Abstract:
The purpose of this research was to study the efficiency of chitosan and rice straw extracts in
inhibiting the growth of Microcystis spp.
There were four referential experiments included in this study. The first three experiments
aimed to find out 1) the appropriate amount of chitosan, 2) the appropriate amount of rice straw
extracts, and 3) the appropriate ratios of chitosan and rice straw extracts in inhibiting the growth of
Microcystis spp. In the first experiment, chitosan at the concentrations of 0, 2, 4, 6, 8 and 10 % was
used. In the second experiment, the rice straw extracts at the concentrations of 0, 2, 4, 6, 8 and 10 %
were used. In the third experiment, the different ratios of chitosan and rice straw extracts3:1, 2:1, 1:1,
1:2, 1:3were used. In the fourth experiment, however, the appropriate ratio of chitosan and rice straw
extracts found in the third experiments was used in the fieldwork to study its efficiency in inhibiting the
growth of Microcystis spp.
The result of this study revealed that 1) the optimum concentration of chitosan in inhibiting the
growth of Microcystis spp. was at 10 % which reduced the algal cells of Microcystis spp. by 82.76 %, 2)
the optimum concentration of rice straw extracts in inhibiting the growth of Microcystis spp. was at
10 % which reduced the algal cells of Microcystis spp. by 79.46 %, 3) the optimum ratio of chitosan and
rice straw extracts in inhibiting the growth of Microcystis spp. was 3:1 which reduced the algal cells of
Microcystis spp. by 84.90 %, and 4) the ratio of chitosan and rice straw extracts of 3:1 reduced the algal
cells of Microcystis spp. by 75.89 % in the fieldwork pond. Based on the Fourth Category of the Standards of Surface Water defined by the National Environmental Board of Thailand (1994), 1) the
levels of the dissolved oxygen increased to 1.7 mg/l, 2) the biochemical oxygen demand decreased to
0.2 mg/l, and 3) the total dissolved solids decreased by 39.1 % which all of obtained values did not
exceed the quality standards. In spite of the decreasing amount of three types of nutrients, 74.39 % of
ammonia-nitrogen, 35.4 % of orthophosphate, and 36.82 % of nitrate-nitrogen; all of them were higher
than the standards in the Fourth Category of the Surface Water Quality Standards.