Compost and circular economy
The circular economy is an industrial economy that is restorative by design and mirrors nature in actively enhancing and optimizing the systems. It applies several principles from nature: production out of waste, resilience through diversity, renewable energy sources, systems thinking, and cascading of materials and energy. Circular economy means reusing, repairing, refurbishing, and recycling the existing materials and products; what was earlier considered to be waste becomes a resource.
The Circular Economy Package, published by the EU Commission in December 2015, paved the way for a resource-efficient society and sustainable recycling industry across Europe. It also contains proposals addressing EU waste legislation to avoid, reuse, and recycle more waste in the future. One of the suggestions was to reduce the landfill of municipal waste to 10% by 2030. In this ambit, food waste fraction plays an important role in recycling and in raising circular economy since up to 50% of municipal solid waste is biogenic. Therefore, the 10% landfill target can only be achieved through sustainable bio-waste management, including composting and anaerobic digestion.The food and other bio-resources that supply cities are produced primarily in rural areas. Having entered the city, they are processed and consumed, and the rest is discarded as a ‘waste’ in the form of by-products, food waste, and sewage.
The volume of discarded material is significant. A 2017 study estimated that each year cities produce 650 million tonnes of organic waste. This volume is projected to double by 2030.
If these resources are managed effectively, they can be part of a circular economy that helps rebuild soil health, recovers valuable resources, and provides feedstock for factories or energy plants. This can be done by converting the waste into compost. Composting is a treatment process that facilitates the decomposition of organic matter in an oxygenated environment and creates a nutrient-rich fertilizer or soil amendment. Food scraps, landscape trimmings, wood products, and animal by-products, packaging, and other discarded material can be made into compost. There are four types of industrial composting, each of which requires specific nutrient balances and feedstocks:
- Vermicomposting: composting in an enclosed bin, facilitated by worms that break down the compost
- Aerated (turned) windrow composting: composting in piled rows (“windrows”) with periodic aeration via manual or mechanical pile turning.
- Aerated static pile composting: composting in a large pile that is aerated using either/both ventilation ducting or organic bulking elements (i.e., wood chips)
- In-vessel composting: composting in a large, enclosed container that monitors and controls the five criteria listed above. Aeration is typically managed through mechanical turning systems within the container.
And yet even in ‘advanced’ OECD countries, less than 40% of organics are recycled into compost, so that each year at least 58 million tonnes of potentially recoverable resources are wasted. The wasted organic matter is dumped into landfills. This results in substantial economic losses, expensive and possibly polluting landfills, and significant greenhouse gas emissions, which are all hallmarks of a linear take-make-waste system.
In a circular economy, bio-waste from food is not landfilled. Instead, it turns in to compost and forms a resource for organic soil improvers, fertilizers, and bio-based products. The carbon and nutrient contents of bio-waste are converted into organic fertilizers for the soil.
By bringing these nutrients back to the soil, rather than letting organic waste rot away in landfills, composting can feed diverse life in the soil. The bacteria, fungi, insects, and worms in compost support better soil health and plant growth, ultimately boosting its resilience to cope with harsh drought conditions.
These nutrients and can also be extracted, modified, or transformed into a range of different bio-based products, too. All these secondary products can replace fossil-based products such as mineral fertilizers, peat, and fossil fuels. After use, the residues of these products can flow back safely into the biosphere, thereby closing carbon and nutrient cycles.
Furthermore, compost has the ability to help regenerate poor soils. The composting process encourages the production of beneficial micro-organisms (mainly bacteria and fungi), which in turn break down organic matter to create humus. Humus–a rich nutrient-filled material–increases the nutrient content in soils and helps soils retain moisture. Compost has also been shown to suppress plant diseases and pests, reduce or eliminate the need for chemical fertilizers, and promote higher yields of agricultural crops.
Composting organic materials that have diverted from landfills prevents the production of methane and leachate formulation in the landfills. Compost can prevent pollutants in stormwater runoff from reaching surface water resources. Compost has also been shown to prevent erosion, silting on embankments parallel to creeks, lakes, and rivers, and avoid erosion and turf loss on roadsides, hillsides, playing fields, and golf courses.
The benefits of improving organic collection for composting are potentially far-reaching. Direct benefits include an improved urban environment for human health, lower greenhouse gas emissions, and reduced costs for municipalities and households. Indirect benefits consist of improved soils in peri-urban areas through the cycling of organic fertilizers, more feedstock for the local bio-economy, clean, renewable energy for electricity, district heating, and even transport systems.
For cities, the economic benefits of organic waste collection and compost conversion over disposal are realized in both jobs and cost reduction. In the Italian city of Parma, 44 jobs were created going from roadside to door-to-door collection. At the same time, annual costs have been reduced by €450,000 (USD 510,000), plus the city received a €710,000 (USD 800,000) financial rebate from the Italian government for achieving the separation targets.
Visualizing a city’s organic waste as a flow of beneficial nutrients is a prerequisite to creating a circular economy for food in cities. In doing so, organic waste can be viewed not as a costly hazard, but as something that can benefit the economy, the quality of urban life, and the wider environment. By 2050, cities will consume 80% of food produced, giving them the power to drive a shift to a less polluting, more regenerative system, as well as unlocking USD 700 billion a year. This will be achieved by reducing edible food waste and ‘valorizing’ organic materials to create new food and products. To realise the many opportunities, better collection systems are needed that divert edible food to citizens and discarded organics away from landfills, rivers, or incinerators, re-routing them instead to factories, energy plants, and farmers’ fields.