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MEMBRANE TECHNOLOGY solutions for water treatment

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Membrane Efficiency

Water reclamation & RO optimization

A supplement to Water & Wastes Digest

MEMBRANE TECHNOLOGY

c o n t e n t s u FALL 2010 04 Synergy: The New Reality 06 Reuse in the Northeast

WATER & WASTES

DIGEST

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Optimizing RO recovery with cyclic ion-exchange softening A sustainable approach to solving water supply challenges at the University of Connecticut Economic analysis: A California groundwater replenishment system application Oxygen transfer technology revolutionizing MBR applications Using LSI to preserve an Arizona treatment plant's distribution systems A California utility's desalter brine and concentrate recovery permitting experience

08 RO Cleaning Frequency: A Balance of Costs 12 Beyond Conventional MBRs 16 Managing Water Balance

Reuse on the Rise

ater reuse applications increasingly are popping up across the globe, many applying membrane technology to put water once deemed a waste product to good use. These new and redevelopment reuse projects range from small-scale to massive, from microfiltration to membrane bioreactors, from graywater treatment in privately owned buildings to effluent treatment at municipal wastewater plants; the treated water may be used for irrigation, toilet flushing, industrial processes or groundwater replenishment, to name some practices. The results of the earliest membrane/reuse projects are becoming clearer, and in many cases the numbers and enduser feedback convey success stories. These testimonials, coupled with the rising quality and declining costs of related technologies, indicate that the logical pairing of membranes and reclamation is here to stay. For proof, look no further than this issue's article "Reuse in the Northeast" (see page 6), which profiles the University of Connecticut's recent efforts to reclaim water in order to ease demand on limited supplies. The sustainably minded university implemented microfiltration, ultraviolet disinfection and reverse osmosis to treat effluent to water fit for athletic field irrigation, cooling towers and to serve as boiler feedwater. Together, projects like those outlined above can make a world of difference in our industry and beyond. They will help conserve potable water (nearly half the global population will live in water-stressed nations by 2015, according to the National Intelligence Council), protect watersheds and source water, control operational costs and educate the public about the value of clean water. Finally, some of you may recognize me as managing editor of Storm Water Solutions and a regular editorial contributor on Water & Wastes Digest. I'll be the new face of Membrane Technology and look forward to delivering the membrane information you need to keep knowledgeable and competitive in today's water and wastewater market. Former managing editor Clare Pierson has relocated to begin a new life chapter; she will be missed, and we wish her all the best.

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18 Minimizing Disposal of a Reusable Resource

ON THE COVER

Ultrafiltration membranes in action. (Photo courtesy of GE Power & Water.)

Scranton Gillette Communications 3030 W. Salt Creek Ln., Ste. 201, Arlington Heights, IL 60005-5025 tel: 847.298.6622 · fax: 847.390.0408 · [email protected] · www.wwdmag.com E D I TO RI A L STA F F Editorial Director Neda Simeonova Managing Editor Caitlin Cunningham Associate Editor Elizabeth Lisican Associate Editor Rebecca Wilhelm Graphic Designer Robin Hicks A Dv E RT I S I n g & S A L E S 6900 E. Camelback, Suite 400 · Scottsdale, AZ 85251 tel: 480.941.0510 · fax: 480.423.1443 Integrated Media Consultant David Rairigh [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) Classified Sales Manager Donna Aly [email protected] (phone x13) Reprint Coordinator Adrienne Miller [email protected] (Arlington Heights office, 847.391.1036) List Rental Contact John Ganis 914.368.1024 Advertising Coordinator Erica Rivera [email protected] (Arlington Heights office, 847.391.1049) M A n Ag E M E 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 O R p O R AT E Chairperson K.S. Gillette President/CEO E.S. Gillette Sr. Vice President A. O'Neill Chairman Emeritus H.S. Gillette (1922-2003)

Caitlin Cunningham, managing editor [email protected]mail.com

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Synergy: The New Reality

Optimizing RO recovery with cyclic ion-exchange softening

By Francis Boodoo

Cyclic ion-exchange softening can reduce desalinated water costs and environmental impacts.

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ightening regulations on concentrate disposal from reverse osmosis (RO) and nanofiltration (NF) plants are pushing the membrane industry to find more ways to improve operating efficiencies. The large volume of concentrate brine generated, typically 15% to 50% of the total, can inhibit future growth of the industry unless new methods are developed to optimize recovery rates and reduce waste. Ion Exchange & Membranes Unite In the past, ion exchange and membranes were regarded as competitive technologies rather than providing complementary functions. The new reality is that synergistic benefits of boosting RO recoveries and minimizing waste are indeed possible, as evidenced by the recent introduction of technology referred to as cyclic ion-exchange softening. This green technology uses shallow shell cation resins to soften the feedwater to the RO and then uses the very dilute reject brine generated by the RO to regenerate the resin. The process can effectively regenerate the resin utilizing brine concentrations as low as 0.5%--20 times lower than the typical 10% concentration used by conventional softeners. No supplemental commercial salt is needed except in cases of extreme variability of feedwater quality. This synergy between ion exchange and membranes opens up new possibilities for reducing membrane treatment costs while minimizing impact on the environment. Of great interest is the capability of the process to efficiently reduce hardness and barium leakages to sub-ppm and -ppb levels, respectively. Potential membrane scaling from sparingly soluble salts (e.g., barium sulfate, calcium sulfate and

