MAKING GOOD BETTER: OPTIMIZING SALINITY MANAGEMENT USING TIME-STEP WATER AND SALT BALANCE. Abstract

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1 MAKING GOOD BETTER: OPTIMIZING SALINITY MANAGEMENT USING TIME-STEP WATER AND SALT BALANCE Charlie (Qun) He, Carollo Engineers, Inc., 4600 E Washington Street, Suite 500, Phoenix, AZ Coauthor: Chao-an Chiu, Carollo Engineers, Inc. Abstract Good, Better, Best. Never let it rest. To proactively manage their limited water resources, many inland utilities and private sector water consumers have embarked and maintained certain level of salinity management activities. This includes developing regional salinity monitoring and control program as part of relevant master planning documents, establishing plans for developing brackish groundwater, surface water, and reclaimed water resources, banning the use of timer-based softeners, setting up local limits on salinity as part of the industrial pretreatment program, etc. Some utilities established water and salt mass balance calculations using excel spreadsheets for their systems or subsystems. These water balance may be sufficient to accomplish their specific and limited objectives in the past. But to better plan for and effectively design, implement, operate, and most importantly, optimize the desalination and concentrate management facilities, accurate tracking of flow and salt concentration (both TDS and individual ions) are crucial. A complete case study is used to demonstrate how more accurately tracking flow and salt concentrations can result in significant saving and performance improvements for salinity management. A sanitary district in Arizona provides tertiary treated effluent to three local golf courses and three parks for irrigation water. The District currently operates a 3.0-mgd Advanced Water Treatment Facility (AWTF), which further treats the effluent by ultra-filtration (UF), for storage and recovery in the aquifer. The quality of the treated effluent, while consistently meeting all permitted water quality standards, has evaluated TDS and sodium, not ideal for turf irrigation. The District evaluated the feasibility of implementing desalination and zero liquid discharge (ZLD) or near ZLD concentrate management alternatives, including unit processes such as primary RO, inorganic pretreatment (Lime Softening plus Granular Media Filtration versus ion exchange), Secondary RO or Electrodialysis Reversal (EDR), Brine Concentrator, Crystallizer, and / or Evaporation Ponds. One unique challenge about the project was about evaporation pond sizing. Considering that the Town is nearly built-out, the maximum possible size of evaporation ponds was limited to 4 to 5 acres. The pond level and operation over time must be modeled closely. Because the actual flow to the AWT and the brine stream generated from the future RO system could change day by day, the conventional way of pond sizing based on monthly average flow and annual average evaporation rates are not sufficient and would result in oversized ponds > 5 acres. A dynamic time-step based mass balance model was utilized to optimize the blending operation so that just enough water is treated by RO to meet the blended water sodium goal (110 mg/l). This approach minimizes the brine stream going to the pond. The daily pond level is animated in the model, allowing the user to track the pond operation and sizing the pond. Other features of this tool include user-friendly graphical interface, treatment alternative analyzer, what-if and sensitivity analyzer were also leveraged to project treated water quality under various conditions, develop a reliable and reasonable basis of design, set forth the footprint requirements, establish an evaporation pond operation plan, and generate capital and O&M costs.

2 The project considered several innovative salinity and concentrate management technologies, including monovalent selective ion exchange membrane, which can selectively remove sodium. Another technology investigated during this study was mineral polarization technologies, which enhance plant growth and remediate soil salinity by acting on charged minerals and polar non-minerals present in water. When salts are hit by a pulsed electrical field, they can break down into an uncoupled charged form, which passes through the root zone easier and faster, facilitating better drainage and turf growing conditions. Due to the proprietary nature of the technology and the difficulty in quantifying any changes in measured sodium concentrations, phone interviews of selected golf courses that are currently using these technologies were conducted. The feedbacks were fairly interesting. The study also touched on establishing comprehensive salinity management strategies for the District regarding the local salinity imbalance. Several supplemental practices that could potentially improve the turf growth on the golf courses were discussed. These items may not be sufficient as stand-alone solutions to the District's salinity issues. However, when used to supplement the proposed engineered alternatives, they could reduce the need of treatment costs. Introduction The Sanitary District (District) produces Class A+ reclaimed water, or effluent, at its wastewater treatment plant (WWTP) for three local golf courses and three parks for irrigation water. The District also operates the Advanced Water Treatment Facility (AWTF), which further treats the effluent by ultra-filtration (UF), for storage in the aquifer and later recovery. The District may send the tertiary effluent directly from the WWTP to the reclaimed water users. However, the current operation is to further treat the effluent at the AWTF and then send the UF permeate water to reclaimed water users as needed. The quality of the treated effluent, while consistently meeting all permitted water quality standards, has levels of total dissolved solids (TDS) and salt composition that is not ideal for irrigation of the types of turfs normally associated with golf courses. Figure 1 depicts a system flow diagram for the District, starting with the WWTP treatment through the AWTF. The final effluent can be conveyed to aquifer storage and recovery (ASR) wells, the golf courses, parks, and Fountain Lake. The District desires to evaluate the feasibility of implementing even more advanced treatment, such as reverse osmosis (RO) treatment, at the AWTF. RO treatment can remove the elevated levels of TDS and provide a more desirable water product for irrigation water for the golf courses. However, the brine generated from the RO and the overall salinity balance challenge must be assessed.

