Composting: clean technology, green process

01/17/2011 - Organic residues correspond to about 50% of the volume of waste produced in cities. The destination of these residues are generally landfills or dumps, where they become sources of methane and wastewater and attract disease vectors. Beyond than shorten the life of landfills, this practice, that is on borrowed time with the recent approval of the National Policy on Solid Waste, is a waste of precious fertilizer material and energy. The controlled composting allows the recycling of nutrients and mitigates methane emissions, resulting in a rich fertilizer to keep the soil alive and productive, without the use of pesticides.

According to the National Policy on Solid Waste (law 12305, August 2010), cities must develop a plan for making good use of the reusable and recyclable solid waste within two years. Until August 2014, they will have to eradicate the dumps and put the waste in landfills that follow environmental standards, otherwise they will no longer receive federal funds. Composting shall be the obligation of the city, which must have a specific area for that. The policy also provides the implementation of waste sorting of recyclable garbage where it doesn’t happen yet, with involvement of collectors in the development of local projects and responsibility shared by the lifecycle of products between the government and supply chain.

In Santa Catarina, law 15112, January 2010, in force since July, but still unregulated, already prohibits the dumping of reusable and recyclable solid waste into open dumps and landfills. And the 3272 Decree of May of this year, establishes the criteria for preparation of a Management Plan for Municipal Urban Solid Waste.

Thus, large and small generators must be adjusted. However, the most important composting project of the state, which was conducted at São José’s supply central by the non-governmental organization Organic Association (Associação Orgânica) and Santa Catarina Federal University (Universidade Federal de Santa Catarina - UFSC) in Florianópolis, was closed three years ago. Since then, around 200 tonnes per month of the supply central’s fruit and vegetable leftovers are transported by the company Proactive to the Biguaçu landfill, at a monthly cost ranging from 11 thousand to 15 thousand reais, as the director of operational support, Felicio Silveira, said.

According to him, composting has become unfeasible for reasons such as lack of environmental permits and not enough space for composting in the yard. There is no concrete prospect of resuming it. "We had to find a suitable area in Biguaçu, seek partnerships with enterprises, there is interest from one company to use biogas for energy production. For now, we are donating for those who want to compost", he says. Foods considered inappropriate for sale, but good for consumption, are donated by Instituto Nutrir (Nurture Institute), based in the supply central, to around 900 registered families, 300 institutions and 130 entities of the federal program Mesa Brasil (Brazil Table). The remaining 200 tons per month, goes to the landfill.

Increasing demand - As projects are canceled, others aren’t able to meet demand. The Organic Association (Associação Orgânica), in partnership with Santa Catarina Federal University and the Company of the Capital’s Improvements (Comcap), treats 130 tons per month of organic waste at the Comcap ‘s sorting central in Itacorubi, in a static windrow system, fully controlled. The windrow’s slurry is collected in a tank and spread again in the material to speed up decomposition. The water used to wash the transport barrels is filtered in a circle of roots system.

The organic materials come from the Direct from the Camp grocery, from the town’s trees pruning and from restaurants, for example. 80% of the compost produced goes for fertilizing the city’s gardens and squares, donations to environmental education projects and school gardens, and 20% is sold. "The reduction in volume is 10 to 1. The compound is clean and the result is excellent with the plants”, says the agronomist Gerson Konig Jr., president of the Organic Association. The plans are to close the cicle: take the manure produced back to the farmers who supply vegetables to the participating restaurants.

The project on Comcap is part of a network of composting yards coordinated by the Santa Catarina Federal University’s Department of Agricultural Engineering, which since 1994 daily collects for composting 40% of total organic waste generated at the university, around three tons a day, with a lower cost than the conventional system. The project also composts the organics of the UFSC’s region population, which are delivered in the Córrego Grande’s park. "We have many requests for the compound, but we can’t attend," says the agronomist and project coordinator at UFSC, Paul Richar Momsen Miller.

In one of the research’s he participated, Miller found that the composting process emits about 10 times less amount of methane, a major greenhouse gas, compared to a landfill. As the composting process is aerobic and generates low amounts of methane per tonne of organic waste, it has great potential for mitigating methane emissions from urban and agribusiness organic waste.

The group of Rural Engineering, along with other groups at the university, is currently researching composting of the sewage sludge at Florianópolis’ unit of Casan - the state sanitation company - currently taken to Biguaçu’s landfill. "We have seen that the treated sludge works well together with other organic waste from the city”, he says. Among the projects, fertilization with treated sewage sludge is being studied in the productivity of banana and papaya, in the fruit quality and soil quality and reuse of sludge as a building material to concrete pipes.

Learn more at (in portuguese):
National Policy on Solid Waste (Política Nacional de Resíduos Sólidos):
Organic Association (Associação Orgânica):
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