Experimental study on the screening of high-efficiency flushing agents and the optimum injection modes adaptable for landfill leachate-contaminated soil

Abstract

Abstract In order to study the flushing efficiency of different leaching agents on the mixed contaminated soil in landfill, five surfactants (SDS (sodium dodecyl sulfate), SDBS (sodium dodecyl benzene sulfonate), Tween 80, RL (rhamnolipid), and saponin) and three chelants (EDDS ([S,S]-ethylene-diamine-disuccinic acid), EDTA (ethylene- diaminetetraacetic acid), and CA (citric acid)) were selected to carry out batch tests and one-dimensional column tests. In addition, the influence of injection conditions on the flushing efficiency of saponin was also evaluated. The results show that the saponin with low COD and degradability performed the best removal efficiency of the selected eluents. The extraction rates of total Cr, Cr (VI), ammonia nitrogen, and COD increase with increasing saponin concentration. In the batch test, the extraction rates of total nitrogen were less than 40%, and it was not sensitive to the concentration. Saponin can simultaneously extract heavy metals (total Cr and Cr (VI)), total nitrogen, ammonia nitrogen, and organics from the contaminated soil. The leaching effect of saponin is obviously different under different injection modes. For contaminated soil dominated by total Cr or Cr (VI), continuous injection is recommended. If total nitrogen or ammonia nitrogen is the priority target, the step-gradient injection can demonstrate better removal efficiency. Muti-pulse injection is preferred when organics are the main factor in mixed contaminated soil.