Persulfate oxidation enhanced extraction to improve the removal of high concentration phenol wastewater

Abstract

Phenolic contamination has caused serious harm to the environment and organisms; therefore, more and more attention has been paid to its recycling and harmless treatment. In this study, a method combining advanced oxidation and extraction was proposed to treat high concentration phenol wastewater. In addition, extraction and persulfate oxidation have been applied individually and coupled to evaluate the purification of high concentration phenol (e.g., 10 000 mg L⁻¹). The resource recovery of phenolic compounds is achieved via extraction, while the remaining low concentration of phenol and residual extractant can be removed by oxidation. Meanwhile, ZnCl₂ activated sludge biochar (ZSBC) was prepared via a pyrolysis process and employed as a catalyst to activate persulphate (PDS) for phenol degradation in wastewater. The results illustrated that the removal efficiency reached 95% within 120 min by adding PDS (1000 mg L⁻¹) with ZSBC (1000 mg L⁻¹), which was obviously superior to that of pristine sludge biochar (SBC) without ZnCl₂. And the removal efficiency of TOC could reach 92%. Besides, ZSBC also ensured excellent PDS decomposition even in a high salinity environment. Quenching experiments and electron spin resonance (ESR) indicated that both a radical mechanism and non-radical mechanism existed in the ZSBC/PDS system, with ¹O₂ playing a determinative role in the non-radical mechanism. With a 100% phenol removal and 95% TOC removal, it is believed that this work offers a high efficiency and low-cost method for the utilization of waste sludge and treatment of high phenol content wastewater.