WHEN IS A BREACH A BREACH? TESTING MF AND RO BARRIERS. Abstract

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1 WHEN IS A BREACH A BREACH? TESTING MF AND RO BARRIERS Nathan Boyle, Hazen and Sawyer, 1149 S Hill St, Suite 450, Los Angeles, CA nboyle@hazenandsawyer.com, Ph: Troy Walker, Hazen and Sawyer, Tempe, AZ Buddy Boysen, Hazen and Sawyer, Houston, TX Art Nunez, City of Scottsdale, Scottsdale, AZ Binga Talabi, City of Scottsdale, Scottsdale, AZ Abstract This project examined the robustness and reliability of treatment barriers that are used in two key process barriers for water reuse, microfiltration and reverse osmosis. The tests were performed at the Scottsdale Water Campus in Arizona which was ideally suited for testing of pressurized ultrafiltration membrane filters and both conventional 8 diameter and newer generation 16 diameter brackish water reverse osmosis membranes since both systems treat the same water source. The project involved observing the response of failures in ultrafiltration and reverse osmosis membranes by intentionally breaching the integrity of the membrane. The tests were performed by intentionally removing reverse osmosis interconnector o-rings and cutting ultrafiltration fibers, to simulate the effects of incorrect installation or product deterioration and failure over time. The reverse osmosis systems were monitored for turbidity, electrical conductivity, common anions/cations and 3D organics fluorescence following progressive removal of interconnector o- rings. The microfiltration testing compared the pressure decay test against filtered water turbidity for a progressive number of severed fibers. The purposeful destruction of these critical barriers and enhanced operational monitoring during these types of failure are unique. The City s operations staff were a key resource during these tests since significant involvement from the operations team provided unique insight into the failure events. Opportunities for hands on work with membrane systems during failure is limited, this testing allowed the operations staff to participate and gain additional perspective on failure modes during the research. Test results confirmed that electrical conductivity and pressure decay test are reliable and sensitive monitoring measurements. The results compare key monitoring parameters used for membrane integrity and discuss the sensitivity of these parameters to system changes. 1

2 Introduction In the modern era of water scarcity and contaminated source supplies, direct potable reuse (DPR) has emerged as a viable and attractive option to supply potable water. Membrane filtration technologies are considered a fundamental pathogen removal process for re-use applications, implemented at a wide range of plants across the world. Although not directly designed for pathogen removal, reverse osmosis also plays a role in pathogen removal as well as providing removal of constituents of emerging concern (CEC). As cities move toward DPR confidence in the performance of the technology and operational reliability of separation processes used to remove pathogens and CEC is vital. Background Recent research has adopted risk based control methods for treatment process development from the food and beverage industry. This project is focused on Hazard Analysis and Critical Control Point (HACCP) methodology, which was originally developed to ensure that food taken into space would be safe for astronauts to consume. This approach, which is endorsed by the USDA, has been highly utilized within the food and beverage industry. The HACCP approach relies on seven principles: Principle 1: Conduct a hazard analysis. Principle 2: Determine the critical control points (CCPs). Principle 3: Establish critical limits. Principle 4: Establish monitoring procedures. Principle 5: Establish corrective actions. Principle 6: Establish verification procedures. Principle 7: Establish record-keeping and documentation procedures. HACCP has been previously studied for the water treatment industry. In 2007, the EPA published a report outlining the methods for HACCP implementation for distribution system monitoring, risk assessment and control in response to the Total Coliform Rule (TCR) [1]. The work was then extended into DPR research by the WateReuse Research Foundation (WRRF). Other ongoing WRRF research has focused on principles 1 through 3. This research program has been developed specifically to establish and verify critical monitoring procedures for DPR. This project aims to quantify the robustness and reliability of treatment barriers that are used in direct potable re-use schemes. In particular, this phase of the project focused on ultrafiltration and reverse osmosis. More specifically, this research focuses on critical control and monitoring of Membrane Filtration (MF) and Reverse Osmosis (RO) in Full Advanced Treatment (FAT) process configurations. Membrane filtration and reverse osmosis technologies provide a critical removal barrier in a FAT treatment process, where they perform pathogen and organic constituent removal. The basis of this project involves intentionally breaching the integrity of ultrafiltration and reverse osmosis 2

