A. Turner, Chemist Project 7 Water Authority P.O. Box 1185 Montrose, CO Phone: Fax:

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1 Pressing Particle Counter Sensitivity Lower for Improved Response T. L. Engelhardt, Drinking Water Specialist Corresponding author Pacific Scientific Instruments 19 Old Town Square, Suite 238 Fort Collins, CO Phone: Fax: C. Collins, Liquid Products Specialist Pacific Scientific Instruments 481 California Avenue Grants Pass, OR Phone: Fax: A. Turner, Chemist Project 7 Water Authority P.O. Box 1185 Montrose, CO Phone: Fax: PROJECT7@MONTROSE.NET Presented at AWWA Particle Counting Symposium, Nashville, Tennessee, March Pacific Scientific Instruments Paper No. 58 June 1999

2 Abstract Many water treatment plant managers and operators have optimized the treatment process to the point where traditional measures, such as turbidity, don t respond to process changes. If a treatment plant consistently produces treated effluent at turbidity values below 0.1 NTU, plant turbidimeters usually draw a straight line. This indicates that there s little or no response to process changes. While changes to turbidimeters have helped improve optical designs, light sources, ratioing techniques, and so on, modern turbidimeters still don t respond to changes at very low turbidity values. So, treatment plant operators and managers turned to particle counting to achieve more detailed measurement. Particle counters have proved they work in the high-performance environment. Today, some treatment plant operations are so refined that even particle counters with two-micron sensitivity yield results of less than 50 particles per milliliter. Some plant operations produce less than five particles per milliliter. In many cases, data from particle counters with two-micron sensitivity may result in drawing a near straight line. This is not a limitation of the particle counter itself, but rather an artificial restriction imposed by selection of the sensitivity of the instrument s sensor. Unlike turbidimeters, particle counters with greater sensitivity are readily available. Using the same water sample, particle counters equipped with a more sensitive one-micron sensor typically provide five to ten times more particles than those with two-micron sensitivity. This paper explores how particle counters with one-micron sensitivity compare to those with two-micron sensitivity at Project 7 Water Authority, a well-managed and operated utility in Montrose, Colorado. 2 Pacific Scientific Instruments Particle Counter Sensitivity

3 The Study Project 7 Water Authority (Project 7) has used particle counting as a water treatment optimization tool since The utility compares fluctuations in particle counter information with other process measurements and changes to make continual process improvements. In an ongoing effort to make improvements at their water treatment plant, Project 7 agreed to participate in a particle counter study with Pacific Scientific Instruments (PSI). As a study team, the two companies set out to compare information between Project 7 s existing two-micron sensitivity particle counter with PSI s Met One brand one-micron sensitivity particle counter. Making discoveries During the study, abnormalities in operation were discovered using a particle counter with one-micron sensor that were not readily apparent with other process measurements at Project 7, including the two-micron sensitivity particle counter. Abnormalities included improper operation of a reclaim pump (backwash water recovery), differences in filter ripening and early filter breakthrough. Describing Project 7 Water Authority Project 7 Water Authority is a consortium of six utilities in the Uncompahgre Valley of western Colorado: the cities of Montrose and Delta, the town of Olathe, Tri-County Water Conservancy District, Menoken Water District and Chipeta Water Company. Member utilities buy water from Project 7 and then distribute it to about 35,000 customers. A seventh member, The Uncompahgre Water Users Association, controls the Gunnison Tunnel, which supplies a large portion of the project s raw water. Raw water collection and transmission and treated water transmission are all through gravity flow. Pacific Scientific Instruments Particle Counter Sensitivity 3

