Aluminum content in coagulants and flocculants for wastewater treatment

Significance of the Topic

Coagulation and flocculation are key processes in the treatment of drinking water and wastewater, enabling the removal of suspended solids and organic contaminants. Chemical dosing with aluminum-based coagulants such as aluminum sulfate and polyaluminum chloride (PAC) can significantly improve the performance of primary clarifiers by reducing turbidity and organic load. Accurate determination of aluminum content is essential to optimize coagulant dosage, ensure process efficiency, and comply with regulatory standards for treatment plant operation.

Objectives and Study Overview

This study demonstrates a fast, reliable method for quantifying aluminum content in coagulants and flocculants in accordance with ABNT NBR 11176. Using thermometric titration, the approach seeks to deliver precise values of aluminum oxide (Al2O3) content, guiding operators in calculating precipitation capacity and adjusting chemical feed rates for optimal water treatment performance.

Methodology and Instrumentation

Samples of PAC and aluminum sulfate were analyzed without additional preparation. The procedure follows the ABNT NBR 11176 protocol and involves:

• Weighing an appropriate sample mass into a titration vessel.
• Adding deionized water, hydrochloric acid, and acetate buffer to stabilize pH.
• Titrating with standardized sodium fluoride solution while monitoring temperature changes.

The core instrumentation included:

• 859 Titrotherm titrator controlled by tiamo™ software
• Thermoprobe HF temperature sensor for high-resolution detection of exothermic reactions in fluoride-containing media
• 10 mL buret, rod stirrer, and standard accessories for thermometric titration

Main Results and Discussion

Five replicate determinations yielded the following mean Al2O3 contents and relative standard deviations (SD):

• PAC (polyaluminum chloride): 10.7 % (m/m), SD(rel) 0.8 %
• Aluminum sulfate: 7.7 % (m/m), SD(rel) 0.5 %

The low relative standard deviations highlight the method’s precision and reproducibility. Thermometric titration compensates for optical interferences and provides rapid end-point detection through subtle temperature shifts, making it well suited for routine quality control.

Benefits and Practical Applications

Key advantages of this thermometric titration approach include:

• Speed: Rapid measurements reduce analysis time and increase laboratory throughput.
• Accuracy: Precise detection of the titration end point enables correct coagulant dosage.
• User-friendly operation: Automated titrator setup and software guidance simplify routine analyses.
• Robustness: Reliable performance in acidic, fluoride-containing matrices without interference from color or turbidity.

This method is directly applicable to water and wastewater treatment facilities, analytical service laboratories, and industrial QA/QC departments seeking fast, reliable aluminum quantification.

Future Trends and Possibilities

Emerging directions for aluminum determination in flocculants and related matrices include:

• On-line or at-line thermometric titration systems for real-time process monitoring and control.
• Integration with digital plant management platforms and advanced chemometric data analysis.
• Extension of thermometric techniques to other metal ions and complex matrices.
• Miniaturization and portable devices for field-based water quality assessment.

Conclusion

Thermometric titration based on ABNT NBR 11176 and implemented using the 859 Titrotherm with a Thermoprobe HF offers a fast, accurate, and user-friendly method for determining aluminum content in coagulants and flocculants. Its high precision and rapid turnaround make it an ideal choice for optimizing chemical dosing and ensuring the efficiency of water and wastewater treatment processes.

References

• ABNT NBR 11176: Water treatment – Determination of aluminum oxide by thermometric titration