United States
Environmental Protection
Agency
Office of Water
EPA820-R-15-097
March 2015
Six Municipalities, One Watershed:
A Collaborative Approach to Remove
Phosphorus in the Assabet River
Watershed
Wachusett Aqueduct spanning the Assabet River at Northborough, Massachusetts
Photographer: Gemma Kite
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Six Municipalities, One Watershed: A Collaborative Approach to Remove Phosphorus in
the Assabet River Watershed
Four wastewater treatment facilities (WWTFs) in Hudson, Marlborough, Maynard, and
Westborough and the six Massachusetts communities they serve (Figure 1) partnered to develop
and implement phosphorus removal strategies. Their goal was to improve water quality in the
Assabet River by reducing phosphorus loads on a watershed scale. After years of joint planning
and collaboration with state and federal
agencies, each facility analyzed the
most important factors (such as
operational concerns, footprint and
flexibility) influencing the decision
about which technology would work
best for its particular site
characteristics. Each WWTF selected a
different phosphorus removal
technology, which was implemented
with other facility improvements. The
portion of the upgrade costs due to
phosphorus removal improvements is
difficult to separate from the total cost
and can vary significantly based on
how the costs are allocated. Three of
the four facilities estimated the
phosphorus removal upgrade to cost
from 4 to 25 million dollars. After the
upgrades, all WWTFs have been
meeting effluent limits of 0.1
milligrams per liter (mg/L) on a 60-day
rolling average, representing over 90%
reduction in total phosphorus loads to
the river from April through October.
The facilities are also meeting effluent
limits of 1 mg/L the rest of the year.
This case study describes the joint
Figure 1. Assabet River Watershed, Major WWTFs,
and the Municipalities They Serve
efforts of the WWTFs and key elements of each WWTF's improvements, and provides a
summary of lessons learned for use by other watersheds and communities seeking to work
together to improve water quality. It also provides a summary of the significant water quality
improvements measured in the Assabet River from 1995 through 2013.
ASSABET RIVER CONSORTIUM AND PHOSPHORUS REMOVAL
The Assabet River is an effluent-dominated river located in central Massachusetts. It receives
treated wastewater discharges from four major municipal WWTFs that serve portions of six
communities, as well as three minor wastewater treatment facilities. During the low-flow periods
of the summer months, the discharges from the four main WWTFs provide approximately 80%
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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of the stream flow. During the 1999 and 2000 summer-time conditions, field investigations
showed that 95 to 97% of the phosphorus loading to the river came from these four WWTFs. In
addition, impoundments by nine dams along the 32-mile river have contributed to the
accumulation of phosphorus in the sediments with the potential for future release.
In Massachusetts' water quality standards, the Assabet River is designated as capable of
providing and supporting habitat for fish and other aquatic wildlife, and for primary and
secondary contact recreation (Class B). However, in 1998 the Massachusetts Department of
Environmental Protection (DEP) listed the Assabet River as impaired, primarily for nutrients and
organic enrichment/low dissolved oxygen. The federal Clean Water Act requires the restoration
of impaired water bodies through the development of a "pollution budget," also referred to as a
total maximum daily load (TMDL). The TMDL identifies the maximum amount of a pollutant
that can be discharged to a water body while maintaining water quality standards for its
designated uses.
After field investigations, a computer modeling effort, and stakeholder involvement, the DEP
decided phosphorus was the cause of the impairment. Phosphorus is a nutrient and acts like a
fertilizer. Its presence or absence controls the extent of plant and algae growth in the water. If too
much phosphorus is present, it causes excess growth of nuisance plants and algae. The DEP
issued a TMDL in 2004 for total phosphorus (TP) entering the Assabet River from direct, treated
wastewater discharges and indirect discharges. The TMDL requires reduction of TP from
WWTF effluent to concentrations of 0.1 mg/L from April through October, and a 90% reduction
of sediment flux.
