Evaluating the use of granular dual-media deep-bed filters for production of potable water

Abstract

The objective of this study is to evaluate the use of granular dual-media deep-bed filters for production of potable
water by applying filter materials (burnt oil palm kernel shell (BOPS) and sand) of varied proportions in assessing
the effects of variations of influent raw water turbidity, filter media and flow rates on filtrate quality. Experiments
were conducted to evaluate the effects of variations of influent raw water turbidity, bed composition, and filtration
rate on the performances of varied percentages of 75%, 50% and 25% sand of dual-media (sand and BOPS) rapid
gravity filters on filtered water turbidity and headloss development. Sieve analysis was carried out to characterize
both media and to determine their effective sizes and uniformity coefficients. Filtered water turbidity was recorded
with time during each experiment. The filter was operated on the principle of constant flow rate and variable head
loss mode. Fifty (50) litres of raw turbid water (10, 30, and 50 NTU) from a tank was passed through rotameter at
different flow rates (36, 48, and 60 l/hr) per experiment. Results obtained indicate that all the filters are capable of
producing water with acceptable turbidity (< 5 NTU as prescribed by World Health Organization Guidelines) when
the turbidity of the influent water is 10 NTU. The 75% and 50% sand dual-media filters proved effective at filtration
rates of 36 l/hr and 48 l/hr for influent turbidity of 30 NTU. The mathematical models formulated in this work could
be used as design and management tools for development of new filtration plants and operation, including upgrading
of existing plants.