Assessing the alteration of physicochemical characteristics in composted organic waste in a prototype decentralized composting facility

This article presents the pilot experience of an integrated biowaste management system developed in Tinos island, Greece, which promoted source separation and decentralized composting in a prototype unit. This system was introduced as a new-to-the-area of implementation and innovation, since landfilling of mixed municipal solid waste has been the common practice in Tinos island, as in many other areas of insular and mainland Greece. The biowaste management system was implemented through a bring scheme that aimed at motivating the public to separate at source the organic fraction of MSW. The system was monitored on an input-output basis of critical parameters used to assess the purity of separately collected biowaste, the treatment efficiency of the prototype unit, the quality characteristics of compost produced, and public's awareness and participation. Results showed that biowaste source separation was practiced effectively by citizens, giving high-purity feed (>98%). Compost samples were examined in comparison with the proposed EU End-of-Waste (EoW) quality criteria and fulfilled the requirements set. More specifically, the average values of compost samples regarding heavy metal content were 72% lower than the EoW limit value for Cd, 43% lower for Ni, 38% lower for Pd, 24% lower for Cu, and 36% lower for Zn. Examined composts also met the EoW criteria for phytotoxicity and pathogenic or parasitic microorganisms, while they showed an approx. 15% decrease in initial organic matter content. Moreover, this study analyzed the carbon balances and the degree that composting can sequestrate carbon. Overall, this study demonstrated that the development and operation of on-island, decentralized composting, when properly practiced, is a sustainable option in order for islands and remote areas to adopt a closed loop approach to the biowaste management problem, in line with the circular economy principles.