Optimization of Reverse Osmosis Brine Treatment using Direct Contact Membrane Distillation and Membrane Fouling Mitigation using Graphene Nanoplatelets

  • Shefaa Mansour

Student thesis: Master's Thesis

Abstract

As desalination industries continue to grow, so does the high salinity byproduct (brine) that is being discharged into the sea harming the marine environment. The need for cost effective management solutions for the protection of the marine environment has become essential. In this study, a pilot scale direct contact membrane distillation (DCMD) system was used for the management of reverse osmosis (RO) brine. Optimization experiments were carried out to determine the best conditions resulting in the optimum water flux and salt rejection with the lowest energy consumption. Using the statistical software Minitab for the design of experiments (DoE), the operating conditions such as the feed inlet temperature (Tf = 75-90 oC), feed flow rate (Qf = 30-90 L/h) and permeate flow rate (Qp = 30-54 L/h) and feed concentration (Cf = 50,000-80,000 ppm) were varied totaling 31 experiments. At experimental conditions of Tf, Qf, Qp, and Cf of 85 oC, 75 L/h, 48 L/h and 57,500 ppm, the highest permeate flux of 16.7 L/m2 h (LMH) was reported with a salt rejection, gained output ratio (GOR) and specific thermal energy consumption of 99.5%, 1.0 and 152 kWh/m3 , respectively. The experimental results of this study provided a better understanding of the DCMD operation working towards the zero salt-water discharge to the environment. One of the major drawbacks associated with the operation of DCMD systems is the fouling of the hydrophobic membranes which impairs their performance. As a result, this study further aimed to investigate the impact of the coating of graphene nanoplatelets onto the membrane for the potential improvement of the polyethylene (PE) membrane characteristics. Different nanoparticle concentrations were used in which the surfaces of the graphene/PE membranes were characterized through different methods such as contact angle (CA), liquid entry pressure (LEP), mean pore size (MPS), scanning iv electron microscope (SEM) and infrared spectroscopy (FTIR) analytical methods then compared to the virgin membrane. The hydrophobicity of the membrane was improved by which the CA was increased from 116o to 120-131o and an increase in the LEP from 8 psi to 20.7-28.1 psi with the coating of graphene concentrations ranging from 0.08 to 0.2 weight percentages. These coated membranes were tested for their improvement in the treatment process of brine using the DCMD upon comparison with the commercial PE membrane. For the fouling mitigation study, the results at 0.08 and 0.16 wt% coating indicated flux stability over a 10-hour operation when compared to the virgin membrane through which 27% flux reduction was observed in the commercial membrane whereas 23% reduction in membrane fouling was reported at 0.08 wt% and 29% at 0.16 wt%. The great impact of graphene on the membrane fouling mitigation in MD operations allowed for an overall improvement in the efficiency of the MD process. It could be concluded that membrane distillation as an emerging technology has a great potential for seawater desalination in the UAE. Further investigations on fouling mitigation should also be explored.
Date of AwardMay 2017
Original languageAmerican English
SupervisorShadi Hasan (Supervisor)

Keywords

  • Desalinization
  • Reverse Osmosis
  • High Salinity Byproduct
  • Brine
  • Contact Membrane Distillation.

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