Advanced digestion facility opens up new options

Monsal Ltd is constructing what is stated to be the largest advanced digestion facility in the UK at Blackburn Sludge Treatment Centre opening, pointing the way to innovative treatment of MSW

Monsal Ltd has been awarded a contract by United Utilities to design and construct the largest advanced digestion facility in the UK.

This company, which specialises in providing environmental products, technology and research capability for the water and waste markets, offers environmental technology for anaerobic digestion, biogas and bioenergy, advanced digestion and specialist processes for the treatment of organic solids and wastewater.

Monsal services range from fundamental research capability through consultancy, design build and optimisation of water and waste projects in our specialist areas. The company says it works closely with its clients to deliver the most optimal solution. Monsal lays claim to be a market leader in the provision of advanced digestion and renewable energy technology.

MSW market

In common with other major specialists in the high tech water and waste sector, the company is increasingly turning its attention to providing solutions in aspects of the MSW sector.

Monsal points out that the use of advanced anaerobic digestion technology is used widely on the Continent for treatment of the organic fraction of MSW - or now more commonly referred to as Biodegradable Municipal Waste (BMW) in the UK . The company told LAWE that Interest in the technology is now developing at a rapid pace and a number of projects are in the development stage.

Blackburn project

The plant at Blackburn wastewater treatment works was awarded as part of Monsal's process framework agreement to supply United Utilities with advanced digestion technology incorporating the United Utilities Enzymic Hydrolysis (EH) system (patent pending). Monsal is also United Utilities' development partner and the exclusive licensee for the process.

Monsal will supply a package of core technology for upgrade of the existing digestion plant including EH reactors, new boiler house, integration equipment with digesters, sludge management system, biogas management system and control of existing digesters. The £2.5 million contract is part of a wider £9 million refurbishment project being undertaken by UU's construction partner KMI on this site.

Advanced Digestion Technology sites

Advanced Digestion technology is now committed at the following UU sites: The commitment from United Utilities to continue upgrade of its major sludge treatment centres to a higher quality sludge product reflects a growing trend in the UK and globally for more advanced digestion technology1.

There are now over 15 full- scale sites in the UK employing advanced digestion processes such as Enzymic Hydrolysis, thermal pasteurisation, thermal hydrolysis and Acid Gas pre-treatment prior to mesophilic digestion. Over 52 digesters have been upgraded using bolt-on technology in AMP3 and this trend is also common in the US. The emphasis on digestion technology will shift to pre-treatment and reactor configuration will be critical to success of these plants in the future.

The plug flow reactor configuration developed by Monsal and United Utilities is unique and ensures optimal conditions for pathogen reduction and hydrolysis reactions prior to anaerobic digestion. The pioneering work in developing the process was acknowledged in 2004 by receiving runner up award in the IChemE water prize.

The new plant at Blackburn is designed to treat a maximum sludge throughput of 741 m3/d at 8% DS or 21,600 TDS per annum (270,500 wet tonnes per annum). The plant is designed to meet the Enhanced sludge quality standards in the UK.

Fast growing technology

Advanced digestion is potentially one of the fastest growing technologies for larger centralised digestion facilities, providing a high quality sludge product whilst optimising VS destruction and renewable energy production. The process incorporating Enzymic hydrolysis, unlike other two-stage digestion processes is plug flow, which allows optimal conditions for the hydrolysis and acidification stages to be carried out1. This optimisation of reactions allows the digestion process to be carried out much faster and hence allows higher loading of existing digester assets, typically over 4.0 kgVS/m3.day The Enzymic hydrolysis reactor is designed to operate at 42oC with a 2 day HRT prior to conventional mesophilic anaerobic digestion.

(1) HARRISON, D., CUMISKEY, A., LE, M.S., MAYHEW, M., ASSADI, M. "Advanced Digestion in the UK - Technology Developments and Options for Optimisation of Sludge Assets". WEFTEC 2004, 77th Annual Technical Exhibition and Conference. New Orleans, USA. October 2-6, 2004.

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