The problem of suspended solids in wastewater whether a by product of food processing such as proteins and oils, or mechanical processes where metals such as arsenic and other metals are suspended in water, and the resolution of that problem arise from the same science- and it isn’t always well explained in the best of reference materials.
Here it is: the smaller the particles, the greater the surface area, and therefore- the greater the amount of electro-chemical charge inherent to the particles is present.
Dissolved air by itself isn’t much to crow about. It rises to the top of any water it’s injected into, and escapes.
The basis of the problem, as I said and the cure, dissolved air flotation, both center on this basic physical fact.
Let’s say you have a cube that is 1 foot on each side. That’s 6 sq ft. of surface area, right? Now cut the cube in half. How much surface do you have? You retain the former area and add two more square feet. That’s 8.
Cut each piece in half again and you have 10.67, each piece contributing 1/3 x its original surface area. You grow the surface area by a substantial fraction each time you divide the original. We have a long way to go here because this can go on and on right down to the molecular level, in theory.
You turn a few sq. ft. of surface area into potentially millions when the division gets to the microscopic or molecular level.
If those billions of individual pieces have an electric charge, let’s say a positive charge, you’ve got problems because the particles now have enough charge and small enough mass that they all repel each other- Voila! suspended and unwanted particles in water. They may settle- in days, weeks, months, years… virtually never. You just may want to return the water a little cleaner than you just made it processing food or textiles, so what now?
Dissolved air, as mentioned, won’t help you alone- but you can give it its own charge too. Trace chemicals, usually based on aluminum, usually in parts per million, can be introduced to your water. Seems like more of a mess, doesn’t it?
The chemicals create their own charge and the particles now have something to which they can bond or attach electrically speaking. If you’ve got positive charges on each waste particle, you introduce negative charges on the newly introduced aluminum. A particle of aluminum may attract many waste particles and form a clump. Now we’ve got suspended clumps.
One more introduction of something in very tiny particles with a lot of surface area- and an opposite charge. Air. Not just air bubbles, but microscopic ones with an attitude (a charge) Now we’ve got action. The water is white with these very microscopic bubbles. They have little mass and buoyancy, so they’re not in a dead run for the surface. They collect plenty of your particle/aluminum clusters on their way to the top with millions of units of opposite charged surfaces. All the clusters- original waste solids, clumped in microscopic size bits around flocculant aluminum or other introduced medium, and billions of tiny air bubbles that collect around these larger particles (the air bubbles are extremely small). All rises to the top in a nice sludge the consistency of cooked oatmeal. Skim it off and you have clear water that is clean enough to send back to town without the taxi fare of pollution credits.
This operation is known as dissolved air flotation and it’s relatively cheap compared to systems that use membranes to squeeze water through under high pressure. The equipment that does this is called a DAF so that the acronym becomes a noun. A DAF uses varied techniques and DAF pumps to achieve the right balance of chemicals, charges and volume to clean the water for each application. Formulas are generally used and adjusted while the waste water flow is analyzed and the balance of flocculant and air are tweaked. The biggest expense of the operation tends to be the DAF pumps, followed by chemicals to use as flocculant. The cost of chemicals is ongoing, but when a DAF pump must be replaced, it can far outweigh what was spent on chemicals. The Keystec Air-Whip DAF pump reduces this replacement cost to a fraction because it’s both cheaper to manufacture and buy and lasts far longer than the 6 or 12 month life expectancy of most competitors.