The Analysis of Heavy Metal Transport Mechanism and Electrolytic Reduction Method for Remediation of Agricultural Ditches

Li-Chi Chiang, and Ci-Jyun Liao

Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei 10617, Taiwan

Abstract: The complex sources of heavy meatal pollution in agricultural lands include: inappropriate discharge, contaminated irrigation water, fertilizer application and atmospheric fallout. The excessive heavy metal concentration can affect crop production and quality. In Taiwan, there are more than 1000 hectare of contaminated agricultural lands, which are mainly located in Taoyuan, Changhua and Kaohsiung. This study aims to analyze the heavy metal concentration in water and the bottom mud to establish the water-sediment heavy metal transport model for the agricultural ditches, Sankuaizho, in Taoyuan, and further evaluate the effect of heavy metal desorption by the electrolytic reduction method. The research results showed that the water body of the Sankuaizho is mainly polluted by heavy metals such as Cu, Ni, and Zn, but only Cu exceeds the water quality standard for irrigation (> 0.2 mg/L). The sediment is polluted by heavy metals, such as Cr, Cu, Ni, Pb and Zn, especially Cu pollution is the most severe one. The electrolytic reduction method could effectively remove heavy metals from bottom mud in terms of the electrolytic reduction efficiency ranged between 43.93% and 97.52%. The WASP simulation results showed that the concentration of heavy metals (copper, zinc, and nickel) at the most downstream (segment 7) are highest when mixed with the polluted water from the upstream flow, which is mainly resulted from the effluent from the electronics factory. Compared to the observed data, the MAPE values of model simulation results are: copper = 47.12%, zinc = 26.62%, nickel = 36.66%, showing that the WASP model performs well and reasonably. The research results of this study could be used as a reference for future decision making to improve the water quality and solve the bottom mud issues.