3 Figure 1. System Flow Diagram Planning Basis Flow, Demand and Capacity According to the District, the maximum month total demand exceeded 3 million gallons per day (mgd). The feasibility study should be able to handle this design flow and condition. It is prudent to establish a design on a conservation basis, but when the constraints on budget and footprint are pushed, the significance of analyzing monthly flow variations and water quality becomes critical, as explained in the late section. Table 1 presents the monthly flow rates for the AWTF and ASR system as well as the reuse demands for the golf courses and parks for a typical year. These flow rates were used as the planning basis for this study. As indicated by the system flow diagram, all effluent is eventually reused at the golf course and park sites. There are no other means of discharge. All AWTF effluent must be reused to meet the golf course demands or recharged via the ASR wells. The recharged groundwater can also be recovered in summer for golf course irrigation use, when the demand exceeds the AWTF flow. On an annual basis, as

4 summarized on the last row of Table 1, 100% of the AWTF effluent is used up to meet the reuse demand. The annual recharge volume equals the annual recovered volume. Figure 2 shows how the total reuse demand by the reclaimed water users was met each month by a combination of AWTF reuse water and ASR recovered water. In the summer months (April through September), all AWTF product water was directly reused and ASR recovered water supplemented the deficit. It also shows how much AWTF flow was reused versus recharged. In general, more water is available for recharge in winter. But a minimum of 0.3 mgd is recharged even during summer months for UF membrane and ASR well maintenance procedures.

5 Table 1 Planning Basis - Flow Rates AWTF ASR System Total Reuse AWTF AWTF AWTF Total ASR ASR Demand Influent Reuse Recharge (mgd) Injected Recovered (mgd) (mgd) (mgd) (mgd) (mgd) (mgd) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Maximum Month Flow Average Flow Total Annual Volume (MG) Abbreviation: MG = million gallons ~590 ~270 ~310 ~570 ~310 ~310 ~580

6 Figure 2. Monthly Flow Analysis for A Typical Year Effluent Water Quality Table 2 summarizes the water quality for the effluent and the ASR well recovered water. The ASR well recovered water contains TDS levels similar to the AWTF effluent, confirming that the ASR wells are recovering the stored effluent.

7 Table 2 Effluent Water Quality Unit Reclaimed Water ASR Well Recovered Water Monitoring Well #5 Monitoring Well #6 Average Range Average Range Average Range Average Range Temperature F ~ 25.4 ph ~ 7.75 Alkalinity mg/l as ~ ~ ~ 160 CaCO 3 Barium, total µg/l ~ ~ ~ ~ 31 Calcium, total mg/l ~ ~ ~ 31 Chloride mg/l ~ ~ ~ 19 Magnesium, Total mg/l ~ ~ ~ 17 Manganese, Total µg/l ~ Nitrate mg/l as N ~ 5.1 Potassium, Total mg/l ~ ~ ~ 3.7 Silica, total mg/l 14 NA ~ 17 Sodium, total mg/l ~ ~ ~ ~ 31 Sulfate mg/l ~ ~ ~ 17 TDS mg/l 1,200 1,200 ~ 1, ~ ~ ~ 260 1,200 1,500 TKN mg/l ~ 2.2 Nitrite mg/l Total Organic mg/l ~ Carbon Nitrogen, Total mg/l ~ 7.7 Nickel µg/l ~ ~ Fluoride mg/l ~ ~ 0.78 SAR ~ ~ ~ 1.0 Adjusted SAR 5.9~ ~ ~ 1.1 Abbreviations: mg/l = milligrams per liter; CaCO 3 = calcium carbonate; µg/l = micrograms per liter; TKN = total Kjeldahl nitrogen; SAR = sodium absorption ratio

