Aluminum sludge as a natural material for the removal of heavy metals from wastewater

A new article in the magazine Sustainability investigated the use of aluminum sludge for the remediation of heavy metal contaminants in wastewater. An international team of scientists from Algeria, Sweden, India, Australia, Saudi Arabia and Tunisia contributed to the research.

Study: Removal of copper and zinc from wastewater using alum sludge recovered from a sewage treatment plant. Image Credit: Poh Smith/Shutterstock.com

Contamination of wastewater by heavy metals

Domestic and industrial activity produces large amounts of wastewater, which poses a hazard to the environment due to contaminants such as organic waste and heavy metals. Heavy metals in particular cause damage to people, animals, plants and fragile ecosystems. Specific heavy metal hazards include their bioavailability, carcinogenicity and teratogenicity.

Several industries are affected by this major environmental and health issue, in particular the steel industry and mining. Additionally, illegal activities and landfills complicate the effective removal of contaminants, with heavy metals entering waterways and aquifers in large quantities every year across the world.

Recognizing the magnitude of this problem, several international bodies, including the EU and WHO, have introduced recommendations and regulations to mitigate the impact of heavy metal contamination.

Map showing the location of sludge sampling in the study area.  a) Algeria;  (b) the town of Bouira;  (c) Water treatment plant.

Map showing the location of sludge sampling in the study area. (a) Algeria; (b) Bouira city; (vs)wastewater treatment plant. Image Credit: Abba, AB et al., Sustainability

Remediation Strategies

Over the past few decades, several strategies have been investigated for the efficient removal of heavy metal ions from wastewater streams. Among the various methods proposed for wide industrial and commercial application, adsorption processes have attracted the interest of researchers and organizations.

While adsorption is a very efficient removal method, some key challenges exist with current technologies. A commonly used material for this purpose is activated carbon, but this material has disadvantages in terms of production costs, difficulties in separation and regeneration.

The use of alternative and abundant natural materials is a key focus of research on adsorption strategies for wastewater treatment. Industrial and commercial waste streams hold particular promise in this area today due to their availability, performance, cost-effectiveness, and ability to recover and convert them into value-added products rather than disposing of them in the waste stream. ‘environment.

Aluminum sludge

Aluminum sludge is a by-product of drinking water treatment. Aluminum salts are added to water to remove particles such as colloidal particles and make it drinkable. Once removed, these particles settle due to flocculation and coagulation processes and form sludge.

Currently, especially in developing countries, this sludge is disposed of in landfills and directly into rivers and streams, causing ecological and water quality problems. Due to the problems caused by sludge disposal, economically sound methods of safe disposal and reuse of aluminum sludge to ensure proper management of this critical waste is essential.

Schematic illustration of the preparation of an alum slurry sample.

Schematic illustration of the preparation of an alum slurry sample. Image Credit: Abba, AB et al., Sustainability

The large quantities of sludge produced annually offer many opportunities for value-added processes and the recovery of this material in accordance with circularity objectives. One of these uses includes the recovery of aluminum itself from sludge for industrial processes. Other opportunities exist with the use of this waste in wastewater treatment.

Some studies have already explored the use of this material for the removal of heavy metal contaminants. Large amounts of sludge and long contact times were used, with a study by Ngatenah et al. demonstrating the effective removal of copper and zinc ions, but at quantities of 2000 mg/L and with contact times of 25 to 180 minutes.

The study

In the new paper, the authors sought to assess the use of these industrial wastes for the removal of heavy metal contaminants from Algerian wastewater streams. They said using this industrial waste could be more cost-effective than current adsorption technologies.

Specifically, the authors studied the use of these industrial wastes for the removal of copper and zinc ions from synthetic wastewater. Aluminum sulphate is commonly used as a coagulant in the treatment of drinking water in Algeria, offering several possibilities of using this precious material for the remediation of contaminants by heavy metal ions.

XRD and SEM were used to analyze the aluminum sludge used in the study. The XRD revealed the presence of kaolinite, with an inadequate sequencing of the muds. SEM revealed the amorphous nature of the material. FTIR was used to examine bonds and functional groups. A considerable amount of organic matter has been observed in the mud, and it possesses a very porous nature with a large surface area.

Effect of the amount of sludge in the elimination of heavy metals in media with different pH.

Effect of the amount of sludge in the elimination of heavy metals in media with different pH.

Effect of the amount of sludge in the elimination of heavy metals in media with different pH. Image Credit: Abba, AB et al., Sustainability

Based on the study of the amount of sludge and the pH, the authors concluded that these factors influence the removal of copper and zinc ions. Different intended uses depending on the amount and pH (industrial wastewater, drinking water treatment, sewage) have been suggested in the article.

A high removal efficiency of zinc ions and copper ions was observed, which led the authors to conclude that this material is suitable for the removal of heavy metal contaminants from wastewater.

In summary, the paper demonstrated the beneficial use of aluminum sludge, a critical drinking water treatment waste stream, for large-scale removal of ionic heavy metal contaminants from wastewater. The authors suggested that future research could improve removal efficiency by considering the impact of time on adsorption methods using this abundant, inexpensive, and renewable waste resource.

Further reading

Abba, AB et al. (2022) Removal of copper and zinc from wastewater using alum sludge recovered from a water treatment plant Sustainability 14(16) 9806 [online] mdpi.com. Available at: https://www.mdpi.com/2071-1050/14/16/9806

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About William J. Harris

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