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To address sustainability issues in wastewater treatment (WWT), Siemens Water Technologies (SWT) has designed a "hybrid" process that couples common activated sludge (AS) and anaerobic digestion (AD) technologies with the novel concepts of AD sludge recycle and biosorption. At least 85% of the hybrid's AD sludge is recycled to the AS process, providing additional sorbent for influent particulate chemical oxygen demand (PCOD) biosorption in contact tanks. Biosorbed PCOD is transported to the AD, where it is converted to methane. The aim of this study is to provide mass balance and microbial community analysis (MCA) of SWT's two hybrid and one conventional pilot plant trains and mathematical modeling of the hybrid process including a novel model of biosorption. A detailed mass balance was performed on each tank and the overall system. The mass balance data supports the hybrid process is more sustainable: It produces 1.5 to 5.5x more methane and 50 to 83% less sludge than the conventional train. The hybrid's superior performance is driven by 4 to 8 times longer solid retention times (SRTs) as compared to conventional trains. However, the conversion of influent COD to methane was low at 15 to 22%, and neither train exhibited significant nitrification or denitrification. Data were inconclusive as to the role of biosorption in the processes. MCA indicated the presence of Archaea and nitrifiers throughout both systems. However, it is inconclusive as to how active Archaea and nitrifiers are under anoxic, aerobic, and anaerobic conditions. Mathematical modeling confirms the hybrid process produces 4 to 20 times more methane and 20 to 83% less sludge than the conventional train under various operating conditions. Neither process removes more than 25% of the influent nitrogen or converts more that 13% to nitrogen gas due to biomass washout in the contact tank and short SRTs in the stabilization tank. In addition, a mathematical relationship was developed to describe PCOD biosorption through adsorption to biomass and floc entrapment. Ultimately, process performance is more heavily influenced by the higher AD SRTs attained when sludge is recycled through the system and less influenced by the inclusion of biosorption kinetics.
ContributorsYoung, Michelle Nichole (Author) / Rittmann, Bruce E. (Thesis advisor) / Fox, Peter (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2011
Description
Anaerobic Digestion (AD) typically stabilizes 40-60% of influent wastewater sludge. Improving the methane yield in wastewater may produce enough energy to power some wastewater treatment processes, while the production of volatile-fatty acids (VFAs) generates economic incentives for yard waste pre-fermentation. In this research, pre-fermenters consisting of inocula composed of media; cellulose, lantana, or grass; and rabbit cecotrope were fed various concentrations of plant matter. The contents of these pre-fermenters were the influent for respective anaerobic digesters. The microbial consortium derived for the lignocellulosic pretreatment with common yard waste in Arizona successfully increased methane production in AD, while producing additional VFAs during pretreatment in all systems. The performance of the system appeared to depend on plant matter loading and operating time, with a higher plant loading increasing the VFA production and a longer operating time increasing soluble chemical oxygen demand (COD) in pre-fermentation, and therefore the methane production in AD increased. The pre-fermenter with the highest plant matter loading and longest operating time –1.44 g plant matter per day at a 9.6% influent concentration and 193 days of total operating time– produced 10,000 mg COD/L of VFA, and its reactor produced about 460 mL methane (CH4) per day, which was almost twice the production of the control AD at 250 mL CH4 per day. This research uses yard waste that would previously be disposed of in landfill to increase valuable product production in AD. The potential value added to wastewater treatment plant (WWTP) processes by these methods could incentivize the expansion of wastewater treatment, thereby increasing sanitation access. The use of net-neutral biogas as a fuel source for WWTPs is additionally an incremental solution for reducing carbon equivalents present in the atmosphere, thereby reducing the greenhouse gas effect.
ContributorsPittman, Smith (Author) / Rittmann, Bruce (Thesis director) / Young, Michelle (Committee member) / Barrett, The Honors College (Contributor) / School of International Letters and Cultures (Contributor) / School of Sustainable Engineering & Built Envirnmt (Contributor)
Created2022-05
Description
Seeking to address sustainability issues associated with food waste (FW), and fat, oil, and grease (FOG) waste disposal, the City of Mesa commissioned the Biodesign Swette Center for Environmental Biotechnology (BSCEB) at Arizona State University (ASU) to study to the impact of implementing FW/FOG co-digestion at the wastewater treatment plant (WWTP). A key issue for the study was the “souring” of the anaerobic digesters (ADs), which means that the microorganism responsible for organic degradation were deactivated, causing failure of the AD. Several bench-scale reactors soured after the introduction of the FW/FOG feed streams. By comparing measurements from stable with measurements from the souring reactors, I identified two different circumstances responsible for souring events. One set of reactors soured rapidly after the introduction of FW/FOG due to the digester’s hydraulic retention times (HRT) becoming too short for stable operation. A second set of reactors soured after a long period of stability due to steady accumulation of fatty acids (FAs) that depleted bicarbonate alkalinity. FA accumulation was caused by the incomplete hydrolysis/fermentation of feedstock protein, leading to insufficient release of ammonium (NH4+). In contrast, carbohydrates were more rapidly hydrolyzed and fermented to FAs.
