Membrane Efficiency - Scranton Gillette Communications, Inc.

MEMBRANE TECHNOLOGYOctober2010
WWW.wwdmag.com

prepared in cooperation with the solutions for water treatment

Membrane Efficiency

Water reclamation & RO optimization

A supplement to Water & Wastes Digest

MEMBRANE TECHNOLOGY WATER & WASTES •editorial

DIGESTc o n t e n t s u FALL 2010 Reuse on
the Rise
04 Synergy: The New Reality
Water reuse applications increas-
Optimizing RO recovery with cyclic ion-exchange softening ingly are popping up across
the globe, many applying
06 Reuse in the Northeast membrane technology to put water once
deemed a waste product to good use.
A sustainable approach to solving water supply challenges at the
University of Connecticut These new and redevelopment reuse
projects range from small-scale to mas-
08 RO Cleaning Frequency: A Balance of Costs sive, from microfiltration to membrane
bioreactors, from graywater treatment in privately owned
Economic analysis: A California groundwater replenishment buildings to effluent treatment at municipal wastewater
system application plants; the treated water may be used for irrigation, toilet
flushing, industrial processes or groundwater replenishment,
12 Beyond Conventional MBRs to name some practices.
The results of the earliest membrane/reuse projects are
Oxygen transfer technology revolutionizing MBR applications becoming clearer, and in many cases the numbers and end-
user feedback convey success stories. These testimonials,
16 Managing Water Balance coupled with the rising quality and declining costs of related
technologies, indicate that the logical pairing of membranes
Using LSI to preserve an Arizona treatment plant’s and reclamation is here to stay.
distribution systems For proof, look no further than this issue’s article “Reuse in
the Northeast” (see page 6), which profiles the University of
18 Minimizing Disposal of a Reusable Resource Connecticut’s recent efforts to reclaim water in order to ease
demand on limited supplies. The sustainably minded univer-
A California utility’s desalter brine and concentrate recovery sity implemented microfiltration, ultraviolet disinfection and
permitting experience reverse osmosis to treat effluent to water fit for athletic field
irrigation, cooling towers and to serve as boiler feedwater.
ON THE COVER Together, projects like those outlined above can make a
world of difference in our industry and beyond. They will
Ultrafiltration membranes in action. help conserve potable water (nearly half the global popula-
(Photo courtesy of GE Power & Water.) tion will live in water-stressed nations by 2015, according to
the National Intelligence Council), protect watersheds and
Scranton Gillette Communications source water, control operational costs and educate the pub-
3030 W. Salt Creek Ln., Ste. 201, Arlington Heights, IL 60005-5025 lic about the value of clean water.
tel: 847.298.6622 • fax: 847.390.0408 • [email protected] • www.wwdmag.com Finally, some of you may recognize me as managing edi-
tor of Storm Water Solutions and a regular editorial con-
EDITORIAL STAFF tributor on Water & Wastes Digest. I’ll be the new face of
Editorial Director Neda Simeonova Membrane Technology and look forward to delivering the
Managing Editor Caitlin Cunningham membrane information you need to keep knowledgeable and
Associate Editor Elizabeth Lisican competitive in today’s water and wastewater market. Former
Associate Editor Rebecca Wilhelm managing editor Clare Pierson has relocated to begin a new
Graphic Designer Robin Hicks life chapter; she will be missed, and we wish her all the best.

A dv ertisi n g & S ales Caitlin Cunningham, managing editor
6900 E. Camelback, Suite 400 • Scottsdale, AZ 85251 [email protected]

tel: 480.941.0510 • fax: 480.423.1443
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[email protected] (phone x25)
Integrated Media Consultantr Eric Smith
[email protected] (phone x14)
Integrated Media Consultant Fred Ferris
[email protected]
(Arlington Heights office, 847.391.1003)
Integrated Media Consultant Brenda Yanez
[email protected] (phone x12)
Integrated Media Consultant Lori Glenn
[email protected] (phone x17)
Regional Sales Managerp Michael Mansour
[email protected] (phone x16)
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[email protected] (phone x13)
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[email protected]
(Arlington Heights office, 847.391.1036)
List Rental Contact John Ganis
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(Arlington Heights office, 847.391.1049)

M a n ag eme n t
Vice President/Publisher Dennis Martyka
[email protected]
Associate Publisher Greg Tres
[email protected]
VP Custom Publishing & Creative Services Diane Vojcanin
VP Events Harry Urban
Circulation Director Mike Serino
Director of Creative Services & Promotions Sandi Stevenson

C or p orate
Chairperson K.S. Gillette
President/CEO E.S. Gillette
Sr. Vice President A. O’Neill
Chairman Emeritus H.S. Gillette (1922-2003)

