Effect of nano-Al2O3 and multi-walled carbon nanotubes on the anaerobic mono-digestion of sludge and the co-digestion of tobacco waste and sludge

Abstract

Anaerobic digestion can help mitigate tobacco waste (TW) pollution. Both the mono-digestion of sludge and the co-digestion of TW and sludge were considered in this study. Additionally, the effects of nano-Al₂O₃ and multi-walled carbon nanotubes (MWCNTs) on these two digestion systems were investigated through a 35 day digestion experiment. The microbial communities in the control reactors and the nano-Al₂O₃ reactors were also examined. Kinetic analysis revealed that the R_m values for the mono- and co-digestion nano-Al₂O₃ reactors increased by 8.88% and 13.5% compared with that of the MWCNTs reactor, respectively. Furthermore, the co-digestion system exhibited a 34.8% higher R_m than the mono-digestion system when nano-Al₂O₃ was added to both systems. Nano-Al₂O₃ was found to shorten the lag phase, while MWCNTs prolonged the lag phase time. Furthermore, 16S RNA amplicon sequencing results indicated that microbial species such as Methanobacterium sp., Hydrogenispora sp., Lutispora sp., and Ruminiclostridium sp. were more abundant in the nano-Al₂O₃ reactor. These results demonstrated that biogas production in co-digestion systems was improved. Moreover, nano-Al₂O₃ addition enhanced biogas production.