Open Windrow Composting

13th December 2016

Windrow composting is used for processing garden waste, such as grass cuttings, pruning and leaves in either an open air environment or within large covered areas where the material can break down in the presence of oxygen.

Key points
The process
Key uses

Overview

In this guidance we outline the processes involved in open windrow composting along with the end uses and markets for material produced through this process.

Users should note from the outset that windrow composting cannot be used to process organic materials which include catering and animal wastes as these have to be processed via in-vessel composting (IVC) or anaerobic digestion (AD) due to their Animal By-Products Regulations (ABPR) categorisation.

To find out about the entire process, use the chapters below:

The process

 

Related

Related

To find information related to that contained in this report, please use the following links:

In vessel composting (IVC) >>
Open windrow composting >>
Anaerobic digestion: A definition for local authorities >>

The process

The process of windrow composting is relatively simple:

  1. The feedstock is shredded, mixed and placed into windrows along a non permeable surface. 
  2. 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 sixteen weeks, depending on maturity requirements. 
  3. 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.

End uses

Compost can be applied in a range of end uses, within gardens, on brownfield sites, landscaping and full scale agriculture.

The screening grades the products to between 0mm and 40mm particles which, dependent on grade, can then be used as soil improver, mulch, topsoil constituent, turf dressing, and growing medium.  

For permitting purposes, open windrows are categorised into three sizes, under 5,000 tonnes per annum, under 25,000 tonnes per annum, and under 75,000 tonnes per annum, however the current permitting process is currently under review.

More information about the permitting of open windrow sites can be found on the Environment Agency web pages.

Where next?

Want to know more about composting? Take a look at our reports, guides, tools and case studies for further information:

Reports >>
Guides >>
Tools >>
Case studies >>

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