When: Wednesday, April 17th, 2013 at 1:15 PM,
Where: TRC Room 206
Student: John Bendick
Dissertation Title: HIGH SHEAR ROTARY MEMBRANE SYSTEM ENHANCEMENTS FOR NAVAL WASTEWATERS
Navy ships are floating cities, requiring infrastructure and resources while generating various wastes: bilge water, black/graywater, industrial wastewaters and solid residuals. Treatment equipment selection is based not only on reliability, operational ease and cost but also on weight and cube. Current treatment systems would benefit from efficient solids removal; however, standard equipment has not been effective, necessitating developing improved technologies.
Membranes systems simple operation and dependability fits shipboard requirements. The high shear rotary membrane system (HSR-MS) has shown a superior ability to remove contaminants and concentrate solids. However, low throughout confines the technology to applications without space limitations. The broad research goal seeks to overcome the throughput and space limitations allowing for shipboard HSR-MS implementation.
HSR-MS often operates at high rotation (w) to improve flux (J) by maximizing shear. However, an understanding of J, w, diameter (D), and pressure provides conflicting relationships. A higher w and larger D maximizes shear (increases J), but also increases rotationally induced backpressure (decreases J). This means membrane inner areas operate under the highest pressure and lowest shear; while membrane outer areas operate under the lowest pressure and highest shear (opposite of what is desired).
To improve HSR-MS performance, J and/or D must increase. Larger D discs require operation with lower w, leading to lost shear (decreased J). This work proposes employing continuous surface cleaning (CSC) and/or backpulsing (BP) to overcome reduced shear and lost J facilitating using larger D discs.
Results showed J was highly dependent on w and D. For every 100 rpm w increase, J increased by 26 L/m2-hr. Flow (Q) was more sensitive providing ~1% increase in Q per mm D increase. The outer membrane third provided ≥ 50% of the total Q, while the inner third provided ~15%. Both BP and CSC produced higher J, proving most beneficial at lower w. J improved by ~75% for w<500 rpm compared with ~25% for w>500 rpm as flow conditions shifted from laminar to turbulent. Membrane inner area J improved with CSC or BP, but the outer area still produced the bulk of overall flow (~80%). Combing experimentally derived flux prediction models and BP/CSC flux improvements with commercially available membrane sizes show that larger D, slower w discs can provide a 25-50% HSR-MS disc count reduction.