Solids Separation and Concentration of Shipboard Wastewaters and

1
Solids Separation and Concentration of Shipboard
Wastewaters and Residuals by a High-Shear Rotary
Membrane System (HSR-MS)
Summary of Process/Technology
Introduction

• The HSR-MS system is a barrier technology that
  uses ultrafiltration (UF) or microfiltration (MF)
  membranes to separate the solute (e.g., solids,
  oils, fibers, colloidal particles) from the
  influent (Fig. 1). With proper membrane
  selection/process operation, the effluent is
  practically solids free.
• During waste treatment solute builds up at the
  membrane surface, increasing the resistance to
  permeate flow. In conventional systems (e.g.,
  tubular systems, Fig. 2.) solute buildup is
  reduced by pumping the feed at high flow
  rates/cross flow velocities so that the membrane
  surface is scoured/cleaned. At high feed
  concentrations/viscosities pumping becomes
  difficult and most of the energy is wasted
  because the entire feed volume is energized.
• In the HSR-MS, which consists of stacked rotating
  membrane disks, turbulence/shear is produced by
  membrane rotation and the energy needed to clean
  the surface is applied exactly where it is needed
  (i.e., membrane surface, Fig. 3).
• To further enhance turbulence/ shear at the
  membrane surface, stationary turbulence promoters
  are located on each side of the membrane disk.
• The decoupling of the feed delivery/pressurization
  from turbulence/shear promotion allows the
  HSR-MS to produce highly concentrated wastes, be
  operated at lower pressures, reduce boundary
  layer compaction/pore plugging, increase membrane
  life, and decrease cleaning frequency/residuals
  production.

Navy ships generate a variety of wastes bilge
water, blackwater, graywater, shipboard
industrial wastes and solid residuals from
existing treatment systems. Many of the Navys
current waste treatment systems would benefit
from the efficient removal of solids. However,
available solids removal technologies have not
been particularly effective, necessitating the
development of improved solids removal
technologies. The High Shear Rotary Membrane
System (HSR-MS) has shown superior abilities to
separate and concentrate Navy and non-Navy
wastewater solids (e.g., oily wastes, underwater
hull cleaning sludge, non-skid deck cleaning
wastewater, tank car latex waste, metal hydroxide
suspensions). However, HSR-MS has been confined
to land-based applications where space is not a
critical design consideration. In this work
methods will be developed to increase the
permeate flux and modify the HSR-MS configuration
so that it can be placed shipboard.
Permeate
Objective and Goals

• The objective is to develop a robust shipboard
  treatment system that can be used to treat a
  variety of Navy solids-bearing wastewaters and
  residuals. Specific goals are
• Increase HSR-MS permeate flux/decrease system
  size by
• employing back pulsing and continuous
  membrane cleaning.
• 2. Increase the active membrane packing
  density (active
• membrane area/system footprint/space) by
  using larger
• diameter overlapping disks.
• 3. Conceptually design, fabricate and test a
  shipboard HSR-MS
• that incorporates back pulsing, continuous
  membrane
• cleaning, larger disks, and disk overlap.
• The shipboard HSR-MS will have an increased
  waste
• treatment throughput, a smaller
  footprint/space requirements,
• be potentially portable, and constructed of
  lighter weight
• and cheaper materials.

Feed (Cross-flow scours surface)
Pressure

Permeate
Fig. 3. High Shear Rotary Membrane
Fig. 2. Conventional Cross-flow Filtration
Disk Size (r)-Rotation Speed (?)-Pressure (P)

• Net transmembrane pressure (PNet-TMP) is a (r
  ?)
• because Pback develops from rotating the
  membrane
• disk (Fig. 4)
• If r or ? are too large, a negative P can result
• Decrease in active membrane area
• Potential membrane destruction
• If lower ? is used, a larger disk is possible
• Decreasing ? increases CP/cake buildup
• Increase in membrane area is offset by lower J
• Increasing ? requires higher TMP
• UF/MF operate best at low TMP (minimizes
• compaction of solute layer)
• Need to operate with lower ? and TMP, but
• maintain high flux
• Need alternatives to reduce the solids layer
• resistance to allow the use of lower ? and
  TMP
• Back-pulsing
• Continuous mechanical cleaning

Benefits

• A shipboard HSR-MS can
• 1. More efficiently remove solids prior to
  existing treatment
• processes.
• 2. Directly replace problematic treatment
  systems with a
• more robust, higher efficiency system.
• 3. Concentrate sludge, waste oil and process
  residuals.
• The ultimate benefit to the DoD is a robust
  barrier
• technology that is easy to operate, not
  labor intensive, is
• capable of being cleaned in place, and can
  withstand harsh
• environments.

