Abstract:
Microcystis sp., one of the most common cyanobacteria releases cyanotoxins which cause
severe ecological consequences to both aquatic organisms and human. There is a high
demand for developing an eco-friendly safer methods to control harmful algal blooms.
Medicinal and antibacterial properties of silver nanoparticles (Ag NPs) has gained a
prominent role in developing such methods. Green synthesis of Ag NPs is eco-friendly
and cost effective than that synthesized by conventional chemical methods. Therefore,
the objectives of the study were to; (1) produce green synthesized AgNPs using 80%
methanol extract of Neolitsea cassia leaves and produce a nanocomposite by overlaying
Ag NPs on soda lime glass beads, and (2) incooperate nanocomposite into an aquarium
tank trickling filter to evaluate its performance as an anti-algal agent against Microcystis
sp. Three concentrations of AgNO3, 0.1, 0.2 and 0.3 mol dm-3 were chemically reduced
to elemental Ag by the plant extract and the synthesized NPs were coated on soda lime
glass beads (4 mm diameter). Ultraviolet-visible spectroscopy, Scanning Electron
Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA) and Fourier Transform
Infrared (FTIR) analysis techniques were used in characterizing green synthesized Ag
NPs. An experiment was conducted for a period of three weeks and at the end of the
experiment, Ag NPs synthesized using 0.3 moldm-3 AgNO3 were found to be more
efficient in inhibiting Microcystis sp. with a percentage of 62.27. There was a significant
difference in the mean chlorophyll content of controls and the three treatments (p<0.05).
Morphological variations of Microcystis colonies depend on Ag NP concentration while
showing the most significant variations in treatments with 0.3 moldm-3 Ag NPs. Disk
diffusion test indicates the highest zone of inhibition (approximately 18 mm) with respect
to 0.3 moldm-3 Ag NPs, affirming the anti-algal activity of green synthesized Ag NPs.
Study conclude that the anti-algal activity remarkably increased with the increasing
concentration of AgNO3 used to synthesize Ag NPs.
