lauren@kelman.ca

TERTIARY TREATMENT TECHNOLOGIES & PRACTICES
concentration can be constantly below
0.05 mg/L, if sufficient ferric is added
into the process.
For the Barrie Wastewater Treatment
Facility (WWTF), Barrie, Ontario, the
liquid treatment processes include a
high purity oxygen process, secondary
clarifiers, rotary biological contactors
(RBCs) and traveling bridge single-media
sand filters. Historical performance
shows that the Barrie WWTF can reliably
achieve effluent TP of 0.15 mg/L with
the existing sand filters operating at their
rated capacity. Under the Lake Simcoe
Phosphorus Reduction Strategy, the
Barrie WWTF needs to produce effluent
with a TP limit of 0.1 mg/L. In order to
reliably meet 0.1 mg/L effluent TP, the
City of Barrie is currently conducting an
engineering design assignment to retrofit
one existing secondary clarifier into an
MBR process. This MBR train will treat
a portion of the total flow to achieve
ultra-low TP concentration of 0.05 mg/L
and below, and the MBR effluent will
be blended with the remaining sand
filtration effluent to meet the effluent TP
concentration of 0.1 mg/L.
Tertiary low-pressure
membrane filtration
Low-pressure membrane filtration
can also be used as a tertiary step to
polish the secondary clarifier effluent.
Microfiltration (MF) membranes have
approximately 0.2 microgram (μm)
pores, and ultrafiltration (UF) membranes
have approximately 0.02-μm pores.
Both MF and UF can be used to provide
tertiary filtration treatment to reliably
FIGURE 1
achieve TP concentration of 0.05 mg/L.
UF membranes are used at the Keswick
Water Pollution Control Plant (WPCP),
Regional Municipality of York, Ontario,
to provide tertiary phosphorus removal.
The Regional Municipality of
York, Ontario, is currently conducting
engineering design for a water
reclamation center (WRC) as part of
the Upper York Sewage Solution (UYSS)
project. Tertiary membrane filtration is
used to treat the secondary effluent to
achieve TP concentration of 0.05 mg/L;
its effluent will then be further polished
by an RO facility.
Reverse osmosis
RO is a high-pressure membrane
process. The pores in an RO membrane
are much smaller than those in lowpressure
membranes. Due to membrane
surface chemistry, charged wastewater
constituents (ions) are blocked or rejected
by the membrane. Molecules larger than
the pores are rejected by size exclusion.
Except at very low pH, orthophosphate
has a negative charge; therefore, it can
be removed from wastewater using
RO membranes. Of the treatment
technologies being considered for
phosphorus removal to ultra-low levels,
RO has demonstrated the lowest effluent
concentrations. However, due to their
higher capital and operating costs, RO
facilities are usually only selected after
ruling out less expensive alternatives.
The WRC of the UYSS project is
currently under engineering design.
The Individual Environmental
Assessment (IEA) process recommended
Process flow diagram of new adsorption and recovery process to achieve ultra-low TP.
48 INFLUENTS Fall 2015
that RO be used to further lower the
tertiary membrane filtration effluent for
the project to consistently achieve the
ultra-low TP limit of 0.02 mg/L.
New technology include phosphorus
recovery: Media adsorption
Recent work suggests that adsorption
is an important part of the phosphorus
removal mechanism, even when using
chemical precipitation. Work by Smith et
al. (2008) indicates that tertiary removal
of phosphorus by metal salts involves
co-precipitation of phosphate along
with the formation of metal hydroxide
floc complexes and adsorption of
phosphate onto the hydrous metal oxide
floc structure. Recent advances include
further development of reactive filtration
options whereby sand filter media is
coated with iron oxide to promote
phosphorus adsorption.
Processes using adsorbent media
(instead of adsorbent floc as described
above) have the advantages of consistent
removal of phosphorus to low
concentrations, minimal sludge formation,
simple recovery of phosphorus and ease of
system maintenance. However, adsorbents,
such as activated alumina and iron oxides,
are not widely used. This is most likely the
result of slow phosphorus removal rates
and non-selectivity for phosphate over
other competing anions requiring large
volumes of adsorbent and large system
footprints and low resistance to acids and
alkalis that inhibit repeated removal and
in-situ regeneration cycles of the media.
A new adsorbent media was developed
by Asahi Kasei Chemical Corporation
(Asahi), along with an integrated
phosphorus adsorption, desorption
and recovery system to overcome the
shortcomings mentioned above. Two
unique aspects of this technology are: i)
its ability to be regenerated in-situ; and
ii) no iron or aluminum chemistry that
might compete with phosphorus recovery
alternatives (such as struvite recovery).
To demonstrate the capability of the new
media in treating municipal wastewater
for TP removal, Black & Veatch
conducted a pilot test on secondary
clarifier effluent at the Lawrence WWTP,
Lawrence, Kansas, during the first half of
2010 (Fitzpatrick et al. 2010). A process
flow diagram for the system is presented
on Figure 1. During the adsorption
process, filtered effluent is passed through
the adsorption towers, and phosphate
Click HERE to return to Table of contents