London Waste opts for in-vessel composting

Alexander Maddan, Managing Director of Agrivert Limited, describes the 30,000 tonnes per year in-vessel composting (IVC) plant that his company is currently in the process of constructing for LondonWaste Limited and which will be commissioned in July 2005.

Due to the long-term nature of waste contracts, it has always been a concern of buyers in the emerging industry of in-vessel composting that the technology that they are buying is tried and tested. Whilst Agrivert is building the first of its design of plant in the UK, some 30 plants using this design have been built in Europe, and have been operating successfully over a ten year period and currently process over 600,000 tonnes per year.

LondonWaste Ltd, a joint venture between North London Waste Authority and SITA, has procured this Agrivert-designed plant in the UK. Agrivert has over 10 years of experience in the recycling of organic wastes across the UK and now provides an innovative design, build, own, operate and recycle service for both green waste and in-vessel composting operations to local authorities and private sector enterprises.

After a rigorous tender process, the Agrivert system was selected for its simplicity, robustness and quality of end product in an odour-sensitive residential area. Construction started in February 2005 and will be completed in July 2005 when the plant will receive the first kitchen waste / green waste deliveries.

ABPR compliant

The stringent new Animal By-Product Regulations (ABPR) have produced new challenges for compost plant design and the Agrivert IVC System has been developed to exceed all current regulations. By use of batching and a one-way flow through the plant, the ABPR are complied with in the most thorough manner. Avoidance of the use of common driving areas ensures the concept is future-proof should the regulations tighten further.

Odour is a very real fact for IVC plants. By use of membrane technology in the Agrivert system odour is controlled by virtue of the pore size of the membrane used. This eliminates odour release from the tunnel but allows moisture to escape to the atmosphere. This simple and very effective system avoids the use of expensive scrubbers and/or biofilters.

Process duration

The In-Vessel part of the process lasts between four and six weeks. This long duration ensures that sanitisation and stabilisation occurs prior to open air windrowing. If this process was shortened, bad odour problems would result during the external maturation phase. By utilising large 215 tonne capacity tunnels, the plant can accommodate this increased retention whilst minimising the capital investment and operational costs involved. The plant has five process stages:

  • Delivery to reception, shredding
    and blending – Daily
    Stage 1 tunnels – 2-3 weeks
  • Stage 2 tunnels – 2-3 weeks
  • Maturation – 8 weeks
  • Screening – Weekly
  • The final product is produced from a 10mm screen for amenity and horticultural use or from a 30mm screen for agricultural use. The oversize fraction is re-used in the process whilst the plastic is separated out and, in the case of the plant described above, sent to the LondonWaste energy-from-waste plant. Agrivert is a specialist recyclers, to land and has outlets for all of the LondonWaste compost end product. Part of the advantage that Agrivert has is its seamless integration with the business’s origins – the recycling of organic material to land.

    Agrivert, which has expanded over a 10 year period, is unique in offering the full design build, own, operate and recycle service within the composting industry, coupled to its extensive experience, firmly driven by a product-led philosophy, as opposed to a process-led philosophy. Working with most of the UK’s waste and regional water companies and for many councils, it now recycles some 750,000 tonnes of organic waste back to land, thereby avoiding adding to landfill.
    The company, which is exhibiting at the CIWM show in Torbay, can look forward to an exciting future in the organic waste industry as demand for kitchen and green waste treatment increases.

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