The UK now has over 260 operational anaerobic digesters treating farm residues, food waste and industrial waste with an operational capacity of around 13 million tonnes of inputs and an installed power of over 200 MWe. This represents an annual increase of around 25% since 2010, equivalent to the construction of 20 to 30 new digesters each year. It is an achievement the industry should be proud of, although not complacent because expansion within the sector at this sort of rate has not been problem-free. The process involves large tanks of (potentially) highly polluting anaerobic slurry generating an explosive gas and with a propensity to produce copious volumes of thick foam that can block gas outlet valves. This gas is stored in large, flexible tanks and itself can contain toxic concentrations of odourous hydrogen sulphide. Since the anaerobic digestion process is biological, the metabolic pathways need to be understood and supported with the right basic diet. Fortunately, major incidents are rare although not unheard of, and a series of pollution incidents caused by containment failures at AD plants has prompted the Environment Agency to place the industry under intense scrutiny.
One problem the industry faces in ensuring the continued safe operation of its digesters, is in sourcing and retaining staff who are appropriately trained and with experience of digester operation and maintenance. Rapid expansion in digester uptake has not been met by a commensurate response from the education and training sector and accredited or recognised training routes to achieve competent operational skills are thin on the ground. This hurts the industry in two ways because not only does it increase the risk of digester failure, it also increases the likelihood that the digester is not operating under optimal conditions, with a consequent loss of revenue from the reduced methane yield.
AD Operators: Aqua Enviro have been offering training for operators of AD plants for over a decade. Initially concentrating on the needs of the water industry, due to the larger market it offered at that time, this training was extended to the organic waste sector as the demand grew. This training provides the background to the process microbiology and biochemistry in order to emphasise that digestion is a long way removed from a black-box process and to link performance and operation with the nature of the digester feedstock. It considers the basic design issues associated with a digester in order to permit a full understanding of parameters such as the hydraulic retention time and organic loading rates. It covers in detail the key aspects of mixing and feeding the digester and stresses how these are operational parameters that have a major impact on performance.
AD Statistics: Our training also includes a statistical training package that introduces a range of simple, statistical skills to allow operators to analyse the data they collect in a more meaningful way and apply the techniques to forward-planning, troubleshooting and digester optimization. By means of case-studies, a range of potential problems and their solutions are covered and include: foaming, odour, containment failure and over and underloading. All of this is delivered within a H&S framework that identifies risk and mitigations at each crucial process stage.
Marketing Digestate: An often overlooked aspect is the digestate that is produced 24hrs a day, 365 days a year. As such, we are developing a training course specifically targeted to marketing digestate to farmers (the current principle outlet for digestate) as well as other potential current/future opportunities.
What makes our training different? We draw on our own field experience with digester troubleshooting in the organic waste sector, backed up by a detailed technical understanding of anaerobic digestion processes (supported by our own in-house laboratory). In addition to training AD operators, we have also provided training for the environmental regulators the Environment Agency and Natural Resources Wales, as well as Zero Waste Scotland.
The next round of training will take place at our Wakefield Training Suite in March and July and more details of the individual courses are available on our website with a number of digester case studies and free access to presentations and papers from Aqua Enviro events that are available to download free of charge.
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