Design Exclusions, Constraints, and Requirements
Project Exclusions
This project excludes the construction of a bench-scale model and full-scale water filtration unit as well as implementation. Therefore, no laboratory or field testing will be conducted for a bench-scale model or full-scale water filtration device. Rather, a final design will be proposed based on laboratory testing of materials and various configurations of these materials. This exclusion is a result of time constraints for this project. Also as a result of time constraints, reaction kinetics for the materials chosen as alternatives cannot be established. The point of breakthrough for each material will also be unknown. Without this information, it is not possible to determine when the material will be exhausted, which makes it impossible to determine time intervals between maintenance. This limits the economic analysis for the project. An economic analysis which includes maintenance, replacement, and lifetime costs for filter materials is not possible in absence of this information.
Design Constraints and Requirements
Taking into consideration the lack of infrastructure and electricity in much of the former Bennett Freeze Area as well as the requests of the Forgotten People organization, the following design constraints and requirements are developed for this project. The constraints impose restrictions on the design of the water filter. Requirements indicate what the design must accomplish.
Design Constraints |
Design Requirements |
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The device must:
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The device must:
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Criteria Descriptions
Point-of-Use
A point-of-use filter is the most viable water filtration option for the residents of the former BFA. This is for several reasons. Residents haul their water from community sources to their homes. According to the Program Director of Forgotten People, Marsha Monestersky, installing any form of water treatment at the wellhead would require a lengthy and bureaucratic permitting process from the Navajo Nation. Therefore, a wellhead water treatment system is not advisable. Additionally, residents have been hauling water in large containers, and they are apt to continue using the same containers if a wellhead water treatment system is installed. These containers may contain uranium and arsenic residuals as well as bacteria. Therefore, it is best that a point-of-use water filter is developed for at home use to treat water after it has left the hauling containers.
No Electricity
Many residents in the former BFA do not have access to electricity. Those that do may utilize low-power solar panels or expensive generators. Therefore, the water filtration design should be able to operate without electricity.
Low-Cost
Most of the residents of the former BFA live in a state of poverty. Therefore, the final cost of materials, construction, and long-term maintenance of the proposed water filter must be kept to a minimum. In order to keep costs low, a low-tech solution will need to be developed. However, due to the project exclusions, noted in section 1.6, it is not possible to determine maintenance and replacement costs of the filter materials, nor is it possible to determine the cost of a full-scale device. Therefore, it is difficult to make a comparison of the design alternatives based on anything other than initial capital costs. While ensuring the cost is minimized is crucial for any water filter that will be implemented in the BFA, it is not feasible at this time to use this constraint as a criteria in design selection. It should be considered, however, in subsequent improvements to this project.
Ease of Maintenance
In order to ensure that the water filter functions as intended with minimal downtime, it must be well-maintained. Maintenance time and complexity should be minimized for the end user so that the filter is easy to service. The filter life should be maximized so that time between necessary maintenance is minimized. If maintenance is time consuming or difficult, residents may decide it is not worth using in their homes. For the same reason described under Low-Cost, and explained in section 1.6, Project Exclusions, required maintenance of the selected filter materials is currently unknown. While ensuring that the ease of maintenance is important, it is not feasible at this time to use this constraint as criteria in design selection. It should be considered, however, in subsequent improvements to this project.
Ease of Waste Disposal
The designed water filtration unit will require some form of waste disposal for the collected uranium and arsenic. The design should be able to facilitate easy and safe waste disposal. However, without current knowledge on the longevity of filter materials and the timeframe for waste disposal needs, it is also not feasible at this time to use this constraint as criteria in design selection.
Reduction of COCs and Coliform-Free Water
The main goal of this project is to design a water filter capable of reducing the uranium and arsenic concentration to levels below their MCLs and to provide coliform-free water in order to provide safe water for drinking.
Operational pH Range
The water filter must be able to operate in an initial water pH range of 7.5-8.4, which is the pH range of the water from the wells in the former BFA, as discussed in section 2.1.1, Water Chemistry of the BFA Wells.
Filtration Time
The water filter should be able to produce clean water in less than four hours, at the request of the client, so that residents do not have to wait for long-periods of time for water purification.