For : Professor Anderson
Prepared by : Joel Patruno
Piseth Toch
Neusa Veiga ndubuisi nduaguba

1. Summary ………………………………………………………………………2
2. Introduction ………………………………………………………………...... 2
3. Technical Progress …………………………………………………………... 3
3.1. Purification Considerations .……………………………………… 3
3.1.1. Reverse Osmosis …….…………………………………… 3
3.1.2. Carbon Filter …………………………………………….. 4
3.1.3. Ultraviolet Radiation ……………………………………. 4
3.1.4. Cloth Filtering …………………………………………… 5
3.2. Technical Implementation ……………………………………....... 6
3.2.1. Physical Filtering ……………………………………....... 6
3.2.2. Ultraviolet radiation …………………………………….. 7
3.2.2.1. UV Hardware design ………………………….. 7
3.2.2.2. Objects Layout ……………………………........ 9
3.2.2.3. Control System ………………………………...10
3.2.2.4. Key features and added value …………….…. 11
4. Future Objectives ………………………………………………………….. 12
4.1. Scalability ……………………………………………………….…12
5. Cost and Scheduling Issues ……………………………………………....... 12
5.1. Budget breakdown ……………………………………………….. 13
6. Bibliography ………………………………………………………………...14
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1. Summary
Starting with a blank plate our task was to take last year’s sun tracking solar panel and apply it to a real world situation, namely water purification. Upon subsequent research we discovered there were many ways we could approach the issue. As future engineers we are obligated to assess and improve our way of life. A major issue concerning the entire world is clean water. At least one fifth of the world’s population does not have access to clean drinking water, a necessity of life. The World Health Organization
(WHO) has discovered that over 2.2 million people die every year from diarrhea disease, many of them being young children
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.
In addition, other water borne illnesses also claim many, many lives. The average human requires at least one ounce of water for every pound of body weight, which translates to just over one gallon of water per day. These deaths resulting from dirty drinking water contribute to the high infant mortality rate and low life expectancies of many third world countries. Also contributing to the problem is the inaccessibility of energy to power such plants which can purify water. This is because many villages in poor countries are located in remote areas where electricity is unavailable.
2. Introduction
By utilizing a solar energy source we are attempting to solve the problem of unhealthy and potentially deadly water. Our solution is to design a “stand alone” water purification system. Last year’s senior design team developed a sun tracking solar panel in order to optimize the amount of energy converted from the sun. Our goal this year is to take that idea to the next level and put the energy to good use. At first we had many ideas on how to purify water using techniques which are already practiced. The general problem we found with many of these techniques is that they are designed to be used where the availability of an energy source is not an issue. With the solar panel only producing approximately 1.9 amp hours per day (a 2.8 amp-hour battery provides storage capacity) at 12 volts we had a great challenge ahead of us in that our system needed to be extremely efficient.
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Another problem with common water purification systems is the assumption of low turbidity water being used. Many systems are used to further treat the water in your average American home, and designed to be used on well water or municipal water sources. As a result, water sources with large amounts of particulate matter tended to decrease effectiveness, reduce lifespan, and cause other problems with purification systems. We looked into many techniques and had to balance out their pros and cons. In the end we desired a system that balanced water quality with ease of use and minimal cost per gallon output.
3. Technical Progress
3.1. Purification Considerations
One common technique we looked into was chemical water purification. This is done by simply introducing chlorine into water. This method is very effective in destroying bacteria and viruses. The United States uses this as a primary method of water sanitation and has been proven to be effective. However we found that the water has to be treated with specific amounts of chlorine and also that it leaves an odor and taste to the water.
This does not meet our notion of being a “foolproof” method; we do not want anyone poisoning themselves. Even if we designed a cartridge or automated chemical additive system, constant upkeep costs for filters or tablets is then introduced into the system. For these reasons we decided against chemical treatment of the water.
3.1.1.
