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UBC Theses and Dissertations

Development and analysis of membrane contactor for resource recovery from wastewater Dutta, Abhishek

Abstract

Dissolved ammonia and methane can be present in wastewater, particularly in effluents from anaerobic bioreactors. Recovery of these compounds from wastewater has garnered interest due to their potential as a fertilizer (NH₃) and biofuel (CH₄). Isothermal Membrane contactors (MCs) are effective in recovering both resources from wastewater but possess drawbacks such as (i) production of overly acidic product and potential for fouling (for NH₃) (ii) low-quality biogas and high energy consumption (for CH₄). In this thesis, I address each of these challenges. Firstly, I study the impact of acid strength (H₂SO₄) on NH₃ recovery by experimentally validating an enhanced mass transfer model that describes the transfer resistance of NH₃ arising from an incomplete acid-base reaction at the draw-membrane interface. The model is then extended to establish that (1) a trade-off exists between acid strength and NH₃ flux, (2) acid concentration can be optimised to achieve usable ammonium salt as fertilizer. To study the extent of fouling and its effect on NH₃ recovery, I employ anaerobically digested food wastewater as feed. With >95% NH₃ recovery, minimal membrane fouling was observed. By performing MCs in isothermal and non-isothermal modes, I identified the deterministic role of transmembrane water vapor flows on fouling. Subsequently, >70% NH₃ recovery was observed from the fouled membranes, indicating process robustness of MCs even when fouled. I then present a solvent-based membrane contactor for dissolved CH₄ recovery. Using a fabricated omniphobic membrane, I demonstrate ≥90% CH₄ recovery from CH₄-saturated wastewater. A comparative energy analysis suggests that this process can enable net energy production, which outperforms other dissolved CH₄ recovery techniques. Finally, using experiments and a mass transfer model, I show that the amount of recovered CH₄ is higher at lower temperatures, flux across the membrane is unaffected by presence of CO₂ (another constituent of biogas), and the process has a considerable fouling tolerance. I also show that producing a biogas with a higher CH₄ fraction is attainable from anaerobic effluents. The findings from this thesis aids advances in MCs for NH₃ and CH₄ recovery by considering the impact of performance limiting parameters on product yield, quality, and membrane performance.

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Attribution-NonCommercial-NoDerivatives 4.0 International