solutionsP R E T R E A T M E N T

W i n t e r 2 0 0 4 / 0 5

float

ing

plan

tAmerica’s Authority in Membrane Treatment

American Membrane Technology Association

Improving America’s Waters Through Membrane Filtration and Desalting

The barge, formally known as a “Mobile Sea Water Desalination Unit” was purchased by the Government of the United Arab Emirates (UAE). To provide potable water by filling water towers on a series of remote islands in the Persian Gulf, the barge is pushed by tug boat and anchored just off the island. Desalted water is pumped through an 8” hose to the on-shore storage tanks.

Ionics designed and built the system to suit the barge. The barge is 130 feet long by 40 feet wide and is approximately 30 feet high. The lower deck houses a maintenance room, UF feed and backwash pumps, fuel for the generators, UF permeate tanks and RO Clean-In-Place (CIP) tanks as well as two 6x8x5 cubic feet intake “sea chests.” The upper deck consists of UF and RO skids, diesel

pumps and generators, chemical tanks, electrical room and living quarters.

UF was chosen for pretreatment because of its compact arrangement, small foot print and proven ability to produce consistently high quality filtrate despite varying quality feed waters. Ionics had performed extensive testing and successful demonstrations of the UF technology in Swakopmund, Namibia; and in the Gulf of Paria, Trinidad. The only pretreatment required on the barge are two 100 micron strainers. No chemicals are added to the UF feed-stream.

The hollow fiber UF membranes are installed in tubular pressure vessels similar to those used with the spiral

In the summer of 2002 Ionics

started-up a mobile 1-MGD

sea water reverse osmosis

(SWRO) plant using a 3 MGD

hollow fiber ultrafiltation (UF)

system for pretreament.

continued on page 15

Compact and ConsistentUF Best Choice For Floating PlantBy: John G. Minnery (jminnery@ionics.com)

hope everyone had a wonderful

holiday season and a prosperous

2004. On the heels of a terrifi c

2004, we have a great calendar

of events planned for 2005. First

up is a Technology Transfer Workshop in

Norfolk, Virginia on May 11 and 12. Our

Symposium will be in Minneapolis, MN

August 2 and 3 and later in the fall we will

be back in Mesa, Arizona for a Technology

Transfer Workshop on November 9 and 10.

I hope you will make plans to attend one or

more of these events.

As you begin 2005, amidst your goal-

setting and New Year’s resolutions,

please consider how you might be able

to give back by becoming involved or

more involved in AMTA. Along with the

satisfaction you’ll get from supporting

an organization dedicated to “Improving

America’s waters through membrane

fi ltration and desalting”, you’ll keep up with

the latest technology, learn from the best

and brightest in our industry, and most

importantly, you’ll make new friends along

the way.

President’s Messaage

This winter issue of our newsletter is

focused on pretreatment. To adapt a

well-known saying (with my apologies to

the author), “In front of every great RO

system is a great pretreatment system.”

As membrane technology is applied

to increasingly challenging feedwater,

the importance of proper pretreatment

is magnifi ed. With new pre-treatment

technologies and techniques emerging all

the time, one of the primary goals of our

newsletter is to update you on the latest

installations and technologies along

with providing the information you need

to understand and stay informed about

membrane technology issues.

Have a great 2005!

Bob Yamada

PUBLICATION SCHEDULE

WinterPretreatment

SpringWater Quality

SummerNew Facilities

FallMembrane Residuals

AMTA Solutions is published quarterly for the members of AMTA. AMTA Solutions is mailed to AMTA members and published on the AMTA website only.

PresidentRobert YamadaSan Diego County Water Authority

First Vice PresidentDavid BrownTown of Jupiter

Second Vice PresidentC. Robert Reiss, P.E.Reiss Environmental, Inc.

TreasurerDavid DerrAfton Pumps, Inc.

SecretaryPeter WaldronMNW Consulting

Past PresidentBen Movahed, P.E.WATEK Engineering Corporation

EditorC. Robert ReissReiss Environmental, Inc.

AMTA Administrative DirectorJanet L. Jaworski, CMP

American MembraneTechnology Association611 S. Federal Highway, Ste. AStuart, FL 34994772-463-0820772-463-0860 (fax)amtaorg@aol.comwww.membranes-amta.org

AMTA2004/2005 Offi cers

P A G E 2

I New Beginningsof Great Ideas

From the Editor

Welcome to the Winter edition of the new and improved AMTA Solutions formerly AMTA Newsletter. Most obvious about this issue is our upgrade in graphics and layout. Our readership has grown in recent years and consistent with that growth, we have strived to provide an increased quality and quantity of information that matches the needs of you the reader. As part of that effort, we have developed the layout that you see in this issue. In addition to being a benefit to the reader, the new layout is a reflection of AMTA and our evolution as the premier organization addressing membrane technologies and their role in water and wastewater treatment.

