Civil & Environmental Engineering
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Item ASSESSING BEST PRACTICES FOR REFORESTATION OF AREAS DEGRADED BY ARTISANAL AND SMALL-SCALE GOLD MINING IN THE PERUVIAN AMAZONIAN REGION OF MADRE DE DIOS(2024) Rodriguez Pascual, Maria Jose; Torrents, Alba; Andrade, Natasha; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Artisanal and Small-Scale Gold Mining (ASGM) have pressured the Peruvian Southern Amazon rainforest, causing deforestation, soil degradation, and mercury (Hg) emissions in large areas. The Peruvian government and NGOs have performed reforestation projects in areas degraded by ASGM in this region using native plant species with an economic value. Previous research has studied the restoration of areas degraded by ASGM in this region. However, there is lack of information about the Hg's distribution, accumulation, and the effects of Hg exposure in native plants in this region. Additionally, few studies have investigated the recovery of soil fertility in these degraded areas during restoration.In this dissertation, the distribution and predictors of Hg accumulation in soil and native plant species from artisanal mining sites and the primary forest near these sites were studied. The highest Hg concentrations in soil were found in the intact primary forest topsoil and the plant rhizosphere area. The highest Hg levels in plants were found in the foliage of the intact primary forests. The Hg levels found in the plant leaves of the primary forest are the highest ever recorded in this region, exceeding values found in forests impacted by Hg pollution worldwide and raising concerns about the extent of the ASGM impact in this ecosystem. The effects of Hg exposure on the survival, growth, health, and rhizosphere microbial communities of three Amazonian agricultural plant species, aji dulce (Capsicum Chinense), sacha culantro (Eryngium foetidum), and uncucha (Xanthosoma sagittifolium L. Schott) were also investigated. The lowest observable concentration of Hg affecting the plant’s health was 2 mg kg-1 dw. This Hg concentration was three times lower than the soil screening level (SSL) for Hg in agricultural soil established in the Peruvian regulation. This suggests that a review of this SSL may be necessary before developing restoration projects in Amazonian areas impacted by ASGM. The soil physic-chemical characteristics, such as soil organic matter (SOM), electrical conductivity (EC), pH, nutrients, and bacterial communities, in the rhizosphere soil of plant species growing in naturally regenerated and reforested areas impacted by ASGM and in the primary forest near these areas were assessed. The results suggest that the plant species Acacia loretensis and Inga sp. (Inga sp. when planted with biochar as a soil amendment) might be good candidates for restoring areas degraded by ASGM, due to the level of nutrients and SOM in their rhizosphere. Finally, the integration of Indigenous and scientific knowledge to monitor and manage land degradation in regions impacted by ASGM was also studied. The findings emphasize the need to use the Indigenous communities’ knowledge of their territory for the early detection of soil degradation and facilitate a dialogue about land degradation and restoration of areas affected by ASGM between local communities, researchers, and policymakers to develop more sustainable and successful restoration projects in Indigenous communities affected by ASGM.Item Evaluation of Roadside Soil Compaction and Restoration Practices on Vegetation Growth and Water Quality(2024) Cunningham, Mikayla; Davis, Allen P.; Aydilek, Ahmet H.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The construction of roads using heavy equipment and cut-and-fill methods leads to heavily compacted roadside soils with low fertility, sparse vegetation, low water infiltration rates, and high erodibility. Poor post-construction vegetation and soil quality lead to higher runoff volumes with higher sediment and nutrient loads to local water bodies. Cost-effective methods are needed to restore roadside soils, establish sufficient vegetative cover, and maintain runoff water quality. A research project was undertaken to assess topsoil application, tillage, and yard waste compost amendment as means of restoring roadside soil quality. A 28-week pot study was used to test how topsoil depth, initial soil density, compaction from mowing equipment, and compost amendment influenced long-term soil density, hydraulic conductivity, and vegetation establishment. A 12-week mesocosm study with weekly simulated storm events was conducted to further examine the effects of soil type and soil bulk density on vegetation on a larger scale. Water quality testing of the simulated rainfall and runoff samples was also implemented to measure soil erosion and nutrient