Optimizing Anaerobic Treatment to Enhance Energy Recovery from High-Strength Waste and Wastewater
Creators: Mou, Anqi
Publisher: name: University of Alberta Library
Year: 2024

<p>Anaerobic digestion (AD) is a promising technology for the sustainable treatment of high-strength waste and wastewater, offering the potential for energy recovery. However, various factors can inhibit the AD process, requiring well-balanced operational strategies to optimize different stages of the AD process, enhancing overall energy recovery, and investigating the dynamics of microbial communities to understand the mechanisms behind these optimizations. <br>
The research chain began by examining pre-treatment methods to accelerate the initial hydrolysis step of AD. Specifically, the efficiency of calcium hypochlorite pre-treatment on thickened waste activated sludge (TWAS) was investigated. The optimal dosage of calcium hypochlorite was determined to minimize sludge volume after aerobic digestion, with a focus on enhancing solubilization and biodegradability of TWAS. After the pre-treatment with 0.1 gCa(ClO)2/gtotal solids (TS), volatile solids (VS) of TWAS were reduced by 65% after 20 days of aerobic digestion - nearly double the reduction observed in un-pretreated TWAS. <br>
Subsequently, the thesis shifted focus to improving syntrophic interactions between four steps of AD. The feasibility of anaerobic calcium phosphate granulation for blackwater treatment was assessed in continuous reactors operated under mesophilic conditions. CaP granules were developed in the up-flow anaerobic sludge blanket (UASB) reactor. An organic loading rate (OLR) of 16.0 g/L/d and hydraulic retention time (HRT) of 0.25 days were achieved, with a total chemical oxygen demand (COD) removal rate of 75.6%, and a methane production rate of 8.4 gCH4-COD/L/d. <br>
This thesis also explored co-digestion methods to reduce the volatile fatty acids (VFAs) accumulations, thereby balancing the four steps of AD. The feasibility of long-term operation for co-digestion of spent caustic wastewater and pot ale wastewater was assessed. The methane yield of co-digestion reactor was higher than that of the pot ale wastewater reactor. The organic loading capacity of co-digestion reactor reached 13.6 g/L/d, which was higher than 7.6 g/L/d achieved in pot ale wastewater reactor. Meanwhile, the co-digestion also improved the hydrolysis efficiency of co-digestion substrates. <br>
In the final stages, this thesis accelerated methanogenesis, the last step of AD process. The effects of granular activated carbon (GAC) spatial distribution in UASB reactors on methane production were examined. Three different GAC placement strategies (top, bottom, and top+bottom) were evaluated to enhance methane production throughout the reactor depth, particularly focusing on treating different solid-content wastewater and enhancing organic loading capacities. Under low OLR (2 g/L/d) treating high solid-content wastewater, the highest methane yield was observed for UASB supplemented with self-floating GAC (74%), which was followed by settled +self-floating GAC reactor (65%), then settled GAC reactor (58%). When treating low solid-content wastewater, all UASBs achieved improved methane yield, and settled +self-floating GAC reactor achieved the highest methane yield (83%). Under high OLR (6 g/L/d) treating high solid-content wastewater, the UASB supplemented with GAC at both bottom and top achieved the highest methane yield (66%), whereas the UASB supplemented with GAC at the top failed. <br>
Throughout the AD process, the role of microorganisms was important. The dynamics of microbial communities in augmented systems were analyzed to highlight their critical role in optimizing performance. This thesis demonstrated the significance of balancing whole AD processes through strategic treatment modifications and highlights the need to consider organic loading capacities and feedstock characteristics, thereby contributing to the development of more sustainable wastewater treatment solutions.</p>