H2O SystemsFormal Design Review

Paulo JacobJennifer LiangJonathan TejadaAmi YamamotoJoy Yuan

March 2, 2006

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 StandardsContaminant 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

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

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

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

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

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

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.

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

Voltage Limitations: Concerns

• Dielectric reduces electric field by a factor of 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.

Pressure LimitationsSurface Tension Couette Flow (2 parallel plates)

∆P = 3µLQ2Wδ3∆P =

T(W+2δ)Wδ

T = surface tension of water = 72.0 dynes/cm (25°C)µ = viscosity of water = 0.01 PoiseQ = flow rate = 1 liter/hour2δ = electrode gap distance = 25 µmW = width of flow areaL = length of flow

Based on these two equations, we find that dimensions ofL = 10 cmW = 2 cm

yield a reasonable pressure difference (under 2 atm) that allows us to achieve our target flow rate.

Design Proposal

Design Proposal

water inwater out

25µmPower Supply

2 cm

10 cm

Anodized TiAnodized Ti

TiTishim stock

water in

water out

PVC tubing

Final Design

Testing bacteria

• Water samples from Charles river– Simultaneous

assessment of bacterial content of experimental and control samples

• Pre-Treatments– Filtration – Dilution– Deionization

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

Gantt chart2/9-2/22 2/23-3/15 3/16-4/5 4/6-4/26 4/27-

5/105/11-5/18

Research

Design

Material Acquisition

Construction

Testing

Modification

Final Presentation Preparation

Questions?

h2o@mit.edu