Year

2017

Degree Name

Doctor of Philosophy

Department

School of Civil, Mining and Environmental Engineering

Abstract

Forward osmosis (FO) is an emerging membrane separation technology that has the potential to serve as a game changer in wastewater treatment. FO-based processes can simultaneously produce high quality effluent and pre-concentrate wastewater for anaerobic treatment to facilitate the recovery of energy and nutrients. Complex wastewaters can be directly pre-treated by FO, and fresh water can be produced when FO is coupled with a draw solute recovery process (i.e. reverse osmosis or membrane distillation). By enriching organic carbon and nutrients for subsequent biogas production, FO extends the resource recovery potential of current wastewater treatment processes. Despite this potential, FO research is still in its infancy, and applications of FO for simultaneous treatment and resource recovery from municipal wastewater are developing. This thesis focuses on investigating and optimising the use of FO membranes for resource recovery applications, with respect to, integrating FO with anaerobic treatment, draw solute selection, mitigating salinity build-up, and membrane fouling.

A selection protocol was developed to determine suitable draw solutes for FO membrane systems that integrate anaerobic treatment for biogas recovery. Draw solutes were evaluated in terms of their ability to induce osmotic pressure, water flux, and reverse solute flux. The compatibility of each draw solute with subsequent anaerobic treatment was assessed by biomethane potential (BMP) analysis. Ten draw solutes were evaluated at the same osmotic pressure (i.e. 30 bar) and each draw solute exhibited diverse flux performance. The results showed a strong influence of draw solute physiochemical properties on water and reverse solute flux. This correlation suggested that a trade-off exists between the selection of highly diffusive draw solutes that display high water flux, and those which show a low reverse solute flux. Sodium acetate (NaOAc) and magnesium acetate (Mg2OAc) displayed unique behaviour compared to other draw solutes, as a high water flux and reverse solute flux selectivity was achieved. BMP analysis indicated that ionic organic draw solutes (e.g., NaOAc and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na)) were most suitable when integrating FO with anaerobic treatment. On the other hand, the reverse solute flux of inorganic draw solutions (e.g. sodium chloride (NaCl)) appeared to inhibit methane production by 11% in FO pre-concentrated wastewater at the concentration corresponding to a ten-fold concentration factor.

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