IVCs can be used to treat food and garden waste mixtures. These systems ensure that composting takes place in an enclosed environment, with accurate temperature control and monitoring.
Overview
There are many different systems, but they can be broadly categorised into six types: containers, silos, agitated bays, tunnels, rotating drums and enclosed halls.
In this guidance material we detail the three stages involved in the process of in vessel composting as well as providing further information about the composting of animal by-products and the screening and production process.
To read through each stage, please use the chapters below:
The process
Stage 1
The food waste, which comes primarily from local authority waste collections, either separate or already mixed with garden waste, as well as commercial and industrial sources, is delivered to an enclosed reception area.
It is then shredded to a uniform size and loaded into what is known as the first ‘barrier’, which will be a bay/tunnel etc depending on the system used. All the material delivered to a facility, plus the first barrier stage, is considered a ‘dirty area’ under ABPR. The regulations ensure that strict procedures are in place to prevent cross-contamination of ‘clean areas’ (where product is processed and stored) from ‘dirty areas’.
The composting process is kick-started by naturally occurring micro-organisms already in the waste. They break down the material, releasing the nutrients and in doing so increase the temperature to the 60-70ºC needed to kill pathogens and weed seeds, and meet the regulations for processing ABP material.
Stage 2
After the first stage (which can take between seven days and three weeks), the material is transferred to the second ‘barrier’, where the composting process continues, usually for a similar duration.
Processing in 2 stages ensures that all parts of the composting mass reaches the required temperature. The oxygen level, moisture and temperature are carefully monitored and controlled during both composting stages to ensure the material is fully sanitised.
Stage 3
Once the sanitisation process is complete the compost is left to mature in an open windrow or an enclosed area for approximately 10-14 weeks to ensure stabilisation.
Further advice: Screening and production
Screening usually takes place pre or post maturation, to produce a range of product grades suitable for various end uses such as soil conditioning. Often the oversize is fed back into the processing system to break down fully.
Facilities which process to BSI PAS 100 and the Quality Protocol for compost produce products which are no longer considered a waste by the Environment Agency.
Further advice: Animal By-Products Regulations (ABPR)
The processing of all animal by-products, including municipal kitchen waste, must comply with the Animal By-Products Regulations (ABPR).
These were introduced in 2003 to ensure that all meat and other products of animal origin (including catering waste from domestic kitchens) meet the treatment standard required to guarantee the protection of the environment and human health.
Under the UK treatment standards for in-vessel composting “catering waste” can be either meat included or meat excluded. ‘Meat-excluded’ requires a one stage barrier system to treat, plus 18 days storage. ‘Meat-included’ requires a two stage system.