Five Good Reasons You Should Support Anaerobic Digestion Including Co-Digestion With WWTW Sludge

Ever thought about endeavoring to support anaerobic digestion including co-digestion of the organic fraction of MSW with sewage sludge? Most people just consider this briefly, then never do anything whatsoever regarding it Most people have no idea of just how to start, so they really never do. Thinking that it'd require too much time to understand the concept discourages some others. Others are too lazy to try, or don't have motivation!!

Now just hang on here a minute! Are those really valid reasons? Did the reasons for receive a fair hearing? Was there enough info on which to base a reasonable decision? The possible benefits don't appear to have been very well considered...

Maybe that needs to be reconsidered. Let's look at 5 top reasons to support anaerobic digestion including co-digestion of MSW with sewage sludge to see how things look from that perspective.

To start with, AD (including co-digestion) has great potential to minimise the impact on the carbon economy by replacing fossil fuel derived power and heat. You've got a valid point as you note that replacing fossil fuel derived power and heat is going to become scarcer and even more expensive. That's a very good point. Even so, take into account that, anaerobic digestion isn't exactly cheap, and to rely on government AD subsidies and incentives lasting as long as they say they will is quite a leap of faith. Moreover, consider that most governments don't last more than 4 to 5 years, when investment is returned on these AD plants over a much longer period.

Second, anaerobic digestion enables diversion of wastes from landfill. That is because all of the output from the anaerobic digester will in future be used in the process. One of several results of this is the fact that there will be virtually no waste from AD Plants that they will need to send to landfill.

Third, by co-digestion (if OFWAT's review gives it the go-ahead in AMP5) society would be avoiding the carbon cost of full treatment of wastes through sewage treatment processes by feeding directly to co-digestion. Moreover, biogas yields may rise by up to 50%, with little or no further investment. Co-digestion simply uses existing headroom in AD Plants that the Water Plcs's engineers have already made more efficient!

Fourth, production of digestate to act as a fertiliser will provide a big phosphate benefit, and this is good as phosphate reserves are finite and may run out sooner than oil.

5th, the locality of AD plants can lead to reduced transportation - optimising the use of embedded carbon in existing assets.

So just look at those points and examine them mentally. All five reasons are persuasive points as to the reasons you really should support anaerobic digestion including co-digestion of MSW with sewage sludge.

Just think it over for a moment. Those reasons were sufficient to convince a lot of people before you. Will they not also persuade you to support anaerobic digestion including co-digestion of msw with sewage sludge?

Find out how you can get involved in the growing Anaerobic Digestion scene, and understand what "digestate" is by going to our What is digestate? page at www.anaerobic-digestion.com/html/what_is_digestate.php.

CIWEM calls for a simplified approach to co-digestion

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’

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