RESEARCH ARTICLE
Process stability and microbial community composition in pig manure and food waste anaerobic co-digesters operated at low HRTs
. Department of Civil Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland.. Teagasc Pig Development Department, Animal and Grassland Research and Innovation Centre, Fermoy, Ireland.. Department of Science, Waterford Institute of Technology, Waterford, Ireland.. Teagasc Animal and Bioscience Research Department, Animal and Grassland Research and Innovation Centre, Dunsany, Meath, Ireland
Available online: 2017-04-07
Abstract
This study assessed the effects of reducing hydraulic retention times (HRTs) from 21 days to 10.5 days when anaerobically co-digesting pig manure and food waste. Continuously stirred tank reactors of 3.75 L working volume were operated in triplicate at 42°C. Digester HRT was progressively decreased from 21 to 15 days to 10.5 days, with an associated increase in organic loading rate (OLR) from 3.1 kg volatile solids (VS)·m ·day to 5.1 kg VS·m ·day to 7.25 kg VS·m ·day . Reducing HRT from 21 days to 15 days caused a decrease in specific methane yields and VS removal rates. Operation at a HRT of 10.5 days initially resulted in the accumulation of isobutyric acid in each reactor. High throughput 16S rRNA gene sequencing revealed that this increase coincided with a shift in acidogenic bacterial populations, which most likely resulted in the increased isobutyric acid concentrations. This may in turn have caused the increase in relative abundance of bacteria, which syntrophically degrade non-acetate volatile fatty acids (VFAs) into H and CO . This, along with the increase in abundance of other syntrophic VFA oxidizers, such as suggests that VFA oxidation plays a role in digester operation at low HRTs. Reducing the HRT to below 21 days compromised the ability of the anaerobic digestion system to reduce enteric indicator organism counts below regulatory limits.
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