What is In-Vessel Composting?
The In-Vessel Composting Plant is an enclosed facility that operates in two stages.
The raw materials mentioned above are delivered to an enclosed reception area, to begin the process. They are then screened and shredded to a uniform size and loaded into three, sealed concrete tunnels. The reception, screen and shred areas, alongside the three tunnels, are considered 'dirty' areas, falling within the scope of APRR regulations. These regulations ensure that procedures are in place to prevent cross contamination between dirty and clean areas of the facility.
Inside one IVC tunnel
The shredded material is left in the tunnels for seven to ten days and the composting process is activated by naturally occurring micro-organisms that are already present in the waste. They break down material, which releases nutrients and increases the temperature to 65OC as they do so. This temperature must be maintained across the whole mass of material for forty eight hours to kill pathogens, weed seeds and meet regulations for processing ABP material. This process is aided by pumping air through spigots situated on the tunnel floors as these allow air to move through the mass. There is a system of water sprinklers in the tunnel roofs so that water may be used to regulate the moisture content within the mass.
Site supervisor inserting temperature probes into IVC to test the mass
The material is then removed from the first stage tunnels to an intermediate area within the IVC where it is de-compacted. In the second stage, it is loaded into another three tunnels where the composting process continues, usually for seven to ten days. It again has to reach the desired temperature of 65OC within this stage for a further period of forty eight hours across the entire mass to meet regulations.
Processing in two stages ensures that all parts of the composting mass reach the required temperature. The oxygen level, moisture and temperature are carefully monitored and controlled during both composting stages to ensure the material is completely sanitised.
Once the sanitisation process is complete, the mulch type compost is dispatched to Gowy Composting Pad, at Mickle Trafford in Chester, where it is left to mature in open windrows for approximately eight to twelve weeks to ensure stabilisation.
Screening takes place at the Pad to produce a product that is suitable for use as a soil conditioner, which is compliant with the industry’s PAS 100 accreditation. This standard, together with quality protocols, produces a product that is no longer considered waste by the Environment Agency.
The maximum capacity of the IVC plant at Wrexham, in line with the supplier's performance guarantee, is 25,000 tonnes per annum. No more than 10% of this total may be cardboard.
The actual tonnage delivered to the IVC facility within the last financial year totals:
- Kerbside collections of green, food and cardboard: 14,400 tonnes
- Household Waste Recycling Centre green collections: 2,600 tonnes
- Other collected green waste: 264 tonnes
The overall tonnage for the last financial year totals 16,943 tonnes.
Up to 1,000 tonnes of the finished product per year is made available for members of the public residing in Wrexham to collect free of charge from the three recycling centres. Other customers include Wrexham Council’s Parks and Gardens departments, local allotment users, farmers and other organisations, such as Youth Projects and community schemes.