H 2 O Systems Formal Design Review Paulo Jacob Jennifer Liang - - PowerPoint PPT Presentation

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H 2 O Systems Formal Design Review Paulo Jacob Jennifer Liang - - PowerPoint PPT Presentation

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H 2 O Systems Formal Design Review Paulo Jacob Jennifer Liang Jonathan Tejada Ami Yamamoto Joy Yuan March 2, 2006 Background Current Water Disinfection Methods Chemical Treatment: Chlorine and Ozone Problem: Formation of

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SLIDE 1

H2O Systems

Formal Design Review

Paulo Jacob Jennifer Liang Jonathan Tejada Ami Yamamoto Joy Yuan March 2, 2006

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SLIDE 2

Background

  • Current Water Disinfection Methods

– Chemical Treatment: Chlorine and Ozone

  • Problem: Formation of hazardous intermediates and

high operating costs – Thermal Treatment

  • Problem: Energy input, change in flavor and

temperature limitation

  • Drinking Water Standards

Contaminant Maximum Contaminant Level (mg/L) Potential health effects from exposure

Cryptosporidium 1% Gastrointestinal illness Giardia lamblia 0.1% Gastrointestinal illness Legionella No limit* Legionnaire’s Disease Viruses (enteric) 0.01% Gastrointestinal illness

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SLIDE 3

Electroporation

  • Definition:

– A process that uses high voltage impulses to create micropores in a cell membrane.

  • Mechanism:

– Local instabilities arise from dielectric breakdown

  • Separation of charge on either side of membrane

→ Membrane grows thinner → Pore is created → Cell lyses = bacteria dies

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Project Outline

  • Purpose:

To create an small device that efficiently treats water supplies contaminated with disease causing bacteria

  • Method:

Electroporation to lyse bacteria cells

  • Formation of pores in the cell membrane from

exposure to high voltage electric fields

  • Design:

Centimeter scale parallel plate electrodes with contaminated water flowing through micron scale gap

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SLIDE 5

Materials Selection

  • Input/output of water
  • Biological samples
  • Device components

– Clear PVC tubing, 1/8” – Polyester shim stock, 12.5 to 500 µm – Polyurethane glue – Polypropylene Luer lock fittings – Syringes – Electrode

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SLIDE 6

Candidate Electrode Materials

  • Stainless Steel

– Susceptible to corrosion under certain conditions – Economical

  • Ti

– Superior mechanical properties – Established electrode material – Corrosion resistant oxide layer

  • Wide band gap semi-conductor

stable in solution

  • Enhanced by anodizing

– Difficult to machine

  • Water jet cutting
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SLIDE 7

Anodizing

  • Surface treatment

– Forms up to 100 nm layer of TiO2

  • Resistivity of 1012-18 Ohms*Cm
  • Enhanced corrosion & wear resistance
  • Method

– SAE specification AMS 2488 – Titanium employed as anode in electrochemical cell – Stainless steel counter-electrode – Caustic electrolytes (e.g. NaOH) – Thickness tuned by voltage

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Voltage Limitations: Effective Lysing

Electric Field required for lysis: E = 1~5 x 105 V/m

  • Verhes. Water Research, 2002.

Our goal: low voltage input V = Ed Aiming for a voltage input of around 12 V, we find that a gap distance of d = 25 µm is required.

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SLIDE 9

Dielectric Considerations

  • Dielectric strength

– Air: 3 x 106 V/m – TiO2 : 4-8 x 106 V/m – Water: dependent on ionic content

  • Partially filled

capacitor treatment

Ti TiO2 H2O

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SLIDE 10

Voltage Limitations: Concerns

  • Dielectric reduces electric field by a factor
  • f dielectric constant
  • E=E0/K
  • Dielectric constant of pure water: 80
  • Given initial voltage (12V), E=6x103 V/m which is less

than required to lyse bacteria (1~5 x 105 V/m)

  • Necessary potential difference would be 1000 V to

achieve lysing electric field.

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SLIDE 11

Pressure Limitations

Surface Tension Couette Flow (2 parallel plates)

∆P = 3µLQ 2Wδ3 ∆P = T(W+2δ) Wδ T = surface tension of water = 72.0 dynes/cm (25°C) µ = viscosity of water = 0.01 Poise Q = flow rate = 1 liter/hour 2δ = electrode gap distance = 25 µm W = width of flow area L = length of flow

Based on these two equations, we find that dimensions of L = 10 cm W = 2 cm yield a reasonable pressure difference (under 2 atm) that allows us to achieve our target flow rate.

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SLIDE 12

Design Proposal

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SLIDE 13
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SLIDE 14
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Design Proposal

water in water out

25µm

Power Supply

2 cm 1 c m

Anodized Ti Anodized Ti Ti Ti shim stock

water in water out

PVC tubing

Final Design

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SLIDE 17

Testing bacteria

  • Water samples from

Charles river

– Simultaneous assessment of bacterial content of experimental and control samples

  • Pre-Treatments

– Filtration – Dilution – Deionization

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Issues & Concerns

Potential Problems Possible Solutions

Fouling Filtration, revise size scale Elimination of variables Testing protocol, further theoretical investigation and modeling Surface roughness tolerance Alter device dimensions Safety (electricity, infectious agents) Maintain high safety standards Budget Efficient use of materials, time Timeline Rigorous adherence to deadlines Electrolysis of water AC current

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SLIDE 19

Gantt chart

2/9-2/22 2/23-3/15 3/16-4/5 4/6-4/26 4/27- 5/10 5/11- 5/18 Research Design Material Acquisition Construction Testing Modification Final Presentation Preparation

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SLIDE 20

Questions?

h2o@mit.edu