published_or_final_version / Biological Sciences / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 150-188). Also available online.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 150-188). Also available in print.

Currently, coal combustion plays an important role in meeting the energy needs of the United States. It is expected that the effective utilization of coal will be crucial for attaining energy independence for the nation in the next 25 to 30 years, if not longer. The United States burns about 20% of the world's annual coal production, second only to China. Strikingly, there are 200-300 more years of burn at our current rate of consumption, considering our massive coal reserves. Almost half of our electricity comes from coal power. Although coal is a fossil fuel that will become more and more depleted, it will be the principal fuel for utilities in the US for decades to come. Therefore, there is a need to design new strategies to clean coal. Mercury can be found in fly ash, bottom ash, and flue gas desulfurization (FGD) material. The Hg is transferred to these coal combustion products (CCPs) from its associated parent coal. These CCPs absorb a significant amount of the Hg released during the combustion process. With the EPA's recent emphasis on controlling the Hg emission by coal-burning electric utilities, the disposal and utilization of CCPs are under an environmental microscope. As EPA regulations become more stringent, Hg concentration in CCPs is expected to increase further; i.e., more Hg will be captured in the scrubber materials. The higher Hg concentrations will have serious consequences for the management of CCPs. Systematic measurements on Hg concentrations in the feed coal and the CCPs produced from two different power plants burning Illinois coal were carried out. Not only were there substantial variations in the total Hg concentration in the parent coal from week to week from a single mine, but there were also significant variations in the weekly Hg content of the CCPs. Surprisingly, there was no linear dependence between Hg content of coal and its CCPs. No correlation was observed between Hg content of fly ash and its loss-on-ignition (LOI) values. In order to control and further understand the fate of Hg in FGD scrubber material, the following was systematically examined: (a) whether there is a strong correlation between the parent coal and the Hg captured in FGD scrubber materials, (b) the thermal behavior of Hg in parent coal, FGD gypsum, and sulfite-rich FGD material, (c) whether there is a potential of Hg re-emission during gypsum-to-hemihydrate-to-gypsum transition, and (d) how Hg behaves in sulfite-rich scrubber material at higher temperatures and pressures. Ultimately, no direct correlation between the total Hg concentration of the parent coal and its associated FGD scrubber materials was found. Mercury desorbed from FGD gypsum at relatively low temperatures (90C < T < 250C), compared to the sulfite-rich scrubber materials which released Hg continuously at ambient pressures up to 600C. However, it was found that mildly-elevated pressures immobilized Hg, even at temperatures as high as 250C. Cleaning and dewatering coal has been a major challenge. Deeper pre-combustion cleaning of ashes and clays from coals can help utilize more of Illinois coal. Efforts have been underway for decades to reduce emissions from flue gas and toxic metal reduction. Now with carbon emissions under scrutiny, the effort to maximize coal's value is more important than ever before. In most coal preparation processes, significant amounts of fines and ultrafines are generated. Because these particles are difficult to dewater, they are often discarded in waste ponds. This translates into a major economic loss for the coal industry, not only because of the fuel value lost but also the substantial economic resources required to manage coal waste ponds in an environmentally-sound manner. A new approach developed using a high intensity sonication process in recovering, cleaning, and dewatering fine/ultrafine coal particles from the waste ponds, while concurrently reducing the Hg concentration in the fine and ultrafine particles was successful. Combining sonication with vegetable oil agglomeration significantly reduced the moisture, ash, and Hg content of the cleaned, recovered coal. Differential scanning calorimetry (DSC) measurements on the recovered coal were used to understand the interaction between the coal particles, water, and oil. The results suggested that vegetable oil was effective in displacing water from the coal-water interface, with the enthalpy of the water-vapor transition of oil-agglomerated coal particles decreasing on sonication of the particles. In fact, combining sonication treatment with oil agglomeration reduced the moisture content of run-of-mine (ROM) coal and waste coal, to 6 wt% and 12 wt% respectively, and increased their loss-on-ignition (LOI) content to 91 wt% and 76 wt%, respectively. Massive quantities of synthetic gypsum are produced when the flue gases from coal burning power plants are wet scrubbed with limestone. The sulfate-rich FGD scrubber material is largely construction-quality gypsum. Because of the large production of FGD gypsum every year, the economic and environmental impetus dictates that strategies be developed to effectively utilize FGD gypsum rather than just landfill it. Beneficial uses have been found in wallboard construction and agriculture. An important aspect of this research was to evaluate whether there was potential of Hg re-emission from scrubber materials during their utilization phase. Mercury emission occurs not only with elevated temperatures but with increased time. While external pressure retards these emissions, they are not the only concern associated with CCPs. The more global, urgent problems of greenhouse gases must be resolved. The dimension of the greenhouse gases problem is daunting; according to the Energy Information Agency, nearly 6 billion metric tons of CO2 were produced in the USA in 2007, with coal-burning power plants contributing about 2 billion metric tons. The success of large-size sequestration of CO2 in coal would hinge on a thorough understanding of coal-CO2 interactions and how these interactions control the mechanical behavior of coal. Moreover, these interactions could play a crucial role in evaluating any potential risks associated with sequestering CO2 in deep, unmineable coal seams. To evaluate the risk under non-equilibrium conditions, dynamic mechanical properties of pressurized Illinois coals were measured. The results suggest that Illinois bituminous coal in its unperturbed state, i.e., when not pressurized with CO2, showed large variations in its mechanical properties. The Young's modulus varied from 0.7 GPa to 3.4 GPa even though samples were extracted from a single chunk. No glass transition was observed for any Illinois bituminous coal under ambient conditions. Upon pressurizing the Illinois bituminous coals with CO2, the DMA results showed a transition at temperatures as low as ambient. This could be a potential risk for the structural integrity of a mine if any man-made or seismic activity were present.

