Windrow composting is a way of generating compost by piling organic matter into extended rows or elongated pyramid-like piles. The piles are turned over by large machinery to preserve even levels of heat, humidity, and oxygen content. Piles will usually range from four to eight feet tall and 14-16 feet in length.
In windrow composting, ground-up garden refuse is formed into long, open-air piles. The piles are turned frequently to introduce oxygen into the pile, and ensure that adequate moisture is present throughout the pile.
Normally windrow systems take about 6 to 12 weeks to make finished compost. The pile is agitated at regular intervals of 1 to 3 times per week to introduce oxygen and water to enhance the composting process.
It is estimated that the unenclosed facilities (unenclosed ASP and windrow composting) will have a unit costs ranging from $38 to $435 per wet ton of biosolids processed. For enclosed composting (enclosed ASP or in-vessel) the cost would be in the range of $55 to $65 per wet ton.
Special vehicles are required to agitate the windrows periodically by turning them upside down, which introduces oxygen and facilitates aerobic decomposition in the windrow.
Odors and other emissions are likely to be a major consideration when evaluating potential environmental impacts of a composting operation, especially an open air windrow. Open-air composting alternatives (unenclosed ASP and windrow composting) have a larger element of risk.