Browsing by Subject "Sorption"
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Item Biochar as a sorbent for naturally occurring and synthetic agricultural chemicals(2018-06) Hall, KathleenThe idea of adding biochar to soil to sequester carbon and improve fertility has soared in popularity over the past few decades; however, a strong scientific understanding of this material and its environmental effects is still lacking. This body of work explores biochar's interactions with chemicals, both naturally occurring (i.e., allelochemicals) and anthropogenically applied (i.e., herbicides), and sheds light on the mechanisms involved and our ability to predict and optimize its sorptive behavior. The first chapter investigates how the feedstock material from which a biochar is produced impacts its sorptive behavior toward allelochemicals. Mixing different feedstocks, such as pine chips and poultry litter, is thought to be a way to create “designer biochars” that combine the beneficial properties of each feedstock. However, results from this study revealed that mixing feedstock materials did not have predictable effects on organic compound sorption. The second chapter begins to evaluate biochar-chemical interactions in soil to better understand realistic applications of biochar as a sorbent. Here, the leaching potentials of six different herbicides were assessed in vulnerable Hawaiian soils, and biochar was tested as a tool to reduce the transport of the most mobile herbicide, aminocyclopyrachlor. It was found that none of the four biochar amendments tested significantly altered the leaching potential of aminocyclopyrachlor in these soils based on fate and transport models. In the third chapter, the focus shifts more towards understanding the mechanisms of biochar-herbicide interactions. Here we specifically looked at glyphosate, the world’s most widely used herbicide, and found that biochar macroporosity and specific surface functionality influenced glyphosate sorption. Additionally, pre-pyrolysis addition of Fe and Cu had no significant effect on sorption. Results from this work also demonstrated the reversibility of glyphosate sorption on biochar in the presence of phosphate, suggesting similar binding mechanisms and potential interferences from phosphate fertilizers. The fourth chapter continues to investigate the sorption mechanisms responsible for the observed biochar-herbicide interactions and simultaneously assesses our ability to optimize biochars for sorption through activation treatments. It was found that activation of a low-temperature biochar by hydrogen peroxide can improve the removal of organic acid herbicides from aqueous solution, but was of little value in optimizing the removal of non-ionizable herbicides. The improved removal efficiency was attributed to pH effects and charge-based interactions with biochar. Collectively, the research presented in this dissertation highlights the variability of biochar's sorptive behavior and illustrates the challenges in predicting this behavior, particularly when feedstocks are combined. While the sorptive applications in soil initially appear limited, there is potential to improve the sorption capacity of these materials through activation, and more targeted improvements will be possible once sorption mechanisms are better understood.Item Biochar Metal Sorption and Effect on Microbial Sulfate Reduction(2016-11) Sande, KippBiochar is a stabilized, recalcitrant carbon compound, created when biomass is heated to temperatures between 300-1000°C, under low oxygen concentrations. It can be produced from a variety of biomass feedstock, such as agricultural residues, wood chips, and manure. Recently, biochars have found several applications in environmental remediation. This study evaluated the effect of biochar on microbial sulfate reduction in cell suspension assays and batch growth experiments, as well as the potential of biochar to remove heavy metals from aqueous solution. Irrespective of dosage (0.5 – 10 g/L), biochar increased the extent of sulfate reduction by Desulfovibrio alaskensis G20 up to 4-fold in suspension assays. Batch growth experiments demonstrated that biochar concentrations up to 10 g/L have no inhibitory effects on microbial sulfate reduction and cell growth. We further compared the sorptive properties of different biochars for copper and nickel. Biochars were pyrolyzed in the presence of magnesium hydroxide (Mg(OH)2) or magnesium chloride (MgCl2) and sorption isotherms for copper and nickel were compared to unmodified biochar. Copper and nickel sorption capacities were greatly improved for the magnesium-enhanced biochars, indicating that biochar mineral supplementation can increase the efficiency of metal adsorption and removal from solution. Ongoing research under this theme aims at the development of a biochar-mineral composite material that promotes biological sulfate reduction and heavy metal adsorption in order to provide an efficient, low-cost, environmentally-friendly absorbent material that can be used for mine water treatment in bioreactors and/or permeable reactive barriers.Item Fate and impact of antibiotics in slow-rate biofiltration processes.