ABSTRACT
Hydrogen peroxide (H2O2) is a widely accepted algicide in controlling cyanobacterial blooms. However, this method includes two disadvantages: 1) a low H2O2 concentration (<5 mg L-1) is required; 2) H2O2-induced cell lysis causes phosphorus (P) contamination. To overcome the drawbacks, a H2O2 slow-releasing composite (HSRC) based on calcium peroxide (CaO2) was fabricated to substitute liquid H2O2. According to the results, a higher CaO2 dose increased H2O2 yield and releasing rate. H2O2 yield of 160 mg L-1 CaO2 in HSRC reached 32.9 mg L-1 and its releasing rate was 0.407 h-1. In addition, a higher temperature decreased H2O2 yield and increased H2O2-releasing rate. Besides, HSRC endowed with a remarkable ability to immobilize P. Higher CaO2 dose, pH value, and temperature increased the rate of P immobilization. The highest rate was 0.185 h-1, which occurred with 160 mg L-1 CaO2 in HSRC at 25 °C and pH 8.0. Toxicity assays showed that HSRC exerted sustaining oxidative stress on Microcystis aeruginosa. Accumulation of intracellular reactive oxygen species resulted in the disruption of enzymatic systems and inactivation of photosystem. Tracking the variations of cell growth and H2O2 concentration during HSRC treatments, it suggested that the lethal effect on Microcystis aeruginosa was achieved with a super-low H2O2 concentration (<0.3 mg L-1). In addition, cell lysis did not cause a sudden rise in P concentration due to the P immobilization by HSRC. Therefore, HSRC successfully offsets the drawbacks of liquid H2O2 in mitigating cyanobacterial blooms. It may be a novel and promising algicide that not only kills cyanobacteria but also reduces eutrophication momentarily.