calcium carbonate) is better controlled. With improved control over scaling potential, RO recovery rate can be increased, provided no limitations are imposed by other contaminants in the water (e.g., silica, organic matter and colloids). For cases in which the latter contaminants are not limiting or are adequately controlled by other pretreatment methods, it is quite possible to design the RO plant for recovery rates of 90% to 95%. Because brine concentrations as low as 0.5% (5,000 mg/L) can be used to regenerate the resin in this new process, both brackish and semi-brackish waters can be softened. Such waters will typically have total dissolved solids (TDS) ranging from 500 mg/L (0.05%) and upward, and at 90% recovery the reject brine concentration would be adequate to regenerate the resin effectively. The new cyclic ion-exchange technology promises to eliminate the handling and feed of hazardous acids, including sulfuric and hydrochloric acid, which typically are used to reduce feedwater pH and control potential calcium carbonate scaling of the RO membranes. A drawback of feeding acid that is not experienced with ion-exchange softening is the formation of carbon dioxide (CO2) gas from neutralization of bicarbonate present in the water by the acid. The resultant CO2 passes through the RO membrane, requiring additional capital and operating cost for a degasser tower to liberate the CO2 gas as well as the feed of caustic soda for post-pH adjustment before the water is distributed. Anti-scalants, more commonly used than acid, provide good control over a wider variety of potential scaling and fouling compounds (e.g., calcium sulfate, barium sulfate, calcium carbonate, iron and

silica). When cyclic ion-exchange softening is combined with anti-scalant dosing, a unique synergy takes place, allowing for higher RO recovery rates than achievable using either technology alone. The rewards are reduced concentrate volume and disposal cost as well as reduced consumption of scarce water supplies. Comparison Points While the benefits of this green technology may be obvious, it is important to assess whether the technology is competitive with the established alternatives of acid or anti-scalant dosing. From a cost standpoint, cyclic ion-exchange softening eliminates three of the major cost components that have inhibited wider use of conventional ion-exchange softening: commercial salt, the associated labor for storage and handling and the increasing cost and complexity for disposal of spent brine. Water consumed in regeneration is also a fraction of that used for conventional water softeners because no salt dilution water is needed and rinse volumes are much lower due to the lower brine concentration. Costs for pumping of the feedwater and for disposal of wastewater are lower, too, because higher recovery rates are achieved. For comparing scale control pretreatment options, a brackish water typical of that found in the southwestern U.S. was used in a desktop evaluation to compare three options: 1. Anti-scalant dosing only; 2. Anti-scalant plus acid dosing; and 3. Anti-scalant plus cyclic ion exchange. A water analysis showed a TDS of 1,254 mg/L, a pH of 7.6 and barium and hardness levels that can significantly limit recovery rates. A permeate flowrate of 100

cu meters/hour was chosen. The comparative operating and amortized capital costs to produce 1 cu meter of permeate, or 264 gal, were then determined. Software from an independent antiscalant vendor was used to determine the appropriate anti-scalant dosage. For option No. 1, using only anti-scalant dosing, RO recovery was limited by potential of calcium carbonate scale formation to 84%. For option No. 2, using anti-scalant and acid dosing, recovery was limited to 86% by potential for barium sulfate scale formation. Option No. 3, using cyclic ion-exchange softening plus anti-scalant dosing at a reduced rate, allowed maximum permeate recovery of 95%--limited not by scaling potential but by silica fouling potential. Softening using the new technology predicted reduction of barium and calcium to less than 0.02 mg/L and 2 mg/L, respectively. In this example, the $46,000 cost of the resin was spread over five years; the capital cost for the ion-exchange vessels was assumed to be $167,000 and amortized over 10 years using straightline depreciation. The cost of water purchases and cost for disposal of reject water were combined and assumed to be low at 50 cents per cubic meter, or about $2 per 1,000 gal. Acid cost was assumed to be 33 cents per kilogram, or 15 cents per pound, while anti-scalant cost was assumed to be $11 per kilogram, or $5 per pound. The comparison shows that option No. 3 with cyclic ion-exchange softening plus reduced anti-scalant dosing was at least 40% lower in overall cost per cubic meter of permeate produced. Savings,

when producing 100 cu meters/hour of permeate and operating continuously, amounted to $43,000 annually. Additional savings include the smaller size and lower cost for the feedwater train and the lower pumping cost for the feedwater. Reject water cost was the largest cost component for all three options. The higher the cost of water, the greater the savings realized with cyclic ion exchange. Because the cost of water and the cost of disposal varies by region, the technology will be more relevant to geographies where water supplies are scarce or where disposal costs are high. While the long-term cost for cyclic ion-exchange softening may be lower than that of competitive alternatives, the extra capital outlay and space requirements needed for implementation may be considered drawbacks, whether for new membrane projects or retrofit of existing plants. But these factors should not be considered in isolation, as water supplies are becoming scarcer and concentrate disposal regulations are increasing in scope and complexity. Implementation of environmentally friendly technology, such as cyclic ionexchange softening, should be an ongoing part of the strategy to reduce overall cost for desalinated water while minimizing impact on the environment. MT

Francis Boodoo is technical sales manager for The Purolite Co. Boodoo can be reached at [email protected] or 800.343.1500. For more information, write in 1101 on this issue's Reader Service Card or visit www.wwdmag.com/lm.cfm/mt101001.

