Recent UK Anaerobic Digestion Developments and Future Projections

The growth of anaerobic digestion in the UK has not met Defra’s strategy target of 2011, when 1,000 new digesters were to be built by 2015. In fact less than half that figure was achieved, nevertheless the industry has been growing rapidly in real terms in the UK. Considering, the difficult economic circumstances, and reticence until quite recently on behalf of potential investors, the number of plants which have been brought on-stream is remarkable.

In the area of Waste Management, the the charity of plants will be needed to process food waste and in particular food waste collected from households. One benefit of slower adoption of anaerobic digestion technology, has been the additional time that has enabled biogas plant process technology to be developed.

It is worth remembering that during the 1980s a host of innovative but unfortunately largely unsuccessful process technologies were heralded as the ideal treatment method for the UK’s industrial organic wastes. A number of new processes were introduced such as:

a) The Upflow Anaerobic Sludge Blanket (UASB)

b) Expanded Granular Sludge Blanket (EGSB)

c) Anaerobic filter.

While such processes were undoubtedly successful for certain quite closely site-specific organic wastes, they were over-sold, and after a rapid initial take-up were then found unable to live up to expectations, and were soon abandoned. Inevitably, this left many clients with heavy costs replacing failing equipment.

A number of commentators have suggested that these experiences left a legacy of distrust in the AD process as a whole which has persisted until quite recently. In the UK this may have led, at least in part, to what was almost a complete absence of industrial anaerobic digestion plants, in the last decade of the century.

When anaerobic digestion plants did start to emerge it was the simplest of single reactor (mesophilic) type of AD plants, which lone UK advocates of anaerobic digestion had continued to espouse. The most successful of these was the plants produced by Michael Chesshire, and his company Farmgas. He was able to show that those processes used in his on-farm biogas plant systems were capable of reliable long-term profitability when the UK DoE (now Defra) chose to award his successor company to Farmgas, named Biogen the funds to demonstrate it on a feed stock of food waste.

At the same time, during the latter part of the 2010s, work by Southampton University researchers showed that problems reported with food waste only biogas plant operation after more than a year from commissioning were avoidable. Process problems would in future simply be avoided by adding certain depleted (and essential) rare earth’s to the feed materials.

The reason that Anaerobic Digestion has been, and still is viewed by UK government department, Defra, as an ideal process which they will subsidise, is because it holds the key to their delivery of a number of government targets, as follows:

- greenhouse gas emisions reduction

- targets for renewable energy generation

- targets for reduction of waste tonnages sent to landfill as required by the EU Landfill Directive

- targets for recycling.

Paradoxically, due to the fact that large quantities of water are added to the standard AD process, this method of waste “treatment” results in a much larger volume of material after the process than before it. It is only made viable to pay what it costs to dispose of the resulting “digestate” volumes, by the high value of the energy produced.

Dry type ananerobic digestion systems which produce less liquid digestate, are being built but don’t achieve as high a biogas yield as the stadard “wet” process. So, while selling the gas remains as the main income, uptake will be likely to remain muted.

Future Projections

The future for the next 5 years of anaerobic digestion industry development will be increasing numbers of biogas plants using essentially the existing core process plant design, in which the vast majority of plants will be single tank mesophilic reactors. It is expected that in accordance with EU requirements, which are likely to be passed requiring all councils to collect and digest household food waste, and government zero-waste pledges, the main demand within the waste management sector will be for food waste digesters.

Source: http://eprints.whiterose.ac.uk/42993/7/horanNJ2.pdf

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