(245d) The Integrity Sensor – A Novel Instrument for Assessing the Performance of Pre-Filtration Membranes

This paper discusses the design and performance evaluation of a novel instrument for detecting the integrity of micro- or ultrafiltration membranes. As such, this instrument, which we refer to as the Integrity Sensor, can be used to determine if some membrane device used for pre-filtration upstream from reverse osmosis modules is performing properly. The operating principle of the Integrity Sensor is based on continuously sampling the effluent stream from the upstream pre-filtration device and measuring the transmembrane pressure across a microfiltration membrane in the Integrity Sensor relative to a reference pressure differential. These two pressure differentials are converted into a dimensionless metric referred to as the π-factor, which is defined as the ratio of the transmembrane pressure to the reference pressure differential. When the Integrity Sensor is put on line, the π-factor has some initial value that corresponds to the microfiltration membrane in the Integrity Sensor being unfouled. However, as the effluent stream from the upstream pre-filtration device is continuously sampled, the π-factor will increase owing to progressive fouling of the microfiltration membrane in the Integrity Sensor. A breech in the integrity of the upstream pre-filtration device is detected by a marked increase in the π-factor. In this paper the performance of the Integrity Sensor is assessed using a feed stream containing a predetermined concentration of a well-characterized foulant. The response of the Integrity Sensor to both the concentration and type of fouling agent in the feed stream is assessed. The time-rate-of-change of the π-factor is shown to correlate reasonably well with the Silt Density Index (SDI) of the feed stream to the Integrity Sensor. The effect of a breech in the integrity of some upstream pre-filtration device is simulated by causing an increase in the foulant concentration in the feed stream. The advantages of the Integrity Sensor then are discussed. These include its convenient retrofitting to water-treatment systems, continuous real-time sensing capability, high sensitivity, reliability, robustness, and low cost.