Im e m b r a n e t e c h n o l o g y 3

•technical article

Synergy: The New Reality

Optimizing RO recovery with cyclic ion-exchange softening

By Francis Boodoo Tightening regulations on con- calcium carbonate) is better controlled.
centrate disposal from reverse
osmosis (RO) and nanofiltration With improved control over scaling poten-
(NF) plants are pushing the membrane tial, RO recovery rate can be increased,
industry to find more ways to improve provided no limitations are imposed by
operating efficiencies. The large volume other contaminants in the water (e.g.,
of concentrate brine generated, typically silica, organic matter and colloids). For
15% to 50% of the total, can inhibit cases in which the latter contaminants are
future growth of the industry unless not limiting or are adequately controlled
new methods are developed to optimize by other pretreatment methods, it is quite
recovery rates and reduce waste. possible to design the RO plant for recov-
ery rates of 90% to 95%.
Ion Exchange & Membranes Unite Because brine concentrations as low
In the past, ion exchange and mem- as 0.5% (5,000 mg/L) can be used to
regenerate the resin in this new process,
branes were regarded as competitive both brackish and semi-brackish waters
technologies rather than providing com- can be softened. Such waters will typi-
plementary functions. The new reality cally have total dissolved solids (TDS)
is that synergistic benefits of boosting ranging from 500 mg/L (0.05%) and
RO recoveries and minimizing waste upward, and at 90% recovery the reject
are indeed possible, as evidenced by brine concentration would be adequate
the recent introduction of technology to regenerate the resin effectively.
referred to as cyclic ion-exchange soften- The new cyclic ion-exchange technol-
ing. This green technology uses shallow ogy promises to eliminate the handling
shell cation resins to soften the feedwater and feed of hazardous acids, including
to the RO and then uses the very dilute sulfuric and hydrochloric acid, which
reject brine generated by the RO to typically are used to reduce feedwater
regenerate the resin. pH and control potential calcium car-
bonate scaling of the RO membranes.
The process can effectively regenerate A drawback of feeding acid that is not
the resin utilizing brine concentrations experienced with ion-exchange softening
as low as 0.5%—20 times lower than is the formation of carbon bdiicoaxribdoen(aCteO2)
the typical 10% concentration used by gas from neutralization of
conventional softeners. No supplemental present in the water by the acid. The
commercial salt is needed except in cases rmeseumltbarnatnCe,Ore2qpuaisrsiensgtahdroduitgiohntahlecRapOital
of extreme variability of feedwater quality. and operating cost for a degasser tower
This synergy between ion exchange and to liberate the CsoOd2a gas as well as the
membranes opens up new possibilities for feed of caustic for post-pH adjust-
reducing membrane treatment costs while ment before the water is distributed.
minimizing impact on the environment. Anti-scalants, more commonly used
than acid, provide good control over a
Of great interest is the capability of wider variety of potential scaling and foul-
the process to efficiently reduce hard- ing compounds (e.g., calcium sulfate, bar-
ness and barium leakages to sub-ppm and ium sulfate, calcium carbonate, iron and
-ppb levels, respectively. Potential mem-
brane scaling from sparingly soluble salts
(e.g., barium sulfate, calcium sulfate and

I4 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

Cyclic ion-exchange
softening can

reduce desalinated
water costs and

environmental impacts.

silica). When cyclic ion-exchange soften- cu meters/hour was chosen. The com- when producing 100 cu meters/hour of
ing is combined with anti-scalant dosing, parative operating and amortized capital permeate and operating continuously,
a unique synergy takes place, allowing costs to produce 1 cu meter of permeate, amounted to $43,000 annually.
for higher RO recovery rates than achiev- or 264 gal, were then determined.
able using either technology alone. The Additional savings include the smaller
rewards are reduced concentrate volume Software from an independent anti- size and lower cost for the feedwater
and disposal cost as well as reduced con- scalant vendor was used to determine train and the lower pumping cost for the
sumption of scarce water supplies. the appropriate anti-scalant dosage. For feedwater. Reject water cost was the larg-
option No. 1, using only anti-scalant dos- est cost component for all three options.
Comparison Points ing, RO recovery was limited by potential The higher the cost of water, the greater
While the benefits of this green tech- of calcium carbonate scale formation to the savings realized with cyclic ion
84%. For option No. 2, using anti-scalant exchange. Because the cost of water and
nology may be obvious, it is important and acid dosing, recovery was limited to the cost of disposal varies by region,
to assess whether the technology is com- 86% by potential for barium sulfate scale the technology will be more relevant
petitive with the established alternatives formation. Option No. 3, using cyclic to geographies where water supplies are
of acid or anti-scalant dosing. From a ion-exchange softening plus anti-scalant scarce or where disposal costs are high.
cost standpoint, cyclic ion-exchange soft- dosing at a reduced rate, allowed maxi-
ening eliminates three of the major cost mum permeate recovery of 95%—limited While the long-term cost for cyclic
components that have inhibited wider not by scaling potential but by silica foul- ion-exchange softening may be lower
use of conventional ion-exchange soften- ing potential. Softening using the new than that of competitive alternatives, the
ing: commercial salt, the associated labor technology predicted reduction of barium extra capital outlay and space require-
for storage and handling and the increas- and calcium to less than 0.02 mg/L and 2 ments needed for implementation may
ing cost and complexity for disposal of mg/L, respectively. be considered drawbacks, whether for
spent brine. Water consumed in regen- new membrane projects or retrofit of
eration is also a fraction of that used for In this example, the $46,000 cost of existing plants. But these factors should
conventional water softeners because no the resin was spread over five years; the not be considered in isolation, as water
salt dilution water is needed and rinse capital cost for the ion-exchange ves- supplies are becoming scarcer and con-
volumes are much lower due to the lower sels was assumed to be $167,000 and centrate disposal regulations are increas-
brine concentration. Costs for pump- amortized over 10 years using straight- ing in scope and complexity.
ing of the feedwater and for disposal of line depreciation. The cost of water
wastewater are lower, too, because higher purchases and cost for disposal of reject Implementation of environmentally
recovery rates are achieved. water were combined and assumed to friendly technology, such as cyclic ion-
be low at 50 cents per cubic meter, or exchange softening, should be an ongo-
For comparing scale control pretreat- about $2 per 1,000 gal. Acid cost was ing part of the strategy to reduce overall
ment options, a brackish water typical of assumed to be 33 cents per kilogram, or cost for desalinated water while mini-
that found in the southwestern U.S. was 15 cents per pound, while anti-scalant mizing impact on the environment. MT
used in a desktop evaluation to compare cost was assumed to be $11 per kilo-
three options: gram, or $5 per pound. Francis Boodoo is technical sales
manager for The Purolite Co. Boodoo can
1. Anti-scalant dosing only; The comparison shows that option be reached at [email protected]
2. Anti-scalant plus acid dosing; and No. 3 with cyclic ion-exchange softening or 800.343.1500.
3. Anti-scalant plus cyclic ion exchange. plus reduced anti-scalant dosing was at
least 40% lower in overall cost per cubic For more information, write in 1101 on
A water analysis showed a TDS of meter of permeate produced. Savings, this issue’s Reader Service Card or visit
1,254 mg/L, a pH of 7.6 and barium and www.wwdmag.com/lm.cfm/mt101001.
hardness levels that can significantly limit
recovery rates. A permeate flowrate of 100

