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published_or_final_version / Civil Engineering / Master / Master of Philosophy

archives@tulane.edu / N/A / 1 / Savannah Steadman

In this study, Smiles?? sorptivity-diffusivity numerical analysis is demonstrated to offer a comprehensive description of dead-end constant-pressure compressible cake filtration for water treatment. In addition to providing an insight on filtration performance and cake behaviour in terms of cake hydraulic permeability and compressibility in good agreement with the results derived using Ruth??s conventional cake filtration theory, the sorptivity-diffusivity model can be used to gain further information on depth-dependent local cake properties and extend our knowledge on the effect of feed suspension conditions (including solution composition, coagulant dosage and mixing) on the characteristics of the particulate assemblages (including size, structure and strength). Feed suspension conditions and primary particle properties exert significant effect on the characteristics of particles in suspensions and the resultant particulate assemblages. In the non-coagulated latex systems, an increase in ionic strength resulted in a suppression of the electric double layer of latex particles as indicated by a significant drop in the zeta potential of the feed suspension which lead to a dramatic reduction in cake hydraulic permeability. In the non-coagulated montmorillonite systems, feed suspensions with high ionic strength (1 M Na+, 50 mM Ca2+ and 50 mM Fe2+) were associated with larger suspended solids which appeared to form assemblages with nematic structures that are denser yet more permeable when compared to those with low ionic strength (0.1 M Na+, 1 mM Ca2+ and 2 mM Fe2+) which appeared to form highly ??cross-linked?? voluminous honeycomb type gel of very low permeability. Pre-coagulation of latex and montmorillonite suspensions with Al-based coagulants (alum and ACH) both resulted in formation of very large flocs which subsequently formed highly permeable solid assemblages. In the latex systems, the ratio of optimal alum to ACH dose was approximately 5:1 on a total coagulant mass basis and 1.3:1 as Al while the ratio of optimal alum to ACH dose was as high as 22:1 on a total coagulant mass basis and 6:1 as Al in the montmorillonite systems. Although both alum and ACH resulted in comparable filtration performances, the distinction in Al concentration and results of local cake properties analysis indicated the presence of different cake structures presumably due to the formation of different Al species.

Sustainable algae biofuel production is rising in demand, and the need to establish an efficient and proper algae harvesting method is extremely essential. Membrane filtration technology seems to be the most promising as a solid-liquid separation process. However, fouling seems to be the major problem for membranes. There is limited research on how to solve the problem of fouling, and cake buildup inside the membranes. A novel membrane design is required to solve the problem of fouling and cake buildup inside the membranes. The objective of this research is to construct a novel two way membrane design for algae biomass harvesting and water recycling. The methods used include culturing algae species, filtering them through the membrane module, and sample analysis for determining the water quality. The results show that the present filtration model had no fouling, or cake buildup as opposed to the previous filtration model. The present model permeate has a very low optical density of 0.007 absorbance at 750 nanometers. This result shows that permeate is completely devoid of algae.

In this study, Smiles?? sorptivity-diffusivity numerical analysis is demonstrated to offer a comprehensive description of dead-end constant-pressure compressible cake filtration for water treatment. In addition to providing an insight on filtration performance and cake behaviour in terms of cake hydraulic permeability and compressibility in good agreement with the results derived using Ruth??s conventional cake filtration theory, the sorptivity-diffusivity model can be used to gain further information on depth-dependent local cake properties and extend our knowledge on the effect of feed suspension conditions (including solution composition, coagulant dosage and mixing) on the characteristics of the particulate assemblages (including size, structure and strength). Feed suspension conditions and primary particle properties exert significant effect on the characteristics of particles in suspensions and the resultant particulate assemblages. In the non-coagulated latex systems, an increase in ionic strength resulted in a suppression of the electric double layer of latex particles as indicated by a significant drop in the zeta potential of the feed suspension which lead to a dramatic reduction in cake hydraulic permeability. In the non-coagulated montmorillonite systems, feed suspensions with high ionic strength (1 M Na+, 50 mM Ca2+ and 50 mM Fe2+) were associated with larger suspended solids which appeared to form assemblages with nematic structures that are denser yet more permeable when compared to those with low ionic strength (0.1 M Na+, 1 mM Ca2+ and 2 mM Fe2+) which appeared to form highly ??cross-linked?? voluminous honeycomb type gel of very low permeability. Pre-coagulation of latex and montmorillonite suspensions with Al-based coagulants (alum and ACH) both resulted in formation of very large flocs which subsequently formed highly permeable solid assemblages. In the latex systems, the ratio of optimal alum to ACH dose was approximately 5:1 on a total coagulant mass basis and 1.3:1 as Al while the ratio of optimal alum to ACH dose was as high as 22:1 on a total coagulant mass basis and 6:1 as Al in the montmorillonite systems. Although both alum and ACH resulted in comparable filtration performances, the distinction in Al concentration and results of local cake properties analysis indicated the presence of different cake structures presumably due to the formation of different Al species.

Surface waters subject to algal blooms have a high rate of fouling water treatment filtration membrane. These waters typically contain high concentrations of hydrophilic organic carbon compounds such as proteins and polysaccharides. These compounds have been found to contribute greatly to membrane fouling. In this study the fouling propensity, and the components of the fouling layer, for microfiltration (MF) and ultrafiltration (UF) membranes, were characterised for samples taken from a wastewater treatment plant with lagoons prone to algal blooms and a blue-green algae culture (Anabaena circinalis). It was found that the organic carbon compounds released during the growth phase (EOM) of Anabaena circinalis have a similar fouling propensity for UF than those released during the lysis phase (AOM), and a slightly higher fouling propensity for MF. However, due to the presence of higher UV-absorbing hydrophilic compounds, higher concentration of intracellular proteins and/or humic acid-like matter in the AOM, irreversible fouling was significantly higher during the lysis phase.

