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.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/01/2009 |
