Grantee Research Project Results
Final Report: Design and Testing of a Point of Use Electrolytic Chlorine Generator for Drinking Water Disinfection in Poor Countries
EPA Grant Number: SU833521Title: Design and Testing of a Point of Use Electrolytic Chlorine Generator for Drinking Water Disinfection in Poor Countries
Investigators: Just, Craig , Tuttle, Robert D. , Meggo, Richard E. , Teed, Richard H. , Lozier, Matthew J. , Moriarty, Holly M. , Gwinnup, Aaron , Keenan, Alexandra , Smith, Jessica , Donham, Joel , Lamb, Jon , Schafer, Michael , Heacock, Nicole , Frystak, Phillip , Rhoads, Thomas
Institution: University of Iowa
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 30, 2007 through May 30, 2008
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2007) RFA Text | Recipients Lists
Research Category: Drinking Water , P3 Challenge Area - Safe and Sustainable Water Resources , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
More than 1 billion people lack access to improved water and as a result, there are 1.6 million annual deaths resulting from unsafe drinking water. Ninety percent of these deaths are children under the age of five.
A growing body of research correlates the usage of pointofuse water treatment and safe storage with improvements in microbial water quality and diarrhea reduction. This pointofuse technology can be:
- Rapidly implemented
- Costeffective
- The most effective of currently available water, health, and sanitation interventions
To realize the potential of pointofuse technology, it must be safe for users and suitably robust for daily use in demanding settings, while simultaneously a culturally sensitive solution that promotes sustainability. A pointofuse water treatment product is only effective in lowering mortality if it is used consistently and correctly, thus emphasizing the need to identify approaches that will increase the acceptance of such a product and contribute to the longterm success of the endeavor.
The U.S. Centers for Disease Control and Prevention and the Pan American Health Organization developed the Safe Water System (SWS). SWS is a pointofuse water treatment approach that employs locally purchased sodium hypochlorite (bleach) for disinfection, followed by safe water storage to prevent recontamination. Maintaining longterm use of the SWS requires significant resources and ongoing donor support for activities such as social marketing, promotion, and product distribution. These demands call into question the sustainability of the SWS.
Household bleach production, through the use of an electrolytic cell, may allow for a onetime product investment as well as a shorter user education period to ensure longterm use. Additionally, this approach may be more feasible in remote areas or areas where decentralized access to bleach may be a more prudent solution.
It is in this context that the following problem definition was developed. The design team must develop and test a low cost, individualized electrolytic chlorine generator that can generate high concentrations of bleach from water containing sodium chloride. The apparatus must also be safe for users, suitably robust to withstand daily use and easy to maintain or repair. To best accomplish the goal of improving the quality of drinking water worldwide while increasing sustainability and establishing global partnerships, the following design objectives were established for the project:
- The final product must be affordable to individual families in developing countries
- The system must be less cumbersome than the current designs
- The chlorinator must be powered by a renewable, easily accessible energy source
- The device must be easy to maintain and resist corrosion
- The device must be safe and portable
Summary/Accomplishments (Outputs/Outcomes):
The final electrode design, which utilizes a mixed metal oxide anode, is the result of multiple refinements made throughout the testing process. The following list of observations, theories, and assumptions contributed to the ultimate design:
- The anode and cathode should be roughly equidistant and relatively close together for maximum ionic interaction
- The action of the rising bubbles should be utilized to enhance mixing and convection of solution in the reaction cell
- The anode needs to be highly oxidation resistant, whereas the cathode needs to be highgrade stainless steel at best
- The entire volume of the cell should be relatively close to the electrode
- The anode should constitute a larger surface area than the cathode
- A “tubeintube” design with a porous anode surrounding the cathode combines these attributes well
The material chosen for the anode is a proprietary product called “ELGARD™ 150 Anode Ribbon Mesh,” and is produced by Corrpro Companies, Inc. The actual substance is referred to as a “mixed metal oxide” coated titanium mesh. This material was chosen for its high corrosion resistance, high conductivity, relatively low cost, and its physical properties (the small mesh enhances fluid mixing). The cathode is highgrade stainless steel “allthread,” which has both good corrosion resistance, and maximized surface area per inch of length.
This electrode operates at ~3.0 volts and while any amperage is sufficient, a minimum of ~300 mA produces hypochlorite reasonably quickly. With the handheld crank generator – which operates “normally” at ~600 mA – the desired hypochlorite concentration is produced in two to three minutes, depending on the volume of chloride solution used. A suitable electrode prototype was developed and tested for output characteristics and predictability. During the hypochlorite production trials, it was established that hypochlorite production is linearly proportional to cranking time and inversely proportional to volume of solution in the reaction cell. The cell was operated for different time durations, and with different volumes of solution. The solution used for all trials was 3% NaCl (w/w).
