Flocculation of Microcystis aeruginosa by steel slag and its safety evaluation

Abstract

This study investigated the flocculation of Microcystis aeruginosa by steel slag and evaluated the safety of treated water. The results showed that algal cells at a steel slag dosage of 0.48 g L−1 were effectively removed from two diluted algal solutions when their algogenic organic matter (AOM) contents were 3.54 and 5.81 mg L−1 (referred to as S1 and S2) with algae removal rates of 93.8 and 92.6 %, respectively. Simultaneously, the concentrations of AOM were reduced in S1 and S2 with removal efficiencies of 72.6 and 70.2 %, respectively. Charge neutralisation and bridging were probably the mechanisms that accelerated the flocculation processes. However, AOM had a priority over the algae in the reaction with the steel slag by producing protein complexation, which adversely affected coagulation and increased coagulant demand. Increased K+ and AOM after flocculation indicated that cell damage occurred at a retention time of 36 h. However, acute toxicity test demonstrated that the inhibition rate did not significantly increase until the retention time reached 48 h. Overall, steel slag has a great potential as a low-cost alternative to control algal bloom and restore aquatic ecosystems.