As widespread distribution of recombinant DNA of genetically modified microorganisms is a threat to the environment, the aim of this research is to investigate the efficiency of photocatalytic degradation of recombinant DNA under visible light. Using response surface methodology, a comprehensive evaluation of Ag doped-TiO2 photocatalytic degradation of recombinant DNA in Hepatitis B surface antigen production plant wastewater was performed. Photocatalytic synthesis parameters including dopant content, calcination temperature, and heating rate were investigated to model and optimize the recombinant DNA degradation efficiency. The Ag doped-TiO2 nanoparticles synthesis validation was accomplished by XRD, UV-vis diffuse reflectance spectra, FESEM and energy-dispersive X-ray spectroscopy. A quadratic polynomial equation, developed by response surface methodology, with the correlation coefficient (R-2) of 0.969 ensured the good fitness of the predicted data with the experimental results. The sensitivity analysis of model indicates that the square of silver content and calcination temperature have the greatest effect on the response, while the heating rate is the least important parameter. Furthermore, the optimum conditions of Ag content of 2.1%, calcination temperature of 485 degrees C, and heating rate of 8 C/min resulted in 80.7% rDNA degradation experimentally. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.