Co-digestion hampered by over-regulation, warn industry leaders

The Chartered Institution of Water & Environmental Management (CIWEM) has said that spare capacity in water company anaerobic digesters should be available to co-digest solid waste together with sewage sludge to generate biogas.

In its new policy position statement on co-digestion, the CIWEM says 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 it is concerned that conflicting regulatory landscape governing sewage sludge on the one side and biodegradable waste on the other has presented difficulties in recycling digestate in a cost-effective way.

The trade association 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.

It also wants 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.

CIWEM’s executive director, Nick Reeves, said: “Co-digestion of sewage sludge with other biodegradable organic wastes 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 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 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.”

Maxine Perella