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LD2668 .T4 1966 C52 / Master of Science

The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1993-1995 / published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Chitosan has been proposed as a "natural" coagulating agent to solve wastewater problems. The main hindrance in this commercial chitosan application has been its low cost effectiveness. The hypothesis in our research is that chitosan complexes with natural polyanions is more effective than chitosan alone, particularly in recovering low concentration proteins from food processing wastewater. Chitosan (Chi) was reacted with alginate (Alg), pectin (Pec) and carrageenan (Car) ex-situ to obtain chitosan-polyanion complexes (Chi-Pol). Analysis by Fourier Transform Infrared (FTER) spectroscopy confirmed electrostatic interactions as the mechanism for complex formation. Scanning electron microscopy revealed a tight, non-porous structure except for the porous Chi-Car complex. Tests with a bovine serum albumin solution revealed low adsorption rates with slightly higher values for Chi-Car suggesting the need for an improved complexation method. Chi-Pol complexes prepared in-situ at different monomeric weight ratios (MR) were evaluated using pH 6 adjusted Cheddar cheese whey and surimi wastewater (SWW). Complexes used at 30 mg complex/L whey showed higher turbidity reductions than at 10 mg/L. MR had no significant effect on turbidity reduction except for Chi-Alg at 30 mg/L; the value (72 %) at MR = 0.2 was higher than for MR = 0.8. UV-Vis spectroscopy confirmed in-situ complex formation with a preference for the adsorption of specific whey protein fractions. Complexes formed at 0.2 and 0.8 MR were evaluated at two concentrations for the treatment of SWW. Tests at 50 mg/L showed a turbidity reduction of up to 97 % at 24 h with a 81-90 % recovery of SWW proteins. At 150 mg/L, similar efficacy was achieved in only 1 h with turbidity reductions ranging 94-99 % and 78-94 % protein recovery. FTIR analyses confirmed the adsorption of proteins as indicated by similarities in the three amide bands for Chi-Alg recovered solids and untreated SWW. Differential scanning calorimetry (DSC) was employed to study interactions of SWW proteins and Chi-Alg complexes. Untreated and complex bound SWW proteins revealed single exothermic peaks at 23.3 and 38.0°C, respectively. This suggested Chi-Alg and SWW protein interactions increased the thermal stability of SWW proteins. However, further thermal analysis studies are needed to confirm this finding. / Graduation date: 2001

Effects of several important source-related and operation-related factors on particle formation and growth as well as potential particle and dissolved organic matter removal by alum coagulation are described. Two representative natural water sources, with low turbidities and high concentrations of dissolved organic matter, and one commercially available crystalline silica, with defined characteristics, were employed to establish initial aquatic particle and dissolved organic matter conditions. Six experimental variables utilized for evaluation include initial pH, initial turbidity, applied pre-ozonation dose, alum dose, flocculation time and sedimentation time. A bench-scale experimental apparatus with capabilities of ozonation, coagulation, sedimentation and membrane filtration was employed to conduct a series of selected experiments. Each factor investigated in this research proves to be able to inpart, individually or collectively, statistically significant effects on particle formation and growth during alum coagulation. While the addition of model particles shows significant enhancement in particle growth, it fails to demonstrate significant improvement in the removal of dissolved organic matter. On the contrary, effects of pH and alum dose on particle formation and growth are accompanied by corresponding effects on the removal of dissolved organic matter. Pre-ozonation of dissolved organic matter renders the dissolved organic matter more hydrophilic by increasing the number of carboxylic acid functional groups. This phenomenon can significantly improve or impede particle growth as well as dissolved organic matter removal during alum coagulation, depending on raw water chemistry and other operational factors. Alum coagulation under all of the conditions investigated in this research is demonstrably more effective in removing aquatic humic susbtances with higher apparent molecular weights and fewer carboxylic acid functional groups, as opposed to those with lower apparent molecular weight and more carboxylic acid functional groups. The predominant removal mechanisms were found to occur at the beginning stage of the coagulation process; that is, the rapid mixing period. The remaining dissolved organic matter and humic substances can form significant amounts of trihalomethanes upon reaction with chlorine.