Potential and limitations of co-fermentation: A review

Abstract

Fermentation is a biotechnological process to generate value from organic waste. During this process, volatile fatty acids (VFA) are obtained as a product, which can be directly used to support other biotechnologies and contribute to the circular economy. However, some substrates present a series of characteristics that are not totally optimal. Co-fermentation is a way to alleviate these drawbacks, which consists on fermenting two or more substrates simultaneously. Co-fermentation is a relatively new approach to the fermentation process as the articles ranging from 2013-2020 account for 77%. A wide range of substrates and combinations have been studied. The more utilised main substrate is waste activated sludge (WAS) followed by primary sludge (PS). Most publications have focused on studying the combination of WAS and food waste (FW) and WAS and agro-industrial (e.g. corn stalk and mushrooms). Most researchers emphasize pH control using chemicals and balancing C/N ratio. Besides, the substrate has been shown to influence the VFA profile as well as the pH. The addition of agro-industrial residue can delay the co-fermentation process due to its high content in lignocellulosic compounds. Overall, other parameters and mixtures should be studied, and more continuous experiments are needed to finish studying co-fermentation