leaching. Compost-amended subsoil improved vegetation (biomass and grass heights) compared to subsoil, but it did not perform as well as topsoil. The yard waste compost was selected and applied at a rate designed to limit nitrogen and phosphorous losses, and it was successful, given that the compost-amended mesocosms did not export higher nutrient loads than mesocosms with inorganic fertilizer. Hydraulic conductivity was observed to primarily depend on soil density. A series of recommendations for highway projects to effectively restore roadside soil quality to improve vegetation and stormwater management are provided. A low-density layer of topsoil at least 20 cm deep is ideal. Yard waste compost should not be applied at a rate that raises soil organic matter by more than 2%.Item Innovative Reuse of Baltimore Harbor Dredged Material as Vegetative Earthen Berms(2024) Smith, Adam; Davis, Allen P; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dredged material (DM) is a sediment excavated from navigable waterways, which haslimited use due to the transport and accumulation of potentially hazardous metals and organic chemicals into these waterways. DM can be used as a recycled material in place of soil, depending on its environmental and physical characteristics, and the specific use. Vegetated Earthen Berms (VEBs), used for stormwater control, is one potential beneficial application of DM. The objective of this research is to assess the environmental and geotechnical suitability of DM in VEBs. A germination study and a battery of column tests were conducted to test the innate properties of the DM and DM amended with straw and sand, as DM blends. Straw and sand were chosen to observe potential improvements to the DM’s physical and chemical parameters. A nine-week mesocosm study was performed to simulate the overall performance of DM and DM blend constructed VEBs for the plant growth and water quality criteria, determined by US EPA water quality limits. Plant cover and growth measurements along with measuring effluent water characteristics were assessed. Straw amended DM was shown to have comparable vegetative establishment parameters relative to topsoil. For the water quality, concentrations of dissolved copper and zinc were reduced relative to typical median stormwater values in DM constructed VEBs. Based on the results of these tests, DM constructed VEBs had reflected desirable qualities for potential reuse based on water quality and vegetative establishment.Item CHEMICALS OF EMERGING CONCERNS IN WASTEWATER TREATMENT: ACUTE AND CHRONIC IMPACTS OF AZOLES ON BIOLOGICAL NITROGEN REMOVAL PROCESSES(2024) Chen, Xiaojue; Li, Guangbin GL; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nitrogen (N) in wastewater presents in the forms of ammonia, nitrite, nitrate, and/or organic N. Discharging of ineffectively treated N-containing wastewater into water bodies could cause eutrophication, threaten the safety of the ecosystem, and impair the water quality for humans. Various Biological Nitrogen Removal (BNR) processes, including nitrification, denitrification, and anaerobic ammonium oxidation (Anammox), have been successfully applied in wastewater treatment plants (WWTP) for N removal. However, the performance and stability of BNR can be adversely impacted by chemical inhibitors present in wastewater. Azoles, classified as emerging organic contaminants (EOCs), are a group of man-made chemicals containing N atoms in the heterocyclic ring systems and have been widely applied as aircraft de-icing agents, in semiconductor manufacturing, and household dishwashing detergents. Various azoles have been detected in wastewater streams and their presence within WWTPs may impact the BNR processes. Azole compounds, such as benzotriazole (BTA), have been used as biocides/fungicides in agriculture. However, limited information is available about the potential inhibition of azoles to BNR processes, while guidelines for preventing BNR processes from azole inhibition and methods for system recovery are also unavailable. In this study, we investigated the short- and long-term impacts of azoles on the major BNR processes, including nitrification, denitrification, and Anammox. Besides, potential inhibitory mechanisms of azoles and resistance/adaptation of BNRs were assessed, aiming to develop an effective strategy to prevent BNRs from system interruption and/or efficiency decreasing caused by azoles present in WWTPs. In short-term impact assessment, both experiment-based lab research and literature review approaches were used to assess the inhibition potential of different azole compounds on major BNR processes. Nine azole compounds (5 diazoles and 4 triazoles) were selected to represent azoles with different structures and physiochemical properties. The concentration (IC50) of azoles needed to inhibit