the use of ultra violet light for the treatment of filtered drinking water

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Report Compiled by Andrew Manic. 17/02/2010

THE USE OF ULTRA VIOLET LIGHT FOR THE TREATMENT OF FILTERED DRINKING WATER

REPORT COMPILED BY: ANDREW MANIC.

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Table of Contents:

1. Overview 3

2. The Treatment of Water using UV Light 3 2.1 The science of UV Light 3 2.2 Factors Influencing UV Effectiveness 4 2.3 The Targeted Microorganism 4 2.4 Advantages of UV-Radiation 4 2.5 UV Range 5 2.6 Disinfecting drinking water 5 2.7 Treating Cryptosporidium 6

3. UV Properties of Plastics; Polymer Degradation 6

3.1 Degradation 6 3.2 How to avoid degradation 7 3.3 Current Plastics being used 7 3.4 Proposed Plastic 8

4. UV Light Emitting Diodes (LED) 9

4.1 Proposed UV LED 9

5. Example of a UV LED Solar Powered Water Filter 10

6. Conclusion and Recommendations 10

7. References 12

8. Appendices 12 Appendix 1 Costing model based on current CWP manufacture

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1. Overview In this report I have gathered information on the use and affects of Ultra violet (UV) treatment for drinking water. This report also provides findings about the possible effects of UV on the plastic receptacle used to contain the water. All information gathered suggests that the use of UV treatment of drinking water can be very effective within certain boundaries.

a. UV spectrum. b. Water flow rate.

One of the constraints of using our current Polypropylene (PP) plastic is that it is easily degraded by UV light. However alternative plastics and additives are available to enhance UV stability in plastics. I have broken this report into several sections for ease of reference; UV treatment, Polymer degradation, Plastic recommendation, UV LED technology and suggested UV LED use in the CWP filter. By no means is this a comprehensive study, and should only been seen as an introduction to the use of LED UV technology for our CWP units.

2. The Treatment of Water using UV Light 2.1 The Science of UV Light: Ultraviolet light is a spectrum of light just below the range visible to the human eye (below the blue spectrum of visible light in the chart below). UV light is divided into four distinct spectral areas-Vacuum UV (100 to 200 nanometers), UV-C (200 to 280 nanometers), UV-B (280 to 315 nanometers), and UV-A (315 to 400 nanometers). The UV-C spectrum (200 to 280 nanometers) is the most lethal range of wavelengths for microorganisms. This range, with 264 nanometers being the peak germicidal wavelength, is known as the Germicidal Spectrum.

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2.2 Factors Influencing UV Effectiveness:

a. The type of lamp used in the application. (low-pressure or medium/high-pressure) b. The length of the lamp being used. (the ARC Length) c. The physical design of the UV's water exposure chamber. d. The condition of the water being treated. e. The water flow rate through the UV's exposure chamber

2.3 The Targeted Microorganism: It is critical to first identify the microorganism. Each type of microorganism requires a specific UV-C radiation exposure rate to successfully complete the disinfection process. The targeted microorganism must be directly exposed to the UV-C radiation long enough for the radiation to penetrate the microorganism's cell wall. However, it takes only seconds for UV-C light rays to inactivate waterborne microorganisms by breaking through the microorganism's cell wall and disrupting their DNA. This often totally destroys the organism, or at the very least will impair its ability to reproduce. [3]

2.4 Advantages of UV-Radiation:

Environmentally friendly, no dangerous chemicals to handle or store, no problems of overdosing

Low initial capital cost and reduced operating expenses when compared with other technologies such as chemical processing

Immediate treatment process, no need for holding tanks, long retention times No chemicals added to water supply; no by-products No change in taste, odour, pH, conductivity or the general chemistry of the water No handling toxic chemicals, no need for specialized storage requirements Simplicity and ease of maintenance, periodic cleaning (if applicable) and annual lamp

replacement Highly compatible with other water and air treatment processes

A research team from the Center for Water Quality (O.S. Mbuya and C.S. Gardner) and the Dept. of Biology (L.A. Latinwo) at Florida A&M University and Teknikon North Gauteng, South Africa (B.J. Mankazana) examined the effectiveness of UV light to inactivate waterborne pathogens (e.g., Escherichia coli, Streptococcus faecalis, Salmonella typhi and Shigella flexneri) under laboratory conditions. [10]

