The Present and Future of Anaerobic
Digestion and Combined Heat and Power
Severn Trent Water Limited:
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Midlands UK coverage
8 Million population served
133 Water Treatment Works
46000 km water pipes
1050 Sewage Works
54000 km sewers
Ken Shapland BSc CSci CChem MRSC FCIWEM
Menu:
• What is AD?
• What is CHP?
• Why AD in the Water Industry?
• Development of AD/CHP in STWL
• Regulatory Framework
• Current Capability and Aspirations for the Future
What is AD?
• Biogas first used for heating bath water in Assyria
during the10th century BC and in Persia during the 16th
century.
• 17th century - Jan Baptita Van Helmont discovered that
decaying organic material produced a flammable gas.
• 1776 - Count Alessandro Volta discovered the amount of
gas produced was proportional to the amount of
organic material used.
• 1808 - Sir Humphrey Davy concluded that methane was
in gases produced by decaying cattle manure.
What is AD (2)?
• First AD built by a leper colony in Mumbai, India in 1859.
• 1895 - biogas collected from a sewage system and used
in street lamps.
• 1930-50’s - research isolated and identified anaerobic
bacteria and studied the best conditions for their
growth.
What is AD (3)?
• Stage 1
– hydrolysis and fermentation - cellulose, protein and lipids in the
organic material broken down by anaerobic micro-organisms.
• Stage 2
– acid phase where organic acids produced in Stage 1 are
converted by acetogenic bacteria to smelly volatile acids (e.g.
acetic, butyric, valeric), carbon dioxide and hydrogen.
• Final ‘Methanogenesis' Stage
– methane-generating micro-organisms produce methane and
carbon dioxide from the volatile acids produced in the earlier
two stages.
ALL STAGES ARE CARRIED OUT IN THE SAME VESSEL AT THE
SAME TIME IN CONTINUOUSLY FED CONVENTIONAL MAD
AD Process
Biodegradable
Organic Waste
Anaerobic
Digester
Continuously Fed
Maintained at 350C
“Mesophillic”
Digestate
Biogas
Agriculture
and other
Outlets
Gas Holder
Biogas
• Methane generated from AD is called Biogas
• Consists of approximately 60% methane and 40%
carbon dioxide together with some minor impurities
(H2S, water, siloxanes)
What is CHP?
• CHP is the combustion of biogas to produce heat and
electricity
• Combustion takes place in engines which are similar to
conventional diesel engines
• Engines are often dual-fuel so they can be operated on
fuel oil if the supply of biogas is interrupted
AD Process
Biodegradable
Organic Waste
Anaerobic
Digester
Continuously Fed
Maintained at 350C
“Mesophillic”
Digestate
Biogas
Agriculture
and other
Outlets
Gas Holder
AD/CHP Process
Biodegradable
Organic Waste
Continuously Fed
Maintained at 350C
“Mesophillic”
Anaerobic
Digester
Digestate
Biogas
Agriculture
and other
Outlets
Gas Holder
Heat
CHP Engines
Power
Why AD is Used in the Water Industry?
• Because plenty of feedstock is received!
• Sludge from our sewage treatment processes.
• Readily biodegradable input to AD
• Produces renewable energy and heat
• Benefits from Renewable Obligation Certificate (ROCs)
• Product from AD is more suitable for use in agriculture
Development of AD/CHP in Severn Trent
• Anaerobic digestion used since 1950s
• First major plant built at Birmingham STW in 1950’s
• Originally used converted marine engines for CHP
• Over 40 AD/CHP installations in 2008
Further Advances in AD Technology
• Acid Phase Digestion (APD) is being introduced
– APD separates the process i.e. acetogenesis and
hydrolysis stages from methanogenesis
• Advantages:
• Greater volatile solids destruction than a conventional
mesophilic process
• Increased gas production
• Achieves greater volatile solids destruction resulting
in a greater reduction of solids
• Disadvantages
• More complex
APD SCADA (MIMIC)
Environmental Regulation
Biogas
• Biogas could be viewed as:
– A product of anaerobic digestion of waste
– A by-product of the above process
– A waste
Biogas
• The Environment Agency consider biogas to
be a waste
– Although it does appear to satisfy European
guidance criteria for by-product status
Biogas
• The Environment Agency consider biogas to
be a waste
– Although it does appear to satisfy European
guidance criteria for by-product status
• Consequence
– Combustion of biogas is fully regulated under
Environmental Permitting Regulations
Environmental Regulation
CHP
• Transposition of IPPC Directive into UK law reduced the
threshold for more rigorous permits from 50 to 3 MW thermal
input
• Installations between 0.4 to 3 MW require an environmental
permit
• Installations under 0.4 MW can be registered as an exempt
activity
• Combustion activities are aggregated if considered
associated or technically connected
Environmental Regulation
CHP
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Transposition of IPPC Directive into UK law reduced the threshold
for more rigorous permits from 50 to 3 MW thermal input
Installations between 0.4 to 3 MW require an environmental permit
Installations under 0.4 MW can be registered as an exempt activity
Combustion activities are aggregated if considered associated or
technically connected
• Consequence
– Does not encourage the innovative provision of CHP
– Incentive to design installations under thresholds despite
capability
– Cost benefit analysis is heavily dependant on permit
requirements
– New entrants are deterred e.g. agricultural sector
Current Capability and Aspirations for the Future
• 41 AD/CHP plants in 2008
• 162 Giga Watt Hours produced in 2007/08
• 17% of the electricity used in the Company in 2007/08
• Sufficient to power over 46,000 homes
• STWL produced 45% of the renewable energy from
biogas in England & Wales in 2007/8
• Additional 3.6 MW being installed in 2008/09
How We Compare to Others in Sector
ROC's Registered By Water Sector During 2006/07
7%
3%
4%
1%
20%
Chart based on Ofgem
ROC register for
2006/07.
42%
16%
3%
4%
Anglian Water Services Limited
Northumbrian Water Ltd
Severn Trent Water Ltd
South West Water Ltd
Southern Water
Thames Water Utilities Ltd
United Utilities
Wessex Water Services Ltd
Yorkshire Water
• In 2006/07 we received 42% of all the ROC’s issued for CHP
• 45% in 2007/08
Support for UK Government Aspirations
“The water industry will be at the hub of a national anaerobic digestion infrastructure.
Where appropriate, water companies will generate additional renewable energy by using
their spare capacity to process other feedstocks such as food waste.”
Key Stakeholder Aim
The water companies will seek to ensure that at least 20% of all energy used by the UK
water industry comes from renewable sources by 2020. Anaerobic digestion will make an
important contribution to this.
Severn Trent Water target is 30% by 2012/13