BNR processes by 50% is calculated. Different BNR processes showed various responses to azoles after short-term exposure (<24h). Pyrazole (PA), triazole (TA), BTA, and methyl-benzotriazole (MBTA) at 6 mg /L caused >90% inhibition of nitrification activity, while higher inhibition resistance to these compounds was observed in the denitrification process with the calculated IC50 (mg /L) of 126, 520, 412, and 152, respectively. In comparison, 50% inhibition of Anammox activity was observed at the concentration of BTA (20 mg /L) and MBTA (18 mg /L). The differences in azole inhibition were suspected to be related to BNR processes’ characteristics including the potential chelation of azoles with enzyme-bound copper (e.g., ammonia monooxygenase, AMO) in nitrifiers, high biodiversity of denitrification sludge, and unique cell structure (e.g., annammmoxosome) in Anammox bacteria. In addition, azoles with more functional groups and/or complicated structures (e.g., climbazole at 20 mg /L & fluconazole at 100 mg /L) exhibited less inhibition on the nitrification (PA and TA at 6 mg/L) and Anammox processes (BTA and MBTA at 20 mg/L). In WWTPs, wastewater contains a variety of different compounds and it is more difficult for azoles with complex structures to chelate with the key BNR enzymes (Kalyani Vikas Jog, 2021). More attention should be paid to azoles with smaller molecule sizes and simpler chemical structures such as PA, BTA, TA, and MBTA. Compared with short-term experiments (<24 hours), results from long-term exposure (3 to 9 months) of BNR processes to azole provide further insights into understanding the impacts of azole and the system’s response under a condition that is closer to practical. Azoles, such as BTA and MBTA, have been found to cause inhibition (>50%) of the Anammox process in short-term experiments at 20 and 18 mg/L levels, separately. However, the long-term influence of azoles, whether inhibitory or not in short-term experiments, on the Anammox process is not well studied. Therefore, in the second part of this work, we aimed to investigate the long-term impact of BTA and PA on the Anammox process and the potential mechanisms by which Anammox bacteria adapt to resist azole inhibition. Through long-term acclimation, the Anammox granular sludge could gain higher resistance to BTA below 30 mg/L. However, further exposure to higher BTA concentrations (40 mg/L) led to a gradual decrease in NAA from 70% to 40%. No inhibition ≥ 10% was observed during short-term exposure at 300 mg/L PA, but long-term exposure to 200 mg/L resulted in more inhibition than short-term exposure. While long-term exposure to 100 mg/L PA did not cause any decrease in Anammox activity, 200 mg/L PA led to 65% reversible inhibition in 40 days. To further investigate the potential mechanisms by which Anammox granular sludge adapts to resist azole inhibition, starvation experiments, ATP content analysis, and microbial composition analysis were conducted. BTA and MBTA were selected as representatives of azoles in the starvation experiment due to their reported inhibitory effects on Anammox granular sludge. Over a 28-day starvation experiment, Anammox activity decreased, and the lag phase increased with starvation time at substrate conditions of 75 mg/L NH4+ -N and 100 mg/L NO2- -N. However, the presence of BTA and MBTA in the starved Anammox sludge did not result in a further reduction of Anammox activity and change in Anammox sludge’s ATP content levels, suggesting that the short-term energy-required mitigation method may not be the major defense mechanism for Anammox bacteria resisting BTA and MBTA inhibition. Overall, the results indicate that a stepwise acclimation strategy could enhance Anammox resistance to azole inhibition. As an important pre-step to conventional (nitrification/denitrification) and advanced (Anammox) BNR, the long-term impacts of azoles on the nitrification process were studied using lab-scale sequencing batch reactors (SBR). BTA and PA were selected as two representatives of the azoles due to their wide usage, detection in wastewater, and their structure as benzene-containing triazoles and diazole. Adapted nitrification sludge had better performance in treating wastewater containing azoles. Before acclimation, the addition of 2.5 mg/L BTA and PA decreased 45% and >90% nitrification activity, respectively. After the acclimation with the stepwise increase strategy, no ammonium and nitrite accumulation was observed in the effluent when 2.5 mg/L BTA and 2.7 mg/L PA were added into the system. The normalized nitrification activity (NNA) of the BTA and PA groups were 72.5 ± 2.5% and 70.2 ± 2.5%, respectively, which were also higher than the non-adapted nitrification sludge in short-term tests. The nitrification sludge developed BTA degradation ability and high degradation rates were