Since late 1999 20 Mm<sup>3</sup>/year (15 MGD) pre-treated IJssel Lake water is subjected to an
integrated membrane system (IMS) at Heemskerk surface water treatment plant. The plant
combines the application of ultrafiltration (UF) and reverse osmosis (RO) and was one of the first
large scale IMS's. Two operational aspects of the UF application asked for special attention:
the Trans Membrane Pressure (TMP) and the membrane integrity. During operation, the TMP
increase in winter became higher each year of operation. In the third winter TMP became so
high that the membranes had to be cleaned intensively with a warm 500 ppm NaOCl
solutions. The related permeability loss may be caused by a loss of negative charge caused
by the use of NaOCl, thereby changing the character of the membrane from hydrophilic to
hydrophobic. This process takes place slowly and may be characterized as ageing.
Measuring TMP or permeability with clean water is insufficient to differentiate between a
change in membrane characteristics (ageing) and fouling. Therefore, methods should be
developed to measure surface charge and fouling. Directly after start-up the fiber breakage of
the Norit X-flow standard (S 225 PVC 0.8 UFC M5 FSFC) UF-membranes was rather high,
leading to an integrity loss of this treatment step. The general idea was that this phenomenon
was caused by weak fibers and should tail away. However, the phenomenon increased
leading to repair shut downs of 4-5 times a year. During the winter season the plant
experienced a higher fiber breakage rate. The majority of the fiber defects (70%) were due to
membrane collapse, most likely caused by high TMP's during filtration and/or backwash. To
overcome these problems a new stronger membrane with a much higher permeability was
developed. This membrane allowed an increase in critical flux rates and a decrease in the
operating pressures. In 2002 pilot testing was started with new prototype elements in
comparison with standard elements. It was shown that during filtration and backwash the
pressure required by the new elements was almost 50% lower than the pressure for the
standard elements. During a period of 14 months zero fiber breakage was found for the new
membranes. Based on the superior pilot data it was decided to replace all membranes in the
full scale plant by the new membranes (SXL 225 PVC 0.8 UFC M5 FSFC). The new
membranes are in operation since September 2005 and run at an average TMP of 0.3 bar (4.3
psid). No fiber breaks were found during the acceptance testing and the first 15
months of operation. Includes 4 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 450 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 10 |
| Published : | 03/01/2007 |
