The present study emphasized the co-digestion of the thermal-H2O2 pretreated wheat straw (WS) and chicken manure (CM) with the waste activated sludge at four levels of C/N (35: 1, 30: 1, 25: 1 and 20: 1). All C/N compositions were found significant (P < 0.05) to enhance methane generation and process stability during the anaerobic co-digestion of WS and CM. The experimental results revealed that the composition having C/N value of 20: 1 was proved as optimum treatment with the methane enhancing capability of 85.11%, CODs removal efficiency of 48.55% and 66.83% VS removal as compared with the untreated WS. The other compositions having C/N of 25: 1, 30: 1 and 35: 1 provided 75.85%, 63.04% and 59.96% enhanced methane respectively as compared with the control. Pretreatment of the WS reduced its C/N value up to 65%. Moreover, to optimize the most suitable C/N composition, the process stability of the co-digestion of WS and CM was deeply monitored. (C) 2016 Elsevier Ltd. All rights reserved.