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

Recent research explored the application of mechanical flocculation ahead o f a novel flotation/filtration process (Counter Current Dissolved Air Flota tion/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 f locculation. Generally, better COCO DAF(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 oppos ed to values of 30-60 s(-1) utilised ahead of conventional treatment. The e ffect of flocculation contact time on the COCO DAFF(TM) process was also st udied. Current design practice typically utilises 20-30 minutes flocculatio n contact time. It was found that process performance, in terms of water qu ality, did not deteriorate excessively if the contact time was reduced to a s little as 2 minutes, but filter run times were found to be proportional t o contact time. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.