United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
>-
Research and Development
EPA/600/S2-85/008 Mar. 1985
Project Summary
Emerging Technology
Assessment of PhoStrip, A/0, and
Bardenpho Processes for
Biological Phosphorus Removal
This technology assessment address-
es the process capabilities and limita-
tions of three proprietary processes
(PhoStrip,* A/O, and Bardenpho) to
biologically remove phosphorus from
municipal wastewaters. These process-
es are used as alternatives to the
conventional method of treatment:
activated sludge with chemicals added
to precipitate phosphorus. The primary
objective of this report is to provide
guidance to individuals involved with
reviewing new processes as part of the
Innovative and Alternative Technology
Program.
PhoStrip, A/O, and Bardenpho pro-
cesses, all developed in the early
1970's, are based on the ability of the
biological system to provide enhanced
or so called "luxury" uptake involving
the mechanism of phosphorus release
by microorganisms under anaerobic
conditions, followed by cellular phos-
phorus uptake under aerobic conditions.
These three systems differ with respect
to their specific process design and to
their ability to provide phosphorus re-
moval, as well as various degrees of
nitrogen removal. The PhoStrip process
employs sidestream (i.e., a portion of
the return sludge) treatment in an
anaerobic contact tank; biologically
bound phosphorus is released to the
aqueous medium, and the supernatant
liquor is treated with lime to precipitate
inorganic phosphorus as calcium hy-
droxyapatite. Both the A/O and Bar-
denpho processes involve mainstream
(influent flow plus sludge recycle)
anaerobic treatment to precondition
the system for phosphorus removal via
waste activated sludge.
*Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
The A/O process can be designed for
phosphorus removal without nitrifica-
tion by using anaerobic/oxic stages, or
for phosphorus removal with nitrifica-
tion by using anaerobic/anoxic/oxic
stages plus additional internal, mixed-
liquor recycle from the oxic to the anoxic
stage. The Bardenpho system is a five-
stage (anaerobic/anoxic/aeration/
anoxic/reaeration) process designed to
provide both phosphorus and total
nitrogen removal.
The development status of these
processes (including a list of pilot
studies and full-scale installations),
process theory, capabilities, and design
considerations are addressed in this
report.
Capital, operation and maintenance,
and total present worth costs for these
three processes, as well as for baseline
technology of conventional processes,
are estimated based on stated assump-
tions to compare these alternatives.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Since the early 1970's, chemical pre-
cipitation with either alum, ferric chloride,
or lime has been widely used as a
demonstrated technology for phosphorus
removal. Where possible, steel mill waste
pickle liquor has provided a relatively
inexpensive chemical source for phos-
phorus precipitation, although it may also
contain other undesirable heavy metals.
The disadvantages of chemical precipita-
tion to remove phosphorus are chemical
costs, chemical handling and storage
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requirements, increased sludge produc-
tion, and related sludge handling and
disposal costs.
Before the present application of sys-
tems specifically designed to remove
phosphorus biologically, a series of
studies and full-scale plant observations
on this removal had been reported. These
studies led to intensive studies on possibly
applying this phenomenon to remove
phosphorus in activated sludge plants. All
the plants successfully removing phos-
phorus were high-rate, non-nitrifying,
plug-flow-type activated sludge plants.
