Wastewater Treatment for Phenol Using Extraction with Ethyl Esters of Carboxylic Acids with Potential for Phenol Regeneration

Phenol is a toxic pollutant in the wastewater of industries such as chemical, petrochemical, oil refining, textile, and others. This study proposes a two-stage phenol wastewater treatment technology that includes an initial stage for extracting most of the phenol content in the effluents using ethyl esters of carboxylic acids as extractants. The second stage involves deep removal of residual phenol impurities within existing biological treatment systems at industrial sites. Based on an analysis of the phenol distribution between organic and aqueous phases during extraction, it was determined that carboxylic acid esters are effective phenol extractants across a broad range of phenol concentrations in wastewater, with distribution coefficients ranging from 20 to 134 depending on extraction conditions and the type of ester used. Ethyl esters of long-chain acids (ethyl laurate and ethyl oleate) and their mixtures with ethyl butyrate were found to be advantageous according to various criteria. Under optimal extraction conditions, the residual concentration of phenol in effluents is reduced to 200 mg/l or lower, achieving a phenol extraction rate of 90–92%. Additionally, the process maintains relatively low extractant consumption, with an extractant-to-water ratio of 1:20 (vol.) for wastewater with phenol contamination up to 3 g/l and a ratio of 1:10 (vol.) for wastewater with higher phenol contamination. It was demonstrated that extracted phenol can be regenerated in the form of sodium phenolate as an additional valuable byproduct of the wastewater treatment process.