Microalgae synthesize and store large volumes of lipids (potentially over 25% of dry weight) which could provide a renewable source of biodiesel. Traditional extraction techniques often produce poor lipid yields particularly from microalgae with robust cell walls. This project investigated the role of power ultrasound as a cell disruption step in lipid extraction from four microalgal species. Nile Red staining was used to assess the time when ultrasound induced increased membrane permeability in each species and lipids were extracted using an ultrasound assisted Bligh and Dyer extraction method. A 20 kHz probe system (40% amplitude, 0.086 W/cm3) caused increased lipid recovery from dry biomass in all cases; D. salina (no cell wall) from 15 to 22.5% of dry biomass after 1 minute (26% when stressed with 35 g/L NaCl). C. concordia (thin cell wall) from 7.5 to 10.5% of dry biomass after 2 minutes (27% with 25% nitrogen reduction in growth media). N. oculata (thick cell wall) from 6.5 to 10% of dry biomass after 16 minutes (31.5% when stressed with 30 g/L NaCl). The stressed cultures yield could be improved to 35% when ultrasound was combined with S070 beating beads. Chlorella sp. (thick cell wall) from 6.3 to 8.7% of dry biomass, after 16 minutes (44% was achieved when harvested at day 9 instead of 15). A Dual Frequency Reactor (16 and 20 kHz, 0.01 W/cm3) flow system with S070 beads demonstrated that high lipid extraction yields could be achieved on a larger level with N. oculata. After 4:48 minutes sonication 24% lipid recovery was achieved. This system could theoretically increase daily microalgal oil production from 3.96 to 5.76 L per day when compared to conventional techniques, at an extra production cost of only 2.9 p/litre (1.5% increase). D. salina, N. oculata and C. concordia resumed normal growth following sonication at 20 kHz after 1-20 days (8 minutes treatment for D. salina, 60 minutes treatment for N. oculata and 16 minutes treatment for C. concordia). It was found that the supernatant of sonicated D. salina and C. concordia when added to established cultures were able to boost their growth.

Drinking water sources are vulnerable to a broad range of contaminant threats. Recent U.S. legislation has focused on protecting public health from pathogens while also managing disinfection byproducts (DBPs) and organic contaminants. Chlorine is known to react with organic matter to form DBPs, thus alternative disinfection schemes are desirable. The goal of our research was to evaluate synergistic inactivation of E. coli with chlorine and sonication in a flow through system. Laboratory experiments were conducted to determine the impact of chlorine dose (0 to 1 mg/L), cavitation intensity (90 to 150 watts) and contact time (0 to 16 minutes) on inactivation. Tests were conducted with a probe system and a flow through cavitation device. Results showed that sonication alone was ineffective for the conditions tested. Sonication applied simultaneously with chlorine did not improve inactivation compared to each disinfectant alone.

Anaerobic digestion is a useful method for stabilizing and reducing the waste activated sludges (WAS) produced from biological secondary treatment. Pretreatments can make anaerobic digestion more efficient. However, the study of anaerobic digestion and pretreatments is limited to a focus in treating conventional WAS. Therefore, WAS from three non-conventional municipal wastewater treatment systems, a rotating biological contactor (RBC), a lagoon, and a moving bed bioreactor (MBBR), were digested anaerobically to determine the sludges’ biogas potentials compared to a conventional WAS. All three WAS had lower biogas potential normalized per volatile solids than conventional sludge by 46% + 6 (MBBR), 63% + 6 (RBC), and 77% + 7 (lagoon). The four sludges were pretreated with ultrasonic energies of 800 - 6550 kJ/kg TS to illustrate impact of sludge type on biogas production, solubilization, and digestion kinetics. All four sludge types responded uniquely to the same levels of sonication energies. The greatest increase in biogas production over the control of pretreated sludge did not coincide consistently with greater sonication energy but occurred within a solubilization range of 2.9 – 7.4% degree of disintegration (DD) and are as follows: 5% + 3 biogas increase for conventional sludge, 12% + 9 for lagoon, 15% + 2 for MBBR and 20% + 2 for RBC. The yield of biogas production related to soluble COD decreases with increased sonication energy. Hence it is likely that sonication produces refractory COD or causes inhibition in biogas production. The effect of sonication on digestion kinetics was inconclusive with the application of Modified Gompertz, Reaction Curve, and First Order models to biogas production. Diauxic growth patterns of biogas production of sonicated conventional waste demonstrates that the active time of digestion can be decreased through the conversion of less preferential substrates into existing, preferential substrates.

