A Model for Bioaugmented Anaerobic Granulation.

Anna Doloman,Amitesh Mahajan,Charles D Miller,Yehor Pererva,Nicholas S Flann

doi:10.3389/fmicb.2020.566826

Abstract

Anaerobic granular sludge comprises of highly organized microorganisms with a sophisticated metabolic network. Such aggregates can withstand storage, temperature fluctuations and changes in the substrate supplied for anaerobic digestion. However, substrate change leads to long adaptation of granular consortia, creating lags in the reactor operations. To speed up adaptation and increase digestion efficiency, bioaugmentation with a robust consortium can be performed. The computational study described here aims to elucidate the mechanisms of bioaugmenting anaerobic granules, utilizing the current body of knowledge on metabolic and biochemical interactions between bacteria in such aggregates. Using a cDynoMiCs simulation environment, an agent-based model was developed to describe bioaugmentation for adaptation of cellobiose-degrading granular consortium to a lipid-rich feed. Lipolytic bacteria were successfully incorporated in silico to the stable granular consortia after 40 days of simulation. The ratio of cellobiose and the lipid-derivative, oleate, in the feed played key role to ensure augmentation. At 0.5 g/L of both cellobiose and oleate in the feed, a homogeneous stable augmented consortium was formed and converted the given amount of substrate to 10.9 mg/L of methane as a final product of anaerobic digestion. The demonstrated model can be used as a planning tool for anaerobic digestion facilities considering transition of the inoculum to a new type of feed.

Highlights

Bioaugmentation is a common strategy in the field of wastewater treatment that is used to introduce a new metabolic capability to either aerobic or anaerobic microbial consortia (Stephenson and Stephenson, 1992; Dhouib et al, 2006; Herrero and Stuckey, 2015)
Discussion of the results is divided into three main parts: (1) model of a granule grown on cellobiose; (2) model of a granule grown on cellobiose without ethanol-degrading bacteria, necessary to fully digest cellobiose, with augmentation at the later stages of granule development; and (3) model of a bioaugmented granule grown on oleate or a mix of oleate and cellobiose
At 1.5 g/L concentration of cellobiose, all five types of bacterial cells grew on the products of cellobiose conversion into lactate, acetate and ethanol (Figure 1)

Summary

Introduction

Bioaugmentation is a common strategy in the field of wastewater treatment that is used to introduce a new metabolic capability to either aerobic or anaerobic microbial consortia (Stephenson and Stephenson, 1992; Dhouib et al, 2006; Herrero and Stuckey, 2015). Success of the bioaugmentation is only possible if there is a substrate-specific niche available for the microbe to be incorporated into the already established consortia (Ellis et al, 2000; Da Silva and Alvarez, 2004; El Fantroussi and Agathos, 2005). Some research suggests a need for tight biochemical interaction to take place between the bioaugmented bacterium and the intact community (Mohan et al, 2007; Schneider and Topalova, 2011). Such biochemical interactions, together with substrate niche availability, will lead to a stratification or compartmentalization of the bioaugmented bacterium in a densely packed microbial consortium. Anaerobic granules are formed in upflow anaerobic sludge blanket (UASB) reactors, where due to the constant upflow velocity of the bottom-fed substrate and attraction toward some microbially-secreted polysaccharides (EPS), bacteria come together to form granules (Liu et al, 2003)

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Conclusion