Investigating the potential of biogas production from BIUST wastewater treatment sludge by co-digestion with slaughterhouse waste

Abstract

Wastewater treatment is a necessity in any community and civilization particularly where water is a scarce natural resource. The Botswana International University of Science and Technology is habitat to a community of just under 5000 people and has its own dedicated wastewater treatment plant. Currently this plant is managed by the university and boasts of 7 ponds. The plant follows a conventional four stage process; starting off with screening and grit removal, then removal of suspended solids through sedimentation, breakdown of organic matter through biological processes, then lastly filtration, disinfection, and use of chemical treatment to ensure compliance with quality standards before final discharge. This research aims at the third stage of biological processing to explore potential for biogas production potential from BIUST wastewater treatment sludge (WTS). Presently the anaerobic digestion ponds are open to the atmosphere and therefore release methane to the atmosphere adding to greenhouse gas emissions. To investigate, four different ratios of sludge (SL) to slaughterhouse waste (SHW) (1:1, 1:3, 3:1, 2:3) were co-digested, and the two substrates mono digested. The experiment was conducted over a retention time of 32 days in 2L reactor vessels. The results for bio-methane potential revealed that sludge: slaughterhouse waste 1:3 accumulated the highest volume of biogas (10,446.4 NmL CH4/gVS), sludge on its own accumulated the lowest volume of biogas (3,134.9 NmL CH4/gVS). The ratio of 2:3 exhibited the most optimal physiochemical properties for biogas production, promising a high turnover of gas produced. The premeditated assumption was later discovered to be false, as the volume accumulated was relatively low (3435.8 NmL CH4/ gVS) only increasing by 9.6% compared to the lone digestion of sludge. Ratio of 3:1 yielded a biogas of 5,686.1 NmL CH4/gVS, showing an 81% increase in biogas yield compared to mono-digestion of sludge. Therefore, co-digestion of sludge with slaughterhouse waste at a 3:1 ratio shows great potential for biogas production from BIUST waste treatment sludge.