By the early 1970's three proprietary
processes to biologically remove phos-
phorus had been developed:
1. PhoStrip, developed by Levin et al.,
and marketed in the United States
by Biosphencs, Inc (4928 Wya-
conda Road, Rockville, MD 20852,
Telephone: 301-770-7700),
2 A/0, developed by Air Products &
Chemicals, Inc., and marketed here
by the Environmental Products
Department of Air Products &
Chemicals, Inc. (Box 538, Allen
town, PA 18105, Telephone 215-
481-4911); and
3. Bardenpho, developed by Barnard
of South Africa, and'marketed m
the United States by EIMCO Process
Machinery Division of Envirotech
Corp. (669 West Second South,
P 0. Box 300, Salt Lake City, UT
84110, Telephone 801-526-2000)
Technology Descriptions
PhoStrip Process
The PhoStrip process is an activated
sludge process that takes advantage of
"luxury" phosphorus uptake and anaero-
bic phosphorus release. This process
differs from conventional activated sludge
in that a portion of the return sludge is
subjected to "phosphorus stripping" by
holding the sludge under anaerobic con-
ditions in a stripper tank. The solids
retention time (SRT) in this tank typically
ranges from 8 to 12 hours. During this
anaerobic period, phosphorus is released
and is elutriated from the sludge in the
stripper tank with a stream that is low in
phosphorus content This stream may
either be the overflow from the chemical
treatment tank (reactor clarifier), as is
shown in Figure 1, or be the primary
effluent. The phosphorus-rich overflow
from the stripper tank passes continuous-
Liquid
Sludge
Raw
Waste
TS~~R~eiurn Activated S/udoe
Final Low
Phosphorus
Effluent
Precipitating
Phosphorus
Pnosphatet
'tripper^ phosphorus
Enriched
Sludge
Sludge
Disposal
Phosphorus Phosphorus Sludge
Stripped Enriched Disposal
Sludge Supernatant
PHOSTRIP
Infl
Anaerobic
Anoxic
Aeration
Anoxic
Aeration
Clarifier
Effi
Return Sludge
BARDENPHO
^ Waste
Sludge
Return Sludge
Waste
, Sludge
Infl
— »
1
1
Anaerobic Stages
1
1
|
1
1
Oxic Stages
\
\
1
1
^
1
tJ Clar
v
v_
Effl
A/0
Figure 1. Phosphorus removal by three biological systems
ly to the chemical treatment tank where
lime is added for phosphorus precipita-
tion.
A/O Process (Anaerobic/Oxic)
The A/0 process is a single-sludge
suspended growth system that can com-
bine anaerobic, anoxic, and aerobic
sections in sequence (Figure 1). The
process can be designed for phosphorus
removal with or without nitrification and
denitrification. All sections are partitioned
into several hydraulic stages to approach
plug-flow and to prevent back-mixing.
Typically, for removal of phosphorus,
three anaerobic stages are followed by
three or more aerobic or oxic stages.
Recycled sludge from the secondary
clarifier is mixed with either raw waste-
water or primary effluent in the anaerobic
section so that there is "sorption" of BOD
by the organisms, with the accompanying
phosphorus release necessary for biolog-
ical removal of phosphorus. The anaerobic
section is covered and equipped with
mechanical mixers for mixing but not for
aeration.
The oxic stage, essential for the metab-
olism of BOD and uptake of the phos-
phorus released in the anaerobic stage,
may be aerated with either air or oxygen.
Phosphorus is removed from the system
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in the waste sludge, which may contain
4- to 6-percent phosphorus by dry weight.
Effluent phosphorus concentrations de-
pend on sludge wasting, which in turn is
controlled by the plant's operating SRT.
Bardenpho Process
Bardenpho stands for flarnard-etenitri-
fication-p/7osphorus, an activated sludge
process designed to accomplish both
biological uptake of phosphorus and
nitrogen removal. The process is patented
by the South African Inventions Devel-
opment Corporation and licensed to
Envirotech Corporation for marketing in
the United States. The Bardenpho process
is very similar to the previously described
A/0 process: anaerobic/anoxic/aerobic/
anoxic/reaeration stages versus A/O's
anaerobic/anoxic/oxic.
As shown in Figure 1, two anoxic stages
are used to accomplish high levels of
biological nitrogen removal by demtrifi-
cation An anaerobic stage is added
ahead of the original four-stage Barden-
pho nitrogen removal system to create
anaerobic-aerobic contacting conditions
necessary for biological uptake of phos-
phorus. Return activated sludge, sepa-
rated from the clarif ier, is mixed with the
influent wastewater beforethe anaerobic
contactor; this initiates the luxury phos-
phorus uptake by first releasing phos-
phate. Mixed liquor from the anaerobic
contactor then flows into the first anoxic
denitrif ication zone where it is mixed with
an internally recycled mixed liquor from
the aerobic nitrification zone. In the first
anoxic demtrification zone, nitrate is
reduced to nitrogen gas using soluble
organic matter in the wastewater as a
carbon source. The mixed liquor then
flows into the aerobic nitrification zone
where luxury phosphorus uptake, am-
monia oxidation, and additional BOD
removal occurs. Following the aerobic
nitrification zone, a second anoxic zone
provides additional nitrate and minimize
nitrate feed-back to the anaerobic con-
tactor. The reaeration zone provides
oxidation of remaining ammonia and
raises dissolved oxygen levels for effluent
discharge.
