PhD Oral Exam - Tahereh Malmir, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This PhD thesis focuses on optimizing municipal solid waste flows and modeling and managing landfill gas generation from organic wastes. First, it presents a statistical survey of waste flow in New York and Montreal and a calculation of the energy recovery potential of food and yard waste in these cities. The results indicate a low diversion rate from landfills, with significant biogas generation potential from these wastes, contributing to around 2.5% of the energy supply in these cities. Second, it evaluates the current and proposed waste management systems in Montreal, applies a life cycle assessment using the IWM-2 software, and optimizes waste flows using a genetic algorithm to decrease energy consumption, greenhouse gas emissions and costs. The optimized waste flow considers 58% landfilling and shows the importance of further research on landfills.

The following chapters study the generation and storage of gas from waste decomposition in municipal solid waste landfills in the province of Quebec, Canada. The fifth chapter addresses the modeling scenarios of landfill gas generation based on a modified first-order decay model. It uses a genetic algorithm to independently fit parameters to methane and hydrogen sulfide generation models. The results show that differentiating more waste types improves the modeling accuracy, and the changes in waste management strategies within a landfill’s decade-long lifetime require various modelling assumptions. Also, the work reveals the importance of considering how different landfill sectors are filled over time. The sixth chapter explores the potential of utilizing stored methane in landfills as an energy source. The study investigates the gas collection system shutdown and restart periods, determining the duration required to maximize collected stored methane. The results show that it takes 0.6 hours to start methane collection and 2.5 hours to reach the maximum collected stored methane. Additionally, the collected stored methane represents 10.5% of landfill gas flow.