Browsing by Subject "Anaerobic digestion"

Now showing 1 - 5 of 5
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    Anaerobic Co-Digestion of Municipal Wastewater Sludge and High Strength Waste: An Evaluation of Waste Degradation Potentials
    (2015-12) Prok, Amy
    Research has demonstrated the abundant treatment and economic opportunities presented by co-digestion of high strength wastewater, but these wastes also have the potential to cause digester failure. Indeed, based on what is known about the disruption of digesters, if a municipality is considering co-digestion, it needs to know the characteristics of high strength wastewaters that have a predictable potential for disruption. The Metropolitan Council-Environmental Services (MCES) is one such municipality interested in pursuing co-digestion. MCES is interested in expanding current digester use to include co-digestion of high strength waste streams to reduce their energy and sludge disposal costs. The objective of this research was to develop a protocol for MCES to be used in evaluating the feasibility of co-digesting municipal wastewater sludge with other high strength wastes. The protocol involves anaerobic biochemical methane potential (BMP) assays inoculated by source anaerobic digesters and amended with PBS, sludge (TPS/TWAS mixture), waste, or waste combined with sludge. Co-digestion experiments examined well-characterized synthetic wastes (starch, gelatin, tween 80, and cysteine) and wastes of interest to MCES with unknown impacts (dimethylformamide, dairy processing waste, propylene glycol, ethylene glycol, thickened primary sludge, thickened waste activated sludge, and scum collected from the primary clarifier at an MCES wastewater treatment facility). These wastes were characterized as degradable, non-degradable, toxic or degradable after an adaptation period. Gelatin, tween 80, dairy processing waste, ethylene glycol, and propylene glycol were degradable, while dimethylformamide was non-degradable. Cysteine, a sulfur-rich waste, was found to be toxic at concentrations greater than 200 mg/L. Scum, ethylene glycol, and propylene glycol required an adaptation period before being degraded. Additionally, the microbial analysis via qPCR indicated that the abundance of Bacteria and methanogens in the co-digestion experiments were not statistically different from the sludge-only experiments, even when different types of wastes were tested (i.e., degradable, non-degradable, toxic, etc.). The developed method and subsequent guidelines will be useful for MCES and other wastewater treatment facilities when making informed decisions about whether or not to accept potential high strength wastes for co-digestion with sludge.
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    The biodegradation and microbiological impacts of micropollutants in methanogenic communities
    (2012-12) McNamara, Patrick Joseph
    Pervasive usage of chemicals generates micropollutants throughout the environment. Anaerobic environments in particular accumulate high levels of hydrophobic micropollutants, and it is estimated that over 200 metric tons of micropollutants are discharged with biosolids each year. It is important to understand how treatment processes impact the fate of micropollutants as well as understand how micropollutants impact microbiological communities so that environmental risks can be minimized. This research elucidated the impact of an emerging treatment process, thermal-hydrolysis coupled to mesophilic anaerobic digestion (TH-MAD), on the fate of nonylphenol ethoxylates as well as the impacts of triclosan and perfluorooctane sulfonate (PFOS) on methanogenic community structure and function. The TH-MAD process inhibited biodegradation of nonylphenol ethoxylates to nonylphenol relative to MAD with no pretreatment. Indeed, the ratio of nonylphenol to the sum of nonylphenol ethoxylates + nonylphenol only increased by 24.6±3.1% in TH-MAD reactors compared to a 56% increase following MAD treatment. While post-aerobic treatment did reduce the sum of nonylphenol ethoxylates + nonylphenol, and concomitantly reduced estrogenicity, this research implied that source control is likely the most efficient option for removing these micropollutants. Triclosan is another wide-spread micropollutant that is persistent under anaerobic conditions. Triclosan is an antimicrobial agent that could therefore impact environmental systems that rely on healthy functioning of microorganisms. Methanogenic communities with no previous exposure to triclosan were able to adapt to triclosan at environmentally relevant levels and maintain function. When previously-exposed communities were exposed to triclosan at 4x current detected environmental levels, community structure shifted and methane production was inhibited. These levels of triclosan also selected for mexB, a gene that confers multidrug resistance, in previously unexposed communities. Lastly, PFOS was found to directly impact methanogenic communities and augment the impacts of triclosan in long-term exposure studies (140 days), but not in short-term (14 day) exposure studies.