achieved during the acclimation process. The removal of N loading didn’t impact the BTA degradation process. The addition of an extra 50 mg/L COD increased the BTA removal rate while the extra 200 mg/L COD decreased the BTA removal rate. According to the results, the heterotrophic bacteria that existed in the nitrification sludge may contribute to the BTA degradation. Reported aromatic compounds/organic compound degraders such as Dechloromonas and Zoogloea were identified in the microbial community. Azoles showed a variable inhibition to denitrifying microorganisms in activated sludge batch tests. In the last part of this work, the long-term inhibition potentials of BTA and PA to the denitrification process were investigated. A stable denitrification process was observed with BTA and PA addition at 2.5 and 2.7 mg/L, respectively, suggesting the low risk of azole inhibiting the denitrification process in WWTPs. No BTA and PA degradation was observed within the 12-hour operation cycle. However, after increasing the reaction time to 7 days, more than 85% BTA and 45% PA degradation are observed during the process. Furthermore, all the denitrification reactors (Control, BTA, and PA) were found to be able to degrade the BTA and PA at similar degradation rates. The removal of N and organic content (acetate as COD source) loading didn’t impact the BTA and PA degradation process. Multiple potential aromatic compound/organic compound degraders were found in the denitrification reactor such as Thauera, Azoarcus, Georgfuchsia, and Dechloromonas. Further investigation is needed to examine the contribution of individual species to azole degradation and their synergistic relationship. The results of this work indicate that the presence of azoles in wastewater has the potential to adversely impact the BNRs in WWTPs, in particular those to which azoles are new. However, proper implementation of the acclimation strategy can enhance the resistance of BNR bacteria to azole inhibition, preventing the system from interruption, even failure, caused by azoles. The synergistic effect of the microbial community may contribute to the attenuation of the azole inhibition to the system. The results provide new insights into understanding how the BNRs respond to chemicals of emerging concerns and are expected to assist WWTP operators in developing effective strategies to recover the system from azole inhibition. This work could provide suggestions for WWTPs to maintain activity and efficiency when treating azole-containing wastewater, identify azole types with high potential risks, and understand which part of the wastewater treatment systems may be impacted.Item ASSESSING THE IMPACTS OF ORGANIC AMENDMENTS ON DISTURBED SOIL PROPERTIES, WATER QUALITY AND VEGETATION GROWTH(2024) Pamuru, Sai Thejaswini; Davis, Allen P; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Deficiencies in essential organic matter (OM) are exhibited in disturbed roadside soils rendering them less favorable for plant growth. Vegetation plays a crucial role in maintaining the health of ecosystems, providing a myriad of benefits in protecting against soil erosion and effectively managing stormwater. National and state transportation departments are therefore prioritizing roadside vegetation using sustainable practices, leading to increased use of organic amendments (OAs) such as compost or related materials. OAs are commonly recycled and repurposed materials that serve as valuable soil conditioners, and their characteristics vary depending on their parent materials. Many OAs are cost-effective, readily available, and offer significant benefits to urban soils, which often are bereft of plant-essential nutrients and stability. This necessitates a better understanding of their impact on soil health and the environment, when applied at “acceptable” rates. This research aims to explore soil-water-plant interactions in urban soils (with and without OAs) focusing on vegetation establishment, soil fertility, and nutrient transport via leaching/runoff. Greenhouse and laboratory experiments were conducted to assess the potential use of these OAs for roadside projects.One set of experiments (greenhouse tub studies) focused on three OAs (leaf compost, shredded aged wood mulch, biosolids) which are widely available across Maryland. The amended soils were mixed to meet the topsoil OM requirements (4 – 8 %) of the state. Water quality results highlighted that the biosolids, while effective in retaining influent rainwater (tap water) phosphorus, caused significant nitrogen losses, exceeding typical stormwater concentrations by 40-200 times. Leaf compost also contributed to nitrogen leaching but only during the initial stages. Mulch reduced nutrient loss but caused limited vegetative cover. The study found that soil properties, such as the