Investigation Into Hydraulic Flocculation With Special Emphasis On The Removal Of Algae

Dissolved air flotation is being used successfully for the Clarification of raw waters for potable supply. Efficient flocculation is essential for effective treatment by flotation. Most flotation plants employ mechanical flocculation for which slow moving paddles provide the agitation required for floc agglomeration. Mechanical flocculation is expensive to operate and needs maintenance. Hydraulic flocculation was investigated as an alternative to mechanical. The work has shown that a Similar flotation treated water quality can be produced by the two processes. Half the flocculation time is required for hydraulic flocculation compared - with mechanical but a higher energy input is needed to compensate for the shorter time. Results showed the optimum G*t value (mean velocity gradient * residence time) at 50 000 and the response to variation in throughput was the same for both processes. The hydraulic flocculator was operated successfully on three different waters, turbid river, stored low turbid cultured and stored algal. ladened waters. The hydraulic flocculator was scaled-up successfully from a 8.0 m3/h pilot plant to a 90.0 m3/h prototype plant. Coagulation and flocculation of algae was studied by measuring their electromobility and by carrying out parallel tests ina - flotation jar tester. All the algal species investigated possessed an electro-negative potential. Coagulation and flocculation of the algae examined in the jar test experiments appeared to be due to charge neutralization.