The effects of temperature on the performance of experimental percolating filters with and without mixed macro-invertebrate populations

Abstract

The performance and biology of small percolating filters (capacity 16·7 dm 3) treating a synthetic sewage at a BOD loading of 0.15 kg m −3 d with and without psychodid flies and enchytraeid worms and maintained at constant temperatures of 7, 10, and 13°C for 280 days were compared. The performance of the filters inoculated with flies and worms was substantially better than that of the controls. In the filters with animals nitrification increased with temperature, the temperature coefficient being much higher than that for the growth of nitrifying bacteria. There appeared to be no nitrification in the filters not inoculated with animals. In most cases the peaks in numbers of flies and worms occurred at intervals predicted by their thermal characteristics. Flies were not successful at 7°C. Psychoda severini was the dominant fly at 7 and 10°C but both P. severini and P. alternata appeared to develop equally well at 13°C. Enchytraeid worms were always more numerous than the fly larvae, the highest densities of worms occurring at the two lower temperatures. Protozoan and fungal populations were studied and the application of published expressions for the effect of temperature on the rate coefficient of BOD removal is discussed.