carbon-to-nitrogen (C:N) ratio and nitrogen content, play a vital role in the magnitude and patterns of nitrogen leaching. Additionally, it was speculated that the presence of soil minerals, such as iron and calcium, successfully retained phosphorus in the amended soils. The shear and hydraulic properties of the soils improved with the incorporation of amendments. Based on the results of the tub studies, leaf compost identified as a suitable OA for plants and water quality. However, the tub studies had limitations in their evaluation of compost amendments derived from different feedstock sources and their impacts on native vegetation growth. Therefore, a pot study was conducted to determine the optimum mixing ratios of soils and OAs to facilitate rapid vegetation growth. Three types of composts (turkey litter, food waste and yard waste) with varying nutrient properties were tested. A wood-based biochar was the fourth chosen OA because of its valuable use in agriculture and environmental remediation. The findings showed that turkey litter compost severely inhibited growth at higher application rates due to excess salts content. However, this compost showed improved plant nitrogen and leaf area whenever vegetation was established. Alternatively, biochar, while not inhibiting growth, resulted in visibly weak plant morphology, and led to nitrogen deficiencies. Yard waste and food waste composts showed positive impacts in terms of coverage, leaf area index and plant N contents. Between the tub studies and the pot study, yard waste compost has consistently emerged as the favorable soil amendment. Given biochar’s well documented advantages for water quality and soil structural properties, a scaled-up mesocosm experiment that simulated sloped road shoulders was conducted to test the effectiveness of combining compost and biochar in urban soils, aiming to meet vegetation and water quality goals. The runoff phosphorus and nitrogen mass transports were highest (261 mg-P/m2 and 8645 mg-N/m2, respectively) when compost was the sole amendment mixed into the control soil. However, adding biochar to the soil reduced these losses by up to 5.6x for phosphorus and 8.8x for nitrogen compared to compost. Strong correlation between soil C:N and effluent N was noted, higher ratios (>20:1) reduced nitrogen losses. Biochar, due to its high carbon content and pH, also helped retain phosphorus in the soils. Conversely, compost, being more readily decomposable than biochar, caused nutrients to run off. Compost-biochar mixtures also showed greater plant growth compared to the control soil. Together, this research shows that not all high-nutrient OAs provide favorable outcomes when incorporated into soils to enhance the OM content. Leaf or yard waste-based composts are preferred for roadside vegetation due to their reduced issues related to nutrient losses compared to other nutrient-rich materials tested in this study. However, the yard waste compost incorporation rate should be limited to achieve a soil OM increase of 1-2% to prevent high nutrient levels in the runoff. Furthermore, combining biochar and yard waste compost offers a promising approach for construction projects particularly on steep terrains to achieve and preserve a balanced soil-water-plant ecosystem.Item PREVENTION AND TREATMENT OF PERSISTENT ORGANIC POLLUTANTS IN STORMWATER AND SEDIMENT(2023) Yuan, Chen; Kjellerup, Birthe V; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polycyclic aromatic hydrocarbons (PAHs) and Polychlorinated biphenyls (PCBs) are two groups of persistent organic pollutants (POPs) with toxicity, carcinogenicity, and teratogenicity. Those compounds are harmful to human health and wildlife. Stormwater is one of the important sources of PAHs and PCBs to aquatic environments. Stormwater control measures (SCMs) have already been used to remove PAHs and PCBs from stormwater, however traditional SCMs can remove PAHs and PCBs in the particle phase, but there still are dissolved PAHs and PCBs in the outflow of SCMs. This study focused on reducing the influence of PAHs and PCBs in stormwater on the environment by 1) improve the treatment performance by adding a polishing treatment procedure after traditional SCMs, and remove the PAHs and PCBs accumulated in the polishing treatment media by bioaugmentation of Pseudomonas putida ATCC 17484 and Paraburkholderia xenovorans LB400 and 2) dechlorination of PCBs in the sediment of aquatic environments by biofilm Dehalobium chlorocoercia DF1 inoculum. The results of polishing treatment showed that all black carbon materials, namely biochar, granular activated carbon (GAC), and regenerated GAC (RAC), were effective to remove dissolved PAHs with removal > 95%. However, all materials had lower removal efficiency on PCBs with removal > 84%, By the comparation of cost and lifetime under the