As AMTA and this publication have grown, the response to the Newsletter has increased. However, periodically we still must search for appropriate and informative articles to publish. My

challenge to you this year is to consider submitting an article for publication. As you will see in this issue, this can be relatively brief but still serves a great purpose in conveying pertinent technical information to the industry regarding current projects (Come on, its time to make New Years resolutions and this is easier to do than the South Beach diet!). Our next issue of the Newsletter will focus on water quality. Please send articles to me at crreiss@reissenv.com or Nate Weisenburger at Nate.Weisenburger@AE2S.com.

Finally, I would like to thank Nate Weisenburger with Advanced Engineering and Environmental Services, Kelcia Edwards with Reiss Environmental, and Janet Jaworski for their leadership and support in making this publication possible in 2004. From sunny Florida I wish you and yours the best for 2005!

Ben’s Tip CornerBy: Ben Mohlenhoff

What Is So Important About Pretreatment?It is reasonably safe to say that all membrane systems will have some type of pretreatment. Depending on the water source it may be as simple as a micron filter or screen to stop large particulate material that might damage the pumps or membranes, while for others it may be a complicated series of treatments to produce a feed water that will protect the membranes from fouling due to some constituents found in the raw water supply.

It is the writers opinion that the correct design and operation of the pretreatment system is probably the most critical factor in the successful operation of any membrane system.

It is no longer good enough to just worry about reducing suspended solids in the feed water. Today’s high recovery systems, that are called upon to treat ever increasingly complex water sources, demand that we pilot test and prove that the proposed pretreatment will also address inhibiting scale formation while keeping other constituents in suspension till they pass through the membrane portion of the system.

It has been my experience that many operationally troubled membrane systems will eventually find relief by adjusting or modifying the pretreatment system. This is most frequently a result of changed conditions of the raw water

supply and not a direct result of a poorly designed pretreatment system.

If a system has operational problems (frequent micron filter changes, membrane cleanings etc), don’t be content to repeatedly replace and clean, look for the real source of the problem. Controlling the problem is almost always more cost effective than just dealing with it.

If you have a tip or a suggestion for a future article please contact Ben Mohlenhoff at (772) 546-6292 or bmohlenhoff@ams-water.com ■

solu

tions

P A G E 3

By: C. Robert Reiss, P.E.

South FloridaP A G E 4

A M T A / S E D AHawk’s Cay Sympmosium

Dodges HurricanesBy: David Brown (davidb@jupiter.fl.us)

At dawn on Thursday, September 23, 2004, weather reports throughout South Florida

became suddenly ominous as the coast was warned to expect landfall of yet another

hurricane (Jeanne). Given the impact that this storm plus the 3 previous siblings who

caused havoc throughout the state this summer, SEDA and AMTA’s Board of Directors

made the wise decision to reschedule the planned Hawk’s Cay Symposium to October.

South FloridaP A G E 5

The result was a well attended event and more-typical tropical paradise weather. With over 20 exhibitors and 105 attendees, the quick rescheduling yielded a very successful symposium. The sessions and events were well attended with over 60 attendees also touring the Florida Keys Aqueduct Authority Marathon RO Plant.

On Tuesday morning before the session, SEDA/AMTA held its 1st Annual Fishing Tournament in which over 20 fishermen and women participated. Gary Smith (City of Port St. Lucie) took the prize for the largest fish (48 lb. amberjack), Bill Glover (Instruments South Corporation) for the smallest fish (0.4 lb. yellowtail snapper) and Robert Dehler (Seminole County) for the most unusual fish (scamp grouper). The event yielded several hard luck stories including one boat which became stranded at sea for two extra hours due to dead batteries. However, the Best Hard Luck Story Prize went to Debby Smith who landed a nice black grouper only to find out it was 1/2-inch smaller than the legal size limit.

On Wednesday evening, attendees and guests took tour buses for an evening in Key West. Needless to say, little if

any pain was being felt by many on the return bus ride home.

AMTA and SEDA are very thankful to the many sponsors of this event. They included:

Boyle Engineering Corporation

CDM

Hazen & Sawyer, P.C.

Koch Membrane Systems, Inc.

Kimley-Horn & Associates, Inc.

Tetra Tech/Hartman & Associates

Harn R/O Systems, Inc.

Reiss Environmental, Inc.

Buckman Laboratories International, Inc.

Professional Water Technologies, Inc.

Without our sponsors’ assistance, these events would not be as successful. ■

David Brown

P A G E 6

Legislative Updates

The congressional elections proved to solidify the Republican majorities in both the House and Senate. Despite the increase in the majority, few changes are anticipated within the key House and Senate water resources committees. Most senior committee members will return to the 109th Congress making changes in leadership limited. In the Senate, the Committee on Energy and Natural Resources will continue to be chaired by Senator Pete Domenici (R-NM) who has been a tireless advocate of membrane technology research. Senator Harry Reid (D-NV) has ascended to the Democratic Leader’s post and should be expected to continue his support for programs that address the West’s need for new water supplies. In the House, Representative Richard Pombo (R-CA) will continue to chair the key Committee on Resources and his Subcommittee on Water and Power is expected to maintain its priority to focus attention on the ongoing drought in the West. Earlier in the year, both Domenici and

Pombo introduced legislation to spur on membrane technology research as part of a larger alternative water supply research and development program. AMTA had supported the legislation with the knowledge that action would likely occur in 2005.