Reverse Osmosis
Reverse Osmosis, commonly known as RO, is another method that produces very clean water. In this method, water is forced through a membrane with extremely small holes using water pressure. This allows water to pass through the membrane and filters out the debris and microbes. This method produces the cleanest water of all the methods we researched. In fact RO is used for many medical and pharmaceutical applications where the purest water is needed. The major downfall of RO is that it requires water pressure, and it is very slow. We do not have the luxury of implementing a power exhaustive pump
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to provide the water pressure. Also RO only produces about 1/4th of a gallon of water per hour. The end product in our eyes was insufficient. We would have expended too much energy for the little water we treated. Another major problem with RO is that it produces a lot of waste water. For every gallon of clean water produced three to nine gallons of water is required depending on how dirty the water is. For these reasons the method of reverse osmosis was not chosen.
3.1.2.
Carbon Filters
Reverse osmosis led us to a series of other filtering devices that were based on the same principle of physical filtration. Simple gravity exploiting carbon filters are effective in purifying water. Many of the common counter top water purifiers today contain carbon elements. This is because they not only filter very small particulate but they can also remove odors and foul tastes from the water. The problem with carbon filters is that they have a very limited filtering capacity. Many only last for a couple of thousand gallons of treatment before they need to be replaced. That value is based on the treatment of clean and safe tap water. The dirtier the water is the shorter the lifespan of the filter. It’s extremely short lifespan caused us to look into other purification techniques.
3.1.3. Ultraviolet Radiation
Ultraviolet rays have been proven to be dangerous to humans. They can damage your eyes and cause skin cancer. However they have also been found to cripple and destroy bacteria and viruses, rendering them harmless to humans. This is because UV radiation alters and can even destroy the DNA of microorganisms. The most dangerous and effective UV is those of shorter wavelengths
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, namely being in the 240nm to 280nm range, this range is commonly refered to as the UV-C range. On the market today are UV lamps that produce the most effective DNA disrupting wavelength of 254nm. In air these lamps can destroy microorganisms from several inches away with only seconds of exposure. Upon further research we found that low powered 12 volt lamps were also available. This could make UV radiation the best option for our project.
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However there was one issue with UV radiation. Since we were purifying dirty water extended exposure would be required depending on the water’s turbidity. This is because these small microorganisms can hide from the UV rays by hiding behind larger particulate in the water. This particulate also acted to significantly diminish the “skin depth” penetration of the UVC rays. Extended exposure would greatly affect how much water we could purify, and the project’s scalability. To be able to use UV radiation the problem of turbidity had to be addressed. This was solved by considering a multi stage filtering system.
By implementing a physical filtration stage before a UV radiation stage we could remove most of the large particulate thus making the UV stage much more effective. This physical filtration stage is extremely important because it saves valuable energy by reducing the UV lamp’s on time. We found that ceramic filters provide very effective filtration with a lifespan many times greater than that of carbon filters. They act to filter out particles and organisms greater than 0.5 microns. They are also cleanable, reusable and easy to maintain. We happened to find ceramic filters which actually have carbon blocks imbedded inside of them. This adds the benefits of odor and taste removal, though only for a fraction of the ceramic filter life.
3.1.4. Cloth Filter
If we were to filter really dirty water with only ceramic filters, this would not only call for more frequent cleaning, but reduce the filter life. To avoid this, the physical stage is also multi-staged. We chose to implement a simple cloth pre-filter that would remove large particles. The benefit of cloth is that is cheap and easy to clean. Studies in villages of Bangladesh have shown that the common cloth of their Sari robes could effectively reduce water bacteria and viruses when used to filter water 4 . This could be seen with a
50% reduction of deaths related to diarrhea diseases. The conclusion of the scientists who implemented the studies was that the cloth acted to block particulate matter which also acted as a common breeding ground for bacteria. This is proof that simple cloth filters are especially helpful in particulate removal.
