Water Technologies

GFH® Media for Arsenic Removal

Municipalities concerned with arsenic in the drinkingwater can employ Granular Ferric Hydroxide (GFH) tocomply with Environmental Protection Agency (EPA)Arsenic Rule. The GFH® system is an adsorption processcapable of removing arsenic and other heavymetalsfrom rawwater supplies. Arsenic is common ingroundwater sources and thehealth effects associatedwithhigh concentrations indrinkingwater include skinlesions, skin cancer, and several internal organ cancers.SiemensWater Technologies realizes the importance ofarsenic removal and the GFH® system is one of oursolutions tomeet the standards of today, as well astomorrow.

The arsenic standard implemented by the EPA of 10parts per billion (ppb) in drinking water has promptedmunicipalities to comply with strict and increasedguidelines when considering arsenic removal options.The GFH® system canmeet the standards set by the EPAwith a simple design process that requires minimaloperator attention and produces a low liquid wastevolume.

The GFH® system utilizes a ferric-based, non-regenerativemedia to adsorb arsenic, selenium,phosphate, chromium and other heavymetals fromdrinking water. Like other adsorption processes, thewater is simply passed through themedia to remove thecontaminants. Once themedia has depleted itsadsorption capacity, it is removed from the vessel andreplacementmedia is installed. In many cases, theexhaustedmedia can be discarded in landfills andclassified as non-hazardous waste after passing a TCLPtest. On-site storage of regeneration chemicals andconcentrated waste disposal issues are eliminated withthe single usemedia.

The adsorption life of themedia relies on rawwater pH,arsenic concentration levels, and operating cycles perday. GFH®media does not require preconditioning orpre-oxidation procedures inmost cases, and the use ofnon-regenerativemedia are design features that areideal for small andwellhead applications, particularlywhere no treatment currently exists.

Simple, Safe Arsenic Removal

Typical raw water quality:pH 5.5 – 9.0Oxygen > 0.5 ppmFerrous Iron < 0.2 ppmManganese < 0.05 ppmAluminum < 0.2 ppmSilica < 20 ppmPhosphate < 0.05 ppm

While these are the general requirements, werecommend providing a complete analysis for specificsystem performance and evaluation. The water supplyshould be free of suspendedmaterial and precipitatediron andmanganese as thesemay affect theadsorption process.

Typical contaminants removed:� Arsenic (III & V)� Phosphate� Chromium� Selenium� Antimony� Copper

The standard GFH® system consists of three verticalpressure vesselswith factory installed internals fordistribution and collection of influent and backwashflows. The vessels include fully finished, paintedinteriors for superior corrosion protection. GFH®mediais field placed on a 9” heavymedia bed. All face pipingand valves are included in the standard system tostreamline installation. A backwash process flow rate of10-12 gpm/sq. ft. (24-29m/hr) is typically required onceevery 2-6weeks to prevent compaction of the bed andremove captured particulate. GFH® systems are ideal forplants that have limitedwaste handling facilities sincethe unit produces unusually low volumes of liquidwasteand on an infrequent basis.

GFH® Pilot unit

TIME EFFECT EXAMPLE

INFLUENT EFFECT EXAMPLE

PH EFFECT EXAMPLE

Efflue

ntArs

enic

(ppb

)

00

Bed VolumesInf. As = 30 ppb Inf. As = 50 ppb Inf. As = 70 ppb

Efflue

ntArs

enic

(ppb

)

00

Bed Volumes

pH = 6 pH = 7 pH = 8

Efflue

ntArs

enic

(ppb

)

00

Bed Volumes

Continuous 1/2 time 1/3 time

trim

The graphs show the effect of influent arsenicconcentration, pH and duty cycle on GFH® systems. Asexpected, lower influent concentrations lead to a longermedia life. Lower rawwater pH also has a positive impactonmedia life. In many cases, pHmay not requireadjustment. For higher influent pH, a correction step canbe included to extendmedia life. Themost interestingoperating parameter is the duty cycle. As shown in thegraph, systems that allow themedia a “rest” period willsee an increase in effectivemedia life in terms of bedvolumes treated. The rest period allows for an inter-particulate diffusion of arsenic to expose freshadsorption sites, thus extending themedia’s useful life.

The GFH®media can be placed into parallel or seriespressure vessel systems depending on your requiredremoval concentrations. If a consistent 90% reduction isneeded across the system, the series design is used.However, if the percentage is less than 90%, then theparallel design is typically applied. Consult SiemensWater Technologies for special conditions that maydefine the use of the series design, particularly if higherremoval rates are required.

Influent, pH and TimeEffect

trim

Influent

Effluent

ParallelFlow–servicemode, allvesselsin–service

Influent

Effluent

Seriesflow–servicemode, twovesselsinseries–oneinstand–by

Stand-byLagLead

The three, in-service vertical pressure vessels in aparallel system are each designed to treat 1/3 of theincoming flow at a hydraulic loading rate of 5gpm/sq. ft. (12m/hr). A fiveminute Empty BedContact Time (EBCT) is provided through the parallelsystem, plus backwash water is supplied solely fromthe in-service vessels where they are backwashedduring the same event. During the initial start-up ofthe plant, one vessel is placed on-line where itbegins the exhaustion curve. Subsequently, thesecond vessel is started and later the third one isactivated. This process causes all the vessels tooperate at varying degrees of exhaustion, and theblended effluent concentration is below the desiredlevel. The blended effluent concentration eventuallyapproaches the acceptable limit, however, andwhen themedia in the longest running vessel isreplaced, the overall blended effluent is reduced.Overall media life is extendedwhen operated in thisfashion.

In a series system two vessels are operated in alead/lagmodewith a third vessel in stand-by. Thehydraulic loading rate is 8 gpm/sq. ft. (19m/hr)and, similar to the parallel system, provides an EBCTof fiveminutes total or 2.5-minute EBCT per vessel.

Backwash water is supplied from the rawwatersource, or returned from the system. Again, as in theparallel system in-service vessels are backwashedduring the same event. When the lead vessel mediais exhausted, it is isolated and the lag vessel shifts tothe lead vessel. At that time, the stand-by vesselprogresses to the lag sequence. Following thisprocess, the exhaustedmedia is replaced in thisvessel and it becomes the stand-by vessel. The seriesflow systems include a by-pass line in order to blendrawwater with the treated water until the desiredeffluent is achieved. In a series design, the lag unitreceives a lower concentration of contaminants,which creates amore consistent removalthroughout the system. The series system, however,treats a lower flow rate than the same size vessels ina parallel unit.

For specific applications, contact Siemens for anestimate of water produced betweenmediareplacement. We also offer on-site verification pilotunits to confirm process design and equipmentselection. The pilot units are provided with the tank,controller andmedia for an efficient study.

Parallel Systems, Series Systems

GFH is a trademark of Siemens, its subsidiaries oraffiliates.

The information provided in this brochure containsmerely general descriptions or characteristics ofperformance which in actual case of use do notalways apply as described or whichmay change as aresult of further development of the products. Anobligation to provide the respective characteristicsshall only exist if expressly agreed in the terms ofcontract.

East Tel: +1.508.849.4600

Central and International Tel: +1. 515.268.8400

West Tel: +1.719.622.5320

GF-GFH-BR-0709Subject to change without prior notice.

©2009 SiemensWater Technologies Corp.

www.siemens.com/water