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Reuse in the Northeast

By Richard Cisterna, Kristen Barrett, Joyeeta Banerjee, Cynthia Castellon, Anni Luck, Alex Wesner & Paul Puckorius

ater and wastewater utilities are beginning to discover that wastewater reuse can be an important component of a comprehensive watershed management program or alternative water supply plan. Removing wastewater streams from surface water bodies can reduce pollutant loads, including nutrients, heavy metals, pharmaceuticals and endocrine-disrupting compounds, to these receiving waters. Instead of discharging wastewater to lakes, rivers or streams that often feed other water supplies, wastewater can be treated to a higher level and reused for beneficial purposes. Wastewater reuse also reduces water demands that potable supplies would otherwise have to satisfy. Although not traditionally viewed as a region having much need for reclaimed water projects, a growing number of facilities in the Northeast are strongly considering the benefits of reclaimed water. There are currently several operational facilities located throughout the Northeast that

A su sta i n a bl e a ppro a c h to so l vi n g w a te r su ppl y c h a l l e n ge s a t th e Un i ve rsi ty o f C o n n e c ti c u t

Recognizing the potential for recurrence, the university's first measure was to implement several restoration and conservation measures. A modification of the withdrawal management protocols at the Fenton River wellfield was implemented; this involved ceasing pumping of the Fenton River wells based on specific stream flow criteria. With these new limits placed on the Fenton River wellfield--coupled with lower yield from the Willimantic River wellfield--UCONN found it necessary to identify other sources of water to consistently meet demands and preserve natural resources. The university's focus on sustainability prompted the decision to implement a reclaimed water program--a first-of-its-kind industrial reuse application in the state of Connecticut, and one of only a handful in the Northeast. Treatment Train The university operates its own water pollution control facility located on the main campus. Treatment includes seasonal chlorination and oxidation ditches that allow for conventional activated sludge aeration, nitrification and denitrification. Following an analysis of current and future potable and nonpotable water demand and wastewater flows, several cutting-edge treatment process alternatives were evaluated to determine the most efficient, practicable and sustainable solution to meet targeted water quality standards for industrial and irrigational reuse. The primary reclaimed water goals discussed with the Connecticut Department of Environmental Protection are total suspended solids less than 5 mg/L and "nondetect" for fecal coliform. The selected alternative entails the construction of a 1-million-gal-per-day reuse facility that utilizes microfiltration (MF), ultraviolet (UV) disinfection and reverse osmosis (RO) to treat wastewater effluent before its use as boiler feedwater, makeup water for cooling towers and irrigation water for turf fields. MF is an innovative, effective treatment process that removes both contaminants and pathogens by filtration through a porous membrane. However, to protect high-pressure boilers and to provide proper maintenance, makeup water for the boiler systems must be high purity. Thus, treated ("reclaimed") water from the pressurized MF system will be further treated using an upgraded, existing RO system for softening and demineralizing prior to use as boiler feedwater. If it is determined that even higher purity water is required, an ion-exchange system will be available upstream of the RO. RO treatment is not needed for the cooling tower system. Instead, the MF effluent for cooling tower makeup will be treated for scale, corrosion and biologicalgrowth control using scale and corrosion inhibitors and biocides. Reclaimed water from the new MF treatment system also will be used for irrigation on campus. For disinfection, both UV light and liquid sodium hypochlorite were considered. While both methods would meet the required disinfection goals, UV was found to be more advantageous, and in-vessel LPHO UV disinfection was selected as the preferred option. The water entering the new 1-million-gal reclaimed water storage tank, however, requires a disinfectant residual to prevent bacterial regrowth. A small dose of chloramines, therefore, will be added as a secondary disinfectant to maintain the required residual for irrigation and prevent biofouling of the water storage tank, distribution pipelines and RO membranes. Sustainable Design Using reclaimed wastewater will make an equivalent amount of water supply available to meet UCONN's existing and future potable water demands--a key component in improving the sustainability of campus operations. Implementing a reuse program will ease the water demands placed on the Fenton River and help to conserve this vital resource while setting a positive, hands-on example for UCONN students regarding sound environmental stewardship. The new reuse facility also incorporates several sustainable design features, including energy conservation through the use of rooftop solar panels coupled with a solar orientation of the facility; sustainable construction through the use of Leadership in Energy and Environmental Design-certified sustainable materials that are locally produced; and collection and reclamation of rooftop storm water by blending with the reclaimed water for beneficial use on site. Also, the project will include a sustainable heat pump system that harnesses the heat from the reclaimed water and converts it into building heat for the new reclaimed water facility building. With the success of this program, water reuse has the potential to become a more common and better understood practice in the region and should help to advance the establishment of regulatory water quality standards in the state. With the increasing emphasis on ensuring a sustainable water supply, coupled with population growth and overburdened water supply sources, water reuse provides a viable means to effectively and safely meet heightened water demands, engendering a reliable supply while conserving natural resources. MT

Richard Cisterna, P.E., Kristen Barrett, P.E., Joyeeta Banerjee, P.E., Cynthia Castellon, E.I., and Anni Luck, P.E., are with Hazen and Sawyer. Alex Wesner, P.E., is with Separation Processes Inc. Paul Puckorius is with Puckorius & Associates Inc. Luck can be reached at [email protected] For more information, write in 1102 on this issue's Reader Service Card or visit www.wwdmag.com/lm.cfm/mt101002.

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have beneficial reuse projects. Utilities typically are steered away due to lack of drivers, lack of public education and acceptance and lack of established regulatory framework (although this is changing for states such as New Jersey and Massachusetts that do have reuse regulations). In recent years, however, more utilities are looking toward wastewater reuse as a way to free up potable water supplies for other uses. This is becoming particularly important for communities that are approaching the limits of their water supply. Drivers Behind UCONN's Reclaimed Water Program The University of Connecticut (UCONN) in Storrs, Conn., provides potable water and wastewater treatment services to its main campus and depot campus, as well as to some adjacent areas within the town of Mansfield. In anticipation of increasing potable water needs on its campus due to a growing population, and faced with a lack of additional water supplies in the area, UCONN sought to implement a long-term, sustainable 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 effluent from UCONN's wastewater treatment plant as feedwater for both the university'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 groundwater supplies: the Fenton and Willimantic river wellfields. In 2005, a portion of the Fenton River ran dry--an event attributed to elevated water withdrawals necessary to meet the seasonal peak demand during drought conditions.

