Ensuring the safety and quality of treated drinking water is a critical responsibility for water treatment facilities across the globe. One of the key concerns in this domain is managing residual aluminum levels after treatment. While aluminum-based coagulants like aluminum sulfate (alum) are widely used for removing turbidity, organic matter, and other impurities, they can leave behind residual aluminum in the final water supply. Elevated levels of residual aluminum may pose health risks and impact water aesthetics, such as taste, clarity, and color.
At Gulbrandsen Technologies, we are committed to supporting water treatment operations with advanced solutions and expertise. In this blog, we explore the best practices to reduce residual aluminum, helping utilities meet stringent safety standards while optimizing their treatment processes.
Why Residual Aluminum Matters
Residual aluminum refers to the aluminum that remains in the treated water post-coagulation and filtration. While regulatory guidelines vary by region, the World Health Organization (WHO) recommends a maximum concentration of 0.2 mg/L for aluminum in drinking water. Exceeding these limits can lead to:
- Health concerns, particularly in vulnerable populations such as infants or patients undergoing dialysis.
- Operational challenges, such as membrane fouling in filtration systems.
- Aesthetic issues, including discoloration and unpleasant taste.
Best Practices for Reducing Residual Aluminum
1. Optimize Coagulant Dosing
Overdosing aluminum-based coagulants is one of the leading causes of elevated residual aluminum. Water treatment plants should:
- Conduct jar testing regularly to determine the optimal dose.
- Implement real-time dosing control systems based on water quality parameters such as pH, turbidity, and alkalinity.
2. Monitor and Adjust pH
The efficiency of aluminum-based coagulants is highly pH-dependent, with the ideal coagulation typically occurring between pH 6.0 and 7.2. Operating outside this range can lead to higher Al residuals if coagulant dosage is high
- Regularly monitor raw and treated water pH.
- Use pH adjusters or buffers if necessary to maintain optimal conditions.
3. Improve Mixing and Flocculation
Proper mixing and flocculation encourage the formation of larger flocs, which are more easily removed during sedimentation and filtration.
- Ensure uniform mixing at the rapid mix stage.
- Provide sufficient retention time and gentle stirring during flocculation to promote strong floc development.
4. Enhance Filtration Efficiency
Inefficient filtration can allow aluminum hydroxide flocs to pass into the finished water.
- Optimize backwashing cycles and filtration rates.
- Consider upgrading filter media or adding coagulant aids (polymers) to improve floc capture.
5. Switch to Alternative Coagulants
Where residual aluminum is a persistent issue, consider using blends of organic – aluminum coagulants or higher basicity coagulant such as:
- Polymeric coagulants or blended solutions that provide effective coagulation with lower dosage and residual metal concentrations.
- High basicity product that having a widen coagulation pH range
At Gulbrandsen Technologies, we offer a range of advanced coagulant solutions tailored to minimize metal residuals and improve overall process performance.