AWWA MTC64558

Since late 1999 20 Mm³/year (15 MGD) pre-treated IJssel Lake water is subjected to anintegrated membrane system (IMS) at Heemskerk surface water treatment plant. The plantcombines the application of ultrafiltration (UF) and reverse osmosis (RO) and was one of the firstlarge 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 TMPincrease in winter became higher each year of operation. In the third winter TMP became sohigh that the membranes had to be cleaned intensively with a warm 500 ppm NaOClsolutions. The related permeability loss may be caused by a loss of negative charge causedby the use of NaOCl, thereby changing the character of the membrane from hydrophilic tohydrophobic. This process takes place slowly and may be characterized as ageing.Measuring TMP or permeability with clean water is insufficient to differentiate between achange in membrane characteristics (ageing) and fouling. Therefore, methods should bedeveloped to measure surface charge and fouling. Directly after start-up the fiber breakage ofthe 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 phenomenonwas caused by weak fibers and should tail away. However, the phenomenon increasedleading to repair shut downs of 4-5 times a year. During the winter season the plantexperienced a higher fiber breakage rate. The majority of the fiber defects (70%) were due tomembrane collapse, most likely caused by high TMP's during filtration and/or backwash. Toovercome these problems a new stronger membrane with a much higher permeability wasdeveloped. This membrane allowed an increase in critical flux rates and a decrease in theoperating pressures. In 2002 pilot testing was started with new prototype elements incomparison with standard elements. It was shown that during filtration and backwash thepressure required by the new elements was almost 50% lower than the pressure for thestandard elements. During a period of 14 months zero fiber breakage was found for the newmembranes. Based on the superior pilot data it was decided to replace all membranes in thefull scale plant by the new membranes (SXL 225 PVC 0.8 UFC M5 FSFC). The newmembranes are in operation since September 2005 and run at an average TMP of 0.3 bar (4.3psid). No fiber breaks were found during the acceptance testing and the first 15months of operation. Includes 4 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

03/01/2007

Number of Pages:

10

File Size:

1 file , 450 KB