The most important contribution of my research is that I identified several leading indicators of souring. In all cases of souring, the accumulation of soluble chemical oxygen demand (SCOD) was an early and easily quantified indicator. A shift in effluent FA concentrations from shorter to longer species also portended souring. A reduction in the yield of methane (CH4) per mass of volatile suspended solids removed (VSSR) also identified souring conditions, but its variability prevented the methane yield from providing advanced warning to allow intervention. For the rapidly soured reactors, reduced bicarbonate alkalinity was the most useful warning sign, and an increasing ratio of SCOD to bicarbonate alkalinity was the clearest sign of souring. Because I buffered the slow-souring reactors with calcium carbonate (CaCO3), I could not rely on bicarbonate alkalinity as an indicator, which put a premium on SCOD as the early warning. I implemented two buffering regimes and demonstrated that early and consistent buffering could lead to reactor recovery.
The most important contribution of my research is that I identified several leading indicators of souring. In all cases of souring, the accumulation of soluble chemical oxygen demand (SCOD) was an early and easily quantified indicator. A shift in effluent FA concentrations from shorter to longer species also portended souring. A reduction in the yield of methane (CH4) per mass of volatile suspended solids removed (VSSR) also identified souring conditions, but its variability prevented the methane yield from providing advanced warning to allow intervention. For the rapidly soured reactors, reduced bicarbonate alkalinity was the most useful warning sign, and an increasing ratio of SCOD to bicarbonate alkalinity was the clearest sign of souring. Because I buffered the slow-souring reactors with calcium carbonate (CaCO3), I could not rely on bicarbonate alkalinity as an indicator, which put a premium on SCOD as the early warning. I implemented two buffering regimes and demonstrated that early and consistent buffering could lead to reactor recovery.
ContributorsKupferer III, Rick Anthony (Author) / Rittmann, Bruce E. (Thesis advisor) / Young, Michelle N (Committee member) / Torres, César I (Committee member) / Arizona State University (Publisher)
Created2020
Description
Eighty-two percent of the United States population reside in urban areas. The centralized treatment of the municipal wastewater produced by this population is a huge energy expenditure, up to three percent of the entire energy budget of the country. A portion of this energy is able to be recovered through the process of anaerobic sludge digestion. Typically, this technology converts the solids separated and generated during the wastewater treatment process into methane, a combustible gas that may be burned to generate electricity. Designing and optimizing anaerobic digestion systems requires the measurement of degradation rates for waste-specific kinetic parameters. In this work, I discuss the ways these kinetic parameters are typically measured. I recommend and demonstrate improvements to these commonly used measuring techniques. I provide experimental results of batch kinetic experiments exploring the effect of sludge pretreatment, a process designed to facilitate rapid breakdown of recalcitrant solids, on energy recovery rates. I explore the use of microbial electrochemical cells, an alternative energy recovery technology able to produce electricity directly from sludge digestion, as precise reporters of degradation kinetics. Finally, I examine a fundamental kinetic limitation of microbial electrochemical cells, acidification of the anode respiring biofilm, to improve their performance as kinetic sensors or energy recovery technologies.
ContributorsHart, Steven Gregg (Author) / Torres, César I (Thesis advisor) / Parameswaran, Prathap (Committee member) / Rittmann, Bruce E. (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2020
Description
As recent statistics from the U.S. Food & Drug Administration (FDA) show, “in the United States, food waste is estimated at between 30-40 percent of the food supply…at the retail and consumer levels, correspond[ing] to approximately 133 billion pounds and $161 billion worth of food in 2010” (“Food Loss and Waste | FDA”, 2020). Not only is excess food waste an economic problem for numerous companies, it’s unsustainable and inefficient when there could be the potential for learning and implementing innovative solutions, both on a large and small scale. The research from this creative project will focus on comparing The Walt Disney Company’s current food waste sustainability practices at Walt Disney World in Orlando, Florida, with Arizona State University’s (ASU’s) local Aramark Catering Services practices and initiatives throughout the Tempe campus’ dining halls. Specifically, the thesis will explore the benefits of anaerobic digesters and The Walt Disney Company’s use of anaerobic digesters at their Walt Disney World Parks and Resorts as a central means of converting food waste material into renewable natural gas. It will also explore Aramark’s current food waste management processes, specifically composting with the City of Phoenix’s industrial-grade composting yard, and the potential for implementing anaerobic digestion via a partnership with the City of Mesa into or in place of their current processes on ASU’s Tempe campus in the future.
ContributorsNagy, Billie Isabella (Author) / Burns, Kevin (Thesis director) / Cloutier, Scott (Committee member) / Dean, W.P. Carey School of Business (Contributor, Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12