Early Warning Indicators and Microbial Mechanisms for Process Failure due to Organic Overloading in Food Waste Digesters

Abstract

This paper aimed to evaluate the process stability and microbial community structure during anaerobic digestion of food waste. Organic loading rate (OLR) disturbances were introduced into a mesophilic anaerobic digester treating food waste. The parameters evaluated included gas production, methane content, alkalinity, and volatile fatty acid (VFA) concentrations. The microbial community of each stage was analyzed by using 454-pyrosequencing. The results revealed that total VFA, acetate, and propionic acid displayed effective responses as indicators of process instability and system recovery. Process instability is closely related to high oil, high salt, and high protein concentrations. Total VFA, acetate, and propionic acid levels warned of impending process instability 7–8 days before system failure. They were also 3–8 days slower than other parameters during system recovery. The transition of the amino acid degradation pathway in bacterial communities was associated with the accumulation of VFA. Proteiniphilum gradually increased from 3 to 26% and became the dominant genus of the microbial community. The relative abundance of Syntrophomonas increased significantly to 2%, whereas Thermovirga decreased from 5 to 1%. This reduced protein and lipid degradation, resulting in an accumulation of long-chain fatty acids (LCFAs). Because of sodium salt intolerance, Methanospirillum dominance was replaced by that of Methanoculleus. Methanoculleus increased from 9.89 to 51.93%, whereas Methanospirillum gradually decreased from 35.35 to 0.46%.