8 Salinity Management Challenges Impact of Elevated Salinity on Golf Courses Golf comprises a significant component to the lifestyle and tourism that are key to the economic wellbeing of the Disctrict. Golf courses are the major users of the District's effluent. Issues associated with the use of high salinity effluent are a serious challenge to the golf courses. Impacts of high salinity water on golf courses are well documented in the Phase I report of the Central Arizona Salinity Study, in Technical Appendix L: Reported Impacts of High Salinity Water on Golf Courses in Central Arizona. This document can be accessed at In summary, the following problems appear wherever high salinity water is used for turf irrigation. TDS High TDS water limits the ability of certain species of grasses to grow and flourish. Salt build-up in the root zone is a prevalent problem. Flushing the salts involves applying more water than normal, dissolving the existing salts in the plant s root zone, and flushing those salts further into the ground. This increases the water usage and reduces the irrigation efficiency. High TDS water stains the facilities. Buildings and cartpaths must be cleaned in order to keep the facility aesthetically pleasing. Moreover, high TDS water creates a shorter useful life for sandtraps and contributes to the clumping and un-playability of sand. Sodium One critical constituent of TDS that requires specific attention is sodium. High sodium causes the soil to disperse, resulting in poor infiltration. Sodium adsorption ratio (SAR) is a measure of the suitability of water for use in agricultural irrigation. The formula for calculating sodium adsorption ratio is as follows: S.A.R. 1 2 Ca Na 2 Mg 2 where sodium, calcium, and magnesium are in milliequivalents/liter (meql/l).

9 If an irrigation water contains relatively high amounts of bicarbonate ion, the bicarbonate can affect the calcium and magnesium concentrations in a soil to which the water is applied. For this reason, alternative ways of adjusted SAR are reported, which often take into account the water's bicarbonate and total salinity besides its calcium, sodium, and magnesium concentrations. It is reported that a water with SAR less than 3 is safe for irrigating turf and other ornamental landscape plants. SAR greater than 9 can cause severe damage to the soil condition. However, SAR is only one of the factors that determine the suitability of water for irrigation. In general, the higher the sodium adsorption ratio, the less suitable the water is for irrigation. Irrigation using water with high SAR may require soil amendments to prevent long-term damage to the soil. If irrigation water with a high SAR is applied to a soil for years, the sodium in the water can displace the calcium and magnesium in the soil. This will cause a decrease in the ability of the soil to form stable aggregates and a loss of soil structure and tilth. This will also lead to a decrease in infiltration and permeability of the soil to water leading to problems with turf production. Nitrate High nitrate levels cause the growing crown of the bent grass greens to thicken and cutting the greens to normal playing height leads to scalping the crown; therefore killing the greens. If the levels of nitrates being delivered by the AWTF reach 10 parts per million (ppm) or greater, serious problems begin to emerge. However, knowing that the District's effluent consistently meets its total nitrogen goal (<10 ppm), this may not be a concern for this study. Salinity Imbalance Attempting to solve the salinity issues at the golf course level without understanding the District's and the region's salinity imbalance is like stopping the sink from overflowing without shutting of the running faucet. Salinity, or TDS, is a measure of the total ionic concentration of dissolved minerals in water. Intuitively, we understand that it is easy to dissolve salt into water, but it is very difficult to remove the salt from water. For instance, boiling the water to retrieve dry salt requires a significant amount of energy. Moreover, as inert ions, most salts cannot be truly removed or destroyed. Essentially all desalinization processes are just redistributing salts between two or more streams, generating a low salinity product water while leaving behind a high salinity brine waste. For an inland community like the District, properly disposing the brine could be very cost prohibitive.