With the ongoing drought throughout the West as well as continuing pressures being placed on limited supplies in other regions of the country, the next Congress is expected to renew efforts to address diminishing water supplies. Central to this focus is a likely attempt to revamp existing water policy. Any legislative effort is expected to focus on promoting research and technology demonstrations. However, these demonstrations would be for the expressed purpose of promoting commercialization of promising advancements. According to congressional staff the intention is to ensure local and regional water supply technology needs are addressed as they relate to meet municipal, industrial, agricultural and environmental demands.

On November 19th and 20th, the House and Senate respectively voted final passage of an omnibus appropriations measure, H.R. 4818, which ensures continued funding of domestic agency programs for the remainder of fiscal year 2005. Enactment of the bill is expected to come by early December when the President is expected to receive the legislation for signing. As passed by Congress, key water resources programs will continue to benefit from decisions not to reduced funding despite an overall budget that shows no growth overall for domestic programs.

Support for desalination programs continues within the U.S. Bureau of Reclamation. The Administration’s Water 2025 program, which seeks among other priorities to promote desalination through technology demonstration assistance, receives $19.5 million. Within this funding, Congress provided $2 million to support work devoted to addressing water quality and environmental issues that will facilitate industry and regulators in developing meaningful responses. It is assumed that management of concentrates is one area that could benefit from this legislative priority for the program. The continued funding of this program means that the Department of Interior will issue a second round of Challenge Grants to provide assistance in the development of technologies that offer the prospect of improved production of desalinated water supplies.

Within the U.S. Bureau of Reclamation’s Science and Technology, Desalination Research and Development Program budget account, Congress reaffirmed its support for the program by directing the use of additional funding toward research and development of technologies to create additional water supplies. As approved, USBR’s research program will receive almost $7 million in fiscal year 2005.

Congress Completes Action on Fiscal Year 2005 Budget

As part of this priority, USBR is directed to identify obstacles such as physical, financial, institutional, and regulatory that creates impediments to the efficient use of desalination technologies. Of special note is the fact that the budget calls on USBR to focus on brine management (or concentrates) and the development of improved membrane filtration capabilities. In an unusual step,

the budget includes language directing the Administration to place renewed emphasis on desalination programs in its future budgets to address the needs of the West as well as other regions of the country. Also within this budget account, the Tularosa, New Mexico project will continue to receive funding assistance with an appropriation of $2.5 million. ■

Congressional Election Returns Signal Few Changes in Water Policy Direction; Legislative Proposals to Spur Desalination Research Expected Next Year

P A G E 7

On October 29, 2004 the Membrane Consortium presented to the Bureau of Reclamation

the outcome of a year-long study whose objective was to develop industry consensus

for standardization of the diameter of a large-capacity RO/NF spiral-wound element for

the purpose of reducing desalination costs. The Membrane Consortium is comprised of

The Dow Chemical Company, Hydranautics, Toray Membrane America, Inc., and TriSep

Corporation. After an extensive economic study conducted by CH2M Hill, together with

industry surveys, discussions with vessel manufacturers, and evaluation of specific

issues such as handling of large-diameter elements, the Consortium has recommended a

nominal diameter of 16 inches as the standard for large-capacity RO and NF spiral wound

elements. The economic study determined that for a 25 mgd (95,000 m3/day) desalination

facility, use of a 16-inch diameter element can save approximately 7% in total plant capital

costs for a seawater plant, and up to approximately 20% in a brackish groundwater plant

compared to an 8-inch diameter element. This translates to a $10-11 million savings in

life-cycle costs for a 25 mgd (95,000 m3/day) facility.

The project was funded by the Bureau of Reclamation as part of their mission to reduce

the cost of desalination, under the Desalination and Water Purification Research and

Development Program. The project was facilitated by Metcalf and Eddy, Inc. For further

information please contact Lisa.Henthorne@ch2m.com ■

PRESS RELEASE Membrane Consortium Results from Large-Diameter Study

On October 25, the President signed into law the Water Supply, Reliability, and Environmental Improvement Act, otherwise known as the Calfed Bay-Delta Authorization Act (Public Law # 108-361). The bill is a five year, $389 million authorization to provide California with federal support in its effort to rehabilitate the San Francisco Bay Delta and meet overall water supply needs. As part of the authorization, Congress provided $90 million to support alternative water supply project needs. This includes support for desalination and recycling projects. Project assistance will be conditioned on Department of Interior approval of projects. While the bill’s enactment is only an authorization, it sets the stage for actual federal support of project needs such as alternative water supply project needs as early as October 1, 2005 when the fiscal year 2006 budget must be finalized and adopted. ■

In addition to this general direction, recent comments on the importance of passing a national energy bill during the next Congress may again see efforts to provide important assistance in the development of alternative water supplies for the production of energy supplies. During last Congress’ debate over an energy bill, AMTA endorsed policy positions were incorporated into the Senate version that would have provided support for membrane technology research assistance as it related to energy production and for the advancement of membrane technologies that would cost effectively remove drinking water contaminants such as arsenic. ■