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2.5 UV Range:

Name Abbreviation Wavelength / Nanometers Energy per Photon

Ultraviolet A, long wave, or black light

UVA 400nm – 315nm 3.10 – 3.94 eV

Near NUV 400nm - 300nm 3.10 – 4.13 eV

Ultraviolet B or medium wave UVB 315nm – 280nm 3.94 – 4.43 eV

Middle MUV 300nm – 200nm 4.13 – 6.20 eV

Ultraviolet C, short wave, or germicidal

UVC 280nm – 100nm 4.43 – 12.4 eV

Far FUV 200nm – 122nm 6.20 – 10.2 eV

Vacuum VUV 200nm – 10nm 6.20 – 124 eV

Low LUV 100nm – 88nm 12.4 – 14.1 eV

Super SUV 150nm – 10nm 8.28 – 124 eV

Extreme EUV 121nm – 10nm 10.2 – 124 eV

Between 200-400 nm, a variety of detector options exist.

2.6 Disinfecting drinking water: UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection is the process of using PET bottles and sunlight to disinfect water.

It used to be thought that UV disinfection was more effective for bacteria and viruses, which have more exposed genetic material, than for larger pathogens which have outer coatings or that form cyst states (e.g., Giardia) that shield their DNA from the UV light. However, it was recently discovered that ultraviolet radiation can be somewhat effective for treating the microorganism Cryptosporidium. [1]

Many treatment plants that take raw water from rivers, lakes, and reservoirs for public drinking water production use conventional filtration technologies. This involves a series of processes including coagulation, flocculation, sedimentation, and filtration. Direct filtration, which is typically used to treat water with low particulate levels, includes coagulation and filtration but not sedimentation. Other common filtration processes including slow sand filters, diatomaceous earth filter and membranes will remove 99% of Cryptosporidium. [4] Membranes and bag and cartridge filters remove Cryptosporidium product-specifically.

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2.7 Treating Cryptosporidium:

While Cryptosporidium is highly resistant to chlorine disinfection, [5] with high enough concentrations and contact time Cryptosporidium will be inactivated by chlorine dioxide and ozone treatment. The required levels of chlorine generally preclude the use of chlorine disinfection as a reliable method to control Cryptosporidium in drinking water. Ultraviolet light treatment at relatively low doses will inactivate Cryptosporidium. Water Research Foundation-funded research originally discovered UV's efficacy in inactivating Cryptosporidium. [6][7]

One of the largest challenges in identifying outbreaks is the ability to identify Cryptosporidium in the laboratory. Real-time monitoring technology is now able to detect Cryptosporidium with online systems, unlike the spot and batch testing methods used in the past.

The most reliable way to decontaminate drinking water which may be contaminated by Cryptosporidium is to boil it. [8][9]

The findings resulted in the use of UV radiation as a viable method to treat drinking water. Giardia in turn has been shown to be very susceptible to UV-C when the tests were based on infectivity rather than excystation. [2] It has been found that protists are able to survive high UV-C doses but are sterilized at low doses.

3. UV Properties of Plastics; Polymer Degradation

3.1 Degradation:

Today there are primarily six commodity polymers in use, namely polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate or PET, polystyrene and polycarbonate. These make up nearly 98% of all polymers and plastics encountered in daily life. Each of these polymers has its own characteristic modes of degradation and resistances to heat, light and chemicals. Polyethylene and polypropylene are sensitive to oxidation and UV radiation.

All types of UV can cause a photochemical effect within the polymer structure, which can be either a benefit or lead to degradation of some sort to the material. Note that compared to our skin, the higher energy UVC is more likely to affect plastics.

It is also important to remember that actual ambient temperature and humidity will accelerate any effect of the intensity level. The Main Effects on Polymers Exposed to UV

UV energy absorbed by plastics can excite photons, which then create free radicals. While many pure plastics cannot absorb UV radiation, the presence of catalyst residues and other impurities will often act as receptors, causing degradation. Only a very small amount of impurity may be needed for the degradation to occur, e.g. trace parts per billion values of sodium in polycarbonate will initiate color instability. In the presence of oxygen the free radicals form oxygen hydroperoxides that can break the double bonds of the backbone chain leading to a brittle structure. This process is often called photo-oxidation. However, in the absence of oxygen there will still be degradation due to the cross-linking process.