10 As mentioned before, effluent from the District is recharged and recovered in the ASR wells and reused on the golf courses. There are no other means of discharge. As a result, salt is accumulating in the local groundwater over years. The more effluent reused and recharged, the worse the salinity imbalance. This is not a problem just for the District. The Central Arizona Salinity Study (CASS) evaluated the salt balance for Central Arizona by quantifying the amount of salt entering and leaving the study area. Salt comes into the valley in potable drinking water sources from the surface waters of the Salt River and the Central Arizona Project (CAP), as well as additions to wastewater from individual water softening systems. The study concluded that nearly 1.1 million tons of salts remain in the Phoenix metropolitan area each year. The results are very applicable to the District. Details of this analysis can be found at In conclusion, the District itself operates like a salt sink. The salinity imbalance cannot be resolved and will become worse and worse unless measures can be taken to reduce the salt coming into the system or to withdraw the salt from the system. Salinity is a regional issue. The District should actively collaborate with neighboring communities (such as Scottsdale) to leverage the experiences and knowledge accumulated from recently completed studies, testing and design, rather than reinventing the wheel. Treated Water Quality Goal Table 3 presents a recommended list of effluent water quality goals for the District. This list is directly relevant to salinity issues and does not reiterate all the other water quality goals that the AWTF effluent currently meets as a part of the APP permit. Considering the adjacency and similarities between the two communities, the recommended water quality goals for the District are in fact very similar to Scottsdale's salinity management goals. Scottsdale's goals were developed based on years of flow and water quality data, intensive study efforts, expert inputs, and agreements with golf courses. They have been implemented for years. Based on experience learned from the Scottsdale Water Campus through the Subregional Operating Group (SROG) Salinity Research and Concentrate Minimization Demonstration Testing Study (Carollo, 2013), sodium, instead of TDS or any other water quality constituents, is believed to be the most critical issue for the north Scottsdale golf courses. In agreement with the golf courses, Scottsdale has adopted a target sodium water quality goal of 125 mg/l for the product water going to the golf course. To provide a safety margin for the operation staff, an operating target of 110 mg/l sodium is being used currently as the basis for the finished water blending plan.

11 Table 3 Parameter Recommended Effluent Salinity Goal for FHSD Unit Current FHSD Effluent Water Quality Scottsdale Water Campus Water Quality Goal Proposed Reclaimed Water Quality Goal for the District Sodium mg/l ~ (110) (1) 125 Total Dissolved Solids mg/l ~1200 ~1,000 ~1,000 Note: 125 mg/l is Scottsdale's actual sodium concentration goal, as specified in the agreement with the golf courses. 110 mg/l is the operating target that provides a safety margin for operational fluctuation. Compared to the sodium goal, the TDS goal listed above is less critical and for reference only. Although most likely, the treatment required for achieving the sodium goal would also reduce TDS in the same time, innovative technologies that provide selective removal of sodium could be effective in addressing the irrigation problem without meeting a specific TDS goal. For a similar reason, a SAR goal of less than 3 could be adopted but not mandatorily. Viable Treatment Schemes Salinity is a significant regional challenge. RO is feasible to address the high effluent salinity / sodium issue for the golf courses, but would produce a concentrate waste stream representing approximately 15% of the total flow in volume. For an inland community like the District, where concentrate disposal options such as deep well injection, surface water discharge, sewer discharge, and land application are not feasible, concentrate management is the tail that wags the dog for the proposed RO facility. No single silver bullet is available to solve this problem for the District. Leveraging the experience and lessons learned from completed studies and projects, particularly those done in the Phoenix area, it was agreed that there is no need to repeat a detailed screening analysis of all desalinization and concentrate management technologies. The best strategy moving forward is to combine the power of the viable technologies for this region and develop a set of customized solutions for the District. Proven Engineered Alternatives Under this section, three engineered alternatives are being proposed. These alternatives consist of proven technologies, can reliably meet the District's product water quality requirements, meet the District's land restrictions and other boundary conditions, and can be implemented right away without extensive research and development efforts.

