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Chromium Removal Water Treatment Companies
Total and hexavalent chromium removal: reduction to Cr(III) and hydroxide precipitation, strong base anion exchange, and membranes for plating and tannery effluent.
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- Chemical Precipitation or Coagulation/Flocculation capabilities
- Suppliers with food-beverage sector experience
- Providers operating in United Kingdom or China
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- 8
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Buyer's Guide
The buyer's guide to chromium removal water treatment
Total and Hexavalent Chromium: Two Different Treatment Problems
Chromium is regulated as a total, and treated as two species. Trivalent chromium is a cation that hydrolyses and precipitates as a hydroxide, which conventional coagulation and settling handle well. Hexavalent chromium exists as chromate and dichromate anions, is far more toxic, is mobile in groundwater, and passes conventional treatment almost untouched. Any flowsheet that does not say which species it is designed for is designed for the easy one.
The limits are moving. WHO holds 50 µg/L for total chromium, chosen on achievability and measurability rather than toxicology alone. The EU tightens its parametric value from 50 to 25 µg/L, to be met at the latest by 12 January 2036 under Annex I Part B of DWD 2020/2184. The US EPA keeps an MCL of 0.1 mg/L for total chromium, while California brought in a hexavalent-specific MCL of 10 µg/L on 1 October 2024 against a public health goal of 0.02 µg/L. A plant designed to a total chromium number today may be asked for a species-specific one within its asset life.
For industrial effluent, plating, anodising, tanning, textile dyeing with chromium mordants and chromate-treated cooling water, the established route is reduction of Cr(VI) to Cr(III) with a sulfite, bisulfite or ferrous salt at low pH, then neutralisation and hydroxide precipitation, settling and filtration. For drinking water at microgram concentrations, strong base anion exchange, coagulation with ferrous iron, and reverse osmosis or nanofiltration are the working options. Watch the oxidation trap in both cases: free chlorine and permanganate in the plant can convert Cr(III) back to Cr(VI), so a train that removes total chromium can still raise the hexavalent fraction. Aguato lists chromium providers across industrial reduction and precipitation, ion exchange and membranes.
Frequently Asked Questions
Why does hexavalent chromium need different treatment from trivalent?
Charge. Trivalent chromium is a cation that hydrolyses and precipitates as chromium hydroxide, so lime or caustic and a settling stage remove it. Hexavalent chromium is present as the chromate or dichromate anion, which does not precipitate as a hydroxide and is not captured by a cation-based process. It has to be reduced to Cr(III) first, or captured by an anion-selective process such as strong base anion exchange or a membrane.
What limit should I design a new plant to?
For drinking water in the EU, design to 25 µg/L rather than the current 50, because Annex I Part B of Directive 2020/2184 requires the tighter value by 12 January 2036, which is inside the asset life of anything built now. WHO holds 50 µg/L total chromium and the US EPA an MCL of 0.1 mg/L total. Where a hexavalent-specific limit exists, as in California at 10 µg/L, that is the binding number and a total chromium design will not meet it reliably.
Can a treatment plant create hexavalent chromium?
Yes, and it is a real failure mode rather than a theoretical one. Strong oxidants used for other purposes, free chlorine and permanganate in particular, will oxidise Cr(III) to Cr(VI) inside the plant. A works can therefore reduce total chromium across the train and still increase the hexavalent fraction leaving it. If you are subject to a species-specific limit, ask for speciated sampling across the plant rather than at the outlet only.
Why is chromium speciation so hard to measure?
Because the ratio changes between the sample point and the laboratory. Cr(VI) can be reduced by organic matter and by ferrous iron in the bottle, and Cr(III) can be oxidised by any residual disinfectant, so an unpreserved sample drifts toward the wrong answer in both directions. Speciated results need the right preservation and holding time, which is why most regulations are still written on total chromium; if you are being asked to demonstrate a hexavalent limit, agree the sampling protocol with the laboratory before the first compliance sample.
A plating shop discharging to sewer was breaching its trade effluent consent for total chromium during rinse-tank changeovers, with peaks above 8 mg/L against a 2 mg/L consent, and had no reliable record of the hexavalent fraction because samples were taken unpreserved.
Chromium-bearing rinses were segregated from the general effluent and routed to a dedicated batch treatment: reduction with sodium metabisulphite at pH 2.5 with ORP control, then neutralisation to pH 8.5 with lime, flocculation, lamella settling and a polishing filter. Sludge was dewatered on site. The sampling protocol was rewritten with the laboratory so that speciated results were preserved at the sample point.
Discharged total chromium held below 0.5 mg/L across all operating modes, giving a four-fold margin on the consent, and the changeover peaks disappeared once the rinses were segregated and batched rather than diluted into the main stream. Speciated sampling confirmed hexavalent chromium below the detection limit after reduction, which the previous unpreserved sampling had been unable to show either way.
Questions to Ask Shortlisted Providers
4 questions
- 1
Is your design based on total chromium or on the hexavalent fraction, and how did you establish the split in our water?
The two species need different processes, and a flowsheet designed on a total chromium figure will underperform if most of the load turns out to be hexavalent.
- 2
If you are proposing reduction and precipitation, what controls the reduction, and what happens on a dose failure?
Reduction of Cr(VI) is pH and ORP dependent and fails silently: unreduced chromate passes the clarifier as if the stage were not there, so the control loop and its alarm are the process.
- 3
Does anything in this train oxidise Cr(III) back to Cr(VI)?
Free chlorine and permanganate dosed elsewhere in the plant can raise the hexavalent fraction downstream of a stage that lowered total chromium, which is invisible unless you sample speciated.
- 4
How will the chromium-bearing sludge be classified and disposed of?
Chromium concentrates into the sludge, and its classification and disposal route are usually the largest recurring cost of the process as well as a permit question in their own right.
Key Regulations & Standards
4 standards
50 µg/L total chromium, set on achievability and measurability as well as toxicology, because routine speciation is unreliable.
Parametric value tightening from 50 to 25 µg/L, to be met at the latest by 12 January 2036, Annex I Part B.
MCL and MCLG 0.1 mg/L total chromium; listed sources include steel and pulp mill discharge and erosion of natural deposits.
Hexavalent chromium MCL 10 µg/L effective 1 October 2024, against a public health goal of 0.02 µg/L set in 2011.
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