Composting is a recognised and sustainable way to break down organic waste into a material that can be reused in a wide range of industries. There are different methods to carry out composting. You should choose a method that is suitable for the type and quantity of waste you will be handling.
In-vessel composting (IVC)
IVC treats food and garden waste in an enclosed vessel where precise temperature control can be maintained. Under the Animal By-Products (ABP) Regulations, food waste containing animal by-products must be treated using an approved IVC system.
Approved in-vessel composting systems have three stages:
- initial processing and treatment in an enclosed vessel (or 'barrier')
- treatment in a second barrier to ensure it reaches the correct temperature
Oxygen and moisture levels should be monitored carefully to make sure that the compost produced is fully sanitised and stable.
Catering waste which is generated, composted and used all on the same premises is exempt from the ABP Regulations. Meat-excluded food waste is not exempt, but may be treated in a simpler, single-barrier system.
Thermophilic aerobic digestion (TAD)
TAD composting allows organic waste to be treated in liquid slurry or in a semi-solid form. Often used to treat sewage sludges in the wastewater industry, the TAD method is also beginning to be used to treat some food waste.
The feedstock is placed in a digester and air forced through to encourage aerobic microbes to multiply. The TAD process usually takes between two and five days to complete. The resulting compost is dried to produce a bio-fertiliser.
Open air composting
The open windrow composting system is used to process garden waste - such as grass cuttings, prunings and leaves. It is important to understand that this type of composting can't be used to process catering or animal wastes under the ABP Regulations.
In an open windrow system, the feedstock is shredded and placed on a non-permeable surface. The materials should be turned on a regular basis, taking up to 16 weeks. The compost that is produced must then be graded and screened to remove any remaining contaminants.
The compost produced can be used in a wide range of applications, from domestic gardens to commercial agriculture, provided it meets certain quality standards - see composting legislation and standards.