12 It is important to note, that a strategy of blending the AWTF UF permeate with the product water of the advanced salinity treatment scheme should be implemented to reduce both the size of the advanced, and costly, systems and the subsequent operating costs, in terms of energy and chemical costs. Blending ratios would change on a monthly or seasonal basis to meet both the water quality goals and water demands. The blending ratio, at maximum demand, is on the order of 40% UF permeate or ASR well recovered water (sodium = 245 mg/l) to 60% desalinization product water (sodium = 6 mg/l) to achieve the final water quality goal of sodium concentration of 125 mg/l. The following two alternatives were evaluated in the first round: Alternative 1- The RO Alternative: AWT Effluent Primary RO + inorganic pretreatment (Lime Softening + Granular Media Filtration) + Secondary RO + Brine Concentrator + Crystallizer Alternative 2 - The Electrodialysis reversal (EDR) Alternative: AWT Effluent Primary EDR + inorganic pretreatment (Ion Exchange Softening) + Secondary EDR + Evaporation Pond A hybrid option was selected for further evaluation and the planning level cost estimates: Alternative 3 - Combined RO and EDR Alternative: AWT Effluent -> Primary RO + organic pretreatment (ozonation + Biological filter) + inorganic pretreatment (Ion Exchange Softening) + Secondary EDR + Brine Concentrator and Crystallizer or a Small Evaporation Pond (< 4 acres) Promising Technologies under Testing This section documents critical information on two innovative technologies, which could very well be part of the solution set for the District's salinity challenge. Compared to the proven engineering solution discussed above, these technologies are either still in the research and development stage or are somewhat proprietary. They have a great potential to resolve the golf courses' irrigation issue and could postpone the need for the engineered solution proposed above. Monovalent Selective Membrane for EDR The first technology uses newly developed monovalent selective ion exchange membranes (sodium selective membrane CR671 and nitrate/chloride selective membrane AR112B by GE Water) using EDR. The technology is designed to preferentially remove monovalent ions such as sodium, potassium and/or chloride, and nitrate from the saline effluent.

13 If used for the District's saline effluent, the monovalent selective membranes are expected to preferentially remove the target monovalent ion (i.e., sodium) at much higher and favorable selectivity compared to RO, nanofiltration (NF), and conventional EDR technologies. Without generating a brine stream with high salt content that is difficult to be disposed of, this technology generates two streams of low or moderate TDS with optimized ion compositions for particular end uses (e.g., one stream with low TDS low sodium and ideal SAR for irrigation, another stream with moderate TDS, high sodium, and relatively low calcium and magnesium, which can be used for lakes on golf courses, wetland creation, etc.). One limitation of this technology may be that the amount of two streams generated may not always match the ideal demands of each stream. A golf course may not have enough demand for the second stream, which has moderate TDS and high sodium. Even if it is difficult to find a practical use for the second stream, the monovalent membrane is still applicable to the District. Instead of treating the effluent, the monovalent selective membrane can also be used to treat primary RO concentrate. In this scenario, the monovalent membrane is being used in lieu of the conventional EDR membrane to enhance sodium rejection. As a result, to achieve the same target sodium goal, less percent of the effluent needs to be treated. The overall project cost would also be lowered. Mineral Polarization Technology Several physical treatment technologies have been studied by Arizona State University as alternatives to ion exchange and water softening. This included capacitive deionization, electrically induced precipitation, template assisted crystallization and electromagnetic water treatment. Most of these technologies have proven to be effective in reducing scaling caused by hardness (calcium, magnesium, etc.). Some, such as the Hydrosmart Electronic Water Conditioning Technology by Customized Water Systems (CWS), claim that their technologies enhance plant growth and remediate soil salinity by acting on charged minerals and polar non-minerals present in water. When salts are hit by a pulsed electrical field, they can break down into an uncoupled charged form. For example, calcium carbonate can break down into calcium and carbonate ions. Sodium and chloride will also be kept uncoupled. Because it takes time for uncoupled salt constituents to reform salts, typically a few days according to CWS, this technology dissociates sodium and chloride, and allows free charges to enter the soil and scavenge out elements of salt that are already in the soil. In this way, the salt washes down to the lower soil layer, so that grass can grow better. More information about how this technology works can be found on the internet (Source: CWS claimed that they have more than 300 installations on golf courses. A list of approximately 50 golf courses is published on their website.

14 Carollo conducted phone interviews of selected golf courses from the list. For Tehama Golf Club, Carmel CA, Mr. Tom Zoller ) gave very positive feedback for this product. According to Mr. Zoller, the Tehama Golf Club uses groundwater from onsite wells plus 15% reclaimed water to irrigate their turf. Due to the high sodium concentration of the groundwater, they experienced severe turf damage, especially on the tee tops and greens. Around 8 to 10 years ago, the golf club installed one unit in an 180,000 gallon holding pond, which provides a retention time around 16 hours and pumped water from the pond to irrigate the turf. They experienced dramatic turnaround in the first year after the installation and the situation improved consistently since then. A summary of the additional interviews and the full list of reference projects are included in Appendix F. Due to the proprietary nature of the technology, and the fact that it is difficult to measure any water quality changes before and after the electromagnetic treatment (i.e., there are no changes in conductivity, TDS, sodium, or calcium concentrations), the most direct and economical approach is to try it out on one golf course and see whether it does improve the turf growth. The unit is relatively inexpensive (less than $30,000), when compared to any of the proposed engineered alternatives. The District should consider collaborating with the golf courses to test it. If proven to provide a cost-effective benefit, there ultimately would be four or five units installed: one at each golf course irrigation pond+. Evaluation of The Selected Alternative As mentioned previously, the following alternative was selected for further evaluation: AWT Effluent Primary RO + Ion Exchange Softening + Secondary EDR + Brine Concentrator + Crystallizer or a Small Evaporation Pond (< 5 acres) One unique challenge about the project was about evaporation pond sizing. Considering that the Town is nearly built-out, the maximum possible size of evaporation ponds was limited to 4 to 5 acres. Knowing the brine concentrator and crystallizer option is still cost prohibitive, it is ideal if the secondary EDR concentrate can be minimized so that 5 acres of pond can handle it without brine concentrator and crystallizer. Several modeling tools were utilized, including RO and EDR projection models and Carollo's Blue Plan-it TM Decision Support System.

15 Primary RO Modeling Based on the estimated effluent water quality presented in Table 2, an RO performance projection was conducted using RO design software IMSDesign (version , IMSdb3 v.43) by Hydranautics. As presented in Appendix A, the projection determined the RO array configuration, elements and vessels, recovery rates, design flux, etc. The projection also provided the anticipated product water quality, operating pressure and chemical requirements. Critical design criteria for the proposed membrane trains are summarized in Table 4. Table 5 presents the projected water quality for product and concentrate. Based on the projection, it is expected that similar to the Scottsdale Water Campus, the primary RO could be designed and operated at 85% recovery. The limiting fouling and scaling factors would be organic fouling, calcium carbonate and calcium phosphate. Silica and barium are not limiting factors, yet, at the 85% recovery. Table 4 Primary RO Performance Projection - Parameters Parameters Values Units Number of Elements per Vessel 7 each per vessel Number of Stages per train 2 each per train Design Recovery 85 % Design Capacity per train (Based on Permeate Flow) 550 gpm Type of Membrane Element ESPA2 - Number of Vessels Design Flux (year 0) Stage 1 16 each Stage 2 8 each Stage 1 12 each Stage 2 12 each

16 Table 5 Primary RO Performance Projection - Projected Water Quality Feed Water (mg/l) Permeate (mg/l) Concentrate (mg/l) Ca Mg Na ,605 K Ba CO HCO ,233 SO ,827 Cl ,712 F NO SiO CO TDS 1, ,645 Secondary EDR Modeling Based on the projected effluent water quality presented in Table 5, an EDR performance projection was conducted using EDR design software WATSYS (version ) by GE Water & Process Technologies. As presented in Appendix A, the projection determined the EDR stack configuration, number of trains, recovery rates, design voltage and amperage, current efficiency, etc. The projection also provided the anticipated product water quality, operating pressure and chemical requirements. Critical design criteria for the proposed membrane trains are summarized in Table 6. Table 7 presents the projected water quality for product and concentrate of the secondary EDR system, assuming an inorganic pretreatment process removed the scale forming ions such as calcium, barium, and magnesium by 90%.

17 Table 6 Parameters Secondary EDR Performance Projection - Parameters Values Type of EDR System Anion Membrane Cation Membrane Spacer Total System Recovery GE L-3S with 6 Line(s) 5 Stage(s) AR204 CR67 Mark IV-2 89% with organic and inorganic pretreatment Table 7 Secondary EDR Performance Projection - Projected Water Quality Feed Water (mg/l) Permeate (mg/l) Concentrate (mg/l) Ca (1) Mg (1) Na K Ba (1) PO4 3- (2) HCO SO Cl F NO SiO CO TDS Blending Analysis Blue Plan-it TM Decision Support System Developed by Carollo, the Blue Plan-it TM Decision Support System assists engineers with feasibility studies, treatment alternative evaluations, facility master plans, and conceptual designs of desalination facilities. Using customized templates for desalination and

18 concentrate management projects, engineers can quickly develop a dynamic design package including a process flow diagram, basis of design criteria, and capital, O&M and life cycle cost estimates. Blue Plan-it TM includes the following functions, which are critical to desalination and concentrate management: Fully customizable process flow diagram using the built-in icon library or a user s own graphics; Perform complex blending analysis to achieve target water quality goals, with simple optimization to minimize costs; Analysis of multiple desalination and concentrate alternatives side by side; Design parameters for wide range of desalination and concentrate management technologies; Import output from RO and antiscalant projection software to improve accuracy; Sizing evaporation ponds and performing annual operation analysis; Planning level cost estimates using reference project costs or Carollo s Unit Cost Database; A customizable dashboard and report modules; Connections with Excel for further data analysis; Animated warnings based on water quality exceedances, unmet demand or capacity deficits; An expandable interface ready for advanced optimization and scenario management features. Steady State Analysis Using Blue Plan-it Decision Support System, Carollo performed a series of blending analyses to develop the basis of design and planning level costs for a proposed desalinization and concentrate treatment facility for the District. This tool was developed to assist engineers with feasibility studies, treatment alternative evaluations, facility master plans, and conceptual designs of desalinization facilities. Using customized templates for desalinization and concentrate management projects, engineers can quickly develop a dynamic design package including a process flow diagram, basis of design criteria, and cost

19 estimates. Figure 3 depicts a screen shot of the mass balance modeling interface. To size the salinity management facility capacity, a steady state analysis for the maximum month condition (June) was conducted using Blue Plan-it. Error! Reference source not found. summarizes the critical inputs and basis used for this analysis. Figure 3. Mass Balance Modeling Using Blue Plan-It

20 Table 8 Blending Analysis Inputs - Maximum Month (June) Steady State Input Parameter Value Units Design AWTF Influent Flow 3.0 mgd Design AWTF Effluent Flow 2.9 mgd Primary RO Recovery 85 % Secondary EDR Recovery 89 % AWTF Effluent Sodium Concentration 245 mg/l ASR Recovered Water Sodium Concentration 230 mg/l Product Water Sodium Goal 125 mg/l Primary RO Product Water Sodium Concentration 5.9 mg/l Secondary EDR Product Water Sodium Concentration 235 mg/l Minimum ASR Recovered Flow 0.3 mgd

21 Table 9 summarizes the results of the maximum month blending analysis. The required size of each desalinization and concentrate management process is presented. Table 9 Blending Analysis Results - Maximum Month (June) Steady State Input Parameter Value Units AWTF Effluent Flow 3 mgd AWTF Effluent for Reuse 2.9 mgd Percent AWTF Reused 100% - ASR Recovery 0.4 mgd ASR Recharge 0 mgd Total Demand 3.2 mgd Percent Bypassed (UF Permeate for Blending) 37% - Primary RO Feed Flow 1.8 mgd Primary RO Permeate Flow 1.5 mgd Primary RO Concentrate Flow / Ozonation and Biological Activated Filter Capacity 0.27 mgd Biological Activated Filter Product Flow / Ion Exchange Capacity 0.26 mgd Ion Exchange Product Flow / Secondary EDR Feed Capacity 0.25 mgd Secondary EDR Concentrate Flow 0.03 mgd 19 gpm The proposed salinity management facility must be sized to handle the maximum month flow conditions established above. If the evaporation pond is sized for the 19 gpm secondary EDR concentrate flow using a steady-state tool, it will require at least 10 acres of evaporation pond. This may lead into an overly conservative design, requiring brine concentrator and crystallizer. Time-Step Analysis However, it is expected that during the other months, especially those winter months, the proposed facility would not be operated at its design capacity. It makes sense to conduct a blending analysis for each month to determine the monthly average concentrate flow and use that in the sizing of the evaporation pond. This could be done manually by repeating the steady state analysis conducted for the maximum month condition twelve times. Using Blue Plan-it TM, Carollo performed a blending analysis to develop the basis of design and planning level costs for a proposed desalination and concentrate treatment facility that produces a product water with a sodium concentration of 110 mg/l or less. Several concentrate management alternatives were evaluated. Blue Plan-it TM model allowed efficient