During the variance trials, all parameters were held constant and the device was operated for 150 seconds, five times. Two operators turned the crank, the output was compared, and basic statistics were calculated. The hypochlorite concentrations were determined using Hach® “High Range, Free Chlorine” test strips. With a target of 400 ppm, a cranking duration of 2.5 minutes was chosen based on previous tests. From the five trials, the average concentration generated was 380 ppm, with a standard deviation of 20.9 ppm. This means a “random” user operating a properly filled unit with a 3% NaCl solution; cranked for 2.5 minutes to treat 20L of water would be 97% certain to produce a final hypochlorite concentration between 3.4 and 4.2 ppm. This suggests that the device can reliably and predictably produce the desired concentration of hypochlorite with no more input than a means of measuring time passage, and a means of measuring mass and volume (to prepare a 3% solution).
One working model reaction cell used for testing was a simple, 10 oz, plastic water bottle, with the electrode fitted to the cap. The anticipated cost of materials to produce an initial run of this design is approximately $8 per unit. The cost per unit to produce boxcar quantities could easily be as low as $5. These tabulations do not include labor. A semiskilled worker can assemble one of these devices in approximately 2 hours. The flashlight housing with integrated power generator design is a refinement of the water bottle design that packages the same technology into a more convenient, portable device. An identical electrode was fitted to the clear body of a standard flashlight with the insides removed. Based on the found relationships between volume and cranking efficiency, the flashlight body should operate with less effort than the water bottle, due to its narrower geometry. The anticipated cost of materials to produce an initial run of this design is approximately $12.50 per unit with most of the cost associated with the flashlight body. The cost per unit to produce boxcar quantities could easily be as low as $8. These tabulations do not include labor. A semiskilled worker can assemble one of these devices in approximately three hours.
The more sophicated, but more expensive, milled housing prototype consists of a single primary PVC unit to maximize durability, as it was determined that a two piece system would make the device more susceptable to damage and corrosion. Furthermore, a onepiece system will allow for easier transport. Pro/E software was used to create a unique, functional housing. The milled housing features the crank in the bottom of the device, room for a circuit or battery (if further iteration required such components) in a sealed compartment in the center of the housing, and the reaction vessel attached in the top compartment. The top is open to allow the saltwater to be poured in and reaction gases to escape. The lid of the device slides over the reaction vessel in a tight slotted interferencefit to protect the electrodes when not in use. Additionally, the lid doubles as a measuring device. A depression on one side of the lid is used to measure the amount of saltwater or freshwater to add to the chlorinator, and on the other side of the lid, a depression is used to measure the amount of salt (if freshwater is used). Having a disconnected lid to measure and pour water/salt eliminated the need to immerse the entire device in water, thereby reducing the risk of component corrosion. The prototype allows the user to place the system on a flat horizontal surface for stability during cranking.
Conclusions:
Through iterative research, design, and testing a workable, sustainable solution to the global issue of unsafe drinking water was developed. Three different designs have been proposed, and all of the initial objectives have been maintained. The proposed device is portable, selfpowered (requires no batteries), effective, simple to use, and can be assembled mostly from ubiquitous materials in the developing world.
Of the three designs, the “water bottle” model seems to be the most sustainable option. All an organization would need to assemble a batch of devices would be the corrosion resistant anode material, a length of stainless steel rod, commonly available minor parts, and welldocumented instructions for assembly and operation. This strategy results in the least unnecessary shipping, the most units produced per dollar spent, and the most adaptability to local materials and customs. Another important aspect of assembly in situ is that local citizens are involved in the program from the beginning. Acceptance and proliferation of programs has been shown to increase when the beneficiaries are included in designing the solutions.
So far, the concepts have been turned into designs, and the designs into prototypes. The prototypes have been tested on the lab bench and approved by users in Mexico. The problem has been clearly stated, and the benefits of their solution calculated. Further development of this proposal would include refining the design specifics for manufacture, thorough testing of the device for longterm performance, procurement of partnerships, and production of an initial run of devices. The costs clearly outweigh the benefits, and the technology is simple and sustainable.
Proposed Phase II Objectives and Strategies
Our Phase II proposal focuses on exploring methods and partnerships for packaging and regional distribution of inexpensive handheld bleach generator construction kits. We will partner with Corrpro, Inc. to determine the most inexpensive and practical means to package and ship the electrode materials needed for a semiskilled worker to construct a portable bleach generator. We will work with our established partner, International Water Management Systems, and we’ll seek additional distribution/implementation partners in Mexico and Haiti.
The Phase II proposal incorporates a novel educational component with the inclusion of a graduate student to oversee the project, seek partnerships, travel to Mexico and/or Haiti to work with distributors and endusers, and to mentor students during two semesters of Design for the Developing World (53:141) to be taught in the fall of 2008 and 2009 in the College of Engineering at the University of Iowa. We feel that students trained at advanced levels in the sustainability principles of the EPA P3 Program will provide amazing longterm benefits to people, our prosperity and the planet.
P3 Phase II:
Design and Testing of a Point of Use Electrolytic Chlorine Generator for Drinking Water Disinfection in Poor CountriesThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.