Behavior of Cylindrospermopsis raciborskii during coagulation and sludge storage – higher potential risk of toxin release than Microcystis aeruginosa?

Abstract

Owing to the global warming and its strong adaptability, Cylindrospermopsis raciborskii has spread world-wide. However, as one of toxic cyanobacteria in many drinking water sources, it has not been drawn proper consideration in drinking water treatment plants so far. The investigation aimed at unveiling the fate of C. raciborskii during polyaluminum ferric chloride (PAFC) coagulation and sludge storage, revealing its differences from Microcystis aeruginosa. Results showed that C. raciborskii cells were effectively removed intactly under optimum coagulation conditions, but PAFC at higher dosages (>10 mg/L) triggered additional cylindrospermopsins release. In sludge storage, coagulated C. raciborskii cells suffered severe oxidative damage, leading to significant cylindrospermopsins release after day 6. C. raciborskii manifested different behaviors from M. aeruginosa which cells didn’t release much microcystins during coagulation and sludge storage. This was mostly due to their differences in physiology and morphology. In flocs, M. aeruginosa could be enveloped by coagulant which can protect cells against the nasty attack from outside, whereas C. raciborskii with long filaments was hard to be wrapped and prone to suffering oxidative damage. These results confirmed C. raciborskii had a higher risk of toxin release in water production process than M. aeruginosa, which should deserve more attention.