Im e m b ra n e t e c h n o lo gy 5

•case study

Reuse in the Northeast

By Richard Cisterna, Water and wastewater utilities have beneficial reuse projects.
Kristen Barrett, Joyeeta Banerjee, are beginning to discover that Utilities typically are steered away
wastewater reuse can be an
Cynthia Castellon, Anni Luck, important component of a comprehen- due to lack of drivers, lack of public edu-
Alex Wesner & Paul Puckorius sive watershed management program or cation and acceptance and lack of estab-
alternative water supply plan. Removing lished regulatory framework (although
wastewater streams from surface water this is changing for states such as New
bodies can reduce pollutant loads, includ- Jersey and Massachusetts that do have
ing nutrients, heavy metals, pharmaceu- reuse regulations). In recent years, how-
ticals and endocrine-disrupting com- ever, more utilities are looking toward
pounds, to these receiving waters. wastewater reuse as a way to free up
potable water supplies for other uses.
Instead of discharging wastewater to This is becoming particularly important
lakes, rivers or streams that often feed for communities that are approaching
other water supplies, wastewater can be the limits of their water supply.
treated to a higher level and reused for
beneficial purposes. Wastewater reuse also Drivers Behind UCONN’s
reduces water demands that potable sup- Reclaimed Water Program
plies would otherwise have to satisfy.
The University of Connecticut
Although not traditionally viewed as (UCONN) in Storrs, Conn., provides
a region having much need for reclaimed potable water and wastewater treatment
water projects, a growing number of facili- services to its main campus and depot
ties in the Northeast are strongly consider- campus, as well as to some adjacent areas
ing the benefits of reclaimed water. There within the town of Mansfield. In antici-
are currently several operational facilities pation of increasing potable water needs
located throughout the Northeast that on its campus due to a growing popula-
tion, and faced with a lack of additional
With new withdrawal limits placed on the Fenton River wellfield and the Willimantic River water supplies in the area, UCONN
wellfield producing a lower yield, UCONN launched a reclaimed water program. sought to implement a long-term, sus-
tainable program to provide an adequate
supply of water to meet the nonpotable
needs of its campus.

Hazen and Sawyer was retained to
study the feasibility of constructing a
reclaimed water facility for the purpose
of utilizing appropriately treated efflu-
ent from UCONN’s wastewater treat-
ment plant as feedwater for both the uni-
versity’s Central Utilities Plant (which
includes boiler and cooling tower water
systems) and turf irrigation.

A key driver for this project was the
limited capacity of UCONN’s existing
water sources, two permitted groundwa-
ter supplies: the Fenton and Willimantic
river wellfields. In 2005, a portion of the
Fenton River ran dry—an event attrib-
uted to elevated water withdrawals neces-
sary to meet the seasonal peak demand
during drought conditions.

I6 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

A sustainable approach to solving
water supply challenges at the University of Connecticut

Recognizing the potential for recur- water for turf fields. a reuse program will ease the water
rence, the university’s first measure was MF is an innovative, effective treat- demands placed on the Fenton River and
to implement several restoration and con- help to conserve this vital resource while
servation measures. A modification of ment process that removes both contami- setting a positive, hands-on example for
the withdrawal management protocols nants and pathogens by filtration through UCONN students regarding sound envi-
at the Fenton River wellfield was imple- a porous membrane. However, to pro- ronmental stewardship.
mented; this involved ceasing pumping of tect high-pressure boilers and to provide
the Fenton River wells based on specific proper maintenance, makeup water for The new reuse facility also incorpo-
stream flow criteria. the boiler systems must be high purity. rates several sustainable design features,
Thus, treated (“reclaimed”) water from including energy conservation through
With these new limits placed on the the pressurized MF system will be further the use of rooftop solar panels coupled
Fenton River wellfield—coupled with treated using an upgraded, existing RO with a solar orientation of the facil-
lower yield from the Willimantic River system for softening and demineralizing ity; sustainable construction through
wellfield—UCONN found it necessary prior to use as boiler feedwater. If it is the use of Leadership in Energy and
to identify other sources of water to con- determined that even higher purity water Environmental Design-certified sus-
sistently meet demands and preserve nat- is required, an ion-exchange system will tainable materials that are locally pro-
ural resources. The university’s focus on be available upstream of the RO. duced; and collection and reclamation
sustainability prompted the decision to of rooftop storm water by blending with
implement a reclaimed water program—a RO treatment is not needed for the the reclaimed water for beneficial use
first-of-its-kind industrial reuse applica- cooling tower system. Instead, the MF on site. Also, the project will include a
tion in the state of Connecticut, and one effluent for cooling tower makeup will be sustainable heat pump system that har-
of only a handful in the Northeast. treated for scale, corrosion and biological- nesses the heat from the reclaimed water
growth control using scale and corrosion and converts it into building heat for the
Treatment Train inhibitors and biocides. Reclaimed water new reclaimed water facility building.
The university operates its own water from the new MF treatment system also
will be used for irrigation on campus. With the success of this program,
pollution control facility located on the water reuse has the potential to become a
main campus. Treatment includes seasonal For disinfection, both UV light and more common and better understood
chlorination and oxidation ditches that liquid sodium hypochlorite were con- practice in the region and should help to
allow for conventional activated sludge sidered. While both methods would advance the establishment of regulatory
aeration, nitrification and denitrification. meet the required disinfection goals, water quality standards in the state.
Following an analysis of current and future UV was found to be more advanta- With the increasing emphasis on ensur-
potable and nonpotable water demand geous, and in-vessel LPHO UV dis- ing a sustainable water supply, coupled
and wastewater flows, several cutting-edge infection was selected as the preferred with population growth and overbur-
treatment process alternatives were evalu- option. The water entering the new dened water supply sources, water reuse
ated to determine the most efficient, prac- 1-million-gal reclaimed water storage provides a viable means to effectively
ticable and sustainable solution to meet tank, however, requires a disinfectant and safely meet heightened water
targeted water quality standards for indus- residual to prevent bacterial regrowth. demands, engendering a reliable supply
trial and irrigational reuse. A small dose of chloramines, therefore, while conserving natural resources. MT
will be added as a secondary disinfec-
The primary reclaimed water tant to maintain the required residual Richard Cisterna, P.E., Kristen Barrett,
goals discussed with the Connecticut for irrigation and prevent biofouling P.E., Joyeeta Banerjee, P.E., Cynthia
Department of Environmental Protection of the water storage tank, distribution Castellon, E.I., and Anni Luck, P.E., are
are total suspended solids less than 5 pipelines and RO membranes. with Hazen and Sawyer. Alex Wesner,
mg/L and “nondetect” for fecal coliform. P.E., is with Separation Processes Inc.
The selected alternative entails the con- Sustainable Design Paul Puckorius is with Puckorius &
struction of a 1-million-gal-per-day reuse Using reclaimed wastewater will make Associates Inc. Luck can be reached at
facility that utilizes microfiltration (MF), [email protected].
ultraviolet (UV) disinfection and reverse an equivalent amount of water supply
osmosis (RO) to treat wastewater effluent available to meet UCONN’s existing and For more information, write in 1102 on
before its use as boiler feedwater, makeup future potable water demands—a key this issue’s Reader Service Card or visit
water for cooling towers and irrigation component in improving the sustainabil- www.wwdmag.com/lm.cfm/mt101002.
ity of campus operations. Implementing

