An Interesting Example of Sewage Disposal 
“Contact” Mineralizing Beds Automatically Operated by the 
Merritt Air-lock System 
vacuum is broken. There are to-day siphons which 
are more positive in their action, but the “Field” 
has in the past, and is still demonstrating in many 
places the utility of devices for controlling the flow of 
sewage, which are free from moving parts, require no 
oiling, and are not subject to wear. In its use for 
the operation of the plant we are describing this 
siphon has for eight years without intermission, auto¬ 
matically discharged the contents of the dosing tank, 
passing intermittent doses through a lo-inch carrier 
to one or other of two filters composed of coarse sand 
found on the property and placed in position five 
feet in depth, well underdrained and enclosed, and 
held in place by earth banks. These filter beds 
were constructed at two levels. The upper bed had 
an area of somewhat less than one-eighth, and the 
lower one slightly less than one-sixth of one acre. 
These beds were probably assumed to be capable of 
handling upward of 20,000 gallons of crude sewage 
per day, judging by the dimensions of the dosing 
tank. 
Sluice gates were provided so that the flow might 
be changed over from one filter to the other, or so 
that the liquid contents of the upper bed could be 
passed, if desired, to the surface of the lower one. 
The underdrains discharge into a small stream 
traversing private gardens and which it is important 
should be as free from contamination as possible. 
The purpose of this first arrangement was to secure 
purification of crude sewage by simple subsidence 
through sand. The large volume collected for each 
dose in comparison with the small filter bed area, 
indicates that the designing engineer who was origi¬ 
nally employed relied too much upon straining the 
sewage and too little upon its bacterial oxidation in 
sand sufficiently supplied with air. 
At first when the volume of sewage was small, 
good results were obtainable. The sewage freed from 
its heaviest solids by deposit in the grit chamber. 
was flushed over the surface of the sand filters, 
where the matters in suspension were collected and 
periodically raked oft'and buried. I'hose matters in 
solution, which it should he mentioned form much 
the greater part of the organic matters in sewage, 
passed into the sand where they adhered to the par¬ 
ticles by “mass action,” allowing the water with 
which sewage is mixed, to pass into the underdrains 
well purified. Later when the population of the 
district had increased, necessitating a larger volume 
of sewage to be treated, the favorable conditions 
governing the successful use of sand filters as the 
only means of purifying sewage water, no longer 
existed, and despite constant manual attention, it 
was found impossible to prevent an accumulation of 
impurities in the sand which choked many of the 
small passageways, causing the filter beds to become 
water logged, that is to say, water was held up in the 
sand by capillarity, long after it should have drained 
away and air should have taken its place. Hence, 
the masses of sand became what is known as “sew¬ 
age sick” and little or no oxidation was possible. 
Like experience has been frequent in connection 
with similar plants, and much money has been spent 
in providing additional filter beds, when as originally 
constructed they would to-day have been effective, if 
those who designed works ten years ago had enjoyed 
the knowledge which is now held in regard to this 
subject. 
In the case to which this paper has reference, san¬ 
itary engineers who were called into consultation 
decided not to increase the number and area of sand 
filters, thus merely postponing the time when a fur¬ 
ther extension would he necessary, and which would 
further increase the labor account for attention to the 
surfaces of the sand beds, but instead to adopt pre¬ 
liminary methods in common use in Europe, which 
Bed of Sand Five Feet in Depth, formerly Relied upon for 
Purifying Crude Sewage. Now Employed for 
Filtering Oxidized Sewage Water 
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