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The Present and Future of Anaerobic Digestion and Combined Heat and Power

This article explores the use of anaerobic digestion (AD) and combined heat and power (CHP) in the water industry, focusing on the development of AD/CHP in Severn Trent Water Limited. It covers the regulatory framework, current capabilities, and aspirations for the future. The article also discusses the history of AD, the AD process, and the advantages and disadvantages of AD technology.

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The Present and Future of Anaerobic Digestion and Combined Heat and Power

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  1. The Present and Future of Anaerobic Digestion and Combined Heat and Power Severn Trent Water Limited: • 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

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. AD Process Continuously Fed Maintained at 350C “Mesophillic” Biodegradable Organic Waste Anaerobic Digester Digestate Biogas Agriculture and other Outlets Gas Holder

  7. 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)

  8. 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

  9. AD Process Continuously Fed Maintained at 350C “Mesophillic” Biodegradable Organic Waste Anaerobic Digester Digestate Biogas Agriculture and other Outlets Gas Holder

  10. AD/CHP Process Continuously Fed Maintained at 350C “Mesophillic” Biodegradable Organic Waste Anaerobic Digester Digestate Biogas Agriculture and other Outlets Gas Holder Heat Power CHP Engines

  11. 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

  12. 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

  13. 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

  14. APD SCADA (MIMIC)

  15. Environmental Regulation Biogas • Biogas could be viewed as: • A product of anaerobic digestion of waste • A by-product of the above process • A waste

  16. Biogas • The Environment Agency consider biogas to be a waste • Although it does appear to satisfy European guidance criteria for by-product status

  17. 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

  18. 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

  19. 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 • 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

  20. 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

  21. How We Compare to Others in Sector ROC's Registered By Water Sector During 2006/07 3% 4% 1% 7% 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

  22. 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

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