With new withdrawal limits placed on the Fenton River wellfield and the Willimantic River wellfield producing a lower yield, UCONN launched a reclaimed water program.

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RO Cleaning Frequency: A Balance of Costs

Economic analysis: A California groundw a t e r replenishment system applica ti o n

The OCWD GWR features an RO system comprised of 15 trains.

By Eric Owens & Mehul Patel

ver the last two decades, reverse osmosis (RO) has become the process of choice for removing dissolved salts and other contaminants from a variety of water sources, including seawater, groundwater and wastewater effluents. RO is a pressure-driven process, where the applied pressure required to drive water through the membrane is a function of the total dissolved solids (TDS) in the feed source. As foulants build up on the membrane surface, the foulant acts as an impediment to flow and the pressure required to drive water through the system increases. Left alone, the fouling can build up until the required pressure exceeds the feed pump capabilities, and a loss of permeate production eventually will occur. Membrane cleaning is used to remove the foulant from the membrane surface and return the system to baseline conditions. RO technology has been adopted by both industrial and municipal users. Industrial RO systems are often smaller (less than 1-million-gal-per-day [mgd] permeate capacity) and sometimes designed without the ability to clean the membrane elements in place within the pressure vessels. In these cases, operators either send membrane elements off site for cleaning, or elements are simply discarded when they have been completely fouled. Municipal systems are often large scale, and they typically range between 1 mgd and 100 mgd in permeate production. Individual RO train capacities typically range from 0.5 mgd to 5 mgd.

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The size of municipal facilities usually requires an operating approach whereby a membrane that is eventually fouled during the treatment process is cleaned in situ using a chemical solution selected based on the type and nature of the foulant on the membrane surface. The cleaning solution is introduced into the membrane system through an ancillary cleaning system. For large municipal systems, membrane cleaning in this manner is more economical and practical than offsite cleaning or replacing the membrane. Through membrane cleaning, the pressure required to operate the RO system is reduced, and hence the energy consumption is minimized. Calculate to Optimize There are industry rules of thumb as well as specific RO manufacturer guidelines for when and how to clean RO membranes. These typically revolve around the parameters of water permeability and normalized differential pressure. Calculated indicators of water permeability (e.g., specific flux, normalized feed pressure, normalized permeate flow and normalized flux) can be used as indicators of the amount of fouling on the membrane surface. The normalized differential pressure offers an indication of the amount of material deposited within the feed/brine spacer of the RO elements, restricting flow through the system. Guidance on membrane cleaning from the industry suggests cleaning the RO train when the water permeability

has decreased by 10% to 25%, or when the normalized differential pressure has increased by 20% to 50%. This guidance, however, does not necessarily offer the most economical point of operation for the RO system. RO cleaning can be considered nothing more than a response against increasing system pressures and energy costs. But rather than follow anecdotal cleaning triggers, operators should examine the balance between the cost of energy associated with fouling and the cost of performing the cleaning for their particular system. All RO systems are somewhat different, and there are many variables that contribute to this examination. In order to identify a balance between fouling and cleaning, the following variables must be considered for a particular system: · Costofenergypaidbythe municipal agency; · Specificfoulingrateofthe RO system; · Thenatureofthefoulantand cleaning effectiveness; · Totalcostofchemicalsolution; · Laborassociatedwithperforming a cleaning; and · Lostpermeateproductiondueto downtime during cleaning. One such examination was performed for the RO trains within the Orange County Water District's (OCWD) groundwater replenishment system (GWR) in California. The following is

a discussion of the economic analysis performed for this RO system in order to identify the balance between fouling costs and cleaning costs. Ultimately, this economic analysis was successful in identifying the optimum cleaning interval given the specific GWR variables. Case Study: OCWD GWR System The RO system for the OCWD's GWR consists of 15 RO trains, each with a 5-mgd capacity, for a total plant production of 70 mgd of RO permeate capacity (N+1 design). The RO trains operate at 85% recovery and a maximum permeate flux of 12 gal per square foot per day. Each train houses 1,050 8-by-40-ft Hydranautics' ESPA2 RO elements in a 78:48:24 array (seven elements per vessel). The membranes within the 15 GWR RO trains have a range of permeability due to intrinsic differences in membrane construction, cleaning effectiveness or exposure to different events and conditions during startup and operation. The inherent permeability of the membrane is the first contributor to the energy costs for an RO system. The second component contributing to the energy costs is the unique fouling rate identified for each train following a cleaning. While this fouling rate is generally anticipated to be similar between trains (due to similar operating conditions), this is not the case for all 15 trains at OCWD. Several trains have demonstrated sharper fouling rates than others. This may be due to previous, less-effective cleanings,

varying hydraulics between trains or some indeterminate issue. Whatever the influences, these two components have contributed to distinct performances and energy costs associated with individual RO trains. For this reason, each individual train was analyzed to determine the most cost-effective cleaning alternative for operating that specific RO train. Because RO trains may operate within a range of flow conditions, temperature and feed salinities, it is not practical to use the actual energy consumption of a given train for this analysis. Instead, the data was normalized in order to represent operation at 5 mgd RO permeate, 1,800 S/cm feed conductivity and 77°F feedwater temperature. The fouling rate of each train was determined from the normalized feed pressure calculated after membrane cleaning occurred. The typical normalized feed pressure trend for membranes operating at the GWR starts out with a steep increase that is followed by a somewhat linear performance. The linear portion of the trend is generally developed within 20 days of the cleaning. For this reason, the performance 20 days after a cleaning was used to model the long-term fouling rate of the individual trains. Based on historical performance at GWR, this linear fouling rate was considered representative of the anticipated fouling rate and used to extrapolate the long-term train performance. A linear model may not offer the best fit for all fouling trends. This expectation should be confirmed as fouling progresses and an appropriate model selected based on actual system performance. This fouling trend model was used to investigate the costs associated with several cleaning interval scenarios. This analysis also assumed that membrane cleanings were consistently effective, regardless of the frequency between cleanings. This goes against the typical operational expectation that as more foulant builds on the membrane surface, the more difficult it will be to remove through cleaning. But based on historical performance data for GWR, this was