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3.2. Technical Implementation
3.2.1. Physical Filtering
The actual implementation of the physical filtration stage consists of two chambers. For these chambers we chose to use five gallon buckets. The reason we chose five gallon buckets was because they are inexpensive and are mass produced. Therefore is we were to scale up our design or mass produce it the cost of the buckets would play a small role in the overall cost. The chambers were separated using screws which were drilled into the side of the lower chamber. The protruding screws could then support the weight of the upper chamber. This upper chamber actually filtered the water while the lower chamber stores it. In the upper chamber were the two stages of cloth and ceramic filtration.
British Berkefeld’s Black Berkey ceramic filter elements were the perfect fit for our design. These elements could filter twelve gallons in a day, the flow speed is one gallon filtered per two hours. In our design we used two and the numbers improve to 24 gallons a day, and one gallon filtered every hour. Their selling quality is that they are gravity fed meaning they rely solely on gravity to do all the filtering work. They also contain carbon elements which remove odor and taste from the water, like many carbon filters, the carbon elements loose absorbency after 2000 gallons; however the Black Berkey retains all other filter traits.
Not only are Black Berky filters quite fast and easy to use they are also practically maintenance free. The filters only need to be scrubbed and rinsed off every 2000 gallons depending on the water’s turbidity. They also offer an extremely long lifespan of 15,000 hours. This is upwards of 10 times longer than its carbon counterpart. At which point in time they become prone to cracking and must be replaced. Our choice of filter has the added feature of silver imbedded within its ceramic elements. This acts to help to prevent growth of bacteria. Bacteria that becomes trapped either on the outside of the element or in the ceramic's pores are controlled by the silver. The silver acts upon contact with water, to release small quantities of positively charged metals ions. These ions are taken into the enzyme system of the bacteria's cell and neutralize it
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. These silver ions are harmless to humans.
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In addition to it significant bacterial reduction properties, research suggest that this physical filtration cascade will remove 95% of heavy metals from the waters. This is important because these minerals build up on downstream components of the system over time, causing long term problems. 85% of nitrites and nitrates are also removed from the water.
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These nitrogen-oxygen chemical units make their way into water systems from two sources; they are used in fertilizer and subject to runoff during heavy rains, but are also found in large concentrations in human and animal waste products
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. Their removal is significant as they interfere with the oxygen-carrying capacity of the child’s blood among other serious health effects.
3.2.2. Ultraviolet radiation
After the particulate matter is properly filtered out, water is stored in the 2 nd
bucket as it awaits the final step, exposure to UVC light. The UV sanitation chamber is designed to kill the remaining bacteria. With the turbidity removed from the water, this job is made much easier. This fact is reflected in the absorption coefficient of water of the UVC light range. Pure water has an absorption coefficient of .01 cm
-1
this translates to 0.995% of absorption of the ultraviolet radiation by one centimeter of water. This means that 99% of the UVC power density is still present at 1cm deep. “Poor quality drinking water”, the category of water we’ll presume is in the 2 nd
bucket, has an absorption coefficient of
.2cm
-1
or 18% loss at 1cm.
3.2.2.1. UV Hardware design - Sanitation Chamber
A worst case scenario where particulate matter of 100 ppm is present in the water, we find the absorption coefficient is .5cm
-1
or 40% loss
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. Planning in the worst case scenario, we will design our UV chamber to purify a one centimeter thick wall of water.
This thickness of water creates less room for turbulent flow in the UV chamber. We are trying to minimize the chances of cross- contamination in our system and a smaller water width helps this.
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We have chosen a UVC lamp that is very stingy when it comes to energy use. It utilizes a 12 volt power source and draws 6 watts; this is .5 amp-hour for operation. The size is approximately 3cm in diameter and +14cm in length. This size will translate to the size of the UV chamber as we will be building the chamber from scratch based upon these numbers. The output of the lamp is given as a power density of .7mW/cm 2 at 15cm. We equated the power density at 2cm from the lamp to be 40mW/cm
2
. This is the distance we determined our water would be held at from the lamp.
