In the present work, Z-scheme composite C3N4/CuWO4 was synthesised by sol-gel method for the photocatalytic degradation of a mixed population of Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). The effect of the photoinactivation was observed for two different types of bacteria in the same medium together and individually in the absence of the nutrients. The lattice structures and phase purities were determined by X-ray diffraction. For morphological and topographical features, SEM and TEM imaging were performed. The oxidation states of the elements and band edges of the semiconductor were determined by XPS and UPS, respectively. The lifetime of the charge carriers and band gap of the semiconductors were determined by time resolved florescence spectroscopy and diffused reflectance spectroscopy, respectively. The photocatalytic experiments were performed for different weight ratios of C3N4 and CuWO4. Scavenger experiments were performed to investigate the exact mechanism and major responsible radicals for photocatalysis. The rate constants and order of the inactivation reactions were obtained by power law kinetics. The rate followed by the inactivation for E. coli and S. aureus were analysed. For E. coli, the order of inactivation reaction is 1.15 while S. aureus inactivation reaction order is 0.9. © 2018 Elsevier B.V.