4 Treating the water Water treatment at Project 7 is a conventional process using sedimentation, coagulation, flocculation, filtration, fluoridation and disinfection. Originally acquired from the City of Montrose and later expanded, the plant includes six dual-media filters with total capacity of 27 million gallons of water per day. Provision for storing large amounts of treated water is an important factor in optimizing treatment. Project 7 and member utilities store enough treated water that the plant can operate at a constant rate 24 hours a day, seven days a week. Treated water reservoirs buffer demand fluctuations of the system. The treatment plant is immune from most intermittent demand loads. Using filters Plant operators and managers at Project 7 accommodate water flow by mixing and matching four large and two smaller dual-media design filters. Filters 1 and 2 were constructed in 1968, with an area of 400 ft 2 each. Filters 3 through 6 were added to the plant in Each one of the four newer filters has an area of 625 ft 2. Project 7 plant operators set water flow through the filters using a raw water control valve. Operators choose which filters to use and when. From there, the supervisory control and data acquisition (SCADA) sets the flow rate of individual filters. Filter runs of about 120 hours are typical. Using particle counters Researchers from Project 7 and PSI used two types of Met One particle counters for the team study: PCX, which is approximately three years old and owned by Project 7, and PCX-10, a newer model provided by Pacific Scientific Instruments. For the experiment, both particle counters monitored the same sample. Project 7 uses two other PCXs. One is a clarifier effluent (common filter influent). The other is a single filter effluent sensor, which can be used to monitor filter effluent of any of the six filters. The water authority anticipates installation of an additional five particle counters to permit continuous monitoring of each filter effluent. 4 Pacific Scientific Instruments Particle Counter Sensitivity

5 Addition of future particle counters was anticipated when the instruments initially were purchased. RS485 network wiring was completed throughout the entire facility during initial installation. Each potential sample location is equipped with a quick-connect junction box to facilitate connection of new instruments into the RS485 network. Comparing the PCX with the PCX-10 Equipped with a Met One DWS sensor, the PCX has two-micron sensitivity and a recommended flow rate of 100 ml/min. Its quartz cell has dimensions of 750X750 µm, which makes the instrument suitable for brush cleaning. In preparation for the study, Project 7 s PCX was returned to the factory for annual calibration. While the PCX-10 uses the same controller electronics as the PCX sensor, it is equipped with a Met One LB1010 sensor with one-micron sensitivity, has sapphire cell windows and cell dimensions of 400X800 µm. Unlike the PCX, dimensions of the PCX-10 cell are not suitable for brush cleaning. Instead, a capillary wire is used for normal cleaning. The recommended flow rate of the PCX-10 is 50 ml/min half that of the PCX. (For a comparison of the two particle counters, see below.) In preparation for the study, PSI supplied a new PCX-10. No electronic adjustments were made by the factory or Project 7 to force the two sensors to 'agree.' Note Both the DWS and LB1010 sensors are light blocking designs. Comparison of the PCX and the PCX-10 PCX PCX-10 Installed at Project 7 Supplied by PSI DWS sensor LB1010 sensor 750 X 750 µm 400 X 800 µm Two-micron sensitivity One-micron sensitivity Flow rate 100 ml/min Flow rate 50 ml/min Quartz cell Sapphire cell Suitable for brush cleaning Not suitable for brush cleaning Light blocking design Light blocking design Pacific Scientific Instruments Particle Counter Sensitivity 5

6 Sampling and sample conditioning Combined effluent was monitored. Only a portion of the treatment plant s filters was required at any one time to meet the low flows during the study period of December 22, 1998 to February 9, No one filter could be operated continuously during the study. Both the PCX and the PCX-10 were plumbed to a single Met One Water Weir 1 flow control device. The Water Weir was modified from its normal bottom-feed configuration by plumbing influent sample water about halfway up the length of the flow control device. (See figure 1.) This modification made two outlet connections available on the bottom of the Water Weir. The PCX was connected to one outlet of the Water Weir, while the PCX-10 was connected to the other. This ensured that exact water samples were provided to each sensor. No strainer was used prior to the water reaching the instruments. Recommended flow rates for both the PCX and PCX-10 were maintained throughout the study, and neither sensor required cleaning. Overflow to waste Overflow to waste Sample in Sample in Sample to PCX Sensor Sample to PCX-10 Sensor Sample to PCX Sensor A B Figure 1. Met One Water Weir configuration. Configuration A illustrates the normal flow pattern. Configuration B represents the modified Water Weir flow pattern designed for the study. 1 US Patent Number 5,644,599 6 Pacific Scientific Instruments Particle Counter Sensitivity

