| Abstract | An investigation of the feasibility of chemical flocculation and air flotation for harvesting of algae from high rate oxidation pond waters was carried out during this research. The objective of
this research was to reveal the most economic coagulant(s) for
flocculation of algae from high rate pond suspension and to perform the removal of the floc from suspension by flotation technique. Several coagulants were tested, aluminum sulfate, lime, ferrous sulfate, ferric sulfate, ferric chloride, and fifty organic commercially available polyelectrolytes. Among the five primary coagulants, alum
was found to be the best on an economic basis. Puriflocs C31, C32, and PEI 600 were noted to be effective coagulant aids to alum flocculation. Coagulation was carried out using the conventional jar test technique. Effects of the factors to the process such as coagulant dose, pH, mixing conditions, polyelectrolyte concentration, and time of addition of polyelectrolyte were investigated. Alum flocculation was found to be optimum on an economic basis at pH 6.5. Initial fast mixing of coagulant at 100 rpm for 60 secs followed by slow mixing at 80 rpm for J minutes were found to be the optimum mixing conditions for algal separation by alum. The polyelectrolytes, being cationic, anionic, and non-ionic were compared as to their relative efficacies as coagulant aids to aluminum sulfate with pH control. Among the different types of polyelectrolytes tested, the cationic polyelectrolytes were noted to be more effective aids than the anionic and nonionic polyelectrolytes. In polyelectrolyte-alum
flocculation, it was found that pH has no significant effect over the efficacy of polyelectrolytes as coagulant aids to alum. pH 6.5 was noted to be the optimum on an economic basis. Volatile solids of the settled flocs after flocculation were analyzed to measure the degree of flocculation achieved. Cost of
coagulant(s) used to yield optimum flocculation were compared to evaluate
coagulant or coagulant combination was economically |
