Plásticos em ecossistemas costeiros e análise da co-gaseificação como alternativa para mitigação de seu impacto ambiental

Abstract

Plastics are materials that are increasingly present in everyday life due to their durability and wide range of applications in various industrial sectors. However, the persistence of plastics in the environment is an emerging concern and can trigger negative consequences for ecosystems, marine life, and human health. Coastal ecosystems are particularly vulnerable to plastic pollution, mainly due to the high population density close to coastal areas, tourism, intensive fishing, and river transport of waste. Given the above, the objectives of the work chapters were (1) to explore the occurrence of plastics in coastal environments worldwide, identifying the characteristics of the most reported items and the countries with the greatest number of studies; and (2) to present gasification technology as a potential alternative for environmental mitigation of plastic waste. It is noteworthy that both objectives cover two areas of literature that are still little explored since no worldwide review studies were found on the occurrence of plastics in coastal environments, nor any studies were identified involving the gasification of plastics together with cashew nutshell, complementary biomass that was used in the tests. In the first chapter of this dissertation, we used the PRISMA methodology, and searches were carried out in the search databases PubMed, Scopus, and Web of Science. It was identified that beaches represent the most widely studied coastal ecosystem, and among the waste frequently found, cigarette butts and white objects stand out. Polyethylene is the most reported typology of plastic, especially in the form of microplastic fragments. Among the countries that investigated the occurrence of plastics in their coastal environments, China and Brazil stand out, in which a greater number of published studies and evaluated coastal environments were observed, respectively. Poor management of urban solid waste is one of the main reasons for the high presence of plastics in coastal environments, as most of these items come from the continent. Therefore, it is crucial to improve current waste treatment and disposal techniques to reduce the number of plastics reaching coastal and marine regions. In this context, in the second chapter of this dissertation, we present the thermochemical gasification process, which appears as a promising alternative for plastics that cannot be recycled traditionally. Post-consumer plastics were gasified together with residual biomass from cashew processing, given the impossibility of plastics being gasified by itself due to the technical limitations of the equipment used in the tests. Furthermore, prior to the gasification process, the waste was subjected to a series of chemical analyses that aimed to characterize its composition. Chemical analyses demonstrated the good potential for using both post-consumer plastic waste and cashew nut shells. Gasification originated a gas with a high content of hydrogen and carbon monoxide, known as synthesis gas, which has a wide range of applications and can be used as a fuel in the generation of heat and electricity, in engines, fuel cells, and in synthesis of chemical products. In this way, gasification can be considered as a complementary option in a set of measures aimed at reducing, recycling, and responsibly treatment of these materials, especially in relation to plastics that cannot be recycled in a traditional way, helping to reduce the accumulation of plastic in coastal and marine regions and, consequently, mitigating environmental impacts.