Unmodified types of plastics that are regarded as having unacceptable resistance to UV are POM (Acetal), PC, ABS and PA6/6. Other plastics such as PET, PP, HDPE, PA12, PA11, PA6, PES, PPO, PBT and PPO are regarded as fair. Note that a PC/ABS alloy is also graded as fair. Good resistance to ultraviolet rays can be achieved from polymers such as PTFE, PVDF, FEP, and PEEKTM.

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PTFE has particularly good UV resistance because of its very strong carbon-fluorine (C-F) bond [almost 30% higher than the carbon-hydrogen (C-H) bond], which is the common side bond that surrounds the carbon (C-C) backbone in a helix and protects it. Most fluoropolymers also do not have the light absorbing chromophore impurities in their structure that can act as an initiator for photo-oxidation. [11]

3.2 How to Avoid UV Degradation:

There are several ways of avoiding UV degradation in plastics — by using stabilizers, absorbers or blockers. For many outdoor applications, the simple addition of carbon black at around a 2% level will provide the protection for the structure by the blocking process. Other pigments such as titanium dioxide can also be effective. Organic compounds such as benzophenones and benzotriazoles are typical absorbers which selectively absorb the UV and re-emit at a less harmful wavelength, mainly as heat. The benzotriazole type is good, as it has a low color and can be used at low dose rates below 0.5%.

The other main mechanism for protection is to add a stabilizer, the most common being a HALS (Hindered Amine Light Stabilizer). These absorb the excited groups and prevent the chemical reaction of the radicals.

In practice, the various types of additives used are in combinations or are compounded into the original polymer to be produced as a special grade for UV protection. It may be attractive to add antioxidants to some plastics to avoid photo-oxidation, but care must be taken that the antioxidant chosen does not act as an UV absorbent, which will actually enhance the degradation process. [11]

3.3 Current Plastics being used:

“Rabbit” Filter - Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

Degradation: Polypropylene is liable to chain degradation from exposure to UV radiation such as that present in sunlight. Oxidation usually occurs at the secondary carbon atom present in every repeat unit. A free radical is formed here, and then reacts further with oxygen, followed by chain scission to yield aldehydes and carboxylic acids. In external applications, it shows up as a network of fine cracks and crazes which become deeper and more severe with time of exposure.

For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures, a common problem during molding operations. Anti-oxidants are normally added to prevent polymer degradation. [12]

“Butterfly”(Thai) Filter - Polyethylene terephthalate commonly abbreviated PET, PETE, or the obsolete PETP or PET-P), is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber.

Degradation: UV resistance fair

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Possible toxicity of PET An article published in Environmental Health Perspectives in November 2009 presented evidence that PET may yield endocrine disruptors under conditions of common use. Possible mechanisms include leaching of phthalates as well as leaching of antimony. [10] The risk of leaching appears to increase as a function of storage temperature and storage duration. [13]

3.4 Proposed Plastic:

Poly (methyl methacrylate) (PMMA) is a transparent thermoplastic.

Chemically, it is the synthetic polymer of methyl methacrylate. It is sold under many trade names, including Policril, Plexiglas, Gavrieli, Vitroflex, Limacryl, R-Cast, Per-Clax, Perspex, Plazcryl, Acrylex, Acrylite, Acrylplast, Altuglas, Polycast, Oroglass, Optix and Lucite and is commonly called acrylic glass, simply acrylic, perspex or Plexiglas. Acrylic, or acrylic fiber, can also refer to polymers or copolymers containing polyacrylonitrile.

Has a density of 1.150–1.190 g/cm3. This is less than half the density of glass, and similar to that of other plastics.

Has good impact strength, higher than that of glass or polystyrene, but significantly lower than that of polycarbonate or engineering polymers. In the majority of applications, it will not shatter but instead breaks into large dull pieces.