President Signs Calfed Authorization into Law

Figure 1. Process Schematic of Pilot Treatment Trains

P A G E 8

Greater Vernon Water, Vernon, British Columbia, Canada is a recently formed entity which oversees the supply and distribution of water to both domestic and irrigation customers for the City of Vernon, District of Coldstream and North Okanagan Water Authority. The source waters consist of two diverse surface waters, Duteau Creek and Kalamalka Lake water. The Duteau Creek water is a low alkalinity (11-12 milligrams/liter (mg/L)), high total organic carbon (TOC) (7.7-8.6 mg/L) and seasonally high turbidity (0.8-1.5 Nephlometric Turbidity Units (NTUs) during piloting, with maximum of 82.7 NTU historically) water. The Kalamalka Lake water is a high alkalinity (146-150 mg/L), low TOC (3.5-3.9 mg/L) and low turbidity (1.2-1.7 NTU) water.

The new Water Master Plan recommended a 21 million gallons per day (mgd) unified water treatment plant with the capacity to treat either one of the sources or a blend of both sources. The pre-design of the water treatment plant included extensive pilot testing of the different source waters with low-pressure membrane filtration. One of the goals of the pilot testing was to evaluate the benefits of clarification using dissolved air flotation (DAF), as pre-treatment to membrane filtration.

Evaluation of Membranes and Dissolved Air Flotation To Treat High Organic and High Turbidity Water By: Sunil Kommineni (skommineni@pirnie.com),

Jack Bryck (jbryck@pirnie.com) and Dennis Mitchell (dmitchell@sandwell.com)

This article summarizes the methods and key findings of pilot testing on Duteau Creek water.

Pre-treatments consisting of coagulation/flocculation/DAF and coagulation/flocculation were simultaneously pilot tested as shown in Figure 1. The test conditions were as follows:

• Coagulation/Flocculation/DAF - Alum was used as the coagulant for DAF since it resulted in light, floatable floc compared to ferric chloride or poly aluminum chloride (PACl). The surface loading rate, detention time and recycle rate for DAF were 4.4 gallons per minute/square foot (gpm/sf), 20-30 minutes and 8-12 percent, respectively.

• Coagulation/Flocculation - PACl was used as the coagulant for coagulation/flocculation trains since it resulted in least change in pH for the low alkalinity water. Flocculation time varied between 5-10 minutes among the membrane systems depending on the size of the membrane feed reservoirs.

• Membrane Filtration - The characteristics of microfiltration (MF) and ultrafiltration (UF) membranes that were pilot tested are summarized in Table 1. The membrane operating conditions were determined and optimized by the membrane manufacturers.

P A G E 9

Table 1. Characteristics of Pilot Tested MF/UF Membranes

Characteristic Membrane A Membrane B Membrane C

Type UF MF UF

Nominal Pore Size 150,000 0.1 micron 0.04 micron Daltons* (nominal) (nominal)

Confi guration Pressurized Pressurized Submerged

Flow Pattern Inside-out Outside-in Outside-in

Air Scour No Yes Yes

Pre-treatment Coagulation/ Coagulation/ Coagulation/ Flocculation/ Flocculation Flocculation DAF

*Molecular weight cut-off

Raw WaterTOC: 7.7-8.6 mg/LTurbidity: 0.8-1.5 NTU

DAF Effl uentTOC: 5.3-8.0 mg/LTurbidity: 0.8-7.7 NTU

Membrane A ProductTOC: 3.1-3.3 mg/LTurbidity: <0.1-0.15 NTU

Membrane B ProductTOC: 2.7-7.5 mg/LTurbidity: <0.1-0.1 NTU

Membrane C ProductTOC: 4.7-7.3 mg/LTurbidity: <0.1-0.1 NTU

Figure 2. Summary of TOCs & Turbidities

Sunil Kommineni Jack Bryck

The TOC and turbidities measured for raw water, DAF effl uent and membrane fi ltered waters are summarized in Figure 2. The values shown are ranges measured over the duration of testing. Pre-treatment optimization for coagulant dose, coagulation pH, mixing time and air application rate (for DAF) was achieved within the initial week of pilot testing. Pre-treatment optimization resulted in higher TOC and turbidity removal. The DAF pre-treatment was able to remove 6-38 percent TOC. The TOC removals after membrane fi ltration at optimized conditions were between 45-70 percent. The higher TOC removal observed in MF system (Membrane B) compared to the UF systems (Membranes A and C) is attributed to the differences in coagulant dose, mixing intensity and fl occulation times among the MF/UF pilot systems. The fi ltered water turbidities for all membrane systems were consistently less than 0.1 NTU (with some occasional spikes between 0.1-0.15 NTU).

The key MF/UF operational fi ndings are:

• Membrane A: On DAF clarifi ed water, the membrane fl ux achieved was about 67 gallons per square foot per day (gfd) at 14° Celsius (C). The estimated CIP was greater than 90 days with caustic enhanced backwash every 14 days.