3 membranes and observing the response to key indicators. Key indicators involve online monitoring and key routine samples that could be used regularly to diagnose changes and integrity breaches in membrane processes. This phase of the project involved full scale trials at an operating potable reuse facility, the Scottsdale Water Campus located in Scottsdale, Arizona. The Scottsdale Water Campus is an advanced treatment facility that has been operational since 1999 and was recently upgraded in Because of the upgrades, the facility represents the current state of the art in FAT water reuse system design. The plant consists of two distinct treatment components, potable large surface water treatment facility that supplies drinking water to the City of Scottsdale and the wastewater plant with an Advanced Water Treatment Facility (AWT) that supplies partially desalinated recycled water to local golf courses for turf irrigation. At times when more water is available than the golf courses need, the additional flow is diverted to a collection of vadose zone wells and ultimately transferred to the local groundwater aquifer. The focus of the study is the AWT process, which treats tertiary wastewater effluent with ozone, chloramination, ultrafiltration, reverse osmosis and UV disinfection. A key benefit to utilizing the Scottsdale Water Campus as the test center is that both conventional 8 diameter and newer generation 16 diameter brackish water RO membranes are used. Because both are in use, this testing was able to compare integrity breach effects for 8 and 16 membrane sizes using the same feed water source. DPR is considered a viable option for securing new water supplies. Public concern on the use of treated waste for potable water is largely based on perception. Hence, confidence in the performance and operation of separation processes used for pathogen removal is vital. Critical Control Points (CCP) are considered process points where specific procedural controls can be implemented as warning signs of plant failure. Early detection results in prevention, reduction or removal of the risks to an acceptable level. For a RO plant CCP performance monitoring includes permeate electrical conductivity and total organic carbon (TOC), for a Membrane Filtration (MF) system the primary CCP performance monitor is the pressure decay test result and the secondary CCP performance monitor is online filtrate turbidity. This test has been developed to evaluate each of the CCP monitoring points. Historical operating experience suggests that RO system integrity and performance is generally impacted by improper o-ring installation or o-ring material failure. Although membrane delamination and glue line can also impact RO system performance, o-ring issues are much more common and have been identified as a critical failure point. Because o-rings removal is nondestructive, o-ring removal has been utilized to simulate RO system integrity failure to allow evaluation of the CCP monitoring procedures. For MF systems, breached integrity can be caused by o-ring failure, stuck or broken valves and valve block assemblies, broken fibers or cracked potting. Historical operating experience suggests that broken fibers are one of the most common methods of hollow fiber MF integrity failure. Because fiber breaks are relatively easy to quantify and produce, fiber breaks were selected for evaluation of MF CCP monitoring procedures during this study. 3

4 Methodology The project test plan was developed to intentionally breach the integrity of key FAT treatment process components to evaluate the effectiveness of CCP monitoring procedures. Two critical systems in the FAT process were tested: Membrane filtration (ultrafiltration) Reverse osmosis Table 1outlines the details of the membranes at Scottsdale Water Campus used for this testing. Table 1 Scottsdale Water Campus Membrane Details 8 inch diameter 16 inch diameter RO RO Ultrafiltration Membrane Make Koch CSM Evoqua Membrane Model TFC-HR-Magnum RE16040-FE Memcor CP-L20N Membrane Material Polyamide Polyamide PVdF Membrane Type Spiral Wound Spiral Wound Hollow Fiber Min Salt Rejection 99.5% 99.7% N/A Effective membrane area per membrane (ft 2 ) 575 1, The outcome of the testing was to review the sensitivity of each critical control monitoring point and the control and operational response. Membrane Filtration Unit 6 at Scottsdale Water Campus, pressurized Evoqua (Memcor) CP (UF) system was used for ultrafiltration testing, which has a membrane pore size of 0.04µm. Initially, the system was operated for a period of thirty minutes and the baseline operating conditions were recorded. The target monitoring parameters, to quantify membrane integrity, were the pressure decay test (PDT) result, calculated log removal value (LRV) and online filtrate turbidity. The pressure decay test was performed according to Evoqua recommendations for this system, which required applying a minimum pressure of 10 psi for a period of two minutes to record the pressure decay value. A minimum of 30 minutes was kept following each startup prior to performing a PDT to allow the system to stabilize. The log removal value was calculated using the online flow and pressure instrumentation. Filtrate turbidity was recorded using an online HACH Filtertrak 600, results from this instrument were confirmed using grab samples and a benchtop HACH 2100N. Figure 1 is a cut away of the ultrafiltration module. The ultrafiltration system was taken offline and a module was removed from the rack (at site 25A) using the module removal tool. 5 fibers were cut using a pair of wire cutters. The module was then re-installed in the rack, the system was operated for a period of at least 30 minutes (including a backwash - every 24 minutes) and the PDT, turbidity and system conditions were measured and recorded. The process of removing the module, cutting fibers, reinstalling the 4

