Selective removal of chlorinated organic compounds from soil flushing emulsions: Adsorbent regeneration with thermal-activated persulfate and surfactant recovery

Abstract

Hydrophobic organic compounds (HOCs) released into the environment can form nonaqueous phase liquids, contaminating soil and groundwater. Surfactant-enhanced aquifer remediation, followed by extracting a highly contaminated emulsion comprising surfactants and contaminants, is a promising technology for remediating polluted sites. However, the sustainable treatment of the emulsion is crucial. This study presents a two-step method for treating emulsions containing HOCs and surfactants. Firstly, pollutants are selectively adsorbed onto granular activated carbon (GAC) in a column. Secondly, spent GAC is regenerated by oxidizing adsorbed pollutants using persulfate activated at 60 °C. The emulsion was obtained from surfactant-enhanced aquifer remediation at a polluted site with lindane production waste, consisting of E-Mulse® 3 surfactant (12 g L−1) and 28 chlorinated organic compounds (COCs) at a concentration of 9.1 gCOCs L−1. Selective adsorption of COCs was observed since the adsorption kinetic constant was much higher than the E3, being 31.60 and 1.76gGAC−W·mgj−1·h−1 respectively. The adsorption-regeneration cycle was repeated three times. It was found that the GAC adsorbed 90 mgCOCs·gGAC−1 were constant after four cycles (70 % of the COCs adsorption capacity in the first step). The surfactant adsorption decreased by approximately 80 % from 108 to 26 mgE3 gGAC−1 after the third cycle, enabling surfactant recovery from the emulsion. In addition, the remaining amount of persulfate increased from 24 to 39 %, reducing oxidant consumption. Finally, the water effluent obtained after regeneration showed reduced toxicity due to the generation of nontoxic by-products, such as short-chain acids and sulphates. The results obtained proved the GAC-based adsorption/regeneration process was effective and stable over multiple cycles.