Enhanced flotation technology using low-density microhollow beads to remove algae from a drinking water source

Abstract

Dissolved air flotation (DAF) is a well-established flotation technology for the pretreatment of water sources with a high algal bloom. However, high shear force generated during injection of microbubbles caused breakage of floc. This study investigated the removal tendency of algae using DAF, sedimentation, and microhollow beads combined with DAF from a water sample collected from the Nakdong River in Korea. The reduction in Chl-a as algae was 8.5 ± 0.8 in DAF and 2.8 ± 0.3 mg/m3 in DAF with 90 mg/L microhollow bead. However, a further increase in the microhollow bead concentration did not show a significant difference in Chl-a reduction. For conventional DAF, the optimum flotation time was achieved in 4 min, with a removal greater than 91 %. For DAF with microhollow beads, optimum flotation time was achieved in 2 min, with a removal greater than 95.4 %. Further, for the sedimentation case, the Chl-a removal observed was 26.7 % and 87.2 % for 5- and 30-min, respectively. Different recycle ratios were tested for DAF, ranging between 5% and 15 %. The Chl-a removal achieved with 90 mg/L microhollow beads was more than 95 % for a 5% recycle ratio. Upon the addition of microhollow beads, the removal was enhanced by 23.6 % compared with DAF. Further, an increase in the recycle ratio with microhollow bead concentration did not show a significant enhancement in Chl-a removal.