Recent research explored the application of mechanical flocculation ahead of a novel flotation/filtration process (Counter Current Dissolved Air Flotation/Filtration - COCO DAFFTM) and compared it to the process performance seen when hydraulic flocculation was used. The energy input to the system, expressed in terms of the mean velocity gradient, G (s−1), and retention time, t, were used as a guideline for comparison between the two types of flocculation. Generally, better COCO DAFFTM performance resulted from using mechanical flocculation as against that using hydraulic flocculation. High G values (in excess of 80 s−1) were found to give best results, as opposed to values of 30-60 s−1 utilised ahead of conventional treatment. The effect of flocculation contact time on the COCO DAFFTM process was also studied. Current design practice typically utilises 20-30 minutes flocculation contact time. It was found that process performance, in terms of water quality, did not deteriorate excessively if the contact time was reduced to as little as 2 minutes, but filter run times were found to be proportional to contact time.

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