In 1999, the DEP invited the municipalities of Hudson, Marlborough, Maynard, Northborough,
Shrewsbury, and Westborough to a meeting to discuss nutrient over-enrichment and TP issues in
the Assabet River and to recommend that the towns work together to address the issue on a
watershed-level. These towns contribute wastewater to the four WWTFs discharging to the
Assabet River, and together formed the Assabet River Consortium as a working group of town
managers and technical representatives. The goals of the Consortium were to quantify current
and future wastewater needs, evaluate needs for TP removal, and identify alternatives for TP
removal as needed. While each town and WWTF developed its own Comprehensive Wastewater
Management Plan (CWMP), the Consortium also went through the process of developing a joint
CWMP as a combination of the other plans. This joint plan enabled the Consortium to represent
the towns as a single voice in discussions with the DEP and the U.S. Environmental Protection
Agency. The Consortium CWMP was funded through Massachusetts' state revolving fund (SRF)
program, developed in parallel with the TMDL, and completed in December 2007. Through the
CWMP process, wastewater alternatives were evaluated for the four WWTFs, and each facility
took a different approach to phosphorus removal, as described in this document.
WWTF UPGRADES FOR HUDSON, MA
In addition to TP reduction, the Hudson WWTF needed to replace and upgrade aging systems
and equipment because no major upgrade had occurred since 1985. During the initial steps of the
TMDL development, nobody knew what TP limit would be needed to restore the Assabet River.
The Hudson WWTF Chief Operator optimized the existing treatment system to reduce effluent
TP concentrations within the existing system, and was able to reduce them to approximately 0.2
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed 2
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mg/L by increasing chemical use and adjusting effluent pH. While the seasonal TMDL limit was
subsequently set to 0.1 mg/L, the efforts by the WWTF Chief Operator allowed for flexibility in
upgrade options.
The WWTF initially considered a number of
technologies and developed a short list of those that
could reliably meet a TP effluent concentration of 0.1
mg/L and other site-specific effluent limits (e.g., silica
from industrial user), be tested onsite through a pilot
system, and have low capital and operation and
maintenance (O&M) costs.
The WWTF pilot-tested three technologies: the Kruger
ActiFlo®, Densadeg®, and IDI AquaDAF™. All three
technologies proved capable of reducing TP to 0.1
mg/L, and lower if needed with additional sand filters.
The Town of Hudson selected the AquaDAF™
dissolved air flotation system primarily for the
following reasons:
• Lowest capital construction cost
• Reduced solids handling costs and ability to use
smaller holding tanks due to the production of a more concentrated, "thick" sludge
• Ease of operation: limited operator adjustments and input required
Dissolved air flotation in general is a process for clarifying water with low-density solids that
cannot be removed efficiently with sedimentation. The AquaDAF™ proprietary system adds
enhancements to the generic process, such as an improved effluent collection system that allows
for higher flow rates on a limited footprint. While the system does not claim to meet 0.1 mg/L
TP effluent by itself, the Hudson WWTF's treatment process had been optimized to reduce the
influent concentration entering the AquaDAF™ system to 0.4 to 0.5 mg/L TP. While the Chief
Operator had achieved effluent concentrations as low as 0.2 mg/L prior to the upgrade, reducing
influent concentrations to the AquaDAF™ to 0.2 mg/L is costly in chemicals and not necessary
to meet final effluent concentrations of 0.1 mg/L. At the Hudson WWTF, the AquaDAF™
system is used as a polishing component to meet the required effluent concentrations.
Total construction costs for the Hudson WWTF upgrade were approximately $15 million. In
addition to the AquaDAF™ system constructed below grade with two treatment trains, this cost
included the construction of a new 4,400 square foot building, sludge pumping, and ferric
chloride storage. The cost associated with phosphorus reduction alone is estimated at
approximately $5 million, or a third of the total costs. Construction of all upgrades took
approximately two years.
