The role of on-site industrial digestion
Gueterbock, R., Clearfleau Limited, UK
(free)
Introduction to on-site anaerobic digestion:
Clearfleau is one of a limited number of British owned anaerobic digestion (AD) technology companies that are developing systems specifically suited to the UK market. The on-site treatment of liquid effluents, waste ingredients and co-products in the food or drink sectors favours a technology that will optimise energy output. There are other opportunities for small-scale AD, like on-farm or community projects but they require a different approach.
UK policymakers and the AD industry tend to be focused on large scale centralised plants with electrical output above1MW. However, compact AD plants that can treat waste and effluents where they are produced, will enable the more effective use of the renewable energy (heat and power) in production processes, replacing purchased fossil fuels.
High-rate liquid digestion plants can be installed on confined sites and facilitate reduced effluent treatment and energy costs, whilst generating revenue from the energy produced. They should accommodate flow and load variations and need to optimise biogas (and revenue) generation in order to maximize payback. Post treatment, the process should facilitate grey water recycling for use on site, or possible watercourse discharge.
Anaerobic Digestion (AD) is a well established technology and in this natural degradation process, the methanogenic bacteria break down organic matter (sugars, fats and proteins) in the absence of oxygen to produce biogas (mainly methane). However, the established high-rate (suspended media) digestion systems that have been used on brewery sites, struggle to handle the higher solids in the feedstocks from the food processing sector.
There are also concerns about the level of investment required for AD plants and how long they will take to produce a return on the investment. This is not normally a concept that is associated with disposal of co-products but novel AD technologies that optimise biogas output can benefit from renewable energy incentives to provide a potential IRR of 20%.
The technology has been used for years to treat agricultural or sewage waste but the UK has been a slow adopter, compared to the rest of the EU. There are also facilities, often located away from public gaze, that treat municipal waste (many operated by the waste management industry). Many food and drink businesses are unaware of the benefits of AD to some extent due to the focus of policy on diverting organic materials from landfill.
