Meta-Analysis of Production of Volatile Fatty Acids From Waste Streams: Towards Creating Decision Support Tools for Process Optimization.

After anaerobic digestion, the sludge in wastewater treatment plants encompasses biosolids and food waste entering the sewer systems through food waste grinders in the kitchen sinks, especially in North America. These digested biosolids and food waste are typically discarded in landfills or incinerated. However, producing volatile fatty acids (VFAs) through fermentation of this waste stream of sludge and food waste is a lucrative value chain to biosolids and food waste management. The co-fermentation of sludge and food waste enhances microbial diversity and provides optimal carbon:nitrogen ratio for VFA generation. However, variation in the source and composition of the food waste significantly impacts the fermentation efficiency. In this study, a meta-analysis of 107 studies from North America was performed to understand the correlation between operational parameters and their effects on VFA production to use it as a tool for process optimization. The 107 studies were selected out of 303 from the database of Scopus and Web of Science from the year 2000 to 2024. The included studies were original research articles with inclusive data on VFA production using food waste as a substrate. Initial substrate concentration was found to be a reliable predictor for VFA production, followed by temperature and pH. Substrate concentrations between 9 and 20 gCOD/L, coupled with temperatures around 25°C or lower and neutral to slightly acidic pH, were observed to create favorable conditions for microbial activity and VFA generation.