Evaluation of Carbon Uptake and Emissions by Forests in Korea During the Last Thirty Years (1973–2002)

The contribution of Korean forests to carbon sequestration for anthropogenic carbon emissions was evaluated. In addition, monitoring of carbon species released from forest fires was conducted. Despite a high carbon uptake by Korean forests, a tremendous increase in fossil fuel burning resulted in a small contribution by forests to carbon removal. The removal efficiency had a 5–31% range with an average of 12% during the period 1973–2002. In 2000, the amount of carbon released from burned trees corresponded to 1.6% of carbon uptake by forests. The distribution of surface CO concentration (ppb) derived from MOPITT (Measurement of Pollution in the Troposphere) showed high CO levels over the East/Japan Sea on April 10, 2000 when the largest forest fires occurred along the east coast of Korea. Trajectory analysis and ground CO measurements also indicated that CO levels over the East/Japan Sea were influenced by forest fires. This study suggests that continuous monitoring of carbon emissions from forest fires is needed for a more reliable estimate of carbon flux in the environment.     

Effects of calibration on L-THIA GIS runoff and pollutant estimation

Urbanization can result in alteration of a watershed's hydrologic response and water quality. To simulate hydrologic and water quality impacts of land use changes, the Long-Term Hydrologic Impact Assessment (L-THIA) system has been used. The L-THIA system estimates pollutant loading based on direct runoff quantity and land use based pollutant coefficients. The accurate estimation of direct runoff is important in assessing water quality impacts of land use changes. An automated program was developed to calibrate the L-THIA model using the millions of curve number (CN) combinations associated with land uses and hydrologic soil groups. L-THIA calibration for the Little Eagle Creek (LEC) watershed near Indianapolis, Indiana was performed using land use data for 1991 and daily rainfall data for six months of 1991 (January 1-June 30) to minimize errors associated with use of different temporal land use data and rainfall data. For the calibration period, the Nash-Sutcliffe coefficient was 0.60 for estimated and observed direct runoff. The calibrated CN values were used for validation of the model for the same year (July 1-December 31), and the Nash-Sutcliffe coefficient was 0.60 for estimated and observed direct runoff. The Nash-Sutcliffe coefficient was 0.52 for January 1, 1991 to December 31, 1991 using uncalibrated CN values. As shown in this study, the use of better input parameters for the L-THIA model can improve accuracy. The effects on direct runoff and pollutant estimation of the calibrated CN values in the L-THIA model were investigated for the LEC. Following calibration, the estimated average annual direct runoff for the LEC watershed increased by 34%, total nitrogen by 24%, total phosphorus by 22%, and total lead by 43%. This study demonstrates that the L-THIA model should be calibrated and validated prior to application in a particular watershed to more accurately assess the effects of land use changes on hydrology and water quality.     

Upgrading food wastes by means of bromelain and papain to enhance growth and immunity of grass carp (<Emphasis Type="Italic">Ctenopharyngodon idella</Emphasis>)

The fast growing of global aquaculture industry accompanied with increasing pressure on the supply and price of traditional feed materials (e.g., fish meal and soy bean meal). This circumstance has urged the need to search alternative sources of feed stuff. Food waste was used as feed stuff in rearing fish which possess substantial protein and lipid. Grass carp are major species reared in Hong Kong with lower nutritional requirements; it is also an ideal species for investigating the feasibility of using food waste as fish feeds for local aquaculture industry. The growth and immunity, reflected by total protein, total immunologlobulin (IgI), and nitroblue tetrazolium (NBT) activity of grass carp blood, were depressed when feeding with food waste feeds without enzymes. However, the supplementation of bromelain and papain in fish feed enhanced the efficient use of food waste by grass carp, which in turn improved the fish immunity. The present results indicated that the addition of those enzymes could enhance the feed utilization by fish and hematological parameters of grass carp, and the improvement on growth and immunity superior to the control (commercial feed) was observed with the addition of bromelain and papain supplement. Addition of 1 and 2 % mixture of bromelain and papain could significantly enhance the lipid utilization in grass carp.     

