Anaerobic co-digestion: A critical review of mathematical modelling for performance optimization

Abstract

Anaerobic co-digestion (AcoD) is a pragmatic approach to simultaneously manage organic wastes and produce renewable energy. This review demonstrates the need for improving AcoD modelling capacities to simulate the complex physicochemical and biochemical processes. Compared to mono-digestion, AcoD is more susceptible to process instability, as it operates at a higher organic loading and significant variation in substrate composition. Data corroborated here reveal that it is essential to model the transient variation in pH and inhibitory intermediates (e.g. ammonia and organic acids) for AcoD optimization. Mechanistic models (based on the ADM1 framework) have become the norm for AcoD modelling. However, key features in current AcoD models, especially relationships between system performance and co-substrates' properties, organic loading, and inhibition mechanisms, remain underdeveloped. It is also necessary to predict biogas quantity and composition as well as biosolids quality by considering the conversion and distribution of sulfur, phosphorus, and nitrogen during AcoD.

A sustainable biomass network design model for bioenergy production by anaerobic digestion technology: using agricultural residues and livestock manure

“…Hashimoto used straw as a carbon source along with poultry waste. Having information on the C/N ratio of available materials in the region, a suitable mixture of wastes, can be selected to feed the biogas plant [31]. According to the literature [28,30,31], the entry of the substances into the digestive process would be a proportion of the poultry feces, the straw, and the cow feces, which would allow the C/N ratio in the digestive solution to be adjusted at an ideal ratio.…”

Perspectives and actions moving forward

“…To further enhance energy production via AD, co-digestion of WAS and other organic feedstocks (e.g. food waste) has been investigated (Xie et al, 2016;Yin et al, 2016). In this co-digestion process, food waste rich in organics was directly fed into the anaerobic digester with WAS to promote the biogas production.…”

Mixing and Transport

“…This study demonstrated that net power production was an appropriate measure to optimize feedstock ratio of co-digestion under three different mixing conditions. (Xie, 2016). In another study, full scale digesters maintained stability under overloaded low mixing conditions.…”

“…In another study, full scale digesters maintained stability under overloaded low mixing conditions. To achieve similar fluid properties of the digestate, an increase in mixing intensity is needed based on varying amounts and types of co-substrates (food wastes) (Xie, 2016). To understand the relationship between mixing and methane yield, two-stage computational simulations should account for biological processes with steady fluid flow and heat transfer.…”