Because the Town of Hudson runs its own non-profit municipal electric utility, the Hudson Light
and Power Department, increased electric use was less important to the Town in the selection
process than other O&M costs such as chemicals and staffing. In addition, while the recycle
pumps from AquaDAF™ system require additional energy, other upgrades have improved
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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overall energy efficiency, partially offsetting the added power needs. The overall upgrades to the
plant required adding one operator and one laborer to the original staff of seven. Generally, the
WWTF has been able to limit the number of required staff by using the department of public
works (DPW) water crew for pipe inspections and repairs at the facility. By selecting the
AquaDAF™ system, the WWTF has been able to optimize the treatment process after the
upgrade to limit the need for additional chemicals such that the upgrades have not resulted in any
significant increase in chemical use. In addition, the WWTF has been successfully reducing
wastewater contributions from infiltration and inflow through the collection system, resulting in
a significant reduction in average daily flow and a further reduction in the need for chemicals.
The upgrades have also improved the consistency of the treatment, enabled the WWTF to more
easily meet its copper effluent limits, and reduced effluent concentrations of total suspended
solids (TSS), biological oxygen demand (BOD), ammonia, and copper. Additional elements of
the upgrade, such as the new supervisory control and data acquisition (SCADA) system, have
improved overall operations at the WWTF.
The WWTF operates the TP removal process year-round because it enables the facility to meet
its copper effluent limit. Since construction was completed, the Hudson WWTF has been
successfully meeting effluent concentrations of 0.1 mg/L from April through October, for a
reduction in its seasonal TP loads to the Assabet River of approximately 2,840 Ibs, or 91%, since
1998.
the
WWTF UPGRADES FOR MARLBOROUGH, MA
The City of Marlborough operates two WWTFs, one of which, the Westerly WWTF, treats
wastewater from the Cities of Marlborough and Northborough and discharges the effluent to
Assabet River. Constructed in 1973 as a secondary treatment facility for a design flow of 2.0
million gallons per day (MGD), the Westerly
WWTF was expanded to 2.9 MGD and upgraded
with single-stage seasonal nitrification in 1988.
The 20-year flow projection estimated during the
needs analysis identified a future flow of 4.4
MGD. Three scenarios were developed to
compare groundwater and surface water
discharges and evaluate the potential need for a
separate Northborough WWTF. A cost-benefit
analysis of the three scenarios showed a single
upgraded facility discharging to the Assabet River
was both the most cost-effective and most
environmentally responsible option, because
additional flow from the WWTF increases the
base flow in the Assabet and potentially improves
water quality.
The City of Marlborough then reviewed and screened a variety of technologies capable of
reducing TP concentrations to 0.1 mg/L or less, and short-listed three of the technologies for a
two-week trailer-mounted pilot study: CoMag™, ActiFlo®, and BluePRO®. After issuing a
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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request for proposals (RFP) for the phosphorus removal system, the City of Marlborough
selected the Blue Water BluePRO® system for the following reasons:
• Lowest capital and O&M costs
• Manufacturer's agreement to guarantees, warranties, and bonds
• Financial backing of the Shaw Group, a Fortune 500 company whose financial backing
indicated some level of confidence in the long-term financial stability of the technology
developers
The BluePRO® reactive filtration system combines co-precipitation and adsorption to a reactive
filter media in an upflow sand filter. Phosphorus removal is achieved by adsorption followed by
filtration.
Total construction costs for the Westerly WWTF upgrade were approximately $27.5 million,
which included increasing the design flow by more than 40%, a number of baseline
improvements to the WWTF, and the TP removal system. The baseline improvements involved
modifications to primary and secondary clarifiers, conversion of the disinfection system from
chlorine gas to ultraviolet (UV) disinfection, a new gravity thickener, new chemical feed
systems, and new electrical distribution and SCADA systems. Many elements of the upgrade
were needed, but not all contributed to improving TP removal; that portion was roughly
estimated at 15% of the total cost, about $4 million. Only a rough estimate can be provided,
because many of the upgraded elements are tied to the need to both increase design flow and
remove TP. Construction of the upgrade occurred over a two-year period.
