Composting Goes High Tech In Magherafelt

With the commissioning of their new state of the art VCU (Vertical Composting Units) in-vessel composting units Magherafelt District Council have become the first Council in Northern Ireland to set up their own in-vessel composter. Built to meet the demands of the new Animal By-Products Regulations the VCU will be used to process material collected in the Council's Brown Bin scheme, which collects kitchen and garden organics from the kerbside. Material collected in the brown bins will be treated to high temperatures in 2 separate stages to ensure that the material is animal by-product compliant and poses no threat to human or animal health. At the moment it is the only system of it's kind, not only in Northern Ireland but also the first of it's kind in the world and has put Magherafelt District Council at the very forefront of waste management in Northern Ireland.

Composting is the oldest form of recycling known to man. Used for generations in farmyards and gardens throughout the world, this age old process still has a huge role to play in the high tech future of sustainable waste management. Highlighted as a key component in the Northern Ireland Waste Management Strategy, composting has also been identified by the three Regional Waste Management Plans, as being central to our ability to divert biodegradable waste from landfill and meet our obligations under the European Landfill Directive and the Northern Ireland Landfill Allowances Scheme.

Most local authorities already rely heavily on the composting of green waste collected at their civic amenity sites to supplement their recycling and diversion rates and some have also introduced kerbside schemes for the collection of kitchen and garden organics for composting. Traditionally all this material was composted using open windrow systems, where the green waste was simply shredded, stockpiled and turned regularly to ensure that it was aerated. However, with the introduction of the Animal By-Product Regulations NI 2003 open windrowing of material that contains any form of animal by-products is inadequate. While pure green waste collected at the civic amenity sites may still be composted in open windrow systems, material that contains animal by-products must be composted in-vessel. That means within a closed reactor composter or in a fully enclosed windrow system. Which ever system is used the compost must be treated to certifiable temperatures for a set period of time and in 2 separate stages to ensure that all the pathogens and organisms contained within the material, that might caused problems to human or animal health are eradicated.

Despite the large amounts of green waste collected each years by local Councils, it is now generally accepted within local authorities throughout Northern Ireland, that we will not comply with the targets set out in the European Landfill Directive and the Northern Ireland Landfill Allowances Scheme, without the introduction of kerbside collections for kitchen and garden organics. The material collected through these schemes will have to be composted to animal by-product standards before being matured as a finished compost and this means in-vessel composting.

Magherafelt District Council were among the first of the Councils in Northern Ireland to introduce a kerbside collection for kitchen and garden organics. In 1998 they introduced 2,500 brown bins on an alternate week collection as part of a pilot project to test the viability of alternate week collections and the kerbside collection of household organics. As a result of the pilot Magherafelt District Council have now introduced alternate week collections and 14,000 blue bins for mixed dry recyclables, one to every household in their District and they have expanded the brown bin scheme to every house an urban area which represents approximately 7,500 household and over 50% of the District.

Initially the material collected through the original brown bin scheme was simply composted using an open windrow system but with the introduction of the Animal By-products Regulation 2003 it became necessary to treat the material in a process that could meet the new Animal By-product Regulations. After looking at a number of different technologies Magherafelt District Council decided to go for VCU Composting who could show a proven track record of obtaining Animal By-Product compliance in the UK.

The VCU technology has been developed in New Zealand and is a fully enclosed aerobic composting system that suits the processing of biological waste in small to medium municipal and industrial applications. Composting takes place inside modular chambers that are 25 cubic metres in capacity and you can have as many chambers as you require. The process is continuous with waste being loaded into the top of the chamber and stabilised material removed from the bottom every day. The unique vertical orientation of the VCU processing chamber enhances a natural process, with aeration provided by natural convection forces and accelerated by a fan mounted on top of each chamber. Odour control is by way of self-biofiltration and leachate is not produced. The VCU offers low operating costs due to low energy, maintenance and labour costs it has a small footprint and offers great flexibility as it's modular design allows it to be easily expanded as collection systems are expanded and the volumes of waste are increased.

The Magherafelt plant is unique, in that it is the first two stage unit to have been designed and built by VCU. Until now the normal VCU plant has been a single stage plant with the second stage required under the Animal By-products Regulations being carried out in open windrow. At the behest of Magherafelt District Council VCU have redesigned their normal linear formation to provide 2 fully enclosed in-vessel stages. As a result material fed into the system is discharged after 8 days as fully Animal By-product compliant material that can be matured into a quality compost.

The process itself is simple. Kitchen and garden organics collected in the Council's brown bin scheme are delivered to a fully enclosed receivals shed where the material is checked for contamination. It is then mixed with wood waste in an industrial shredder/mixed until it is at the right consistency and mix to be fed into stage one of the process. The wood waste is an essential component of the process as it provides a matrix within the material and ensures that air can flow through the mass of the material, keeping it aerobic. All feeding of material into the system is done via fully enclosed computer controlled conveyors that move material from the shredder/mixer to stage one and again from stage one to stage two. Material remains in each stage for four days where it reaches temperatures in excess of 70 degrees celcius. After 8 days, (4 days in each stage) the material is discharged into a skip as fully animal by-product compliant material and removed for maturation into finished compost. Integral temperature probes in the internal walls of the chambers record the temperature of the mass of the compost as it passes through the chamber and all this information is recorded in the central computer which controls the whole process.

The new composting operation will allow Magherafelt District Council to expand their existing brown bin scheme to the rest of their District and to meet the demands of the Animal By-products Regulations while complying with the targets set out in the European landfill Directive and the Northern Ireland Landfill Allowances Scheme. With a household recycling rate that is already approximately 35% and the introduction of this new composting facility Magherafelt District Council look well placed to meet not only the 2010 targets but also the 2013 and the 2020 targets.