Effect of short-chain organic acids on the enhanced desorption of phenanthrene by rhamnolipid biosurfactant in soil–water environment

This study investigated the effect of short-chain organic acids on biosurfactant-enhanced mobilization of phenanthrene in soil–water system. The desorption characteristics of phenanthrene by soils were assessed in the presence of rhamnolipid and four SCOAs, including acetic acid, oxalic acid, tartaric acid and citric acid. The tests with rhamnolipid and different organic acids could attain the higher desorption of phenanthrene compared to those with only rhamnolipid. Among the different combinations, the series with rhamnolipid and citric acid exhibited more significant effect on the desorption performance. The removal of phenanthrene using rhamnolipid and SCOAs gradually increased as the SCOA concentration increased up to a concentration of 300 mmol/L. The effects of pH, soil dissolved organic matter and ionic strength were further evaluated in the presence of both biosurfactant and SCOAs. The results showed that the extent of phenanthrene desorption was more significant at pH 6 and 9. Desorption of phenanthrene was relatively lower in the DOM-removed soils with the addition of biosurfactant and SCOAs. The presence of more salt ions made phenanthrene more persistent on the solid phase and adversely affected its desorption from contaminated soil. The results from this study may have important implications for soil washing technologies used to treat PAH-contaminated soil and groundwater.

► SCOAs facilitate the phenanthrene desorption in the presence of rhamnolipid.
► Ternary and binary SCOAs at high concentration lead to more desorption.
► Soil property influences phenanthrene behaviors with use of rhamnolipid and SCOAs.
► Adjusting the pH and ionic strength can control the combined effect.
► The overall behavior is a sum of many individual events with different mechanisms.