Water Treatment > Quality Water Solutions > Operational Issues > Coagulant Trials

Making a coagulant change is far from straightforward. The new material must satisfy multiple treatment goals and hold the line on solids disposal, pH adjustment chemicals and other costs. In changing out a coagulant, many utilities look at the published data and speak with other plants. They then follow this with jar tests on likely candidates to measure settled and filtered turbidities, settled pH and filterability index. The tests should include other process chemicals used to see how they work with the coagulant.

Those that look promising should be trialed. Set clear goals for the trial and pay careful attention to scheduling, training, coagulant introduction, equipment used, monitoring and much more. Make the trial long enough (30 to 60 days) to include a range of water conditions. Train the trial team carefully, walking through all procedures and equipment to be used. Extend training into the early portion of a trial.

Many facilities shift from one coagulant to another by adding the new one at 25% of its expected dose and reducing the incumbent by 25%. They then increase the new coagulant to 50% and then 75% and finally 100%, and decrease the existing one accordingly. Each step is taken when water quality remains stable. Start with a conservative dose. Adjust filter or settling aids and other products systematically to see how they work with the new coagulant.

During the trial, sample collection points should encompass the entire system starting near the addition point. Locations having good historical data typically provide the most useful data. Monitoring sites can include the centerwell of a clarifier, the flocculation zone, the top of filters, filter effluent and the middle of the settling basin. Define jar test stirring, settling and turbidity procedures for water collected at the various monitoring points.

Gather a broad range of data, e.g., settled and filtered water turbidity, treated water pH, particle counts, total organic carbon removal, filter run length, chemical addition, chemical residue, sludge amounts, backwash water and more. Use a trial data sheet to track key parameters and record actions taken. The economic impact of a new coagulant in a treatment system is typically analyzed based on at least 30 days worth of data. Compare the incumbent and new coagulants for similar raw water types. Look for savings that combine better operations and water quality.