Common heavy metals present in wastewater and how they are treated 

Common heavy metals include lead, arsenic, mercury and chromium. They pose a significant risk to health and the environment, due to their persistence, bioaccumulation and their toxicity. 

Effective treatment is crucial and there are several treatment methods available, including chemical precipitation, adsorption and ion exchange.  

Let’s take a further look… 

Sources of heavy metal contaminants 

When heavy metals are found to be present in wastewater, they can usually be traced back to one of three sources:  

Industrial discharge  

Primary culprits in contamination, manufacturing industries such as electronics, textiles, and metal finishing release metals like lead, cadmium, and mercury into water systems.  

Mining runoff 

Mining can also result in pollution through acid mine drainage, where sulphur-rich ores react with air and water to form acidic runoff full of heavy metal contaminants.  

Agricultural practices  

Industrial agriculture can impact pollution levels through the overuse of metal-based pesticides and fertilisers that can contaminate soils and leach into groundwater over time. 

Common heavy metals present in wastewater  

Industrial wastewater effluents often contain a variety of heavy metals. The most common pollutants are:  

Lead: often present in wastewater due to its historical use in pipes, paints, and petrol.  

Mercury: enters wastewater primarily through industrial processes such as coal combustion and chlorine production.  

Cadmium: often a by-product of zinc, lead, and copper extraction. 

Arsenic: naturally present in some groundwater sources, it can also be introduced through agricultural and industrial activities.  

Chromium: commonly used in chrome plating, leather tanning, and as an anti-corrosive agent.  

Other common pollutants include copper, nickel and zinc.  

Risks posed by heavy metals 

When heavy metals infiltrate water systems, they pose significant environmental and health risks:  

Persistence & bioaccumulation  

Heavy metals are non-biodegradable and therefore can persist in aquatic environments, posing severe long term health and environmental risks.  

Even at low concentrations, they accumulate in sediments, water, and aquatic organisms, disrupting ecosystems and entering the food chain.  

Bioaccumulation exacerbates these risks: as metals are ingested by organisms, they accumulate in tissues over time, increasing in concentration as they move up the food chain. 

Examples:  

• Lead: can accumulate in the body over time, causing irreversible harm. 

• Mercury: tuna and swordfish can contain mercury levels 10,000 times higher than the surrounding water. Due to bioaccumulation, any predator or human that consumes them is then particularly susceptible to poisoning. 

• Cadium: its persistence in the environment, coupled with its ability to bioaccumulate, necessitates stringent monitoring and treatment. 

Toxicity  

Even at low levels, heavy metals not only harm aquatic life but also threaten human health through contaminated water supplies and seafood consumption.  

Examples: 

• Lead: prolonged exposure can lead to neurological damage, particularly in children. 

• Mercury: consumption of contaminated water or fish can lead to severe neurological disorders, 

• Cadium: exposure is linked to kidney damage and bone demineralisation. 

• Arsenic: chronic exposure can lead to skin lesions, cancer, and cardiovascular diseases. 

• Chromium: a known carcinogen. 

Ecosystem disruption 

Heavy metals can alter water chemistry, reduce biodiversity, and impair the functioning of aquatic habitats. These disruptions can be catastrophic, cascading through ecosystems and affecting everything from water quality to bird species that rely on aquatic resources. 

Examples:  

• Copper can inhibit photosynthesis in algae at concentrations, disrupting the base of the food chain.  

• Zinc can interfere with the reproductive systems of aquatic invertebrates, leading to population declines.  

Treating heavy metals 

Due to their inherent risks, it is critical that heavy metals are removed from wastewaters.  

There are several treatment methods offering targeted solutions:  

Chemical precipitation  

One of the primary treatment methods for heavy metal removal. Chemical precipitants such as lime and sodium hydroxide are added to wastewater, causing heavy metals to form insoluble compounds that settle as sludge. 

Things to consider:  

• A cost-effective treatment method for heavy metals. 

• Requires careful monitoring of pH, temperature, and chemical dosage to be effective. 

• Generated sludge will also require further treatment, which may have implications for cost and overall efficiency. 

Adsorption 

Porous materials such as activated carbon, zeolites, and silica gel trap heavy metals from wastewater. Treatment can be tailored to target specific heavy metal contaminants, making it a highly efficient and versatile treatment solution.   

Things to consider:  

• To work optimally, the right adsorbent and optimising contact time must be selected.   

Ion exchange 

This treatment method involves the exchange of metal ions in wastewater with ions immobilised on a solid resin. 

The process is highly selective and can achieve near-complete removal of targeted heavy metals. 

Things to consider:  

• This method may require occasional replacement of the resin  

• Careful management of wastewater pH and chemistry is required to maintain optimal performance. 

Membrane filtration 

Membrane filtration technologies, such as reverse osmosis and nanofiltration, rely on semipermeable membranes to separate heavy metal ions present in water molecules based on size and charge. 

This treatment method offers high removal efficiency and requires minimal chemical usage. 

Things to consider: 

• Membrane fouling presents a challenge, requiring pretreatment steps like coagulation or microfiltration to extend membrane life. 

• This treatment method can also be energy-intensive. 

Electrochemical 

Electrochemical treatment methods, including electrocoagulation and electrochemical precipitation, rely on the application of electric current to induce the formation of insoluble metal hydroxides, which can be easily separated from wastewater. 

Things to consider 

• Electrochemical methods can be integrated with renewable energy sources for sustainable operation. 

Biological  

Biological treatments, such as biosorption and microbial reduction, harness the metabolic activities of microorganisms to sequester or transform heavy metals present in wastewater. 

Things to consider  

• Biological treatments methods are environmentally friendly, offering low operating costs and minimal chemical usage.  

• However, they may require longer treatment times, therefore integrating them with other treatment methods may enhance efficiency.   

Choosing the right heavy metal treatment solution for your business 

Heavy metals like lead, cadmium, mercury, and arsenic present in wastewater effluents, pose significant environmental and health risks.  

Their removal is critical and a variety of treatment methods are available, each with their own strengths and limitations.  

Aqua Advice can assess your treatment requirements to ascertain the most suitable solution. 

Contact us today for a free consultation.