Design of ternary Ni(OH)2/graphene oxide/TiO2 nanocomposite for enhanced photocatalytic degradation of organic, microbial contaminants, and aerobic digestion of dairy wastewater

Abstract In the present study, solar light active nickel(II) hydroxide (Ni(OH)2) decorated on graphene oxide (GO) and modified titania (TiO2) nanocomposite was fabricated and used for the treatment of complex wastewater containing toxic organics, microbes and high lipid in dairy wastewater. The nanocomposite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, and photoluminescence (PL) spectroscopy. Due to the strong visible light absorbance and electron harvesting ability of Ni(OH)2/GO/TiO2 nanocomposite, it was investigated for the degradation of 2-chlorophenol (2-CP) and pre-treatment of dairy wastewater for the removal of microbial pollutants and improved digestibility via aerobic digestion. The results showed that Ni(OH)2/GO/TiO2 actively removed 80% of the 2-CP from synthetic wastewater of 25 mg/l concentration within 4 h, at pH 6.0. Moreover, a significant reduction in the microbial counts from 450 ± 50 × 1011 CFU/ml to 350 ± 50 × 108 CFU/ml was observed after the Ni(OH)2/GO/TiO2 photocatalytic treatment. The pre-treatment of dairy wastewater improves the organic solubilization where soluble chemical oxygen demand (sCOD) content increased from 272 to 631 mg/l within 6 h of photocatalysis. The sCOD was 45.8% higher in photocatalytic pretreated dairy wastewater as compared to that in dairy wastewater subjected to photolysis (without catalyst). In the subsequent aerobic treatment, the digestibility of pretreated dairy wastewater was significantly improved by achieving a decrease in total chemical oxygen demand from 832 to 54 mg/l after 40 days of treatment process. This study showed the potential of Ni(OH)2/GO/TiO2 nanocomposite for the highly efficient wastewater treatment applications.