5 module and running the system was repeated to produce data points at 5, 20 and 50 cut fibers from the same module. The next test involved removing the two upper module o-rings and filtrate cup seals from the module. The module was re-installed in the rack, the system was operated for a period of thirty minutes (including a backwash every 24 minutes) and the PDT, filtrate turbidity and system conditions were measured and recorded. Following testing, a new module was installed in the rack. Figure 1 Ultrafiltration Module Cutaway Reverse Osmosis RO train 16 at Scottsdale which is the 8 inch diameter RO system used for this study. The train is a 3 stage system that has been in operation for approximately 15 years, the membranes in this unit are greater than 5 years old. The tested RO train contained 39 pressure vessels. During testing, the train was started and operated at typical conditions for a period of 30 minutes. Permeate was then sampled from each pressure vessel to obtain a performance profile of the RO unit. Online instrumentation values were recorded which included feed and permeate flow, ph, differential pressure and conductivity. Grab samples were collected at the feed and combined permeate sampling points and analyzed in the onsite water quality laboratory by the City s laboratory staff. Specific water quality tests and the minimum detection limit (MDL) are outlined in Table 2. In addition to these tests, samples were also collected and sent to Hazen and Sawyers laboratory in Raleigh, NC for 3D organic fluorescence analysis. 5

6 Table 2 Water Quality Test Methods Analyte Method MDL Calcium EPA mg/l Sulfate EPA ng/l Caffeine LC/tandem mass spectroscopy 1 ng/l Sucralose LC/tandem mass spectroscopy 10 ng/l Total Organic Carbon (TOC) Standard Methods 5310C 0.5 mg/l Total Dissolved Solids (TDS) Standard Methods 2540C 20 mg/l Conductivity Standard Methods 2510B 2 umho UV254 Standard Methods 5910B at 1cm quartz cell The next component of testing was to shut down the RO system, release stored pressure and remove an endcap on the second stage feed. Two o-rings on the endcap connector were removed, Figure 2 shows a cutaway of the membrane pressure vessel internals and indicates the location of these o-rings. The endcap was reinstalled in the system and the RO was restarted. The system was operated for a period of 30 minutes to reach a stabilized state before data and samples were collected. The process of o-ring removal, system restart and sample collection was repeated to remove o-rings on one endcap interconnector in a total of 1, 5 and 39 (all of the skid) pressure vessels. The endcaps removed were from the tail elements in the first and third stages and the feed elements in the second stage. The purpose of this testing was to simulate the effect of rolled, damaged or incorrectly installed o-rings. Figure 2 Reverse Osmosis Vessel Cutaway To test a more significant integrity breach, a first stage endcap interconnector was removed from the system. The interconnector removal was evaluated as an additive breach, previously removed o-rings were not reinstalled during this test. Following the removal of the interconnector, the system was restarted, stabilized for 30 minute period before samples were collected. The purpose of this test was to simulate the effect of a broken interconnector or a membrane installation error 6

