Efficiency of Glutinous Rice Straw Extracts (RD-Six) and Water Hyacinth in Inhibiting Algal Growth and Reducing Nutrients from a Hyper-eutrophic Pond

Abstract

Eutrophication is one of the main water pollution problems, which occurs throughout Thailand. This research focused on the use of glutinous rice straw (RD-Six) extract and water hyacinth to reduce nutrients and to inhibit phytoplankton growth in hypereutrophic water. In this research, we used (1) control without glutinous rice straw extract and water hyacinth; and (2) experimental treatment with glutinous rice straw extract and water hyacinth. Experiments were set up for eight days in ten concrete circle pit blocks (0.80 m in diameter and 0.40 m in height) in year 2020 (five replicates for each control and experimental treatment). Water quality was analyzed physically, chemically, and biologically, and the effect of glutinous rice straw extract on phytoplankton and the growth rate of water hyacinth were also determined. The result showed that values of water quality parameters (turbidity, DO, BOD, SS, TKN, NH3-N, NO2, TP, SRP, TN, and Chlorophyll-a) were improved. The values of water quality were significantly lower in experimental treatments than in controls. Glutinous rice straw extract had no effect on water hyacinth growth. The study of phytoplankton composition demonstrated that, prior to the experiment, Cyanophyta was the dominant group in both control and experimental treatments. After the experiment, Cyanophyta became less abundant in experimental treatments. Reduction of Cyanophyta could be caused by the direct effect of allelochemicals (phenolic compounds) from glutinous rice straw extract. Therefore, this combined method has displayed their effectiveness in reducing nutrients and inhibiting phytoplankton growth in eutrophic water.