The upgrade resulted in increased power consumption (approximately 40% more than the
original energy use), particularly because the Marlborough WWTF uses the BluePRO® system
year-round. However, while ferric chloride is now dosed in multiple locations throughout the
treatment process, the overall use of chemicals is approximately unchanged from use before the
upgrade. The overall upgrades to the plant required one additional operator on staff and training
for the existing operators, but a senior chemist position was eliminated, resulting in no overall
staff increase.
The upgrades for advanced TP removal also resulted in reduced effluent concentrations for TSS,
BOD, copper, and aluminum. Overall upgrades also resulted in easier facility management
(through the SCADA system), improved screening and grit removal, and better sludge handling.
Since the upgrade was completed in summer 2012, the Marlborough WWTF has been
successfully meeting effluent concentration limits of 0.1 mg/L from April through October, for a
reduction in its seasonal TP loads to the Assabet River of approximately 13,050 Ibs, or 97%,
since 1998. The 2013 seasonal average TP concentration in Marlborough's effluent was
approximately 0.094 mg/L, slightly below the seasonal TMDL requirement.
WWTF UPGRADES FOR MAYNARD, MA
The Town of Maynard WWTF dates back to the 1930s, and it was converted from an activated
sludge to a rotating biological contactor system in 1986. The WWTF screened technologies for
pilot testing to meet the following needs: a constrained budget, a site with no space for a new
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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tertiary treatment building, optimization of existing hydraulics, additional equipment, and
upgraded and enhanced SCADA and control systems.
The WWTF piloted technologies to confirm their ability to achieve TP concentrations of 0.1
mg/L or less, verify their operational simplicity, and test their impacts on sludge handling and
production. Sludge handling considerations were important for the Maynard WWTF because the
limited available real estate at the facility made it challenging to manage additional sludge. The
WWTF selected the Siemens CoMag™ system for the following main reasons:
• Partial re-use of existing aeration basins
• Ability to use a polishing filter to achieve 0.05
mg/L TP in the effluent
• Preferred O&M by existing operators
The CoMag™ process uses conventional coagulation and
flocculation with the addition of finely ground magnetite as
a ballasting agent. Magnetite is denser than suspended
solids and sand, and generates heavy, dense floes that settle
rapidly, resulting in a high-rate sedimentation process.
Once precipitated, the phosphorus and other pollutants are
removed effectively. The footprint required to install
CoMag™ clarifiers is small compared to other phosphorus
removal processes, and the existing aeration basins were
re-used to further minimize construction costs. The
rectangular clarifiers for the CoMag™ technology
optimized the use of the existing facility, allowed for a
submerged inlet design to eliminate turbulence, and
improved access to equipment.
Construction costs for the Maynard WWTF upgrade totaled approximately $12 million, but as
with other WWTFs, these costs were not limited to upgraded TP removal. The construction of
the CoMag™ system was combined with additional streamlining of facilities for chemical
management and sludge storage, the replacement of major mechanical equipment for which
operational costs had recently significantly increased due to repeated failures, and a complete
electrical and instrumentation upgrade (e.g., SCADA).
Due to the limited available real estate at the facility, pumps had to be incorporated into a
compact footprint, and the upgrades resulted in increased electric use. The facility does not need
to operate the CoMag™ system off-season because the TMDL waste load allocation of 1 mg/L
from November through March for TP can be met without it. Bypassing the CoMag™ system
reduces electric use during those months and limits the wear and tear of the system, but the Chief
Operator noticed aluminum effluent concentrations increased significantly, so the facility might
run the system during the off-season. While new chemicals were needed for the TP process,
including poly-aluminum chloride (PAC) and polymers for flocculation, sodium hydroxide for
pH adjustment, and magnetite, the total amount of chemicals used at the facility was reduced.
PAC is still used in the off-season to meet TP and other effluent limits, so that chemical use is
relatively consistent throughout the year. Following the upgrades, the DEP-mandated staffing
/
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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rose from 4 to 4.8 operators, including a sludge truck driver/operator position that can potentially
be outsourced.
In addition to TP reduction, the upgrades resulted in reduced effluent concentrations for TSS,
BOD, and copper, and the facility is more confident in meeting its secondary treatment
requirements.