7 in which an interconnector was accidentally left from the system. Following completion of this test the interconnector was re-inserted and new o-rings were installed where they had been removed for testing. The system was restarted and tested for leaks before being returned to full service. Following completion of the 8 inch RO testing, a similar process was followed to test 16 inch membranes. The 16 inch membranes, which are less than 5 years old, are newer than the 8 inch membranes and have not been operated as extensively as the 8 inch trains at the Scottsdale Water Campus. The train has a total of 20 pressure vessels. The system was operated for a period of two hours before recording baseline conditions. Afterwards, a testing approach similar to the one described previously for the 8 inch elements was used. 16 inch RO train testing involved removing an endcap from the tail end of the first stage pressure vessel. The endcap interconnector o-rings were removed and then the endcap was re-installed and the system was re-started. During 16 inch testing, the system was operated for a period of 30 minutes to reach a stabilized state before data and samples were collected. The procedure of o- ring removal, system restart and sample collection was repeated to remove o-rings in a total of 1, 5 and 10 pressure vessels all in the tail section of the first stage. During testing there were concerns that removing the interconnecting adapter for the 16 inch vessels completely from the endcap could cause the membranes to move when started and result in damage. To continue to test, an interconnector was modified. The end nozzle component of the connector that inserts into the permeate tube was cut completely and eight small holes were drilled into the side of the connector to allow feed water to bypass directly to the permeate tube, simulating removing of an interconnector whilst retaining the structural setup in the pressure vessel. The o-rings which were previously removed remained removed during this test to progressively capture the effect of change. Following completion of the testing, the modified endcap interconnector was replaced, and new o-rings were installed before the system was returned to full service. Using the data collected for both 8 inch and 16 inch vessels, key membrane monitoring parameters were calculated such as recovery, transmembrane pressure and differential pressure. The data collected for each case was normalized against the baseline data to evaluate normalized flow and normalized salt passage. Results The focus of this test was to observe the response of online and ad hoc water quality and process monitoring on the ability to detect integrity changes in membrane systems. The integrity of the microfiltration and reverse osmosis systems were progressively intentionally breached to see an increasing trend of change. As a safety measure, the testing was performed at a time when the AWT was producing water for agricultural use and not potable reuse. The operational response at the plant was also considered, at no point during the testing were critical operating parameters and system alarms bypassed. 7

8 Membrane Filtration During the course of the test period, the raw water turbidity to the MF unit remained constant. Table 3 outlines the data from the microfiltration testing, a baseline PDT result of 0.15 psi/min was recorded, which was typical of historical system performance for membrane filtration units at the Scottsdale Water Campus. The number of fibers that had failed in the module prior to testing was unknown but not of relevance since the baseline conditions were recorded. It would be expected that the baseline PDT would be high, if the membranes were significantly breached prior to testing. The number of fibers broken during the test period are assumed to be inclusive of an entire train, as the data was collected in the terms of the overall train. Increasing the number of cut fibers increased the pressure decay test result. Figure 3 is a graphical comparison of the pressure decay test and filtered turbidity during the test period which shows the exponential style increase with the varied test conditions. 50 fibers cut increased the pressure decay to 0.28 psi/min which represents an 86% increase over the baseline result. Removal of the filtrate cup o-rings gave a more distinguishable pressure decay result of 0.41 psi/min which represents a 173% increase over the baseline test result. The filtrate turbidity did not change a significant or distinguishable amount regardless of the fibers that were cut. The turbidity did show an increase, however this was very small and still perfectly acceptable for a filtered water feeding an RO system. Non-FAT processes will be more influenced by turbidity increases than those with RO treatment. Advanced oxidation processes such as UV and ozone rely on low turbidity to avoid particle shielding and maximize treatment. The data collected indicates that the pressure decay test provides superior resolution over the filtrate turbidity for detection of change in the system, which is an expected result. The log removal value (LRV) reduced from 4.69 at the baseline measurement to 4.58 with 50 fibers cut and filtrate cup o-rings removed. It should be noted that one ultrafiltration module was altered out of a total of 204 on the membrane filtration unit. Further to this, if one assumes there are 10,000 hollow fibers in each module the then the percentage of the system changed with 50 fibers cut is %. The number of fibers cut, 50 was assumed to be the upper limit of a typical event in a single Siemens membrane module. Experience during prior commissioning has suggested there are usually a portion of modules which require some pinning of fibers, which is a factor with membrane manufacture, transportation and commissioning. The number of fiber breakages in a typical event varies between different membrane manufacturers as a function of the fiber strength. Test Table 3 Membrane Filtration Test Results Baseline 5 fibers 8 20 fibers 50 fibers 50 fibers + o- rings PDT (psi/min) Feed Water Temperature ( C) Feed Water Turbidity (NTU) Unit Flowrate (GPM)