Oligomannosides prevalently exist as cell surface antigens. They play important roles in diseases such as viral infection and cancer, and they have been shown to be useful as candidates for vaccines. HIV, one of the most devastating modern diseases, has a high content of mannose sugars on its envelope glycoprotein gp120. Oligomannosides of the HIV virus, also called Man9, which are found on the glycoprotein gp120, have been shown to play a protective role for the HIV virus, shielding highly conserved protein domains of gp120 from proteolytic attacks. Thus gp120 plays an important role in HIV infection of cells, being responsible for the attachment and penetration of cells to be infected and is thus the target for immunotherapy or vaccine development. The synthesis of complex oligomannosides is still very challenging as numerous methods have been reported but not all are very reproducible. The use of sonication as a new methodology tool for the synthesis of oligomannosides was investigated. A convenient sonication-mediated protocol applicable to glycosylation was developed. The synthesis of oligomannosides such as Man3, Man6, and Man9, was achieved under sonication conditions. The use of less reactive or so-called "disarmed" mannopyranosyl donors, such as acyl and thiophenyl donors, was investigated and interestingly the results gave good yields. These disarmed donors are easy to synthesize but it is difficult to perform glycosylation using traditional methods (low yields and longer reaction time). A fast and convenient method for the synthesis of this compound will be very beneficial in this field. Also, the investigation of the solid phase synthesis of carbohydrates under sonication conditions was conducted and the preliminary results were good. The research investigated a new methodology for the synthesis of complex oligomannosides and oligosaccharides in general and also to improve the glycosylation process where necessary by using sonication methodology and thus establishing an accessible route for the solid phase synthesis of these compounds.

The main objective of this research was to evaluate the effects of chemical treatment and ultrasound processing (sonication) on the fiber composition and rumen degradability of date palm seeds (DPS). For this purpose, five trials were conducted. In the first trial, the effects of treating DPS with 4% sodium hydroxide (NaOH) at different temperatures (23, 50 and 100 0C) and for different times (30, 60 and 356 min) on seeds fiber content and ruminal degradability were evaluated. Relative to untreated seeds, treated seeds had lower (P<0.05) lignin and hemicellulose, and greater (P<0.05) neutral detergent fiber (NDF), acid detergent fiber (ADF) and cellulose content, particularly at high temperatures. The degradability of seeds organic matter (OM) and NDF were greater (P<0.01) in the treated (41.79 and 35.44%) than untreated seeds (24.71 and 22.77; respectively), particularly when incubated at 23 0C. Treatment time, however, had no effect (P>0.01) on seeds OM and NDF degradability.

The emergence of pathogens that are more difficult to inactivate than bacteria, such as C. parvum and G. lamblia, has led to the enactment of more stringent drinking water regulations. The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), promulgated in January 2006, requires increased inactivation of C. parvum. However, increasing the disinfectant dose to enhance inactivation, especially when using chlorine, increases production of carcinogenic disinfection by-products (DBPs) such as trihalomethanes (THMs). As a result of the risks posed by DBPs, the Stage 2 Disinfectants and Disinfection By-Products Rule (Stage 2 D/DBP) was promulgated to limit exposure to DBPs by requiring systems to monitor concentrations at the worst cases locations in the distribution system. The purpose of this study was to evaluate sonication as an alternate disinfection strategy to reduce THM formation. Prior research has demonstrated the inactivation kinetics of sonication. Therefore, if sonication also reduces THM formation, this disinfection technology could help water utilities simultaneously comply with the Stage 2 D/DBP Rule and the LT2ESWTR. Water samples were prepared with varying concentrations of natural organic matter (NOM). THM formation potential reduction was evaluated by treating the water samples with sonication at 20 kHz for 0 seconds, 30 seconds, 60 seconds, 5 minutes and 10 minutes. After treatment, the samples were chlorinated and incubated at 20„aC to form THMs. After incubation times from 1 to 7 days, THMs were extracted, and gas chromatography with electron capture detection was used to quantify THM concentrations in treated and control samples. For experimental water with an NOM concentration of 1 mg/L that was dosed with 6 mg/L of NaOCl, the average THM formation potential reduction was 40% for sonication times of 30 seconds, 5 minutes and 10 minutes. The data for 60 seconds of treatment do not follow the same trends as the other data. Additional study is necessary to increase precision of the experimental data; however, this study supports sonication as a potential method of THM reduction.