Desoaping Method

After chopping the plastic water bottles, we are going to wash the chopped pieces, including microplastics and macroplastics. To implement this properly in our microplastic removal system, we must utilize a washing system that does not interfere with our ferrofluid. We have conducted tests on the interaction of dawn dish soap with microplastics and determined a combination of this soaping method with a portable washer rinse will be most beneficial to our project. Refer to the “Ferrofluid Interaction” memo for our preliminary thoughts and background research that influenced our decision.

Desoaping Method

When testing the soap against ferrofluid in water, the ferrofluid had a repelling reaction to the dawn dish soap. This reaction then concentrated the ferrofluid into itself and contained it from spreading out more. They act as immiscible liquids when placed together in water, so they will not combine. Their differing densities play into their inability to combine, with dawn dish soap having a density of 1.06 g/mL and ferrofluid having a density of 1.2-1.42 g/mL. When combined with plastic, the ferrofluid will latch onto the plastic before dawn dish soap does and be left with soap and water left in the 5-gallon stock pot. Due to this interaction, we will desoap the system by using a pump to move the soap, water, and excess ferrofluid mixture to a waste bin. The waste bin will be the mixing bin that the senior design group used last year. Without the presence of plastic in the waste bin, separation of the various liquids can occur there. We are not worried about trace amounts of soap being on the same piece of microplastic as ferrofluid since that did not influence the electromagnets ability to pick up the microplastics.

Rinsing Method

Our group will use a portable washer at the base of our 5-gallon stock pot to rinse the plastic and move the liquid around for separation. Our pot will have a 5mm mesh screen halfway up the water line to keep the macroplastics separate from the microplastics. A drawing of our washing system design can be seen on our website under semester II products. To properly rinse the microplastics, our washer will be run for approximately 40 seconds, with a reversal of the direction of washing at 20 seconds into the process. The portable washer creates a circular motion in the 5-gallon stock pot that will rinse the plastic along with the ferrofluid and soap. The 5mm mesh screen will keep the macroplastics separate at the top and let the microplastics fall into the lower portion of the stock pot to be collected by the electromagnets due to the ferrofluid-coated microplastic’s attraction.  

The combination of desoaping the system by pumping the wastewater stream with soap to another bin and rinsing the plastic by using a portable washer will allow our ferrofluid system to work properly. Since soap does not have an effect on our ferrofluid system, we are not concerned about getting full separation from soap and our ferrofluid system. The wastewater storage bin can be utilized later for separation of ferrofluid, soap, and water for potential recycling back into the system.