Heavy Metals in Wastewater: Causes, Impacts, and Treatment Processes

Introduction

In the modern industrialization process, a large amount of wastewater is generated every day. Some of this wastewater contains significant amounts of heavy metals, such as cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), and nickel (Ni). If this wastewater is discharged without treatment, the heavy metal components will accumulate in the food chain, harming human health, aquatic organisms, and the ecosystem. Today, AquaSust will assess the sources and impacts of heavy metal-containing wastewater in this article and introduce some effective treatment methods.

 

Main Causes of Heavy Metals in Wastewater

Industrial activities are the main sources of heavy metals in wastewater, including the following industries:

(1) Chemical Manufacturing: This includes the petroleum, paint, dye, and soap industries. The heavy metals in these industries come from various sources, such as raw materials, improper disposal of chemical waste, and leakage from chemical material pipelines. The heavy metals associated with this industry mainly include aluminum, lead, mercury, chromium, nickel, zinc, mercury, cadmium, and arsenic.

(2) Mining: When we process ores (crushing, grinding, and chemical treatment) or smelt and refine metals, heavy metals such as copper, lead, and zinc are released during high-temperature smelting. After processes like washing and purification, they flow into surrounding water bodies with the wastewater and accumulate in sludge and ore sands. According to relevant statistics, for every 1 ton of copper ore mined, approximately 5 - 10 cubic meters of heavy metal-containing wastewater is generated.

(3) Electroplating: In the automotive, electronics, and jewelry industries, workers often use a large amount of electroplating solutions containing heavy metals to coat a protective layer on the surface of products. During the cleaning process after electroplating, these electroplating solutions will diffuse into the wastewater, leaving behind high concentrations of heavy metal ions, such as chromium, nickel, and zinc.


Impacts of Heavy Metals in Wastewater Discharge

 Eutrophicate water bodies, leading to the massive proliferation of algae and the depletion of oxygen.

 Interfere with the nervous systems of aquatic organisms, affecting their embryonic development and reproductive capabilities.

 Accumulate through the food chain and ultimately in the human body. This can damage the human nervous system, hematopoietic system, and digestive system, especially in children.


What are the Heavy Metal Removal Technologies?

（1）Chemical Precipitation Method

In the chemical precipitation method, chemical agents are added to the wastewater, causing the heavy metal ions to react chemically with certain components in the agents. They will form insoluble precipitates, which are then separated from the wastewater through tube settlers. This method is relatively simple to operate and has a low cost, but it generates a large amount of precipitates. These precipitates need to be properly disposed of; otherwise, they may cause secondary pollution.

 

（2）Ion Exchange Method

Ion exchange resins are polymer materials with ion exchange functions, and their surfaces are equipped with exchangeable ion groups. When the wastewater passes through an ion exchange resin column, the exchangeable ions on the resin react with the heavy metal ions in the wastewater, adsorbing the heavy metal ions onto the resin.

 

（3）Biological Filtration Method

The biological filtration method mainly relies on biological processes to remove heavy metals from wastewater, and MBBR or MBR reactors may be used. Certain specific microorganisms, such as some bacteria, fungi, and algae, can bind or transform heavy metal ions, making them easier to remove from the wastewater.

 

（4）Adsorption Method

Common adsorbents include activated carbon, zeolite, bentonite, etc. They adsorb heavy metal ions through their large specific surface areas and abundant microporous structures. This adsorption method is based on physical and chemical adsorption. Physical adsorption is based on van der Waals forces, while chemical adsorption includes the chemical reactions between the functional groups on the surface of activated carbon and heavy metal ions.

 

（5）Membrane Separation Technology

Sometimes, membrane separation technologies such as electrodialysis and reverse osmosis are also used to separate heavy metal ions from wastewater. In electrodialysis, under the action of a direct current electric field, the selective permeability of anion and cation exchange membranes to anions and cations in the solution is utilized to separate heavy metal ions from water. Reverse osmosis, on the other hand, forces water molecules to pass through a semi-permeable membrane under a pressure higher than the osmotic pressure of the solution, retaining solutes such as heavy metal ions.

 

（6）Electrochemical Treatment Method

It relies on electrochemical processes to convert heavy metal ions into less harmful forms or directly remove them from the wastewater. In an electrolytic cell, through the application of direct current, oxidation occurs at the anode and reduction occurs at the cathode. This method can remove various heavy metal ions and does not require a large amount of chemical agents to be added.


Conclusion

Now we have understood the main causes of heavy metal pollution and effective management methods for heavy metals in wastewater. As a pioneer in the water treatment industry, AquaSust can provide effective heavy metal solutions for different industrial applications. If you are interested, please let us know in the comments or contact us. 

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