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considered an acceptable assumption for this RO system. Other RO facilities with different fouling characteristics and cleaning effectiveness may not be able to make this assumption if consistent and repeatable cleanings cannot be achieved. The cost associated with membrane cleanings included the labor cost, the chemical costs of the district's cleaning procedure and the cost of lost production due to offline time. While the GWR system design accounts for one of the 15 trains being offline (N+1), it was assumed the fifteenth train could be offline for any number of other reasons; lost production due to cleaning was factored into this analysis. For this investigation, the total cleaning cost amounted to $15,929 multiplied by the number of cleanings per year. Even though the energy costs decrease with an increased frequency of cleanings, the reduced energy costs are offset by the

additional cost of the cleanings. This investigation was taken further to determine the minimum operation All RO system operators should analyze energy and cleaning costs to and maintenance find a balance between cost-effectiveness and performance. (O&M) costs for CIP intervals ranging from 30 days chemical costs due to frequent cleanings. to 365 days. The total cleaning and total The total O&M costs to the righthand side of the parabolic curve are more energy costs were compared and comheavily weighted toward energy costs as bined for this range of CIP intervals in a result of accepting more fouling within order to determine the optimum cleaning the RO train. The minimum O&M interval that offered the minimum total costs can be determined by identifying operating costs. the minimum point on the curve. Summing the two costs together This analysis was applied to each resulted in a "Total O&M Cost" curve RO train and its unique condition and with a shape similar to that of a parabfouling rate in order to determine the ola. In this presentation, the total O&M minimum total O&M costs related to costs toward the lefthand side of the parcleaning and fouling. Depending on the abolic curve are heavily weighted toward

unique performance of each train, the optimum cleaning interval could fall on either side of the six-month interval. The results of the analysis of 15 individual trains were as follows: The most economical cleaning frequency for seven of the trains was determined as every five months. The most economical cleaning frequency for seven of the trains was calculated as every eight months. One RO train calculated an optimum cleaning frequency of every 10 months. The optimum CIP interval and minimum annual energy and CIP costs were determined from the parabolic curves for each train. Adopting a Similar Approach Industry standards for CIP triggers may not offer the most efficient point of operation for RO systems. An economic analysis investigating the balance between energy costs and cleaning costs

should be applied to any RO system to ensure that the current cleaning regime offers the most cost-effective operation and performance. The analysis described herein was based on a combination of real-world data and observations but assumes the cleanings applied are consistently effective. It also assumes the modeled fouling rates are observed and repeatable following each cleaning. This is generally the case at OCWD, but should the fouling rate or cleaning effectiveness deviate from the model, the evaluation would need to be redone. If this analysis indicates the benefit of a longer cleaning frequency, it would be wise for operators to confirm their assumptions through gradual implementation of longer cleaning frequencies. This would allow verification of the modeled fouling rate and confirm consistent cleanability is achieved.

A significant savings of approximately $250,000 per year was identified at OCWD through performing an economic analysis to identify the optimum cleaning interval for the district's system. Not all RO systems are guaranteed the same degree of savings determined for OCWD, but most would likely benefit from applying a similar approach to their cleaning philosophy. MT

Eric Owens, P.E., is project manager for Separation Processes Inc. Owens can be reached at [email protected] Mehul Patel, P.E., is principal process engineer for the Orange County Water District. Patel can be reached at [email protected] For more information, write in 1103 on this issue's Reader Service Card or visit www.wwdmag.com/lm.cfm/mt101003.

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Beyond Conventional MBRs

Oxygen transfer technology revolutionizing MBR applications

ubmerged membrane bioreactor (MBR) technology continues to gain traction on a global level as a cost-effective means for treating wastewater. Moreover, given the high effluent quality, MBR systems increasingly are being used for water recycling and as feed to reverse osmosis systems. The advantages of the technology are well documented in literature and include, among others, small footprint, superior effluent and ease of operation. Despite the substantial upside of owning and operating an MBR, there is also a downside to consider. If an MBR system is not properly designed to run efficiently or is not operated in an energy-efficient manner--or some combination thereof--what looks sustainable on paper will not be in real life. The perception, and in some cases reality, that MBR systems are "energy hogs" chewing up kilowatts at rates two to 20 times the theoretically achievable value of 0.32 kWh/cu meter (1,200 kWh/MG) is not specific to one membrane technology. A growing body of evidence appears to support the idea that membrane geometry may have less to do with actual system energy consumption than other factors. For example, in a recent survey of nine U.S. MBR installations--some using hollow-fiber membranes and others using flat plates-- aggregate consumpSDOX oxygen transfer technology is based on simple physics. tion numbers varied 12

suspended solids (MLSS) concentrations between 2% and 3%; and 3. Controlling the dissolved oxygen (DO) in the reactor to achieve simultaneous nitrification and denitrification (SNdN). None of these steps is necessarily new, with the exception of the method by which oxygen is being added to the process. The oxygen transfer technology, called SDOX, is novel in the wastewater industry but is based on simple physics. The other parts, running at high mixed liquor and achieving SNdN, are well documented in literature and have many references in the U.S. and abroad. Oxygen Delivery Instead of trying to add oxygen to a process using gas bubbles rising through

