Pilot-scale comparison of sodium silicates, orthophosphate and pH adjustment to reduce lead release from lead service lines
Kimia Aghasadeghi, Sigrid Peldszus, Benjamin F. Trueman, Anushka Mishrra, Mitchell G. Cooke, Robin M. Slawson, Daniel E. Giammar, Graham A. Gagnon, Peter M. Huck, Water Research, Volume 195,2021,116955,ISSN 0043-1354, https://doi.org/10.1016/j.watres.2021.116955
In 2018, the Chair team undertook a collaborative pilot-scale study to compare three different corrosion control treatments (i.e. sodium silicates, orthophosphate and pH adjustment) for reducing lead release from lead service lines. At that time very few studies were available on using sodium silicates for controlling lead release. The pilot set up was commissioned in August 2018 at the Lake Huron water treatment plant (Grand Bend, ON) and was operated continuously for 68 weeks. In this study a harvested service line was used that was excavated by the City of London. The pilot study concluded at the end of 2019 after which scale analysis at Washington University (St. Louis, Missouri, USA) and biofilm accumulation analysis at Wilfrid Laurier University (Waterloo, ON) were completed. Lead analysis was done at Dalhousie University (Halifax, NS) and it included the detection of colloidal dispersions containing lead which provided important insights for the interpretation of the lead release data. The results were published in February 2021 in Water Research as open access (journal subscription is not needed for accessing the paper). The paper abstract which outlines the key findings is provided below. The full paper can be accessed and downloaded via this link: https://doi.org/10.1016/j.watres.2021.116955
If you have any questions about this study, please contact Kimia Aghasadeghi at kimia.aghasadeghi@uwaterloo.ca.
Abstract:
Sodium
silicate
is
thought
to
mitigate
lead
release
via
two
mechanisms:
by
increasing
pH
and
by
forming
a
protective
silica
film.
A
pilot-scale
study
using
an
excavated
lead
service
line
(LSL)
fed
with
water
from
a
Great
Lakes
source
was
undertaken
to:
(1)
clearly
distinguish
the
pH
effect
and
the
silica
effect;
(2)
compare
sodium
silicate
to
orthophosphate
and
pH
adjustment;
(3)
determine
the
nature
of
silica
accumulation
in
the
pipe
scale.
The
LSL
was
cut
into
segments
and
acclimated
with
water
at
pH
7.1.
Median
dissolved
lead
was
197
μg/L
in
the
last
8
weeks
of
acclimation
and
dropped
to
16
μg/L,
54
μg/L,
and
85
μg/L
following
treatment
with
orthophosphate
(dose:
2.6
mg-PO4/L,
pH:
7.9),
pH
adjustment
(pH:
7.9)
and
sodium
silicate
(dose:
20
mg-SiO2/L,
pH:
7.9),
respectively.
When
silica
dose
was
increased
from
20
mg-SiO2/L
to
25
mg-SiO2/L
(pH:
8.1),
lead
release
destabilized
and
increased
(median
dissolved
lead:
141
μg/L)
due
to
formation
of
colloidal
dispersions
composed
mainly
of
lead-
and
aluminum-rich
phases
as
detected
by
field
flow
fractionation
used
with
inductively
coupled
plasma
mass
spectrometry.
Si
was
present
in
the
scale
at
a
maximum
of
2.2
atomic
%
after
17
weeks
of
silica
dosing
at
20
mg-
SiO2/L.
Under
the
conditions
tested,
sodium
silicate
did
not
offer
any
benefits
for
reducing
lead
release
from
this
LSL
other
than
increasing
pH.
However,
sodium
silicate
resulted
in
lower
levels
of
biofilm
accumulation
on
pipe
walls,
as
measured
by
heterotrophic
plate
counts,
when
compared
to
orthophosphate.