In recent years, there has been a huge interest from local communities in decentralized composting. Decentralized community composting refers to a community-scale network in a specific neighborhood that diverts and composts biowaste in a controlled operative environment. In fact, the lack of centralized composting facilities in small towns or rural areas can be supported by decentralized solutions. Decentralizing waste treatment facilities and thus creating local solutions to urban waste management strategies will help to achieve the resource recovery and valorization targets in line with the circular economy.
Considering the limitations of centralized waste treatment facilities originating from diverting food waste and increased costs for collecting and transporting waste in long distances, some of municipal composting programs may not be fully successful. In addition, high operational costs and operational complexity are other factors that should be taken into consideration for centralized systems . At this point, alternative strategies must be identified and developed, such as decentralized collection and treatment. Decentralized composting, also known as community composting, refers to a community-scale network in a specific neighborhood that diverts and composts biowaste in a controlled operative environment . The main advantages of decentralized composting over centralized systems are summarized in Table 1. In a broad perspective, decentralized composting can help to decrease the cost and effort for transportation of waste for processing and treatment, and further reduce the need to construct new disposal facilities, enable local reuse of organic matter, create local small-scale enterprises as well as reduce costs associated with commercial fertilizer purchase . Furthermore, the final compost product is comparatively of higher quality due to efficient separation and less intercontamination of wastes . Community composting is thus attracting some attention from policymakers, who consider this as a logical implementation . However, some drawbacks are also faced during decentralized composting. The collection of organic waste in containers may result in an uncontrolled degradation of organic matter that leads to odor problems and leachate generation in the case of poor management . Furthermore, logistic problems can lead to unsatisfactory implementations . In this regard, new composting technologies should be well-addressed, and the information gathered from the operative environments should be thoroughly analyzed for a win-win situation for all stakeholders.
When a decentralized composting system at the community-scale is demonstrated in a specific city or urban area, current and future proposed land use availability, and status of vacant land and community interest are initially considered within the regulatory frameworks. Once the location type and the individual site within each area are selected, the composting capacity is latter calculated within the city or specific region, based on the population size and waste generation trend . The next step is then the decision on the composting technology. Community composting reactors can be different, in other words, “simpler”, than centralized composters. Plastic bins in any shapes (i.e., rectangular, cylindrical, conical) are often used for community composting reactors . Plastic drum reactors were also recently reported . These reactors can be operated in batch, semi-continuous or continuous mode, based on the sustainability of the wastes. The reactor capacity is usually between 100–1000 L . In most cases, holes are constructed at the bottom or on the periphery for aeration and turning/mixing is applied manually. Some examples of decentralized composting practices in Europe are presented in Table 2. The biggest drawbacks of these bin-type reactors is the uncontrolled emission of GHGs, such as methane, ammonia or nitrous oxide , non-homogenous matrix of the final compost product due to inadequate mixing ; odor and leachate . For instance, gas emissions (i.e., (CH4, N2O, NH3 and volatile organic compounds (VOCs)) of a bin-type composter were calculated in the range of 30–148 kg CO2 eq/Mg leftovers of raw fruits and vegetables .
Table 2. Characteristics of selected decentralized composting systems in Europe.
In most agri-environmental programs, the lack of participation of interested stakeholders in designing frameworks, the poor information basis to support policy formulation and the failure to consider local specificities in the scheme design are reported to be the main reasons for low success achievements . In a recent survey , the farmers’ perception of compost production was found to be 83.9%, in which the participants showed also a high, yet lower, willingness level (63.6%) of the more salient option to produce compost themselves and use it in agriculture. In another survey, 67% of respondents indicated that they are interested or very interested in community composting systems . Without a doubt, public acceptance and encouragement are the key factors for a successful decentralized composting implementation. As the actual processing volume is dependent on the participation of residents in a community, low participation rates can be a major challenge in such cases . By community composting, local resources community participation can be established  and people may be more motivated to reduce their food waste when they see it separated out from the rest of their waste . In a common sense, decentralized composting systems should be inexpensive, require low maintenance and easy handling . Identifying a suitable location in a city/region is critical and logistical characteristics such as the distance from waste sources, need/use of compost, demographic characteristics, and environmental characteristics such as drainage, potential or existing environmental conditions, should be all considered during the identification. A lack of technical support in operating and building community composting facilities has also been a critical challenge in maintaining decentralized composting systems . Hence, training and navigating the community within the specific region is crucial.