Influence of pre-treatments and anaerobic co-digestion of slaughterhouse waste with vegetable, fruit and flower market wastes for enhanced methane production

Considerable amounts of slaughterhouse wastes (SHW) are generated in Indian urban centres causing serious environmental issues that demand effective treatment and disposal. The present study evaluates the effect of pasteurization (70 °C for 1 h) and extrusion pre-treatment on pathogen removal and methane production from SHW in anaerobic mono- and co-digestion with mixed vegetable, fruit and flower market wastes (VMW) under controlled batch anaerobic digestion (AD) tests. The complete destruction of pathogen was observed in post-pasteurized SHW, whereas the post-extruded SHW showed significant reduction (p < 0.05) in pathogen concentration (with a Salmonella count of 29.3 × 103 CFUs/g). The results of AD test revealed that the maximum specific methane yield (SMY) of 273.2 mLN/g oDM was obtained by anaerobic co-digestion of SHW:VMW in 1:3 proportion. Further enhancement in the SMY was obtained with extrusion pre-treatment of SHW (SHWE) by 11.5% (i.e. 304.8 mLN/g oDM) in 1:3 proportion of SHWE:VMW. Modified Gompertz and logistics models fitted the kinetic data of AD process well. Results confirmed that the proposed extrusion pre-treatment of SHW coupled with anaerobic co-digestion improved the oDM reduction, methane potentials and pathogen removal, thereby making it a suitable pre-treatment during anaerobic co-treatment of SHW with VMW from centralized wholesale markets from urban centres.