Bon-Wun Gu

Evaluation of sediment capping with activated carbon and nonwoven fabric mat to interrupt nutrient release from lake sediments

The aim of this study was to assess the potential application of activated carbon (AC) and nonwoven fabric mats (NWFM) for thin-layer capping in remediation of sediments containing high amounts of carbon, nitrogen, and phosphorus. Laboratory column incubation experiments were performed to analyze the efficiencies of AC and NWFM for blocking nutrients. Under uncapped conditions, dissolved oxygen (DO) was exhausted within three days but under NWFM/AC capping conditions (with NWFM above the AC capping layer), the presence of DO was prolonged until Day 33. Chemical oxygen demand (COD) was lower under all capped conditions than under uncapped conditions, with lowest COD observed with NWFM/AC capping. NH4-N occupied the highest percentage of total nitrogen in the overlying water and its percentage increased as the DO concentration decreased. The capping efficiencies for NH4-N, T-N, and PO4-P with NWFM/AC capping were (66.0, 54.2, and 73.1) %, respectively, which were higher than for other capping conditions. In the case of T-P, capping efficiencies under all capping conditions were almost 100%, indicating that both AC and NWFM effectively interrupted phosphorus release from sediments. Placing NWFM above the AC capping layer was more effective than the opposite arrangement. It can be concluded that NWFM and AC can be successfully used for remediation of lake sediments with high amounts of nitrogen and phosphorus.

Evaluation of sediment capping using zeolite, montmorillonite, and steel slag to immobilize heavy metals

Capping contaminated sediments is an in situ remediation technique by placing capping material on top of the sediments to prevent continued contamination of surface water and biota from contaminated sediments. Capping is considered as much cheaper than dredging and is expected to be very effective to block the diffusion of contaminants in short-term. The research on capping material for controlling the contaminants has been conducted and different capping materials used for each contaminants. Laboratory experiments in a flat flow tank were performed to evaluate the effect of capping materials on heavy metals. The results showed that all capping materials used this study were not effective in interrupting release of As and higher As concentrations in capped condition were observed than uncapped condition. Zeolite had negative effect on the block of Cr release but Cr was significantly reduced by 5 cm of steel slag capping. In contrast to As and Cr, the release of Cd, Ni, and Pb was not observed in all cases including uncapped sediments. Cu and Zn were the heavy metals, which were most significantly influenced by the capping conditions. Cu release from the marine sediments were effectively blocked by capping materials, whereas Cu concentration in uncapped condition were above the Cu criteria concentration during the experimental run. All capping materials were also found to be effective in interrupting release of Zn from the marine sediments. It was concluded that the zeolite, montmorillonite, and steel slag could be used as a potential capping material for interrupting the release of Cd, Cu, Ni, Pb and Zn from the contaminated marine sediments.

Application of response surface methodology and semi-mechanistic model to optimize fluoride removal using crushed concrete in a fixed-bed column

ABSTRACT The aim of this study was to investigate the removal of fluoride from aqueous solutions by using crushed concrete fines as a filter medium under varying conditions of pH 3–7, flow rate of 0.3–0.7 mL/min, and filter depth of 10–20 cm. The performance of fixed-bed columns was evaluated on the basis of the removal ratio (Re), uptake capacity (qe), degree of sorbent used (DoSU), and sorbent usage rate (SUR) obtained from breakthrough curves (BTCs). Three widely used semi-mechanistic models, that is, Bohart-Adams, Thomas, and Yoon-Nelson models, were applied to simulate the BTCs and to derive the design parameters. The Box-Behnken design of response surface methodology (RSM) was used to elucidate the individual and interactive effects of the three operational parameters on the column performance and to optimize these parameters. The results demonstrated that pH is the most important factor in the performance of fluoride removal by a fixed-bed column. The flow rate had a significant negative influence on Re and DoSU, and the effect of filter depth was observed only in the regression model for DoSU. Statistical analysis indicated that the model attained from the RSM study is suitable for describing the semi-mechanistic model parameters.

Assessment on Environmental Characteristics of Organic Paddy and Conventional Paddy by Comparing Their Soil Properties and Water Quality

In this study, we investigated the environmental impact of organic and conventional paddy by monitoring soil properties and water quality. We sampled and analyzed topsoil (0~15 cm), subsoil (15~30 cm), and water of organic and conventional paddy fields in Yongin and Anseong, South Korea. The statistical significance between groups was determined by Duncans multiple range test. The results show that T-P concentrations in both topsoil and subsoil of Anseong paddy were higher than those of Yongin paddy. The significant difference of T-P between organic and conventional paddy was observed in Anseong but not in Yongin. T-N of organic paddy soil was lower than that of conventional paddy in both Anseong and Yongin region. Water content for subsoil of organic paddy in Anseong was significantly different from others, which is consistent with the results of silt-clay content. pH and EC of water in conventional paddy were higher than those in organic paddy. In Anseong, COD, T-P, and PO4-P concentration of conventional paddy were higher than those of organic paddy. The regression analysis presented that there were no significant relationship between soil properties and water quality data except T-N.