RO  Concentrate  Treatment  &  Recovery  Pilot  Study  Project  Report  

June  20,  2012  

Prepared  for    

Chino  Basin  Desalter  Authority  Western  Municipal  Water  District  

City  of  Ontario  Jurupa  Community  Services  District  

SECTION  1.0  –    INTRODUCTION  

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1.1 – PROJECT BACKGROUND The Chino II Desalter is a groundwater treatment facility located in Jurupa Valley, California, with a combined ion exchange (IX) and reverse osmosis (RO) treatment capacity of 20.5 million gallons per day (MGD). The facility is one of two plants managed and operated by the Chino Basin Desalter Authority (CDA). Both IX and RO treatment trains are used to treat brackish groundwater from eight wells that also have elevated nitrate concentrations. A 6.5-MGD expansion of the Chino II RO treatment capacity has been constructed. However, due in part to the high cost of waste brine disposal, the CDA is evaluating means of maximizing the efficiency of the RO treatment system to reduce brine disposal costs and increase permeate production. RO process efficiency is typically limited by the concentration factors that can be applied before specific minerals present in the raw water begin to precipitate on the concentrate side of the membranes. With the current mineral content of the groundwater treated at the Chino II RO facilities, the RO recovery is approximately 82%. The remaining 18% is discharged into the Inland Empire Brine Line (IEBL) as RO concentrate. The concentrate reduction strategy being evaluated involves the use of precipitative softening to remove the limiting foulants from the RO concentrate, primarily calcium and silica, followed by treatment of the softened water through a secondary RO (SRO) process and blending its permeate with the permeate of the primary RO process. A schematic of the initial configuration of the overall treatment train is shown in Figure 1-1. A filtration step is needed downstream of the precipitative softening process to provide particulate removal upstream of SRO. Treated water (SRO permeate) from the brine concentrate reduction facilities would be blended with the primary RO (PRO) permeate. The SRO concentrate would be disposed into the IEBL. Using this system may allow the total water recovery from the RO system to increase from 82% to as high as 95%, substantially reducing the volume of brine disposed into the IEBL while increasing permeate production.

Figure 1-1: Initial Brine Concentrate Reduction Strategy Using Pellet Softening and Secondary RO

The precipitative softening technology being considered for PRO concentrate treatment is the pellet softening process. The pellet softening process consists of an upflow reactor with a granular material added at the bottom of the reactor to act as the seed onto which calcium carbonate (CaCO3), silica (SiO2), and other minerals precipitate. Fine sand is commonly used as the seed material, but other seed material can also be used. Figure 1-2 is a schematic diagram of the upflow pellet softening process. Caustic soda (NaOH) and/or lime (Ca(OH)2) with or without soda ash (Na2CO3) are added to the feed

SECTION 1 – INTRODUCTION RO CONCENTRATE TREATMENT & RECOVERY PILOT STUDY

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water to increase pH and promote precipitation. As precipitates build up on the seed material, the small granules grow to larger “pellets”. The pellets eventually reach a size that can no longer remain fluidized. Large pellets sink to the bottom of the vessel and are removed from the vessel at a specified frequency.

Figure 1-2: Pellet Softening Schematic The pellet softening process generates hard and durable pellets that are readily dewatered and easy to handle and transport compared to the thick, heavy, wet sludge produced by a conventional softening process. After its planned expansion, the Chino II Desalter facilities had been forecast to generate up to 38 tons of dry pellets each day. The produced pellets may be a value-added product that can be utilized in a variety of industrial applications, thus converting a waste stream of a water treatment process into a usable commodity. The Pellet Market Survey1 conducted by Western Municipal Water District prior to this project determined that the pellets produced by the pellet softening process have a commercial value to a number of industries. In advance of the design of the concentrate treatment and recovery facility, pilot-scale testing of the planned treatment train was conducted at the Chino II Desalter facilities between March 2011 and March 2012. This report describes the specifics of the pilot testing program, presents and discusses the testing results, and makes recommendations for the design and operation of a full-scale facility. 1.2 – PILOT TESTING OBJECTIVES The objectives of the pilot-scale testing project were as follows:

1. To determine whether the planned treatment process train could achieve the treated water goals or if modifications need to be made to it.

2. To develop design and operational data and information for the full-scale facility

3. To confirm or revise the capital and operations and maintenance (O&M) costs associated with the implementation of the concentrate treatment facility at the Chino II Desalter

1 Market Survey for the Softening Pellets to be Generated at the Chino II Desalter, Report prepared for the Western

Municipal Water District, City of Ontario, Jurupa Community Services District and Chino Basin Desalter Authority, 10/15/2010.