Since the new facility came online in 2011, the Maynard WWTF has been successfully meeting
effluent concentration limits of 0.1 mg/L from April through October, for a reduction in its
seasonal TP loads to the Assabet River of approximately 1,940 Ibs, or 92%, since 1998. The
2013 seasonal average TP concentration in Maynard's effluent was approximately 0.093 mg/L,
slightly below the seasonal TMDL requirement.
WWTF UPGRADES FOR WESTBOROUGH, MA
The original Westborough WWTF was built in 1899, upgraded in the early 1970s, and improved
again in 1987. It receives the bulk of its 7.68 MGD wastewater design flow from the towns of
Westborough (2.89 MGD allocation) and Shrewsbury (4.39 MGD), and only 5% of its flow from
the Town of Hopkinton (0.4 MGD). During the design of the upgrades, the WWTF initially
considered a number of technologies and developed a short list that could reliably, and with
limited power use, meet a TP effluent limit of 0.1
mg/L (with the option to meet 0.05 mg/L with added
polishing), operate with different coagulants, handle
extreme loading conditions, and remove metals.
The WWTF pilot-tested four technologies:
BluePRO®, AquaDAF™, ActiFLO®, and
CoMag™. Evaluation criteria for the technologies
focused on performance, costs and O&M,
environmental and aesthetic impacts, footprint, and
responsiveness of the manufacturer. The Town of
Westborough selected the ActiFLO® system by
Kruger, Inc. for the following reasons:
• Lowest 20-year life cycle cost
• Track record and full-scale operations for TP
removal in the US
• Ability to use multiple chemicals to achieve
low TP levels
• Ability to fit the system within the existing
hydraulics of the WWTF
ActiFLO® is a high-rate compact chemical and
physical water clarification process in which water is flocculated with polymer and micro-sand
prior to settling. The micro-sand enhances flocculation and acts as ballast, increasing the floes'
settling velocity. The properties of the resulting micro-sand ballasted floes allow for clarifier
design with short retention times, high rise rates, and a compact system footprint.
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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Construction costs for the upgraded WWTF totaled $54 million, which included significant
baseline facility upgrades in addition to the 100% redundant ActiFLO® system, upgraded sludge
processing, and other elements implemented for TP removal. Most elements of the WWTF were
either upgraded or replaced, including the pavement and roofs of existing buildings. The WWTF
also replaced aerators, enhanced odor control capture and capacity, rehabilitated primary and
secondary clarifiers, replaced chemical disinfection with UV, converted the chlorine contact
tanks to post aeration tanks, upgraded the entire electrical and process control system, added a
SCAD A system, and implemented green infrastructure. Many elements of the upgrade were
needed but not all contributed to improving TP removal; that portion was roughly estimated at
47% of the total cost, or about $25 million. The Westborough WWTF now takes advantage of
solar power to reduce its energy costs; solar energy accounts for approximately 5% of the
facility's current energy use. Funding for construction on this project was secured through a
combination of federal stimulus funds (American Recovery and Reinvestment Act - ARRA),
SRF funds with a 0% interest rate, and an energy rebate. In addition, the WWTF receives an
alternative energy credit rebate on an annual basis that helps to cover O&M costs. Construction
activities occurred over a 30-month period.
The upgrades for TP removal purposes resulted in increased chemical and energy use. The
current energy use is approximately 10% higher than prior to the upgrades, and is expected to
further increase when flows increase. The energy impact at full capacity was budgeted at
approximately 30% of pre-upgrade energy use. However, that additional energy use is not solely
due to TP removal, and has been mitigated by the upgrades to a number of systems throughout
the facility to more energy-efficient systems. Total energy costs are also partially offset by the
implementation of solar energy generation. The overall upgrades to the WWTF required one
additional operator on staff, raising total staff from 10.5 full-time equivalent (FTE) staff to 11.5
FTEs.
The upgrades have reduced effluent concentrations of TSS and BOD. Additional elements of the
upgrade, such as the new bio-selector for phosphorus control and the grease collection system,
have improved overall operations at the WWTF.
