Separation and Purification Technology
Most researches focused on the high efficiency removal of cyanobacteria from water phase during drinking
water treatment, but did not address the potential danger of cyanobacterial cells being transferred
into the sludge, especially during the dewatering process. In this study, the characteristics of cell lysis
and microcystin (MC) release in the filtration of cyanobacteria-containing sludge were investigated. By
evaluating filtration rates, filtrate microcystins (MCs) and turbidity levels, and SEM micrographs of the
sludge in different operating conditions, the influences of mechanical actions and physical/chemical
effects on the integrity of cyanobacterial cells were explicated, and the corresponding operation conditions
were also optimized. The results showed that the sludge accumulation on unit filter area had significant
influence on sludge dewatering characteristics, and with increase in the volume of sludge
filtrated, more and more sludge accumulated on the surface of the filter media, resulting in reduced filtration
rates and potential cyanobacteria lysis. More hydrophilic filter media with lower porosity should
be chosen to enhance filtration efficiency. Compared with positive pressure filtration, vacuum filtration
with low-destructibility should be a better choice considering the MC release. Under increased vacuum
pressure, cyanobacteria-containing sludge had increasing filtration rate without causing damage of
cyanobacterial cells. While the storage time of cyanobacteria-containing sludge should be severely
restricted in actual water supply factories (4 d for AlCl3 sludge and 2 d for PACl sludge) to avoid the
adverse influences of cyanobacteria lysis on sludge dewaterability and filtrate quality. This study produced
deeper knowledge on the fate of cyanobacterial cells and intracellular MCs in the sludge dewatering
process, and the results provided valuable scientific references for volume reduction of
cyanobacteria-containing sludge in the actual treatment operations.