Search

Background: The present study aims to explore the feasibility of using flocculation combined with filtration for microalgae harvesting, i.e., Chlorella vulgaris. This is important because microalgae have small sizes and its broth is stable, which makes it difficult to be harvested. The aforementioned facts cause the harvesting cost to be relatively high and become the bottleneck of microalgae processes. Objective: The objective of this research is to find the relation between microalgae concentration, chitosan dosing as a flocculant, and its filterability on membranes. Methods: Research was performed by first cultivating the microalgae in a lab-scale photobioreactor, followed by jar test, flocculation, and filtration experiment. Jar test flocculation was performed using chitosan and microalgae with different concentrations, by simply mixing it in a 100-mL bottle and analyzing the results with UV Vis Spectroscopy. Filtration experiments were performed using lab-made polyvinylidene fluoride membrane, in a 100-mL dead-end filtration cell and in a 5-L tank for submerged filtration. During both filtration tests, filtration flux and fouling were monitored and compared. Results: Results showed that the chitosan concentration needed as a flocculant depends on the microalgae biomass concentration. For the filterability tests, the results proved that flocculation with chitosan enhanced the filterability of the microalgae broth both in dead-end and submerged filtration mode. For the used biomass concentration of around 400 mg/L, the filterability test showed an optimum concentration of chitosan at 7.5 to 10 mg/L, which resulted in a higher filtration flux and lower irreversible fouling in the dead-end filtration and a higher critical flux in the submerged filtration setup. Conclusion: This increased filterability allowed higher fluxes to be operated, thus resulting in a more efficient harvesting process.

Mixed-matrix membranes (MMMs) have been investigated to render energy-intensive separations more efficiently by combining the selectivity and permeability performance, robustness, and nonaging properties of the filler with the easy processing, handling, and scaling up of the polymer. However, truly combining all in one single material has proven very challenging. In this work, we filled a commercial polyimide with ultrahigh loadings of a high–aspect ratio, CO 2 -philic Na-SSZ-39 zeolite with a three-dimensional channel system that precisely separates gas molecules. By carefully designing both zeolite and MMM synthesis, we created a gas-percolation highway across a flexible and aging-resistant (more than 1 year) membrane. The combination of a CO 2 -CH 4 mixed-gas selectivity of ~423 and a CO 2 permeability of ~8300 Barrer outperformed all existing polymer-based membranes and even most zeolite-only membranes.

The occurrence of metal ion exchange in Zn3[Co(CN)6]2 and Cu3[Co(CN)6]2 Prussian blue analogues (Zn-Co and Cu-Co PBAs) was demonstrated for the first time. While Cu(ii) ion exchange easily occurs in Zn-Co PBA, the exchange of Cu(ii) atoms in Cu-Co PBA by Zn(ii) proved to be more difficult. At low to medium Cu(ii) loadings, the catalytic activity of the exchanged PBAs for the A3 coupling reaction of benzaldehyde, piperidine and phenylacetylene was higher than that of the bimetallic PBAs and that of multi metal PBAs of similar composition prepared by co-precipitation. This result showcases the benefits of the ion exchange process as a preparation method of PBA catalysts, since it is believed to lead to the incorporation of the desired metal in a more accessible position for reactant molecules. At higher Cu(ii) loadings, ion exchange with Cu(CH3COO)2·H2O also resulted in co-incorporation of CH3COO-. This incorporation considerably boosted the catalytic activity of the PBAs by providing a basic function that facilitates the C-H activation of phenylacetylene. The most active of the studied PBAs, catallytically outperforms other Cu(ii) based A3 coupling catalysts and completely suppresses the activity for the homocoupling of phenylacetylene, even under oxidative conditions. Furthermore, the basicity of the PBAs was investigated in the nitroaldol (Henry) reaction, where a clear effect of the presence of CH3COO- was observed. The CH3COO- containing PBAs exhibited an activity three times higher than the rest of the PBAs. The presence of the basic CH3COO- groups represents the first case of basic functionalization of PBAs.

