UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    EFFECTIVENESS ASSESSMENT OF FNA IN IMPROVING SOLUBILIZATION AND CONTROLLING PROBLEMATIC MICROORGANISMS IN PRE-TREATMENT OF FOOD WASTE
    (2022) Proano, Camila A; Li, Guangbin; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Anaerobic digestion (AD) is a sustainable waste-to-energy method for converting organic waste to methane. Various pre-treatment of food waste (FW) with free nitrous acid (FNA; pKa=3.25) were used to stabilize FW and mitigate obstacles (odor in FW storage and pathogenic bacteria) in AD. FNA concentrations ranging from 0-5 mg-N/L were tested in this study at pH ranging from 3-5.5, and volatile solids (VS) content of 16.8-135 g/L. Solubilization of organic material, inhibition of N-related biological processes, and control of problematic microorganisms, including sulfate-reducing bacteria (SRB) and pathogenic bacteria, were compared with the groups without FNA addition. At the tested pH (3, 4, and 5) and concentrations of FNA (0.3-5.0 mg-N/L), FNA addition showed inhibition to N-related biological processes contributing to a consistent FNA concentration over the 72 hours pre-treatment. However, it did not enhance the solubilization of organic materials compared with control group without FNA addition. The FNA concentration affected the bacterial inhibition of SRB. As the concentration of FNA increased from 0.3-5.0 mg-N/L, so did SRB inhibition. Similarly, increasing FNA concentration resulted in a faster reduction (2.5 logs within 4 hours) in pathogenic bacteria compared with the group without FNA addition. Overall, a shorter pre-treatment time (<24 hours) is recommended for using low FNA concentration (1.5 mg N/L) and high solids content (> 80.57 g /L), as the effective FNA concentration cannot be maintained for longer due to NO2- and bioavailable organic carbon consumption by N-related or other microorganisms that remain active or recoverable under the added FNA concentration.
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    IMPACTS OF FREE NITROUS ACID (FNA) ON STABLIZING FOOD WASTE (FW) AND SEWAGE SLUDGE (SS) FOR ANAEROBIC CO-DIGESTION
    (2021) Liu, Ruizhe; Li, Guangbin GL; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Anaerobic digestion (AD) is a sustainable waste-to-energy method for converting organic wastes to methane. In this work, a pretreatment of food waste (FW) with free nitrous acid (FNA) was proposed, and various pretreatment times (4 hrs, 72 hrs, and 28 days) and FNA concentrations (1.07, 2.13, and 5 mg FNA-N/L) were tested to evaluate its effectiveness in stabilizing FW and sewage sludge (SS). Soluble chemical oxygen demand (sCOD), soluble protein (sP), and soluble polysaccharide (sPS) in the groups with 50%:50% (w/w VS) pretreated at 5 mg FNA-N/L for 72 hrs were significantly increased by 631, 530, and 780 %, respectively, compared with the control group without FNA addition. Additionally, less sulfide was detected in the groups with FNA addition, indicating an effective reduction in sulfide-odor during the storage/pretreatment of FW and SS. The potential of biogas production of FNA-pretreated FW was assessed using biochemical methane potential (BMP) test, and the results showed that the groups with FNA pretreatment produced up to 91.97% more methane than the group without FNA. The results from this work indicated an improved digestibility of FW and/or SS for AD using FNA pretreatment, and suggested the optimal pretreatment condition at 2 mg FNA-N/L for 24 hrs for FW and FW/SS.