AWWA MTC69745

In 2005, the City of Minneapolis installed a 70 MGD ultrafiltration (UF) system at Columbia Heights, provided by GEIonics, and based on Norit membranes. The objective of this paper was to demonstrate the development of tools based on permeability measurement to assist operational personnel with the monitoring and assessment of their plant, and provide guidelines for decision making. At the design conditions used in commercial UF plants, fouling rates increase exponentially with flux. Selection of flux is therefore a finely balanced trade off between capital and operating cost, since an excessive flux will lead to high operational pressures and high chemical usage. Once a UF plant has been installed, permeability can be monitored to assess operational stability of the plant, and determine the effectiveness of the chemical wash procedures. However, permeability trends can provide an overwhelming level of data, especially for a multi-rack system. This paper provides a method of analyzing data to assist the monitoring process, and proposes the use of two simple indices. The Permeability Recovery Index (PRI) measures the fouling propensity of the feed and the extent of recovery of permeability from one Chemically Enhanced Backwash (CEB) to the next. PRI could indicate an ineffective CEB procedure, perhaps due to a mechanical failure such as a sticking valve, failed pump, or poor chemical distribution between racks. The Cleaning Effectiveness Index (CEI) measures the effectiveness of a series of CEBs, and would demonstrate the suitability of the chosen protocol. This indicates whether the CEB strategy has been effective over a period of time, and quantifies long term downward trends. CEI can be used to both assess the effectiveness of the CEB procedure and predict the need for a Clean In Place (CIP). The monitoring indices have been used together with absolute levels of permeability, to provide operational guidance, and ensure stable plant operation. Data is presented for a 2 year period to illustrate the use of the indices at Columbia Heights. The combination CEI and PRI monitoring indices can be used to define a trigger for action at two different levels. Includes 4 references, tables, figures.