The extraction efficiency of heavy metals from soils using three forms of gamma poly-glutamic acid (γ-PGA) as the washing agents was investigated. Controlling factors including agent concentrations, extraction time, pH, and liquid to soil ratio were evaluated to determine the optimum operational conditions. The distribution of heavy metal species in soils before and after extraction processes was analyzed. Up to 46 and 74% of heavy metal removal efficiencies were achieved with one round and a sequential extraction process using H-bonding form of γ-PGA (200 mM) with washing time of 40 min, liquid to solid ratio of 10 to 1, and pH of 6. Major heavy metal removal mechanisms were (1) γ-PGA-promoted dissolution and (2) complexation of heavy metal with free carboxyl groups in γ-PGA, which resulted in heavy metal desorption from soils. Metal species on soils were redistributed after washing, and soils were remediated without destruction of soil structures and productivity.
In this study, a full survey of pollutant sources and water quality was conducted, followed by the application of a water quality model (Water Quality Analysis Simulation Program, WASP) to establish strategies of water quality control in Carp Lake, Taiwan. Results of the field investigation show that both point and non-point source (NPS) pollutants were responsible for the poor water quality. The contributions of biochemical oxygen demand (BOD) from point source and NPS pollution were 45.9 and 55.1%, respectively. About 80% of total phosphorus (TP) were contributed by NPS. Additionally, point source and NPS pollution discharged 55.5 and 44.5% of NH 3 -N load, respectively. The Carlson's Trophic State Index ranged from 61.9 to 69.2 showing serious eutrophic problems in Carp Lake. The calculated BOD, NH 3 -N, and TP carrying capacity were approximately 2.8, 0.42, and 0.15 kg per day, respectively. However, the current pollutant loadings are approximately 3.0-5.5 times the calculated carrying capacity. With the help of the calibrated WASP model, remedial strategies for the lake water from short-term to long-term were developed. The completion of the small local sewer system to remove 80% of the point source pollution can serve as a short-term goal while 40-60% of NPS removal by natural treatment systems may serve as a mid-term goal. Furthermore, 80% of both source point and NPS pollution removal can be considered as a long-term strategy. Results of heavy metal analysis show that the enriched sediment would be safe for agricultural applications.
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