The WWTF operates the TP removal process year-round with reduced chemical use during the
off-season, except when the system is taken offline for maintenance and cleanout, enabling the
facility to meet an effluent TP concentration of 0.5 to 0.6 mg/L, or half the off-season limit.
Since the new facility was completed in 2012, the Westborough WWTF has been successfully
meeting effluent concentration limits of 0.1 mg/L from April through October, for a reduction in
its seasonal TP loads to the Assabet River of approximately 9,170 Ibs, or 95%, since 1998. The
2013 seasonal average TP concentration in Westborough's effluent was approximately 0.05
mg/L, half the seasonal TMDL requirement.
ASSABET RIVER WATER QUALITY IMPROVEMENTS
The Organization for the Assabet River (OAR) started sampling the river at a number of
sampling locations more than 20 years ago. OAR then expanded their efforts to the Sudbury and
Concord Rivers, and changed its name to OARS, but continued sampling the Assabet River at
the same locations. According to OARS data (Figure 2), water quality in the main stem of the
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed 8
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1.0
Assabet River has significantly improved since the mid-90s, as TP concentrations were reduced
by almost two orders of magnitude following successive reductions in effluent TP concentrations
at the four main WWTFs discharging to the river.
According to OARS, the following TP effluent reductions were achieved by the WWTFs through
the years, which help explain the significant TP reductions in the river observed in Figure 2:
• Pre-1993: No phosphorus removal
• 1993: Westborough and Marlborough reduce summer TP effluent to 1.0 mg/L
• 2000: All four WWTFs reduce summer TP effluent to 0.75 mg/L (interim permit limit)
• 2004: DEP issues the Assabet River Nutrient TMDL
• 2005-6: Phosphorus limits with compliance schedules are put into permits for all four
WWTFs
• 2007-8: All four
WWTFs reduce
winter TP effluent
to 1.0 mg/L
• 2009: The Hudson
WWTF reduces
summer TP
effluent to 0.1
mg/L
• 2011: The
Maynard WWTF
reduces summer
TP effluent to 0.1
mg/L
• 2012: All four
WWTFs are
meeting summer
TP effluent
Average Summer Concentration for Assabet River -
Main Stem
Ecoregion XIV Recommended Nutrient Criterion -
concentrations of
0.1 mg/L or less
a
1
o
U
1995 1997
1999 2001
2003 2005
Year
2007 2009
2011
2013
Figure 2. Average Summer TP Concentrations for the Main Stem of
the Assabet River (OARS data)
Massachusetts does not have numeric phosphorus criteria for its rivers and streams in its water
quality standards, and the TMDL for the Assabet River did not establish an in-stream target
concentration; instead it used a weight-of-evidence approach for determining the desired load
reductions. However, to give a frame of reference for how the river has improved, Figure 2
shows the average summer concentrations of phosphorus from 1995 to 2013 compared to the
EPA's recommended nutrient criterion of 0.031 mg/L TP for rivers and streams in Ecoregion
XIV (EPA, 2000), shown by the red line. After the most recent WWTF upgrades, summer TP
concentrations in the Assabet River have dropped to levels close to the EPA's recommended
value, indicating significant improvements in water quality.
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed
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SUMMARY
Although the Assabet River Consortium no longer meets regularly, it played a key role in uniting
the WWTFs into a single voice during conversations with state and federal regulators, and
demonstrated that a watershed-based approach to nutrient management can be implemented
effectively through collaboration. Partnership between regulators and stakeholders can improve
the permitting process through regular communication and result in a better understanding of
cost implications for attaining certain environmental conditions.
This case study was developed from publicly available information and interviews with key
people at the Consortium and the WWTFs. Each WWTF evaluated factors like capital and O&M
costs, reuse of existing infrastructure, ease of operation, and land availability when choosing the
treatment technology that would work best for its facility. The chief operators from the WWTFs
all highly recommended conducting side-by-side pilot testing to confirm that a process works for
a particular facility before investing in construction. Some of the operators also recommended
asking for 20-year costs or life cycle costs in an RFP, because a technology with lower capital
costs could incur significant O&M costs, resulting in higher long-term costs. For example,
implementing a system where pumping is needed will require energy use that could be avoided
with a gravity flow or feed system. An additional recommendation is to track chemical and
energy use before and after the upgrade.
