Windrow Composting
Open Air Windrow Composting (OAW) uses naturally occurring microbes which feed on organic material (garden waste) and require oxygen. By feeding on the Garden Waste, the microbes break down the material and turn it into compost.
OAW is not suitable for Food Waste because the process needed to deal with Food Waste has not been performed in an enclosed vessel and in the open air. The Animal By-Products Regulations (ABPR) prevent food waste being treated in this manner in order to protect animal and human health[1].
What is OAW used to treat?
OAW is a relatively inexpensive way of treating Waste Collection Authority Green Waste e.g. twigs, leaves, glass cuttings and branch prunings etc.
The Process[1]:
- The material is delivered to an OAW composting licensed site and sorted to remove any contamination, plastics, metals etc. The material is then shredded.
- The shredded material is then placed into piles in long rows known as ‘windrows’, in the open air.
- Naturally occurring microbes feed on the materials. This creates heat and windrows will often give off steam.
- The windrows are regularly turned to make sure that there is enough oxygen for the microbes to work.
- The process to turn the original material into compost takes around 12 – 16 weeks.
The compost is checked to make sure that it meets the [PAS 100] Quality Standard regularly. Any contaminants which were missed in the first stage are removed and the compost is graded. The grading also removes any pieces of material which have not completely broken down. This can include items like small tree branches which are often too thick to fully compost. These items are then put back through the process outlined above.[1]
The different grades of compost can be used for different purposes. Some grades are used as agricultural soil conditioners, others as mulches and others are suitable for landscape gardening or finer grades can be used on golf courses.