Coal Ash Water Treatment: Heavy Metals Removal Through Enhanced Filtration

Eric Bradley-1

Eric Bradley | July 23, 2018

ProAct services has been active in the treatment of coal ash pond water throughout the US since prior to 2016. In many of these ponds, levels of arsenic, hexavalent chromium, selenium, thallium, and suspended solids are found at critical levels. Each contaminant may be present in various forms including particulate, depending on water conditions such as pH and temperature.  These contaminants are highly toxic and require customized dewatering treatment through chemically enhanced filtration mechanisms.

process-water-newProAct’s specialized treatment methods of filtration enhanced with HaloKlear's Natural Flocculants and dissolved-metal targeting methods were put into place utilized to treat the contaminated water. The goal of this treatment was to significantly reduce the levels of toxicants in the coal ash water to below discharge limits, which may be as stringent as 10 μg/L.

ProAct's mobilized treatment system began with pH adjustment, as the solubility of each metal is in part a function of the acidity of water. Iron salts were next injected into the treatment train, a flocculant method historically proven to reduce dissolved arsenic concentrations. While efficient in capturing dissolved arsenic, these particles remain difficult to remove through physical filtration because of their small size.

To remove iron flocs and particulate metals, two of HaloKlear’s natural flocculants were coupled to increase filtration efficacy. Adding the two flocculants together added weight to smaller particles, so a clarifier could be used to remove the metals. Collected sludge from each clarifier was then sent to geotextile bags for bulk dewatering and sediment control. These bags removed the treated flocs that resulted from the paired flocculants, reduced sludge volume, and associated disposal costs as decant water was returned to the treatment process. This water then passed through sand and bag filters and through a final polishing filter. The usage rate of bag filter elements was dramatically decreased through the enhancement of the chemical treatment steps.

Over the course of dewatering activities on site, ProAct's filtration and HaloKlear's Natural Flocculants treated over 227.6 million gallons of water at flows up to 3,000 gpm with no discharge violations. The system’s successful performance will be the basis for future dewatering application design and operation.