Green, food and specific organic waste collected from homes and businesses is delivered or collected on behalf of the local authority. This waste is then shredded and blended to produce a homogeneous mix for composting. Blended material is loaded into the in-vessel bunker system, which features an aeration system, temperature control and wireless data logging probes to decompose it in a controlled manner which meets EU composting standards.
The system processes the waste in a fully enclosed computer-controlled environment. Once the tunnels of the in-vessel bunker system are filled and the doors are closed, fans blow air through the perforated floors of the tunnels. The air passes through the composting material and is re-circulated within the tunnels. When the oxygen level within the tunnel drops below a minimum set level, fresh air is drawn in, allowing very tight control of oxygen levels and temperature within the material. Following the in-vessel stage is the stabilisation phase where the compost is arranged in rows and turned on a regular basis with a dedicated turner.
After 6 to 8 weeks the material is ready for screening into a peat free high quality PAS 100 compost.
Open Windrow Composting
This type of composting is conducted in the open air, similar to the stabilisation phase in in-vessel composting.
The process of open windrow composting is as follows:
- The feedstock is shredded, mixed and placed into windrows.
- The windrows are turned on a regular basis to improve oxygen content, distribute heat to regulate temperature and to distribute moisture. The windrows are turned multiple times during the composting process, which takes on average eight weeks, depending on maturity requirements.
- The last part of the process involves screening the compost to remove contaminants such as plastics and metals, and to also grade the compost for various end uses. Oversized materials are also removed and can be put back through the whole process until they have composted down sufficiently.