Abstract:
Groundwater supply has been
one of the pillars of socio and economic
development, especially in the dry regions of Sri
Lanka, where reliable water sources are very
scarce. With the rising water demand, water
conservation through recycling and reusing has
become an important strategy in a sustainable
built environment. The Murunkan aquifer is
one of the most utilized aquifer systems in
Northern Province. The average extraction
from the Murunkan aquifer is approximately
10,000 m3
/d. The yield is nearing saturated, thus
leading to a few water quality variations.
Variations in turbidity level in Murunkan
groundwater sources could be a consequence of
precipitation of insoluble reduced iron (Fe2+),
manganese (Mn2+) and other oxides. The study
is focused on investigating the effectiveness of
chlorine as a pre-oxidation mechanism in rapid
sand filtration for turbidity removal in
groundwater. The pilot filter consists of particle
sizes of 25mm, 16mm, 10mm, 2-5mm with a
layer thickness of 75 mm, 50mm, 30mm, and
50mm, respectively, and sieved ordinary silica
sand as filter media with 700 mm layer
thickness. The chlorine solution is added at the
inlet point of the filter. A retention time is
maintained between 20-25 minutes to allow
oxidation above the sand bed within the rapid
sand filter model. The effluent from the filter
was tested for turbidity based on APHA
standards for 15 trials. Raw water turbidity
ranges between 0.27-3 NTU, while treated water
turbidity ranges between 0.21-0.68 NTU. The
maximum turbidity removal percentage was
77% while turbidity removal was observed in
60% of samples. It is also found that there is a
trend in increasing removal percentage with the
increase of raw water turbidity and the number
of trials conducted, however, removal efficiency
does not have any definite trend with chlorine
concentration.
