Impact of Storage Conditions on the Methanogenic Activity of Anaerobic Digestion Inocula

Sergi Astals,Sasha D Hafner,Sören Weinrich,Konrad Koch,Miriam Peces,Stephan Tait

doi:10.3390/w12051321

Abstract

The impact of storage temperature (4, 22 and 37 °C) and storage time (7, 14 and 21 days) on anaerobic digestion inocula was investigated through specific methanogenic activity assays. Experimental results showed that methanogenic activity decreased over time with storage, regardless of storage temperature. However, the rate at which the methanogenic activity decreased was two and five times slower at 4 °C than at 22 and 37 °C, respectively. The inoculum stored at 4 °C and room temperature (22 °C) maintained methanogenic activity close to that of fresh inoculum for 14 days (<10% difference). However, a storage temperature of 4 °C is preferred because of the slower decrease in activity with lengthier storage time. From this research, it was concluded that inoculum storage time should generally be kept to a minimum, but that storage at 4 °C could help maintain methanogenic activity for longer.

Highlights

Anaerobic digestion is a technology used for the treatment of organic-rich waste streams, which produces biogas as a renewable energy source
Inoculum, there were no clear differences between the specific methanogenic activity (SMA) of fresh inoculum and the SMA of inoculum stored under different temperature conditions
Results from Experiment 1 and Experiment 2 showed that a 1-day pre-incubation at 37 ◦ C to acclimatise the inoculum to the test temperature did not affect the inoculum methanogenic activity

Summary

Introduction

Anaerobic digestion is a technology used for the treatment of organic-rich waste streams, which produces biogas as a renewable energy source. The growing importance of anaerobic digestion application and research has required technicians, practitioners and academics to increasingly conduct: (1) metabolic assays to assess the activity of a digester’s microbial community (e.g., specific methanogenic activity (SMA)) [1,2]; (2) biochemical methane potential (BMP) tests to quantify the methane yield of a digester’s feedstock [3,4,5,6]; (3) residual methane potential tests to determine the methane potential of a digester’s effluent and the efficiency of the anaerobic digestion process [7,8]; and (4) anaerobic toxicity assays (ATA) to determine the resilience of a digester’s microbial community towards an inhibitor [9,10] These assays provide crucial insights to guide successful anaerobic digestion operations. Water 2020, 12, 1321 existing infrastructure, and the increasingly widespread adoption of co-digestion to divert residues away from landfill and boosts local renewable energy supply To conduct these assays, it is generally preferred to use fresh inoculum [3,4,11,12]. This introduces uncertainty regarding the potential impacts that different transport and storage conditions have on inoculum activity and on the efficacy of the inoculum when used in the assay

Methods

Results

Discussion

Conclusion