Table 1 provides a side-by-side comparison summary of the WWTF upgrades for each facility.
Table 1. Comparison of WWTF upgrades
WWTF Upgrade Characteristics
Design flow (average daily in MGD)
Technology for advanced TP removal
Effluent TP (mg/L)
Seasonal (1998, source: TMDL)
Hudson
2.65
AquaDAF™
0.64
Seasonal pre-upgrade (2004, DEP) 0.20
Seasonal post-upgrade (2013, DEP)
Reduction in seasonal TP loads since
1998
Construction cost (US$ million-M)
Total cost
TP upgrade cost (approximate)
O&M impacts
Staffing increase (additional staff
relative to existing staff)*
Chemical use impact
Electric use impact
0.10
91%
Marlborough
4.15
BluePRO®
3.44
0.44
0.09
97%
Maynard
1.45
CoMag™
0.64
0.55
0.09
92%
Westborough
7.68
ActiFLO®
0.79
0.67
0.05
95%
$15 M $27.5 M $12 M $54 M
~$5M ~$4M Unknown ~$25 M
2 (+30%) 0 (0%) 0.8 (+20%) 1 (+9.5%)
Almost none Almost none Reduction Increase
Increase
Increase
Increase
Increase**
* Additional staff hired due to overall upgrades, not necessarily TP removal process.
**Addition of solar power partially balanced the overall increase in energy demand at the Westborough WWTF.
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The bar graph in Figure 3 shows the seasonal TP loads for the four WWTFs from 1998 to 2013,
and compares the loads to the TMDL allocations. The 1998 bar represents TP loads before
discussions with the DEP. The 2000 bar represents an initial reduction achieved when all
WWTFs started to adjust their existing systems to reduce TP loads. The 2004 bar represents the
loads from the
WWTFs following
their commitment to
reduce their
seasonal effluent
concentrations to
0.75 mg/L. This was
achieved before the
WWTFs were
upgraded. The 2013
bar represents actual
achievements in TP
load reduction after
the upgrades.
Comparing the 2013
and TMDL bars
shows that overall
the facilities
achieved greater
load reductions than
the TMDL requires.
30,000
25,000
•g 20,000
•a
P.15,000
H
X
•d
! 10,000
5,000
Maynard
Hudson
Marlborough
Westborough
1998
TMDL
Figure 3. Cumulative Seasonal Loads for the WWTFs
The consecutive efforts of these four WWTFs over the past 20 years, culminating with the most
recent infrastructure investments, have positively impacted water quality in the Assabet River.
Summer TP concentrations in the river have been reduced by almost two orders of magnitude.
REFERENCES
Massachusetts Executive Office of Environmental Affairs. 2004. Assabet River Total Maximum
Daily Load for Total Phosphorus. Report Number: MA82B-01-2004-01 Control Number CN
201.0
New England Water Environment Association (NEWEA) Annual Conference. 2013. Plant
Operations I - The Assabet River—Four Plants, Four Treatment Technologies for
Phosphorus Removal Boston, MA. January 27-30, 2013
OARS. 1995 - 2013. Total Phosphorus Concentration Measurements along the Assabet River.
Personal Communications with WWTF Operators and Engineers, and Consortium Members.
February, March, and August 2014.
Six Municipalities, One Watershed:
A Collaborative Approach to Remove Phosphorus in the Assabet River Watershed 11
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U.S. Environmental Protection Agency. 2000. Ambient Water Quality Criteria
Recommendations - Information Supporting the Development of State and Tribal Nutrient
Criteria - Rivers and Streams in Nutrient Ecoregion XIV. EPA 822-B-00-022
U.S. Environmental Protection Agency. 2013. Emerging Technologies for Wastewater Treatment
andln-Plant Wet Weather Management. EPA 832-R-12-011
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