7 Configuring the particle counters The PCX and PCX-10 are each equipped with a Remote Multiple Channel Analyzer (RMCA) card that allows users to configure many channels. The PCX was configured with channel sizes 2, 3, 5 and 8 µm. The PCX-10 was configured similarly, but included a 1 µm channel. Both particle counters were connected through a daisy-chain RS485 network to Met One s WQS Vista software. Within the software, a combination of cumulative and differential channels were established for both sensors: >2 µm, 2-3 µm, 3-5 µm, 5-8 µm and >8 µm. A cumulative channel of >1 µm was set for the PCX-10. The PCX was connected to the plant s central control system by a 4-20 ma output signal for a channel of >2 µm. Since both particle counters had a cumulative channel set for >2 µm, study data were compared to find out how well the two sensors agreed at this size. Normally, two particle counter sensors, especially those of different design, won t provide the exact same count values. As stated earlier, the study team did not adjust the PCX and PCX-10 to agree. Nevertheless, agreement between the two sensors was very good during the course of the study. This uniform information provided the team with confidence that variations in measurement between the two particle counters were due to differences in the number of particles and not to differences in sensor design. Pacific Scientific Instruments Particle Counter Sensitivity 7

8 Figures 2 and 3 Figures 2 and 3 illustrate typical 24-hour time periods comparing the PCX and PCX-10 at >2 µm for December 27, 1998 and for January 10, /12/27 00: /12/27 01: /12/27 02: /12/27 03: /12/27 04: /12/27 05: /12/27 06: /12/27 07: /12/27 08: /12/27 09: /12/27 10: /12/27 11: /12/27 12: /12/27 13: /12/27 14: /12/27 15: /12/27 16: /12/27 17: /12/27 18: /12/27 19: /12/27 20: /12/27 21: /12/27 22: /12/27 23:08 Particles/ml >2 µm PCX >2 µm Effluent PCX-10:>2 µm Effluent PCX>2 µm Figure 2. Comparing the PCX and PCX-10 at >2 µm for December 27, Particles/ml >2 µm PCX >2 µm 1999/01/10 00: /01/10 01: /01/10 01: /01/10 02: /01/10 03: /01/10 04: /01/10 05: /01/10 06: /01/10 07: /01/10 08: /01/10 09: /01/10 10: /01/10 11: /01/10 12: /01/10 12: /01/10 13: /01/10 14: /01/10 15: /01/10 16: /01/10 17: /01/10 18: /01/10 19: /01/10 20: /01/10 21: /01/10 22: /01/10 23: /01/10 23:55 Effluent PCX-10:>2 µm Effluent PCX: >2 µm Figure 3. Comparing the PCX and PCX-10 at >2 µm for January 10, Pacific Scientific Instruments Particle Counter Sensitivity

9 Looking at the results The study ran from December 22, 1998 to February 9, On February 9, the study team conducted an extensive review of particle counting data and other operational records at Project 7. Based on that examination, a number of operational phenomena compared to particle count data were identified. In some cases, both the PCX and the PCX-10 recorded an event. In others, only the PCX- 10 recorded an event. Documenting a significant event The most significant event in the study happened from December 24 through December 25, Figures 4, 5 and 6 demonstrate this event. Figures 4 and 5 also document effluent particle count data during a 48-hour period from December 24 to December 25. Figures 4 and 5 Figure 4 shows a dramatic and significant rise in cumulative particle counts >1 µm on the PCX-10 beginning at about 18:00 on December 24. It also shows that there is little, if any, response from the >2 µm channels on either the PCX or PCX-10. This event was preceded by an excursion at about 16:30, indicated by the >2 µm channels on the PCX and PCX-10, as well as the >1 µm channel on the PCX-10. Filters 1, 4 and 6 were in use at 16:00 with 122, 66 and 23 hours of service, respectively. The reclaim pump (backwash recovery) was started at 16:00. Filter 1 was taken off line at about 16:30. While taking filter 1 off line might appear to have caused an additional hydraulic load on the remaining two filters, other Project 7 records indicate no increase in filter flow for filters 4 and 6. Pacific Scientific Instruments Particle Counter Sensitivity 9