• Membrane B: On coagulated/fl occulated water, the fl ux pilot tested was between 40-51 gfd at 14° C. At

a design fl ux rate of 60 gfd, with an enhanced fi ber cleaning procedure using chlorine every 12-24 hours, the estimated CIP is 30 days.

• Membrane C: Stable performance with cleaning interval of greater than 60 days was achieved at a fl ux rate of 34 gfd at 14° C on coagulated/fl occulated water. The use of citric acid rather than chlorine as the fi ber cleaning agent was needed for the CIP.

Both coagulation/fl occulation/DAF and coagulation/fl occulation pre-treatments met the water quality goals in terms of turbidity removal. Even though clarifi cation using DAF resulted in higher membrane fl ux and longer CIP interval,

it did not improve the overall TOC removal signifi cantly. For Duteau Creek water, clarifi cation may not be necessary to achieve the targeted TOC of less than 3 mg/L in fi ltered water. An optimization of coagulant type, dose and contact time in pre-treatment with coagulation/fl occulation would be suffi cient to meet the fi ltered water quality goals with respect to turbidity and TOC. ■

About the AuthorsSunil Kommineni, Ph.D., P.E. is a Senior Project Engineer with the Drinking Water Process & Planning Resource Team of Malcolm Pirnie, Inc. in Phoenix, AZ offi ce. Jack Bryck, P.Eng is a Senior Associate with Design/Design Services During Construction Resource Team of Malcolm Pirnie, Inc. in Phoenix, AZ offi ce. Dennis Mitchell, P.Eng is a Technical Specialist for Sandwell Engineering, Inc. in Vancouver, British Columbia, Canada. Dennis was the Program Manager for the study.

P A G E 1 0

Desalination Cost Reduction by Co-LocationBy: Nikolay Voutchkov (nvoutchkov@poseidon1.com) O

ver the last ten years seawater desalination has broken numerous technological and cost barriers evolving into a

viable water supply alternative for many arid areas of the world. One of the innovative concepts that would allow to further improve the economics of seawater desalination is the co-location of desalination plants with power generation stations.

What is Co-location?The key feature of the co-location concept is the direct connection of the membrane desalination plant intake and discharge facilities to the discharge outfall of an adjacently located coastal power generation plant. This approach allows using the power plant cooling water both as source water for the seawater desalination plant and as a blending water to reduce the salinity of the desalination plant concentrate prior to the discharge to the ocean. Figure 1 illustrates the conceptual implementation of the co-location approach for the 50 MGD seawater desalination plant planned to be constructed in Carlsbad, California.

As shown on Figure 1, under typical operational conditions approximately 600 MGD of seawater enters the power plant intake facilities and after screening is pumped through the plant’s condensers to cool them and thereby to remove the waste heat created during

Figure 1 – Co-location Concept for the Carlsbad Seawater Desalination Plant

Seawater

P A G E 1 1

the electricity generation process. The cooling water discharged from the condensers typically is 10 to 20° F warmer than the source ocean water and is conveyed to the ocean via a separate discharge canal. The Carlsbad desalination plant intake structure will be connected to the end of this canal and under normal operational conditions would divert approximately 100 MGD of the 600 MGD of cooling water for production of fresh water. Approximately 50 MGD of the diverted cooling seawater will be desalinated via reverse osmosis and conveyed for potable use. The remaining 50 MGD will have salinity two times higher than that of the ocean water (67 ppt vs. 33.5 ppt). This seawater concentrate will be returned to the power plant discharge canal for blending with the cooling water prior to conveyance to the Pacific Ocean. Under average conditions, the blend of 500 MGD of cooling water and 50 MGD of concentrate would have discharge salinity of 36.2 ppt, which is within the natural fluctuation of the ocean water salinity in the vicinity of the existing power plant discharge.

Co-location with a power station in a large scale was first used by Poseidon Resources for the Tampa Bay Seawater Desalination Project, and since than has been considered for numerous plants in the United States and worldwide. The intake and discharge of the Tampa Bay Seawater Desalination Plant are connected directly to the cooling water discharge outfalls of the Tampa Electric (TECO) Big Bend Power Station (Figure 2).

The TECO power station discharges an average of 1.4 billion gallons of cooling water per day of which the desalination plant takes an average of 44 MGD to produce 25 MGD of fresh potable water. The desalination plant concentrate is discharged to the same TECO cooling water outfalls downstream from the point of seawater desalination plant intake connection.

In order for the co-location concept to be cost-effective and possible to implement, the power plant cooling water discharge

flow has to be larger than the desalination plant capacity and the power plant outfall configuration has to be adequate to avoid entrainment and recirculation of concentrate into the desalination plant intake. It is preferable that the length of the power plant outfall downstream of the point of connection of the desalination plant discharge is adequate to achieve complete mixing prior to the point of entrance into the ocean.

A special consideration has to be given to the effect of the power plant operations on the cooling water quality, since this discharge is used as source water for the desalination plant. For example, if the power plant discharge contains levels of copper, nickel or iron significantly higher than these levels of the ambient seawater, this power plant discharge may be not be suitable for co-location because these metals may cause irreversible fouling of the membrane elements.

