Pilot-scale experiment on anaerobic landfill bioreactor in Tanzania
Landfill bioreactors have been developed in industrialized countries as a long-term municipal solid waste (MSW) management option, but in East Africa no landfills have yet been designed and operated as recirculated landfills or bioreactors. Treatment of leachate and landfill gas emanating from landfilling remains a major environmental concern despite improved techniques of landfilling of solid wastes. This paper presents findings from a comparative study of a pilot scale landfill bioreactor and sanitary landfill conducted in Dar es Salaam city, Tanzania, to study the effect of leachate recirculation on waste degradation and acidification, landfill gas production, and in situ leachate treatment to provide insights for the successful operation of landfill bioreactors in developing countries. Two reactors R1 and R2 were built and each filled with about 2.3 tons of wet waste predominantly food waste (about 60%) of moisture content about 64% collected from municipal waste transfer stations. R1 was operated as a control reactor simulating a sanitary landfill and R2 was a simulated landfill bioreactor (LFB). Throughout the study of 52 weeks R1 was run as a flow through system whereas R2 was broken into two phases. During phase one of R2 the leachate was recirculated directly to the top of the reactor and phase two involved recirculation of leachate after treatment via an Up-flow Anaerobic Sludge Blanket reactor as an in-situ pre-treatment measure of the leachate. The study revealed that acidification of the leachate in the LFB without production of landfill gas (LFG) during a certain period is possible and that the LFB can be used for the first two steps of anaerobic digestion (i.e. hydrolysis and acidification) and then the remaining step of methanogenesis can be carried out in a separate reactor to produce biogas at a shorter period. The study also showed that biogas production in the reactor with recirculation of leachate strongly increases the total biogas production compared to the reactor with no recirculation of leachate. Overall, this study indicated the feasibility of operation of the LFB with waste characteristics of Tanzania to accelerate the stabilization of organic-rich wastes, enhance LFG production and achieve a degree of leachate treatment.