9 Pressure Decay (psi/min) TMP (psi) Flux (GFD) C LRV Filtered Turbidity (NTU) Baseline 5 fibres 20 fibres 50 fibres 50 fibres + O-ring Fibres Cut PDT (psi/min) Turbidity (NTU) Figure 3 Membrane Filtration Pressure Decay Test Results Reverse Osmosis The primary purpose of an RO unit is salt rejection and hence the primary online indicator for operation of an RO is the electrical conductivity. Conductivity measures the ability for a water to transmit electricity and is proportional to the concentration of salt. Figure 4 shows the change in permeate conductivity through the trial period. The 8 inch RO had a 5% change in permeate conductivity through the removal of one set of o-rings and a 13% increase with five sets of missing o-rings. Removing o-rings from all vessels resulted in a noticeable 50% increase in the permeate conductivity. The response in permeate conductivity for the 16 inch RO was detectable after a single set of o- rings were removed. With only one impacted vessel, a 63% increase in conductivity was observed. This is likely due to a larger and thicker o-ring in comparison to an 8 inch vessel, leading to a larger void for salt passage. The total flow through a 16 inch pressure vessel is also much higher than an 8 inch vessel, resulting in a higher overall influence. 9

10 Permeate Conductivity (µs/cm) Baseline Remove O-rings 1 vessel Remove O-rings 5 vessels Remove O-rings all/10 vessels Remove Interconnector 8-inch RO 16-inch RO Figure 4 RO Permeate Conductivity When the normalized salt passage is plotted for each membrane size in Figure 5 and Figure 6 it provides a clear indication of a membrane integrity failure. For the 8 inch system when o-rings were removed from the endcaps of 5 vessels, the resolution was enough to provide a detectable change that could be picked up on the treatment plant as an issue. On the 16 inch system the salt passage change was detected after o-ring removal in only one pressure vessel. This data suggests, that normalized salt passage is a good measure of membrane integrity, which is an expected finding. Salt passage can be monitored continuously via calculation online and can provide the operator with important information on membrane integrity. The normalized permeate flow is also plotted in Figure 5 and Figure 6. The normalized permeate flow did not provide significant differential information to diagnose integrity issues. 10

11 Permeate Flow (gpm) Salt Passage (%) Permeate Flow (gpm) Salt Passage (%) % 30% 25% 20% % % 100 5% 0 Baseline Remove O- rings 1 vessel Remove O- rings 5 vessels Remove O- rings all vessels Remove Interconnector 0% Normalized Permeate Flow Normalized Salt Passage Figure 5 Normalized Flow and Salt Passage Unit 16 (8 inch RO) Baseline Remove O- rings 1 vessel Remove O- rings 5 vessels Remove O- rings 10 vessels Remove Interconnector 35% 30% 25% 20% 15% 10% 5% 0% Normalized Permeate Flow Normalized Salt Passage Figure 6 Normalized Flow and Salt Passage Unit 21 (16 inch RO) Permeate normalized flow was reduced slightly when an interconnector was removed, which is counterintuitive to what would be expected. Given the larger passage and less resistance with an interconnector removed, it could be inferred the flow should increase as there is a larger path for flow. The reduction in normalized flow is due to reduced net driving pressure, as shown in the ASTM normalization calculation in Equation 1 [2]. In the equation the subscript s refers to standard conditions and the subscript a refers to measured conditions. The differential pressure 11

