How to Reduce Heavy Metals From Wastewater

By: WebFx
Post Date: January 6th 2025

Various industries that produce wastewater, such as manufacturing, may contain heavy metals that are eventually released into trenches and rivers. These are toxic substances detrimental to the environment. When not monitored and processed properly, metals in wastewater can pollute the ecosystem and may cause adverse effects on human health. Thus, reducing toxic metals should be a priority in wastewater treatment.

For plant operators, significantly removing metals in wastewater is crucial for environmental regulation compliance and worker safety. Learn more about wastewater treatment methods that reduce metals, enable sustainable operations and help safeguard the public’s health.

Do Wastewater Treatment Plants Remove Heavy Metals?

Yes, wastewater treatment plants can remove heavy metals. However, depending on the treatment procedure, some methods may be insufficient or improperly implemented by facilities. Treatment methods must be carefully reviewed to ensure toxic metal levels are adequately reduced. Wastewater treatment plants must also comply with government standards.

The United States Environmental Protection Agency (EPA) enforces laws and regulations to minimize water pollution and monitor the quality of surface waters. Under the Clean Water Act (CWA), the EPA implements heavy metal standards in wastewater treatment.

5 Types of Heavy Metal Removal Methods for Wastewater

Industrial and commercial wastewater treatment plants can leverage various technological advancements to reduce toxic metals. Adopting practical and efficient metal removal procedures can raise a facility’s wastewater treatment quality. Review five effective metal extraction methods below.

1. Adsorption

Adsorption is a process where molecules, atoms or ions are captured on the surface of a gas or liquid mixture. This method uses adsorbent material that extracts the substance to separate it from a solution. When applied in wastewater treatment, it’s considered one of the most efficient techniques for cleaning polluted water.

Research published in 2022 found that cryogels are highly effective adsorbent materials that capture heavy metal ions from wastewater. Cryogels are synthetic polymers with macropores that support the efficient extraction of heavy metal ions. This material removes heavy metals from industrial wastewater effectively. Cryogels have high porosity for the rapid transport of fluids, increased capacity to capture more metal ions and unrestricted flow for contaminants to reach the adsorption surface quickly.

Cryogels also efficiently separate metal ions from wastewater with multiple compounds. They are versatile adsorbents that can be modified to capture different contaminants — these include toxic metals in wastewater, such as mercury, silver, nickel, copper and cadmium, organic dyes, biomolecules and nutrients.

2. Chemical Precipitation

Chemical precipitation is a widely used heavy metal removal method in wastewater treatment. This process involves adding a coagulant to convert dissolved metal ions into solid, insoluble particles called precipitates. Chemical precipitation occurs when the coagulant alters the wastewater’s pH level, which is the measure of its acidity or hydrogen ion concentration. Once transformed, these solid precipitates settle at the bottom of the wastewater, making them easy to filter and remove.

The following are examples of coagulants used in chemical precipitation:

• Calcium hydroxide: When added to wastewater, it reacts to heavy metal ions such as lead, copper, nickel, zinc and chromium. It produces metal hydroxide precipitates that can be collected from the water.
• Sulfides: Adding sulfides to wastewater reacts to metal ions such as zinc, copper, lead and cadmium. This produces sulfide precipitates and hydrogen sulfide gas, a pungent, flammable gas that requires proper safety management.
• Carbonates: Calcium carbonate reacts with metals such as manganese, copper, zinc and lead. This produces metal carbonates, releases carbon dioxide and forms less sludge than sulfide precipitation.

3. Chemical Coagulation

Another process for removing heavy metals from wastewater is chemical coagulation. This uses a positively charged metallic coagulant like inorganic aluminum sulfate to weaken the metal particles’ negative repelling force. A flocculant is added to clump the suspended metal particles together, forming larger particle groups called flocs. Though this process is widely implemented, inorganic coagulates may be costly to import and can produce high quantities of sludge.

In a 2024 study, researchers effectively used an organic coagulant from date seeds powder to reduce heavy metals in steel mill wastewater. As the flocculant, they used aluminum chloride to form larger clumps that can easily settle out of the water. The process removed a significant percentage of manganese, iron, aluminum, zinc and nickel from the wastewater.

4. Ion Exchange Treatment

In the ion exchange method, a chemical reaction replaces the heavy metal ions from the wastewater with harmless metal ions. The ion exchange materials used are solid mediums, such as synthetic resins and natural zeolites. This process can remove various heavy metals, including mercury, copper, lead, vanadium, chromium, zinc, cadmium and nickel.

Though ion exchange can be effective, it comes with a few limitations:

• Capacity: The ion exchange capacity can diminish after several operations. The presence of multiple metal ions can also hinder the process, making it ineffective for specific metals.
• Sensitive pH levels: Sensitive pH levels suggest that a higher pH can reduce the efficacy of the process. Routine maintenance and cleaning are ideal to avoid significant pH changes.
• Regeneration: The ion exchange material requires regeneration with the use of chemical solutions, such as sodium chloride or acids. This adds more waste and is not the most environmentally friendly solution.
• Cost: Procuring synthetic resins and zeolites is expensive compared to other metal removal methods. This considerably increases wastewater treatment costs.

5. Membrane Filtration

To facilitate the removal of heavy metals from wastewater, membrane filtration treatment uses semi-permeable membranes to separate heavy metals and other contaminants. Wastewater treatment plants increasingly use this method due to efficient heavy metal removal and convenient operation, requiring less space than other methods.

Various membranes with different pore sizes and pressure levels are used in this process. The following are types of filtration membranes:

• Nanofiltration: With very small pores, this membrane focuses on removing divalent ions and larger monovalent ions. It effectively removes heavy metals such as chromium, cadmium and copper.
• Reverse osmosis: This membrane uses high pressure, allowing water molecules to pass and blocking off toxic contaminants. It removes metals such as arsenic, zinc, lead, copper, nickel and chromium.
• Electrodialysis: Electricity is applied across this membrane, with exchange membranes that selectively allow specific ions to pass. This can remove metal ions such as lead and nickel from wastewater.

Effectively Enhance the Wastewater Treatment Process With SSI Aeration, Inc.

Ready to enhance the wastewater treatment process with compliant methods that efficiently remove metals? Consult with SSI Aeration, Inc. for suitable wastewater treatment systems. We are a premier supplier of effluent and sewage treatment plants, participating in all phases of a wastewater project.

With staff and experts from all over the world, SSI Aeration, Inc. diligently serves all 50 states and over 80 countries globally. Contact us today to improve wastewater treatment operations.