SEW AC,! : DISPOSAL. ,S 5 



through with a minimum amount of resistance. There are various ways of obtaining the purification 

 of sewage, and some of the reasonable methods suitable for private property will be reviewed. 



The old system of discharging the whole of the sewage into a cesspool, or midden, and allowing 

 the liquid to gradually filter into the adjoining land, though a convenient form of &quot; disposal,&quot; is hardly 

 such as will be accepted to-day, and the more modern local bye-laws now compel all cesspools to be water 

 tight without an overflow. This has rendered the cesspool system very costly and inconvenient, OWUIL; 

 to the continual necessity of cleansing and emptying. Many people still contend that the old open cesspits 

 should be allowed where it is not reasonably probable for wells to become contaminated. It should be 

 remembered, however, that liquids percolate and travel to a vast distance, and the health ol the community 

 at lai f^e must be considered. \Ylien it is taken into account that bacilli (such as that ol typhoid) will 

 not be rendered harmless by any amount of ordinary filtration, every endeavour should be made to conduct 

 the eliluent into the most harmless channel. All sewage, then, should be treated to obtain a reasonablv 

 high standard of purity, and the sludge and effluent disposed ol in the safest manner. 



Though the open cesspool or pit is not to be recommended, a modification of it may, in certain 

 circumstances, be allowable. This consists of an ordinary water-tight tank, into which the crude sewage 

 is discharged and the overflow conducted to bacteria beds, as described later ; it should, however, only 

 be adopted as a temporary measure. Present knowledge indicates that the septic tank, which has had 

 a long trial, gives general results which have proved satisfactory. The system has many advantages. 

 and is undoubtedly the most convenient form. The method of treating sewage chemically by addin; 

 iron and lime, and \Yuis causing precipitation, is not one which can be cordially recommended for private 

 houses; the labour and consequent cost and trouble are such as to render it undesirable. Moreover, the 

 eliluent from chemically-treated sewage is not so satisfactory as that obtained from properly-designed 

 septic tanks and bacteria beds, and the comparatively large proportion of sludge resulting from the 

 chemical process has to be cleared out and disposed of. The general lay-out of a septic system consists 

 ol three main divisions (it) preliminary chamber or detritus tank, (l&amp;gt;) septic tanks, (&amp;lt; ) bacteria beds (often 

 misnamed filters). The detritus tank should be arranged to retain all foreign matter, including, as far 

 as possible, sand and grit. Screens should be insetted so that the sewage has a path with the least possible 

 resistance. Where the rain-water is discharged into the sewage system, an overflow pipe should be 

 connected to this chamber, so that a sudden rush of water will not unduly disturb the septic tanks. The 

 connection from this preliminary chamber to the septic tank should be so arranged as to allow a free flow, 

 but at the same time to cause as little disturbance as possible. In order to obtain this result, the inlet 

 may be brought in at the top of the tank, but discharged about six inches above the bottom. Septic 

 tanks are plain chambers without any tilling, and with outlets taken from the top, though the pipe dips 

 to about six inches from the floor, and they remain lull. During the course of putrefaction the gases 

 cause a thick scum to form on the top, which should not be disturbed ; hence the arrangement of inlet 

 and outlet as described. Provided that the septic action is not interfered with, there will be practically 

 no sediment or sludge in the septic tanks. 



The preliminary, or detritus, tank will require cleaning out at certain periods, but the septic tanks 

 should not require this. The action in the septic, or anaerobic, tanks should reduce the organic solids 

 by about eighty-five to ninety per cent. To ensure this result it is better to have about three septic 

 tanks together, as a better and surer result will be obtained with three small tanks than with one large one. 

 They should be of sufficient capacity to take not less than thirty-six hours discharge. No such tank 

 or tanks will give an effluent of sufficient purity to be discharged without further treatment ; therefore 

 bacteria beds (or so-called filters) are used. These beds are open to the atmosphere, whereas the septic 

 tanks are closed (with the exception of small safety-valves to relieve undue pressure formed by the gases). 

 For private installations these bacteria beds should be of such a size that not more than fifty gallons is 

 passed through the beds for every yard superficial per day of twenty-four hours, and the beds should be 

 not less than four feet deep. 



To ensure proper action in the bacteria bed, which is essentially aerobic, the filling material must 

 be of such a nature as to allow free and easy circulation of air, and material which gives the greatest 

 surface in contact with the air reduces the size of the beds, and is thus the most economical. Such 

 material, however, should not be one that easily clogs or in any way disintegrates. Of the many that 

 are in use, coke probably gives the best results. The percentage of voids in coke beds varies according 

 to the size of material used, but an average of about thirty-five per cent, may be safely taken, and coke will 

 absorb water up to about fourteen per cent, of its own weight. There is thus a large surface free to the air, 

 and experiments show that large porosity and power of reabsorbing atmospheric oxygen are necessary. 

 In all aerobic beds it is essential that periodical and proper periods be allowed for &quot; rest,&quot; so that they 

 may become thoroughly aerated. The time allowed varies according to circumstances : but for private 

 installations, if two aerobic beds are in use, one bed would be filling for twenty-four hours, and should then 

 be allowed to stand full for, say, three hours. If then emptied, twenty-one hours are allowed for aerating. 

 Provided coke bacteria beds are allowed proper time for aeration, they do^ not become choked. If 



