In this experimental investigation, de-oiled seed cake of Karanja (SCK), an organic industrial waste obtained from Karanja biodiesel industries was mixed with cow dung (CD) in four different proportions, viz., 75:25, 50:50, 25:75, and 0:100 percentages on a mass basis, and the mixtures were denoted as sample S-1, S-2, S-3 and S-4 respectively. The samples were kept in four different reactors and investigated simultaneously, for biogas production. Important parameters, such as the pH, temperature, hydraulic retention time (HRT), and carbon/nitrogen ratio (C/N) were evaluated and analyzed. The results indicated that sample S-3 gave best result, in comparison with the other samples, and the methane (CH4) and carbon dioxide (CO2) content in the biogas was found to be 73% and 17% respectively. The biogas and the slurry were characterized to observe the various properties for suitable application and the environmental impacts. The fertilizer value for S3 was found to be better than that of other samples and the slurry became nontoxic, environmental friendly fertilizer. (C) 2015 Elsevier Ltd. All rights reserved.