Im e m b ra n e t e c h n o lo gy 7

•case study

RO Cleaning Frequency:
A Balance of Costs

Economic analysis: A California groundwater
replenishment system application

By Eric Owens & Mehul Patel Over the last two decades, reverse The size of municipal facilities usually
osmosis (RO) has become the requires an operating approach whereby
process of choice for removing a membrane that is eventually fouled
dissolved salts and other contaminants during the treatment process is cleaned
from a variety of water sources, includ- in situ using a chemical solution selected
ing seawater, groundwater and wastewater based on the type and nature of the
effluents. RO is a pressure-driven pro- foulant on the membrane surface. The
cess, where the applied pressure required cleaning solution is introduced into the
to drive water through the membrane membrane system through an ancillary
is a function of the total dissolved sol- cleaning system. For large municipal sys-
ids (TDS) in the feed source. As fou- tems, membrane cleaning in this manner
lants build up on the membrane surface, is more economical and practical than
the foulant acts as an impediment to offsite cleaning or replacing the mem-
flow and the pressure required to drive brane. Through membrane cleaning,
water through the system increases. Left the pressure required to operate the RO
alone, the fouling can build up until the system is reduced, and hence the energy
required pressure exceeds the feed pump consumption is minimized.
capabilities, and a loss of permeate pro-
duction eventually will occur. Membrane Calculate to Optimize
cleaning is used to remove the foulant There are industry rules of thumb
from the membrane surface and return
the system to baseline conditions. as well as specific RO manufacturer
guidelines for when and how to clean
RO technology has been adopted RO membranes. These typically revolve
by both industrial and municipal users. around the parameters of water perme-
Industrial RO systems are often smaller ability and normalized differential pres-
(less than 1-million-gal-per-day [mgd] sure. Calculated indicators of water per-
permeate capacity) and sometimes meability (e.g., specific flux, normalized
designed without the ability to clean the feed pressure, normalized permeate flow
membrane elements in place within the and normalized flux) can be used as indi-
pressure vessels. In these cases, operators cators of the amount of fouling on the
either send membrane elements off site for membrane surface. The normalized dif-
cleaning, or elements are simply discarded ferential pressure offers an indication of
when they have been completely fouled. the amount of material deposited within
the feed/brine spacer of the RO elements,
Municipal systems are often large restricting flow through the system.
scale, and they typically range between
1 mgd and 100 mgd in permeate pro- Guidance on membrane cleaning
duction. Individual RO train capacities from the industry suggests cleaning the
typically range from 0.5 mgd to 5 mgd. RO train when the water permeability

