March 8, 1919: Municipal Journalarticle. Sprinkling Filter Flies. “One of the objectionable features connected with sprinkling [trickling] filters is the prevalence at most of them, during certain seasons of the year, of myriads of small flies. This fly is small and moth-like, 3 to 5 mm. long, the body and wings covered with fine hair. Millions will breed in a filter during a season. They may be carried by favorable winds three-quarters of a mile from the plant, but generally remain rather close to it. Ordinary window screens do not keep them out.
The result of experiments conducted at the sprinkling filters of Plainfield, N. J., was set forth by C. S. Beckwith, assistant entomologist of the New Jersey State Agricultural Experiment Station, in a recent issue of “New Jersey Municipalities.” His statement was as follows:
In studying the habits of the flies it was determined that the breeding continues throughout the entire season. During the cold months they are present in the larval and pupal stages, emerging with the coming of warm weather. The abundance of the flies during the warm season seems to be correlated with the thickness of the film on the stones of the filter. A thick film means more flies, and a thin film, fewer flies. The thick film of late spring gives rise to a tremendous brood. After the film has broken down and sluffed off the number is greatly reduced. Again with the thickening of the film in late summer, the flies become abundant….
It thus seemed that submergence for 24 hours destroyed 100 per cent of the larvae and pupae. To make the matter more certain, one-fourth of the Plainfield sprinkling filter, amounting to a little less than one-half acre, was submerged for a period of 24 hours with ordinary sewage water as it came from the dosing tank. At the end of this period the water was released and many samples were taken. Enormous numbers of larvae and pupae came out with the water, and not one could be found that was alive.”
Reference: “Sprinkling Filter Flies.” 1919. Municipal Journal. 46:10(March 8, 1919): 196.