1965 Volume 31 Issue 12 Pages 977-982
In the previous paper4), it was pointed out by experiments with 4 filters of Suma Aquarium of Kobe City that the oxygen dissolved in breeding water was considerably consumed during its passing through the sand beds, and that there was a close correlation (coefficient=0.97) between the oxygen consumption and the BOD decrease during filtration.
The oxygen consumption during filtration (abbreviated to OCF) seems to be due to biochemical oxidation by the microorganisms propagating in the filter. The present studies have been carried out in order to know whether OCF can be used as an index in evaluating the degree of purification of breeding water by filtration. For this purpose, special experimental filters were designed (Fig. 1), to which the breeding water of Surna Aquarium was introduced.
The results obtained are as follows.
1. There is a close correlation (coefficient=0.63) between OCF and the BOD decrease during filtration of breeding water through sand layers of various depths (Fig. 2).
2. During filtration of breeding water, ammonia decreases in concentration in response to depths through which the water is filtered through sand layer (Fig. 3). Since this decrease may be almost attributed to nitrification, on the assumption that the change in the concentration of ammonia and nitrite during filtration are only due to the oxidation of ammonia, the oxygen consumption by nitrification can be estimated from this change. The relation between calculated oxygen consumption by nitrification and depth of sand layer is similar to that between OCF and sand depth (Fig. 4).
3. Deduced from the data thus calculated, the oxygen consumption by nitrification occupies 34% of OCF in experiment 1, and 53% in experiment 2 (Fig. 4).
These results confirm that OCF can be used as a satisfactory index in evaluating synthetically the degree of purification of breeding water by filtration.
