"Composting conserves landfill space, reduces greenhouse gas emissions and creates nutrient rich soil," according to the 2010 City of Vancouver fact sheet about the city's composting program. Vancouver has the goal of becoming the greenest city in the world by 2020, and large-scale composting is essential to achieving the goal. Many municipal and state governments have begun composting projects since the latter part of the 20th century.
Change in Outlook
Large-scale composting has grown because the markets for commercial compost have expanded, it is promoted in the agricultural sector, and backyard composting has been readily accepted. Citizen cooperation in recycling has increased with the understanding of environmental problems related to landfills. Composting is an important part of an overall strategy for waste reduction.
City waste management services are responsible for food, grass and yard wastes as well as sewage sludge. Since the early 2000s, there has been an increase in the use of composting as a method for recycling these materials. "Up to 70 percent of waste products may be organic," according to a North Carolina University report, and "composting is an effective strategy."
Composting is the decomposition of organic materials by microorganisms such as bacteria and fungi. Heat and water aid the process and oxygen speeds it up. Large-scale composting operations often use blowers to increase oxygen. An oxygen content of 16 to 18.5 percent is ideal; lower amounts of oxygen cause odors to develop and the decay process to slow). It takes two to nine months for the decay process to complete, and another one to four months to cure.
Composting methods include passive piles, windrows, static piles and in-vessel composting. Bins, beds, silos, transportable containers and rotating drums are examples of in-vessel composting systems. Windrows are the most common method for rapid composting of yard wastes. They are aerated daily by turning the pile mechanically. Passive piles can take a year or more to decompose.
Large- and small-scale composting has been found to transmute some pesticides, according to a study in the May 2010 issue of the Journal of the Science of Food and Agriculture. The U.S. Environmental Protection Agency recommends composting as a method for reducing the harmful effects of soil containing wood preservatives, chlorinated and non-chlorinated hydrocarbons, heavy metals and explosives.