Recovery of Wastewater Treatment Chemicals from Fly Ash

Abstract

Fly ash is currently being generated at a rate of millions of tons every year and represents a growing solid waste disposal problem. In an effort to examine alternative uses for this waste product, fly ash was investigated as a source for wastewater treatment chemicals. Through a sequential caustic/acid leaching process, portions of the iron, aluminum, and silica in fly ash were solubilized allowing for the recovery of these materials in a useable form. Synthetic additives derived from this process were evaluated as coagulants in wastewater treatment and as conditioners for sludge prior to mechanical dewatering. Conventional laboratory scale jar tests were conducted for comparing coagulant effectiveness. Sludge conditioners were evaluated by performing vacuum filtration tests using a Buchner Funnel apparatus. The fly ash derived additives performed as well or better than commercially available chemicals. Synergistic activity is believed to occur when using the synthetic materials due to the mutual effectiveness of the solubilized portions of aluminum, iron, and silica present in the treatment additive. The synthetic additives are more cost effective in the treatment of wastewater and sludge than ferric chloride and aluminum sulfate.