10 Particles/ml PCX-10 > 1 µm PCX-10 > 1 µm Filter 1 off line after 122 hours Reclaim pump started at 16:00 PCX> 2 µm 1998/12/24 00: /12/24 07: /12/24 08: /12/24 09: /12/24 10: /12/24 11: /12/24 11: /12/24 12: /12/24 13: /12/24 14: /12/24 14: /12/24 15: /12/24 16: /12/24 17: /12/24 17: /12/24 18: /12/24 19: /12/24 20: /12/24 20: /12/24 21: /12/24 22: /12/24 23: Particles/ml PCX and Effluent PCX-10:>1µm Effluent PCX-10:>2 µm Effluent:PCX >2 µm Figure 4. Shows the significant rise in cumulative particle counts >1 µm on the PCX-10. As figure 5 shows, the excursion continued until December 25, 1998 with a decrease in the >1 µm counts, starting at about 03:00 and leveling off to nearly normal levels by about 09:00. Particles/ml PCX-10 > 1 µm PCX> 2 µm Reclaim pump found to be operating improperly. Problem corrected. PCX-10 > 2 µm PCX-10 >1 µm :04 01:38 03:21 04:56 06:31 08:05 09:40 11:15 12:50 14:25 16:00 17:35 19:10 20:45 22:20 23:55 Particles/ml PCX and Effluent 1µm:>1µm Effluent PCX-10:>2 µm Effluent PCX: >2 µm Figure 5. Shows the excursion leveling off by about 09: Pacific Scientific Instruments Particle Counter Sensitivity

11 Figure 6 Figure 6 covers the time period from 15:00 on December 24, 1998 to 8:00 on December 25, This figure shows particle counts and turbidity measurements from the clarifier effluent (filter influent) and the >1 µm counts from the effluent PCX-10. Notice that the 1 µm particles rapidly increase in the combined effluent, while total particle counts in the filter influent drop significantly. Unfortunately, no >1 µm particle count data are available for the clarifier. After reviewing other plant records and interviewing Project 7 staff, the study team determined that at about 02:00 on December 25, 1998, the reclaim pump was operating improperly. Records show that problems with pump operation were caused by operational error and were corrected. These records coincide with the decrease in particle counts for >1 µm. At the same time, there was a dramatic change in clarifier particle counts and turbidity measurement. While Project 7 operations staff don t know the exact cause of the >1 µm particle excursion beginning on December 24, they believe it s related to operation of the reclaim pump Effluent PCX-10 > 1µm Particles/ml Effluent Turbidity Clarifier Turbidity Clarifier PCX >2 µm /12/24 15: /12/24 16: /12/24 17: /12/24 19: /12/24 20: /12/24 22: /12/24 23:34 00:58 02:31 03:56 05:21 06:46 Turbidity, NTU Clarifier PCX >2 µm Effluent PCX-10: >1 µm Clarifier:Turbidity Effluent:Turbidity Figure 6. Shows particle counts and turbidity measurements from the clarifier effluent and the >1 µm counts from the effluent PCX-10. Pacific Scientific Instruments Particle Counter Sensitivity 11

