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No description available.

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No description available.

No description available.

We analyze a simplified mathematical model of the complete degradation of monochlorophenol. The model takes form of a system of six ordinary differential equations, the dynamics of which can be reduced to the dynamics of a three-dimensional system on the invariant set. We extend the previous analysis by considering multiple substrate inflow. We also focus on the bifurcations occurring in the system and their biological meaning. / Thesis / Master of Science (MSc)

Anaerobic digestion (AD) is an essential process in wastewater treatment to stabilize waste organic solids and produce biogas. This research is comprised of two projects in the discipline of anaerobic digestion. First, the effect of high sulfate concentration on anaerobic digestion of wastewater sludge was investigated. Secondly, the performance of acetoclastic methanogens Methanosaeta spp. and Methanosarcina spp. were investigated under intensified AD operation conditions (i.e., elevated acetate concentrations, vigorous mixing, etc.). In the sulfate experiments, the cumulative biogas and methane production decreased linearly with increasing initial sulfate doses (0 – 3,300 mg S L-1) and the correlation between the sulfate dose and methane production was verified with theoretical predictions, indicating complete reduction of sulfate to sulfide in AD. The examined sulfate concentrations resulted in no clear negative effects on the COD (chemical oxygen demand) removal or VSS (volatile suspended solids) destruction of the wastewater sludge, indicating that previous findings on sulfide toxicity might have been attributed to potential COD overestimation of digested sludge with high levels of sulfide. To avoid potential misinterpretation of AD performance on sulfide toxicity effects, we proposed a new method for COD correction for digested sludge. In the second project focused on acetoclastic methanogens, vigorous mixing conditions substantially decreased Methanosarcina spp. growth and methane production, and the decreased methanogenesis was more pronounced at higher acetate concentrations. Methanosarcina spp. prefer to grow in clusters and the vigorous mixing can disrupt cluster formation; as a result, reduced chances for cluster formation limited the growth of Methanosarcina spp.. While Methanosarcina spp. growth and methane production increased with the increasing acetate concentration, Methanosaeta spp. growth was unaffected by the examined vigorous mixing and soluble substrate conditions with negligible relative growth. Thus, rapid enrichment of Methanosarcina spp. is critical for successful operation intensified of AD processes under high organic loading conditions. / Thesis / Master of Applied Science (MASc)

Anaerobic digester design and operation influences the biomass degradation efficiency performed by complex and diverse microbial communities. Optimum anaerobic digester design and operational parameters in residential on-site wastewater treatment sites (OWTS) establishes physiochemical environments suitable for the growth and stability of the microbial communities responsible for organic waste degradation. A comparative study of the microbial communities and their functional profiles between different OWTS designs and operational parameters have not been done despite their functional importance in residential organic waste removal. Using whole-metagenome shotgun sequencing, microbial community compositions and functions were compared between two digester designs: conventional box septic tanks and septic tanks equipped with a novel closed-conduit tube called the InnerTubeTM. Wastewater was sampled along the length of each digester to explore the microbial community stratification during the anaerobic digestion treatment process. Additionally, the effect of effluent, aerobic recirculating-lines on the digester microbiome was also explored. Physiochemical characteristics in the form of oxygen demand, nitrogen and solids content was used as endpoints and correlated with microbial community and functional gene abundances to explore the microbes driving anaerobic digestion. Conventional digesters were characterized by syntrophic proprionate-oxidizing microbes and acetoclastic methanogens, while InnerTube™ digesters were characterized by syntrophic sulfate-reducing microbes and hydrogenotrophic methanogens. Recirculating digesters were enriched with denitrifying microbial consortia in syntrophy with hydrogenotrophic methanogens. Microbial communities were organized according to hydrolytic, acidogenic, acetogenic, and methanogenic groups along the digester treatment process. Insight into the core microbiome of OWTS can inform bioaugmentation and digester design and operation optimization strategies to improve the treatment of decentralized residential sewage sources. / Thesis / Master of Science (MSc) / Anaerobic digesters are used throughout North America to treat residential sewage. Despite their prevalence, the composition and function of the microbial communities driving sewage degradation in residential digesters has not been studied. We used DNA sequencing to compare the microbial communities and functional genes in different anaerobic digester designs across Southern Ontario. Our findings suggest there are successive microbial groups along the length of septic tanks and that different septic tank designs harbor characteristic sulfidogenic and methanogenic microbes. Characterization of these microbes could inform septic tank bioaugmentation, design and operational optimization strategies to improve sewage treatment performance.

Yes / A novel Euler-Lagrangian (EL) computational uid dynamics (CFD) nite volume-based model to simulate the gas mixing of sludge for anaerobic digestion is developed and described. Fluid motion is driven by momentum transfer from bubbles to liquid. Model validation is undertaken by assessing the ow eld in a labscale model with particle image velocimetry (PIV). Conclusions are drawn about the upscaling and applicability of the model to full-scale problems, and recommendations are given for optimum application.

Yes / For the first time, a set of Lattice-Boltzmann two-way coupling pointwise Euler-Lagrange models is applied to gas mixing of sludge for anaerobic digestion. The set comprises a local model, a “first-neighbour” (viz., back-coupling occurs to the voxel where a particle sits, plus its first neighbours) and a “smoothing-kernel” (forward- and back-coupling occur through a smoothed-kernel averaging procedure). Laboratory-scale tests display grid-independence problems due to bubble diameter being larger than voxel size, thereby breaking the pointwise Euler-Lagrange assumption of negligible particle size. To tackle this problem and thereby have grid-independent results, a novel data-scaling approach to pointwise Euler-Lagrange grid independence evaluation, based on an application of the Buckingham π theorem, is proposed. Evaluation of laboratory-scale flow patterns and comparison to experimental data show only marginal differences in between the models, and between numerical modelling and experimental data. Pilot-scale simulations show that all the models produce grid-independent, coherent data if the Euler-Lagrange assumption of negligible (or at least, small) particle size is recovered. In both cases, a second-order convergence was achieved. A discussion follows on the opportunity of applying the proposed data-scaling approach rather than the smoothing-kernel model.