Surfactant screening for soil washing: Comparison of foamability and biodegradability of a plant‐based surfactant with commercial surfactants

Abstract

Batch shaker‐flask experiments using a consortium of sewage microorganisms were conducted to study the aerobic biodegradation of a plant‐based natural surfactant (Ritha) and four anionic / nonionic commercial surfactants. Foaming potential, foam decay, microbial growth and ultimate biodegradation (mineralization) of natural surfactant were compared to those of synthetic surfactants, namely anionic sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS), and nonionic alcohol ethoxylate Tergitol 15‐S‐12 and Witconol SN‐90. The natural surfactant showed the lowest foaming potential among the selected surfactants (SDBS > SDS > Tergitol > Witconol > Ritha). The natural surfactant also performed better than commercial surfactants in terms of biodegradability at concentrations above critical micelle concentrations (supra‐CMCs). However, surface‐active components resisted biodegradation and foams from the natural surfactant were more persistent than SDS, Tergitol, and Witconol. Concurrent with an increase in initial surfactant concentration to supra‐CMCs, microbial growth rate (μ) was significantly increased for the natural surfactant, whereas a decreased growth rate was noted for some synthetic surfactants at supra‐CMC. Due to the fact that synthetic surfactants have considerable losses via precipitation / adsorption or phase change, toxicity to microorganisms, and have lowered biodegradability at supra‐CMC, natural surfactant may be promising in soil washing and flushing for the clean‐up of contaminated soils.