Catalytic ozonation of polyethylene glycol in aqueous solution by copper slag: Efficiency, active substances and mechanisms

Polyethylene glycols (PEG) are widely employed and frequently detected in wastewater, and between 0.5 and 68 mg L−1 of PEG were found in river water and seawater. It puts significant pressure on COD treatment of the water environment. Nevertheless, PEG is not easily broken down by biological processes, and other treatment methods include drawbacks such as membrane blockage and stringent pH requirements. Ozone oxidation technology can overcome these drawbacks, but low ozone utilization and higher catalytic costs limit the industrialization of the technology to some extent. In this research, discarded copper slag was used as an in situ iron donator, and modified into a catalyst for ozone catalytic oxidation, which achieved lower costs and waste reuse. Based on the Response Surface Methodology simulation and experimental tests, to achieve the greatest catalytic performance, the copper slag was calcined at 710 °C for 3.5 h. Under optimal conditions, with the introduction of CS-710,3.5 to ozone oxidation, the removal rate of PEG was improved from 79.27 % to 97.40 % in 10 min with an initial PEG concentration of 20 mg L−1. In addition, the COD removal rate was increased by 18.3 % and the first-order rate constant (k) was 2.66 times higher than that of the individual ozone system. After 10 cycles of reuse, the removal rate still reached 73.8 %, indicating the catalyst's good stability. The concentration of Pb and Zn dissolved was 1.6 and 4.4 μg L−1, respectively, sufficient to meet Environmental quality standards for surface water (GB 3838-2002, China). Thus, the safety of the catalyst is proven. The reaction process based on the free radical mechanism, according to density functional theory (DFT), CS-710,3.5 enhanced the conversion of ozone to OH, O− 2, and 1O2, and hastened the degradation of PEG. Despite taking a while to mineralize fully, PEG was effective in breaking down macromolecules into smaller ones. As such, it can be regarded as a successful PEG pretreatment technique. •As an in situ iron donator, the modified copper slag was used as the ozone oxidation catalytic in the water treatment field.•Under optimal conditions, with theaddition of modified copper slag, the removal rate was improved from 79.27 % to 97.40 %.•The modified copper slag promoted the conversion of ozone to •OH, O2-, and 1O2, and accelerated the degradation of PEG.