Optimising Filtration Processes through Online Floc Particle Characterization

This report will be available as a Pay-Per-View item only.


The quantitative analysis of floc particles either on- or offline is not widely used in the operations of surface water plants, which use granular media filtration. Floc particle analysis is defined as photographically analyzing the floc for cross sectional area, diameter, and particle count. Several technologies are commercially available for accomplishing this task, yet little has been done in the way of investigating the possibility of improving water quality and plant operations with these measurements. Considering that flocculation will continue to be a key process in water treatment, it is worthwhile to improve the consistency and quality of treated water, ensuring public health and operational consistency for years to come. The objectives of this project were to establish and demonstrate the benefit of floc particle measurements both at bench- and full-scale operations at surface water treatment plants.


The researchers planned to demonstrate the following two main hypotheses on pilot- and full-scale:

Bench floc particle analysis predicts filtration particle removal
In situ floc particle analysis is a sensitive measure of process performance



Findings of this study demonstrated that bench-scale floc particle diameter analysis predicts granular media filtration particle removal on pilot scale. This is true primarily for the charge neutral mechanism, usually employed in direct filtration and DAF. The charge neutral floc particles predicted filtration particle removal much more sensitively than sweep floc particles. This was due to the nature of sweep floc and enmeshment of hydroxide flocs. In situ floc particle analysis showed high sensitivity to process and chemical changes. The floc particles were monitored on pilot scale on a limited basis during sweep floc conditions. The floc particles indicated large differences in floc characteristics depending upon hydrolyzing metal salt (HMS) dosage. In addition, the online floc particle measurement at pilot-scale was sensitive to the addition of floc-aid polymer at very low doses of 0.3 mg/L. Floc particle analysis at full-scale was carried out at three different treatment plants that use different unit processes. Granular media filtration employed at the three facilities was a combination of anthracite and sand. The City of Golden uses conventional treatment with coagulation-flocculation-sedimentation-filtration. The City of Boulder uses dissolved air flotation (DAF) instead of sedimentation. The Utah Valley Water Plant employs direct filtration.