12 in the second stage was low due to increased flow through this stage (from the removed interconnector). Reduced overall net driving pressure results in a lower permeate normalized flow. Equation 1 ASTM Normalized Permeate Flow Equation Differential pressure is an important RO monitoring parameter, pressure changes indicate a change in operating conditions or may indicate there is membrane damage. Figure 7 and Figure 8 illustrate the change in differential pressure for each test for the 8 inch and 16 inch RO membranes. For both membrane sizes, no significant changes in pressure could be detected with removal of the o-rings. Although differential pressure changes were negligible during o-ring removal, the differential pressure in the 8 inch RO train was significantly impacted by the removal of the interconnector. Ad hoc samples are unlikely to be a good indicator for process control given the time to analyze the samples. Ad hoc sampling is however, useful to validate the performance and diagnose issues that may be forming. Sucralose is an artificial sweetener used in food products which passes through the human body. The small size of the molecule makes it generally unable to be removed with conventional water and wastewater processes. RO is capable of removing sucralose and this provides a good indicator of rejection performance. Caffeine is an indicator for wastewater contamination providing similar results to fecal bacteria, caffeine can be removed by RO and conventional wastewater processes. Caffeine rejection was reduced with increasing membrane integrity breaches, although the difference was not clearly distinguishable. Sulfate is a highly rejected divalent anion that is well rejected under most operating conditions. Sulfate levels were clearly distinguishable on the 8 inch system when the interconnector was removed and was present in the RO permeate on the 16 inch membranes even when the o-rings were removed from only one vessel. 12

13 Figure 7 Lab results Calcium and Sulfate (8 inch and 16 inch) Figure 8 Lab results Caffeine and Sucralose (8 inch and 16 inch) Total organic carbon (TOC) is considered an excellent indicator test of RO system failure. A clear trend can be drawn from Figure 9 when the conductivity and TOC is plotted together. It was interesting to note that the 16 inch RO displayed very measurable signs of permeate quality decreases when o-rings were removed in 1-5 vessels, whereas in comparison the 8 inch needed o-rings removed in all of the vessels to indicate a similar reduction in performance. This finding 13

14 is consistent with the salt passage and ad-hoc sampling data discussed previously indicating that a single o-ring failure in a 16 inch is of concern as compared to an 8 inch which required removing o-rings in all endcaps to provide a similar magnitude of detectable change. Online and ad-hoc measuring points used are compared in Table 4. Table 4 Comparison of RO monitoring parameters for measuring induced failures Benefits Differential Pressure Online measurement Does not require regular calibration Accurate Electrical conductivity Online measurement Normalized salt passage Excellent resolution TOC Excellent resolution Sucralose Excellent resolution Caffeine Excellent resolution Negatives Not distinguishable to identify small failures Not significant resolution to identify influence in 8 inch RO systems Requires calculation using input parameters that may change with membrane products. Requires a significant amount of additional instrumentation that must be included in the train design and maintained. Requires a higher level of user input to be valid. Lab measurement, online TOC instruments can be capitally expensive. Requires a higher level of user input to be valid. Lab measurement Lab measurement Not distinguishable to provide resolution to identify small failures Low level Caffeine samples are easily contaminated, greater lab QC required. 14

