| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 97 === Water is one of our most treasured natural resources. Nevertheless, a rapidly increasing population, climate change, type of irrigation, and long-term water waste is a threat to the water supply worldwide. Recycling treated wastewater is considered one way to fill the deficit in water resources, but there are risks involved. It is important to eliminate those risks to human health and the environment when the recycled wastewater is used to replace irrigation water.
Electronic industries are concentrated in science research parks in Taiwan and their wastewater is collected and treated in wastewater treatment plants. The water quality of treated wastewater must meet regulation standards with a fixed discharge point. Recently, there were 220,000 tons per day of total treated wastewater captured in these wastewater treatment plants. This study investigated the adsorption ability of heavy metals on a top layer of agriculture soil with batch absorption experiments. In addition, soil column tests were used to exanimate the changed soil physical and chemical properties, and total and DTPA-extractable concentrations of heavy metals after it had been irrigated with the electrical industry effluent. Two types of soils, Ts and Cf, were used in this study. The total concentrations of Cd, Cr, Fe, and Mn in soil Ts and the total concentrations of Cd, Fe, Mn, and Zn in soil Cf had significantly decreased due to leaching. Meanwhile, the total decreased concentrations of metals were greater than DTPA-extracted concentrations with different pore volume tests that suggested DTPA-extracted concentrations cannot represent the leached metals. The soil properties had a greater impact on metal leaching concentrations. The leaching concentrations of metals (Cu, Fe, Mn, Ni, and Zn) in the Ts soil were greater than concentrations in soil Cf with the same pore volume of leaching water. The results suggested the higher metal mobility occurred in low pH soil.
Three different pore volume leaching conditions simulated 6.3, 12.5, and 25 years of irrigations in Taiwan. The nine metals did not show similar accumulation to the soil control standards. However, most of the metal concentrations were reduced in the soil after the leaching tests. In addition, concentrations of chloride and sulfate, electric conductivity, and total nitrogen in the effluent were greater than the irrigation water quality standards for the electrical industrial wastewater effluent. If the effluent is used as irrigation water, strict guidelines are required as these water parameters could cause adverse effects to soil and plants. The soil pH can enhance the metal leaching ability which can cause metal leaching to groundwater and adsorption by plants.
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