(2010-12) Wunder, David BarnesAntibiotics have been detected in surface waters worldwide at concentrations up to 1.9 micrograms/L, but are typically detected at low nanogram/L concentrations. The potential health effects of exposure to low levels of these compounds via tap water are not known, but there is significant concern among water consumers regarding the occurrence of antibiotics and other pharmaceutical compounds in water supplies. Thus, a significant amount of research has been performed recently to investigate the removal of pharmaceuticals via conventional and advanced water treatment processes. While conventional treatment processes (i.e., coagulation, flocculation, sedimentation, and filtration) are generally not effective, oxidation processes (e.g., chlorination, ozonation) and granular activated carbon exhibit some effectiveness at removing pharmaceuticals. As expected, removals are highly dependent on compound structure. Furthermore, some oxidants, such as chloramines, are not effective at oxidizing pharmaceuticals. Slow-rate biofiltration processes (SRBF), such as slow sand filtration (SSF) and riverbank filtration (RBF), are drinking water treatmeant systems comprised of two stages in sequence: 1) a relatively shallow biotic region where media (i.e., filter sand or aquifer material) is colonized by biofilm bacteria, followed by 2) an deeper abiotic filtration zone. These processes are extensively used in Europe and developing global regions and are seeing increased usage in the United States. There is evidence in the literature that SRBFs can remove a wide variety of trace organic pollutants including: pesticides, disinfection byproducts, and some pharmaceuticals. Little is known regarding the ability of SRBF processes to remove antibiotics from water supplies nor has any work been done to investigate the potential adverse effects of antibiotics on the biofilm bacteria that are critical to SRBF system performance. Thus, this research was performed to determine the extent and mechanisms (i.e., sorption versus biodegradation) of antibiotic removal in SRBF processes and the effects of antibiotics on biofilm bacteria (i.e., activity and community composition). The effect of antibiotics on bacterial activity and community structure was investigated by growing biofilm in the presence and absence of a mixture of antibiotics in a continuous-flow rotating annular bioreactor (CFRAB) with acetate as substrate. Three representative compounds were selected for use in this research: sulfamethoxazole (SMX), erythromycin (ERY), and ciprofloxacin (CIP). These antibiotics were selected because they: 1) represent three prominent classes of antibiotics with differing mechanisms of action against bacteria, 2) have been detected in surface water, 3) exhibit different chemical characteristics, and 4) have differing levels of biodegradability. Areal acetate utilization rates for a constant feed of antibiotics were similar to the control experiments, and utilization rates did not change during an antibiotic shock loading experiment. Attached biomass levels were greater for experiments involving a high CIP concentration (3.33 micrograms/L), however, yielding comparatively lower steady-state biomass-normalized substrate utilization rates. Microbial community analyses via automated ribosomal intergenic spacer analysis (ARISA) revealed shifts in community structure for the high dose CIP experiments. A CFRAB was also used to investigate antibiotic sorption to bacterial biofilm. The extent of sorption, as indicated by the organic carbon partition coefficient (Koc), was 15 to 23 times greater for CIP compared to ERY and SMX. The Koc values did not correlate with experimentally-determined Kow values, suggesting that the sorption of relatively hydrophilic (i.e. Kow < 1.7) and charged antibiotics to typically negatively charged biofilm is driven by ionic interactions (i.e. ion exchange) rather than hydrophobic interactions. The attenuation and impact of antibiotics in SRBF systems was investigated by conducting bench-scale filter column experiments with mixtures of SMX, ERY, and CIP at high (3.33 micrograms/L, each) and low (0.33 microgram/L, each) antibiotic feed conditions. Consistent with the CFRAB experiments, antibiotic breakthrough times were greatest for CIP, with very little uptake of SMX or ERY. Biodegradation was not observed for any antibiotic during 6-weeks of filter column operation or in complementary batch experiments. A one-dimensional advection-dispersion equation (with linear sorption) model was validated against experimental results and used to compare antibiotic retardation in SSF, RBF, and rapid gravity biofiltration (RGBF) systems. Of the modeled systems, antibiotic retardation was greatest in RBF, with little antibiotic removal expected for SSF. Based on analysis of ARISA data, the community structure of bacterial