12 This example demonstrates how important it is to have multiple measurements from multiple instruments when identifying and assessing operational malfunctions and errors. Conflicting instrument measurements often afford the greatest opportunity to discern anomalous process operation. Cyclic filter performance At various times during the study period, cumulative >1 µm particle counts were found to produce a nearly straight line response. On the other hand, cumulative counts for >2 µm counts climbed. The study team discovered that this climb normally preceded a period of cyclic particle counts in all channels. Figure 7 Figure 7 illustrates one example of this upward trend for December 31, (A similar phenomenon on January 14, 1999 is illustrated by figure 8.) Particles/ml PCX-10 >1 µm :01 PCX >2 µm 01:51 03:41 05:31 07:21 PCX-10 >1 µm 09:11 11:01 12:51 14:41 16:31 18:21 20:11 22:01 23: Particles/ml PCX and Effluent PCX-10:>1µm Effluent PCX-10:>2 µm Effluent PCX >2 µm Figure 7. Shows an example of upward trend. As stated earlier, Project 7 routinely operates filters for about 120 hours. In the scenario illustrated in figure 7, filter 5 had been in service for 86 hours by 08: Pacific Scientific Instruments Particle Counter Sensitivity

13 Particles/ml PCX-10 > 1 µm PCX-10 >1 µm PCX >2 µm 1999/01/14 00: /01/14 01: /01/14 02: /01/14 03: /01/14 04: /01/14 05: /01/14 06: /01/14 07: /01/14 08: /01/14 09: /01/14 10: /01/14 11: /01/14 12: /01/14 13: /01/14 14: /01/14 15: /01/14 16: /01/14 17: /01/14 18: /01/14 19: /01/14 20: /01/14 21: /01/14 22: /01/14 23:08 Effluent PCX-10:>1µm Effluent PCX-10 >2µm Effluent PCX >2 µm Particles/ml PCX and PCX-10 > 2 µm Figure 8. Shows filter 3 after being in service for 84 hours. Figure 8 Similar to the scenario in figure 7, filter 3 in figure 8 had been in service 84 hours by 14:00. The study team found two items of interest. One is the cyclic particle counts recorded by both the PCX and PCX-10. The other is that even though the cumulative particle counts >1 µm are cyclic, they remain fairly constant on both days. By contrast, the >2 µm channels of both the PCX-10 and PCX record cyclic and increasing particle counts >2 µm. Based on this observation, the Project 7 operations staff is reviewing operating procedures that allow filters to stay on line for 120 hours. Experiments are being conducted to determine whether adjustment of the procedure for adding filter aid would be beneficial. Finding opportunities for further study As the example involving the reclaim pump shows, conflicting information from multiple measurements provided an opportunity for further study. While particle counts >1 µm and >2 µm demonstrated the cyclic filter operation, the difference in the trends gave warning of the event. Though further study is needed, it appears that the cyclic operation after many hours in service may be filter specific. This is one reason Project 7 plans to add particle counters to individual filter effluents. Pacific Scientific Instruments Particle Counter Sensitivity 13

14 Filter ripening Figure 9 Figure 9 illustrates particle count operations on January 7, Filter 5 was placed in service at 10:00. Filter 6 was taken off line at about 14:00, after 126 hours of service. In this case, the study team observed no cyclic particle counts, even though filter 6 operated more than 120 hours. This lends credence to staff suspicions that the cyclic events are filter specific Particles/ml >1 µm Filter 5 in service PCX-10 > 1µm PCX > 2µm Filter 6 out of service PCX-10 >2µm Particles/ml PCX and :01 01:51 03:40 05:30 07:20 09:10 11:00 12:50 14:40 16:30 18:20 20:10 22:00 23:50 Effluent PCX-10:>1µm Effluent PCX-10:>2 µm Effluent PCX: >2 µm Figure 9. Shows particle count operations on January 7, Rescaling the graph in figure 9, it s clear that filter ripening occurred more quickly for particles <2 µm than for particles >2 µm. (See figure 10.) 14 Pacific Scientific Instruments Particle Counter Sensitivity

