Mild electrokinetic treatment of cadmium-polluted manure for improved applicability in greenhouse soil
Applications of cadmium (Cd) and salinity-containing manures contribute to Cd pollution and salinization in greenhouse soils. In this study, chicken manure polluted with Cd (5.6 mg/kg) was mildly electrokinetically treated (0.25 V/cm) for 48 h with intermittent replacement of catholyte with 20 mM acetic acid solution to remove Cd and salinity for application without need of post-treatment in greenhouse soil. The electrokinetic treatment created pH conditions mainly ranging from 5.0 to 8.0 within the manure for minimizing re-precipitation of desorbed Cd and evaporative loss of ammonium. However, without manure pre-acidification, electrokinetic treatment resulted in negligible removal of total Cd but 61.7% of increase in the small fraction of exchangeable Cd, due to poor desorption but enhanced formation of exchangeable Cd. In contrast, manure pre-acidification with 20 mM acetic acid favored Cd desorption, leading to electrokinetic removal of exchangeable, carbonate-bound, and total Cd by 32.2%, 34.5%, and 14.5%, respectively. Mild electrokinetic treatment of manure with and without pre-acidification resulted in similar removal of salinity (72.3% and 68.0%), similar pH condition (7.2 and 7.4), and basically same evaporative loss of ammonium (14.6% and 14.2%). Overall, the mild electrokinetic treatment considerably lowered the risk of Cd and the salinity from the pre-acidified manure for improved applicability in greenhouse soil, and more studies are needed to enhance the performance of electrokinetic Cd removal from manure.
KeywordsCadmium pollution Ammonium nitrogen Electrokinetic treatment Manure Salinization
Funding for this work was provided by the project “Safe utilization of Cadmium and Lead-polluted Farmland in Typical Sewage Irrigation Area in Northern China” (2015BAD05B03) funded by Ministry of Science and Technology, China, the project “Technology and Product Development for Nitrogen and Phosphorus Pollution Reduction in Greenhouse Soil” (2017YFD08004) funded by Ministry of Science and Technology, China, and the project “Electrokinetic Remediation of Manures Polluted with Heavy Metals” (F14-231-1-41) funded by Bureau of Science and Technology, Shenyang City, China.
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