Filtration of fly ash

[gacguy]

There is a pond that contains cooling tower and boiler blowdown water that has been used to sluice fly ash. I have an opportunity to bid on supplying filters to filter the supernatant water from the pond. I have no information on the particle size distribution or concentration.

For this application, what would be the highest gpm/sq ft
that should be used for sizing the media filter? What combination of media would you suggest? I was thinking of using sand and garnet.

 

[DeltaCascade]

Hi. Yes, multimedia filter looks like a good place to start; flowrates are likely high enough to justify it, too. The particle size will likely be highly variable. The waste water you are using will likley be very high in hardness (supersaturated) and relatively high in phosphate concentration. Adding alkaline fly-ash will cause hardness to precipitate out. Particle size may be small .. colloidal in nature. Filter aid chemical use may be recommended. You will likely have pH control problems as alkaline hardness sludge settles to the bottom of the pond. Depending upon flowrates and economics, I wonder if feeding ash and the wastewater to a clarifier may be best; the "free" alkalinity and hardness precipitation may soften the water (the softened water may be recycled to cooling tower, although dissolved solids (salts) may increase conductivity and corrosivity somewhat.

Either way it appears that your ultimate waste water will be rather salty.

Hope this helps a bit. Good luck.