The increasing use of membrane filtration in water treatment application has focused greater attention on the need to optimize chemical pretreatment to minimize membrane fouling; for example, the City of Minneapolis draws water from the Mississippi River and has found that control of lime-softening is critical to protect its new ultrafiltration plant. Alkalinity is a fundamental and widely measured parameter in water treatment, but the options for online measurement of alkalinity are very limited. Most alkalinity measuring instruments are expensive, complex, and not responsive enough for online monitoring and control. Instead alkalinity is routinely measured manually with trained technicians conducting time-consuming titrations. The proposed research will test the concept of using a novel dual membrane alkalinity sensor to measure alkalinity in water samples. The component parts are not expensive, and the use of two membrane modules provides automatic correction for temperature effects and varying dissolved gas concentrations. A theoretical analysis of the sensor suggests that it is capable of measuring alkalinity to +/- 0.3 mg/L as calcium carbonate with a response time of less than 2 seconds. The precision and accuracy of the sensor and its response rate will be measured on standard samples and then field tested side-by-side against titrations performed at the Minneapolis Water Works by trained technicians. It also will be linked with calcium and pH measurements to determine the calcium carbonated saturation index of water automatically. Statistical analyses of these data will prove whether the sensor is capable of meeting the expected theoretical performance. The important design features of the sensor will be identified, and a preliminary cost analysis will be made. Results This study will demonstrate that a dual-membrane sensor can provide reliable, accurate, and rapid measurements of alkalinity. The sensor should be fast enough that it can be used for real-time process control, and it also should automatically correct for changes in temperature and dissolved gas concentrations that are common during water treatment. This study will identify the important design criteria for sensor construction, including the range and specifications of the component parts, the membrane type, membrane module design, sample volume requirements, and sensor response times. Operating issues such as: humidity limits, the alkalinity range, sensitivity and noise issues, accuracy, stability, and so on, will be determined in this study. A complete review of prior attempts to develop an automatic alkalinity sensor have required gas sparging to remove dissolved carbon dioxide, and sophisticated equipment, including infra-red analyzers, spectrophotometers, and precision pumps. The concept that Technology Specialists is proposing to test takes advantage of two gas permeable membranes to sense changes in the equilibrium gas pressure. Hollow fiber membranes with small gas volumes and a large specific surface area provide an excellent means of doing this. Several earlier approaches have attempted to use the same principle but in different ways. Technology Specialists believes that its approach will prove both simpler and more robust. In addition, Technology Specialists believes that the cost of this sensor could be significantly lower than previous designs. This Phase I effort will provide proof of concept for a patent application. Technology SpecialistsÂ’ research results will identify the sensorÂ’s capabilities and limitations, which will determine whether or not the sensor is worthy of further development. If the project is successful, the research will identify important design criteria and system specifications that will enable Technology Specialists to move forward with sensor development in Phase II. Potential Commercial Application Alkalinity is a fundamental water quality parameter that is measured frequently in many water and wastewater treatment processes. It is important in regulating process pH and needs to be monitored routinely to optimize treatment process performance. Alkalinity also is a significant parameter in corrosion control. Currently, accurate alkalinity measurements are made on collected samples by titration with an acid, which requires a trained technician and a well-equipped laboratory. As a result, frequent alkalinity measurements are time consuming and expensive, and many water and wastewater treatment plants spend a great deal of money each year on these analyses. The alkalinity sensor would not only reduce the cost of these analyses but also would lend itself to online monitoring, which would aid process control. With increasing water re-use, and more and more membrane applications in water treatment, process control is becoming more important and an online alkalinity sensor would be very beneficial for process optimization. Alkalinity is measured routinely in thousands of water and wastewater treatment plants in the United States alone. States, counties, EPA and the U.S. Geological Survey all have programs to monitor surface water quality, and a large number of water samples are analyzed for alkalinity each year. Many industries, including the power industry, need to monitor alkalinity accurately as part of their water quality control strategy. In addition, accurate alkalinity measurements are key to many research projects involving both engineered and natural environmental systems, for example, the influence of global warming and the effects of increasing carbon dioxide concentration on freshwater and marine ecology. In all of these applications, an accurate easy-to-use sensor would reduce the costs of analysis dramatically. In addition, an online sensor would open new opportunities in both process control and corrosion control. This project will enable the concept to be tested and proven. The data collected in this study will be used to apply for a patent. At this time, Technology Specialists is interested in licensing the product to an appropriate instrument manufacturer to take advantage of its development and marketing capability. Supplemental
Keywords: small business, SBIR, EPA, alkalinity sensor, water treatment, chemical pretreatment, water monitoring, membrane module, water quality, marine ecology, global warming, online alkalinity sensor, corrosion control
