Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. George Nakhla and Dr. Jesse Zhu

Abstract

Among the various biological wastewater treatment processes for industrial and municipal wastewater treatment, fluidized bed bioreactors (FBBR) demonstrate numerous advantages compared to suspended growth systems such as lower hydraulic retention time, high surface area and accordingly high biomass retention time, higher volumetric conversion rates, lower sensitivity to temperature, and less sludge production. Despite the numerous biofilm bioreactor configurations and system schemes that are currently available for a wide variety of environmental applications, the development and optimization of a stable biofilm that is capable of offering effective and integrated functions, i.e. biodegradation, biomass-liquid separation, and biomass retention along with a substantial reduction of nitrous oxide (N2O) emissions is still challenging.

To achieve this goal, this work addresses four separate but interconnected projects with a focus on denitrifying biofilm in FBBR. First, biofilm morphology and structure was investigated by changing the media properties, i.e. sphericity, surface roughness, and specific surface area. Four different types of media (natural and artificial) were tested and it was found that particles with sphericity of 0.9 (multi-blast plastic (MB) and natural zeolite (NZ)) maintained a fluffy protruding biofilm and achieved slightly higher nutrient removal efficiencies as compared to particles with a sphericity of 0.5 (maxi-blast plastic (MX) and lava rock (LR)), which exhibited a patchy biofilm at low COD-to-nitrogen (COD/N) ratio.

The second study explored influent wastewater characteristics to change and control the biofilm thickness, morphology, and structure in denitrifying FBBRs as well as enhance biofilm strength. The DFBBRs were operated on a synthetic municipal wastewater at five different characteristics at two different COD/N ratios of 5 and 3.5.

The third study involved the use of the developed methodology to mitigate N2O emissions from denitrification processes. It was found that the N2O conversion rate at typical municipal wastewater was about 0.53% of the influent nitrogen loading, whereas the N2O conversion rates for R120,R180,and R240 were 0.34%, 0.42%, and 0.41%, respectively. At the higher nitrogen loading, the N2O conversion rate of R60 increased three folds to 1.57% of the influent nitrogen loading.

Finally, a biofilm calibration protocol was developed for biofilm one-dimensional (1-D) fully dynamic and steady-state biofilm simulation models. The developed calibration protocol sets a complete strategy to model particulate biofilm reactors and proposes a method to collect the data and translate it to useful information. The detailed calibration procedures presented here will not only help the process engineers design and retrofit plants but also plan sampling and monitoring requirements for process optimization. Sensitivity analysis was also used to identify the most important biofilm parameters and guide experimental measurements.


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