D.Phil. (Chemistry) / Polycaprolactone (PCL), a linear, biodegradable polymer, and ethylene vinyl acetate (EVA), a branched copolymer, were used to prepare PCNs via the melt-blending method. Organoclay of the type Cloisite® 20A (C20A) and bentonite clay were used as fillers. The results show that the structure of a polymer matrix plays a significant role towards compatibilisation with the silicate layers of the clay. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed an exfoliated-intercalated mixed morphology for the PCL matrix. However, for the EVA matrix, silicate layers agglomerated to form tactoids and resulted primarily in an intercalated morphology. Fourier transform infrared (FT-IR) spectroscopy was used to determine the nature of the interactions between the polymer and the filler. The thermal properties were investigated using thermogravimetric analysis (TGA) and indicated that, with an increase in clay loading, the thermal stability was reduced for both matrices, notwithstanding the type of polymer or clay used. Using EVA and C20A, this study revealed that more exfoliated nanocomposite structures can be obtained by using a modified solution-blending technique. This technique is a hybrid of the melt-blending and solution-blending methods. When compared to the melt-blending method, the modified solution method was found to be an efficient method for producing nanocomposite strips with uniform dispersion of the clay at organoclay loading of 8% and crystallinity by extrusion. However, the melt-blending method produced nanocomposites with high porosity, intercalation and thermal stability whereas the modified solution-blending technique resulted in more intercalated-exfoliated morphology, but less porosity and thermal stability. Despite the positives drawn from the modified solution method, the melt-blending method was used throughout for nanocomposites intended for application in water treatment. This was done because the solution used in the modified solution method could not be completely removed from the nanocomposite. Organic solvents can have a negative effect on the environment and human life.

Ph.D. (Chemistry) / The ultrafiltration membranes presented in this study were synthesized using the phase inversion method by casting on a nonwoven fabric. The polymer solutions were mixed with synthetic and bio additives in order to improve the resultant membrane performance. Synthetic additives (polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP)) were compared with a novel and cheap bio additive, lignin. Based on the knowledge that the additives must be soluble in water in order to increase the pore sizes of the membranes, sodium hydroxide was used to elute residual additives that remain in the membrane during coagulation. In order to trace the residual additives remaining, ATR-FTIR was used. Contact-angle analysis and water-absorption experiments were used to elucidate the hydrophilic properties of the prepared membranes. Membranes modified with lignin (Lig) were found to absorb more water (94% water uptake) when compared to the other membranes. In general, the contact angles were found to be low for membranes that were treated with NaOH. Membrane permeability followed the trend, Lig_PSf>PVP_PSf>PEG_PSf which is similar to the trend followed during water uptake. Pore size and pore distribution analysis showed that membranes modified with lignin and PVP had a narrow range (had pore sizes ranging from 10 to 24 nm) compared to that of PEG-PSf membrane (which ranged from 2.5 to 22 nm). A Robeson plot showed that Lig_PSf membranes had high separation factors regardless of the size of the solute being rejected. This study shows the possibility of using cheap and readily available additives to increase the performance of membranes......

To minimize membrane fouling many water treatment plants pre-treat water prior to microfiltration (MF) or ultrafiltration (UF). Coagulation/flocculation/sedimentation is a common form of pre-treatment, but little research has been conducted on floatation as a part of the pre-treatment. The objective of this thesis is to compare pre-treatment with floatation and with sedimentation for Ottawa River water, a typical Northern Canadian water with a high natural organic matter (NOM) content and a large hydrophobic (HPO) NOM fraction. Fouling tests consisted of multiple filtration/backwashing cycles performed by an automated bench-scale UF hollow fiber membrane system. Test were conducted with Ottawa River water (ORW) and ORW subjected to three different types of pre-treatment conducted at closely-located full-scale water treatment plants, including one using floatation. Both Alum pre-treatments resulted in decreases in NOM (63% and 68% TOC) and HPO NOM (56% and 68%TOC) which helped to reduce fouling. However, the remaining NOM and HPO NOM still caused significant hydraulically and chemical irreversible fouling. The water pre-treated with floatation produced the least severe hydraulically irreversible fouling for all experiments while Raw ORW produced the highest. During the early stages of membrane filtration (~10 hours), the TMP sharply increases which may imply that adsorption is dominant. Statistical analysis during the initial stages of filtration showed that the HPO fraction of NOM was linked to hydraulically irreversible fouling, which may be attributed to adsorption. Raw ORW also had the highest hydraulically reversible fouling while all pre-treatments were able to reduce this type of fouling. Statistical analysis suggested that the transphilic (TPI) fraction of NOM and particulate organic carbon (POC) were responsible for hydraulically reversible fouling during subcritical flux experiments, which may be attributed to cake formation on the membrane surface. It was found that for all waters and experiments, hydraulically irreversible fouling was greater than hydraulically reversible fouling. This may be because of the high HPO concentrations in the ORW. Hydraulically reversible fouling and backwash efficiencies were found to fluctuate with time. It is hypothesised that the cake formation adheres to the membrane surface and is not fully removed until enough backwash pressure has developed. Further investigation into alternative cleaning procedures is required as the NaOH cleaning was not very effective for some of the pre-treated waters.