Carbon nitride/titania nanotubes composite for photocatalytic degradation of organics in water and sludge: Pre-treatment of sludge, anaerobic digestion and biogas production

In this study, carbon nitride/titania nanotubes (C3N4/TiO2 NTs) composites were synthesized for the enhanced visible light mediated photocatalytic degradation and pre-treatment of wastewater sludge for enhanced biogas production. The co-existence of C3N4 and TiO2 NTs and visible light activity was confirmed by XRD, TEM, UV-visible and PL spectroscopy. The photocatalytic performance of TiO2 NTs with 2% of melamine (precursor of C3N4), enhanced the degradation of 2-chlorophenol (2-CP) (k = 0.0176 min−1), where 96.6% removal was achieved at optimum pH 7.0 and 2-CP concentration of 30 mg/L. On the other hand, the application of C3N4/TiO2 NTs for solubilization of the rigid structure of sludge by photocatalysis released the soluble organics showing an improvement in sCOD production (4587 mg/L). Subsequently, anaerobic digestion of solubilized sludge has improved the methane production (723.4 ml kg−1 VS) by 1.37 and 1.6 times compared to that in anaerobic digestion with photolytic and raw sludge, thus showing a promising applicability for biogas production from sludge and wastewater treatment.