Is softer and more easily scratched than glass. Scratch-resistant coatings (which may also have other functions) are often added to PMMA sheets.

Transmits up to 92% of visible light (3 mm thickness), and gives a reflection of about 4% from each of its surfaces on account of its refractive index of 1.4893 to 1.4899.

Filters ultraviolet (UV) light at wavelengths below about 300 nm (similar to ordinary window glass). Some manufacturers add coatings or additives to PMMA to improve absorption in the 300–400 nm range.

Allows infrared light of up to 2800 nm wavelength to pass. IR of longer wavelengths, up to 25 µm, is essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).

Has excellent environmental stability compared to other plastics such as polycarbonate, and is therefore often the material of choice for outdoor applications.

Has poor resistance to solvents, as it swells and dissolves easily. It also has poor resistance to many other chemicals on account of its easily hydrolyzed ester groups.

Modification of properties

Pure poly (methyl methacrylate) homopolymer is rarely sold as an end product, since it is not optimized for most applications. Rather, modified formulations with varying amounts of other comonomers, additives, and fillers are created for uses where specific properties are required. For example,

A small amount of acrylate comonomers are routinely used in PMMA grades destined for heat processing, since this stabilizes the polymer to depolymerization ("unzipping") during processing.

Comonomers such as butyl acrylate are often added to improve impact strength. Comonomers such as methacrylic acid can be added to increase the glass transition

temperature of the polymer for higher temperature use such as in lighting applications. Plasticizers may be added to improve processing properties, lower the glass transition

temperature, or improve impact properties.

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Dyes may be added to give color for decorative applications, or to protect against (or filter) UV light.

Fillers may be added to improve cost-effectiveness.

4. UV Light Emitting Diodes (LED)

The DNA strands for several common bacteria are strongly affected by radiation at 265 nm, which makes 265 nm UV LEDs an ideal source for water purification and food sterilization. [14]

There are basically 3 different types of UV LED lenses available (different variations of the 3 main types are also available); Flat window lens, Ball Lens and Hemispherical Lens. I have chosen the Flat window lens as it offers the best emission pattern of 120° compared to only 6° spread of the Ball and Hemispherical Lens.

4.1 Proposed UV LED: UVTOP 260 TO39 FW

Absolute Maximum Ratings at TA = 25°C

Parameter Unit Max. Rated Value

Power Dissipation, DC mW 150 (TO-39)

Forward Current, DC mA 30

Pulse Forward Current (Duty Factor=1%, Freq=1KHz)

mA 200

Reverse Voltage V 6

Operating Temp. Range °C -30 to +55

Storage Temp. °C -30 to +100

Electro-Optical Characteristics at TA = 25°C, IF = 20mA

Peak Wavelength λp(nm) Typical

PKG Type

Lens Type

Part Number

Optical Power

Pout(µW)

Min Typ.

Forward Voltage VF

(V)

Typ. Max

Viewing Angle

201/2 (°)

Typical

FWHM (nm)

Typ. Max

265nm Min: 260nm Max: 269nm

TO-39 FW UVTOP260 TO39FW

180 300 6.5 8.0 120° 12 15

Notes: [15] Peak wavelength measurements tolerance is +/- 2nm Optical power output measurement tolerances is +/- 10% Forward voltage measurement tolerance is +/- 2% Typical Emission Pattern of Flat Window LED: [15]

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5. Example of a UV LED Solar Powered Water Filter Based on current receptacle:

6. Conclusion and Recommendations (Disclaimer: The views and

opinions below are my personal recommendations and should be substantiated through laboratory testing and further analysis and trial before consideration or implementation)

In conclusion I think it is feasible to design and implement a UV LED water filter. It would make a beneficial add-on to the current CWP unit and future designs. It has been stated in various documents that just treating source water alone with UV is not totally affective, as some bacteria can hide in debris and particles which protect the bacteria from UV exposure.

So in theory, coupled with the current Ceramic filter technology acting as a pre filter there should be total elimination of pathogens and other water borne contaminants.

