This study aims to provide the latest understanding of cutting-edge technologies that enable wastewater organic carbon diversion and recovery through the enhancement of sludge production and blending, digestibility, dewaterability, and dewatered cake odor emission control. A comprehensive literature review showed that iron-based coagulants tend to show less negative impact than aluminum-based coagulants. This can be attributed to the reduction of ferric to ferrous ions in the course of anaerobic digestion (AD), which leads to a suite of changes in protein bioavailability, alkalinity, and hydrogen sulfide levels, and in turn the sludge dewaterability and odor potential. In terms of the roles of thermal hydrolysis pretreatment (THP), the mechanism review indicated that the improvement of sludge dewaterability and anaerobic digestibility as a result of THP was because of the destruction of extracellular polymeric substances and increase of hydrolysis rate. However, THP also brings side effects such as high free residual ammonia and recalcitrant dissolved organic nitrogen (rDON) in the effluent. Besides, a comprehensive understanding of the formation of the odorous compounds in the sludge treatment processes indicated that sulfurous and nitrogenous compounds are usually regarded as the major odor-causing substances. A Pilot THP-AD study indicated that adding aluminum to produce primary sludge can improve overall plant sludge digestibility, dewaterability, and well as the rDON reduction. Moreover, results from a pilot THP-AD and biochemical methane potential (BMP) test study indicated that adding a secondary thermal hydrolysis after a primary thermal hydrolysis-AD system can still create new BMP. Finally, a pilot study was conducted to evaluate the effect of aeration in the sludge holding tank on biosolids odor emission. The two rounds of bench-scale aeration studies indicated that aerating the sludge in holding tanks reduced peak emission concentrations of sulfurous odorous compounds. Further full-scale validation confirmed that aeration can be used by utilities as a simple means for biosolids odor control. / Doctor of Philosophy / Public wastewater treatment annually consumed 3-4% energy production and contributed 1% greenhouse gas emission in the U.S. Meanwhile, the chemical energy contained in wastewater was estimated to be 9.3 times the energy it takes to treat it. Therefore, harvesting wastewater energy is proposed as a viable means for achieving energy and carbon neutral wastewater treatment. The approach to sending wastewater energy as much as possible to anaerobic digesters in which microorganisms help harvest useful energy in the form of flammable methane was evaluated in this study. From literature, we learned that chemicals used for upstream wastewater energy capture and nutrient removal may make the downstream energy recovery difficult. While, thermal hydrolysis pretreatment, an industrial-scale pressure cooker, can be used to improve the ease of microbial bioenergy harvesting by making organics more biodegradable. However, thermal hydrolysis may also bring side effect in terms of recalcitrant organic formation. Also, in the course of energy recovery, the production and emission of nuisance odor may occur but can be controlled. Building on this existing knowledge, this study evaluated the pros and cons of the approach to using chemicals to capture and recover energy from wastewater. The results showed that the extents of energy recovery and savings was greater than the compromised solids reduction from the process. Moreover, results from a biochemical methane potential test study indicated that adding a secondary thermal hydrolysis can recover even more chemical energy from wastewater. In the end, a pilot study was conducted to develop a simple and economical approach to mitigating the odor emission issue during sludge handling. Results showed that pumping air into the sludge holding tank can substantially reduce peak odor emission. This approach was later verified in a full-scale test and recommended to utilities as a simple means for biosolids odor control.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/116659 |
| Date | 13 November 2023 |
| Creators | Luo, Hao |
| Contributors | Civil and Environmental Engineering, Wang, Zhiwu, Nguyen, Caroline Kimmy, Dietrich, Andrea M., Novak, John Thomas |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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