Improving anaerobic biodigestion of manioc wastewater with human urine as co-substrate

This study investigated anaerobic co-digestion of cassava liquid waste (very acid and poor in nitrogen) and human urine. Three experimental digesters were used: manioc effluent; manioc effluent + urine; manioc effluent + urine + cow dung. All digesters have functioned with mesophilic temperatures between 24.0 and 35.6°C. Digesters without urine have a pH varying between 3 and 4 during experimentation. In reactors containing urine, the pH oscillated between 6.46 and 10.29. The COD/TKN ratios recorded in digesters buffered with human urine are lower than those observed in digester without human urine. Volume of gas produced by the two digesters containing human urine was significantly higher than that of the digester without urine. The additions of human urine and cow dung improve highly the methane potential during anaerobic co-digestion of manioc effluent. The flammability test is positive except for the digester without urine. Using human urine as a co-substrate for anaerobic digestion of cassava wastewater requires a large quantity of urine (40% in terms of proportion) for a best productivity. As well as allowing biogas production as a source of renewable energy, this system of co-digestion could help to resolve the sensitive problem of human excreta management in poor area. Indeed, human urine with an alkaline pH and richness in nitrogen can substitute chemicals commonly used to correct the pH during anaerobic biodigestion, in particular for the treatment of cassava wastewater which is very acid.