Single-Stage Water Filter with Dual Sand Media Sizes

The goal of the project is to develop a filtration system that utilizes two sand sizes to increase the efficiency of clearing water of suspended solids.

=Problem Definition=

Scope:

Form multidisciplinary engineering design team to explore novel approaches to efficiently integrate two similar water treatment stages into one. Designs and deliverables will inform sustainable water reuse and recovery systems and form a foundation for next generation treatment technologies.

Background
Water filtration systems are useful tools for removing contaminants from water. This is done all around the world for many reasons, from agriculture work, food processing, and even simply making a source of clean drinking water. There are also many forms of filtration systems. Systems that use sand as the filter have been used for many years, as sand filtering is one of the best methods of cleaning water. Currently at the University of Idaho campus are two of these filtering systems that each use a different sand, with the water going through both systems. Combining those systems so that water is filtered with two sands within a single cycle would be a beneficial improvement.

Deliverables
Fall

Model 1 - no screen

Model 1 - with screen

Flow Analysis 1

Flow Analysis 2

Colored Sand

Spring

Specifications

 * Minimum 75% separation of the two sand sizes.
 * Chemical and corrosion resistance.
 * Minimum upflow rate of 1.8 gallons per minute.
 * Maintain a bed turnover rate of 0.7 to 1.4 inches per minute.
 * Continuous operation with a maximum of 30 minutes of routine weekly maintenance.

=Design Considerations=


 * Assessing wear on components
 * Airlift with Dual Inlets
 * Achieving 75% sand separation

=Project Learning=

Design One




 * Water turbine forces sand to the sides of the box
 * The two sands move to have the fine sand against the walls while the coarse sand is closer to the augur
 * A swirled layering of fine and coarse sand occurs, like soft serve ice cream

Cons:
 * exacerbates erosion on surfaces with sand
 * Maintaining pressure head can be difficult without the use of a pump
 * Turbine and augur system add substantial complexity and cost to the system

Design Two




 * Sand Separation using Elutriation.
 * Separated beds to ensure particle segregation.
 * Water up flow through channels separates particles based on unique settling Velocities

Cons:
 * Changes in head pressure affect velocities
 * Concentric Tubes do not allow multiple airlift inputs
 * Separated beds may results in emptying/filling bed areas
 * Difficult to test and adjust up flow velocities.

Design Three




 * Segregation using Wedge wire screen
 * Bed segregation created by different outlet locations.
 * Airlift with two inlets.

Considerations:
 * Airlift inlet may result in contaminated sand getting deposited into fine bed.
 * Bed turnover / airlift inlet rate must ensure no clogging from Course outlet.
 * Brazilian Nut affect (Coarse sand migrating upward)
 * Ensure 75% segregation.

Current Design


 * Test stand fully built and ready to be implemented

Ideas










 * Separates particles by elutriation
 * Lighter particles are moved upwards by the airstream and heavier particles can fall through

=Final Design= Performance Testing

To analyze the effectiveness of the water filter at maintaining bed separation, a random sample was taken from the fine bed and weighed before any filtering took place. After the mass of the mixed sand was taken, the sand was filtered through the same perforated sheets as used in the design of the device. All the particles that fell through the screen were correctly placed in the right bed, while any residual particles were a result of incorrect separation. The governing equation for testing is,

1)

Where %filtration is how much correct sand filtration is occurring in each bed, and m is the mass of each sample.

Upon running this analysis with the wet sand, the % filtration rate was found to be 84% on average. This was found to be higher than our requirement of >75% separation therefore deeming our objective met for separation.

Addressing Risks

To improve the effectiveness of the filter, certain risks should be addressed. This will enable further prototypes to be more effective, and to improve on the objectives mentioned earlier for this design.

The first risk to work on is the presence of rust on system components. By using a liner for all high traffic sand areas for the sheet metal, this should lower rust dramatically. The type of liner recommended should be a steel, cement, cast basalt liner. This will also protect against any scratching coming from debris that lodges out from the sand. The base material to be used should be either stainless steel or some type of rust resistant high-strength plastic.

The second risk to address is proper sealing of the bed separation layer. This can be improved by using wedge wire and changing geometry of the tank for a better fit. A wedge screen would be lighter than the current separator and increase water up flow. It may also be cheaper but requires further viability testing.

Another future development to focus on would be creating a gradient for the bottom layer of each sand bed to minimize clumping. This would be easy to implement in further geometry tested models and should minimize stagnant sand that refuses to restart its cleaning cycles. A simple ramp leading to each airlift would be cheap and increase cleaning effectiveness.

Improving Designs

The biggest design improvement would be creating a part to allow sand up flow into a single up flow pipe. A prototype part was designed for the capstone project, but it needed further design testing to enable proper suction. The part that was designed was a couple with holes in the side that would act as suction holes. In concept, this would suck sand in from the fine bed while having the up flow pipes grab coarse sand and then mix it on its way to the wash box. If this part could be further developed, only one up flow pipe would be necessary, and it may free up additional space in the tank while increasing volumetric flow rates of sand. =Validation=

Clean water is arguably the world’s most valuable resource; therefore, it is important to invest in water filtration technology. Currently the U of I’s Clean Water Machine design is a two-stage dual media sand filter, but by refining the design to require a single filtration stage, a significant reduction in maintenance and increased efficiency can hopefully be achieved.

=Team Members=

=Additional Documentation=

Project Schedule



Meeting Minutes



Presentations



Client Interview