Engineering application of in-situ remediation technology of groundwater pollution in ionic rare earth mining area
The feasible in-situ remediation technology route was explored to solve the groundwater acidification and high concentration nitrogen pollution in ionic rare earth mining areas.A typical remaining ionic rare earth mining area in Guangdong Province was selected as pilot site.The project of spanned seven months and employed an integrated technology combing phytoremediation,in-situ chemically coupled microbial remediation and permeable reactive barrier(PRB).For the phytoremediation project,high nitrogen-absorbing herbs such as vetiver and Miscanthus were planted with density of 4 plants per m2,and the seeding amount was 25 g·m-2.This strategy effectively reduced the downward migration of surface soil nitrogen.For in-situ chemically coupled microbial remediation project,300 injection wells were installed in the area with high concentration of NH4+-N polluted for targeted remediation.The process involved dynamically regulated of aerobic nitrification and anaerobic denitrification through intermittent aeration and high-pressure injection of alkali,microbial agent and zero-valent iron(ZVI).The technical parameters such as pH was adjusted to 7～8,with effective bacteria and Fe content in aquifer medium exceeding 105 CFU·g-1 and 2 mg·g-1,respectively.The PRB,positioned downstream of the pilot area,further purified the groundwater.The volume of PRB was 20 m×10.5 m×4.9 m,filling with 11 t microbial agent,20 t ZVI,3 t alkali agent,22 t corncob,400 t zeolite and 100 t biochar.After remediation,the high value of groundwater NH4+-N pollution in the pilot site was reduced by more than 90％.The water quality downstream of the PRB was better than the Class Ⅲ standard(GB/T 14848-2017),and the highest removal rates of NH4+-N and NO3--N reached 99.7％and 96.9％,respectively.The pilot project showed remarkable remediation efficacy,placing it at the forefront of similar applications,and holding considerable engineering and practical value for future implementations.
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