Process stability and microbial community composition in pig manure and food waste anaerobic co-digesters operated at low HRTs

Conor Dennehy, Peadar G. Lawlor, Gillian E. Gardiner, Yan Jiang, Paul Cormican, Matthew S. McCabe, Xinmin Zhan

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)

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–3·day–1 to 5.1 kg VS·m–3·day–1 to 7.25 kg VS·m–3·day–1. 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 Clocamonaceae bacteria, which syntrophically degrade non-acetate volatile fatty acids (VFAs) into H2 and CO2. This, along with the increase in abundance of other syntrophic VFA oxidizers, such as Spiorchatetes, 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. [Figure not available: see fulltext.]

Original languageEnglish
Article number4
JournalFrontiers of Environmental Science and Engineering
Volume11
Issue number3
DOIs
Publication statusPublished - 01 Jun 2017

Keywords

  • Biogas
  • Biosafety
  • Clocamonaceae
  • Isobutyrate
  • Sequencing
  • Spiorchatetes

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