Organoclay used to lower cost of activated carbon use
Organic hydrocarbons and PCB’s were to be removed from the sediments of a creek bed in western New York State as part of a NYSDEC consent order. The contractor proposed and designed a system that resembled an environmental dewatering project, including adsorption treatment of the effluent process stream.
The contractor designed a wastewater treatment system, which included two 7000-gallon multiplayer media sand filters, which included organically modified clay (organoclay), and two 7000-gallon activated carbon adsorbers. The creek bed sediments weere contaminated with PCB’s and hydrocarbons. The sediments were dredged from the creek, lime stabilized, and passed through an 80 cubic foot plate frame filter press. The effluent was then passed through the multi stage adsorbed system.
The first multi-layer adsorber vessel had three layers, which comprised: one foot of pea gravel over a retaining screen, then four feet of grade 68 sand, and on top of this 1 foot (2000 lb) organoclay from Biomin, Inc., Ferndale, MI. The organoclay was used primarily to remove the organic hydrocarbons, such as hydraulic oils, and the PCB. The PCB was partitioned into the hydraulic oil. The activated carbon was used as a polisher, to ensure no PCB would escape in the effluent. Organoclay is a bentonite modified with quaternary amines. The granules are blended with anthracite to keep the interstitional pore spaces open.
Organoclay removes seven times as much oil as activated carbon, and lowers operations costs by 50% or more. Periodically, the organoclay was replaced as it became saturated with hydraulic oils. Because the organoclay comprised the uppermost layer, it was easy to remove the flanges of the vessel to gain access to the system and remove the organoclay/anthracite blend.
A laboratory test revealed that the spent organoclay contained levels of less than 50 ppm PCB, which meant that, under New York regulations, the spent organoclay could be disposed of in a standard landfill.
It is suggested that this set up, including the organoclay/activated carbon combination, be used for the Hudson River cleanup.