Garnet rich mineral sand based filter media for Removal of fresh water algae
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Date
2018
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Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Algal blooms have become a stigma for present day stagnant surface water
bodies. Therefore, consumption of water without treatment would be harmful.
Garnet granules have the ability of reduction of bed expansion and particle
abrasion in multi-media filters during back flushing due to its high specific
gravity and high hardness. In this study, garnet granules separated from beach
sand in southwestern costal area in Sri Lanka were investigated as a filter media
to remove fresh water algae. Microscopic and particle size analysis indicated
that the beach sand consists predominantly of garnet, quartz and ilmenite. The
garnet grains are round to elongate shaped in the size range between 1 mm and
0.15 mm. Particle size and shape of the extracted garnet are optimum for the use
as water filtering medium. Garnet enrich fraction grains (1 mm — 0.15 mm)
were further concentrated by density separation via panning. Algae samples
from Beira Lake, Colombo were collected, in the depth at illumination level 1%
from surface. Algae were grown giving nutrient, sunlight and aeration. Nutrient
medium used was the Bristol solution. For varying flow rates, algae filtered
through 0.50 mm and 0.15 mm sieved fractions. Parallel determination for the
efficiency of the filter bed with time was done and turbidity was measured by
turbidity meter. When considering the algae filtration, removal of Microcystis is
efficient for 0.15 mm panned fraction. Removal of Closterium was not efficient
probably due to shape of the organism. Chroococcus and Volvox, were not
removed well possibly due to their small size. Removal of algae was decreasing
with the time from both filter beds. The study concludes that prepared garnet
filter is useful in filtering Microcystis and further modifications should be done
prior to use as a filter.
Keywords: Algae, Garnet, Panning, Filtration, Mineral sand
Description
Keywords
Materials Sciences, Mineral Sciences