Biochemical pathways: the route to accelerating revenue generation from anaerobic digestion
Smyth, M.1 and Horan, N.J.1,2, 1Aqua Enviro Limited, 2University of Leeds, UK
(free)
Abstract
Operation of anaerobic digesters is not a simple process. But in view of the potential value of the methane generated and the opportunities to produce additional methane through a fully optimised digester, it is worth ensuring that strategies are in place to achieve this. Many options are available but analysis of the composition of the volatile fatty acids (VFAs) in the digester provides a sophisticated approach that permits fine tuning of digester performance. This paper describes the theory of control through analysis of VFAs, outlines methods for their analysis, and describes how the results can be applied to digester control.
Key words
Anaerobic digestion, volatile fatty acids, organic wastes, biosolids, digester operation
Introduction
Over the past decade there has been a surge of interest in anaerobic digestion, in particular from the waste industry for its application to the digestion of biodegradable organic wastes. The UK Government has also recognised the important contribution that anaerobic digestion can make to help it achieve a number of key national targets, for instance use of renewable energy, reducing CO2 and other greenhouse gas emissions and reducing the amount of biodegradable municipal waste sent to landfill. The Water industry also sees anaerobic digestion playing an increasingly important role as it seeks to ensure that at least 20% of all its energy use comes from renewable sources by 2020. But all organic wastes are not equal. Sewage sludge is actually a poor feed source for anaerobic digestion as it is high in nitrogen and low in carbon thus the methane yield is reduced as a result both of the paucity of carbon and the ammonia released during digestion which may prove inhibitory to the process. Animal wastes such as cow slurry and chicken manure all suffer similar problems. By contrast food and vegetable waste are high in carbon and lack nitrogen and phosphorus and so although can generate a higher yield during digestion, this requires careful operation to ensure the reactions of acid production do not exceed the reduction of these acids to methane, with a resultant digester failure.
