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Title: Hybrid sorbent-ultrafiltration systems for the removal of hormones and fluoride from water
Author: Akanyeti, Ime
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2013
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The presence of trace contaminants in drinking water resources has been related to adverse health effects in living organisms and humans. Current technologies do not adequately remove these contaminants from water and/or require high energy supply. Exploring low cost, low energy processes in order to eliminate trace contaminants is essential considering that access to clean drinking water and energy is becoming more challenging in many parts of the world. Hormones and fluoride are the two contaminants studied in this research and hybrid systems which combine sorption with low pressure ultrafiltration are proposed for their removal. Sorption is a promising removal mechanism if efficient sorbents and operational conditions are selected, however, the introduction of sorbent materials can cause fouling in ultrafiltration. Fouling reduces the membrane permeability and increases the energy requirement of the system. The overall aim is to study the proposed hybrid sorbent- ultrafiltration systems in terms of contaminant sorption capacity and membrane performance. The systems are tested under varying sorbent size (52-3000 nm for hormone, < 38-500 μm for fluoride removal) sorbent concentration (1.7-84 mg/L for hormone, 1-50 g/L for fluoride removal), sorbate concentration (100 ng/L hormone and 5-500 mg/L fluoride) and solution pH (3-12). The thesis can be split into two parts: one part for hormones and the other for fluoride. In the first part, a hybrid polystyrene nanoparticle-ultrafiltration system is investigated for hormone removal. Polystyrene nanoparticles are employed as they provide a large active surface area for the sorption and they can easily be manufactured in different sizes and with various functional groups. The results show that the system can only compete with the existing nanofiltration/reverse osmosis membrane systems if the sorption capacity of the polystyrene nanoparticles is increased. For this reason, carboxyl functionalized polystyrene nanoparticles were also tested. Contrary to expectations, even less hormone sorption is achieved with the functionalized particles. Further investigation of other functional groups such as amine/amidine for their hormone sorption capacity is recommended. In the second part, laterite and bone char are selected as two sorbents for the hybrid sorbent-UF system for fluoride removal as they are locally sourced, low cost materials in parts of Ghana and Tanzania, respectively, where fluoride contamination is a major problem. The sorption capacity and the membrane fouling of the hybrid system with the two selected sorbents are compared. Fluoride sorption capacity of the bone char system is higher than the laterite system and this is attributed to the difference in the available surface area. The fouling of the membranes operated with laterite at high initial fluoride concentrations and alkaline solutions is linked to the precipitation of iron and aluminium complexes. With further system optimization, both hybrid laterite and bone char systems show the potential to be viable solutions for fluoride removal, noting that the bone char system is more feasible for high fluoride concentrations above 10 mg/L. Based on lab scale experimental results, two hybrid laterite-ultrafiltration systems are designed to be tested in Ghana. The two systems, one with submerged hollow fibre and the other with direct dead end tubular ultrafiltration membrane modules, are operated with real surface and ground waters. The findings indicate that the amount of sorption obtained in the field is lower than that which is obtained with laboratory experiments due to the presence of interfering co-ions in the real waters and differences in membrane systems. The systems also show the potential to remove arsenic, uranium and lead. The system with hollow fibre membranes can be suggested as an appropriate system for ground water applications as it did not experience any fouling and the investment cost could be lower compared to the tubular membranes. However, if the surface waters are to be treated with the proposed hybrid system, the tubular membranes offers a system with no fouling. The hybrid laterite-UF system shows to be a promising treatment technology for fluoride contaminated waters in Ghana.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available