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The financial and eco-benefits of investing in anaerobic
digestion (AD) technology to generate energy from food waste
is something that all processors should be considering, according
to InSource Energy.
Anaerobic Digestion (AD) is a biological process that happens
naturally when bacteria breaks down organic matter such as
food, in environments with little or no oxygen. It is a treatment
that composts waste and produces a biogas that can be used
to generate electricity and heat.
AD has been attracting huge attention and, last year, the
UK government made development of the technology a central
part of its waste reduction strategy - but, since then, only
a handful of subsidised projects have been realised.
However, last month, Premier Foods, one of the UK’s largest
food companies, announced that construction of a closed loop
commercial-scale anaerobic digestion plant at its RF Brookes
ready meals factory in Wales was underway.
The £5m facility will convert food waste into energy to
help power the factory, providing significant savings in waste
disposal and energy bills and reducing carbon emissions by
around 8,500 tonnes per year. The AD plant, which will be
owned by Insource
Energy, is scheduled for completion by the end of
2010 and is expected to be fully operational in early 2011.
The facility, which received a £0.5m subsidy from WRAP Crymu,
will have the capacity to process around 10,000 tonnes of
food waste a year and is expected to generate 300kW total
energy. It will supply power for about six per cent of the
food processor’s electrical consumption and around the same
amount for its hot water usage, John Scott, InSource Energy
managing director told FoodProductionDaily.
This is believed to be the first example in Wales of a factory
being partially powered by its own waste in this manner and
is one of only a handful of such closed loop facilities in
the UK, he added.
While nobody disputes the environmental benefits of recycling
food waste, the question for industry is whether anaerobic
digestion plants are both technically feasible and economically
viable.
Scott declared it to be technically possible as long as
there was a ready and consistent source of solid or semi-solid
food waste. The amount needed depends on the nature and concentration
of organic material, he said. “Any food processing plant can
use AD - but, whether it is economically viable will depend
on whether the food source is of suitable quality or quantity.”
AD can theoretically use any raw materials used in food
processing. Feed stock comes from rejected foods that are
not fit for use, trimmings from food preparation and food
sludge in effluent collected in drains after wash-downs.
While it is very difficult to generalise, the annual waste
volume needed to make AD economically workable would be around
3,000 tonnes, said Scott. Almost inevitably, major industry
players - with their larger capacities and economies of scale
- were more likely to be able to generate the volumes needed.
“Any food processor should at least be thinking about this
and whether it is doing enough with its waste,” he added.
“The bigger companies should be considering the full scope
of their options.”
While the size of an AD plant varies according to its capacity,
Scott said “it’s not massive, but it’s not small” - advising
that firms should factor in between a third to half an acre
(1,300 - 2,000 sq meters).
The largest single item is the digestion tank, where waste
foodstuff is held for a sufficient time to allow the bacteria
to break it down and release the energy. Typical digestion
time is between 30-40 days, said Scott. An AD plant with a
capacity to process three thousand tonnes of food annually
would need a digestion tank to cope with of 10 tonnes of food
waste per day over this period.
Scott added that several companies contributing waste to
- and getting energy from - a single AD plant could be a practical
solution where space is an issue. However, he said that, at
present, there appears to be a cultural concern among companies
about doing this
“There does seem to be concern among food processors about
bringing in waste from another site,” said Scott. “They are
happy to use their own, but there is a reluctance to use waste
from other plants - even if they are part of the same firm.
Food companies do not want to be seen as part of the waste
management process.
"This is a view that we hope will change, because there
is a big difference between waste food material from the processing
stream and kerbside waste collected by councils.
“We hope that, with time, industry players will think more
intelligently about it - it is not waste but fuel,” he concluded.
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