I8 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

The OCWD GWR a discussion of the economic analysis varying hydraulics between trains or
features an RO system performed for this RO system in order some indeterminate issue. Whatever the
comprised of 15 trains. to identify the balance between fouling influences, these two components have
costs and cleaning costs. Ultimately, this contributed to distinct performances and
has decreased by 10% to 25%, or when economic analysis was successful in iden- energy costs associated with individual
the normalized differential pressure has tifying the optimum cleaning interval RO trains. For this reason, each individ-
increased by 20% to 50%. This guid- given the specific GWR variables. ual train was analyzed to determine the
ance, however, does not necessarily offer most cost-effective cleaning alternative
the most economical point of operation Case Study: OCWD GWR System for operating that specific RO train.
for the RO system. The RO system for the OCWD’s
Because RO trains may operate
RO cleaning can be considered GWR consists of 15 RO trains, each with within a range of flow conditions, tem-
nothing more than a response against a 5-mgd capacity, for a total plant produc- perature and feed salinities, it is not
increasing system pressures and energy tion of 70 mgd of RO permeate capac- practical to use the actual energy con-
costs. But rather than follow anecdotal ity (N+1 design). The RO trains operate sumption of a given train for this analy-
cleaning triggers, operators should exam- at 85% recovery and a maximum per- sis. Instead, the data was normalized in
ine the balance between the cost of meate flux of 12 gal per square foot per order to represent operation at 5 mgd
energy associated with fouling and the day. Each train houses 1,050 8-by-40-ft RO permeate, 1,800 μS/cm feed conduc-
cost of performing the cleaning for their Hydranautics’ ESPA2 RO elements in a tivity and 77°F feedwater temperature.
particular system. All RO systems are 78:48:24 array (seven elements per vessel).
somewhat different, and there are many The fouling rate of each train was
variables that contribute to this exami- The membranes within the 15 GWR determined from the normalized feed
nation. In order to identify a balance RO trains have a range of permeability pressure calculated after membrane
between fouling and cleaning, the fol- due to intrinsic differences in membrane cleaning occurred. The typical normal-
lowing variables must be considered for a construction, cleaning effectiveness or ized feed pressure trend for membranes
particular system: exposure to different events and condi- operating at the GWR starts out with a
tions during startup and operation. The steep increase that is followed by a some-
• Cost of energy paid by the inherent permeability of the membrane what linear performance. The linear
municipal agency; is the first contributor to the energy portion of the trend is generally devel-
costs for an RO system. The second oped within 20 days of the cleaning. For
• Specific fouling rate of the component contributing to the energy this reason, the performance 20 days
RO system; costs is the unique fouling rate identi- after a cleaning was used to model the
fied for each train following a cleaning. long-term fouling rate of the individual
• The nature of the foulant and While this fouling rate is generally antic- trains. Based on historical performance
cleaning effectiveness; ipated to be similar between trains (due at GWR, this linear fouling rate was
to similar operating conditions), this is considered representative of the antici-
• Total cost of chemical solution; not the case for all 15 trains at OCWD. pated fouling rate and used to extrapo-
• Labor associated with performing Several trains have demonstrated sharper late the long-term train performance.
fouling rates than others. This may be
a cleaning; and due to previous, less-effective cleanings, A linear model may not offer the best
• Lost permeate production due to fit for all fouling trends. This expecta-
tion should be confirmed as fouling
downtime during cleaning. progresses and an appropriate model
One such examination was performed selected based on actual system perfor-
for the RO trains within the Orange mance. This fouling trend model was
County Water District’s (OCWD) used to investigate the costs associated
groundwater replenishment system with several cleaning interval scenarios.
(GWR) in California. The following is
This analysis also assumed that mem-
brane cleanings were consistently effec-
tive, regardless of the frequency between
cleanings. This goes against the typi-
cal operational expectation that as more
foulant builds on the membrane surface,
the more difficult it will be to remove
through cleaning. But based on histori-
cal performance data for GWR, this was

Im e m b ra n e t e c h n o lo gy 9

•case study

considered an acceptable assumption additional cost
for this RO system. Other RO facilities of the cleanings.
with different fouling characteristics and This investiga-
cleaning effectiveness may not be able to tion was taken
make this assumption if consistent and further to deter-
repeatable cleanings cannot be achieved. mine the mini-
mum operation All RO system operators should analyze energy and cleaning costs to
The cost associated with membrane and maintenance find a balance between cost-effectiveness and performance.
cleanings included the labor cost, the (O&M) costs
chemical costs of the district’s cleaning for CIP intervals ranging from 30 days chemical costs due to frequent cleanings.
procedure and the cost of lost produc- to 365 days. The total cleaning and total The total O&M costs to the righthand
tion due to offline time. While the GWR energy costs were compared and com- side of the parabolic curve are more
system design accounts for one of the 15 bined for this range of CIP intervals in heavily weighted toward energy costs as
trains being offline (N+1), it was assumed order to determine the optimum cleaning a result of accepting more fouling within
the fifteenth train could be offline for interval that offered the minimum total the RO train. The minimum O&M
any number of other reasons; lost produc- operating costs. costs can be determined by identifying
tion due to cleaning was factored into this Summing the two costs together the minimum point on the curve.
analysis. For this investigation, the total resulted in a “Total O&M Cost” curve This analysis was applied to each
cleaning cost amounted to $15,929 multi- with a shape similar to that of a parab- RO train and its unique condition and
plied by the number of cleanings per year. ola. In this presentation, the total O&M fouling rate in order to determine the
costs toward the lefthand side of the par- minimum total O&M costs related to
Even though the energy costs decrease abolic curve are heavily weighted toward cleaning and fouling. Depending on the
with an increased frequency of cleanings,
the reduced energy costs are offset by the

Write in 401

I10 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

unique performance of each train, the should be applied to any RO system to A significant savings of approximately
optimum cleaning interval could fall on ensure that the current cleaning regime $250,000 per year was identified at
either side of the six-month interval. offers the most cost-effective operation OCWD through performing an eco-
and performance. The analysis described nomic analysis to identify the optimum
The results of the analysis of 15 indi- herein was based on a combination of cleaning interval for the district’s system.
vidual trains were as follows: The most real-world data and observations but Not all RO systems are guaranteed the
economical cleaning frequency for seven assumes the cleanings applied are con- same degree of savings determined for
of the trains was determined as every five sistently effective. It also assumes the OCWD, but most would likely benefit
months. The most economical cleaning modeled fouling rates are observed and from applying a similar approach to their
frequency for seven of the trains was calcu- repeatable following each cleaning. cleaning philosophy. MT
lated as every eight months. One RO train
calculated an optimum cleaning frequency This is generally the case at OCWD, Eric Owens, P.E., is project manager
of every 10 months. The optimum CIP but should the fouling rate or cleaning for Separation Processes Inc. Owens
interval and minimum annual energy and effectiveness deviate from the model, can be reached at eowens@spi-
CIP costs were determined from the para- the evaluation would need to be redone. engineering.com. Mehul Patel, P.E.,
bolic curves for each train. If this analysis indicates the benefit of is principal process engineer for the
a longer cleaning frequency, it would Orange County Water District. Patel
Adopting a Similar Approach be wise for operators to confirm their can be reached at [email protected].
Industry standards for CIP triggers assumptions through gradual imple-
mentation of longer cleaning frequen- For more information, write in 1103 on
may not offer the most efficient point cies. This would allow verification of the this issue’s Reader Service Card or visit
of operation for RO systems. An eco- modeled fouling rate and confirm con- www.wwdmag.com/lm.cfm/mt101003.
nomic analysis investigating the balance sistent cleanability is achieved.
between energy costs and cleaning costs

