PRESSURIZED ULTRAFILTRATION MEMBRANE PERFORMANCE AT THE VENTURA, CALIFORNIA DEMONSTRATION PLANT. Abstract

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1 PRESSURIZED ULTRAFILTRATION MEMBRANE PERFORMANCE AT THE VENTURA, CALIFORNIA DEMONSTRATION PLANT Susan Guibert, Author, Toray Membrane USA Inc Danielson Street Poway, CA Ph: (289) Sean Carter, Presenter, Toray Membrane USA Inc Danielson Street Poway, CA 92064, Ph: (858) Gina Dorrington, Ventura Water, Ventura, CA John WiIIis, Ventura Water, Ventura, CA Andrew Salveson, Carollo Engineers, Walnut Creek, CA Elisa Garvey, Carollo Engineers, Walnut Creek, CA Justin Sutherland, Carollo Engineers, Austin, TX Curt Elwell, Toray Membrane USA, Poway, CA Abstract Severe drought over the last five years in have forced municipalities to search for alternate sustainable sources of potable water. In January 2014, Governor Brown declared a drought state of emergency and directed state agencies to take all necessary actions to respond to drought conditions. Part of the series of actions were to invest in new technologies that will make more drought resilient. Numerous pilot studies have emerged where municipal wastewater is converted to potable water using a multi-barrier approach including hollow fiber Ultrafiltration (UF), Reverse Osmosis (RO) and an Advanced Oxidation Process (AOP) for Direct or Indirect Potable Reuse (DPR / IPR) future applications. DPR plants would send the final treated water directly into a drinking water distribution system, whereas IPR plants would send the final treated water to an aquifer or surface water source for a period of time before being treated by a separate Public Water System (PWS). In addition to the pilot studies, several demonstration and full-scale plants have also been built in recent years based on the knowledge gained from pilot studies. Ultrafiltration is one of the main unit operations in these DPR/IPR systems. This paper will specifically discuss detailed operations of the Ventura UF pilot unit in Ventura,. Understanding the operating parameters and design options available of the UF system in these plants will assist Utilities in their choice of membrane products for planning an advanced water purification facility. 1

2 Introduction In the search for new safe sources of drinking water, significant effort has been focused on Direct and Indirect Potable Reuse (IPR/DPR) of municipal wastewater. Pioneers in this field include Orange County and West Basin, both in. West Basin currently treats over 40 million gallons per day (mgd) of municipal secondary effluent and produces five different recycled water qualities. Orange County Water Districts Groundwater Replenishment System (GWRS) currently treats 100 mgd of secondary effluent for groundwater recharge and maintenance of a seawater intrusion barrier. Both Orange County and West Basin utilize low pressure Microfiltration (MF) / Ultrafiltration (UF) hollow fiber membranes followed by Reverse Osmosis (RO) and then an Advanced Oxidation Process (AOP) in their IPR plants. The UF membrane with a pore size of 0.01 micron can treat secondary or tertiary effluent from a conventional wastewater treatment plant and remove turbidity, bacteria and in combination with disinfection a high log removal of viruses. The UF product water can be further treated with Reverse Osmosis for dissolved solids removal and then finally UV or an Advanced Oxidation Process (AOP) to further treat the RO permeate. The prolonged drought in has opened the door to additional pilot studies and full-scale opportunities in treating secondary and tertiary municipal effluent for IPR as well as DPR projects. New advances in hollow fiber UF systems such as non-proprietary system integrators as well as Flexible /Universal racks and systems have greatly improved the choices available to utilities and end-users. Understanding the operating parameters and design options available of the UF system in these plants will assist Utilities in their choice of membrane products for planning an advanced water purification facility. Recent IPR/DPR Pilot Studies and Full-Scale Plants In 2011 the San Diego North City Demonstration Plant was commissioned. The process flow included one train of UF, one train of MF followed by RO then an AOP. The City chose two different MF/UF membrane manufacturers to treat the tertiary municipal effluent. Toray (UF) TIPS and Asahi (MF) TIPS were the selected membranes. An open-source supplier (H2O Innovation) and a proprietary supplier (Pall) were selected to build the two demonstration trains. Since Pall and Asahi have an exclusive agreement to work together their offering is described as proprietary. Whereas H2O Innovation and Toray are free to work with other membrane manufacturers and other OEM s, so their offering is described at non-proprietary or open source. The non-proprietary / open source arrangement is similar to the current RO market. Since the North City demonstration plant went on-line, several IPR/DPR pilot studies utilizing hollow fiber Ultrafiltration (UF) have been conducted. As previously mentioned, West Basin 2

