Spare capacity in water company anaerobic digesters should be available to co-digest solid waste together with sewage sludge and generate ’renewable’ biogas, says the Chartered Institution of Water and Environmental Management (CIWEM) in its new Policy Position Statement on co-digestion.
Too often this is hampered by complex regulations governing the recycling to land of the solid output (a useful soil conditioner) and wrangling over how the financial proceeds should be reinvested into the tightly regulated water industry.
CIWEM believes that co-digestion of solid waste with sewage sludge represents the best solution for the environment where headroom water company digester capacity exists, as it makes efficient use of existing infrastructure and expertise. But a conflicting regulatory landscape governing sewage sludge on the one side and biodegradable waste on the other, means it can be difficult or expensive to recycle digestate to the environment beneficially. This is despite Defra and DECC promoting anaerobic digestion (AD) as a method of generating renewable fuel and diverting organic waste from landfill, and Defra stating that it sees the water industry as being central to the expansion of AD.
CIWEM is calling for a range of changes, including revision of the Sludge Use in Agriculture Regulations to reflect the benefits of co-digestion and establish a clear legislative framework for all treated organic residuals; a financial regulatory framework which meets the needs of both the water and waste industries and an update to the Quality Protocol for Anaerobic Digestate (PAS 110) to include provision for the use of sewage sludge as a component of the feedstock.
These issues will be discussed at CIWEM’s forthcoming conference, The Water, Waste & Energy Interface - Realising the Potential of Anaerobic Digestion: Removing the Barriers on 28th June in London.
CIWEM’s Executive Director, Nick Reeves, says:
’Co-digestion of sewage sludge with other biodegradable organic wastes clearly represents a sensible solution, particularly where there is headroom capacity in existing digesters which are treating sewage sludge, but also in other areas where a critical mass of feedstock is required in order to make an AD scheme economically viable. There are a number of obstacles which are by no means insurmountable but which are proving frustratingly slow to resolve. This is all the more frustrating when, clearly, we should be maximising the production of biogas from wastes where we can, and recycling organic material back to land is eminently sensible given the widespread degradation of soils. Whether solutions are regulatory, technical, or a combination of these, we really should move to a situation where it is possible to digest together two waste streams which individually pose no problems’