Influence of carbon-to-nitrogen ratio on the mixed-acid fermentation of wastewater sludge and pretreated bagasse

► Co-digestion of wastewater sludge and bagasse enhances mixed acids yield. ► Highest conversion occurred at a C/N ratio of 30, and the highest yield occurred at 13.2-25 g C/g N. ► Yield was mostly affected at the extreme C/N ratios. ► Yield was on average about 0.42 g Aceq/g VS fed for mixtures S30 to S100. ► Protein from sludge enhance i-butyric, valeric and i-valeric acids production.