3 and Orange County have been treating wastewater for several years using membrane technology and were pioneers in the field. They too are conducting further studies with the latest UF membrane products to expand and upgrade their plants. A partial list of these studies are described below: Table 1 IPR/DPR Pilot Studies Project Name Location UF Feed Source and Pretreatment Date of Study Monterey Secondary effluent treated with chloramines and ozone Nov to July 2014 Ventura Secondary effluent followed by sand filters and chloramine addition also piloted pasteurization system July 2015 April 2016 Mankato Minnesota Secondary effluent followed by Actiflo clarifiers Aug. - Nov West Basin Secondary effluent with 5 mg/l chloramines in UF feedwater Oct ongoing Orange County 80% activated sludge and 20% trickling filter effluent April ongoing San Diego Pure Water Tertiary effluent followed by Ozone and Biologically Activated Filters January ongoing Daly City Secondary effluent with coagulant addition March ongoing San Angelo Water Reuse Research Texas Secondary effluent followed by disk filters and chloramine addition New Jersey Not available February July 2016 June April 2016 In addition to the pilot studies, demonstration and full-scale plants have been recently built. A partial list is shown in Table 2 on the following page. 3

4 Table 2 Full-Scale Plants and Large Scale Demonstration Plants Project Name Location Feed Source San Diego North City Demonstration Plant West Basin Containerized Padre Dam Demonstration Plant Installed Capacity (MGD) Date of Start-up Municipal Tertiary effluent 0.65 Jun-11 Municipal Secondary effluent 1.0 Sep-14 Municipal Secondary effluent 0.12 Mar-15 Carlsbad Municipal Secondary effluent 3.4 Apr-16 West Deptford New Jersey Municipal Tertiary effluent 0.4 Dec-15 Valencia Municipal Tertiary effluent 12 TBD Santa Barbara Municipal Tertiary effluent 3.0 Summer 2015 Knowledge gained from these pilot and demonstration studies, along with full-scale plants, has helped to educate the public and optimize designs for IPR/DPR systems. The pilot study at Ventura was also a public demonstration of the membrane technologies and AOP with free tours available and educational videos on the city website. Figure 1 Ventura Water Pure Demonstration Facility 4

5 Ventura Water Pure Potable Reuse Facility Project Feedwater for the UF pilot unit at the Ventura Facility was municipal secondary effluent followed by sand filters and chloramine addition. In Phase 1 of the study, feed water to the UF pilot unit came from a conventional wastewater treatment plant with nitrification then denitrification followed by media filters. Chlorine and ammonia were added on the pilot skid upstream of the UF membranes to maintain a chloramine residual of mg/l. The first phase took place from July 10 to December 22nd, For the second phase of the pilot study, a pasteurization system was brought on-line further treating the tertiary effluent by raising the temperature to 157 deg. F (69.4 deg. C). The UF feed water was then cooled to 77 deg. F (25 deg. C) before contact with the UF membranes. The addition of chlorine and ammonia was maintained to a mg/l residual until April 1st, The pilot continued to operate for an additional 20 days without any TMP rise. The stable TMP proved pasteurization was effective at neutralizing the biological foulants and the chloramines were no longer required in the UF pretreatment. The second phase took place from January 4th to April 21st, The following UF feed water and UF filtrate analyses were provided by Carollo Engineers: Parameter Table 3 UF Feedwater Analysis Unit Data Min. Avg. Max. Total Dissolved Solids (TDS) mg/l 1,152 1,469 1,707 Dissolved Oxygen (DO) mg/l Conductivity µs/cm 1,930 2,341 2,610 Turbidity NTU Total Organic Carbon (TOC) mg/l Dissolved Organic Carbon (DOC) mg/l Total Iron (Fe) mg/l Total Manganese (Mn) mg/l N/A N/A 0.01 Chloride (Cl) mg/l Sulfate (SO4 2- ) mg/l Phosphate (PO4 3- ) mg/l Ammonia (NH3) mg/l

6 Parameter Unit Data Min. Avg. Max. Nitrates (NO3) mg/l Silica (SI) mg/l Total Coliform MPN/100 ml ,419 Fecal Coliform MPN/100 ml ,419 UV Transmittance 250 nm Alkalinity (as CaCO3) mg/l Total Hardness (as CaCO3) mg/l ,136 ph SU Temperature deg C Table 4: UF Filtrate Water Analysis Parameter Unit Data Min. Avg. Max. Total Organic Carbon (TOC) mg/l Dissolved Organic Carbon (DOC) mg/l Total Coliform MPN/100 ml Total Chlorine mg/l UV Transmittance 250 nm Ultrafiltration Operational Results The Ventura UF pilot study ran from July 10, 2015 to April 21, The UF membrane module successfully treated the Tertiary Effluent (Phase 1) as well as the Pasteurized Tertiary Effluent (Phase 2) from the Ventura Wastewater Reclamation Facility. Initially two Toray HFU-2020N UF modules were installed and the instantaneous flux rate was 17.7 gfd and 95% recovery then on August 20th one of the modules was removed and the flux rate doubled to 35.4 gfd and 95% recovery. This can be seen in the logsheet data below provided by Ventura Water s Wastewater Plant Supervisor. 6