Fig. 4. Disk Size-Rotational Speed-Pressure
Relationship
2
Tracy Carole1, Momar Seck1, John Bendick2 and
Brian E. Reed3, 1NSWC Carderock Division,
Bethesda, MD, 2NAVICP, Mechanicsburg, PA,
3Department of Civil and Environmental
Engineering, Univ. of Maryland, BC
Testing Approach (Year 1 in Red)
Stirred Cell Test Results
Fig. 5. SCT Apparatus
Fig. 6. Example SCT Data for Black/Gray
Wastewater
Fig. 7. Summary of Black/Gray WW Tests - Avg. J
Permeate Turbidity
Task 1. Develop Synthetic Wastes

• Based on discussions with Navy personnel, four
  wastes were identified
• 1. Bilge water oily water, mixed detergent,
  and particles
• 2. Blackwater/graywater mixture 700-2,400 mg/L
  total suspended solids (TSS)
• 3. Biosolids 2-3 solids
• Plasma Arc Waste Destruction System (PAWDS)
  wastewater quench water
• from solid waste thermal destruction system
  (inert ash at 6 g/L solids)
• Based on Navy needs, bilge water and
  black/graywater are highest priority.

Run Number
Fig. 9. Summary of Bilge Water Tests - Avg. J
Permeate Turbidity
Fig. 8. Example SCT Data for Bilge Water

• Summary of Blackwater/Graywater Stirred Cell
  Tests (Figures 6 and 7)
• SS-3 um had highest flux PTFE, SS-0.1 um, and
  SS-0.5 um membranes had similar fluxes (J).
• Turbidities decreased with run number and were
  generally lower than 5 NTU. PTFE had higher
• turbidities but may be due to poor fitting in
  the stirred cell.
• Only PTFE can be cleaned with 1 bleach
  solution, significantly decreasing the cleaning
  procedure.
• Select SS-316-03 and PTFE for further study of
  black/gray wastewater in Task 3.
• Summary of Bilge Water Stirred Cell Tests
  (Figures 8 and 9)
• Flux PTFE gt SS-3 um gt SS-0.5 um gt SS-0.1 um
• Turbidities were similar at high run numbers
  and were much lower than the feed turbidity.
• Combination of 2 detergents and pH adjusted to
  11.5 was an effective cleaning solution.
• Select SS-316-03 and PTFE for further study of
  bilge water in Task 3.

Task 2. ID and Screen Membranes

• Four commercially available membranes were
  identified.
• Membranes procured and are undergoing stirred
  cell testing (SCT) using
• the four identified wastes.

Task 3. Baseline HSR-MS Tests

• SpinTek constructed two automated pilot-scale
  HSR-MS
• units.
• Baseline testing on bilge and black/gray
  wastewaters
• will commence December 2009.
• Baseline data will be used to judge the
  improvements
• due to continuous mechanical cleaning and
  back pulsing.

Stirred Cell Testing Procedure (Fig. 5 SCT
apparatus) 1. Clean water flux (CWF) on virgin
membrane to estimate membrane resistance. 2.
Waste treated by membrane at constant pressure,
permeate volume measured as function of
time. At end of run, composite permeate turbidity
measured. 3. Stirred cell flush with tap water,
cleaned according to membrane manufacturer
specifications, flushed again with tap water, and
CWF performed. 4. Repeat steps 2 and 3 several
times. 5. Results are presented as permeate flux
(volume permeate/membrane area-time, m3/m2-d)
versus time and CF composite permeate turbidity.
Acknowledgements This work is funded by the
Strategic Environmental Research and Development
Program (SERDP) and the Office of Naval Research
(ONR).