EXXFLOW/EXXPRESS Demonstration Unit
EPOC WATER, INC.
(Precipitation, Microfiltration, and Sludge Dewatering)
TECHNOLOGY DESCRIPTION:
The precipitation, microfiltration, and sludge dewatering treatment process uses a combination of processes to treat a variety of wastes. In the first step of the process, heavy metals are chemically precipitated. Precipitates and all particles larger than 0.2 micron are filtered through a unique tubular textile crossflow microfilter (EXXFLOW). The concentrate stream is then dewatered in an automatic tubular filter press of the same material (EXXPRESS).
EXXFLOW microfilter modules are fabricated from a proprietary tubular woven polyester. Wastes pumped into the polyester tubes form a dynamic membrane, which produces a high quality filtrate and removes all particle sizes larger than 0.2 micron. The flow velocity continually maintains the membrane, maximizing treatment efficiency.
Metals are removed via precipitation by adjusting the pH in the EXXFLOW feed tank. Metal hydroxides or oxides form a dynamic membrane with any other suspended solids. The EXXFLOW concentrate stream, which contains up to 5 percent solids, enters the EXXPRESS modules with the discharge valve closed. A semidry cake, up to 0.25 inch thick, is formed inside the tubular filter. When the discharge valve is opened, rollers on the outside of the tubes move to form a venturi within the tubes. The venturi creates an area of high velocity within the tubes, which aggressively cleans the cloth and discharges the cake in chip form onto a wedge wire screen. Discharge water is recycled to the feed tank. EXXPRESS filter cakes are typically 40 to 60 percent solids by weight.
Other constituents can be removed using seeded slurry methods in EXXFLOW. Hardness can be removed by using lime. Oil and grease can be removed by adding adsorbents. Nonvolatile organics and solvents can be removed using adsorbents, activated carbon or powdered ion-exchange resins. If the raw feed contains a high percentage of solids, EXXPRESS can be used first, with EXXFLOW acting as a final polish for the product water.
The EXXFLOW/EXXPRESS demonstration unit (see photograph on previous page) is transpor-table and is mounted on skids. The unit is designed to process approximately 30 pounds of solids per hour and 10 gallons of wastewater per minute.
WASTE APPLICABILITY:
When flocculation and precipitation techniques are used at close to stoichiometric dosing rates, the EXXFLOW technology removes mixed metals, total organic carbon (TOC), dissolved and suspended silica (including fumed silica), and other lapping and grinding compounds sized at 0.10 micron.
When the EXXFLOW technology operates with finely divided adsorbent powders, it removes contaminants such as isophthalic acid, acetic acid, methyl ethyl ketone, fluorides, and phos-phates from effluents generated by semiconduc-tor manufacture. Treated effluents can then be reclaimed for reuse.
The EXXPRESS system can handle waste streams containing up to 5 percent solids to produce semi-dry cake of 40 to 60 percent solids by weight.
STATUS:
This technology was accepted into the SITE Demonstration Program in 1989. Bench-scale tests were conducted in 1990. The SITE demonstration was conducted during May and June 1992 on highly acidic mine drainage from the Old Number 8 mine seep at the Iron Mountain Superfund site in Redding, California. Reports will be available in 1995.
This technology was commercialized in 1988. Treatment systems have since been installed at over 45 sites worldwide. System capacities range from 1 gallon per minute to over 2 million gallons per day.
DEMONSTRATION RESULTS:
Developer claims for metal removal efficiencies on acid mine drainage, when neutralizing with sodium hydroxide (NaOH) and calcium hydrox-ide [Ca(OH)2], were generally met or exceeded except for aluminum. This was most likely due to excessive alkalinity (very high pH) produced by the added NaOH and Ca(OH)2, which redis-solved the aluminum. The claims for all metals, including aluminum, were exceeded when mag-nesium oxide (MgO) was used as the neutralizing agent. In most cases, there were no detec-table concentrations of heavy metals in the permeate samples.
Filter cake produced from the demonstration test contained approximately 12 percent, 31 percent, and 30 percent solids when NaOH, Ca(OH)2, and MgO, respectively, were used as the treatment chemicals. Toxicity characteristic leaching procedure (TCLP) tests performed on the filter cake showed that leachable levels of TCLP metals were below regulatory limits for each treatment chemical tested.
FOR FURTHER INFORMATION:
EPA PROJECT MANAGER:
Jack Hubbard
U.S. EPA
National Risk Management Research
Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7507
Fax: 513-569-7620
TECHNOLOGY DEVELOPER CONTACT:
Rodney Squires
EPOC Water, Inc.
3065 North Sunnyside
Fresno, CA 93727
209-291-8144
Fax: 209-291-4926