Some of the other benefits apart from UV ability to inhibit bacteria are that it could potentially remove the need for Silver Colloidal treatment, leaving the ceramic filter to just filter debris and turbidity hence reducing cost. It could also extend the life span of the ceramic filter, as the ceramic filter won’t be relied upon to remove bacteria; so won’t require cleaning as often apart from the need to improve flow rate.

One of the drawbacks for effectively using UV treatment commercially is flow rate. With our CWP units producing 2 – 3 liters of water per hour; this seems to be ample time for effective UV treatment.

Encapsulated or sealed cavity housing UV LED’s

Water tight rechargeable 9V battery pack.

Solar Panel

Example of UV spread

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There will be added cost to the CWP units with the requirement of UVLED’s x 4, a rechargeable battery pack and solar panel. [See Appendix 1] However I believe that with the benefits of this technology and the potential for a more aesthetically pleasing receptacle it should offer an excellent marketing and selling approach to end users, particularly the poorer communities that will see the use of UV LED’s and solar systems as a technical advancement and something to be proud of owning.

Another way to combat the increased price would be to tie in with a selected micro finance institution to offer loans and repayment schemes for the rural poor.

Another recommendation I have is to introduce advertising space onto the receptacle in the form of a printed label. This could be an excellent selling point for companies. Imagine every time the end user proceeds to fill their cup of water, and in front of them is advertising for a selected company. The benefit of this advertising would be that it could subsidize the cost of the CWP unit to the customer. If we sold advertising space for $2 a unit, that’s $2 less the disadvantaged needs to outlay for a CWP unit and access to clean water.

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7. References:

[1] http://en.wikipedia.org/wiki/Ultraviolet [2] Ware, M. W. et al. (PDF). Inactivation of Giardia muris by Low Pressure Ultraviolet Light. United States Environmental Protection Agency. http://www.epa.gov/nerl/news/forum2003/water/ware_poster.pdf. Retrieved 2008-12-28. [3] http://www.uvcomparison.com/uvscience.php [4] "The Interim Enhanced Surface Water Treatment Rule – What Does it Mean to You?" (pdf). USEPA. http://www.epa.gov/safewater/mdbp/ieswtrwhatdoesitmeantoyou.pdf. Retrieved 2007-05-06. [5] Korich DG, Mead JR, Madore MS, Sinclair NA, Sterling CR (May 1990). "Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability". Appl. Environ. Microbiol. 56 (5): 1423–8. PMID 2339894. PMC 184422. http://aem.asm.org/cgi/pmidlookup?view=long&pmid=2339894. [6] Rochelle, PAUL A.; Fallar, D; Marshall, MM; Montelone, BA; Upton, SJ; Woods, K (2004 Sep-October). "Irreversible UV inactivation of Cryptosporidium spp. despite the presence of UV repair genes". J Eukaryot Microbiol 51 (5): 553–62. doi:10.1111/j.1550-7408.2004.tb00291.x. PMID 15537090. [7] "Ultraviolet Disinfection and Treatment". WaterResearchFoundation (formerly AwwaRF). http://www.waterresearchfoundation.org/research/TopicsAndProjects/topicSnapshot.aspx?topic=uv. Retrieved 2007-05-06. [8] "Boil water warning 'precaution'" (html). BBC. http://news.bbc.co.uk/1/hi/wales/7589839.stm. Retrieved 2009-09-07 [9] "Boil water 'into January' warning" (html). BBC. http://news.bbc.co.uk/1/hi/wales/4484946.stm. Retrieved 2009-09-07. [10] http://www.usawaterquality.org/themes/health/research/ultraviolet.html [11] http://www.symmetrybalance.com/techinfo/techinfo.asp?htmlfile=Zeus_UV_Properties.htm&id=834 [12] http://en.wikipedia.org/wiki/Polypropylene [13] http://en.wikipedia.org/wiki/Polyethylene_terephthalate#Degradation [14] Japanese Journal of Applied Physics Vol. 44, No. 3, 2005, pp. L 98–L 100 Milliwatt Pulse Operation of 265nm AlGa Light Emitting Diodes [15] http://www.s-et.com/datasheet/SET_UVTOP_Catalog.pdf

8. Appendices: Appendix 1 Costing model based on current CWP manufacture (please see as attachment)

the use of ultra violet light for the treatment of filtered drinking water

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