Theses and Dissertations from UMD
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Item DESIGN MODIFICATIONS TO MINIMIZE POLLUTANT LEACHING FROM COMPOST-AMENDED BIORETENTION(2024) Lei, Lei; Davis, Allen P.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention is an effective stormwater control measure (SCM) recognized for its ability to capture and treat urban runoff within a shallow basin using engineered soils and vegetation. Bioretention studies at laboratory and field scales have shown good to excellent removal efficiency for heavy metals (> 80% to > 90%) and have observed high variablility ranging from negative (net export) to 99% in phosphorus and nitrogen removals. Water quality studies have shown that media selection for bioretention is critical in determining pollutant removal.Incorporating compost into bioretention media is an eco-friendly strategy that not only diverts organic waste from landfills but also provides several benefits improving the performance of bioretention system. This approach enriches the media with organic matter and nutrients for vegetation, boosts water holding and cation exchange capacity, stabilizes the soil structure, and improves the retention of pollutants. However, careful management is essential to mitigate the potential releasing pollutants, including dissolved organic matter (DOM), soluble nutrients, and metals readily associated with DOM, particularly if the compost is derived from biosolids... To maximize the benefits of compost in bioretention, special design modifications aimed at enhancing pollutant removal should be implemented. The objective of this research was to investigate ways to optimize the use of compost in bioretention while minimizing pollutant leaching, Design modifications investigated include layering compost over media, aluminum-based drinking water treatment residual (Al-WTR) addition, and incorporation of an internal water storage (IWS) layer. Treatment performances were evaluated through extractions, batch adsorption studies, large column mesocosms, and column media characterizations. Al-WTR amendment improved sorption of phosphorus, copper and zinc, with capacities increasing from 22.5 mg/kg to 161 mg/kg and 193 mg/kg for P, from 121 mg/kg to 166 mg/kg and then to 186 mg/kg for Cu, and from 121 mg/kg to 166 mg/kg and 186 mg/kg for Zn with 0%, 2% and 4% Al-WTR additions. The multilayered system containing a compost incorporated top layer and an Al-WTR amended bottom layer showed good removal of phosphorus (94% and 96%), copper (88% and 86%) and zinc (92% and 96%), and enhanced nitrogen retention (74.1%) from the stormwater load compared to a mixed system (32.8%) as reported by Owen et al. (2023). The installation of an IWS layer did not show statistically significant influences on phosphorus (91% to 93%, p > 0.05), copper (66% to 90%, p > 0.05) or zinc (94% to 95%, p > 0.05) removals, had limited effect on nitrogen retention from stormwater load during storm events (-117% to -188%, p > 0.05), but promoted denitrification during dry periods. With the IWS layer installed, high levels of iron leaching (130 to 11800 µg/L) were detected, likely due to change in the redox potential (from aerobic to anaerobic). With the objective of removing phosphorus and heavy metals from the stormwater, 5.3% of compost (by dry mass) can be used when layering compost over the Al-WTR amended bioretention media. When the design goal is to remove nitrogen, a fraction of compost up to 2.6%, by dry mass can be used, with layering the compost over the bioretention media and an IWS installed at the bottom.Item EVALUATING THE BENEFITS, SUSTAINABILITY, AND RESILIENCE OF GREEN INFRASTRUCTURE ON A SUSTAINABLE RESIDENTIAL HOME(2018) Thompson, Rhea Ava; Tilley, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With global populations becoming increasingly urbanized, green infrastructure (GI) is progressively being recognized as a sustainable approach to mitigating urban environmental problems. Unlike traditional ‘hard’ engineering approaches that historically viewed problems in isolation and solutions in singular terms, implementation of GI promises some deferment from the effects of urbanization by providing a multitude of benefits such as reduced stormwater runoff and flooding, decreased heat waves, and enlivened local environments and ecological habitats. These benefits are important considering many cities are projected to be more vulnerable to the effects of urbanization with climate change, especially as the vast amount of the global population lives in coastal urban environments. However, the diversity of GI benefits has not been fully characterized, and they are increasingly applied in residential settings. Furthermore, current research has not fully explored the beneficial role of GI in achieving sustainable and resilient communities. Using an Integrated Water: Energy Monitoring System measuring meteorological, water, and energy fluxes over two years (July 2014-June 2016) on a sustainable home in Rockville, Maryland, U.S., the following objectives were explored: (1) Examined how a sloped modular extensive green roof, constructed wetland and bioretention designed in-series affected site hydrology. Furthermore, we studied the effect of season, antecedent substrate water content, storm characteristics (size, intensity, frequency), and vegetation development (green roof only) on hydrological performance. (2) Characterized the seasonal thermal performance of the green roof (to the building and surrounding environment) relative to the cool roof. Evaluated how green roof thermal performance related to evapotranspiration, solar reflectance (albedo) and thermal conductance (U-value). Additionally, the effect of substrate water content, vegetation development, and microclimate on evapotranspiration, albedo and U-values was assessed. (3) Green roof evapotranspiration was measured and compared to values predicted with the FAO-56 Penman-Monteith model. Furthermore, the effects of substrate water content, vegetation characteristics and microclimate on evapotranspiration rates was also evaluated. (4) Finally, using emergy theory, GI sustainability and resilience relative to a gray wastewater system and natural forest was explored.Item Understanding Urban Stormwater Denitrification in Bioretention Internal Water Storage Zones(2016) Igielski, Sara Jasmine; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Free-draining bioretention systems commonly demonstrate poor nitrate removal. In this study, column tests verified the necessity of a permanently saturated zone to target nitrate removal via denitrification. Experiments determined a first-order denitrification rate constant of 0.0011 min-1 specific to Willow Oak woodchip media. A 2.6-day retention time reduced 3.0 mgN/L to below 0.05 mg-N/L. During simulated storm events, hydraulic