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12
Relative Temperatures of the Atmosphere and of the Sewage and Effluents.
In Table 2 (page 19) the detailed temperature readings of the atmosphere and the effluents
daring December, 1899, are given. From a general consideration of the averages of these readings it
appears that when the atmosphere was at a temperature of 38.5° Fahr. the sewage flowed into the
primary beds at a temperature of 53° Fahr.; and that after it had remained in the primary beds
for two hours it flowed into the secondary beds at a temperature of 46° from bed A and of 44'5°
from bed B, the air temperature at that time being 38'0°. After the sewage had remained in the
secondary beds for two hours it was drawn off, and showed a temperature of 44° from bed Al, and
42.5° from bed Bl, the air temperature at the time being 37.5°. It will be observed that the
average temperature of the outside air fell during the whole process 1° Fahr., and that the sewage
fell 7° while it remained for two hours in the primary bed A, and a further 2° while it remained
another two hours in the secondary bed A 1, or 9 degrees out of a possible 15.5 degrees fall during
the whole process. In series B the sewage fell in temperature 8.5° after two hours' rest in the
primary bed and a further 2° after another two hours in the secondary bed, or 10.5 degrees out of a
possible fall of 15.5 degrees during the whole process.
In considering this question of temperatures the following facts must be borne in mind—
(1) that the beds were small in area; (2) that their position was exposed, that they stood in
metal tanks supported entirely above the ground level, and that each tank was widely separated
from the others; and (3) that since the tanks were constructed of thin galvanised iron, their
exteriors readily lost beat by radiation as well as by contact with the cold air.
The somewhat lower temperatures found in series B are explained by the fact that the
latter is somewhat more exposed than series A, which stands between series B and a wooden
wind-screen.
In another series of readings which are given in Table 3 (page 20) the air temperature fell
2.5° Fahr. during the process of treatment of the sewage—from 43.5° to 41°; and the temperature
of the sewage fell in both series of beds (A and B) 4.5° in its passage through the primary beds,
and 1 degree more in passing through the secondary beds—a total fall of 5'5° out of a possible
9.5°. In series A the temperature of the beds themselves was taken about four hours after they
had been emptied, and the average temperature of the primary bed was found to be equal to that
of the sewage which had flowed into the bed, viz., 50.5° Fahr., while the outside air stood at 42°.
The average temperature of the interior of the secondary bed was 48°, or 2° higher than that of
the effluent from the primary bed with which it had been filled, and 3° above that of the effluent
when it was drawn off four hours previous to the test, the outside air standing at 41° Fahr.
These details may be summarised as follows—The temperature of the liquid, while it was
standing in the primary bed, fell 4.5 Fahr., but after the liquid had been drawn off, the bed
recovered from this loss of temperature in four hours; this recovery could evidently only be
effected by some internal action which was attended with the production of heat, and is probably
due to the action of the bacteria upon the moist suspended matters contained in the bed.
The liquid, in passing through the secondary bed, lost a further degree in temperature, but the
bed, after standing empty for four hours, rose in temperature again to the extent of 3° Fahr.
Composition of the Air contaired in the Body of the Primary Bed B.
Many analyses were made of the air contained in the empty coke-beds. The detailed
results are given in Table 4 (pp. 20 and 21). From the 19th October to the end of 1899 the air present in
the intertices of the coke-bed, after it had remained empty for the average time of twenty-one
hours on several different occasions, contained the following average percentages of oxygen and carbon
dioxide—
Oxygen 10.3
Carbon dioxide 5.7
Between January 1st and February 23rd, 1900, when the bed had remained empty on many
occasions for an average period of five hours, the following average percentages were found in the
interstitial air—
Oxygen 8.0
Carbon dioxide 5.7
Fresh air contains on an average the following percentages-
Oxygen 20.96
Carbon dioxide 0.04
The average proportion of oxygen present in the air at the bottom of the bed, as compared
with that present in fresh air therefore was, up to the end of 1899, with the bed standing empty
for twenty-one hours, about 50 per cent. From the commencement of the present year until 23rd
February, with the bed standing empty for the average period of five hours, the aeration, as
measured by the above proportion of oxygen, has been about 38 per cent. This is by no means so
satisfactory a condition as could be desired, and is probably due to the fact that the bed had become
clogged by the heavy suspended matters of the crude sewage, and that the putrifactive bacteria
acting on these matters rapidly absorb oxygen from the air and liberate carbon dioxide and other
gases.
Suitability of the Effluent to Maintain Fish life.—The effluent from the primary beds was
capable of sustaining the life of gold fish apparently indefinitely. Less hardy fish, such as roach
dace, and perch, became sickly after living in the effluent for a week or two. It should be
remarked, however, that the fish were in a somewhat sickly condition before they were placed in
the effluent.