Clean water shortage is one of the global major concerns. To overcome this problem, membrane-based desalination process, such as reverse osmosis (RO) have been developed in the recent years. However, this technology operates at a high hydraulic pressure to overcome the seawater osmotic pressure, making this desalination process still relatively expensive. Recently, forward osmosis (FO) process has become increasingly attractive over RO since it is capable to produce clean water by using natural osmotic pressure as the separation driving force provided by draw solution (DS), which eliminates the usage of high hydraulic pressure. DS is a critical material in the FO process, playing a key role in determining the separation performance and energy cost. After the FO process, DS requires a regeneration step to reconcentrate it to its initial state. As a result, the development of effective draw solution is essential for the advancement of FO technology.In this master thesis work, the feasibility of light-responsive TiO2 nanoparticles was investigated as a draw solute in the FO process. Several dispersions of TiO2 nanoparticles in demineralized water (DI) with different concentration were prepared. These dispersions were tested for their FO performance with DI and saline water as feed solutions, respectively. The colloidal stability of TiO2 nanoparticles was achieved by deviation from the isoelectric point of the nanoparticles with a pH adjustment from 6 to 4.5.The effects of TiO2 nanoparticle concentration, ultrasonication time, UV irradiation, primary particle size, and FO membrane orientation were tested using DI water as the feed solution. A concentration of 20 g / L of TiO2 was found as the optimum concentration for FO performance. The generated water flux was not linearly dependent on the nanoparticles concentrations but appeared to be dependent on how well the nanoparticles were dispersed. The effect of UV was investigated by testing the same amount of TiO2 with and without a UV treatment. The UV treated and sonicated before and after UV treatment generated a significantly higher water flux than the pristine one. The effect of the primary size of the nanoparticles was expressed in their response to UV radiation. In comparison to P5 (=5 nm), P15 (=15 nm), and P25 (= 25 nm), P5 showed the highest UV response. The effect of membrane orientation, namely pressure retarded osmosis (PRO) and forward osmosis (FO) mode were tested and the PRO mode resulted in a significantly higher water flux than FO mode due to its low concentration polarization effect, which consequently led to higher driving force than FO mode. The TiO2 nanoparticles draw solutions were also characterized using DLS and FTIR to investigate the effect of UV on the particle size and hydrophilicity respectively. The DLS result showed a larger hydrodynamic diameter after UV treatment comparing to the pristine one but after ultrasonication, the hydrodynamic diameter was significantly decreased. This result confirmed that UV treatment promoted the agglomeration of nanoparticles. Longer UV irradiation time led to a moderately more hydrophilic surface than the shorter period as confirmed from the FTIR result. The highest water flux generated with DI water feed solution by using the optimum concentration and parameters without any functionalization or capping agent was 15.8 LMH and this is quite promising.

Salinity Gradient Power - Reverse Electrodialysis (SGP-RED) is a promising membrane-based technology to harvest the energy of mixing from solutions of different ionic concentration. Unfortunately, currently available commercial ion exchange membranes – being not specifically designed for RED – are far from satisfying the requirements of this operation, especially when operated with hyper-concentrated brines. In this work, novel sulfonated polyethersulfone (sPES) cation exchange membranes (CEM) were prepared by phase inversion method and tested under high salinity gradients. Use of 5 M NaCl electrolyte for immersion precipitation coagulation bath facilitated the self-standing membrane formation as a result of the electrostatic interaction between the fixed charged groups and electrolyte solution. Microscopy results revealed that dense or asymmetric membranes with non-connected pores were formed by solvent evaporation or immersion precipitation, respectively. The membranes were characterized for ion exchange capacity, water uptake, charge density and thickness, and further studied by electrochemical impedance spectroscopy. The obtained properties of the newly developed membranes were subsequently compared to those of commercial CMX (Neosepta, Japan) and Fuji-CEM-Type 1 (Fujifilm, The Netherlands) membranes. The asymmetric membranes resulted in a very low resistance especially for high ionic gradients but relatively low permselectivity, while dense membranes still had a low resistance compared to commercial membranes and exhibited high permselectivity. Interestingly, in terms of power density, lab-made membranes outperformed the commercial benchmarks when tested for RED applications with brackish water (0.1 M NaCl)/hypersaline brine (4 M NaCl) feeds; power density of CMX and Fuji-CEM-Type 1 were 3.23 and 3.77 W/m2, respectively, while power density of asymmetric and dense sPES membranes were 3.64 and 3.92 W/m2, respectively.