SECTION 1 – INTRODUCTION RO CONCENTRATE TREATMENT & RECOVERY PILOT STUDY

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1.3 – PILOT STUDY OVERVIEW The pilot study was performed in two phases. Phase 1 was conducted between June and November 2011. During Phase 1, the originally planned treatment train of softening filtration SRO was evaluated. As discussed in this report, this treatment train failed to meet the water quality and operational goals because of the inability of the filtration process to handle the large amount of turbidity generated by the pellet softening process. The project was then modified by adding Phase 2 activities, which were conducted from January through March 2012. During Phase 2, the treatment train was modified to include a clarification step between the softening and filtration processes. Phase 2 testing was conducted as a combination of pilot-scale softening, coupled with bench-scale clarification and filtration. SRO process performance was not tested in Phase 2. Instead, process modeling was conducted to quantify water recovery and process performance. Each phase of the study is described in more detail below. 1.3.1 – Phase 1: SofteningFiltrationSRO Phase 1 testing began in early June 2011 with operation of the pellet softener using PRO concentrate from the full-scale Chino II Desalter facilities as the pilot plant feedwater. Figure 1-3 shows a schematic of the treatment train as originally planned, which included pellet softening, media filtration, and secondary RO. This process train was defined in the Predesign Report (PDR) for the Chino II Desalter Phase 3 Expansion2. The design criteria for the treatment train were based on the results of Western Municipal Water District’s Arlington Desalter RO Concentrate Treatment Pilot Study3. The pilot-scale pellet softener was operated using caustic soda and a combination of caustic soda and lime. Granular media filtration was operated downstream of the pellet softener to provide solids removal upstream of the SRO process. However, media filtration could not meet the study goals for water quality and water production for the SRO using the pellet softener effluent. The media filtration process was then replaced with ultrafiltration (UF) membranes. However, extensive testing of the UF pilot system showed that the UF system also could not be operated to meet the study goals with the pellet softener effluent.

Figure 1-3: Original Phase 1 Process Train From the start of the study, it was understood that silica and calcium were the main foulants in the primary RO concentrate. In fact, silica is the controlling foulant that currently limits the maximum recovery of the PRO system at the Chino II Desalter facilities. The reason is that the maximum allowable silica recommended by the suppliers of scale inhibitor chemical in a concentrate stream from an RO process

2 Revised Final Report for Chino Desalter Phase 3 Comprehensive Predesign, prepared for Jurupa Community

Services District, City of Ontario, and Western Municipal Water District, December 2010. 3 Final Report for the RO Concentrate Treatment Pilot Study, prepared for Western Municipal Water District, January

2009.

SECTION 1 – INTRODUCTION RO CONCENTRATE TREATMENT & RECOVERY PILOT STUDY

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with pH <9.5 is approximately 200 mg/L, above which severe fouling of the RO membranes begins to take place. The silica concentration in the PRO concentrate is between 180 and 190 mg/L. This is a six-fold concentration increase from the raw groundwater silica level of approximately 30 mg/L. The primary goal of the softening process is to reduce the concentration of calcium and silica from the primary RO concentrate to allow for approximately 66% water recovery through the SRO process. With the planned operation of the SRO process at an elevated pH of approximately 9.5, achieving 66% recovery through the process would require that the silica concentration in the influent water to the secondary RO process not exceed 80 mg/L as SiO2. Therefore, the combined treatment process train of pellet softening and filtration needed to reduce the silica concentration from approximately 180 mg/L in the primary RO concentrate to less than 80 mg/L. At the same time, sufficient calcium must be removed from the PRO concentrate to allow operation of the SRO at a pH of 9.5 or greater without fouling from calcium carbonate precipitation. 1.3.2 – Phase 2: SofteningClarificationFiltrationSRO As presented later in this report, the Phase 1 treatment train of softeningfiltrationSRO could not meet the water quality and performance goals. The reason was that the removal of silica to the goal of <80 mg/L required that the pellet softener be operated at a pH between 11 and 12. In that pH range, the pellet softener effluent contained turbidity in excess of several hundred NTUs, which could not then be adequately removed by the filtration process. Therefore, Phase 2 testing focused on evaluating the use of a clarification process between the softening and filtration processes to remove the majority of the suspended material before the water is treated with filtration. A schematic diagram of the modified treatment train is shown in Figure 1-4.

Figure 1-4: Modified Treatment Process Train Showing Clarification Phase 2 included both bench- and pilot-scale testing to develop information necessary for the design of the clarifier. The only process that was operated at the pilot scale in Phase 2 was the pellet softener in order to collect softened water for bench-scale testing. Bench-scale testing was then used to evaluate the settleability of the solids in the softener effluent, as well as the filterability of the settled water. Additional information developed in Phase 2 included optimum softening chemical dosages and coagulant dose into the clarifier. The SRO process was not pilot-tested during Phase 2.