15 Figure 10 The study team often observed that after a filter was placed in operation and another taken out of service, the <2 µm particle counts decreased to initial values more quickly than particle counts >2 µm. So, filter ripening does not occur as quickly for particles >2 µm as for particles <2 µm. Trend lines on figure 10 help to visually explain this phenomenon. Particles/ml >1 µm :01 00:31 01:01 01:31 02:01 02:31 03:00 03:30 04:00 04:30 05:00 05:30 06:00 06:30 07:00 07:30 08:00 08:30 09:00 09:30 10:00 10: Effluent PCX-10:>1µm Effluent PCX-10:>2 µm Effluent PCX: >2 µm Particles/ml PCX and Linear (Effluent PCX: >2 µm) Linear (Effluent PCX-10:>2 µm) Linear (Effluent PCX-10:>1µm) Figure 10. Shows trend lines regarding filter ripening for particles <2 µm versus >2 µm. Turning conflicts into opportunities Obviously, there are several opportunities for the operations staff to continue to study and make further improvements. But that is what well operated utilities do strive for continuous improvement. Data collected during this study clearly demonstrates the value of having multiple measurements. It is usually not a single measurement, or a series of measurements from a single instrument, that is most valuable in assessing water treatment operational events and procedures. Instead, measurements from multiple instruments provide the greatest information and the most value. Pacific Scientific Instruments Particle Counter Sensitivity 15

16 Measurements from two different instruments sometimes provide the same trend information or the same instantaneous response to an event. Thus, one measurement confirms the other. In some cases, conflicting information from different instruments provides opportunities for further study. Looking back Figures 4 and 5 demonstrate the circumstance where measurements conflict. These figures also show the value of two measurements corroborating one another. In the first instance, the data for particles >1 µm showed significant deviation from normal. Yet, data for particles >2 µm, which came from two different instruments, showed close agreement and little variation. Agreement of the >2 µm counts from the PCX and PCX-10 effluent particle counters indicates proper >2 µm operation of both instruments. But the sudden increase in >1 µm counts does not indicate instrument error in the >1 µm channel of the PCX-10. Instead, the sudden change in the >2 µm clarifier particle counts corroborates a significant process change. Thus, the validity and sensitivity of the response in the >1 µm channel of the PCX-10 on the effluent is established. Conclusion The original goal of this study was to determine whether or not the inherent higher particle counts from a particle counter with one-micron sensitivity would provide more statistical confidence or measurement precision than those from a sensor with two-micron sensitivity. For much of the study period, the trends displayed by the two sensors were parallel. As is often the case, conflicting values provided the most information. A large amount of significant data gathered by Project 7 during this eight week study period is still being analyzed and compared with other records to determine exact operational causes. The study shows that using a particle counter with one-micron sensitivity is valuable for improving water treatment process programs. Each instance cited in this report, along with others still under investigation, has been directly related to an operational cause such as operator error, chemical feed adjustments, effect of the reclaim system or filter run time. 16 Pacific Scientific Instruments Particle Counter Sensitivity

17 The study team also identified differences in techniques of individual operators in control of the unit processes. Each of these events had the potential for detrimental impact on the quality of product offered to customers. Specific observations include: 1. The lack of a particle counter on each filter effluent hampered the process of establishing cause/effect relationships in observations. The study team believes that some of the events observed directly relate to the integrity of one or more filters. 2. Operation of the reclaim system to minimize impact on plant operation requires further study. 3. Filter run times of 120 hours may not be appropriate. Other possible adjustments to help minimize or eliminate variations in operation include chemical feed practices and dosages. 4. Project 7 plans to install eight sensors in the plant by year-end. Based on observations made during this study, staff is considering installing at least one sensor with one-micron sensitivity. This sensor would monitor combined filter effluent, but could be moved around the system to monitor specific filters or other unit processes. This is possible because quick connect wiring at the plant has already been installed, making the instrument easy to move around within the network. Thanks and acknowledgments The authors recognize the contribution to this paper in review and critique by Joel Sorem and John Hunt of Pacific Scientific Instruments, and Richard Margetts, Manager for Project 7 Water Authority. Pacific Scientific Instruments Particle Counter Sensitivity 17