15 Electrical Conductivity (µs/cm) Total Organic Carbon (mg/l) RO Feed Baseline Remove O- rings - 1 vessel Remove O- rings - 5 vessel Figure 9 Conductivity and TOC Remove O- rings - all vessels Remove inter-connect Conductivity (8inch) Conductivity (16 inch) TOC (8inch) TOC (16inch) This form of testing is useful not only for the recycled water community but also for the water authority in terms of training. Practical research studies such as the one outlined in this paper give operators and engineers a chance to get intimate with membrane systems and see firsthand the results of integrity breaches. This can help to calibrate an operators expectations in terms of what could be considered normal operation and when integrity of the barrier is potentially breached. Research based techniques can also identify potential issues such as seal degradation and any inconsistencies with methodology in routine test methods Conclusion A multi-barrier treatment approach is preferred when operating water treatment facilities and this is especially true for DPR systems. One key outcome from this research is identification that there is no single critical control point that can be used to identify failures in membrane systems. Different parameters have different resolution and can provide indication of an issue but also could be overlooked by normal operation within the typical operating zone. Multiple measuring parameters using a mix of both online and laboratory analysis is required to track and identify the integrity of membranes processes used in DPR. For membrane filtration, the use of online turbidity monitoring did not show significant changes with cut fibers. Even though the cut fibers were performed on one module, the changes were considered to be the total influence per train. The data obtained from the microfiltration test indicated there was a reduction in the LRV with increasing fiber breaks in the system. The PDT results provided excellent resolution on changes to the system but is not a continuous online test. The filtered water turbidity was relatively consistent during all changes suggesting this is not a good monitoring tool for small breakages but rather to diagnose large failures and significant process changes. Online electrical conductivity measuring RO permeate appeared to provide the accuracy to be able to detect changes in both 8 inch and 16 inch systems with even only 1 set of o-rings 15

16 removed (5% change). However, the likelihood that an operator would identify an integrity breach is low, since the typical operating range for scaling and cleaning triggers is within 10%. It is possible that changes of this magnitude would go unnoticed. For large system breaches with large changes >20%, the operator would pick this as an abnormally high value but may attribute the issue to scaling or membrane damage. Further investigation is required to determine the root cause of the issue. Performing individual RO conductivity profiles in parallel with the online combined permeate would identify a salt passage breach in a single module. Permeate conductivity is a good CCP performance indicator for RO, at times when conductivity changes, individual conductivity profiling can be used to isolate the source of the salt passage increase. An interesting observation was made in the difference between 8 inch and 16 inch RO. For the 16 inch RO it could be inferred that void size and influence from removal of ten o-rings was almost equal to that of an interconnector integrity breach. The 8 inch vessels appeared to have a closer tolerance between the connector and permeate tube and thus the removal of the interconnector provided a larger passage for salt to pass. This observation is significant in that issues may be detected earlier on a larger system but the influence to the permeate quality is more severe. The general conception amongst water industry professionals is that 16 inch vessels would be more resilient to integrity breaches, such as o-ring failure due to a lower number of vessels and hence less likelihood for incorrect installation. This testing identified that even with 1 set of o-rings removed, simulating a failure, a large increase in salt passage was observed. The 8 inch RO, by comparison showed only minor increases. Detectable changes in calcium and sulfate rejection were observed across the range of analysis. RO membranes typically reject divalent ions well, unless the membrane is scaled, even in mechanically damaged membranes. Whilst a noticeable change was observed in this study for both 8 inch and 16 inch RO with removal of more than five sets of o-rings, other constituents such as organics or monovalent ions may be a better indicator of a breach in membrane integrity. Organics fluorescence spectroscopy characterization provided distinguishable resolution which identified increased organics in permeate with only one o-ring removed. The 8 inch and 16 inch RO membranes showed visibly similar organics profiling results between the organics charts. The major drawback of this type of measurement is it is expensive and discrete, not allowing continuous monitoring. Perhaps more research and development into online and more cost effective organics characterization is a worthwhile initiative for DPR. TOC is another organics measurement which showed good resolution for major process changes. Online TOC analyzers can be used to provide constant measurement. Measurement of caffeine provided limited resolution to identify breaches in system integrity. Sucralose showed a significant and identifiable change through a laboratory test. This test may be good to provide regular confidence in results but is unlikely to be useful for continuous monitoring and critical control point action. Feedback tests such as laboratory organics and 3D fluorescence can be used as verification of the online instrumentation. The conductivity and organics results are linked, an unexpected conductivity result could be used as a trigger to perform organics sampling to verify the nature and magnitude of the TOC. 16

17 References 1. HDR et. al. Hazard Analysis Critical Control Point (HACCP_ Strategies for Distribution System Monitoring, Hazard Assessment and Control. USEPA Contract No. 68-C Washington D.C., ASTM D 4516 Standard Practice for Standardizing Reverse Osmosis Performance Data. ASTM International. Pennsylvania, USA