Process Capability and
Limitations
All three proprietary processes have
been demonstrated as capable of remov-
ing phosphorus from the 4- to 12-mg/L
range normally found in municipal
wastewaters down to the 1- to 2-mg/L
ranges as total phosphorus (TP). It is
important to consider effluent limitations
in each specific case to determine the
applicability of each of these processes.
For example, the Great Lakes and Florida-
Tampa Bay regions call for effluent limita-
tions of 1 mg/L as TP, and some areas in
South Africa have a standard of less than
1 mg/L of orthophosphate (0-P04) as P.
Since these processes are often "mar-
ginal" in producing effluent quality of less
than 1 to 2 mg/L as TP, or 1 mg/L as
PO-i-P, other provisions, such as supple-
mental mineral addition to precipitate
residual phosphorus and/or effluent fil-
ters, may be necessary unless the reliabil-
ity of the selected process is demonstrated
by treatability tests or pilot-plant data for
a specific case.
Since PhoStrip, A/0, and Bardenpho
are proprietary processes, typical design
parameters and other considerations
important to each should be sought when
designing a specific biological system to
remove phosphorus.
Cost Comparison
In the report, seven tables and eight
figures provide estimated capital costs,
operations and maintenance, total pre-
sent worth for 1,890 mVd (0.5 mgd),
18,920 mVd (5 mgd), and 189,200 m"
(50 mgd) systems. Estimates of the energy
requirements for each system are also
provided.
Risk Assessment
All three proprietary processes have
been reasonably well developed. Gener-
ally, they are capable of providing 1 to 2
mg/L of residual phosphorus. Therefore,
the risk involved in using any of these
processes is not in its complete failure,
but in its capability to meet a specific set
of effluent limitations. From available
data presented inTables 1,2, and 3 of the
project report, it can be seen that these
processes can, at times, marginally meet
the total phosphorus concentrations of 1
to 2 mg/L. Conducting pilot tests to obtain
data for application in a specific case,
before design, can minimize such risk.
Providing additional facilities treatment,
such as the use of effluent filters and
supplemental mineral addition, will fur-
ther reduce the risk of not meeting the
effluent requirements. Such a provision
would, however, reduce the cost-savings
benefit that can be gained from the use of
these alternative processes.
Comments from the three U.S. market-
ing firms are attached in the appendix to
permit the user to identify specific sup-
plier disagreements with the report and
to pursue those issues with those sup-
pliers when considering system(s) appli-
cation.
Recommendations
All three proprietary processes for
biological removal of phosphorus are
based on the mechanisms that uses
anaerobic treatment to pre-condition the
microorganisms for subsequent enhanced
uptake of phosphorus under aerobic
conditions. Although significant data and
experience have been obtained to sub-
stantiate the validity of the fundamental
concept, numerous complex factors af-
fecting the performance of the three
different systems are not yet fully under-
stood. Some of the more important
aspects of research needs are:
• Basic studies involving organisms
selection, physiological states, surviv-
al, and the direct impact of the anaero-
bic zone must be conducted before
biologically removing phosphorus can
be understood fully.
• Current design of the anaerobic section
in each of the three proprietary pro-
cesses appears to be empirical, and
there is a lack of rational basis for
sizing the anaerobic stage.
• The three processes are capable of
producing effluent TP of less than 2
mg/L; however, effluent TP concen-
trations of 1 to 2 mg/L appear in the
marginal area that can hardly be
predicted with certainty. The TP con-
sists of soluble phosphorus as well as
phosphorus associated with the sus-
pended solids form. The soluble phos-
phorus in the effluent is related to the
performance of the process employed,
whereas the phosphorus in the solids
form is related to the settling charac-
teristics of sludge maintained in the
system. Further research is necessary
to develop a better basis for predicting
effluent quality under various opera-
ting conditions and wastewater char-
acteristics.
The full report was submitted in partial
fulfillment of Contract No. 68-03-3055 to
Weston, Inc., under sponsorship of the
U.S. Environmental Protection Agency.
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This Project Summary was prepared by staff of Weston, Inc., West Chester, PA
19380.
E. F. Barth was the EPA Project Officer (see below for present contact).
The complete report, entitled "Emerging Technology Assessment of PhoStrip,
A/0, and Bardenpho Processes for Biological Phosphorus Removal." (Order
No. PB85-165 744/AS; Cost: $ 13.00, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA contact is James F. Kreissl and can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
U.S. GOVERNMENT PRINTING OFFICE. 1985-559-016/27008
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