A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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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.
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    EFFECTS OF FULL-SCALE THERMAL HYDROLYSIS-ANAEROBIC DIGESTION ON THE TEMPORAL TRENDS OF POLYBROMINATED DIPHENYL ETHERS IN BIOSOLIDS AND THEIR PHYSICAL AND BIOLOGICAL DEGRADATION DURING WASTEWATER TREATMENT
    (2020) Motley, Taylor Ann; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Biosolids produced at wastewater treatment plants (WWTPs) are rich in recovered nutrients and are often recycled through soil amendment on agricultural land. Advanced solids treatment strategies, including thermal hydrolysis pretreatment (THP) and anaerobic digestion (AnD), are utilized to produce cleaner, safer biosolids based on EPA classifications. Despite the phase-out of the flame retardant polybrominated diphenyl ethers (PBDEs) from commercial use in the U.S., they are still present in biosolids and can be degraded to toxic byproducts during solids treatment. Their transformation during solids treatment is not well understood. This work shows that while phase-outs of PBDEs did not affect their concentrations in biosolids from the target WWTP, the implementation of THP-AnD treatment in 2014 led to increased PBDE degradation during solids treatment. This significantly lowered PBDE concentrations and shifted congener distribution to favor smaller, more toxic congeners in final biosolids compared to lime-stabilized biosolids historically produced at the target WWTP. Comparisons between the target WWTP and other AnD facilities without THP revealed that more efficient PBDE degradation occurred during THP-AnD treatment despite lower abundances of debrominating bacteria in digesters. Future work will examine if PBDE degradation during THP-AnD treatment is due to physical or biological processes.
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    FULL SCALE STUDY OF PATHOGEN, METAL POLLUTANTS, NUTRIENTS, AND POLYBROMINATED DIPHENYL ETHERS IN CLASS A BIOSOLIDS STABILIZED BY THERMAL HYDROLYSIS AND ANAEROBIC DIGESTION PROCESSES
    (2017) Wang, Xuanzhao; Torrents, Alba; Andrade, Natasha Almeida; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Class A biosolids are solid by-product of wastewater treatment which meet Environmental Protection Agency requirements to be used as fertilizer in farms, vegetable gardens, and can be sold directly to consumers. In 2014, this study’s target nutrient recovery facility adopted thermal hydrolysis pretreatment and anaerobic digestion to upgrade biosolids quality from Class B (previously lime-stabilized) to Class A. In order to certify if this newly produced material met all regulatory requirements, we performed laboratory analysis to characterize fecal coliforms, volatile solids, and metals content. In addition, we showed a baseline for nutrient management of total nitrogen, phosphorus, and the change in levels of polybrominated diphenyl ethers (PBDEs). Samples were collected for over a year since the start of THP-AD operation. Results were compared with the Class B biosolids produced at the same facility. Based on EPA standards, Class A biosolids were produced with stable quality after March, 2015, 16 weeks after process initiation. This work suggests that THP-AD is effective in producing Class A biosolids. In general, PBDEs in biosolids decreased from 1790 ± 528 (Class B) to 720 ± 110 µg/kg d.w. Our results suggest that the total levels of PBDEs decrease, however, the impact of the THP-AD on specific congeners are complex.