The impact of physico-chemical water treatment on a novel flotation/filtration process

Recent research explored the application of mechanical flocculation ahead of a novel flotation/filtration process (Counter Current Dissolved Air Flotation/Filtration -- COCO DAFF(TM)) 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 DAFF(TM) 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 DAFF(TM) 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