Anaerobic Digestion (AD) is an essential component in wastewater treatment to recover energy from waste and deals with sludge management issues effectively. AD is a treatment process that converts organic matter to methane and carbon dioxide with multi-step biological reactions. Methanogenesis, the subprocess of AD that produces methane, is an important indicator of the stability of AD and is influenced by pH, temperature, ammonia, volatile fatty acids (VFAs), and solids concentrations among other factors. Ammonia is an essential nutrient for methanogenic bacteria but at certain ammonia concentrations and pH levels, ammonia is said to be a toxicant for methanogenic archaea. Substrates that are high in ammonia content can include those high in protein, such as food waste, which can be inhibitory to methanogens in the digestion process. Thickened waste activated sludge (TWAS) also contains a large amount of nitrogen with its higher solids concentration, promoting methane production. VFAs are produced during acidogenesis and they can negatively affect methanogenic archaea. High organic loading rates into AD can lead to an accumulation of VFAs and thus inhibition of methanogenic activity. Even with well-known inhibitory effects of ammonia and VFAs on methanogenesis, there are limited tools available for modelling these inhibitions, especially when evaluating diverse compositions of substrate. The objectives of this research work are to experiment for various pairings of pH, ammonia, and acetate levels using batch reactors and to quantify the inhibition on the overall methane production using an AD-based model focused on biological reactions. / Thesis / Master of Applied Science (MASc)

Sludge management is the highest operating cost in municipal wastewater treatment. Anaerobic digestion (AD) is used to stabilize the sludge and reduce biosolids generation. Hydrolysis kinetics limit the rate of anaerobic digestion and must be improved to increase the overall process rate. In this study a new sludge characterization analysis was used to evaluate hydrolysis in a lab-scale pretreatment process operated at 55℃, 65℃, and 75℃. The experimental results were used to develop a new AD mathematical model, the hydrolysis digestion model (HDM). The model developed is easier to use, as the number of processes and variables were reduced by half, in comparison to existing models. The model variables can be measured using standard sludge characterization analysis, and the hydrolysis reactions included the fermenting microorganism to more accurately model the two-phase hydrolysis model. Model simulations were found to be a good fit of the experimental results, accurately predicting the rate and extent of hydrolysis in the pretreatment digester. / Thesis / Master of Applied Science (MASc)