USFilter will feature its new GFH™ media systems at the American Water Works Show in New Orleans, LA, June 16-19. Municipalities concerned with arsenic in the drinking water can employ the company's Granular Ferric Hydroxide (GFH) to battle the contaminant. The GFH system is an adsorption process capable of removing arsenic and other heavy metals from raw water.
USFilter has entered into an exclusive marketing agreement with GEH Wasserchemie GmbH of Germany to market the media, which has been used in Europe for many years to help municipalities meet the World Health Organization arsenic standard of 10 micrograms per liter.
GFH media systems remove arsenic, chromium, lead selenium, antimony, uranium and other heavy metals from groundwater.
The system is operated as a fixed bed adsorber. Typical installation is in pressure vessels to allow a single pumping stage for the treatment system. Water continuously passes through the media bed where arsenic is adsorbed from the water onto the media. The vessels are arranged in parallel or series arrangement with an empty bed contact time of five minutes. The pressure vessels are backwashed once every two to six weeks to prevent bed compaction and remove trapped particulate.
Once the GFH media is exhausted, it is removed from the vessels and new media is installed. Exhausted media has passed TCLP tests and in most instances can be disposed of in a non-hazardous landfill.
Parallel or series operation depends on the required removal concentrations. If a consistent 90 percent reduction is needed across the system, the series design is used. However, if the percentage is less than 90 percent, then the parallel design is typically applied.
Parallel Systems
The three, in-service vertical pressure vessels in a parallel system are each designed to treat 1/3 of the incoming flow at a hydraulic loading rate of 5 gpm/sq.ft. A five-minute empty bed contact time (EBCT) is provided through the parallel system, plus backwash water is supplied solely from the in-service vessels where they are backwashed during the same event. During the initial start-up of the plant, one vessel is placed on-line where it begins the exhaustion curve. Subsequently, the second vessel is started and later the third one is activated. This process causes all the vessels to operate at varying degrees of exhaustion, and the blended effluent concentration is below the desired level.
Series Systems
The three pressure vessels in a series system function in a lead, lag, stand-by sequence. The hydraulic loading rate is 8 gpm/sq.ft. and, similar to the parallel system, provides an EBCT of five minutes total or 2.5 minute EBCT per vessel. Backwash water is supplied from the raw water source, or returned from the system. Again, as in the parallel system, in-service vessels are backwashed during the same event. When the lead vessel media is exhausted, it is isolated and the lag vessel shifts to the lead vessel. At that time, the stand-by vessel progresses to the lag sequence. Following this process, the exhausted media is replaced in this vessel and it becomes the stand-by vessel.
The series flow systems include a by-pass line in order to blend raw water with the treated water until the desired effluent is achieved. In a series design, the lag unit receives a lower concentration of contaminants, which creates a more consistent removal throughout the system. The series system, however, treats a lower flow rate than the same size vessels in a parallel unit.