Vermicompost processes combine worms and organic waste in a controlled system to create compost. The process can be high tech, low tech or in between. Compost worms, usually red wigglers or Eisenia fetida, will usually do their job regardless of the technology used, merrily munching on garbage and converting it in their guts to worm manure or vermicompost, a valuable soil amendment.
Midscale vermicompost processing systems rely on windrows, simply a long line of heaped material, as well as waste heaps. Also simple to set up are small-scale systems for home or school vermicomposting, which may be as basic as a storage tote with ventilation perforations. Fancier worm bins for home hobbyists consist of stacking systems in molded plastic. Municipal governments often encourage the use of these simple technologies by homeowners to reduce urban waste. Completely automated continuous flow reactors designed for large-scale production consist of a raised box with a mesh bottom, keep under cover, with a scraper bar to scrape the completed vermicompost through the mesh to the ground below.
Outdoor vermicomposting can occur in the winter by use of thin layers of organic waste that begin thermophilic or "hot" composting based on bacterial action, notes Ohio State soil ecology professor Clive Arthur Edwards in "Earthworm Ecology." Year-round production needs to be done under cover to create cooling in the summer. Heating is not necessary if thicker layers of compost are applied during cold periods. Windrows process wastes relatively slowly, taking six to 12 months. Continuous-flow reactors can process organic wastes in 30 to 45 days. Home systems fall in between, taken two to three months to completely process organic matter.
Outdoor beds or windrows can be of any length, but the width needs to be no more than 8 feet to allow for inspection. Similarly, many commercial continuous flow reactors are 7 feet wide by 18 to 34 feet long.
France has developed a complete vermicomposting recycling system. Waste goes through a selector that removes plastic wastes, followed by manual sorting of bottles and pulling out ferrous metals using magnets, Edwards writes. The waste goes into a regular compost system for 30 days and then a deep continuous flow system for 60 days. The system can remove as much as 27 percent of the waste stream into vermicompost, which can be sold. Vermiculture technology in the Philippines relies on worms kept in pits about a yard deep and 3 by 4 yards across, with compost harvested using sieves and worms removed by hand, the Food and Agriculture Organization of the United Nations reports. In Cuba, growers use cement troughs and windrows, while in India, growers often use wooden bins.
Growers have little initial outlay for windrows except for land, but labor costs are high. Windrows and stacked boxes or containers pose difficulty in harvesting the compost, which usually much be screened. Edwards writes that continuous flow reactors have the best economic potential to produce high-grade plant media quickly and more efficiently than windrows and ground beds. Automated reactors run $35,000 to $100,000, are able to process up to three tons of waste a day and require ancillary equipment, such as moving belts and loaders. Their running and labor costs are quite low, Edwards notes, and the initial investment can be recouped in one to two years.