Chemical pretreatment for reduction of membrane fouling caused by algae

Batch filtration experiments in dead-end mode were carried out to investigate the membrane fouling phenomenon while treating algal-laden water with and without pretreatment. The three types of water samples used were dispersed Chlorella laden water, chemically conditioned Chlorella algae, and natural water from pond. Chemical pretreatment was done using alum and ozone. It was found that algae can cause significant fouling of membranes. For dispersed Chlorella algae, initially when the deposition was less, the resistance was very low or negligible. As the deposition increased, the resistance increased exponentially and then a linear increase was observed. The cake resistance was found to be 1.23 × 1013/m for an algal deposition of 9.6 g/m2. The cake resistance offered by chemically conditioned Chlorella sample was half, as compared to that of the dispersed sample for the same amount of deposition. Coagulation with alum and pretreatment with ozone were found to be effective in controlling the fouling of membranes for all three types of sample. An alum dose of 0.50–0.62 mg/mg of algal cells can reduce the cake resistance by 70% or more. Membrane cleaning using hydrodynamic shear force and anthracite was able to reduce resistance by more than 99% for all three samples.

Research highlights
► Algae can cause significant fouling of both PVDF and cellulose acetate membrane.
► Addition of coagulants increases floc size and thus helps in reducing resistance.
► Ozone reacted with extracellular organic matter reducing cell size and fouling.
► Physical cleaning with anthracite as scrubbing agent was able to reduce fouling.