Microbial and Phenyl Acid Dynamics during the Start-up Phase of Anaerobic Straw Degradation in Meso- and Thermophilic Batch Reactors.

Eva Maria Prem,Rudolf Markt,Andreas Otto Wagner,Paul Illmer,Nina Lackner

doi:10.3390/microorganisms7120657

Abstract

Aromatic compounds like phenyl acids derived from lignocellulose degradation have been suspected to negatively influence biogas production processes. However, results on this topic are still inconclusive. To study phenyl acid formation in batch reactors during the start-up phase of anaerobic degradation, different amounts of straw from grain were mixed with mesophilic and thermophilic sludge, respectively. Molecular biological parameters were assessed using next-generation sequencing and qPCR analyses. Metagenomic predictions were done via the program, piphillin. Methane production, concentrations of phenylacetate, phenylpropionate, phenylbutyrate, and volatile fatty acids were monitored chromatographically. Methanosarcina spp. was the dominant methanogen when high straw loads were effectively degraded, and thus confirmed its robustness towards overload conditions. Several microorganisms correlated negatively with phenyl acids; however, a negative effect, specifically on methanogens, could not be proven. A cascade-like increase/decrease from phenylacetate to phenylpropionate, and then to phenylbutyrate could be observed when methanogenesis was highly active. Due to these results, phenylacetate was shown to be an early sign for overload conditions, whereas an increase in phenylbutyrate possibly indicated a switch from degradation of easily available to more complex substrates. These dynamics during the start-up phase might be relevant for biogas plant operators using complex organic wastes for energy exploitation.

Highlights

In the few decades, humankind will increasingly face challenges due to global energy demand and the resultant efforts to reduce greenhouse gas emissions from fossil fuel utilisation and combustion
The analyses focused on general biochemical pathways and on pathways regarding anaerobic degradation/turnover of aromatic compounds: degradation of aromatic compounds (KEGG orthology ko01220), phenylpropanoid biosynthesis (KEGG orthology ko00940), benzoate degradation (KEGG orthology ko00362), and aminobenzoate degradation (KEGG orthology ko00627)
Methane production during the start-up phase of straw degradation is depicted in Figure 1 for the control, as well as the low (LCL), medium (MCL), and high (HCL) carbon load

Summary

Introduction

In the few decades, humankind will increasingly face challenges due to global energy demand and the resultant efforts to reduce greenhouse gas emissions from fossil fuel utilisation and combustion. One drawback of using (pre-treated) organic waste products is the concurrent entry of undesirable compounds like ammonia [3] or aromatic compounds [4,5,6] that can cause severe disturbances during the cascade-like proceeding anaerobic degradation process [7]. This can lead to restricted biogas production performances and to tremendous financial problems for the operators who are dependent upon specified quantities of methane to economically sustain the facility [5,8,9]. Thermophilic plants have a clear advantage over mesophilic plants in terms of pathogen removal, exploitation efficiency, biochemical reaction rate, and occupation of ecological niches [10,11]

Methods

Results

Discussion

Conclusion