การประเมินผลเชิงวิศวกรรมและเศรษฐศาสตร์ในการฟื้นฟูดินนาข้าวปนเปื้อนแคดเมียมโดยใช้อนุภาคเหล็กประจุศูนย์เป็นสารปรับเสถียรและสารสกัดล้างดินที่เป็นมิตรต่อสิ่งแวดล้อม

Abstract

This study was conducted to evaluate remediation techniques for Cd contaminated soil in paddy fields in Mae Sot District, Tak Province, and Northwestern Thailand. These areas in important agricultural areas have fields that are contaminated with Cd. Studies have shown that rice samples from these areas contain unsafe levels of Cd and effect on health villagers. It is necessary therefore to find methods to decontaminate these fields. The remediation techniques included using ZVI for Cd immobilization as a soil amendment, separation of contaminated ZVI from the soil by the machine as soil washing on paddy field as pilot-scaled and solar-powered electrokinetic separation in the batch experiment. In addition, the economic decision analysis was assessed to make an appropriate decision on a remedial selection. The pilot-scale experiments on Cd-contaminated paddy restoration performed via magnet-assisted soil washing using zerovalent iron (ZVI) particles and compared soil amendment using biochar, ZVI, and a combination of biochar and ZVI (BZVI) by researchers and community researchers. Magnet-assisted soil washing followed by ZVI amendment (0.5%) successfully reduced the Cd concentration in rice grain to 0.33 mg kg-1 to lower than the safety guideline (0.4 mg kg 1) and caused slight stress on rice growth. Therefore, a magnet-assisted soil washing followed by the ZVI amendment (0.5%) is a promising alternative from all compared techniques. An alternative technique to the batch experiment, using ZVI (MZVI, NZVI, and Fe-rod) with the solar-powered electrokinetic separation was evaluated for this Cd contaminated area in the batch experiment. The results revealed the application EK&NZVI with SC can increase the voltage (from 6.61V to 7.38V), decrease the Cd in soil (53.14%-66.31%) and increase the Cd adsorption in NZVI (16.5%-20.66%) more than other iron (MZVI and Fe-iron). The EK&NZVI with SC is also able to reduce the exchangeable CD form and increase Fe-Mn oxide and residual forms especially Fe-Mn oxide. Therefore, using EK&NZVI with SC is the best for Cd reduction and Cd movement to the cathode region when compared to MZVI and Fe-iron.

However, techniques (biochar amendment, soil washing and electrokinetic) were assessed with the integrated economic decision analysis. The decision analysis will make an appropriate decision on a remedial selection with maximum social benefit. Alternative techniques were compared with phytoremediation and other risk assessments and management activities in the past and using Monte Carlo Simulation to predict the health costs of a villager living an area where there are contamination problems. This result indicates that the highest cost is in non-remediation and the only risk assessment and management by the Thai government around 3.6 million-baht rai-1 year-1, which was derived from health costs. While the alternative restoration costs present lower costs due to the reduction of the health costs of villagers and imply that in that area, they should apply the alternative restoration methods for reducing contamination and adverse health effects. This study recommends applying soil washing for Cd contamination in agricultural soil in the Mae Sot District, Tak Province in Thailand at an approximate cost of 1,404-baht rai-1 over 2 years.

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