retention time may be used as a predictive measurement of nitrate fate and removal. A minimum 4.0 hour retention time was necessary for in-storm denitrification defined by a minimum 20% nitrate removal. Additional environmental parameters, e.g., pH, temperature, oxidation-reduction potential, and dissolved oxygen, affect denitrification rate and response, but macroscale measurements may not be an accurate depiction of denitrifying biofilm conditions. A simple model was developed to predict annual bioretention nitrate performance. Novel bioretention design should incorporate bowl storage and large subsurface denitrifying zones to maximize treatment volume and contact time.Item USE OF DRINKING WATER TREATMENT RESIDUALS AS A SOIL AMENDMENT FOR STORMWATER NUTRIENT TREATMENT(2010) O'Neill, Sean William; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stormwater runoff has been implicated as a major source of excess nutrients to surface waters, contributing to the development of eutrophic conditions. Bioretention, a promising technology for urban stormwater pollution treatment, was investigated to determine if an aluminum-based water treatment residual (WTR) amended bioretention soil media (BSM) could adsorb phosphorus to produce discharge concentrations below 25 μg/L. Batch, small column, and vegetated column studies were employed to determine both the optimal BSM mixture and media performance. Media tests demonstrated P adsorption proportional to WTR addition. Final selected experimental media consisted of 75% sand, 10% silt, 5.8% clay, 5.2% WTR, and 3.4% bark mulch (air dry mass basis).This media showed excellent P removal relative to a non-WTR-amended media. Whereas the control media leached P (71.1% increase in mass), the experimental media adsorbed 85.7% of the P mass applied, displaying a cumulative effluent EMC of 16.1 μg/L, below the 25 μg/L goal.Item Pedogenesis in Rain Gardens: The Role of Earthworms and Other Organisms in Long-Term Soil Development(2009) Ayers, Emily Mitchell; Kangas, Patrick; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As bioretention comes into widespread use, it has become increasingly important to understand the development of bioretention soils over time. The objective of this research is to investigate the development of bioretention soils and the importance of ecological processes in the performance of rain gardens. The research includes descriptive studies of pre-existing rain garden soil profiles, laboratory experiments quantifying the effect of earthworms on infiltration rates, and a simulation model describing the influence of earthworms and soil organic matter on infiltration. Surveys of several different rain gardens of various ages provide the first detailed descriptions of rain garden soil profiles. The study revealed a great deal of biological activity in rain gardens, and evidence of pedogenesis even in very young sites. The uppermost soil layers were found to be enriched with organic matter, plant roots, and soil organisms. The field sites surveyed showed no signs of clogging due to the trapping of suspended solids carried in stormwater runoff. Some evidence was found of higher than expected infiltration rates at the field sites, which may be attributable to the effects of bioturbation by living organisms. The ability of earthworms to mitigate the effects of trapped suspended solids on bioretention soils was assessed in the laboratory. Results show that earthworms are capable of maintaining the infiltration rate of bioretention soils, but that their effects have a high degree of variability. This variability is attributed to soil aggregate instability caused by the oversimplification of the ecosystem. Other organisms play a significant role in stabilizing earthworm burrows and casts, and may be essential ingredients in a self-maintaining bioretention ecosystem. A simulation model of the action of earthworms on soil infiltration rates was developed in order to illustrate the physical processes taking place as a result of earthworm activity. The model was calibrated using data from the field study and microcosm experiment. This research is intended to provide a first glimpse into the biological processes at work in rain garden soils. The research shows that soil organisms are present in rain gardens, and suggests that their impact on bioretention performance may be significant.Item Transport and Catpture of Bacteria from Urban Stormwater Runoff Using Bioretention(2008-11-14) Zhang, Lan; Davis, Allen P; Seagren, Eric A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention, a nature-based treatment practice, has significant potential for reducing the threat of microbial pollutants from urban stormwater runoff to receiving water bodies. The overall goal of this research was to evaluate the removal efficiency for bacteria from urban stormwater runoff in bioretention systems and the potential of an engineered media (iron oxide-coated sand (IOCS)) for enhancing bacterial removal. This investigation was accomplished through laboratory column studies coupled with field tests. Column studies on the transport and destruction of Escherichia coli O157:H7 strain B6914 (a surrogate of pathogenic E. coli) in conventional bioretention media (CBM) and IOCS demonstrated that the bacteria were well removed in CBM (a mean 70% efficiency), but IOCS significantly enhanced the capture of strain B6914 (a mean 99.4% efficiency) due to the greater positive charge and surface roughness. However, the decay of trapped strain B6914 cells was much faster in CBM compared to the IOCS. More than 99.98% of B6914 cells attached to CBM died off within one week, while approximately 48% of trapped cells still survived in the IOCS after one week. Predation by indigenous protozoa in the CBM appears to play a dominant role in the faster decline of the number of trapped B6914 cells in CBM. Additionally, long-term (18 months) column experiments indicated that during the periodic application of simulated rainfall, the removal efficiency for strain B6914 improved over time, achieving 97% or higher efficiency after six months. Consistent with the laboratory studies, two years of field studies showed that bioretention systems reduced the concentration of indicator bacteria in the outflow during most storm events and increased the probability of meeting specific water quality criteria. The concentration of indicator bacteria in the input flow generally increased with higher daily temperature. No clear trend for the bacterial removal efficiency with respect to temperature was found in laboratory and field studies. However, the bacterial decay coefficients in CBM increased exponentially with elevated temperature. Based on these results, it is concluded that CBM not only achieves good removal for bacteria, but also has the potential to render the process sustainable.