condition that 50% polishing media are used in the polishing treatment facility. RAC which has a lifetime>147 years based on the precipitation of Maryland and Washington and cost <3.79 $-m3-yr-1, was the best material for polishing treatment. Results of treatment train with a traditional SCM media column and polishing treatment column indicated that average removal of PAHs can be improved from 94.56% of BSM columns to 99.61% of polishing treatment columns, and removal of PCBs can be improved from 84.61% to 95.16%. Results of bioaugmentation of polishing treatment media showed no biodegradation took place in the mesocosms with polishing media. However, the liquid mesocosms showed P.putida degraded 97.9% of pyrene. The bacteria colony on plates after the biodegradation experiment showed that there were less P.putida and P.xenovorans colony of polishing media mesocosms than liquid mesocosms. Therefore, the limitation of biodegradation of polishing media mesocosms may cause by the limited bioavailability and less active inoculated bacteria. The results of dechlorination by Dehalobium chlorocoercia DF1 biofilm shows that there were native bacteria, such as Gemmatimonadetes, Actinobacteria, Proteobacteria and Firmicutes in the sediment that can dechlorinate PCBs. The three treated mesocosm groups (addition of biochar, bioaugmentation with DF1 biofilm and liquid DF1 culture) all can improve dechlorination, of 28.09%, 21.30%, and 17.10%, respectively. Those three groups had dechlorination extent higher than negative control (4.60%), and abiotic control (-1.02%). The microbial community analysis indicated that biofilm inoculation improved abundance of DF1 and had a more stable influence on the community than liquid inoculation. Overall, biofilm inoculation and addition of biochar dechlorinate PCBs in sediment efficiently, and polishing treatment is an efficient approach to improve traditional SCMs, while treating the polishing media with bioaugmentation need further study.Item Interactions and Treatment of Metals in Urban Stormwater(2023) Croft, Kristen; Kjellerup, Birthe V; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increasing urbanization and a changing climate will only exacerbate the magnitude of pollution entering our waterways, threatening our drinking water source and aquatic ecosystems. Urban stormwater contains a cornucopia of pollutants that pose direct toxicity risks (e.g., metals, organics, pathogens) and indirect adverse effects (e.g., sediments, nutrients) to aquatic life. Metals, specifically copper (Cu) and zinc (Zn), are both ubiquitous in the urban environment and detrimental to aquatic ecosystems at low concentrations (approximately 10 ppb). Targeting this growing source of pollution upstream is critical in providing necessary environmental protections, especially as the intensifying effects of climate change and urbanization are imminent. This leads to the main research question – how can Cu and Zn loads in stormwater be reduced to protect aquatic ecosystems?Bioretention is a stormwater control measure (SCM) that mimics natural systems to take advantage of the natural filtering processes. In addition to hydrologic benefits, bioretention provides removal of particulate matter (PM) through filtration and sedimentation, and potential removal of dissolved constituents through chemical and biological processes. Studies including characterization of stormwater, road-deposited sediments (RDS), and performance of a mature bioretention cell were performed to determine treatability, mobility, and bioavailability of Cu and Zn in stormwater and through bioretention treatment. Both metals accumulated in the finest (<25 μm) fraction of RDS samples, however particulate bound (PB) Zn concentrations were enriched in stormwater compared to finer fractions of RDS, while PB-Cu was not. This indicated that PB-Zn is more mobile than PB-Cu, likely due to different sources of these metals in urban environments. The PM and PB metal loads were reduced by 82% and 83%, respectively, showing that mature bioretention cells are effective at reducing PM and PB contaminant loads. However, dissolved constituents were essentially unchanged through bioretention treatment, and concentrations of dissolved metals were measured at levels that potentially cause aquatic toxicity. Thus, alternative media amendments were investigated for further reduction of dissolved metal contents. Black carbon (BC) media including biochar, granular activated carbon (GAC), regenerated activated carbon (RAC), and a natural mineral sorbent, clinoptilolite zeolite, were tested in continuous columns, and in up-scaled modular treatment columns. The four tested BC media performed similarly for Cu and Zn removal, with Zn having an earlier breakthrough compared to Cu. This technology is predicted to provide reduction of dissolved