Improving bioenergy production in a microbial community

Anaerobic digestion (AD) makes use of an undefined microbial population to degrade organic waste to produce biogas (a mixture of methane and carbon dioxide) and a nitrogen-rich "digestate" that is suitable for use as fertiliser. The microbial community utilised in AD has been treated essentially as a black box. Relatively little use has been made of molecular methods to assess the health of AD systems beyond utilising 16S rRNA sequencing to identify the components of the microbial community. These results have yet to provide effective measurements for predicting how a given microbial population will perform with a particular feedstock.

This project aims to identify parameters that cause a reduction in efficiency of the microbial conversion of organic waste to biogas by investigating feedstocks identified by Clearfleau Limited (a commercial AD solution provider) as less tractable to anaerobic digestion. "Difficult-to-digest" samples will be fed to lab-scale (30L) AD systems, and the performance of these systems will be monitored using a range of conventional methods (e.g. Chemical Oxygen Demand, Biological Oxygen Demand, Volatile Fatty Acid concentration and composition, etc) but also examined using molecular techniques in order to establish the underlying mechanisms that affect the efficacy of the microbial community. Shotgun metagenomics will be used to establish the composition of different microbial "seed" populations used for digestions. These data will be complemented with metatranscriptomic and metabolomic measurements. Mass spectrometry will be used to examine the molecular composition of less tractable feedstocks in order to identify potentially inhibitory compounds. Over the last three years Dr Chong's group (the academic partner) has gained considerable experience in the fabrication and long-term operation of lab-scale AD reactors through a current BBSRC CASE studentship sponsored by Clearfleau Ltd (the non-academic partner). The current PhD project has also developed protocols for the effective isolation of DNA and RNA from AD samples for next generation DNA sequencing, which will be used in the investigations described above.

The student will correlate the performance (i.e. conversion of feedstock into biogas assessed by volume and composition) of different microbial seed populations in the anaerobic digestion of the same challenging feedstock (or vice versa) to identify key species for the utilisation / degradation of inhibitory molecules over time courses of several months. Where possible, optimal seed populations will then be tested at an increased scale using Clearfleau's pilot-scale facility (8000 litres) as part of the industrial placement. During the placement, the student will gain experience of operating a pilot-scale AD system and of working in a commercial setting.