biofilm was not affected in filters exposed to antibiotics at low concentrations (i.e. 0.33 microgram/L, each) similar to those found in surface waters, with a few species impacted under high concentration conditions (3.33 microgram/L, each). The results of this work will help those interested in understanding and predicting antibiotic fate in engineered and natural systems where biofilm is present. The results indicate that antibiotic removal in SRBF processes will be dictated by compound properties such as charge and hydrophobicity, and that limited removal of antibiotics in SRBF processes can be expected. Finally, the results suggest that that mixtures of antibiotics at concentrations typically observed in surface waters are unlikely to adversely affect SRBF biofilm bacteria or process performance.Item Hygroscopicity of pharmaceutical crystals.(2009-01) Chen, DabingThe active pharmaceutical ingredients (APIs) as well as excipients in a solid dosage form can take up water vapor both during manufacture and subsequent storage of the product. Uptake of unacceptable amount of water can cause adverse effects on physical and chemical stability of APIs and functionality of excipients. It is prudent to select drug candidates with low hygroscopicity to minimize the development risk and time. The objectives of this study are: (i) to investigate the risk in predicting long-term water uptake from short-term water sorption studies, (ii) to understand the thermodynamic and kinetic factors that affect water uptake by pharmaceutical crystals. Automated sorption microbalance (ASM) is often used to determine the hygroscopicity, in which the small sample size and gas purge are believed to accelerate the water sorption process so that equilibrium could be attained in a short time period. However, caution must be exercised when the rates of water vapor diffusion or heat transfer at the solid-vapor interface are not the limiting factors. Four cases are discussed in this thesis, in which ASM failed to predict long-term water uptake. 1) Water vapor was believed to diffuse into the lattice of a metastable crystalline form and induced a polymorphic transformation. The crystallization of the stable form led to a decrease in water content. 2) Adsorbed water formed a surface solution and enhanced the mobility of surface molecules. Nucleation rate of hydrate could be the rate-limiting step. 3) Water sorption induced a crystal to liquid crystal transformation in a surface-active compound, where the latter retains orientational but lacks positional order of molecular packing. 4) The formation of a metastable liquid crystalline phase was kinetically favored for amorphous materials formed in surface-active compounds. The metastable liquid crystalline phase was stable for 3 months when stored under ambient conditions.Item Water Quality Benefits of a MN Floodwater Storage Impoundment(2017-09) Guzner, MariyaNutrient and sediment pollution in Lake Winnipeg and its watershed, the Red River Basin, MN, are degrading water quality and impairing aquatic health, fishability, swimmability and recreational potential. It is necessary to capture and store the pollutants phosphorus (P), nitrogen (N), and total suspended solids (TSS) on the landscape, to improve water quality and protect valuable water resources in the region. Floodwater storage impoundments have the potential to effectively capture and store nutrient pollutants and suspended sediments, and consequently improve downstream water quality. There are already several dozen similar impoundments in the state, and plans to build approximately 200 in total. The water quality benefits of a floodwater storage impoundment in the Red River Basin were tested through various methods in this study. Nutrient budgets were built for the impoundment in 2014, 2015, and 2016. Load and concentration reductions were calculated for water entering and leaving the system, for nitrogen, phosphorus, and total suspended solids. In 2016, nitrogen and phosphorus reductions of 73% and 66%, respectively, were achieved. A hypothetical load reduction calculation was also modeled to determine the effects of impoundment water release speed on pollutant capture. The soil phosphorus storage potential of the impoundment was determined through a laboratory sorption experiment. Soils at the site were analyzed for their linear adsorption coefficient (K) and equilibrium P concentration at zero-sorption (EPC0). Analysis compared soils under various land uses, including: cropped, planted with native vegetation, and flooded. Results suggest that all soils within the impoundment outperform soils at the exterior of the structure regarding phosphorus storage and buffering potential. Variation in soil-phosphorus sorption properties between sites with different vegetation types will advise cropping and planting plans to optimize water quality benefits. Results of this research are intended to advise management of the study site, similar impoundments, and constructed wetlands for water quality treatment.