By Dennis Livingston

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between 5,400 kWh/MG and 16,000 kWh/MG. For comparison, a typical energy estimate for a new MBR plant will be approximately 3,000 kWh/MG and conventional activated sludge plants have reported usages averaging less than 3,500 kWh/cu meter. A more granular look at many of these plants reveals that they can and do run efficiently near design flows but become increasingly inefficient as less water is treated. The decrease in efficiency is often due to a lack of process turndown and specifically may be caused by so-called parasitic loads (e.g., mixers, blowers and pumps). Other factors such as system complexity and compounding equipment inefficiencies may contribute to the high energy usage rates and ultimately may determine the fate of MBR technology rather than the type of membrane equipment used for filtration. New Technology EcoBlox systems are specifically designed for ease of operation, requiring 70% less automation; the biggest advantage to end-users, however, may ultimately be reduced installation costs. Whereas recent data suggests that conventional MBR systems may cost between $7.80/gal and $13.80/gal to build, contractor estimates indicate that EcoBlox systems may cost less than $4/gal to construct due to the reduced footprint, reduced concrete and overall process simplicity. The process can be described as taking three primary steps: 1. Saturating screened raw wastewater with oxygen under pressure (typically 80 to 100 psig); 2. Sending the oxygen-laden wastewater to the high-rate MBR for treatment running at mixed liquor

a water column (diffused air, etc.), water is aerosolized, or turned into small droplets, and contacted with pure oxygen in a small tank. Using this method eliminates the variable influence of mixed liquor and greatly simplifies maintenance. The physics part, Henry's Law, relates gas pressure in the tank to the saturation oxygen concentration in the water. If the screened influent is pressurized to 100 psig and put in contact with pure oxygen, it will contain 300 mg/L oxygen when sent to the reactor. If the tank pressure drops, the oxygen concentration drops. If the pressure is increased, the oxygen concentration increases proportionally. In an EcoBlox system, the oxygen delivery rate is controlled by changing the liquid level in the contact tank based on the DO measured in the permeate--not the mixed liquor. Bouncing

between low DO set points can be used to promote SNdN. Supply oxygen is made up on site using a vacuum swing adsorption technology manufactured by PCI, called DOCS. The energy demand of an EcoBlox system is primarily due to the highpressure pump, oxygen makeup system and air scouring requirements. All of these demands combined equate to less than 4,000 kWh/MG. DO Control DO control in conventional MBR systems using diffused aeration is a strong function of mixed liquor conditions or properties. For example, at times MBRs are run at very high MLSS concentrations to reduce waste solids handling costs, but the increased concentration also drives down fine-bubble diffuser performance.

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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 investment program is the implementation of nano ltration treatment, which will begin to replace the older conventional lime softening water treatment facility in 2011. The 14.5 million gpd nano ltration facility will utilize a fresh shallow aquifer as its supply and will provide town residents with the ultimate barrier against viruses and bacteria. Paul Jurczak, manager of the Town of Jupiter, will discuss the construction of the Nano ltration Treatment Plant that is currently underway.

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

This webinar made possible by:

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Figure 1. DO Control Trial

In other cases, operators may choose to run at lower or thinner solids concentrations, but that can lead to excessive, uncontrollable DO in recycle streams and inhibit denitrification. Whatever the process conditions, submerged instruments are prone

to getting out of calibration or malfunctioning. The ideal situation is to monitor permeate conditions for control purposes, eliminating some of the problems with conventional and multistage MBR processes. The ability to control the oxygen concentration in a single-stage MBR by monitoring permeate was demonstrated in a full-scale pilot conducted earlier this year. During several trials, a sharp saw-tooth DO profile was observed bouncing between varying high and low set points in roughly

15-minute intervals. In trial DO, for example, set points were 1 mg/L and 2 mg/L (see Figure 1). This same type of profile was observed during pilot testing conducted by BlueInGreen in cooperation with CH2M Hill-OMI at a wastewater treatment plant in Fayetteville, Ark. During the study, both mixed liquor and plant effluent where used as feed to an SDOX system in different trials to demonstrate performance. With the capability of transferring and controlling oxygen delivery to a highrate MBR now proven, the advantages of the technology are significant. MT

Dennis Livingston, P.E., is director, MBR Systems, for Enviroquip, a Div. of Eimco Water Technologies. Livingston can be reached at [email protected] For more information, write in 1104 on 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.

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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, transportation and energy industry shows throughout 2010-2011. Quarterly editions will be e-mailed in October 2010 and in January, April, July and October 2011.

Visit www.infrastructuresolutionsmag.com

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

From the editorial staff of Water & Wastes Digest, Roads & Bridges, Transportation Management & Engineering and Storm Water Solutions

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Managing Water Balance

U s i ng L S I t o p res erv e a n A rizo na treatment plant's distribution syste m s

By Heather Rekalske

T

he first thing anyone who manages water and wastewater learns is that water is the universal solvent. Because of the unique properties of that dihydrogen monoxide molecule, owing to the extreme electronegativity of the oxygen atom, water is highly polarized and dissolves almost everything with which it comes into contact. This fact is important when one has to maintain equipment and structures that process

and distribute water because what the water has dissolved in it can cause it to be corrosive or scaling. What water generally has dissolved in it is at least some carbon dioxide and some calcium carbonate. Carbon dioxide is ubiquitous and dissolves at the surface of the water, forming carbonic acid in solution. Calcium carbonate, dissolved by the carbonic acid, is globally present in rock formations (limestone), as well as in the physiological structures of organisms (particularly oceanic organisms) that excrete it. Calcium carbonate in its various forms is also used to buffer pH and stabilize solution 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 equipment 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 managing 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

