Removal of polyethylene glycols from wastewater: A comparison of different approaches

Physicochemical methods such as adsorption on activated carbon, oxidation with either ozone or Fenton reagent, and chemical precipitation (coagulation), were assessed for the removal of polyethylene glycol (PEG) from wastewater. This contaminant is rarely investigated due to its low toxicity, although its presence limits the use of large water resources. The experimental tests showed that adsorption on activated carbon is well approximated by a Langmuir isotherm, and influenced by contact time, PEG molecular weight, pH, temperature, and initial PEG concentration. Ozonation allowed fragmenting the polymeric chains but was unable to remove completely the PEG, while about 85% of the total organic carbon (TOC) was removed by Fenton oxidation reaction by using a ratio between H₂O₂ and Fe^II close to 4. Coagulation did not produce results worthy of note, most likely because the uncharged PEG molecule does not interact with the iron hydroxide flocs. However, when performed after the Fenton oxidation (i.e., by simply raising the pH to values > 8), it allowed a further reduction of the residual TOC, up to 96% of the total, in the best case. Based on the resources used by each process studied and in consideration of the effectiveness of each of them, a semi-quantitative comparison on the sustainability of the different approaches is proposed.