No / Accepted for conference.

No description available.

No description available.

No description available.

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No description available.

This thesis reports on the work performed on the manipulation of micro­-particles on substrate surfaces using short laser pulses. For particles with diameters on the order of microns, the binding forces to surfaces are significantly larger than gravitational forces. To overcome these binding forces and manipulate the particles the use of femtosecond laser pulses has been investigated. Individual micro-particles (poly-divinylbenzene, glass and silver materials) with diameters around 2 um were removed from substrate surfaces (dielectric, semiconductor and metal substrates) us­ing a Ti:Sapphire laser system. The pulses produced at 800 nm had pulse lengths around 140 fs and were tightly focussed onto the surface using 5x and 10x micro­scope objectives. The peak fluence thresholds for particle removal were determined and the surfaces examined after irradiation by a scanning electron microscope and atomic force microscope to check for damage. The experimental results indicate that ablation of the substrate below the micro-particles is most likely to be respon­sible for micro-particle removal from the substrate surface when using femtosecond pulses. Ablation pits were observed for the dielectric micro-spheres on semiconductor substrates. It is also believed that ablation is responsible for the removal of other types of micro-particles from various substrates. Unlike the dielectric micro-sphere on semiconductor substrate results, the other particle-substrate combinations show a close correspondence between the removal and substrate ablation thresholds. It is believed that these results indicate the occurrence of ablation leading to the removal of the micro-particles. Calculations of the local electromagnetic fields around the micro-particles have also been carried out and the distributions used to interpret the experimental results. / Thesis / Master of Applied Science (MASc)

A 0.2-hectare wetland was constructed in the floodplain of Opequon Creek in Northern Virginia as a best management practice (BMP) for stormwater management. The research goals were to 1) determine if wetland hydrology existed and quantify the role of groundwater exchange in the constructed wetland (CW) water budget, 2) estimate wetland hydraulic characteristics during overbank flows, and 3) quantify the event-scale nutrient assimilative capacity of the constructed wetland. CW water table elevations and hydraulic gradients were measured through an array of nested piezometers. During controlled flooding events, stream water was pumped from the creek and amended with nutrients and a conservative tracer in two seasons to determine hydraulic characteristics and nutrient reduction. Samples were collected at the inlet, outlet structure, and at three locations along three transects along the wetland flowpath. Water table elevation monitoring demonstrated that wetland hydrology existed on the site. The mean residence time of the wetland was found to be 100 min for flow-rates of 4.25-5.1 m3/min. Residence time distributions of the high and low marsh features identified a considerable degree of flow dispersion. Manning's n varied between macrotopographic features and was significantly higher in the spring event as compared to the fall event, likely due to the presence of rigid-stem vegetation. Average wetland n was 0.62. Total suspended solid concentrations decreased with increasing residence time during both experiments. Mass reduction of pollutants were 73% total suspended solids (TSS), 54% ammonia-nitrogen (NH3-N), 16% nitrate-N (NO3-N), 16% total nitrogen (TN), 23% orthophosphate-phosphorus (PO4-P), and 37% total P (TP) in the fall, and 69% TSS, 58% NH3-N, 7% NO3-N, 22% TN, 8% PO4-P, and 25% TP in the spring. Linear regression of mass flux over the event hydrograph was used to determine pollutant removal rates between the wetland inlet and outlet. Pollutant removal rates were determined through linear regression of mass flux and were higher in the spring event than in the fall. Dissolved nitrogen species were more rapidly removed than dissolved phosphorus. TSS, TP, and TN removal were greater and faster than dissolved nutrient species, suggesting that physical settling was the dominant removal mechanism for stormwater pollutants. / Ph. D.

A key strategy to motivate proenvironmental behavior (PEB) involves the promise of monetary rewards. Financial incentives are intuitively appealing because they can increase an individual's expected benefits for engaging in the PEB; however, there is concern that incentives can transform motivations for the PEB. The purpose of this study was to examine the role of financial incentives on behavior across time. Specifically, I used an experimental design to examine the immediate effects payments on litter-removal effort (Phase 1) followed by effort after payments were no longer available (Phase 2). Undergraduate students were recruited for a trail evaluation study and randomly assigned to a control treatment or a financial incentive treatment. In Phase 1 I asked students to pick up discarded litter during their trail evaluation (PEB). The incentive condition offered students $0.25 for each of the possible 16 items of trash planted along the trail. The control condition simply asked students to help by picking up trash. Students were again asked to collect trash in Phase 2 but the financial incentive condition was not offered a payment. In accordance with self-determination theory I expected payments to increase effort in the short term and suppress effort when the incentive was no longer provided. Although there was an overall decrease in effort between phases within both conditions, the results of a repeated-measures ANOVA indicated no difference between the control and incentive condition in either phase. Given the lack of a statistically significant finding, it is possible that there are conditions under which payments provide no greater inducement than a simple request for help. This idea is supported by a meta-analysis, which identifies a consistent lack of effect for easily-performed tasks. Additional research is needed to further understand the conditions under which financial incentives can motivate and sustain PEBs. / Master of Science

Waste sludge is frequently treated by anaerobic digestion to kill pathogens, generate methane gas and reduce odors so the sludge can be safely land applied. In an attempt to reduce sludge volumes and improve sludge dewatering properties, the use of thermal hydrolysis (TH), a sludge pretreatment method, has been adopted by numerous wastewater treatment plants, among them being the District of Columbia Water and Sewage Authority (DC WASA). The use of anaerobic digestion in collaboration with thermal hydrolysis has been shown to increase VS removal, COD removal and biogas production. The sludge generated also dewaters to a higher cake solids than from conventional anaerobic digestion. Unfortunately, DC WASA has found that the use of thermal hydrolysis had brought about two major issues. These are: (a) does thermal hydrolysis increase destruction of fats, oils and greases compared to conventional digestion? and (b) is the mixing method used at Virginia Tech (recirculating gas mixing) capable of stripping ammonia from the digester? Therefore the main purpose of this study is to evaluate these issues which occur with the use of the thermal hydrolysis process. Experiments were conducted in two phases. The first phase was to assess the performance of anaerobic digesters via their biogas production with and without long chain fatty acid addition and with or without thermal hydrolysis. This research was further carried out in two stages. First a mixture of unsaturated long chain fatty acids (hydrolyzed and unhydrolyzed) was used. The fatty acid mixture included oleic, linoleic and linolenic acids, which contain one, two and three double bonds, respectively. In the second stage, the effect of a single unsaturated fatty acid (hydrolyzed and unhydrolyzed) was analyzed. If extra gas is generated, grease addition to the digesters will be implemented. If thermal hydrolysis produces more gas, the greases will be added through the thermal hydrolysis unit rather than being added directly to the digester. The results showed that addition of long chain fatty acids greatly increased gas production and the long chain fatty acids that were thermally hydrolyzed generated more gas than the untreated long chain fatty acids, although the gain was not large. The second phase of the study was carried out by alternating the type of recirculating gas mixing (partial and continuous) in the anaerobic bioreactor. To achieve this goal, short-term anaerobic bioreactor studies were conducted by varying the frequency of the gas. The result showed that continuous gas recirculation at the bottom of the digester was responsible for stripping ammonia from the system. It appeared that up to 500 mg/L of ammonia was being stripped from the digester operating at 20 day solids retention time. This suggests that ammonia can be stripped if a reduction of ammonia in the digester was desired. / Master of Science