The UV sanitation chamber design relies on the characteristics of the lamp we have chosen. The length will be 14cm in length and enclosed in an outer shell made of PVC, as it is watertight and rugged. The inner shell must be transparent to allow UV radiation to pass through. First we looked (Figure1.) at glass tubes but we realized that glass acts to absorb the 254nm wavelength waves. We found that “glass” made of transparent quartz allowed the penetration of UVC waves with minimal loss in power density. A 5 centimeter (inside) diameter quartz tube with a thickness of ½cm has a power density permittivity
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of about 90%. Using this as the inner water wall of the UV chamber the center of the water flow is exactly 2cm from the UVC Lamp. This is presuming we utilize a PVC pipe of a 7.5cm inside diameter.
B. megatherium sp.(spores)
B.subtilis
B. subtilis spores
Escherichia coli
Micrococcus candidus
Micrococcus sphaeroides
Neisseria catarrhalis
Proteus vulgaris
Pseudomonas fluorescens
Spirillum rubrum
Staphylococcus albus
Bacteria
Energy to kill - in Power Density Per Second
Sterilisation up to 99%
5.46
14.20
24.00
6.00
12.10
20.00
5.28
7.00
39.40
5.20
4.32
Figure1. Amount of 254nm germicidal radiation required for destruction of bacteria
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3.2.2.2. Objects Layout
These three objects (see Figure 2.), the quartz tube, PVC pipe, and UV lamp will be structured in a radial manner. The gap between the quartz and PVC will contain inlet and outlet valves on either end, perhaps 2 per side to allow for more even water flow. The capacity of this perceived sanitation chamber is +8oz. of water. The total power density apparent on the (middle point) water column is 30mW/cm
2
when acting upon “poor quality drinking water”; the outer edge of this system (only .5cm further away) sees
20mW/cm
2
. This discrepancy is due to the inverse square law of the radial emitting UVC lamp and absorption coefficient of the water. This demonstrates the importance of precision engineering when we begin to tweak our final design. The numbers relating to
(100 ppm particulate) unclean water are ~ 24mW/cm
2
at the middle and 14mW/cm
2 at the outside edge.
Figure2. Modified Design of the filtration unit
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3.2.2.3. Control System
Equally important as the UV sanitation chamber design, the control system, see Figure 3., will be calculated to maximize the performance of the UVC lamp, while serving to eliminate chances of cross contamination. The UV sanitation chamber will have to be built and tested before the fine details of the controller come to focus, but we have basic presumptions. Killing bacteria requires minimal amounts of energy. We have found that
“time to kill” bacteria can be found by multiplying power density by time. Pseudomonas fluoresces bacterium needs to be exposed to 39.4(mW/cm2 * seconds) of energy at the
254nm range (the highest resistance bacteria we have come across, ranging from 4.23 to
39.4). Taking our minimum power density number (from unclean water at 2.5cm) we would need 3 seconds of exposure to kill this bacterium. Factoring in loss of UVC lamp intensity over time by doubling the exposure, we are thinking about 6 seconds for an exposure “cycle”. This would amount to 5x dose in poor quality water or a 2x dose under dismal conditions. In the same poor quality water this would amount to 20x the dose to eliminate Escherichia coli. This cycle time of 6 seconds will be utilized in the following manner.
Figure3. State-Diagram for Control System
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When the physical stage passes a said amount of water into the 2 nd
bucket, it will trigger a water-level switch and marks the beginning of the “batch”. This switch will be connected to a PLD brain. The UV lamp will turn on and the system will wait 6 seconds, at which point a pinch valve will open and allow a flow of water (all gravity powered).
About 2/3 the capacity of the UV chamber will be released into a “ready to drink” (3 rd
) bucket, and water from the 2 nd
bucket will take its place. Another cycle of waiting and refilling will occur. After a said amount of cycles takes place (equivalent to the 2 nd bucket water level) the UVC lamp will power down and the system will once again wait for another water-level switch input to start the next batch.
