Domestic low-tech anaerobic digesters in Guiné-Bissau : a bench-scale preliminary study on locally available waste and wastewater

Solid organic waste (SOW) and sewage (SEW), in developing contexts as Guine´-Bissau, can be converted into biogas in domestic low-tech anaerobic digesters (AD), avoiding their dispersion in the environment (cause of infective diseases) and simultaneously providing local sustainable/clean fuel to substitute firewood (cause of deforestation and respiratory diseases). Here, SOW and SEW, sampled from local markets/households of Bissau City, were processed in a bench-scale reactor, to define the potentials of low-tech mesophilic (30–37 C) AD in removing pathogen microbial population, responsible for infective diseases spreading through untreated SOW/SEW and in domestic fuel generation in substitution to firewood. Pathogens removal above 99.9 % were obtained for E. coli and Streptococci. Considering a target scenario (4-persons household unit), a low-tech AD of 2.35 m3 functional volume, co-digesting 32 L day-1 of SEW and 8 kg day-1 of SOW, would produce about 1:5 Sm3 biogasday1 and substitute nearly 11 kg day-1 of firewood for cooking needs, avoiding black carbon particles emissions and inhalation in households. Alternatively, ten biogas lamps could work for 3 h day-1 or a 1-kW electric power generator run for over 2 h day-1 , with important socio-economic benefits. Finally, firewood substitution and the use of digestate as soil conditioner can simultaneously contribute in limiting deforestation and desertification, particularly in transition sub-Saharan tropical areas, such as Guine´-Bissau.