Pharmaceutically active compounds: Their removal during slow sand filtration and their impact on slow sand filtration bacterial removal
Highlights
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- Pharmaceutically active compounds were removed in slow sand filters.
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- Removal of caffeine, estrone and 17-beta estradiol was observed.
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- Removal of carbamazepine, gemfibrozil, and phenazone was minimal.
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- Biologically mature filters removed more than 99% of total coliforms and E. coli.
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- Caffeine and estrogens may impact bacteria removal and schmutzdecke microorganisms.
Abstract
Slow
sand filtration (SSF) has been widely used as a means of providing
potable water due to its efficacy, low cost, and minimal maintenance.
Advances in analytical instrumentation have revealed the occurrence of
pharmaceutically active compounds (PhACs) in surface water as well as in
groundwater. It is unclear if the presence of these compounds in the
feed water can interfere with the performances of an SSF unit. The aim
of this work was to examine i) the ability of two SSF units to remove
six PhACs (caffeine, carbamazepine, 17-β estradiol [E2], estrone [E1],
gemfibrozil, and phenazone), and ii) the impact of these PhACs on the
removal of bacteria by two SSF units. The presence of PhACs in feed
water for SSF can occur in surface waters impacted by wastewater or
leakage from sewers and septic tanks, as well as in developing countries
where unregulated use and improper disposal are prevalent. Two
pilot-scale SSF units were used during the study. Unit B1 was fed with
stream water with 1% of primary effluent added, while unit B2 was fed
with stream water alone. Although limited removal (< 10%) of
carbamazepine, gemfibrozil, and phenazone occurred, the complete removal
of caffeine, and the partial removal (11–92%) of E2 and E1 were
observed in the two SSF units. The results of this study suggest that
the occurrence of the selected PhACs, probably estrogens and caffeine,
in the feed water at 50 μg L− 1 affected the ability of the schmutzdecke to remove total coliform and Escherichia coli. The bacterial removal achieved within the schmutzdecke
dropped from 95% to less than 20% by the end of the study. This
decrease in removal may be related to the change in the microbial
community within the schmutzdecke. A diverse microbial
community, including Bacteroidetes and several classes of
Proteobacteria, was replaced by a microbial community in which
Gammaproteobacteria was the predominant phylum (99%). Despite the low
removal achieved within the schmutzdecke, removal of total coliform and E. coli
greater than 99% occurred after both SSF units throughout the study.
Bacterial removal occurred in the upper half of the sand filter. This
was probably due to a diverse microbial community established in the
packing material, in which Bacteroidetes (13–25%), Acidobacteria (7–17%)
and several classes of Proteobacteria (35–52%) (Alpha-, Beta-, Delta-,
and Gammaproteobacteria) were the predominant phyla.
Keywords
- Slow sand filtration;
- Bacterial removal;
- PhACs;
- Schmutzdecke
Copyright © 2015 Elsevier B.V. All rights reserved.
