manipulation of operating temperature, the balance of macro and micro-nutrients, digester mixing and mass transfer characteristics, uncoupling of solid and liquid retention times, phase separation in multistage digesters, in-situ gas or product extraction, and dynamic control through continuous monitoring linked to operational interventions. These approaches need to be matched to feedstock type and operational objectives. To be fully effective, they should be hypothesis-driven and linked to an understanding of the physiology and functionality of the microbiome. There is still considerable scope, however, for improvements in process efficiency achieved through both empirical and theoretically-driven approaches to improving the engineering/microbiology interface.
Optimisation of AD Processes
In the simplest sense, optimisation is the process carried out when there is a range of parameters that can be controlled and a single variable to be maximised or minimised: in the case of anaerobic systems for energy production this might be the biogas yield, or in the case of waste management, the quantity of residual waste solids for disposal. Alternatively, there may be complex output parameters, such as a balance between capital cost and revenue or performance and stability; and a range of possible input parameters that could satisfy them. In practical applications of anaerobic digestion, it is rare for the desired outcome to be precisely formulated, and in general too little is known about the systems being designed or operated, or the factors that influence them, to allow a high degree of control. The word ‘optimisation’ is therefore often used in a looser, non-mathematical sense to mean obtaining a result which lies in an acceptable range and is better than at least some of the alternatives. To improve upon this current situation requires a much more fundamental understanding of the factors that influence the digestion process, including the specific requirements of the microbiome, the interface between it and the engineering design of the digester and the way the digester is operated. Research in this area may consider different ways of increasing the metabolic capacity of the digestion process through