Effect of Inoculum Pretreatment on the Composition of Microbial Communities in Anaerobic Digesters Producing Volatile Fatty Acids.

Satu Ervasti,Minna Kahala,Lucia Blasco,Saija Rasi,Markku Vainio,Elina Tampio

doi:10.3390/microorganisms8040581

Satu Ervasti, Minna Kahala + Show 4 more

Open Access

https://doi.org/10.3390/microorganisms8040581

Copy DOI

Abstract

Volatile fatty acids (VFAs) are intermediates in the methane formation pathway of anaerobic digestion and can be produced through the fermentation of organic wastes. VFAs have become an anticipated resource- and cost-effective way to replace fossil resources with higher added value and more versatile fuels and chemicals. However, there are still challenges in the production of targeted compounds from diverse and complex biomasses, such as urban biowastes. In this study, the aim was to modulate the microbial communities through inoculum treatment to enhance the production of green chemicals. Thermal and freeze-thaw treatments were applied to the anaerobic digester inoculum to inhibit the growth of methanogens and to enhance the performance of acidogenic and acetogenic bacteria. VFA fermentation after different inoculum treatments was studied in batch scale using urban biowaste as the substrate and the process performance was assessed with chemical and microbial analyses. Inoculum treatments, especially thermal treatment, were shown to increase VFA yields, which were also correlating with the dynamics of the microbial communities and retention times of the test. There was a strong correlation between VFA production and the relative abundances of the microbial orders Clostridiales (families Ruminococcaceae, Lachnospiraceae and Clostridiaceae), and Lactobacillales. A syntrophic relationship of these taxa with members of the Methanobacteriales order was also presumed.

Highlights

To enable the recycling of organic carbon in the society, the valorization of organic biomasses, such as urban biowastes (BW), is essential
Similar microbial communities could be harnessed to ferment biomass to volatile fatty acids (VFAs) which are intermediate compounds formed during acidogenesis and acetogenesis by e.g., Clostridium and Butyribacterium [1]
We found a correlation between Methanobacteriaceae and VFA production, suggesting that a symbiosis was established between this family and some Firmicutes

Summary

Introduction

To enable the recycling of organic carbon in the society, the valorization of organic biomasses, such as urban biowastes (BW), is essential. BWs are often valorized through anaerobic digestion, which facilitates simultaneous production of renewable energy in the form of methane and production of nutrient-rich residue, digestate. Anaerobic digestion is a synergistic process of mixed bacteria and archaea, where hydrolysis, acidogenesis, acetogenesis and methanogenesis occur simultaneously to degrade organic matter. Similar microbial communities could be harnessed to ferment biomass to volatile fatty acids (VFAs) which are intermediate compounds formed during acidogenesis and acetogenesis by e.g., Clostridium and Butyribacterium [1]. VFAs are short chain carboxylic acids which can be harvested and further used as substrates and precursors in microbial or chemical transformations, e.g., in the production of polyhydroxyalkanoates (PHA) [2] or docosahexaenoic acid (DHA) [3]. VFAs have become an anticipated resource- and cost-effective way to replace fossil resources in extensive industrial production of chemicals and fuels

Methods

Results

Discussion

Conclusion