Water Quality - Filtration of water samples; two new filters available In Reply Refer To: August 14, 1980 EGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM N0. 80.22 Subject: Water Quality - Filtration of water samples; two new filters available This is to bring to your attention two new products that may prove useful in filtering water samples. One is a pleated membrane capsule filter by Gelman Sciences, Ann Arbor, Michigan and the other is a 102 mm submersible backflushing filter system by Leonard Mold and Die Works, Denver, Colorado. Both products have been tested by the Quality of Water Branch and found acceptable for use. In the course of your normal field operations you may find situations where one or both of these products will be particularly convenient. Gelman Sciences now markets a disposable 0.45-m minicapsule filter, product no. 12123, that can be used to replace a plate filter for routine or difficult filtering operations. The minicapsule filter sells for $9.00 each. It has an effective filter area of 500 square centimeters, which is almost 4 times the filter area of a 142 mm plate filter and 7.5 times the 102 mm plate filter. The cartridge is not replacable so the complete capsule is discarded after use. It cannot be reused for filtering other samples once is has been used. The minicapsule filter has a 1/2 inch diameter hose fitting molded to it so it can be used as an inline filter in connection with a peristaltic pump. Tubing adaptors will be required, though, since most of the pumps used are not outfitted with 1/2 inch diameter tubing. Tests conducted by the Denver Central Laboratory indicate that no significant concentrations of major ions, nutrients, or trace elements are leached from the capsule filter after a rinse of 500 ml of distilled water. The company recommends passing 3 liters of distilled water through the capsule to remove all traces of the wetting agent and other leachates. Based on these results the Branch recommends that for field filtration, 2 liters of distilled water should be flushed through it followed by 500 ml of sample before collecting the filtered sample for chemical analysis. Leonard Mold and Die Works now markets a 102 mm diameter submersible backflushing filter system selling for $70 each. It is molded from clear polycarbonate and has an adapter plate that can be added to converting it to an inline filter. The submersible backflushing filter is used by connecting it to the intake line of a peristaltic pump. The filter is placed directly into the churn splitter or other large mouth container used to composite the sample, The peristaltic pump draws only filtered water through the system keeping the tubing clear of sediment material. When using the submersible filter do not use tubing that has been used to pump water- suspended sediment samples. Backflushing is conducted by reversing the pump direction, then slowly pumping back about 10 ml of filtered water. The sediment cake is forced off the filter face, restoring the filtering capability of the membrane filter to near its original capacity. It should be remembered that all representative water-suspended sediment samples should be taken from the churn splitter prior to the filtering operation, because the contents of the churn splitter will cannot be considered a representative sample after the filtering has taken place. Since the filter is placed directly in the sample it should be kept clean at all times and stored in a plastic bag between use. the field technician should be equipped with several filters, each cleaned and bagged. After use, the filter should be returned to the field service lab for cleaning before it is reused. A high-strength membrane filter is used in the submersible filter system. Regular cellulose filters cannot be used unless no backflushing operation is conducted. There is no support on the sediment side of the membrane and during backflushing the membrane stretches slightly, thereby helping to rinse the sediment cake off. When forward filtering is resumed the membrane must pull back smooth or be strong enough to prevent cracking if a crease develops. Leonard Mold and Die Works sells a 0.45 micron membrane filter to use with the system that is designed to operate under the conditions imposed by the backflushing operation. R. J. Pickering WRD Distribution: A, B, S, FO, PO