A production site had an issue with high TOC content in their wastewater stream. This translated into over $5 million spent each year in disposal costs. The contaminant was a mixture of ethoxylated surfactants and polyethylene glycol at 10% total solids. The plant wanted a cost effective method to clean the waste water.
The problem was two-fold, finding a method to remove both surfactant and the dissolved polymer. As the Cc values were not known of the mixture, best guesses inferring negative values were used. Hansen Solubility was used to identify the top solvent extraction candidates.
Dichloromethane was identified as having similar HSP values. It also had the benefit of having a -14 EACN value. This would push most ordinary surfactants into +HLD territory, resulting in both surfactant (w/o emulsion) and PEG dissolved in the oil phase. This would then be allowed to phase separate for easy removal of contaminant.
The results were confirmed through use of Salager diagrams to verify +HLD, and LOD test to confirm the extraction of both surfactant and polymer. All surfactant was removed in the first wash, with 1% remaining polymer to be removed in the second, smaller extraction.
Without knowing our Cc values of the surfactant, we solved the problem by using the HLD framework to shift the system to a w/o emulsion through choice of oil. The oil was further able to extract the polymer with its similar HSP values.