ALGAL FLOCCULATION-SEDIMENTATION BY PH INCREASE IN A CONTINUOUS REACTOR

The effectiveness of microalgae flocculation by pH increase was invest igated using the jar test procedure. The results indicated that pH val ues between 11.8 and 12 induced extensive flocculation without need of adding magnesium. pH was increased by sodium hydroxide or calcium hyd roxide. In both cases, the total solids abatement was more than 95% pr oduciIlg sludge of excellent settleability and good mechanical resista nce quantified by a destructive test. The next step was the operation of a continuous flocculator which might optionally be packed with gran ular sand or inert resin. It was shown that a fluidized bed or any oth er mechanical energy transfer device was not required to obtain more t han 95% efficiency with a superficial upflow velocity of 30 m/h corres ponding to a residence time through the whole unit of 5 minutes only.