Integrated membrane systems for toxic cyanobacteria removal

Abstract

Blue-green algae (cyanobacteria) provide a major problem for the water industry as they can produce metabolites toxic to humans in addition to taste and odour (T&O) compounds that make drinking water aesthetically displeasing. This problem is likely to be intensified by the effects of climate change through reservoir warming. Microfiltration (MF) provides a potential solution for dealing with blooms of toxic blue green algae. In the past, coagulation and sand filtration have been successfully used for removal of cyanobacteria, however as membrane technology has become more economically viable, the demand for information on the application of membranes for cyanobacterial metabolite removal has increased. MF pore size is a key matter as cyanobacterial metabolites should permeate such membranes. However, if cyanobacterial metabolites remain within the algal cells MF might be effective through the removal of these intact cells. This study investigated an integrated membrane system incorporating coagulation, powdered activated carbon and MF for the removal of intracellular and extracellular cyanobacterial metabolites. A laboratory scale MF unit was designed and studied. It utilised PVDF fibres with a nominal 0.02 micron pore size. Three species of blue-green algae were tested and three different coagulants were used on each species for removal of intact cells. Powdered activated carbon (PAC) was dosed prior to the MF at 20mg/L to remove extracellular metabolites. Cell counts as well as analysis for total and extracellular toxin and T&O were undertaken to assess each stage of the IMS. The results of this study are promising.