Association of dissolved air flotation (DAF) with microfiltration for cyanobacterial removal in water supply

The removal of filamentous cyanobacteria in natural water was investigated by a sequential treatment involving dissolved air flotation (DAF) (preceded by coagulation/flocculation) and microfiltration (MF) technologies. The combined treatment was considered to evaluate the contribution of the DAF process as a pre-treatment for MF to mitigate the impact on the microfiltration performance caused by the presence of the cells. The bench-scale experiments were conducted with surface water samples. For C/F steps, a dose of 40 mg L-1 of aluminium sulphate was used, and several operational conditions were adopted for the DAF tests. For the MF experiments, polyvinylidene fluoride (PVDF) membranes (0.3 mu m) and a working pressure of 1 bar were used. The parameters colour, turbidity, UV254 (nm) absorbance, DOC and cyanobacterial density, were evaluated. The DAF-MF sequence showed a considerable reduction in the residual values for all parameters compared with the DAF process alone. MF was able to remove cyanobacterial cells completely. The use of DAF as an MF pre-treatment indicated an increase in the percentages of removal. However, the particulates remaining in the water from the DAF process resulted in clogging of the membrane. The results indicate that the association of DAF and MF technologies can be a viable option to be used for water treatment with cyanobacterial cells.