Gary Lyons manages LSI at an Arizona water treatment facility using the Ultrameter II 6Psi.

takes 70 million gal per day (mgd) of water from the Central Arizona Project canal and treats it for residential and commercial use. Within the 143-acre campus, the plant processes 20 mgd to of wastewater from the city of Scottsdale collection system using microfiltration and reverse osmosis (RO). Water coming from the RO treatment process is acidic around pH 5.5. It is then moved to decarbonation towers and lime is added to bring the LSI value close to zero. The water reclamation plant features 8 mgd of storage capacity. Recycled water treated by the plant is used for the irrigation of 20 Scottsdale golf courses. There is great concern about how the water balance will affect this distribution system over time, especially due to higher total dissolved solids values. Plant technicians compute LSI values in the field with the 6Psi hand-held to determine what adjustments should be made and how in real time. The LSI calculator allows them to perform whatif scenarios on changes in pH, alkalinity, hardness and temperature. They are able to measure the effects of changes immediately as well in the facility and at distribution points. Hardness and alkalinity are variables in the LSI calculation because they account for the availability of calcium in various forms in the water. Variables such as temperature and pH contribute to the likelihood of the formation of

calcium carbonate. The version of the LSI calculation used by the 6Psi LSI calculator is: LSI = pH + TF + CF + AF ­ 12.1 In this calculation, pH = the measured value of pH in pH units; TF = 0.0117 x temperature ­ 0.4116; CF = 0.4341 x ln(Hrd) ­ 0.3926; and AF = 0.4341 x ln(AL) ­ 0.0074. Indicator Analysis LSI has been useful as a scaling/ corrosion indicator in municipal water treatment for more than 70 years. The original Langelier Saturation (or Stability) Index calculation was developed by Dr. Wilfred Langelier in 1936 to be used as a tool to develop strategies to counteract corrosion of plumbing in municipal water distribution systems. It is a statement about the change in pH required to bring the calcium carbonate in water to equilibrium. LSI is a measure of the disparity between the pH of the system and the pH at which the system is saturated with calcium carbonate: LSI = pH ­ pH of saturation. As such, the LSI indicates the change in pH required to bring water to equilibrium. If the LSI is +1, then the pH needs to be lowered by one unit to bring the water to equilibrium. If the LSI is -1, the pH needs to be raised by one unit to bring the water to equilibrium. A positive saturation index means

that the pH of the water is above equilibrium. The water is scaling because as pH increases, total alkalinity concentration increases. This is due to an increase in the carbonate ion, which bonds with calcium ions present in solution to form calcium carbonate (reference the carbonic acid equilibrium, in which hydrogen ions bond with carbonate ions to form bicarbonate and hydrogen ions bond with bicarbonate to form carbonic acid). Thus, any positive value for LSI is scaling. If the pH is less than the pH of saturation, the index will be negative, which is corrosive. This means that the water is more acidic than it would be at equilibrium. There are less carbonate ions present, according to the carbonic acid equilibrium. The water will be aggressive because it has room for more ions in solution. Thus, any negative value for LSI indicates that the water may tend to be corrosive. The use of LSI as an indicator is well documented and time-tested. Managing water balance through LSI analysis will prevent loss of efficiency and failure of equipment and structures, saving time and money. MT

Heather Rekalske is technical writer for Myron L Co. Rekalske can be reached at [email protected] For more information, write in 1105 on this issue's Reader Service Card or visit www.wwdmag.com/lm.cfm/mt101005.

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Minimizing Disposal of a Reusable Resource

A California utility's desalter brine and concentrate recovery permitting experience

By Carl W. Spangenberg

T

wo membrane facilities operated by the same water district generate concentrate waste streams that are handled in distinctly different manners. Here we investigate the steps and methods used by California's Irvine Ranch Water District (IRWD) on the permitting and concentrate recovery methods for the Irvine Desalter Project (IDP) and the Deep Aquifer Treatment System (DATS). IDP Primary Treatment Plant (PTP) The IDP-PTP removes moderately high levels of total dissolved solids (TDS) and nitrates pumped from the principal aquifer within the Irvine groundwater basin. A full-scale reverse osmosis (RO) plant was put into operation in 2006 and can treat up to five wells that are 1,000 ft deep

Table 1. Concentrate Flow & Water Quality Concentrate IDP-PTP Flow 0.67 mgd 0.65 mgd 0.16 mgd* Water Quality TDS: 3,500 mg/L Mn: 266 g/L Silica: 184 mg/L TDS: 900 mg/L Color: 2,500 to 3,000 color units

and deliver 5.9 million gal per day (mgd) of raw water to the treatment plant. Approximately 2.7 mgd is treated by RO operated at 75.5% recovery, 15.4 gal per sq ft per day (gfd), feed pressures up to 300 psig and blended with the remaining raw bypass water. A total of 434 membrane elements are used at the IDP-PTP facility. Water production levels vary according to fluctuations in the raw water feed. Targeted constituent levels in the product water include a TDS of 420 mg/L and nitrates less than 10 mg/L as nitrogen. DATS The goal of the DATS is to remove high color (300 color units) caused by natural organic matter from groundwater pumped from the Santa Ana River Basin below five color units. A fullscale nanofiltration (NF) plant was constructed utilizing a design/build approach, with operation of the facility initiated in February 2002. The DATS facility is an 8-mgd NF plant designed to operate at 98% recovery, 16 gfd at operating pressures up to 125 psig. It includes two deep wells approximately 2,000 ft deep; water collection; and membrane treatment, concentrate recovery and concentrate disposal facilities. A total of 1,398 membrane elements are used for the DATS facility. Concentrate Disposal Options The water quality of the concentrate from the IDP-PTP and the DATS are significantly different; this was the secondary factor dictating the ultimate disposal method of these resources, with brine line capital costs being the primary factor. The IDP-PTP concentrate contains a TDS level of 3,500 mg/L, Mn of 266 g/L and silica of 184 mg/L, whereas the DATS contains high color in excess of 2,000 color units with a TDS of 900 mg/L that is close to that of drinking water. The differences

