Application of different strategies to improve anaerobic digestion for organic fraction of municipal solid waste

Abstract

Municipal Solid Waste (MSW) management is a worldwide issue with significant effects on public health, community welfare, environmental sustainability, and economic progress which includes items like packaging, food scraps, newspapers, and more, coming from homes, businesses, and industries. Effective MSW management is vital for sustainable urban development, emphasizing waste segregation, recycling, and treatment to minimize landfill reliance and harness waste-to-energy technologies. Tailoring waste management systems to local contexts is crucial, considering factors like waste composition and financial resources. From this perspective, this thesis focused on the characterization of MSW and increasing biogas production by applying different pretreatment strategies to organic fraction of MSW (OFMSW). Due to increasing population worldwide, it is essential to understand the MSW characteristics to apply efficient waste management strategies. The organic fraction of MSW (OFMSW) holds potential for energy recovery through anaerobic digestion (AD), offering municipalities economic opportunities besides environmental benefits. In the first study, waste composition and physiochemical of the mechanically separated OFMSW (ms-OFMSW) at a full-scale AD plant in Türkiye was evaluated. ms-OFMSW predominantly comprised of organic matter (76.45 ± 1.71%), alongside recyclable (8.99 ± 1.56%) and non-recyclable (14.56 ± 1.69%) components according to the findings of this study. Environmental assessment was conducted using Environmental Protection Agency's online tool (Recyculator tool) underscored the substantial energy and water savings associated with segregating recyclable materials (metal, glass and plastic) from the waste stream. Moreover, this study highlighted the importance of efficient pre-separation units in enhancing OFMSW digestibility and maximizing environmental benefits. AD is recognized as an effective waste management strategy for different types of waste with the potential to mitigate greenhouse gas emissions (GHGs) while concurrently generating renewable energy. The physicochemical characteristics of OFMSW can significantly influence the AD process's efficiency and biogas production. Hydrolysis, a pivotal step in AD, is often rate-limiting for degradation of waste, particularly for substrates like OFMSW. In the second and third studies, electrohydrolysis and enzyme pretreatment were explored to improve hydrolysis efficiency. Experiments showed that doubling electrohydrolysis treatment time (from 30 minutes to 60 minutes) led to notable improvements in methane production, with a significant reduction in the lag phase. Methane production increased by 3–10% following electrohydrolysis pretreatment, underscoring its potential to expedite the AD process and enhance biogas yields. While in the enzyme pretreatment, anaerobic degradation of organic waste was investigated by employing alpha amylase enzyme which was obtained from Aspergillus oryzae. According to the results, a significant increase in the methane yield and a decrease in the lag phase was observed. Optimum results were obtained with the addition of 0.5 mg of enzyme per g volatile solids (VS) added, highlighting the effectiveness of alpha amylase in enhancing the biodegradability and biogas production of OFMSW. In summary, this thesis sheds light on the importance of understanding and managing OFMSW characteristics to optimize AD efficiency and maximize environmental benefits. Efficient pre-separation units, electrohydrolysis and enzyme pretreatment emerge as promising strategies for enhancing OFMSW digestibility and biogas production in AD processes. However, further research is warranted to fully explore and optimize these approaches for practical implementation on a larger scale. By leveraging these advancements, the waste management sector can move towards more sustainable practices, reducing environmental impact and contributing to the transition to a circular economy.