Filtration Gutters
The gutters which I have used, and which have been found to answer in a manner which has far exceeded my expectations, are constructed as follows:—
A trench 2 feet deep and 18 inches wide, and of a length varying with the circumstances, is dug, and filled up with porous material, such as builders' rubbish, old crockery, and tins, stones, &c., &c., to within a few inches of the surface, and upon this rubbish, previously rammed, walls of concrete or honeycomb brickwork are formed, provided with a ledge sufficiently wide to support a perforated tile, the perforations being big enough to admit a large sized knitting-needle, say ⅛ in. in diameter. The porous rubbish reaches to within an inch of the under surface of the tile, and the sides are planted. The gutter may, if necessary, be protected by a grating.
Fig. 26.—Filtration Gutter.
Or the gutter may with great advantage be placed upon a bank with gradually sloping sides.
In both cases the sides of the gutter should be planted with quick-growing shrubs, and it will soon become ornamental. Such a slop-gutter on a raised and planted bank would form a most excellent boundary fence. These gutters are shown in figs. [26] and [27]. The perforated tile which forms the floor of this gutter is a most important part of it, because it allows the gutter to be cleared of dead leaves and other rubbish, which inevitably fall into it, and it protects the porous material from getting clogged. It breaks the force of the water and prevents the downpour from the pipes from ploughing up the rubble, which is a most important matter. I have used various things for forming the floors of these gutters, and have found nothing better than the perforated tiles which are used for forming the floors of malt kilns. I have no doubt that the gutter could be made perfectly well in galvanised iron. What lengths of such gutters should be provided? To answer this question I can only give my own experiences.
Two years ago I constructed such a gutter for a girls' school where there are between 30 and 40 day scholars and boarders. I dug out my trench leading into a natural rivulet, and I formed a gutter 40 feet long. I do not think the slops in this case have ever travelled as much as six feet, and there is no evidence that a drop of slop-water has ever touched the rivulet. The privets have grown, but the gutter has never been foul, and when the tiles have been taken up the porous rubbish beneath has been found perfectly sweet, and there has been no sloppiness at the sides.
Fig. 27.—Filtration Gutter on Bank.
A similar gutter on a bank was provided for a six-roomed house, and the slop-water has never travelled to the end, or anywhere near it, notwithstanding a considerable fall.
The water of a fixed bath has run for nine years into a gutter 20 feet long, and at times as much as 120 gallons a day has flowed into it, but the water is never visible two minutes after the waste has ceased to flow; there has been no foulness of any kind, and the only effect has been to make the shrubs grow.
The bedroom slops of a country mansion with twenty-three inhabitants were taken, eighteen months ago, into a plantation, and the only result has been that the limes have thrown up suckers, but there has been neither sloppiness nor foulness.
The bedroom slops of a cottage with five inhabitants have run for five or six years along a gutter 12 feet long, at the foot of a privet hedge, and there has been neither sloppiness nor foulness, except when, as stated above, I produced stagnation.
4. When it is feasible, it is advisable to allow different varieties of slops to flow in separate gutters.
The waste of fixed baths is almost clean, containing nothing but a little soap at most; bedroom waste contains soap and urine, but no solid particles of any size to give trouble, except a stray bit of paper, or an old match, or a few hairs, and some fluff from towels, which will all be caught upon the perforated tiles, and can be swept up occasionally.
Fig. 28.—Kitchen Sink with Duplicated Outside Filter.
The waste from kitchen and pantry sinks needs careful straining and filtering before it is allowed to flow into an open gutter. I have mentioned the necessity of providing strainers and a sink-basket, and I now proceed to describe the slop-filter which is advisable for the kitchen sink (fig. [28]). The waste-pipe of the sink must terminate 2 feet or 2 feet 6 inches above the ground level, and be provided with a reversible nozzle delivering over a filtering vessel made of concrete or iron. This filter is in duplicate, and is provided with a diaphragm reaching to within an inch of the bottom. Each half of the vessel measures 1 foot by 1 foot 6 inches, and is 2 feet 6 inches deep, and has a capacity of 3·75 cubic feet. The outflow is immediately beneath the diaphragm, and empties into the open gutter. Each half of the filter is filled with stones varying in size from a hazel-nut to a walnut, and the waste is allowed to flow through one half of the filter, and then, when that half gets foul, the nozzle is reversed, and the second half is brought into use, and the half first used can be cleaned out. The filter must be provided with a fine copper strainer, and if the slops be carefully strained the filter will not get foul for months; but if lumps of fat and slabs of cabbage-leaves be allowed to get into the filter, it soon gets foul, as does the abomination known as a fat-trap.
The method of purifying sewage by 'intermittent downward filtration' is well understood, and the methods advocated here are merely modifications of what has been done in this country, and also by the Massachusetts Board of Health.
What is meant by 'intermittent downward filtration'? How frequent are the intermissions?
The intermissions usually recommended are 'sewage for six hours and rest for twenty-four hours,' but my belief is that the purifying action of the filter-bed ceases directly the filter is filled and water-logged. The intermissions must be perpetual. The supply of slop-water in a private house is essentially intermittent, and this perpetual intermission is the secret of the success of the methods I have indicated. Between nine at night and seven in the morning—ten hours out of every twenty-four—the flow of slop-water is usually nil. Between 8 A.M. and 11 A.M. is the time of the bulkiest flow, but even this intermits. A housemaid's pail with its three or four gallons will come once in ten or fifteen minutes, so that the filter is always being emptied, and as the water drains off the fresh air follows it. The water of a fixed bath is practically clean, and gives the filtration gutter a vigorous stir, which does nothing but good. The domestic intermissions are invaluable. When sewage is collected in a tank and is then allowed to flow without intermission for six hours at a stretch, it is doubtful if the greatest purifying power is obtained from the filter.