THE ROLE OF PARTICLE-SIZE AND DENSITY IN DISSOLVED AIR FLOTATION AND SEDIMENTATION

Conventional (sedimentation) and advanced (dissolved air flotation) tr eatment were studied in the context of removal of the single cells for m of the cyanobacteria Microcystis aeruginosa. This cyanobacterium spe cies is recognised as an ideal surrogate for process removal efficienc y assessment of particles of the problematic size range (3-10 m). The agglomeration (coagulation/flocculation) phase has been indicated as e ssential and determining the down-stream process efficiency, hence it is a prerequisite for process improvement. Relevant process parameters have been addressed on a laboratory (model water) and pilot plant (re servoir water) scale, including the influence of coagulant (FeCl3) dos e, coagulation pH, flocculation time, energy input (G value), single s tage versus tapered flocculation and application of cationic polymer a s coagulant aid. The process efficiency was assessed as a function of the preceeding agglomeration (coagulation/flocculation) phase and the obtained panicle (floc) size distributions. The particle (floc) size-d ensity relationship was addressed in the context of more accurate proc ess kinetic modelling. (C) 1997 IAWQ. Published by Elsevier Science Lt d.