Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Civil and Environmental Engineering
Supervisor
Dagnew, Martha
Abstract
This research addresses the dual challenge of nitrogen pollution and greenhouse gas (GHG) emissions from wastewater treatment systems. It encompasses studies to evaluate and enhance total nitrogen (TN) removal efficiency and reduce GHG emissions in simultaneous nitrification and denitrification (SND) and partial denitrification (PDN) processes through biofilm technology. The first study introduced a novel approach to achieve SND under dynamic load conditions using rope-type biofilm technology beneficial for remote and decentralized communities. The process used a carbon management strategy with constant timer-based intermittent aeration control versus online sensor dynamic control strategies. The most optimal nitrification and total inorganic nitrogen (TIN) removal efficiencies were 89% and 72%, respectively. Additionally, the study employs multivariate approaches to delineate key operational factors affecting SND process and a comprehensive microbial community analysis revealed complex interactions among various bacteria under different aeration conditions that further deepens the understanding of the system.
Furthermore, the study explored the PDN pathway to generate stable nitrite accumulation benefiting the anammox process pathway for TIN removal. The process viability, biofilm community evolution, and functional enzyme formation in rope-type biofilm reactors using primary effluent (PE) and anaerobically pretreated wastewater carbon sources were studied for the first time. The internal carbons resulted in thinner biofilms; nevertheless, modest nitrite accumulation (0.24 g N/m2/d) occurred with elevated pH. The highest accumulation (0.79 g N/m2/d) was exhibited in the biofilm thickness-controlled acetate-fed reactor, featuring porous biofilms dominated by denitrifier Thauera (10.24%) and imbalance between Nar, Nap, and Nir reductases. Lastly, the research extended to monitor and mitigate nitrous oxide (N2O) emissions in the PDN process. This research is the first to evaluate N2O emissions within the co-diffusion biofilm PDN process, reporting 0.0008 to 0.053 g N2O-N/m2/d N2O emissions, representing 0.1% to 18% of the removed nitrate, which was further mitigated by manipulating the COD/N ratio.
Overall, this research provided a holistic understanding of fixed biofilm technology in wastewater treatment. By advancing SND and PDN processes with a focus on operational development, microbial community analysis, and environmental impact, the study presented a significant step forward in developing efficient and sustainable treatment methodologies.
Summary for Lay Audience
In the face of growing environmental concerns, two critical issues stand out: nutrient pollution in our water bodies and the escalating crisis of greenhouse gas emissions. This summary introduces these challenges and a problem solver by rope-type biofilm media reactors.
Our water bodies are increasingly plagued by nutrient pollution, primarily excessive nitrogen and phosphorus. This overabundance, largely from agricultural runoff and wastewater, leads to eutrophication. Simultaneously, releasing greenhouse gases like carbon dioxide and, notably, nitrous oxide contributes significantly to global warming. Nitrous oxide, a by-product of microbial processes in nitrogen-rich water bodies, is a potent greenhouse gas, linking nutrient pollution to climate change. However, traditional wastewater treatments by separate nitrification or denitrification in suspended activated sludge systems often fail to remove all nitrogen forms. Developing more effective methods for total nitrogen removal is essential for mitigating water pollution and climate change impacts.
The development of rope-type media biofilm reactors offers a promising approach. These reactors, with passive operation and small footprint, relying on the attached growth of microorganisms, are more efficient than traditional methods and can reduce both nutrient pollution and greenhouse gas emissions effectively. The first aim of the thesis was to enhance the simultaneous nitrification-denitrification process using rope-type media. The research sought to evaluate and simulate the operational conditions and refine the aeration strategies for better nitrogen removal efficiency with less energy by conducting long-term field studies. Additionally, this thesis focused on developing another advanced treatment process, partial denitrification, by utilizing internal and external carbon sources, examining its characteristics of nitrite accumulation performance, biofilm kinetics and properties, and microbial communities with functional enzymes to develop nitrogen removal efficacy.
To assess the potential of greenhouse emissions from the partial denitrification process, the first evaluation of nitrous oxide release from rope-type biofilm reactors was conducted with a correlation analysis of the comprehensive effects of operational conditions.
This research stands at the intersection of innovation and environmental stewardship, aiming to enhance water quality and mitigate climate change. Through this work, we endeavor to contribute a viable, eco-friendly approach to wastewater treatment.
Recommended Citation
Sun, Lin, "Addressing nitrogen pollution and greenhouse gas emissions in advanced wastewater treatment processes using rope-type biofilm reactors" (2024). Electronic Thesis and Dissertation Repository. 10415.
https://ir.lib.uwo.ca/etd/10415