard to achieve great removal efficiency; also a large SA/CA ratio, receiving low concentration of influent EMC, will find it hard to achieve great removal efficiency. With this, SA/CA ratio and influent characteristics such as EMC or load should be considered among the design factors of CWs. The performance data of the two CWs were used to consider the most cost-effective design of a hybrid CW. The optimum facility capacity (ratio of total runoff volume to storage volume) that is applicable for a target volume reduction and removal efficiency was provided in this study.