7 Figure 2 Before, During and After Backwash Instantaneous Flux Also evident from Figure 1 is the backwash instantaneous flux rate was set at approximately 1.15 times the filtrate flux. For the HFU-2020N module the backwash flux rate is normally in the range of 1.1 to 1.5 times the filtrate flux. After August 20th, only one module operated at an instantaneous flux rate of 35 gfd, 95% recovery and a backwash flux rate of 41 gfd. In addition to the logsheet data which was manually gathered, PLC data was downloaded from the pilot unit. Only a portion of the data set will be shown in this report to add further clarification to the logsheet data. PLC data for November 2015 shown in Figure 3 on the following page confirms the instantaneous flux rate of 35 gfd. 7

8 Figure 3 Instantaneous Flux, Temperature and Temperature Corrected Flux Figure 3 above shows a clearer picture of how the temperature corrected flux rate changed with the feedwater temperature. Since the feedwater temperature ranged between 20 and 30 deg C the temperature corrected flux was slightly lower than the instantaneous flux. The temperature corrected flux ranged from gfd at 20 deg C. Figure 4 Temperature Corrected Flux and Temperature 8

9 Six (6) CIP cleans were performed over the 9-month pilot study. Figure 5 below shows the before and after backwash Trans-Membrane Pressure (TMP) and the dates of when the CIP cleans were performed. During Phase 1, the first CIP was performed August 19 20, 2015, even though the TMP was stable at less than 10 psi. This CIP was performed to ensure the membranes were clean before increasing the flux rate to 35 gfd. At 35 gfd, the UF pilot operated for 48 days in between CIP #1 and CIP #2 and operated for 76 days in between CIP #2 and CIP #3. Normally the goal is to limit the CIP cleans to once every 30 days or more. From the two long runs observed in Figure 5, we estimate a CIP cleaning frequency of once every days on this water source. Figure 5 Instantaneous Trans-Membrane Pressure (TMP) In Phase 2, when the pasteurization system was initially placed on line, three short runs occurred all operating less than 30 days. It is believed the short runs were due to issues with maintaining a stable pasteurization temperature or ineffective CIP cleans. Figure 6, on the following page shows the pasteurization temperature and TMP. It is evident once the pasteurization temperature was stabilized the TMP also stabilized resulting in a 50-day run with a TMP around 15 psi. This is only half the allowable operating TMP of 29 psi for the HFU-2020N module. 9

10 Once a stable TMP was achieved it was decided to stop the addition of chlorine and ammonia in the UF feedwater on April 1, Figure 6 Phase 2 TMP and Pasteurization Temperature Figure 6 above shows that the TMP remained stable for an additional 20 days proving chloramines are not required in the UF pre-treatment if there is a pasteurization system. Temperature Corrected (TC) Permeability ranged from 1.3 up to 6.0 gfd/psi, see Figure 7 on the following page. PLC data in Figure 8 shows the permeability in detail after CIP #6. The permeability was initially in the 5-6 gfd/psi range and then quickly stabilized in the 3-4 gfd/psi range. Further details of the permeability gain due to CIP cleaning are discussed on page 12 under Cleaning Results. 10

11 Figure 7 Temperature Corrected Permeability (Specific Flux) Figure 8 TC Permeability for March 2016 Post CIP #6 11

12 Ultrafiltration Cleaning Results Maintenance Cleans were not performed during this pilot study. Maintenance Cleans (MCs) involve soaking the membranes in a low dosage chemical solution for approximately 20 minutes. The frequency of MC s depend on feed water quality. The addition of chlorine during each backwash, known as Chemically Enhanced Backwashes (CEBs), was also not performed during this study. The only time chemicals were added to the membranes was during Clean-In-Place (CIP) cleans. Figure 9 below was compiled from data gathered before, during and after the CIP cleans. Figure 9 CIP Clean Results From Figure 9 we see citric acid was more effective in CIP #2 at increasing the permeability than phosphoric acid used in CIP s #3, 4 & 5. In CIP #6 sulfuric acid was added to the citric acid to reduce the cleaning solution ph down to 1.6. This is sometimes helpful in removing aluminum and manganese foulants. By comparing CIP s #2 and #6 the permeability gain is similar so it s not conclusive that the sulfuric acid was more effective than just citric acid. For the full-scale plant we recommend citric acid is used to remove inorganic foulants. If permeability is not restored back to the 5 gfd/psi we recommend adding sulfuric or hydrochloric acid to reduce the ph to the range of 1.3 to 1.6 to help remove the inorganic foulants. 12

