The Effect of Temperature on the Performance and Microbial Community of Anaerobic Membrane Bioreactors for Treatment of Domestic Wastewater

Aeration costs in traditional activated sludge systems are the highest operational cost of wastewater treatment plants and account for approximately 0.75% of the total U.S. energy consumption. In an effort to subset these energy costs, anaerobic wastewater treatment allows for the generation of methane-rich biogas, making a normally energy-intensive process energy-neutral or even energy-positive. Efficient operation of anaerobic processes usually require heating wastewater to mesophilic or thermophilic temperatures, which is not feasible for secondary treatment. Therefore, operating anaerobic bioreactors in cold climate conditions is a challenge. The slow growth of microbes at cold temperatures impacts the efficiency of anaerobic bioreactors causing a need for long solid retention times (SRTs). Anaerobic membrane bioreactors (AnMBR) eliminate sludge washout, increase SRTs, and allow for treatment of wastewater at low temperatures. However, membrane fouling and reliable treatment at low temperatures remain as two primary challenges for AnMBRs. Since the temperature of untreated domestic wastewater (DWW) in the South Carolina ranges from 13 to 27ºC, it is necessary to characterize the performance of AnMBRs for DWW treatment within these ranges of seasonal variation. The performance of the reactor is likely to vary as a result of the changing microbial community that is responsible for converting complex organics in the waste (like carbohydrates, proteins, and lipids) to their end product of methane through a complex series of biochemical reactions. One goal of this study is to evaluate the change in reactor performance as a function of varying bioreactor temperature. Performance is evaluated by monitoring biogas production and chemical oxygen demand (COD) removal. Another goal is to quantify mcrA gene expression in RNA as a function of varying bioreactor temperature. The mcrA gene is a functional gene that has been related to the production of methane by methanogenic communities. The last objective of the study is to establish a relationship between the microbial community structure at different temperatures and the AnMBR performance. This will be done by completing a metagenomic analysis on the communities existing at different temperatures. By further understanding the microbial components and relating them with the performance of the AnMBR, we can better understand the functionality of specific microbial comminutes and therefore better inform, operate, and design anaerobic resource recovery processes for maximum effectiveness

Generalized Ellipsometry Based Methods to Measure and Visualize the Deposition of Titanium Dioxide Nanoparticles Onto Model Rough Surfaces

In recent years, characterization and detection of engineered nanoparticles like titanium dioxide nanoparticles (nTiO2) have increased importance in the fields of environmental engineering. They can enter the subsurface and interact with natural soils and sands. Due to highly heterogeneous rough surfaces of natural substrates (e.g., soils and sediments), measuring the interaction of nTiO2 and natural substrates has been very challenging. In this dissertation, three-dimensional nanostructured slanted columnar thin films (SCTFs) with well-defined height were used to mimic surface roughness on proposed substrates (i.e., QCM-D sensors, glass). Interactions between nTiO2 and SCTF surfaces were measured in-situ using QCM-D and generalized ellipsometry (GE) techniques simultaneously. The effects of various parameters, such as roughness height and ionic strength of the solution, on the deposition of nTiO2 on SCTF surfaces were evaluated. It was discovered that typical QCM-D models based on viscoelastic effect only could overestimate the attached areal mass density of nTiO2 due to the water entrapment in between nanoparticles and the pore structure of SCTF. A new model was developed to couple viscoelastic and surface roughness effect. For the first time, this work was able to evaluate the porosity of attached nTiO2 on SCTF surface using appropriate QCM-D and GE model. Another significant contribution of this work is to detect pico-grams of nTiO2 attached on anisotropy surface of SCTFs using a newly developed anisotropy contrast optical microscopy (ACOM) that operates based on generalized ellipsometry technique. Using this technique, we were able to image and quantify the deposition of nTiO2 on SCTF surfaces in a label-free manner. In order to investigate the role of flow on the deposition of nTiO2, we developed a glass microfluidic channel with built-in SCTF surface. The method of preparing the microfluidic channel was meticulously designed not to invade SCTF structure. Using ACOM technique and the microfluidic channel, we present the first effort to sense the transport of nTiO2 over time and quantify the distribution of deposited titanium dioxide nanoparticles on the model surfaces

Improving the Sweeping Efficiency of Permanganate into Low Permeable Zones To Treat TCE: Experimental Results and Model Development

The residual buildup and treatment of dissolved contaminants in low permeable zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat dissolved-phase TCE. This was accomplished by conducting transport experiments that quantified the ability of xanthan-MnO4− solutions to penetrate and cover (i.e., sweep) an LPZ that was surrounded by transmissive sands. By incorporating the non-Newtonian fluid xanthan with MnO4−, penetration of MnO4− into the LPZ improved dramatically and sweeping efficiency reached 100% in fewer pore volumes. To quantify how xanthan improved TCE removal, we spiked the LPZ and surrounding sands with 14C-lableled TCE and used a multistep flooding procedure that quantified the mass of 14C-TCE oxidized and bypassed during treatment. Results showed that TCE mass removal was 1.4 times greater in experiments where xanthan was employed. Combining xanthan with MnO4− also reduced the mass of TCE in the LPZ that was potentially available for rebound. By coupling a multiple species reactive transport model with the Brinkman equation for non-Newtonian flow, the simulated amount of 14C-TCE oxidized during transport matched experimental results. These observations support the use of xanthan as a means of enhancing MnO4− delivery into LPZs for the treatment of dissolved-phase TCE. Includes Supplementary Data

Improving the Sweeping Efficiency of Permanganate into Low Permeable Zones To Treat TCE: Experimental Results and Model Development

The residual buildup and treatment of dissolved contaminants in low permeable zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat dissolved-phase TCE. This was accomplished by conducting transport experiments that quantified the ability of xanthan-MnO₄^– solutions to penetrate and cover (i.e., sweep) an LPZ that was surrounded by transmissive sands. By incorporating the non-Newtonian fluid xanthan with MnO₄^–, penetration of MnO₄^– into the LPZ improved dramatically and sweeping efficiency reached 100% in fewer pore volumes. To quantify how xanthan improved TCE removal, we spiked the LPZ and surrounding sands with ¹⁴C-lableled TCE and used a multistep flooding procedure that quantified the mass of ¹⁴C-TCE oxidized and bypassed during treatment. Results showed that TCE mass removal was 1.4 times greater in experiments where xanthan was employed. Combining xanthan with MnO₄^– also reduced the mass of TCE in the LPZ that was potentially available for rebound. By coupling a multiple species reactive transport model with the Brinkman equation for non-Newtonian flow, the simulated amount of ¹⁴C-TCE oxidized during transport matched experimental results. These observations support the use of xanthan as a means of enhancing MnO₄^– delivery into LPZs for the treatment of dissolved-phase TCE