Another potential problem could be the location of the disposal of the power plant intake screenings. In most power plants the screening debris are removed from the intake cooling water and disposed off site. However, this disposal practice may change during the course of the power plant and desalination plant operations. For example, in the case of the Tampa Bay seawater desalination plant, during the final phase of the desalination plant construction the power plant decided to change their screenings disposal practices and to discharge their intake screenings just upstream of the desalination plant intake rather than to continue disposing them off site. This change in power plant operations had a dramatic effect on the Tampa Bay Water desalination plant start up and operations, and especially on the pretreatment system performance. Since the desalination plant was pilot tested and designed around the original method of power plant operations under which all screenings were removed form the cooling water, the desalination plant was not built with its own separate intake screening facilities. The presence of power plant waste screenings in the desalination plant intake water had a

detrimental effect of the pretreatment filter operations because the screening debris frequently clogged the filter distribution piping, airlifts and sand media. Although this problem has a significant effect on the desalination plant operations it also has relatively straightforward solutions – either installing separate fine screening facilities for the desalination plant or moving the point of the power plant screening debris discharge downstream of the desalination plant intake.

Benefits of Sharing Intake FacilitiesUsually, coastal power plants with once-trough cooling use large volumes of seawater. Because the power plant intake seawater has to pass through the small diameter (typically 7/8-inches or less) tubes of the plant condensers to cool them, the plant discharge cooling water is already screened through bar racks and fine screens similar to these used at surface water intake desalination plants. Therefore, a desalination plant which intake is connected to the discharge outfall of a power plant usually does not require the construction of a separate intake structure, intake pipeline and screening facilities (bar-racks and coarse screens). Since the cost of a new surface water intake structure for a desalination plant is typically 5 to 20 % of the total plant construction expenditure, power plant co-location could yield significant construction cost savings. The need for installation of additional fine screening facilities for the desalination plant intake is driven by the screenings disposal practice adopted by the power plant and the type of desalination plant pretreatment system. As indicated previously, power plants typically remove the screenings retained at their bar racks and fine screens, and dispose these waste debris to a landfill or return them back to the ocean. However, in some cases the screenings collected at the power plant’s mechanical screens are discharged into the cooling water downstream from the plant’s condensers. In this case, the power plant discharge would contain screenings that need to be removed at the desalination plant intake.

P A G E 1 2

Sharing intake infrastructure also has environmental benefits because it avoids the need for new construction in the ocean and the seashore area near the desalination plant. The construction of a separate new open intake structure and pipeline for the desalination plant could cause measurable disturbance of the benthic marine organisms on the ocean floor.

Another clear environmental benefit of the co-location of power generation stations and desalination plants is the overall reduction of entrainment, impingement and entrapment of marine organisms as compared to the construction of two separate open intake structures – one for the power plant and one for the desalination plant. This benefit stems from the fact that total biomass of the impacted marine organisms is typically proportional to the volume of the intake seawater. By using the same intake seawater twice (once for cooling and the second time for desalination) the net intake inflow of seawater and marine organisms is minimized.

Benefits of Sharing Discharge OutfallsUnder the co-location configuration, the power plant discharge serves both as an intake and discharge to the desalination plant. This arrangement yields four key benefits: (1) the construction of a separate desalination plant outfall structure is avoided thereby reducing the overall cost of desalinated water; (2) the salinity of the desalination plant discharge is reduced as a result of the mixing and dilution of the membrane concentrate with the power plant discharge, which has ambient seawater salinity; (3) because a portion of the discharge water is converted into potable water, the power plant thermal discharge load is decreased, which in turn lessens the negative effect of the power plant thermal plume on the aquatic environment; (4) the blending of the desalination plant and the power plant discharges results in accelerated

Blending the desalination plant concentrate

with the lower salinity power plant cooling

water often allows reducing the overall

salinity of the ocean discharge within the

range of natural variability of the seawater

at the end of the discharge pipe, thereby

completely alleviating the need for complex

and costly discharge diffuser structures.

Figure 2 – Colocation of Tampa Bay Seawater Desalination Plans

P A G E 1 3

dissipation of both the salinity and the thermal discharges.

The cost of construction of a separate ocean outfall could be significant and its avoidance would result in a measurable reduction of plant construction expenditures. In addition, the length and configuration of the desalination plant concentrate discharge outfall are closely related to the discharge salinity. Usually, the lower the discharge salinity, the shorter the outfall and the less sophisticated the discharge diffuser configuration needed to achieve environmentally safe concentrate discharge. Blending the desalination plant concentrate with the lower salinity power plant cooling water often allows reducing the overall salinity of the ocean discharge within the range of natural variability of the seawater at the end of the discharge pipe, thereby completely alleviating the need for complex and costly discharge diffuser structures.

In addition, the power plant thermal discharge is lighter than the ambient ocean water because of its elevated temperature and therefore, it tends to float on the ocean surface. The heavier saline discharge from the desalination plant draws the lighter cooling water downwards and thereby engages the entire depth of the ocean water column into the heat and salinity dissipation process. As a result the time for dissipation of both discharges shortens significantly and the area of their impact is reduced.

