Systematic review and meta-analysis on the use of LCA to assess the environmental impacts of the composting process

Following the industrial revolution, major economic and populational growth took place, and, therefore, solid waste generation increased exponentially. Nowadays, waste management still generates major impacts because the current wide offer of waste management strategies includes many solutions that produce suboptimal results, such as landfill or waste incineration. From a circular economy perspective, composting is a potentially sustainable option to treat the organic fraction of solid waste and has the advantage of recycling many organic compounds that can be reintroduced into the natural processes. This study aimed to provide a meta-analysis using the Life Cycle Assessment (LCA) method to evaluate the impacts of composting by performing a systematic literature review of the diversity of approaches and assessing environmental impacts. The results of the impact assessment were highly dependent on the choices made over the system boundary and the functional units. The most cited environmental impacts were GlobalWarming Potential, Acidification Potential, Eutrophication Potential, Photochemical Oxidation Potential, and Ozone Layer Depletion, as gaseous emissions from the transport and decomposition represent the main contributors to these categories. Using a smaller dataset and evaluating the use of the CML method and the most cited impacts categories, it was found that In-vessel Composting and Home Composting were considered the best environmental options among the studied composting methods. Composting environmental impacts were also highly related to the use of non-renewable energy sources, which puts composting at a disadvantage when compared with the use of anaerobic digestion. Such results emphasize the benefits of using these waste management technologies as complementary instead of substitutes.This work received funding from COMPETE 2020—Competitiveness and Internationalization Operational Program, Portugal 2020 and FEDER, through the project BioComp 2.0—Integrated Approach to the Valorisation of Water Hyacinth, and the financial support of CIMO (Centro de Investigação de Montanha) (UIDB/00690/2020) and SUSTEC (Laboratório Associado para a Sustentabilidade e Tecnologia em Regiões de Montanha) through national funds Fundação para a Ciência e a Tecnologia (FCT)/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES).