Sustainable Low-Pressure Reverse Osmosis Concentrate Management: Eight Years and Counting

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1 emerging issues/reuse CO LIN H O B B S, JO RGE A RE VA L O, D AV I D P R AH, J O H N N O BL E, D AV I D P O N I T Z, AN D S AM BU T LER Sustainable Low-Pressure Reverse Osmosis Management: Eight s and Counting A SUSTAINABLE METHOD FOR CONCENTRATE MANAGEMENT IS HELPING THE CITY OF ORMOND BEACH, FLA., SUCCESSFULLY TRANSFORM AN UNDESIRABLE BY-PRODUCT INTO A VALUABLE RESOURCE. 38 T he management and disposal of concentrate is often considered the most significant obstacle to implementing membrane technology. When faced with the need to manage and dispose of up to 1.0 mgd of concentrate generated from a new, 4.0-mgd, low-pressure reverse osmosis (LPRO) expansion of its water treatment plant (WTP), the City of Ormond Beach, Fla., rejected traditional strategies and embarked on a mission to implement an innovative and sustainable method of concentrate management. This article discusses the eight years of operating data collected at the Ormond Beach WTP and waste water treatment plant (WWTP) following the commissioning of the 4.0-mgd LPRO expansion and the implementation of this concentrate management strategy. Specific discussion in this article addresses the topics of water quantity and quality, benefits realized, operational challenges faced and overcome, and recommendations for similar projects in the future. NOVEMBER 2016 JOURNAL AWWA 108:11 HOBBS ET AL.

2 BACKGROUND During the late 1990s and early 2000s, population increases in Ormond Beach placed increased demands on the existing 8.0-mgd lime softening WTP. Although the need to expand the WTP was irrefutable, the gradual deterioration of the city s groundwater supplies precluded the use of supplemental lime softening units to satisfy increasing demands. The city elected to expand its WTP through the addition of four 1.0-mgd LPRO units to improve the reliability of the WTP, to extend the longevity of the existing lime softening treatment process, and to ensure that the WTP would provide high-quality potable water as the quality of the raw water supplies deteriorates. Given its desire to construct a 4.0-mgd LPRO expansion for its WTP, Ormond Beach was faced with the challenge of managing and disposing of up to 1.0 mgd of concentrate. In response, the city evaluated numerous concentrate management strategies, including discharge to a surface water body, injection into a deep well, and discharge to the city s WWTP an advanced domestic wastewater treatment facility and the sole source of water for the city s public-access reclaimed water system. With assistance from CDM Smith, Ormond Beach selected, permitted, and implemented an innovative and sustainable method of concentrate management that consisted of blending the concentrate with treated wastewater in the effluent equalization basin of the WWTP. IMPACT OF CONCENTRATE BLENDING ON THE RECLAIMED WATER SYSTEM was first introduced into the effluent equalization basin in January 2008 when the LPRO expansion was commissioned. When the LPRO expansion is operated at its design recovery rate of 85%, 0.18 mil gal of concentrate is produced for every 1.0 mil gal of permeate produced. To satisfy potable water demands and maintain desired finished water quality, Ormond Beach typically has produced between 1.0 and 3.0 mgd of permeate on a continual basis since the commissioning of the WTP expansion. Historical operating data from January 2008 through December 2015 indicate that an average of 0.36 mgd of concentrate was generated during this eight-year operating period., treated wastewater, and reclaimed water flow and water quality data for this period are summarized in Table 1. Reclaimed water quality. As indicated in Table 1, blending concentrate with treated wastewater affected the quality of reclaimed water supplies; however, the impact was nominal and the suitability of the reclaimed water supplies for its intended purposes (i.e., irrigation) was not compromised. Specific parameters to ensure that the reclaimed water supplies were of suitable quality included total dissolved solids, sodium and the sodium adsorption ratio (SAR), and chloride. TABLE 1 Total dissolved solids. The total dissolved solids concentration of the reclaimed water averaged 743 mg/l during the first eight years of operation. This represents a 34% increase over the average treated wastewater concentration of 555 mg/l during the same period. While both of these values exceeded the US Environmental Protection Agency s Secondary Drinking Water Standard of 500 mg/l, they were well below the maximum background groundwater total dissolved solids concentration of 1,400 mg/l (USEPA 2016), which supersedes the Secondary Drinking Water Standard per Chapter (2) of the Florida Administrative Code. Furthermore, the total dissolved solids concentration of the reclaimed water represents a fraction of the 50% yieldreduction values for common turf grasses found within the city s reclaimed water service area (Table 2). Sodium and SAR. During the first eight years of operation, the sodium concentration of the reclaimed water averaged 139 mg/l, a 9% increase over the average treated wastewater concentration (127 mg/l) for the Average concentrate, treated wastewater, and reclaimed water flow and water quality Parameter Average Average Treated Wastewater Reclaimed Water Flow mgd Barium mg/l Sodium mg/l Chloride mg/l Fluoride mg/l Sulfate mg/l Total dissolved solids mg/l 2, ph Radium pci/l Sodium adsorption ratio 3.4 NA 3.4 Source: Data provided by the City of Ormond Beach, Fla. NA not applicable Flow value for concentrate, treated wastewater, and reclaimed water represents the average flow for the referenced process stream from January 2008 through December Water quality values for the concentrate, treated wastewater, and reclaimed water represent the average of values obtained from the 2008 through 2015 reclaimed water or effluent analysis reports for the referenced process stream. HOBBS ET AL. 108:11 JOURNAL AWWA NOVEMBER

3 same period. This value is below the Florida Primary Drinking Water Standard of 160 mg/l. Furthermore, the SAR of the reclaimed water averaged 3.4 during the first eight years of operation, which indicates that the deterioration of the soil structure due to sodium adsorption is unlikely (Unurh & Elliott 1999). Chloride. The chloride concentration of the reclaimed water averaged 203 mg/l during the first TABLE 2 Reclaimed-Water Customer a Residential customers Oceanside Golf Course Tomoka Oaks Golf Course Nova Recreational Complex Volusia Memorial Cemetery eight years of operation. Although this represents an 8% increase over the average treated wastewater concentration of 188 mg/l during the same period, this value is below the Florida Secondary Drinking Water Standard of 250 mg/l and well below 400 mg/l, the chloride limit identified by Project Greenleaf that may result in damage to salt-sensitive ornamental plants (Parnell 1987). Salt tolerance of various turf grasses within the reclaimed water service area Major Vegetation a Various turf grasses Bermuda grass and rye grass Bermuda grass and rye grass Various turf grasses St. Augustine grass and Bermuda grass Salt Tolerance b Total Dissolved Solids Concentration at 50% Yield Reduction mg/l b Fair to excellent 6,000 24,000 Good to excellent 8,000 18,000 Good to excellent 8,000 18,000 Fair to excellent 6,000 24,000 Excellent 15,000 18,000 a Reclaimed water customer and major vegetation data obtained from FDEP Permit Number FL b Salt tolerance and total dissolved solids concentration data obtained from Unurh & Elliott TABLE 3 Reclaimed water supply and use Treated Wastewater Annual Average Day Flow mgd Total Available Reclaimed Water Supply Reclaimed Water Use NA NA NA Source: Data provided by the City of Ormond Beach, Fla. NA not applicable Reclaimed water supply and use. Before commissioning the LPRO expansion in 2008, treated wastewater from the WWTP was the sole source of reclaimed water for Ormond Beach. During the threeyear period that preceded the startup of the LPRO expansion (2005 through 2007), influent wastewater flows to the city s WWTP ranged from 3.87 to 4.51 mgd on an annual average-day basis. Assuming negligible water losses through the WWTP, the treated wastewater flow, and therefore the total available reclaimed water supply, was equal to the influent wastewater flow during this time. Upon the completion of the LPRO expansion, two sources of water contributed to the reclaimed water supply treated wastewater and concentrate from the LPRO process. In the eight years following the commissioning of the LPRO expansion, the treated wastewater flow ranged from 3.84 to 4.73 mgd, and the concentrate flow ranged from 0.24 to 0.42 mgd, which resulted in a total available re claimed water supply between 4.08 and 5.02 mgd, all on annual average-day bases. Customer use of reclaimed water was evaluated in a similar manner. From 2005 through 2007, reclaimed water use on an annual average-day basis ranged from 1.25 to 1.99 mgd. Following the construction of the LPRO expansion, average annual customer use of reclaimed water ranged from a minimum of 1.82 mgd in 2008 to a maximum of 3.43 mgd in Annual average-day flows for treated wastewater, concentrate, total available reclaimed water supply, and reclaimed water use are summarized in Table 3. Monthly flows for each of these streams are presented graphically in Figure 1. The benefit of implementing this concentrate management strategy is evident from the perspective of total available reclaimed water supply; however, the benefit is not as apparent from the perspective of re - claimed water use because the 40 NOVEMBER 2016 JOURNAL AWWA 108:11 HOBBS ET AL.

4 treated wastewater flow always exceeded the reclaimed water use on an annual average-day basis. As such, a more rigorous analysis of the data was performed. This analysis focused on daily reclaimed water use as a percentage of the treated wastewater flow, as well as the flow and percentage of the concentrate reclaimed and reused for irrigation. Reclaimed water use exceeds treated wastewater supply. To demonstrate the benefit this concentrate management strategy had on reclaimed water use, the percentage of reclaimed water used with respect to treated wastewater supply was calculated on a daily basis. These percentages were used to determine if and how frequently the demand for reclaimed water equaled or exceeded the treated wastewater supply. For the three-year period that preceded the commissioning of the LPRO expansion ( ), percentages equal to 100% suggest that reclaimed-water customers would have consumed more reclaimed water had additional supplies been available and that some of the reclaimedwater customers, most likely residential, may have used potable water supplies to supplement their irrigation needs. For the period that followed the commissioning of the LPRO expansion ( ), percentages greater than or equal to 100% suggest that some reclaimed water customers, most likely residential, may have used potable water supplies to supplement their irrigation needs had concentrate not been available to augment treated wastewater supplies. The number of days in which reclaimed water use percentages equaled or exceeded 100% of the treated wastewater supplies is summarized in Table 4. In the three-year period that preceded the commissioning of the LPRO expansion, the reclaimed water use equaled the treated wastewater supply on a total of 46 days. In the eight-year period that followed the commissioning of the LPRO expansion, the reclaimed FIGURE 1 Flow mgd Monthly reclaimed water supply and use Total available reclaimed water supply Treated wastewater Total reclaimed water use Low-pressure reverse osmosis expansion was placed into service in TABLE 4 Reclaimed water use meeting or exceeding 100% of treated wastewater supplies Number of Days When Reclaimed Water Use Equaled or Exceeded Treated Wastewater Supply Average Process Streamflow When Reclaimed Water Use Equaled or Exceeded Treated Wastewater Supply mgd Treated Wastewater Total Reclaimed Water NA NA NA NA NA Source: Data provided by the City of Ormond Beach, Fla. NA not applicable HOBBS ET AL. 108:11 JOURNAL AWWA NOVEMBER

5 water use equaled or exceeded the treated wastewater supply on a total of 684 days. While the number of days during which the reclaimed water use equaled or exceeded the treated wastewater supply is somewhat arbitrary (primarily due to this parameter s dependence on the weather), the fact remains that during each of these 684 days, customers demanded more reclaimed water than was available from treated wastewater supplies and these demands were met in part by concentrate. Furthermore, this rigorous analysis revealed that 100% of the concentrate was reclaimed and reused for irrigation on 849 out of 2,922 days (approximately 29%) following the commissioning of the LPRO expansion. reuse. flow generated by the LPRO expansion averaged 0.36 mgd during its eight-year operating history. During this time, the concentrate increased Ormond Beach s total available reclaimed water supplies by more than 1 bil gal. Of this volume, approximately 650 mil gal (62%) has been reused for irrigation purposes. OPERATIONAL CHALLENGES AND SOLUTIONS During the past eight years of operation, several noteworthy operational challenges were encountered and successfully overcome, as described. Nutrients. The anti-scalant product used to prevent the precipitation of sparingly soluble salts within the LPRO process contained low concentrations of both nitrogen- and phosphorus-containing compounds. These compounds are concentrated through the LPRO process and are ultimately removed from the system via the concentrate stream. Because the point at which the concentrate entered the WWTP was downstream of all wastewater treatment This analysis focused on daily reclaimed water use as a percentage of the treated wastewater flow, as well as the flow and percentage of the concentrate reclaimed and reused for irrigation. processes (i.e., the effluent equalization basin), increased concentrations of nitrogen and phosphorus were initially observed in reclaimed water samples. Although the increase in nitrogen concentrations did not present any concerns with regulatory compliance, the increase in phosphorus concentrations resulted in exceeding the permitted phosphorus limit on several occasions. As a result, operators increased the dosage of alum to chemically precipitate and remove more phosphorus in the wastewater treatment process (i.e., prior to concentrate blending) to ensure compliance with permit requirements. Blending ratio and concentrate piping. generated by the LPRO process was originally piped directly to the effluent equalization basin at the WWTP. To maintain compliance with the permitted treated wastewater-to-concentrate blending ratio, it was necessary to limit the production of the LPRO expansion during late night and early morning hours when flows through the WWTP were reduced. This operational limitation was successfully overcome through a minor modification of the concentrate piping and WWTP operational procedures. By installing one tee, two valves, and approximately 150 ft of piping, significant flexibility was added to the operations. This new piping configuration allowed the City of Ormond Beach to comply with the permitted treated wastewater/concentrate blending ratio during periods of reduced wastewater flow by either limiting the production rate of the LPRO expansion or by diverting the concentrate directly to the surface water outfall. Despite the fact that the new piping configuration provided Ormond Beach with additional operational flexibility, the city sought to further enhance and optimize operations. Supported by years of successful operating data, the Florida Department of Environmental Protection allowed the city to install a new 750-ft segment of concentrate piping to redirect the concentrate from the WWTP to the reclaimed water storage tank. While the city preserved the ability to discharge the concentrate to the effluent equalization basin and the surface water outfall, discharging the concentrate to the reclaimed water storage tank is the current standard operating procedure. Since the implementation of this new procedure in October 2014, 99% of the concentrate generated from the LPRO expansion was reused for irrigation purposes (165.8 out of mil gal). LOOKING AHEAD A significant increase in customer demand for reclaimed water supplies in the City of Ormond Beach has been observed over the past 11 years. In 2005, the annual average-day demand for these supplies was 1.25 mgd. During the ensuing 11-year period, this demand increased more than 270% to 3.43 mgd in A simple linear regression of the monthly reclaimed water demand data indicated that demands generally increased at a rate of 0.2 mgd annually. A similar evaluation of treated wastewater supplies revealed that wastewater flows remained relatively constant from 2005 through Due to the significant discrepancy between the rates at which these two parameters changed, customer demands were projected to exhaust reclaimed water 42 NOVEMBER 2016 JOURNAL AWWA 108:11 HOBBS ET AL.

6 supplies by 2019 if treated wastewater had remained the sole source of reclaimed water (Figure 2). Following the completion of the LPRO expansion, the reclaimed water supply comprised two sources of water treated wastewater and concentrate. A linear regression of the monthly data for reclaimed water supplies (i.e., treated wastewater flow plus concentrate flow) indicated that the total available reclaimed water supplies generally increased at a rate of 0.03 mgd/year during the past eight years. Although the increase in reclaimed water demands exceeded the increase in reclaimed water supplies, the concentrate-augmented reclaimed water supplies were projected to satisfy demands through 2022, three years longer than treated wastewater supplies alone. These projected time frames do not account for future projects that may affect the city s existing potable water, wastewater, or reclaimed water service areas or the effects of continued efforts to promote public awareness of reclaimed water supplies, efficient use of all water supplies, and conservation of limited resources. SUMMARY Operation of the WTP and WWTP in Ormond Beach over the past eight years has demonstrated that a traditionally undesirable byproduct of the LPRO treatment process can be successfully transformed into a valuable resource. Since the LPRO expansion was commissioned in 2008, the City of Ormond Beach increased the total available reclaimed water supplies by more than 1 bil gal by blending concentrate with the treated wastewater and reused approximately 650 mil gal of concentrate for irrigation. In addition to the environmental benefits realized from the implementation of this innovative and sustainable concentrate management strategy, the city avoided significant capital expenditures FIGURE 2 Flow mgd Monthly projected reclaimed water supply and use Total available reclaimed water supply Treated wastewater Total reclaimed water use In 2019, demands are projected to exceed reclaimed water supplies (first black line). By placing the low-pressure reverse osmosis expansion into service for concentrate management, projected customer demands for reclaimed water supplies will be met for an additional three years (second black line). associated with the implementation of alternative concentrate management strategies. ABOUT THE AUTHORS Colin Hobbs (to whom correspondence may be addressed) is a senior environmental engineer with CDM Smith, 2301 Maitland Center Pkwy., Ste. 300, Maitland, FL USA; hobbscm@cdmsmith. com. He specializes in the application of membrane processes for the treatment of potable and nonpotable supplies. He has more than 15 years of experience in the consulting engineering industry, as well as extensive experience with domestic and international membrane projects. Hobbs work has ranged from bench-top/pilot studies to conceptual/feasibility analyses to the final design, construction, startup, and operation of full-scale facilities. Jorge Arevalo is a senior environmental engineer and David Prah is a senior environmental engineer, both with CDM Smith in Maitland, Fla. John Noble is city engineer, David Ponitz is utilities manager, and Sam Butler is chief treatment plant operator, all for the City of Ormond Beach, Fla. REFERENCES Parnell, J.R., Project Greenleaf Executive Summary. St. Petersburg, Fla. Unurh, J.B. & Elliott, M.L. (editors), 1999 (2nd ed.). Best Management Practices for Florida Golf Courses. University of Florida Institute of Food and Agricultural Sciences, Gainesville, Fla. USEPA (US Environmental Protection Agency), Secondary Drinking Water Standards: Guidance for Nuisance Chemicals. www. epa.gov/dwstandardsregulations/ secondary-drinking-water-standardsguidance-nuisance-chemicals (accessed Aug. 22, 2016). HOBBS ET AL. 108:11 JOURNAL AWWA NOVEMBER