The U.S. Air Force participates in a wide array of activities such as fire training and washing of aircraft that generate wastewater containing suspended solids, oils and greases (O&G), petroleum hydrocarbons, emulsion stabilizing agents, and aqueous, film-forming foam (AFFF) liquids. Addressing these waste streams often causes fouling of existing treatment equipment, commonly oil/water separators, or risk of discharges to the environment that exceed regulatory standards. This project demonstrated Air-Sparged Hydrocyclone (ASH) technology with a trailer-mounted mobile unit to treat a variety of these aqueous waste streams at nine separate Department of Defense (DoD) installations.
The ASH technology combines the principles of froth flotation with the flow characteristics of a hydrocyclone to remove contaminants at a very low residence time. Air bubbles are introduced at the porous wall of the hydrocyclone while the centrifugal forces increase the inertia of fine particles and oil droplets to facilitate their attachment to the bubbles. AFFF is removed via adsorption to hydrophobic particles and by utilization of its own foam-forming capabilities.
At a throughput of 50-100 gallons per minute (gpm), the ASH technology provided 80-100 percent removal of O&G, petroleum hydrocarbons and AFFF from a variety of vehicle maintenance, vehicle wash rack, aircraft wash rack, jet engine test cell, and fire-fighting training pit waste streams. A residual AFFF level of less than 50 parts per million was achieved for each waste in which it was a constituent. Operation of the mobile unit was easy and could be quickly optimized to treat different waste types.
ASH technology removes O&G, oily solids, and AFFF from waste streams at low cost. Capital cost estimates range from $173,000 at 50 gpm to $225,000 at 150 gpm. Utility and chemical costs would range from approximately $0.17 per 1,000 gallons for AFFF removal only (i.e., no chemical treatment) to $2.54 per 1,000 gallons for extremely high O&G concentrations. In addition, repair and replacement costs for the alternative, more inefficient, oil/water separators are avoided. One estimate conducted by the U.S. Army Environmental Center stated that these repair and replacement costs of existing separators are on the order of $100 million.
Intermittent operation of an ASH unit is envisaged. The payback would vary from 2-7 years depending on the volume of the waste stream to be periodically treated, the concentration of the contaminants, and the cost of current treatment or disposal methods. Implementation of the ASH technology at DoD installations has already begun with delivery of a 50 gpm system to Naval Station Mayport in Florida. (Project Completed - 2003)