Other Co-location BenefitsOne of the key additional benefits of co-location is the overall reduction of the desalination plant power demand and associated costs of water production as a result of the use of warmer source water. The source water of the RO plant is typically 10 to 20° F warmer than the temperature of the ambient ocean water. This is a significant benefit, especially for desalination plants with cold source seawater (such as the Pacific Ocean water), because the feed pressure required for RO membrane separation decreases with 6 % to 8 % for

every 15° F of source water temperature increase. Since the power costs are approximately 30 to 40 % of the total costs for production of desalinated water, the use of warmer source water could have a measurable beneficial effect on the overall water production expenditures.

As a result of the co-location the desalination plant unit power costs could be further decreased by avoiding the need for using the power grid and the associated transmission fees. Typically, the power tariff (unit power cost) structure includes two components: fees for power production and for power grid transmission. Often, the power transmission grid portion of the tariff is 30 to 50 % of the total unit power cost. By connecting the desalination plant directly to the power plant electricity generation equipment, the grid transmission portion of the power fees could be substantially reduced or completely avoided, thereby further reducing the overall seawater desalination cost.

Co-location of power and desalination plants may also have advantages for

the power plant host. In addition to the benefit of having a new customer and generating revenue by leasing power plant property to locate the desalination plant, the power plant host also gains a customer of a steady power demand and a high power load factor. This continuous high-quality power demand allows the power plant host to operate its power generation units at optimal regime, which in turn reduces the overall costs of power production.

ConclusionsCo-location of desalination plants with large power generation stations may yield measurable improvement of the economics of seawater desalination and offer cost-reduction advantages because of the use of shared intake and discharge facilities and reduced desalination power costs. In addition, this innovative approach can yield significant environmental benefits associated with the accelerated dissipation of the thermal and saline discharges and the reduction of impact on the marine benthic and seashore habitats by avoiding the construction of new facilities. ■

About the AuthorMr. Voutchkov has over twenty years of experience in the field of seawater desalination and water and wastewater treatment. He is a Senior Vice President and Corporate Technical Director for Poseidon Resources, a US company specialized in developing of large water infrastructure projects. His areas of expertise are: pilot testing and full-scale implementation of membrane treatment technologies for production of potable water from seawater and

industrial water reuse; assessment of the effects of seawater desalination plant discharges on the marine environment; and product water quality integration of desalinated water with other sources of potable water. Mr. Voutchkov is author of over 40 technical publications in the field of desalination, water and wastewater treatment, and reuse. Currently, he is one of the principal authors of the American Water Works Association’s updated Manual of Water Supply Practices (AWWA M46) on Reverse Osmosis and Desalination. Mr. Voutchkov is a registered professional engineer and a Diplomate of the American Academy of Environmental Engineering. He is a member of the American Membrane Association, the International Desalination Association, the American Water Works Association and the International Association on Water Quality.

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In the article, it is mentioned that the beach wells are normally carried above the elevation where flooding might occur. This is true of collector wells (and vertical wells) at sites where a surface water body is close by, especially along inlands and river sites. It is also possible to finish the well structure at or below grade and install submersible pumps to minimize visual impacts. There are a number of collector wells completed this way, including one seawater collector well in northern California where the top of the well is actually below the level of the beach sand so that the well is completely hidden under normal circumstances.

In the paper it is also mentioned that erosion occurred around the wells and the possibility that this erosion caused the well casing to “tilt” toward the ocean. In this case, the wells are about 100 feet deep I believe, so I believe that the relatively deep burial depth would prevent the caisson from tilting, especially if the erosion is limited to the upper 5-10 feet. Of course, with a shallower well, if sufficient erosion

occurred, it is possible that the entire caisson could tilt, if the proportion of caisson above grade exceeded that below grade and were subject to extreme forces. Typically, we build the caisson with structural continuity so that caisson extensions above grade (in some cases this might be 20-40 feet) are not at risk of failure. Since we did not build these caissons (we projected the lateral well screens), I am not sure how the caisson lift sections were tied together, but I assume that good engineering was followed.

It is not uncommon for the entire caisson to tilt a bit as a result of the original installation process. Often, during the excavation process, the caisson strays from vertical alignment (normal tolerance is 1.5 feet per 100 foot of depth) due to the digging process, and since the beach sands to the ocean side may have been less dense in the upper layers, the caisson may have begun tilting from the outset and then continued at a slight angle during the course of the entire sinking process. It is unusual (we are not aware of any that

have) for a caisson to tilt after it has been sunk, especially to a depth of 100 feet or so. In one case about 6 years ago, we were able to correct the alignment (although not completely) when the caisson had reached a depth of about 60 or 70 feet (total depth was to be about 120 feet), however, extreme measures had to be taken to get the caisson to shift at all, including deep augering and jetting. Since the caissons at Salina Cruz were constructed by a local company, not experienced in sinking caissons, they may not have monitored the alignment during construction, or they could have taken steps to correct any tilt while the caisson was fairly shallow, and still correctable. In recent years, we have developed a hydraulic jacking system that applies uniform weight to the top of the caisson during excavation to assist in overcoming skin friction and to maintain alignment from the outset to assure more plumb caissons. It has been our experience over the years that maintaining plumbness during the first few sections of the caisson is critical to help keep the entire caisson plumb during the sinking process.

