Many heavy metals, such as chrome, have been found in harmful concentrations in surface waters due to contamination introduced from industrial pollution.  Once present, chromium compounds are very persistent in water and often, are present in particulate form as sediment. Some of the particulate chromium will remain as suspended matter and ultimately be deposited in sediments.

Industrial use of chromium includes in metal alloys such as stainless steel; protective coatings on metal; magnetic tapes; and pigments for paints, cement, paper, rubber, composition floor covering and other materials. 

Increased urbanization and the drinking water demand in areas of industrial activity has increased the attention paid to this problem metal.  Improper handling and or discharge into local sewers and the environment createst the potential for contamination of drinking water sources.  The presence of chrome in potable drinking water sources has the potential to cause damage to liver, kidney, circulatory and nerve tissues and skin irritation from long-term exposures at levels above the Maximum Contaminant Level (MCL).  Currently, the US Environmental Protection Agency's (EPA) MCL in drinking water for chrome has been set at 0.1 parts per million (ppm). 

Additionally, removal of chrome from wastewater is also needed to achieve the water quality level needed for reuse and recycling.  Many industries are turning to reuse and recycling practices to reduce the cost and volume of makeup water.

The US EPA has designated the following treatment methods as Best Available Technology (BAT) for removing chromium from water.

Ion exchange is a frequently used  treatment technology for chromium removal.  This technology removes chromium ions from the aqueous phase by replacing them with the anion present in the ion exchange resin.  As contaminated water is passed through the resin, contaminant ions are exchanged for other ions such as chlorides or hydroxides in the resin. 

Siemens Water Technologies offers both permanent, hard-piped systems as well as service-ion exchange which features removable systems.  Our service ion exchange approach integrates equipment and service option combinations, thereby minimizing a plant’s capital investment and reducing overall space requirements.  The system vessels are selected based upon available manpower, space limitations, access limitation and the specific water quality required.  Based on the application (potable vs. non-potable), contaminant to be removed and quality requirements, we have access to a variety of ion exchange resins and other removal medias, such as activated carbon.  Service ion exchange provides the ultimate flexibility to add or remove treatment capacity as your business grows or compliance limits change.  If needs change, we can simply change the media types and/or tank size, thereby saving our customers significant capital expense.

Once exhausted, the exchange vessels are removed and replaced with fresh, DOT-compliant vessels and returned to service. For non-potable applications, exhausted vessels are transferred to our central treatment and processing facility where the hazardous/non-hazardous contaminants are removed from the resin prior to disposal or reuse.  For potable applications, the resins are removed from the site and delivered to a local resin regeneration facility for thermal destruction and disposal.  Alternatively, single-use, non-regenerable ion exchange resins may also be used. 

Service ion exchange minimizes the need for handling and on-site storage of chemicals and wastes for improved safety and compliance at your site. This option also saves valuable manufacturing space while minimizing your maintenance and installation requirements.

(Note:  Ion exchange is often preceded by treatments such as filtration to remove organics, suspended solids, and other contaminants that can foul the resins and reduce their effectiveness.)

Wastewater discharge compliance is also achieved by reducing hexavalent chromium to trivalent chromium with precipitation to chromium hydroxide, a non-toxic substance.  Coagulation and/or filtration technology consists of decreasing the pH level (as low as 4 or 5) and increasing the feed rate of a chemical coagulant combined with mechanical flocculation to allow fine suspended and some dissolved solids to clump together (floc). There are a variety of coagulants available (e.g. aluminum sulfate, ferric chloride, ferric sulfate, poly aluminum chloride, etc.), and the choice of one depends on water quality, contaminant removal requirements and cost. The majority of the floc and other suspended solids are removed by settling and easily separated and disposed of.

The remaining suspended particles are removed by filtration using multimedia filters. Water passes through the filtration media bed and the suspended solids are captured in the bed.  This continues until the bed has reached a maximum solids loading.  The flow is reversed causing bed expansion and release of the captured solids.

Filter backwash waste water and spent filtration medias all require special handling and disposal considerations which Siemens can provide assistance with.

Hexavalent Chrome Removal Treatment Technologies

Ion Exchange
Coagulation
Flocculation