Modeling Biofilm on Reactive Surface

• Other Authors: Wang, Boya (author)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Civil engineering; Environmental engineering
• Online Access: http://purl.flvc.org/fsu/fd/2019_Fall_Wang_fsu_0071E_15625

Biofilms were first used to treat wastewater in the late 19th century, and still play an important role in today’s wastewater treatment plants. Biofilm model is one of the most essential and powerful tools for studying biofilm process, understanding the mechanisms both inside the biofilm and between the biofilm and outside environment, and controlling the performance of the biofilm reactors. Usually the biofilm grows on inert and impermeable surfaces, but sometimes it develops on ‘active’ surfaces, which makes it more challenging to simulate. This dissertation is focused on modeling biofilm on reactive surface. It also develops a method to estimate kinetic parameters of biodegradation to be used in models. Homoacetogenesis and methanogenesis, which usually occur during anaerobic trichloroethene (TCE) dechlorination, affect the removal of TCE and its daughter products. This study develops a one-dimensional, multi-species H2-based biofilm model to simulate the interactions among six solid biomass species (Dehalococcoides, Geobacter, methanogens, homoacetogens, inert biomass (IB), and extracellular polymeric substances (EPS)) and 10 dissolved chemical species (TCE, dichloroethene (DCE), vinyl chloride (VC), ethene, hydrogen (H2), methane, acetate, bicarbonate, utilization associated products (UAP), and biomass associated products (BAP)). To evaluate and parameterize the model, parameter values from the literature were input into the model to simulate conditions reported for an experiment. The biomass species distribution in the biofilm and the chemical species concentrations in the reactor effluent at steady state were generally consistent between the experiments and the model. The predicted 15-µm biofilm consisted of three layers, each dominated by a different active biomass type: homoacetogens in the layer next to the membrane, Geobacter in the biofilm surface layer (next to the water), and Dehalococcoides in-between. About two thirds of the TCE was converted to ethene and one third to VC due to the large half-maximum-rate concentration of VC. The effluent concentration of VC is far beyond the drinking-water maximum contaminant level (MCL) of 2 µg/L. To achieve complete removal of TCE, DCE, and VC, we evaluated the influence of various operating conditions like H2 pressure, biofilm detachment rate (kdet), and multiple stages. Through all the simulation results, we demonstrated that VC could be completely removed from the reactor when the H2 pressure was between 0.01 and 0.1 atm and kdet was between 1 and 3.6 cm-1day-1. We also found that a 2-stage system was more efficient than a single-stage reactor. All biofilm models use kinetic parameters of biodegradation. For microbial consortia, the traditional method for kinetic parameter estimation is based on the total biomass concentration and assumes that all the microorganisms are capable of degrading the contaminant. This work proposed an improved method that selects the responsible microbial groups and uses their concentrations for parameter estimation. We conducted batch experiments to track the change of contaminant and biomass concentrations, and used 16s rRNA sequencing to analyze the microbial community. Based on the correlation between the contaminant and microbial abundance, we then found the groups that were likely responsible for bio-degradation of the contaminant. PEST, the industry standard software package for parameter estimation and uncertainty analysis of complex environmental and other computer models, was used to estimate biodegradation parameters. By comparing to the conventional method, we found that the accuracy of this method was higher than that of the conventional method. === A Dissertation submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === 2019 === November 8, 2019. === 1,4-dioxane, biofilm, model, reactive surface, TCE === Includes bibliographical references. === Youneng Tang, Professor Directing Dissertation; Juan Ordonez, University Representative; Gang Chen, Committee Member; Wenrui Huang, Committee Member.