Thank you for this opportunity to respond to this article. ■

Henry Hunt (hchunt@collectorwellsint.com)Sr. Project Manager/HydrogeologistCollector Wells International, Inc.

Letter to the EditorAfter reading the article by Nikolay Voutchkov in the Summer 2004 issue of AMTA News, entitled “Considerations for Using Beach Wells for Large SWRO Plants”, I wanted to clarify several points.

Reiss Environmental, a growing consulting engineering firm specializing in

water and wastewater treatment processes is currently hiring experienced

engineers (junior, mid-level, and senior). We offer a great environment,

comprehensive benefits, growth potential and a collaborative “think-tank”

atmosphere. Please submit electronic resume along with salary history to

www.reissenv.com.

Janet L. Jaworski American Membrane Technology Association611 S. Federal Highway, Ste. AStuart, FL 34994772-463-0820772-463-0860 (fax)amtaorg@aol.com

A form is available on the website at www.membranes-amta.org/publications.html

Newsletter Advertisement is Available.Please Contact AMTA for rates and availability.

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wound SWRO membranes. Because the horizontally mounted vessels can be stacked vertically, the foot print for the 3 MGD UF system is the same as the 1 MGD RO system. Each system occupies approximately 23 x 20 feet.

The silt density index (SDI15) for the UF permeate is routinely between 1 and 2, well below the RO-membrane manufacturer’s warranty level, and comfortably below a desirable level of 3. The high quality RO feed water results in reduced fouling, lower cleaning costs and extended RO-membrane life.

With the success of this pretreatment system, significant growth in this application is expected. In addition to using UF as the main unit operation on fresh surface water, UF will be used in pretreatment to protect RO systems used for desalination and reuse applications throughout the U.S. ■

About The AuthorJohn G. Minnery has been with Ionics for over five and a half years. As a Senior Engineer in Applied R&D, Mr. Minnery spent over a year and a half in the field working in Africa, the Middle East, the Caribbean, and throughout the United States. He has worked with Ionics ultrafiltration product in the field, operating Ionics’ first hollow fiber ultrafiltration pilots. Mr. Minnery worked as a Project Engineer on several jobs and assisted in commissioning large start-ups in Trinidad, California, and Abu Dhabi.

Mr. Minnery has a Bachelors degree in Civil Engineering and a Masters degree in Chemical Engineering from the Industrial Membrane Research Institute at the University of Ottawa, Ottawa, Canada. Mr. Minnery will soon complete a Masters degree in Public Health from the Department of Environmental Health at Boston University.

Floating Plantcontinued from page 1

Calendar of EventsNew MembersOur AMTA membership is growing! Since our last newsletter we have welcomed 4 new members.Dave N. CommonsEdward L. KimmelAudrey D. Levine LifeStream Waterstems Inc.Wayne Miller

Jan. 12, 2005 AMTA Board Meeting, Dallas, TX

Jan. 19, 2005 SEDA Membrane Pilot Plant Operations Tech. Transfer, Palm Coast, FL

Jan. 20, 2005 SEDA Membrane Separation Systems Tech. Transfer, Palm Coast, FL

Jan. 31- Feb. 4, 2005 SEDA MOC School, Jupiter, FL

March 6-9, 2005 AWWA, Membrane Technology Conference, Phoenix, AZ

March 30, 2005 SEDA Pump School, Port St. Lucie, FL

May 11-12, 2005 AMTA Technology Transfer Workshop, Norfolk, VA

May 13, 2005 AMTA Board Meeting, Norfolk, VA

Aug. 1-3, 2005 AMTA Symposium, Minneapolis, MN

Aug. 4, 2005 AMTA Board Meeting, Minneapolis, MN

Sept. 11-16, 2005 IDA World Congress, Singapore

Nov. 9-10, 2005 AMTA Technology Transfer Workshop, Mesa, AZ

Nov. 11, 2005 AMTA Board Meeting, Mesa, AZ

PresortedStandard

U.S. PostageP A I D

Rush MailingAmerican Membrane Technology Association

611 S. Federal Highway, Ste. AStuart, FL 34994

Contact the following organizations for more information regarding their listed events:

AMTA - 772-463-0820, amtaorg@aol.com, www.membranes-amta.org

SEDA - 772-781-7698, administrator@southeastdesalting.com, www.southeastdesalting.com

IDA - 978-887-0410, paburke@idadesal.org, www.idadesal.org

AWWA - 800-926-7337, www.awwa.org/conferences/membrane

Our thoughts and prayers go out to the victims and the families affected by the December 26 earthquake and tsunami in Asia.

As the greatest relief effort in history gets underway, one of the critical needs for survivors is clean water. As this issue of the newsletter goes to print, AMTA is currently identifying the best means that we as an organization can assist the relief effort, particularly in getting clean water to survivors. If you would like to register with US AID/The Center for International Disaster Information for offers of goods or services, please visit the following website: http://lolo.cidi.org/datain.htm