22 comparison of multiple alternatives. The model successfully handled various design conditions, switching seamlessly between steady state analysis for cost estimate, annual time step analysis for evaporation pond sizing. It also optimizes blending ratios to achieve the target water quality on monthly time step. One unique benefit of using Blue Plan-it model is its ability to handle all complex recirculation streams and its flexibility in handling monthly conditions besides the maximum month steady state condition. This helps to determine the anticipated percent of flow that must be reused and treated for each month, providing a useful operation guide for the District. Table 10 summarizes the results of the monthly blending analysis. As summarized in Table 10, 12 to 100% of the AWTF effluent would be reused, with 0 to 37% treated by RO. This would generate 3.5 to 19 gpm of concentrate from the Secondary EDR process. As discussed in Section 3.4.1, a brine concentrator and crystallizer or a small evaporation pond would be required to further manage this concentrate. Table 11 sizes the evaporation pond required based on rainfall and evapotranspiration rates for the area. Instead of sizing the pond based on the maximum month concentrate flow, which is overly conservative, this approach assesses the inflow (concentrate flow and rainfall) and outflow (evaporation) in a whole year's operation cycle. As a result, it concluded that a pond around 5 acres is sufficient to handle the secondary EDR brine, which means the brine concentrator and crystallizer could be avoided. Additional Comparison Basis of design, footprint analysis, and planning level capital, O&M and life cycle costs are also conducted as part of the study. They are presented elsewhere in details. Figure 4 below presents a cost comparison to illustrate the different results in the evaporation pond sizing methodology. As presented above, when steady state pond sizing option was used to size the facility capacity based on the maximum month flow, the proposed train of Primary RO + Ozonation + Biological Filtration + Ion Exchange + Secondary EDR would result in a final concentrate flow of 19 gpm, requiring more than 10 acres of evaporation pond. Due to the land restriction, this train must be followed by Brine Concentrator and Crystallizer. The total capital costs for this alternative is $22.3 M. The estimated footprint of the facility: 3 acres, including 2 acres of emergency storage pond. When a time based facility sizing methodology was used, considering the monthly average flow, the proposed train of Primary RO + Ozonation + Biological Filtration + Ion Exchange + Secondary EDR would require < 5 acres of evaporation ponds, therefore avoid the brine

23 concentrator and crystallizer. The total capital costs for this alternative is $15.2 M. Estimated footprint of the facility is around 6 acres, including 5 acres of evaporation pond Capital Costs ($M) Steady State Pond Sizing (Brine Concentrator and Cyrstallizer) Time Step Pond Sizing (<5 acres ponds) Figure 4. Comparison of Capital Costs between Pond Sizing Methods

24 Table 10 Blending Analysis Results - Monthly AWTF Effluent ASR Recovered AWTF Reuse Percentage of AWTF Reused AWTF Recharge Percent Bypass RO Influent Ozone BAF Influent Ion Exchange Influent 2nd EDR Influent Final Concentrate Flow Total Reuse Demand Total Product Water Product Water Sodium Product Water TDS mgd mgd mgd % mgd % mgd mgd mgd mgd gpm mgd mgd mgd mg/l mg/l Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

25 Table Acre Evaporation Pond Analysis by Month Average Rainfall (inches) (1) Average Evapotranspiration (inches) (1) Average Temperature ( F) (1) Days Concentration or Inflow (gpm) Concentration Factor (2) Inflow (inches per month) (3) Level (inches) Level Change (inches) January February March April May June July August September October November December TOTAL Notes: (1) Based on 2005 to 2015 Arizona meteorological network data - Desert Bridge (2) Evaporation decreases exponentially with increasing salinity (Leaney & Christen, 2000) (3) Based on 4.5 acres of pond.

26 Conclusions This project produced a feasibility study for the District to address its reclaimed water salinity challenge using RO and associated concentrate treatment technologies. Besides presenting the planning basis, evaluated alternatives, modeling results, the case study presented here in demonstrated that the advantage of sizing the treatment facility capacity requirements using a time-step methodology compared to a steady state methodology using maximum month design criteria. It is more accurate, avoiding an overly conservative design, resulting in practical and more economic solutions for the District. References Central Arizona Salinity Study, in Technical Appendix L: Reported Impacts of High Salinity Water on Golf Courses in Central Arizona. Subregional Operating Group (SROG) Salinity Research and Concentrate Minimization Demonstration Testing Study (Carollo, 2013)