Chromium (Cr) is a heavy metal that is used extensively within the mining and metals, leather tanning, paint and pigments, electronics, and chemical industries, among others, and it can exist in various forms and compounds—some of which are toxic to plant and animal life. As such, it is sometimes necessary for industrial facilities to invest in treatment technologies that remove chromium from process water and wastewater.
In this article, we’ll take a look at what chromium is and how it’s used in industry, then explore the most common reasons industrial facilities need to remove it from industrial water streams so you can determine whether or not your facility needs to analyze its own chromium removal solutions.
What is chromium and where does it come from?
Chromium is a heavy metal that offers several distinctive properties, such as hardness, high polish, a high melting point, and resistance to tarnish and corrosion. Native chromium metal is not generally found in nature, but is instead found in the form of ore deposits consisting mostly of a compound known as chromite (iron chromium oxide). Chromite ore is mined from deposits scattered around the world, with the highest production occurring in South Africa, Kazakhstan, India, and Turkey.
In industry, metallurgy accounts for the highest demand for chromium, as the metal is used extensively in the production of stainless steel and other metal alloys and in chrome plating applications. The chemical industry is another significant consumer of chromium with its use of compounds such as chrome oxide, chromic acid, and potassium dichromate as catalysts and reagents to support a variety of production processes.
Various other chromium compounds are important for producing goods and materials across other industries as well. Chromium (III) sulfate, for example, is used extensively as a tanning agent by leather producers, as it provides a fast and reliable means of stabilizing the collagen in leather and animal skins to form a long-lasting, stretchable material. Chromium oxide is important to the refractory industry for production of fire-resistant and anti-corrosive bricks, tiles, and surface coverings. Additionally, many chromium compounds have intense coloring, making them useful in the production of paints and pigments. Still other uses of chromium occur in the electronics industry, where the metal is used in the production of lasers, as well as audio and video device components.
What are the main reasons to remove chromium from wastewater?
Improper discharge and disposal of chromium-contaminated wastewater poses a hazard to human, plant, and animal life. As with other heavy metals like copper or lead, chromium can enter waterways and drinking water supplies when industrial wastewater is not discharged responsibly, potentially resulting in harm to aquatic plant and animal life, accumulation in soil, and other environmental and agricultural damage.
It is worth noting that the type of chromium present in industrial wastewater has some bearing on the relative level of risk. This is because chromium found in industrial wastewater exists as either trivalent chromium (Cr III) or hexavalent chromium (Cr VI). Of these oxidative states, Cr III is far less toxic, and there is even some research to suggest that small amounts are nutritionally beneficial. Cr VI, on the other hand, is highly toxic to humans when inhaled or ingested in food or drinking water. Even tiny amounts of Cr VI can present a number of health hazards for humans, including gastrointestinal and respiratory inflammation, organ damage, cancer, and birth defects.
As such, the most important reason to treat wastewater for chromium is to protect public health and safety, although there are also other reasons to consider chromium removal as part of an overall wastewater treatment strategy. We’ll address these in more detail below:
Compliance with wastewater discharge permit limitations
Hazardous metals like chromium are usually regulated closely by governmental agencies. In the United States, the Environmental Protection Agency (US EPA) defines limits for chromium based on US regulatory standards, which allow for variations based on the industry, facility size, and location. These limits are enforced by issuance of National Pollutant Discharge Elimination System (NPDES) permits, which delineate the sampling methods, testing frequency, and the maximum and average limits allowable for chromium and other contaminants present in any wastewater that is discharged to public waterways. Failure to comply with relevant discharge limitations can result in substantial fines and legal action.
In general, permissible daily maximum discharge of Cr VI is typically limited to only 40 μg/L, while average monthly discharge limits are usually no more than 20 μg/L, but while these limits offer a ballpark range, it is worth noting that NPDES permit limits are determined on a case-by-case basis and will vary by facility and location.
In short, if your facility discharges waste to US waterways and chromium content in your wastewater either regularly or occasionally exceeds the limits of your NPDES permit, then you will likely need a chromium removal solution. For facilities outside the US, similar standards will likely apply, so it is critical to check with local agencies to assess wastewater discharge compliance protocols.
Compliance with wastewater treatment facility requirements
Many industrial facilities discharge wastewater to a centralized wastewater treatment facility, such as municipal sewers or publicly-owned treatment works (POTW). Often, however, POTWs are not set up to handle high concentrations of heavy metals like chromium. Excess levels of chromium can compromise the performance of activated sludge systems typically used by POTWs, potentially allowing the breakthrough of chromium into treated effluent streams and leading to the contamination of waterways.
In order to ensure that POTWs operate reliably, industrial facilities are typically required to meet certain water quality standards in order to maintain their authorization for discharging wastewater to the receiving facility. In the US, this is enforced by the US EPA’s National Pretreatment Program, which grants receiving facilities the power to administer wastewater discharge permits and enforce water quality standards. While the US EPA defines several different levels of control for regulating wastewater discharge, centralized wastewater treatment facilities are typically required to keep total recoverable chromium levels in wastewater well below 10 μg/L. Given these stringent guidelines, a POTW may require that industrial facilities pretreat their wastewater to ensure that chromium is reduced to levels that can be safely managed by the wastewater treatment technology in place at the POTW. Thus, if your facility discharges wastewater to a POTW and your chromium levels exceed the daily or monthly limits set by the receiving facility, then you may need to adopt chromium removal as part of a pretreatment strategy. Failure to do so can jeopardize existing wastewater discharge agreements with the receiving facility and result in fines or legal action.
Reclamation and recycling
Today’s industrial facilities are under growing pressure to make more efficient use of raw materials and fresh water. Whether for economic or environmental reasons, facilities are increasingly adopting separation technologies for treating process and wastewater as part of a metals recovery or reclamation strategy. Membrane filtration systems, such as ultrafiltration (UF) and reverse osmosis (RO), for example, have helped leather tanneries and chrome electroplating facilities capture and reuse chromium from spent streams, while also reducing the volume of liquid and solid wastes generated by their normal operations.
If your facility is looking for ways to reduce raw material consumption and sourcing costs, then chromium removal and reclamation may be worth considering. When properly implemented, reclamation strategies not only deliver costs savings benefits by reducing sourcing costs for water and other materials, but also by helping facilities to achieve compliance with wastewater quality standards and reducing overall liquid discharge volumes.
Can SAMCO help?
SAMCO has over 40 years’ experience custom-designing and manufacturing wastewater treatment and process separation systems, so please feel free to reach out to us with your questions. For more information or to get in touch, contact us here. You can also visit our website to set up a call with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for your wastewater treatment system to meet your chromium and heavy metals removal needs.
For more articles on wastewater treatment, head on over to our blog. Some that might be of interest to you include:
- How Do You Know If An Industrial Facility Needs a Wastewater Treatment System?
- How to Choose the Best Wastewater Treatment System for Your Plant
- Seven Ways Your Facility Isn’t Meeting Effluent Regulations and How to Solve Them
- The Importance of Wastewater Treatment for Your Facility: Is it Necessary?
- 9 of the Best Industrial Wastewater Treatment Equipment Supply and Technology Companies
- What Is a Wastewater Treatability Study and How Does it Work?
- How Much Does a Water/Wastewater Treatability Study Cost for Your Plant?
- What Are the New Steam Electric Power Generating Effluent Guidelines and What Do They Mean for Your Plant?
- How Much Does a Wastewater Treatment System Cost? (Pricing, Factors, Etc.)