Fabrication of HO slow-releasing composites for simultaneous Microcystis mitigation and phosphate immobilization.

Hydrogen peroxide (HO) is a widely accepted algicide in controlling cyanobacterial blooms. However, this method includes two disadvantages: 1) a low HO concentration (<5 mg L) is required; 2) HO-induced cell lysis causes phosphorus (P) contamination. To overcome the drawbacks, a HO slow-releasing composite (HSRC) based on calcium peroxide (CaO) was fabricated to substitute liquid HO. According to the results, a higher CaO dose increased HO yield and releasing rate. HO yield of 160 mg L CaO in HSRC reached 32.9 mg L and its releasing rate was 0.407 h. In addition, a higher temperature decreased HO yield and increased HO-releasing rate. Besides, HSRC endowed with a remarkable ability to immobilize P. Higher CaO dose, pH value, and temperature increased the rate of P immobilization. The highest rate was 0.185 h, which occurred with 160 mg L CaO 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 HO concentration during HSRC treatments, it suggested that the lethal effect on Microcystis aeruginosa was achieved with a super-low HO concentration (<0.3 mg L). 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 HO in mitigating cyanobacterial blooms. It may be a novel and promising algicide that not only kills cyanobacteria but also reduces eutrophication momentarily.