in water quality between the DATS and IDP-PTP concentrates are significant (see Table 1): The DATS concentrate is more amenable for concentrate recovery due to low TDS levels and the removal of color as the primary constituent controlling post-concentrate treatment, in comparison to the higher TDS, Mn and silica levels being the controlling, more difficult and costly constituents to remove in the IDPPTP concentrate. IDP-PTP Concentrate Two alternatives were identified in the early part of 2000 for the IDPPTP concentrate: 1. Construction of a regional brine line connecting these two concentrate wastes and other brine disposal wastes within the region with its terminus downstream of the Orange County Sanitation District's (OCSD) Plant No. 1 for ultimate disposal to the ocean. The estimated cost of construction for this regional brine line, with average flows from both current and future membrane facilities around 4.32 mgd, was $33 million in 2004 dollars and would require construction of approximately 24 miles of pipelines of various sizes crossing a minimum of four cities in highly developed and utilized thoroughfares. Concentrate flow would be generated from four IRWD membrane facilities (existing IDP-PTP and DATS, plus two future facilities), two desalting facilities in the city of Tustin, three future shallow groundwater dewatering facilities owned by the city of Irvine and one facility owned by the Transportation Corridor Agency. Major jurisdictional hurdles that would need to be overcome to make this brine disposal line a realization included the city of Irvine, city of Santa Ana, city of Tustin, Caltrans, OCSD, California Coastal "Commission" and Santa Ana Regional Water Quality Control Board.

DATS

2. Construction of a dedicated 5-mile brine line at a cost of $4.4 million for the IDP-PTP concentrate at an average discharge rate of 0.68 mgd that would convey the concentrate to a newly constructed ocean outfall pump station at the Los Alisos Water Recycling Plant. This ocean outfall pump station would discharge excess treated wastewater and concentrate via an existing land outfall directly to the South Orange County Wastewater Authority (SOCWA) Aliso Creek Ocean Outfall (ACOO) that is blended with other wastewater effluents prior to discharge to the ocean. Jurisdictional hurdles included the city of Irvine and city of Lake Forest (pipeline routing through two cities), SOCWA, San Diego Regional Water Quality Control Board (ocean outfall permit addendum) and the California Coastal Commission. DATS Concentrate Given the low salt levels in the DATS concentrate as noted in Table 1, only one alternative was evaluated: connection to an existing sewer located in the city of Santa Ana with eventual treatment and disposal at the OCSD Plant No. 1, located in Fountain Valley, Calif. In order to minimize the quantity of concentrate discharged to OCSD and to maximize recovery of the concentrate from the DATS, IRWD performed pilot and demonstration scale testing from 2004 to 2006 to allow recovery of the concentrate. This resulted in the construction of a concentrate recovery NF fourth train, at a cost of $1.2 million, that increased the recovery of the DATS from 92% to 98% in 2007 with a payback of two years based on savings of concentrate disposal and treatment alone. Selected Disposal Options The concentrate disposal options implemented at the IDP-PTP and the DATS are summarized in Table 2 along with the

key permits that were obtained from identified jurisdictions. The key reasons for the selected concentrate disposal options for each membrane facility included jurisdictional hurdles, capital costs, ease and timing of securing required permits and ability for concentrate to be treated and recovered for potable use. The ocean disposal method to the SOCWA ACOO for the IDP-PTP concentrate was based on: · Lowercapitalcostsvs.disposal via a regional brine line to the OCSD facility ($4.4 million vs. $33 million); · Multi-agencyagreementsrequired to construct the regional brine line vs. a single point of contact with SOCWA; and · LimitationsoftheIDP-PTPconcentrate silica levels for application of concentrate recovery. A combination of concentrate recovery and discharge to OCSD sewer for disposal and treatment was selected for the DATS concentrate based on: · Demonstrationofthetreatmentand recovery of concentrate due to color removal being the factor controlling treatment, not solubility of salts; · Paybackoftwoyearsforconcentrate treatment facility; and · Sewerconnectionpointbeing adjacent to the DATS facility. Editor's Note: The information in this article originally was presented by the author at the 2010 AMTA Annual Conference. MT

Carl W. Spangenberg, P.E., is senior engineer for the Irvine Ranch Water District. Spangenberg can be reached at [email protected] For more information, write in 1106 on this issue's Reader Service Card or visit www.wwdmag.com/lm.cfm/mt101006.

*With concentrate recovery

Table 2. Selected Concentrate Disposal Options & Key Permits/Actions Concentrate Disposal Method Concentrate Recovery Required Permits/Actions · Addendum No. 3, Order No. 2001-08 NPDES Permit No. CA01070611, Waste Discharge Requirements for SOCWA to ACOO · SOCWA Project Committee Interagency Agreement Amendments · Coastal Commission Ruling · Required Acute and Chronic Toxicity Testing · Reviewed Every Five Years · OCSD Class I Industrial Waste Discharge Permit · No Toxicity Testing Required · Renewable Every Two Years Disposal Costsa

IDP-PTP

Ocean Outfall

No

$153,000 b

DATS

Sewer

Yes

$445,000 c $67,000 d

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

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