Dissolved Oxygen Changes During Filtration

Abstract

In connection with experiments conducted at the Highland Park water filter plant to locate the cause of air-binding in filters, the dissolved oxygen was run on a sample of the water entering the filter bed and also on a sample taken from the effluent pipe of the same filter. An interesting fact was discovered. There was a decrease in dissolved oxygen, even though the filter on being washed did not show any entrapped air. This decrease was also evident when the water was not supersaturated with oxygen. It was decided to run a series of tests at intervals during the year when the water was at different temperatures and discover if the temperature had any effect on the decrease in dissolved oxygen during filtration. There are few references in the literature dealing with changes in the dissolved gases of waters that are subjected to sand filtration. This is probably due to the fact that the changes are small, have no apparent practical importance, and vary (as in the case of most water problems) with the quality and treatment of the water. This means that numerous accurate determinations must be made before fair conclusions can be reached. In Germany, Noll (1) made a very extensive and accurate study of dissolved oxygen changes on filtration and found that the change in dissolved oxygen in passing through sand filters was greater than the changes in the oxygen consumed. He states the oxygen may have been used up as follows: (a) by the bacteria, (6) by chemical reactions within the filters, or (c) by escaping from the filters. However, he attached little importance to the last possibility. The raw water source at the Highland Park plant is the Lake St. Claire and is therefore a typical Great Lakes water. Its quality is practically the same the year round and it is an ideal water on which to make the determinations reported in this paper. It is pumped 11 miles before filtration against a 43-foot head, the pressure at the