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    The fate of antibiotic resistance genes during treatment and disposal of residual municipal wastewater solids
    (2013-12) Burch, Tucker Ramsey
    The development of resistance to antibiotics among pathogens is a global public health dilemma with significant consequences for the length and quality of human life. As a result, the bacterial antibiotic resistance genes (ARGs) that confer resistance are increasingly regarded as environmental contaminants. A significant body of knowledge has been generated that catalogues the occurrence of ARGs in numerous environmental reservoirs, among which residual municipal wastewater solids are one of the largest. Only a handful of studies, however, make the critical paradigm shift to considering treatment technologies and management strategies intended to reduce the quantities of ARGs in those reservoirs. The objective of the work presented here was to evaluate various treatment technologies and management strategies for reducing the quantity of ARGs discharged from the municipal wastewater treatment process during treatment and disposal of residual solids. Aerobic digestion, air drying, and hyperthermophilic (¡Ý 60¡ãC) anaerobic digestion were evaluated for their abilities to reduce ARG quantities in residual municipal wastewater solids using laboratory-scale treatment units. The technologies were compared among each other and to mesophilic (40¡ãC) and thermophilic (56¡ãC) anaerobic digestion on the basis of the kinetics of ARG removal from residual solids. While all technologies were effective, hyperthermophilic anaerobic digestion tended to exhibit the fastest kinetics. In addition, class 1 integrons were identified as a candidate design gene, and batch or semi-batch flow configurations were demonstrated to be a potential means of optimizing the removal of ARGs from residual solids during aerobic digestion, thermophilic anaerobic digestion, and hyperthermophilic anaerobic digestion. The fate of ARGs in soil following simulated disposal was also investigated by applying treated residual solids from full-scale treatment facilities and from numerous laboratory-scale treatment units to soil microcosms. ARGs from residual solids treated at typical full-scale treatment facilities persisted in soil at high concentrations for relatively long periods of time, with half-lives on the order of months. Alkali stabilization, thermophilic anaerobic digestion, hyperthermophilic anaerobic digestion, and pasteurization, however, caused drastic decreases in ARG quantities in soil within one month. The results presented here can be used to optimize and design the residual municipal wastewater solids treatment and disposal process to remove ARGs.
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    Industrial symbiosis: corn ethanol fermentation, hydrothermal carbonization, and anaerobic digestion
    (2012-12) Wood, Brandon M.
    The production of dry-grind corn ethanol results in the generation of intermediate products, thin and whole stillage, which require energy-intensive downstream processing for conversion into commercial co-products. Alternative treatment methods, specifically hydrothermal carbonization of thin and whole stillage coupled with anaerobic digestion were investigated to determine if they provide an opportunity to recover some of this value. By substantially eliminating evaporation of water, reductions in downstream energy consumption from 65-73% were achieved, while hydrochar, fatty acids, treated process water, and biogas co-products were generated, providing new opportunities for the industry. Processing whole stillage in this manner produced the four co-products, eliminated centrifugation and evaporation, and substantially reduced drying. With thin stillage, all co-products were again produced, as well as a high quality animal feed. Anaerobic digestion of the undiluted aqueous product stream from thin stillage hydrothermal carbonization reduced chemical oxygen demand (COD) in this product stream by more than 90% and converted 83% the initial COD to methane. Internal use of this biogas could entirely fuel the HTC process and reduce natural gas overall usage.
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    Polyethylene glycol as a robust, biocompatible encapsulant for two-stage treatment of food and beverage wastewater
    (2023-05) Gutenberger, Gretchen
    This research investigates encapsulation of microorganisms for two-stage anaerobic treatment of industrial food and beverage wastewater. Encapsulants were tested in batch reactors to determine the potential for biological inhibition during encapsulation. Flow through reactors were to test the leakage of microorganisms from the encapsulants over time. Five different reactor designs were explored to assess the effects of reactor conditions on encapsulant longevity and activity. It was found that polyethylene glycol (PEG) beads encapsulating biomass grown in suspension did not change in shape, activity, or protein concentration over one month in flow-through reactors. In reactors mixed by stir bars, PEG beads encapsulating suspended biomass lasted 6-10 months. PEG beads encapsulating PAC-supported biofilms improved methane production approximately 27 times compared to PEG beads encapsulating suspended biomass. This study provides information on encapsulant performance that will be used to select encapsulants for a future pilot demonstration of the pretreatment system at a brewery.