Co-digestion of wastewater sludge with different waste additives for biogas production;( A case study of the Bugolobi wastewater treatment plant)
Umutesi, Irene Shina
Nakigudde, Christine Kagwa
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Available data suggests that only 8% of the wastewater generated is treated in low income countries. This implies that the biggest population is not connected to the sewerage system despite the existence of sewerage treatment plants. In 2014, the number of active sewers connections to the Kampala sewerage network was estimated at 8,359 bringing in a maximum dry weather flow of 14,500m3/day. With these insufficient connections to the Kampala sewerage network, the new Wastewater Treatment Plant (WWTP) in Bugolobi will not be able to achieve the design flow of 45,000m3/day. Therefore, treatment of the available wastewater will not yield the required sludge of 19,119kgDS/day for anaerobic digestion to produce the desired biogas to run the plant. This therefore poses a challenge to the new WWTP to find means of optimizing biogas production through co-digestion of the available sludge with additives like cow dung, market waste or water hyacinths in appropriate mix ratios. The aim of the study was to compare the performance of various substrates in co digestion with wastewater sludge generated at Bugolobi Sewage treatment plant, Kampala, Uganda as a means of enhancing biogas production from the sludge. A study was conducted on wastewater from Bugolobi Sewage Treatment Plant (STP) co-digested with market waste, cow dung and water hyacinth in different proportions. The study was done using laboratory scale serum bottles at mesophilic temperature and sludge retention time of 30 days. Results from the study showed that co-digestion of wastewater with cow dung produced most bio-gas with an increase by a factor of 3.7 followed by co digestion of wastewater and market waste. Digesters containing all substrates ceased gas production at 8 days due to acidification as a result of high organic loading. In conclusion, to improve bio-gas yield from wastewater sludge, cow dung should be co-digested with wastewater sludge due to higher bio-gas yield and minimum pretreatment required as compared to the other substrates.