Particle-size-fractioned transfer of dioxins from sediments to water columns by resuspension process

Particle-size-fractioned transfer of dioxins from sediments to water columns by resuspension process was investigated, using supernatant samples obtained from shaking experiments of sediment-water pairs simulating natural disturbances. The concentrations (dry-matter mass basis) of individual compounds (Cfraction) in two particle size fractions (0.1-1 and 1-10 μm) in the supernatants were generally slightly higher than those in the original sediment (Csed). Cfraction/Csed ratios ranged from 0.45 to 5.9 (median 1.5) without consistent differences among congener groups or consistent correlations against the number of chlorine atoms. The dioxin concentrations in the water column associated with the remaining sediment particles can therefore be estimated by those in the original sediment and by the concentration of suspended sediment particles in the water. The concentration of each compound in the remaining sediment particles (mostly 0.1-10 μm in size) can be roughly estimated by multiplying the concentration in the original sediment by 1.5.     

PCDD/DF concentrations at the inlets and outlets of wet scrubbers in Korean waste incinerators

To further understand the effects of wet scrubbers on PCDD/DF levels, it was measured the concentrations of PCDD/DF, dust, and other gaseous pollutants at both the inlets and the outlets of seven wet scrubbers. As a result, the concentrations of PCDD/DF at the inlets and outlets of the wet scrubbers ranged from 0.2 to 37.4, and 0.8 to 6.0 ng TEQ N m-3, respectively. With the exceptions of wet scrubbers F and G, the PCDD/DF levels decreased by and large in most wet scrubbers. It was thought that their relatively high removal efficiencies were more increased with heavier loads of dust and particle-bound PCDD/DF. On the other hand, it was also surveyed the increase of gaseous PCDD/DF in wet scrubber, where the total level of PCDD/DF was decreased. However, it was not sure whether it had been resulted from the thermal adsorption/desorption phenomenon between packing materials and emission gases or not. At the very least, however, although there still remains an unexplained aspect for the increase of gaseous PCDD/DF, it is clear that wet scrubbers can be sufficiently applied to remove PCDD/DF to a certain extent, if only removal efficiencies for the particle loads are high, and if a significant part of the PCDD/DF at the inlets is particle associated.     

Effect of amorphous silica and silica sand on removal of chromium(VI) by zero-valent iron

The effect of two surfaces (amorphous silica and silica sand) on the reduction of chromium(VI) by zero-valent iron (Fe(0)) was investigated using batch reactors. The amendment of both surfaces significantly increased the rate and extent of Cr(VI) removal. The rate enhancement by amended surfaces is presumed to result from scavenging of Fe(0)-Cr(VI) reaction products by the provided surfaces, which minimized surface deactivation of Fe(0). The rate enhancing effect was greater for silica compared to sand, and the difference is attributed to silica's higher surface area, greater affinity for reaction products and pH buffering effect. For a given mass of Fe(0), the reactivity and longevity of Fe(0) to treat Cr(VI) increased with increasing dose of silica. Elemental analyses of the reacted iron and silica revealed that chromium removed from the solution was associated with both surfaces, with its mass distribution being approximately 1:1 per mass of iron and silica. The overall result suggests reductive precipitation was a predominant Cr(VI) removal pathway, which involves initial reduction of Cr(VI) to Cr(III), followed by formation of Cr(III)/Fe(III) hydroxides precipitates.     

Reductive dechlorination and biodegradation of 2,4,6-trichlorophenol using sequential permeable reactive barriers: laboratory studies

The reductive dechlorination and biodegradation of 2,4,6-trichlorophenol (2,4,6-TCP) was investigated in a laboratory-scale sequential barrier system consisting of a chemical and biological reactive barrier. Palladium coated iron (Pd/Fe) was used as a reactive barrier medium for the chemical degradation of 2,4,6-TCP, and a sand column seeded with anaerobic microbes was used as a biobarrier following the chemical reactive barrier in this study. Only phenol was detected in the effluent from the Pd/Fe column reactor, indicating that the complete dechlorination of 2,4,6-TCP was achieved. The residence time of 30.2-21.2h was required for the complete dechlorination of 2,4,6-TCP of 100 mg l(-1) in the column reactor. The surface area-normalized rate constant (k(SA)) is 3.84 (+/-0.48)x10(-5)lm(-2)h(-1). The reaction rate in the column tests was one order of magnitude slower than that in the batch test. In the operation of the biobarrier, about 100 microM of phenol was completely removed with a residence time of 7-8d. Consequently, the dechlorination prior to biodegradation turns out to increase the overall treatability. Moreover, the sequential permeable reactive barriers, consisting of iron barrier and biobarrier, could be recommended for groundwater contaminated with toxic organic compounds such as chlorophenols.     