13 Ultrafiltration Integrity Test Results Indirect Integrity Monitoring Indirect integrity monitoring was performed using an on-line turbidimeter. Throughout the pilot study all filtrate turbidity values were less than 0.1 NTU and averaged NTU. Feed turbidity values ranged from 0.3 NTU to 2.3 NTU. Please see Figure 9 below for further details: Figure 9 CIP Clean Results Direct Integrity Monitoring Direct integrity monitoring for this pilot study was based on a Pressure Decay Test (PDT). This test was conducted by draining the feed side of the module and then pressurizing the feed side of the membrane lumen with oil-free clean air. The air pressure was held for five (5) minutes and the air decay rate was monitored. The LRV calculations are based on the EPA s Membrane Filtration Guidance Manual published in November If the calculated LRV value, based on the actual pressure decay test, is greater than 4-log then the test result was considered a pass for this study. 13

14 Figure 10 below shows the calculated LRV values for the last month of operation, April Figure 10 LRV Values for April 2016 Throughout the pilot study the LRV values were greater than 4-log except for a short period in January 2016 when a rise in the air decay rate was due to a leaky ball valve. Once the ball valve was replaced the decay rates returned to normal and the LRV calculated values back to greater than 4-log. No fiber repairs were required at any time on the pilot test modules. New Advances in Ultrafiltration Systems New advances in UF design include the Universal / Flexible UF systems which can accommodate several pressurized UF modules from different membrane manufacturers. This flexibility allows end-users the option to go out for competitive bids when their installed UF modules reach the end of their useful life. This non-proprietary arrangement is similar to the current RO market. A 14

15 partial list of OEM s who offer Universal/Flexible UF systems are H2O Innovation (FiberFlex), SUEZ (SmartRack), WesTech Engineering (Versa Filters), and Wigen Water Technologies (Spectrum). What has allowed this development has been the introduction to new pressurized UF modules to the market from membrane manufacturers well known for their Reverse Osmosis elements. Companies such as Dow, Hydranautics and Toray all have PVDF hollow fiber UF products with similar pressurized module configurations and similar membrane surface areas. Newcomers to the water industry such as LG and Econity also have pressurized UF modules which can be used in Flexible UF Systems. Below is a partial list of full-scale plants where a Universal/Flexible UF system have been or are being implemented. Table 5 Full-Scale Universal/Flexible UF systems Awarded Project Name Location Feed Source Installed Capacity (MGD) Clifton Colorado Surface Water 12 Valencia Municipal Tertiary Effluent Sherman Texas Surface Water 11.3 Innisfil Ontario Surface Water 10 Lebanon Oregon Surface Water 4.5 Bloomsburg Pennsylvania Surface Water 4.0 Englishman River British Columbia Surface Water Carlsbad Municipal Secondary effluent 3.4 Santa Barbara Public Wholesale District #25 Municipal Secondary effluent 3.0 Kansas Well Water 1.0 Loudoun Virginia Well Water 0.9 West Deptford New Jersey Municipal Tertiary effluent

16 Conclusions Based on the results obtained during the on-site pilot study at Ventura Water the HFU-2020N TIPS UF module proved to be a reliable option in the treatment of tertiary wastewater. Filtrate turbidity readings were all less than 0.1 NTU and on average equal to NTU. Daily Direct Integrity Tests confirmed 4-log or greater removal of cryptosporidium and no fiber repairs were required. The instantaneous flux rate of 35 gfd and 95% recovery was achievable in both Phase 1 and Phase 2. CIP cleaning requirements treating tertiary effluent are estimated to be every days and treating tertiary pasteurized effluent is estimated to be every 50 days or more. Pasteurization in the UF pretreatment eliminates the need for chloramine addition upstream of the UF membranes. For a stable TMP the pasteurization temperature needs to be 156 deg F or higher. In summary, hollow fiber UF membranes are a critical component in many DPR / IPR plants and will continue to remove turbidity and pathogens and provide excellent pretreatment to downstream RO systems. New advances in hollow fiber UF systems such as open source / nonproprietary system integrators as well as Flexible /Universal racks and systems have greatly improved the choices available to utilities and end-users. References Vickers, James C. et. al. (2016) West Basin s Universal Membrane System Pressurized PVDF Performance Pilot Program Particulars. A W W A / A M T A 2016 Membrane technology Conference & Exposition. (San Antonio, Texas). Knoell, Tom et. al. (2016) Evaluating the Latest Low-Pressure Membrane Technologies for the Groundwater Replenishment System. WEFTEC (New Orleans, Louisiana). 16