Ultrameter II™ 6Psi

bluDockTM Enabled NEW! bluDock™ Wireless
Data Transfer (optional)
www.myronl.com

NEW! LSI and Hardness
Calculator

CONDUCTIVITY, RESISTIVITY, TDS, pH, OPR, FREE CHLORINE & TEMP

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m e m b ra n e t e c h n o lo gy I 11

•technical article

Beyond Conventional MBRs

Oxygen transfer technology revolutionizing MBR applications

By Dennis Livingston Submerged membrane bioreactor between 5,400 kWh/MG and 16,000
(MBR) technology continues to kWh/MG. For comparison, a typical
gain traction on a global level as a energy estimate for a new MBR plant
cost-effective means for treating waste- will be approximately 3,000 kWh/MG
water. Moreover, given the high efflu- and conventional activated sludge plants
ent quality, MBR systems increasingly have reported usages averaging less than
are being used for water recycling and 3,500 kWh/cu meter.
as feed to reverse osmosis systems. The
advantages of the technology are well A more granular look at many of
documented in literature and include, these plants reveals that they can and
among others, small footprint, superior do run efficiently near design flows but
effluent and ease of operation. become increasingly inefficient as less
Despite the substantial upside of water is treated. The decrease in effi-
owning and operating an MBR, there ciency is often due to a lack of process
is also a downside to consider. If an turndown and specifically may be caused
MBR system is not properly designed to by so-called parasitic loads (e.g., mixers,
run efficiently or is not operated in an blowers and pumps). Other factors such
energy-efficient manner—or some com- as system complexity and compounding
bination thereof—what looks sustainable equipment inefficiencies may contribute
on paper will not be in real life. to the high energy usage rates and ulti-
The perception, and in some cases mately may determine the fate of MBR
reality, that MBR systems are “energy technology rather than the type of mem-
hogs” chewing up kilowatts at rates two brane equipment used for filtration.
to 20 times the theoretically achiev-
able value of 0.32 kWh/cu meter (1,200 New Technology
kWh/MG) is not specific to one mem- EcoBlox systems are specifically
brane technology.
A growing body of designed for ease of operation, requiring
evidence appears to 70% less automation; the biggest advan-
support the idea that tage to end-users, however, may ultimately
membrane geometry be reduced installation costs. Whereas
may have less to do recent data suggests that conventional
with actual system MBR systems may cost between $7.80/gal
energy consumption and $13.80/gal to build, contractor esti-
than other factors. mates indicate that EcoBlox systems may
For example, in a cost less than $4/gal to construct due to
recent survey of nine the reduced footprint, reduced concrete
U.S. MBR installa- and overall process simplicity.
tions—some using
hollow-fiber mem- The process can be described as tak-
branes and others ing three primary steps:
using flat plates—
aggregate consump- 1. Saturating screened raw wastewa-
SDOX oxygen transfer technology is based on simple physics. tion numbers varied ter with oxygen under pressure
(typically 80 to 100 psig);

2. Sending the oxygen-laden waste-
water to the high-rate MBR for
treatment running at mixed liquor

I12 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

suspended solids (MLSS) concen- a water column (diffused air, etc.), water between low DO set points can be used
trations between 2% and 3%; and is aerosolized, or turned into small drop- to promote SNdN. Supply oxygen is
3. Controlling the dissolved oxygen lets, and contacted with pure oxygen in a made up on site using a vacuum swing
(DO) in the reactor to achieve small tank. Using this method eliminates adsorption technology manufactured by
simultaneous nitrification and the variable influence of mixed liquor and PCI, called DOCS.
denitrification (SNdN). greatly simplifies maintenance.
The energy demand of an EcoBlox
None of these steps is necessarily The physics part, Henry’s Law, relates system is primarily due to the high-
new, with the exception of the method gas pressure in the tank to the saturation pressure pump, oxygen makeup system
by which oxygen is being added to the oxygen concentration in the water. If the and air scouring requirements. All of
process. The oxygen transfer technology, screened influent is pressurized to 100 these demands combined equate to less
called SDOX, is novel in the wastewater psig and put in contact with pure oxygen, than 4,000 kWh/MG.
industry but is based on simple physics. it will contain 300 mg/L oxygen when
The other parts, running at high mixed sent to the reactor. If the tank pressure DO Control
liquor and achieving SNdN, are well drops, the oxygen concentration drops. If DO control in conventional MBR sys-
documented in literature and have many the pressure is increased, the oxygen con-
references in the U.S. and abroad. centration increases proportionally. tems using diffused aeration is a strong
function of mixed liquor conditions or
Oxygen Delivery In an EcoBlox system, the oxygen properties. For example, at times MBRs
Instead of trying to add oxygen to a delivery rate is controlled by chang- are run at very high MLSS concentrations
ing the liquid level in the contact tank to reduce waste solids handling costs, but
process using gas bubbles rising through based on the DO measured in the per- the increased concentration also drives
meate—not the mixed liquor. Bouncing down fine-bubble diffuser performance.

WWD Membrane Technology

Webinar Series

in af liation with AMTA

Topic: Split-Feed Nanofiltration — Jupiter, Fla.

Thursday, Oct. 28 at 2 p.m. EST (30-minute session)

A major component of the Jupiter Utilities community Featured Project
investment program is the implementation of nano ltration
treatment, which will begin to replace the older The town of Jupiter water
conventional lime softening water treatment facility in 2011. treatment facility has a total
capacity of 30 million gpd. It
The 14.5 million gpd nano ltration facility will utilize a fresh serves more than 80,000 people
shallow aquifer as its supply and will provide town residents living in Jupiter, Juno Beach and
with the ultimate barrier against viruses and bacteria. unincorporated areas of Palm
Beach and Martin Counties.
Paul Jurczak, manager of the Town of Jupiter, will discuss the construction of
the Nano ltration Treatment Plant that is currently underway. This webinar made possible by:

Register today at:
www.wwdmag.com/membranewebinar4

A registration fee of $25 will apply to both the live and
archived presentations.

