The feasibility of using bentonite, illite, and zeolite as capping materials to stabilize nutrients and interrupt their release from contaminated lake sediments.

The aim of this study was to assess the feasibility of using bentonite, illite, and zeolite as capping materials to interrupt the release of and sequestrate carbon, nitrogen, and phosphorus from contaminated sediments. Their efficiency was assessed in batch isotherm, column incubation experiments, and nitrogen and phosphorus extraction from the capping materials and sediments. All capping materials contributed to the reduction of dissolved oxygen depletion and chemical oxygen demand in overlying water. Zeolite showed a high adsorption capacity for NH4-N; the zeolite cap produced the lowest NH4-N flux constituting the highest percentage of total nitrogen in the overlying water. Significant changes in water conditions, such as an increased pH (>8) and lowered oxidation reduction potential (<-80 mV) were observed when a bentonite cap was used. Illite showed high capping efficiency (>130%) for both PO4-P and total phosphorus, and phosphorus was adsorbed mainly as the high residual-P fraction (≈90%) in its strongest adsorbed form. The results of this study indicate that illite has potential for use as an agent to deactivate phosphorus in lake eutrophication control techniques.

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

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.

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.