Remediation of Contaminated Soils Using a Plant Based Surfactant.

Abstract

A plant based surfactant extracted from fruit pericarps of Sapindus mukurossi (Ritha) is employed for the first time to investigate remediation of contaminated soils. A method for preparing natural surfactant solutions was developed and the solutions were characterized followed by generation and characterization of colloidal gas aphron (CGA) suspensions produced with these solutions. The variation of hexachlorobenzene (HCB) solubility with natural surfactant solutions was estimated and desorption of HCB from soils was investigated with batch and on-dimensional column experiments. Bioenhancement of soil microorganisms in natural surfactant solutions was studied under both aerobic and anaerobic conditions. The empirical formula for natural surfactant solutions was found to be $\rm(C\sb{26}H\sb{31}O\sb{10})\sb{n}$ with a critical micelle concentration (CMC) of 0.1%. CGA suspensions generated from natural surfactant have (i) comparable size distribution characteristics, (ii) more stability and (iii) lower gas fraction than those generated with commercial surfactants. Natural surfactant concentrations beyond 1.5% were not suitable for generating CGAs due to low quality of the suspensions. Solubility of HCB in natural surfactant solutions increased linearly with surfactant concentration beyond the CMC. The mass of dry Ritha powder required to solubilize 1 mg of HCB in one liter was found comparable to several commercial surfactants. Natural surfactant solutions were able to desorb HCB up to 90% of the HCB solubility in the respective solutions in batch studies. Natural surfactant solutions performed more efficiently than CGA suspensions of similar concentration in recovering HCB from one dimensional soil columns, with removals as high as 80% of the solubility of the respective solutions. HCB recovery also increased with increasing surfactant concentration. However, natural surfactant concentrations beyond 2.5% developed a high pressure drop across the soil columns and resulted in termination of the experiment. Natural surfactant solutions supported microbial growth and degraded to a considerable degree under both oxygen rich and anoxic conditions. The presence of a chlorinated organic compound, HCB, did not affect the growth and did not undergo any transformations under both aerobic and anaerobic conditions. Significantly higher growth in nutrient amended cultures indicate that the microbial population may be nutrient limited.