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Development of a hybrid wheat straw adsorption and microfiltration system for oily wastewater treatment

  • Author / Creator
    Suresh, Kavya
  • Effective, economical, and sustainable treatment technologies are highly desirable for treating oily wastewater generated from various industries as well as municipal and commercial establishments. The performance of traditional polymeric membranes is largely constrained by their high fouling tendency to oil and hence renders this highly efficient technology for separating emulsified oil inappropriate. Therefore, a unique integrated treatment train coupling polyamide-imide (PAI) microfiltration membrane with an adsorption system using a chemically modified agricultural by-product, wheat straw, was implemented to decrease the fouling and increase the membrane life span. In the first work, we modified wheat straw through a simple radical polymerization to graft biocompatible PMMA in order to enhance the hydrophobicity. The substantial increase in oil adhesivity after grafting PMMA was evident from the 0º oil contact angle for PMMA-g-WS film. Oil absorptivity was thoroughly evaluated by batch oil adsorption study using variable adsorbent dosages and oil emulsion concentrations. The PMMA-g-WS exhibited the highest oil adsorption capacity of ca. 1129 mg/g, as determined by the kinetic equilibrium study. The adsorption capacity was explicitly high compared to that of the pristine (ca. 346 mg/g) and pre-treated (ca. 741 mg/g) samples due to exposure of numerous mesopores and micropores and which made an avenue for deeper oil penetration. The shape of the hysteresis loops indicated the predominance of mesopores in all three samples, which was also confirmed by the pore width values ranging from 1.6-32 nm. In addition, the strong hydrophobic interactions due to the grafted surface functionalities significantly added to the oil adsorptivity. Langmuir and Freundlich adsorption isotherms were applied to evaluate the adsorption mechanism. The experimental data fitted well with Freundlich isotherm, indicating a multilayer adsorption process and heterogeneity of adsorption sites. On the other hand, they also fitted well with the pseudo-second-order rate equation with R2 as high as 0.999. This also indicated indicate multilayer adsorption where the initial rate of monolayer adsorption is faster than the rate of subsequent multilayer formation. The high oil adsorption capacity of the PMMA-g-WS makes it a very promising material oily wastewater treatment. This will simultaneously resolve issues with the treatment of oily wastewater and the handling of abundant quantities of waste wheat straw. In the second work, the breakthrough curves for different oil concentrations were obtained using a bench-scale set up of a fixed-bed column. The oil removal efficiency decreased only by 18% during the subsequent cycle after regeneration for 100 ppm oil concentration. This system was then coupled with the PAI membrane fabricated by the non-solvent induced phase separation technique. Polyvinylpyrrolidone (PVP) was blended to enhance the hydrophilicity. The flux decline was as low as 4% for 100 ppm feed with pre-treatment and 40% for the feed without pre-treatment. More importantly, the pre-treatment increased the FRR from 84% to 95% in the case of 200, 300, and 500 ppm feed. The performance of commercial PES membranes was compared with the fabricated PAI. They exhibited a higher flux recovery ratio (FRR) for the pre-treated feed in case of low oil concentrations. Higher oil concentrations, however, caused irreversible fouling of the membrane by pore blocking, as a result of which the FRR was very poor after regeneration. Therefore, the results indicated an exceptional improvement in flux and FRR for pre-treated oil emulsions. Also, the PAI membranes exhibited robust performance during the consecutive two cycles; each provided 100% removal efficiency for oil. The integration of adsorption with naturally derived eco-friendly and cost-effective wheat straw grafted with PMMA and PAI microfiltration system offered outstanding oil removal and prolonged the membrane lifespan at the same time as the membrane fouling was diminished.

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  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Master of Science
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