Rapid photocatalytic treatment of high-strength olive mill wastewater by sunlight and UV-induced CuCr2O4@CaFe–LDO

Abstract

An efficient and cost-competitive hybrid CuCr2O4@CaFe–LDO catalyst was successfully synthesized for the decontamination of olive mill wastewater. CuCr2O4@CaFe–LDO has a bandgap of 2.56 eV, exhibited stable photocurrent response of ∼4.48 μA cm–2, possesses a wide range of pores with an average size and pore surface area of 12.51 nm and 8.25 m2 g–1, respectively. The constituent elements and optical activity of the CuCr2O4@CaFe–LDO were established by an X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy, respectively. Under optimized conditions; 50 mg CuCr2O4@CaFe–LDO achieved 54.8 % degradation of phenolics after 4 h without an oxidant in the dark, while 90 % degradation was attained within 40 min with sunlight-assisted irradiation in the presence of 0.05 M K2S2O8. Under UV assisted system, CuCr2O4@CaFe–LDO/K2S2O8 consumed 19.22 kW h m−3 (0.96$) electrical energy with an apparent rate constant, kapp =0.00598 min−1 within 120 min which resulted to 99 % degradation of the phenolics, 95.1 % COD removal (%) and 84.6 % BOD removal efficiency. The spent catalyst was rapidly recovered from the bulk solution due to its sufficient saturation magnetization of 54.7 emu g−1 and retained 93 % reuse efficiency after four consecutive recycling tests. The multiprocess mechanism was established considering the contribution of active species (OH, SO4−, h+ and O2−).