3.2.2.4. Key features and added value
This design of sanitizing water in batches has several advantages over other options.
Turning the UVC lamp on and off repeatedly will reduce the lamp life, and uses extra power at each start-up. By using batches we keep the lamp on for longer periods of time, effectively increasing lamp life, and conserving our power. By having the water pass through the chamber at a relatively steady pace it helps carry away generated heat, and helps prevent the lamp from prematurely solarizing (the act of heat altering the lamp, creating a loss in transmitted wavelength). This also fits in well with the scalability of the system.
Let’s look at the big picture of the UVC lamp, UV sanitation chamber, and control system, and how it relates to our all important limiting factor: energy. Assuming 6 seconds and 5 ounces per cycle, with a 4 second filling/draining period, we can process
30 ounces per minute, and can do a gallon in four minutes, or 15 gallons/hour. The power consumption of the lamp is .5 amps/per hour, our total power availability is ~
1.9amp-hours. We will make a gross assumption that the control system for the solar panel and water purifier consumes .4amp-hours per day. At this rate we can process up to
45 gallons per day of full sun, of good clean water. This will be limited by the physical processing stage of the system which only processes 24 gallons of water per day. But
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this is not a bad thing as the system will have some play if perhaps it is not sunny out one day.
4. Future Objectives
4.1. Scalability
We took a quick look into the scalability of the system and should mention our findings.
If the solar collector system was increased in size from a 1 foot panel to a 2 foot panel system it would yield four times the amount of energy. The batteries of the system would also be required to be increased to better accommodate the higher energy production.
This would increase the output energy to 7.5amp-hours at 12V, but not significantly increase the tracking system energy consumption. These changes would increase the cost of the system from $200 to about $500.
5. Cost and Scheduling Issues
Our sanitation system as we envision it will run about $275. By spending about $500 we could increase our throughput to about 100 gallons per day (or 4 gallons per hour) by adding more ceramic filters and increasing our bucket sizes. The planned UV chamber itself has a throughput of approximately 15 gallons per hour and does not need significant changes. Figure 4. shows our estimated budget.
The lifespan of the system remains relatively unchanged. At 100 gallons per day the UV lamp life is about 3-4 years. The ceramic filter elements must still be cleaned and rinsed every 2-3 months, and will still last for more than 3 years. This up-scaled system could provide proper sanitation for more than 250 gallons of water on a full day’s sunlight and
100,000 gallons before a $400 dollar tune up. Of course there will be unspecified set up costs involved with implementing the system, and training on the maintenance of the system. This system though, could provide clean water for a hundred members of a church missionary or remote village in need. From far away, it appears that it would cost approximately $10 per person to provide clean drinking water for 3 years, this breaks down to 1 cent per gallon. It’s a small cost for life.
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Figure4. Budget table, maximum allocated budget requirements
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Bibliography
1) US Environmental Protection Agency - Ground water and drinking water report ~ http://www.epa.gov/safewater/contaminants/dw_contamfs/nitrates.html
2) Black Berkefeld - British Berkefeld Doulton ceramic filter element ~ http://www.british-berkefeld-water-filters.com/british-berkefeld-doulton-ceramicfilter-elements.html
3) 7 – Pollution Prevention Report Page 13 ~ http://www.p2pays.org/ref/03/02919.pdf
4) BBC News report on world water supplies. http://news.bbc.co.uk/1/hi/health/2640307.stm
5) UV light technology @ glowshop.com - Effect of UV on microbes http://www.uv-light.co.uk/applications/disinfection/uv_disinfection.htm
6) Technical Glass - Technical data ~ http://www.technicalglass.com/tech.htm#values
7) World health Organization – Water Sanitation report - http://www.who.int/water_sanitation_health/monitoring/en/Glassessment6.pdf
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