ELIMINATION OF MICROCYSTIS CYANOBACTERIA (BLUE-GREEN-ALGAE) BY AN OZOFLOTATION PROCESS - A PILOT-PLANT STUDY

It is now known that since cyanobacteria (blue-green algae) occur in b oth swimming and drinking water supplies, and lakes and rivers, they r epresent an increasing hazard to animal Life and human population. Mor eover, high algal contents pose also a number of operation problems fo r water purification plants. The objective of the work is to study the elimination of a Microcystis strain of cyanobacateria by the use of a n ozoflotation process which associates the oxidizing properties of oz one and the physical aspects of flotation. The functioning and the eff iciency of a pilot unit is presented according to such parameters as: ozone dose, flow rare, coagulants and raw water quality. The use of oz one in pretreatment leads to an inactivation of the algal cells. Exper iments let us calculate the specific ozone utilisation rate of Microcy stis and the [C.t] (ozone concentration, contact time) curve is determ ined versus algal removal. Under real conditions, a previous coagulati on stage is necessary; best results are obtained with ferric chloride. Preozonation is also of influence on the enhancement of the coagulati on efficiency. Association of the ozoflotation process and bilayer fil tration can solve the algae problems of waters presenting low turbidit y and low organic content, and improve water quality.