Source identification and characterization of the accumulating non-biodegradable organics in Korean reservoirs

An increase in the chemical oxygen demand (COD) has been noticed in most Korean reservoirs. Therefore, this research systematically investigated the causes of organic accumulation. Samples of soil affecting the quality of water of reservoirs were collected at various sources and analyzed for their organic characteristics. The COD to biochemical oxygen demand (BOD) ratio was used as the key parameter in the evaluation of non-biodegradable (NBD) organic accumulation in the reservoirs. Soil samples containing plant roots were agitated, with the supernatant showing COD/BOD ratios of less than 2.8, while those of the composted tree leaves were greater than 5.0, suggesting that humic substances produced in forest areas are a major cause of NBD organic accumulation in reservoirs. In addition, the organic fractionation of the leachate from leaching tests showed that of the various types of hydrophobic natural organic matter (NOM), the larger molecular weight humic acid makes a greater contribution than fulvic acid to the increase in the NBD COD in Korean reservoirs.     

Enhancement of turbulent scalar mixing and its application by a multihole nozzle in selective catalytic reduction of NOx

The mixing characteristics of a passive scalar in the turbulent flow of a selective catalytic reduction process were numerically and experimentally investigated, focusing especially on an injection nozzle with multiple holes for the reducing agent. The multihole injection nozzle studied has six holes that are perpendicular to the ambient flue gas flow and are located near the tip of the nozzle. Large eddy simulation was applied to the turbulent flow and mixing fields to elucidate the mixing mechanism of the proposed nozzle compared with the single-hole nozzle that is commonly used in the conventional selective catalytic reduction process. From the results, there exist broader regions of higher turbulent intensities for the multihole nozzle than for the conventional single-hole nozzle. These regions are well matched with the positions of high vorticity in the near upstream region of the jet flow issuing from the multiple holes of the nozzle. Consequently, the high turbulent intensities and vorticity magnitudes lead to intensified mixing between the flue gas and the reducing agent. Hence, the most suitable molar ratio between NOx and the reducing agent for the catalytic reaction can be easily obtained within a shorter physical mixing length as a result of the enhanced scalar mixing. Finally, the numerical results were applied to a trial design version of a multihole nozzle, and this nozzle was experimentally tested to confirm its mixing performance.     

Wastewater treatment plants (WWTPs) as a source of sediment contamination by toxic organic pollutants and fecal sterols in a semi-enclosed bay in Korea

Toxic organic contaminants and a macrobenthic community were assayed in sediments collected near a wastewater treatment plant (WWTP) outfall to assess the impact of WWTP discharges on an aquatic environment. Average concentrations of toxic organic contaminants in sediments from 20 locations were 96.7ng TEQ/kg dry matter for PCDD/Fs, 1.84ng TEQ/kg dry matter for dioxin-like PCBs, 29.1microg/kg dry matter for PBDEs, 411microg/kg dry matter for nonylphenols, 1021microg/kg dry matter for fecal sterols, and 928microg/kg dry matter for PAHs. Concentrations of all the organic contaminants and fecal sterols varied widely and there was a clear decrease in concentration gradients with increasing distances from the WWTP outfall. This result suggests that WWTP activities contribute to contamination by organic chemicals. A survey of benthic organisms showed the dominance of a few polychaete species, indicating a deterioration of the macrobenthic community by the WWTP discharge. Non-parametric multidimensional scaling (MDS) ordination and Spearman correlation analyses showed that organic contamination is associated with the benthic community structure. For polychaete species, the sensitive species for organic contaminants was Paraprionospio pinnata, while contaminant-tolerant species were Spiochaetopterus koreana and Capitella capitata. BIOENV analyses of all locations suggested PCDDs and PCDFs as the major contaminants influencing the structure of the macrobenthic community. The present study highlights that continuous WWTP discharges contribute to severe organic contamination and risks for the benthic community in an aquatic ecosystem.