Cu for up to 60 years with current rainfall predictions. Modular treatment columns showed that traditional bioretention soil media (BSM) provided effective removal of dissolved Zn (71%) and ineffective removal of Cu (17%). The subsequent BC polishing module was effective for Cu removal (40%), and zeolite showed potential for Zn removal. Overall, dissolved metals in stormwater are the most mobile, bioavailable, and difficult to remove through traditional filtration-based SCMs. This research has shown that fresh BSM can provide effective removal of dissolved Zn, and BC amendments are a potential solution for removal of dissolved Cu in stormwater. Refreshing the top few centimeters of an existing bioretention with fresh BSM can provide treatment of dissolved Zn. Retrofitting bioretention to include a polishing module either layered or in series with a mix of BC and zeolite can further reduce dissolved Cu and Zn loads in stormwater.Item In Situ and laboratory studies of soil treatment areas experiencing flooding(2023) Waris, Aleem; Kjellerup, Birthe V.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Onsite wastewater treatment is used by over one in five American households to treat wastewater by soil biogeochemical transformations. In Maryland alone, 420,000 septic systems are in use primarily in rural and near coastal areas. Issues of sea level rise can threaten coastal infrastructure due to flooding damage that also can impact the ability of soil to efficiently treat nutrients found in wastewater. In this study, two onsite wastewater treatment systems with different soil types and treatment techniques were assessed in Anne Arundel County, Maryland. It was found that soil texture can impact the health of a soil in its function of treating wastewater, in addition to treatment techniques affecting inorganic nitrogen in the soil treatment area. To model the impacts of flooding damage to a soil treatment area, tidal flooding with fresh, brackish and saltwater was simulated in a laboratory-scale column study. The results from the month-long study showed decreases in the treatment efficiency for inorganic nitrogen and dissolved organic solids.Item NUTRIENT MOVEMENT IN A VEGETATED COMPOST BLANKET AMENDING A VEGETATED FILTER STRIP ON A HIGHWAY SLOPE(2022) Forgione, Erica Rose; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Excess stormwater runoff caused by rapid urbanization and exacerbated by climate change generates many challenges for public safety and the environment. Large runoff volumes contribute to flooding and pollutants in stormwater runoff pose risks to human and environmental health, including toxicity to the aquatic environment caused by heavy metals and nutrient pollution leading to eutrophication, the cause of harmful algal blooms. An effort is being made to improve the efficiency of existing highway stormwater control systems which have limited performance in terms of volume reduction and pollutant removal. To address this issue, amendment of highway Vegetated Filter Strips (VFS) with a Vegetated Compost Blanket (VCB), a layer of seeded compost placed on an established slope, has been proposed. Compost has high water holding capacity and organic matter content which can immobilize contaminants of concern. However, the high nutrient content of compost poses a threat to net beneficial performance since excess nutrient leaching occurs after application. This research has posed the question: Can a VCB be used as a stormwater control measure (SCM) while avoiding excessive nutrient leaching?The VCB/VFS system was assessed through lab-scale, greenhouse-scale, and field-scale experiments. Hydrologic performance was evaluated in field and greenhouse experiments through evaluation of dynamic flow modification, event volume storage, and cumulative volume retention. Water quality performance was assessed through analysis of Total Suspended Solids (TSS), Nitrate + Nitrite (NOx), Total Kjeldahl Nitrogen (TKN), Total Nitrogen (TN), Total Phosphorus (TP), filtered and total Copper, and total Zinc concentrations. Nitrogen (N) and phosphorus (P) in compost are naturally transformed from organic to inorganic, soluble forms through the microbially-mediated process of mineralization. Nutrient removal occurs through adsorption as compost leachate passes through the VFS soil layer. To further investigate nutrient movement, small scale laboratory experiments were completed to determine the N and P compost mineralization rates and theoretical soil adsorption capacities. Nutrient data from greenhouse and field experiments were empirically evaluated using the lab-obtained mineralization data. Nutrient release was simulated and compared to experimental field data using a new open-source software, OpenHydroQual, which combines hydraulic and water quality modeling. VCBs were found to