Algal Inhibiting Effects of Salicylic Acid Sustained-Release Microspheres on Algae in Different Growth Cycles

Abstract

Microcystis blooms and microcystins caused by eutrophication are harmful to the environment. At present, algicide based on allelochemicals is widely used in algae control. Environment-friendly sustained-release salicylate chitosan microspheres (SA-CS) were prepared by acylation of chitosan and glutaraldehyde. SA-CS was characterized by scanning electron microscopy, Fourier transform infrared spectral analysis, and laser particle sizer. The inhibitory effects of SA-CS on Microcystis aeruginosa at different stages, and the environmental impact of the inorganic index, were studied. The results showed that the mean size of SA-CS was 53.3 μm, the encapsulation rate was 40.66%, and SA-CS had a good sustained-release effect (stable release within 25 days). On the seventh day, a 90% inhibition rate in the lag phase required 105 mg/L of SA-CS, whereas a 90% inhibition rate in the log phase required 675 mg/L of SA-CS. The sensitivity of Microcystis aeruginosa at the lag phase to salicylic acid was about 1.4 times that of the log phase, thus, it is recommended to control the algae in the lag phase. The long-term inhibition effect of SA-CS on algae was detected after adding sufficient SA-CS. In terms of salicylic acid, pH, and dissolved oxygen, no lousy effect was observed for the addition of SA-CS. SA-CS could effectively reduce the concentration of microcystin-LR by 50%. SA-CS is an environment-friendly sustained-release microsphere with good algal inhibition performance for Microcystis aeruginosa.

Keywords: Microcystis aeruginosa; chitosan; microcystin-LR; microcystins; microspheres.

Figure 1

Influence of the light and dark conditions on SA in water: (A) shows the effect of darkness on SA and SA-CS; (B) shows the effect of light on SA released from SA and SA-CS.

Figure 2

SEM of SA-CS and IR spectra of CS and SA-CS: (A) SEM of SA-CS; (B) IR spectra of (a) CS and (b) SA-CS.

Figure 3

Short-term and long-term Chl-a concentration change of lag phase and log phase: (A) short-term Chl-a concentration change of lag phase; (B) long-term Chl-a concentration changes of lag phase; (C) short-term Chl-a concentration change of log phase; (D) long-term Chl-a concentration changes of log phase.

Figure 3

Short-term and long-term Chl-a concentration change of lag phase and log phase: (A) short-term Chl-a concentration change of lag phase; (B) long-term Chl-a concentration changes of lag phase; (C) short-term Chl-a concentration change of log phase; (D) long-term Chl-a concentration changes of log phase.

Figure 4

The effect of SA-CS on the concentration of SA in algal liquid at lag phase and log phase: (A) the effect of SA-CS on SA at lag phase; (B) the effect of SA-CS on SA at log phase.

Figure 5

The effect of SA-CS on the concentration of pH in algal liquid at lag phase and log phase: (A) the effect of SA-CS on pH at lag phase; (B) the effect of SA-CS on pH at log phase.

Figure 6

The effect of SA-CS on the concentration of DO in algal liquid at lag phase and log phase: (A) the effect of SA-CS on DO at lag phase; (B) the effect of SA-CS on DO at log phase.

Figure 7

The effect of SA-CS on the concentration of MC-LR in algal liquid at lag phase and log phase: (A) the effect of SA-CS on MC-LR at lag phase; (B) the effect of SA-CS on MC-LR at log phase.