Harnessing the methanogenic potential of the organic fraction of municipal solid wastes generated in the Metropolitan Area of Guadalajara

Abstract

MSW generation rate has been rapidly raising in the last decades and is expected to continue increasing, especially in developing countries. Globally, the organic fraction of the MSW (OFMSW) is the largest waste category. This waste stream is characterized by its high nutritional content that translates into high energy recovery potential. For this reason, anaerobic digestion (AD) has been proposed as a waste management (WM) strategy to treat the OFMSW. AD is a Waste-to-Energy (WtE) technology that allows to simultaneously recovery of energy from waste in the form of biogas, a mixture mainly composed of methane (CH4) and carbon dioxide (CO2), and to recycle nutrients in the form of digestate, a liquid by-product with high potential for fertilization and soil amendment applications. The aim of the present work was to evaluate the biochemical methane potential of the OFMSW generated in the Metropolitan Area of Guadalajara (MAG), a large city in a developing country. This thesis presents a systematic review of the implementation of pilot and full-scale AD plants to treat the OFMSW in developing countries reported in the last ten years. The review aimed to analyze the literature gathered from a technical perspective focusing on the operating parameters, feedstock characteristics, and biogas, digestate, and energy production reported for each AD plant. In this work, a comparison of the implementation level of this technology in developing and developed countries was carried out to identify practices and lessons learned in developed countries that could be applied to AD plants in developing countries. The technical, economical, and political challenges identified surrounding the implementation of AD in developing countries were identified and discussed. As noted in this work, a large difference between the maturity of the technology between developing and developed countries was observed, the majority of AD plants in developing countries treat the OFMSW in mono-digestion with the purpose to obtain electricity; whereas in developed countries, AD systems treat this waste in co-digestion with different industrial waste streams and exploit the technology further from only generation electrical power, obtaining other high market-value products. This thesis also presents AD as a WM strategy to treat the organic fraction of the municipal solid waste generated in the Metropolitan Area of Guadalajara (MAG) located in Mexico. In this work, an experimental approach to sample the OFMSW generated in different socioeconomic strata of the MAG and to evaluate its biochemical methane potential (BMP) at a lab-scale AD system is presented. From a microscale perspective, the microbiome was analyzed using high-throughput sequencing to assess the microbial dynamics and its relationship to the composition 8 of biogas generated throughout the assays. From a macroscale perspective, a multi-Gompertz kinetic model was used to describe the cumulative biogas production and to estimate the potential biogas and methane production of the OFMSW generated in the MAG. Furthermore, this estimation was used to assess the potential environmental, economic, and energetic benefits of implementing AD as the WM practice to treat the OFMSW in the MAG. As highlighted in this work, with a biochemical methane potential of 732.8 L·kg-1 VS, an estimated 8.5 MWh·year-1 of electrical power could be produced, representing a revenue of 1.13 million USD per year and a reduction in GHG emissions of 10,519 tonnes CO2eq·year-1 in the MAG. Anaerobic digestion represents an important opportunity for developing countries to shift to sustainable WM systems, especially in the case of the OFMSW, since this waste stream represents a large untapped potential source of clean energy. AD offers significant environmental and economic advantages as a WtE and WM practice that could help developing countries, like Mexico, reach their greenhouse gas (GHG) emissions reduction and clean energy generation goals. However, further research is required to harness the methanogenic potential of the OFMSW generated in the MAG. Opportunities to optimize the AD system from a microbiological and from an operational perspective, such as using other regional waste streams as co-feedstocks, should be explored. Different political, technical, and financial barriers are preventing the full-scale implementation of AD in developing countries, nonetheless, forming alliances in which the public, private and institutional sectors work together can help overcome these challenges.