Monsal is a long established UK based turnkey, design and build, contractor in Anaerobic Digestion.
Monsal has developed its own advanced digestion process, known as Enhanced Enzymic Hydrolysis (EEH), and has constructed a number of plants using this technology in the UK, notably for Anglian Water, the East Anglia wide water company, Scottish Water, and Severn Trent Water.
Their skills lie with the digestion of sewage sludges, especially activated sludge for many of water companies, and in particular (as in our case study below), from Anglian Water’s sewage treatment works.
The company is also, we understand, now involved in the anaerobic digestion of garden, animal, and food waste.
The following Case Study is an extract from the July edition of Water and Wastewater Treatment Magazine, published by Faversham House Group ( http://www.wwt-magazine.info):-
A six-reactor EEH system was instated at a newly constructed sludge treatment centre at Kings Lynn, undertaking mesophilic and thermophilic duties.
The Kings Lynn project stands on a greenfield site and can treat up to 19,000 tonnes DS (Dry Solids) per year in a newly constructed sludge treatment centre.
Monsal delivered the technology to the principal contractor, the Galliford Try Meica (GTM) joint venture, tested in a competitive tender.
The plant treats a variable load, including waste from local vegetable processing operations, and is currently treating between 25-25 tonnes DS/day.
The sludge feed contains a high content of waste activated sludge at 55% on this site due to the large activated sludge plant at Kings Lynn. The Monsal plant has achieved takeover in June 2008.
From the outset, the plant was designed to maximise biogas and have an optimal energy balance. The project team worked closely to integrate pre-treatment with digestion and CHP so that all available heat could be utilised in the process, both low-grade and high-grade.
Biogas production is a significant indicator of process performance and in the case of Kings Lynn, the production rates being achieved equate to more than 400m3/tonne DS treated. This compares with conventional digestion of 300m3/tonne DS, typically a 30% uplift in performance.
The Kings Lynn plant is currently producing about 12,000m3 of biogas from about 11,000 tonnes DS, and delivering 980kW of energy at the engine without any fuel requirements. The percentage of VS destruction, recently measured at 60% conversion, is also consistently high. The project hit a key milestone in May and the anaerobic digestion (AD) plant is now providing all the energy requirements across the whole site, both wastewater and sludge treatment.
Great Billing is the largest of Anglian's planned AD sites in AMP 4 and will process about 40% of all the sludge in the company's biosolids programme. The strategy for Great Billing demonstrates the ability of advanced technology to optimise digestion and energy outputs.
Here AD technology will increase digester loading, deliver an enhanced treated product at the cake and maximise biogas production. The existing five digesters on this site, with a total volume of 17,000m3, will be upgraded from their existing indigenous load of 13,000 tonnes DS to 39,000 tonnes DS a year by importing cake.
This new sludge super centre will collect from four regional centres at Corby, Broadholme, Flag Fen and Northampton. The plant incorporates a number of the latest features including the secondary stage steam disintegration units.
A major advantage is that the process starts with dewatered sludge above 15% DS. Sludge is dewatered to cake at Corby, Broadholme and Flag fen and re-wetted at Great Billing to 7-8% on site.
The use of cake re-wetting can deliver a higher percentage of DS to the digesters more reliably than thickening up and is a recommenced process at large centres.
This key strategic advantage means that all significant sludge imports coming to site are in the form of cake, therefore reducing transport costs and having a lower carbon footprint.
The key features of the project include:
- 26,000 tonnes DS of sludge cake imports
- 13,000 tonnes DS of indigenous sludge
- New cake import facilities for re-wetting cake with indigenous sludge
- Advanced Monsal EEH system with a capacity of 40,000 tonnes DS per annum
- Upgrade of existing digester mixing systems and biogas handling
- Expanded CHP capacity on site to more than 4MW of energy generated
- Existing digestion capacity of only 17,000m3
- Increased processing capacity by 300% in same digester volume
There are now (July 2008) 11 full-scale Monsal plants committed to anaerobic digestion using this technology in the UK in Anglian Water, Southern, United Utilities, Wessex and Welsh Water.
That number is expected to grow rapidly as the strategic benefits of digestion optimisation become clear.
For the Monsal anaerobic digestion web site continue here.