Quantification of methane losses from the acclimatisation of anaerobic digestion to marine salt concentrations

Keiron Roberts, Sonia Heaven, Charles J. Banks

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Abstract

The research assessed losses in methane production as a result of raising digester salt concentrations to marine values, and of increasing the feedstock sulphate concentration. Acclimatisation of inoculum from a municipal wastewater biosolids digester was begun by raising the concentration of chloride salts (Na, Mg, Ca and K) to 6–9 g L−1, as initial experiments showed higher concentrations caused severe inhibition. After stable operation for four retention times salt content in the reactors and the feed was increased by 1 g L−1 every 14 days, up to 31.1 g L−1. The digesters were fed daily in semi-continuous mode and monitored for performance and stability criteria including specific methane production (SMP). SMP was 6–7% less than in controls using the same feedstock without saline addition. After steady-state conditions were achieved at high chloride salinity, magnesium chloride was partially replaced by magnesium sulphate to give a range of sulphate concentrations. Higher sulphate concentrations caused initial instability, indicated by volatile fatty acid accumulation. This subsequently reduced and stable operation was achieved at marine sulphate concentrations, but with a ∼5% loss in SMP due to interspecies substrate competition. High sulphate also affected pH, leading to gaseous H2S production proportional to the applied sulphate load.

Original languageEnglish
Pages (from-to)497-506
Number of pages10
JournalRenewable Energy
Volume86
Early online date3 Sep 2015
DOIs
Publication statusPublished - 1 Feb 2016

Keywords

  • RCUK
  • EPSRC
  • EU FP7 ALL-GAS project (268208)
  • EU FP7 ECOFUEL project (246772)
  • EP/J500537/1

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