This is a simple ‘low-tech’ aerobic process that requires the mixing and turning of chipped green waste and other organic material to produce a stabilised product. Material is stored and processed on an open flat area in long rows. The rows can be handled in one or a combination of ways:
Turned – windrow is turned by mechanical action; and
Forced air - air is forced though the windrows from underneath.
Turning and forced aeration speeds up the composting process. Processing times range from three to five weeks up to 14-20 weeks.72
This system can be operated with quite low capital costs compared to other composting systems, but a degree of attention is required to ensure the compost rows are properly and regularly turned. As a result this system may require a larger labour force and greater running costs. Purpose-manufactured windrow turners are available; however, a front-end loader would suffice in relatively small operations.
Disadvantages of this system include a relatively large amount of space is required and the inability of the windrow technique to generate high temperatures during the composting process, which may result in health and safety issues if bio-solids, food and manures are to be processed. There is less process control compared to other systems and greater potential for leachate runoff, as well as attracting flies and vermin and emitting odour. Typically odours are released when turning the windrows and this is most often the cause of complaints by members of the community living near these facilities.