have a significant impact on both flow and volume reduction, though at the highest flowrates, VCBs were unable to significantly reduce flow and instead acted as conveyance. A useful design estimate for representative storage capacity using the saturated moisture content and wilting point of both the VCB and VFS was determined. Significant TSS removal was observed in both the field and greenhouse studies and particulate metals were largely removed; however dissolved copper leaching was observed in the field experiment, as has been observed previously for some compost in stormwater systems. Highly elevated concentrations of nutrients (as high as 100 mg/L TN and 12 mg/L TP) were observed in the effluent of both field and greenhouse experiments, resulting in net nutrient leaching and concentrations above recommended EPA freshwater limits even after 1-2 years. Additionally, mass loading rates at the field site (as high as 41 kg/ac/yr for TN and 14 kg/ac/yr for TP) were 1-2 magnitudes higher than observed influent mass loading rates (~3.8 kg/ha/yr for TN and ~0.47 kg/ha/yr for TP). Through laboratory mineralization studies, N and P mineralization rates were found to differ between compost batches, with initial nutrient content and age/leaching of compost being important factors. Adsorption experiments indicated increasing P adsorption from compost leachate with increasing soil Al+Fe content. Comparisons to greenhouse and field data showed differences in N speciation, likely due to differences in moisture content and temperature causing differing amounts of nitrification and volatilization. OpenHydroQual modeling showed modest results, with varying levels of accuracy for storm hydrograph simulation and mass release. VCBs are not currently recommended for use due to the risk of nutrient and metals pollution, especially in nutrient and metals sensitive watersheds. However, several impactful factors were identified that may reduce nutrient leaching, including compost composition, compost age/leaching, and VFS soil type.Item ENHANCING BIOREMEDIATION OF TCE-CONTAMINATED GROUNDWATER AT THE BEAVERDAM ROAD LANDFILL(2022) Saffari Ghandehari, Shahrzad; Kjellerup, Birthe; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trichloroethene (TCE) is one of the most frequently found groundwater contaminants, thus remediating TCE-contaminated groundwater bodies is crucial in providing safe drinking water to people around the world. However, due to the resistance of its intermediates to degradation and their toxicity, TCE bioremediation is still challenging. Years after the installation of a permeable reactive barrier (PRB), the levels of toxic TCE dechlorination intermediates had increased downgradient from the PRB, indicating the need for actions to prevent the contaminated water from reaching a stream nearby. A review of the reports and monitoring results showed that low groundwater residence time and low pH levels were contributing to the inefficiency of the PRB. A trench was purposed to be installed upgradient from this PRB to increase the groundwater contact time with the microorganisms and organic carbon content of the soil using wastewater biosolids, limestone, and biochar to increase the buffer capacity of the soil and the sorption of TCE to the soil. Bench-scale studies were conducted with biosolids and limestone to observe the effect of the biosolids microbial population on a TCE-dechlorinating mixed microbial community. Both dechlorinating bacteria and methanogens use hydrogen in their metabolism and potentially can compete with each other. While biosolids-limestone reactors produced significantly higher concentrations of methane, the activity of methane-producing microorganisms did not adversely affect TCE dechlorination. Furthermore, the characterization of the microbial community of the reactors indicated the positive effect of biosolids. Based on the results from this study, the trench was installed in January 2020 at the site. The sampling and monitoring results nine months after its installation indicated that the trench filling material had positively affected the soil microbial community and decreased the TCE levels downgradient from the trench. To further characterize the microbial community of the site, passive samplers using biochar were installed upgradient and inside the PRB to compare the activity of the dechlorinating bacteria. It was shown that the PRB microbial population was capable of complete dechlorination of TCE, while dechlorinating bacteria detected in the upgradient samples were not active, resulting in the different TCE concentrations observed in these locations. Overall, the study showed that biosolids can be used as an amendment in the TCE bioremediation purposes. Future work should focus on further monitoring the effect of the treatments, applied in this site.