The present study describes a novel green approach of waste to energy generation without use of any chemical in the pretreatment process. Lignocellulosic waste Rice Straw (RS) was taken as substrate and petha waste water (PWW) was used for the pretreatment of RS. Cow dung (CD) and soil were used as mixed microbial sources. Eight different batch reactors were set up with CD and soil as microbial sources separately. These reactors contained PWW pretreated RS which was ultrasonicated for 5, 10 and 15 min for three separate reactors and the fourth reactor was set up without ultrasonication. Methane was analysed by gas chromatograph (GC) equipped with thermal conductivity detector (TCD) and ethanol was analysed using chromic acid method by UV-Visible spectrophotometer (584 nm). Various physical parameters like COD degradation, pH, TS, TDS, TSS, VS were also analysed as per standard methods to check the feasibility of the process. Maximum methane yield was 47.8% with soil culture and maximum ethanol yield was 126.53 mg/L with CD, in the reactors with 15 min ultrasonication of RS and PWW. The methane and ethanol yields were about three times and two times more than that of reactors without ultrasonication with soil and CD respectively. (C) 2019 Elsevier Ltd. All rights reserved.