Write in 403

m e m b ra n e t e c h n o lo gy I 13

•technical article

Figure 1. DO Control Trial to getting out 15-minute intervals. In trial DO, for
In other cases, operators may choose to of calibration example, set points were 1 mg/L and 2
run at lower or thinner solids concen- or malfunction- mg/L (see Figure 1).
trations, but that can lead to excessive, ing. The ideal
uncontrollable DO in recycle streams and situation is to This same type of profile was observed
inhibit denitrification. monitor perme- during pilot testing conducted by
ate conditions BlueInGreen in cooperation with CH2M
Whatever the process conditions, for control pur- Hill-OMI at a wastewater treatment plant
submerged instruments are prone poses, eliminat- in Fayetteville, Ark. During the study,
ing some of the both mixed liquor and plant effluent
problems with where used as feed to an SDOX system in
conventional different trials to demonstrate perfor-
and multistage mance. With the capability of transferring
MBR processes. and controlling oxygen delivery to a high-
rate MBR now proven, the advantages of
The ability to the technology are significant. MT
control the oxy-
gen concentra- Dennis Livingston, P.E., is director, MBR
tion in a single-stage MBR by monitoring Systems, for Enviroquip, a Div. of Eimco
permeate was demonstrated in a full-scale Water Technologies. Livingston can be
pilot conducted earlier this year. During reached at [email protected].
several trials, a sharp saw-tooth DO pro-
file was observed bouncing between vary- For more information, write in 1104 on
ing high and low set points in roughly this issue’s Reader Service Card or visit
www.wwdmag.com/lm.cfm/mt101004.

Water. Transportation. Energy.

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The nation’s aging water and energy utilities, roads, bridges and transit systems are
facing funding and maintenance pressures.

Introducing Infrastructure Solutions

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more than 40,000 industry professionals, looking for solutions.

See it online — October 2010

October issue focus: Green Building, Wastewater Infrastructure
Contents: Project updates, feature articles, case studies

Infrastructure Solutions also will receive print distribution at major water/wastewater, From the editorial staff of Water & Wastes Digest, Roads & Bridges,
transportation and energy industry shows throughout 2010-2011. Quarterly editions Transportation Management & Engineering and Storm Water Solutions
will be e-mailed in October 2010 and in January, April, July and October 2011.

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For more information, contact Larry Scott at
480.941.0510 x22 or by e-mail at [email protected].

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I14 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

•case study

Managing Water

Using LSI to preserve an Arizona treatment plant’s distribution systems

By Heather Rekalske T he first thing anyone who man- and distribute water because what the
ages water and wastewater learns water has dissolved in it can cause it to be
is that water is the universal sol- corrosive or scaling. What water generally
vent. Because of the unique properties has dissolved in it is at least some carbon
of that dihydrogen monoxide molecule, dioxide and some calcium carbonate.
owing to the extreme electronegativity of
the oxygen atom, water is highly polar- Carbon dioxide is ubiquitous and dis-
ized and dissolves almost everything with solves at the surface of the water, form-
which it comes into contact. This fact ing carbonic acid in solution. Calcium
is important when one has to maintain carbonate, dissolved by the carbonic
equipment and structures that process acid, is globally present in rock forma-
tions (limestone), as well as in the physi-
Gary Lyons manages LSI at an Arizona water treatment facility using the Ultrameter II 6Psi. ological structures of organisms (particu-
larly oceanic organisms) that excrete it.
Calcium carbonate in its various forms is
also used to buffer pH and stabilize solu-
tion in process control. Managing the
calcium carbonate equilibrium becomes
critical to managing any water and
wastewater treatment process.

Too little calcium carbonate yields
water that is not saturated and may
cause corrosion and deteriorate equip-
ment and structures. A supersaturated
solution will likely precipitate calcium
carbonate, causing scale, reducing
efficiency and eventually leading to
system failure.

LSI in AZ
One method for analyzing and man-

aging corrosion and scale deposition of
water is to use the Langelier Saturation
Index (LSI). In Scottsdale, Ariz., Gary
Lyons is managing LSI at his water
treatment facility using the Ultrameter
II 6Psi by Myron L. Co.

