Anaerobic co-digestion approach for the valorization of livestock and agricultural waste from critical regions of Jalisco

Abstract

Livestock waste is common nonpoint-source pollution with adverse implications on the environment. Given the logistical difficulties of the manure recollecting process, these nutrient-rich residues have negative repercussions on nearby aquatic ecosystems, such as rivers and lakes. Swine and cattle residues are rich in nitrogen, phosphorus, and organic matter, which cause an ecological imbalance after they reach bodies of water through the action of rainfall. As a consequence of this nutrient runoff, watersheds' total nitrogen and phosphorus concentrations rise to harmful levels; thus, developing a phenomenon often known as eutrophication. Abnormal growth of phytoplankton and other macrophytes characterizes eutrophic and hypereutrophic aquatic environments. These algal blooms consume most of the dissolved oxygen, reducing the available oxygen for other species to survive. Livestock manure should be collected before runoff transfers nutrients to the basins to avoid eutrophication. Then, these residues must be treated so they can be disposed of without harming the environment. This work proposes a waste valorization approach to reduce the nitrogen, phosphorus, and carbon concentrations in livestock residues while producing a high-quality renewable energy source. Anaerobic co-digestions with lignocellulosic-rich residues were performed to enhance biogas production while maximizing the overall nutrient removal. The complete process followed in this work is segmented into four separate chapters. The first chapter states the problem, the research questions, the proposed solution, the objectives, and the main contributions of the project. Chapter two proposes a methodological approach to determine critical regions for eutrophication based on public online databases and the use of geographical information systems. This methodology applies machine learning algorithms coupled with spatial operators to analyze large areas of study, such as states, basins, hydrographic regions, and other regions. The case study of the state of Jalisco, in Mexico, is also presented in that chapter to obtain the most critical sub-basins and their correlation with environmental factors, such as rainfall and land use. In chapter three, critical municipalities were selected based on chapter two’s methodology, along with livestock production data in Jalisco. Then, crops were selected from the municipalities' yearly agricultural production to evaluate the co-digestions potential to produce biogas, mixing it with livestock waste. Eighteen different treatments were assessed by their biochemical methane potential and nutrient removal capacity. Chapter three also proposes a waste valorization index that uses both indicators (biochemical methane potential and nutrient removal capacity) to determine the best treatments. Finally, the future perspectives and general conclusions for this work are in chapter four.