His drinking water treatment plant

I16 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0

Balance

takes 70 million gal per day (mgd) calcium carbonate. that the pH of the water is above
of water from the Central Arizona The version of the LSI calculation equilibrium. The water is scaling
Project canal and treats it for residen- because as pH increases, total alkalin-
tial and commercial use. Within the used by the 6Psi LSI calculator is: ity concentration increases. This is due
143-acre campus, the plant processes to an increase in the carbonate ion,
20 mgd to of wastewater from the city LSI = pH + TF + CF + AF – 12.1 which bonds with calcium ions pres-
of Scottsdale collection system using ent in solution to form calcium carbon-
microfiltration and reverse osmo- In this calculation, pH = the mea- ate (reference the carbonic acid equi-
sis (RO). Water coming from the RO sured value of pH in pH units; TF = librium, in which hydrogen ions bond
treatment process is acidic around pH 0.0117 x temperature – 0.4116; CF = with carbonate ions to form bicarbon-
5.5. It is then moved to decarbonation 0.4341 x ln(Hrd) – 0.3926; and AF = ate and hydrogen ions bond with bicar-
towers and lime is added to bring the 0.4341 x ln(AL) – 0.0074. bonate to form carbonic acid). Thus,
LSI value close to zero. The water rec- any positive value for LSI is scaling.
lamation plant features 8 mgd of stor- Indicator Analysis
age capacity. Recycled water treated by LSI has been useful as a scaling/ If the pH is less than the pH of satu-
the plant is used for the irrigation of 20 ration, the index will be negative, which
Scottsdale golf courses. corrosion indicator in municipal water is corrosive. This means that the water
treatment for more than 70 years. is more acidic than it would be at equi-
There is great concern about how The original Langelier Saturation (or librium. There are less carbonate ions
the water balance will affect this distri- Stability) Index calculation was devel- present, according to the carbonic acid
bution system over time, especially due oped by Dr. Wilfred Langelier in 1936 equilibrium. The water will be aggres-
to higher total dissolved solids values. to be used as a tool to develop strategies sive because it has room for more ions
Plant technicians compute LSI values to counteract corrosion of plumbing in in solution. Thus, any negative value for
in the field with the 6Psi hand-held to municipal water distribution systems. It LSI indicates that the water may tend to
determine what adjustments should be is a statement about the change in pH be corrosive.
made and how in real time. The LSI required to bring the calcium carbonate
calculator allows them to perform what- in water to equilibrium. LSI is a measure The use of LSI as an indicator is well
if scenarios on changes in pH, alkalin- of the disparity between the pH of the documented and time-tested. Managing
ity, hardness and temperature. They are system and the pH at which the system water balance through LSI analysis will
able to measure the effects of changes is saturated with calcium carbonate: prevent loss of efficiency and failure of
immediately as well in the facility and LSI = pH – pH of saturation. equipment and structures, saving time
at distribution points. and money. MT
As such, the LSI indicates the change
Hardness and alkalinity are vari- in pH required to bring water to equi- Heather Rekalske is technical writer for
ables in the LSI calculation because they librium. If the LSI is +1, then the pH Myron L Co. Rekalske can be reached at
account for the availability of calcium needs to be lowered by one unit to bring [email protected].
in various forms in the water. Variables the water to equilibrium. If the LSI is -1,
such as temperature and pH contribute the pH needs to be raised by one unit to For more information, write in 1105 on
to the likelihood of the formation of bring the water to equilibrium. this issue’s Reader Service Card or visit
www.wwdmag.com/lm.cfm/mt101005.
A positive saturation index means

m e m b ra n e t e c h n o lo gy I 17

•technical article

Minimizing Disposal of a Reusable

By Carl W. Spangenberg Two membrane facilities operated and deliver 5.9 million gal per day (mgd)
by the same water district gen- of raw water to the treatment plant.
erate concentrate waste streams Approximately 2.7 mgd is treated by RO
that are handled in distinctly different operated at 75.5% recovery, 15.4 gal per
manners. Here we investigate the steps sq ft per day (gfd), feed pressures up to
and methods used by California’s Irvine 300 psig and blended with the remaining
Ranch Water District (IRWD) on the raw bypass water.
permitting and concentrate recovery
methods for the Irvine Desalter Project A total of 434 membrane elements
(IDP) and the Deep Aquifer Treatment are used at the IDP-PTP facility. Water
System (DATS). production levels vary according to fluc-
tuations in the raw water feed. Targeted
Table 1. Concentrate Flow & Water Quality IDP Primary Treatment constituent levels in the product water
Plant (PTP) include a TDS of 420 mg/L and nitrates
Concentrate Flow Water Quality less than 10 mg/L as nitrogen.
The IDP-PTP removes mod-
IDP-PTP 0.67 mgd TDS: 3,500 mg/L erately high levels of total dis- DATS
Mn: 266 μg/L solved solids (TDS) and nitrates The goal of the DATS is to remove
DATS 0.65 mgd Silica: 184 mg/L pumped from the principal aqui-
0.16 mgd* fer within the Irvine groundwater high color (300 color units) caused by
TDS: 900 mg/L basin. A full-scale reverse osmosis natural organic matter from groundwa-
Color: 2,500 to (RO) plant was put into operation ter pumped from the Santa Ana River
3,000 color units in 2006 and can treat up to five Basin below five color units. A full-
wells that are 1,000 ft deep scale nanofiltration (NF) plant was
*With concentrate recovery constructed utilizing a design/build
approach, with operation of the facility
Table 2. Selected Concentrate Disposal Options & Key Permits/Actions initiated in February 2002.

Concentrate Disposal Concentrate Required Permits/Actions Disposal The DATS facility is an 8-mgd NF
Method Recovery Costsa plant designed to operate at 98% recov-
No • Addendum No. 3, Order No. ery, 16 gfd at operating pressures up
IDP-PTP Ocean 2001-08 NPDES Permit No. $153,000b to 125 psig. It includes two deep wells
Outfall CA01070611, Waste Discharge approximately 2,000 ft deep; water col-
Requirements for SOCWA $445,000c lection; and membrane treatment, con-
to ACOO $67,000d centrate recovery and concentrate disposal
facilities. A total of 1,398 membrane ele-
• SOCWA Project Committee ments are used for the DATS facility.
Interagency Agreement
Amendments Concentrate Disposal Options
The water quality of the concentrate
• Coastal Commission Ruling
• Required Acute and Chronic from the IDP-PTP and the DATS are sig-
nificantly different; this was the second-
Toxicity Testing ary factor dictating the ultimate disposal
• Reviewed Every Five Years method of these resources, with brine line
capital costs being the primary factor.
• OCSD Class I Industrial Waste
The IDP-PTP concentrate contains a
DATS Sewer Yes Discharge Permit TDS level of 3,500 mg/L, Mn of 266 μg/L
• No Toxicity Testing Required and silica of 184 mg/L, whereas the DATS
contains high color in excess of 2,000 color
• Renewable Every Two Years units with a TDS of 900 mg/L that is close
to that of drinking water. The differences
a: Annual disposal and wastewater treatment costs, excludes pumping costs
b: Cost for 2007/08 fiscal year
c: Prior to implementation of concentrate recovery, cost for 2006/07 fiscal year
d: After implementation of concentrate recovery, cost for 2007/08 fiscal year

I18 m e m b ra n e t e c h n o lo gy fa l l 2 0 1 0