[Sidenote: Vegetation of some kind, useful or weeds, _will_ grow from
sewage, and must be frequently removed from land or contact bed.]
This is a matter of vital importance, because when sewage is
_intermittently_ applied to land of any kind or to coke beds,
vegetation of some kind or other must result and must be removed in
order to leave a clear course for the next dose of sewage; the cost of
removal and destruction of weeds will be found very great when contact
beds are tried on any working scale and would be quite prohibitive if
allowed to grow on irrigated land.
Hence we must crowd out the weeds as much as possible by useful plants
which will bring something towards the cost of their removal; and as
that return from perishable greenstuff is dependent upon its immediate
sale or consumption on the farm, the manager must cast about for
demands for his abundant supply; but as both the sunshine (in this
climate) and markets are very capricious factors in the problem, he
has no easy task always to make both ends meet.
Theoretically the town which yields the sewage ought to provide an
abundant demand, but in practice it can rarely be depended upon,
Edinburgh being the only exception, where the Craigentinny sewage
meadows are rented at a very high figure by the cow-keepers of a city
situated in the heart of an arable district.
[Sidenote: Alternative destinations for vegetation thus removed. Milk
(everywhere in demand) or a destructor furnace.]
Fortunately, however, there is always an unlimited demand for milk,
and if he has the means of keeping a herd of cows on the farm, or can
arrange with a neighbouring cow-keeper to take all the grass and roots
he can supply at a low rate, it is about the best course a manager can
adopt.
If he maintains a herd of cows, tied up in good, well ventilated
stables, and has them daily brushed and groomed like horses, they
require no exercise and produce milk in perfection for an average
period of fifteen months from date of purchase after their third or
fourth calving.
Such a herd will consume rye-grass carted from the field from April to
November, and mangolds, kohl-rabi, and rye-grass hay during the
winter, thus securing a uniform demand for produce of the sewage land
throughout the year, and such cows will only require a little cotton
cake and oat straw bedding (of which latter they eat a good deal) to
fit them for sale to the butcher as soon as they become dry.
The advantage of such a steady demand is so great when rye-grass and
mangolds, etc., are indicated as the main crops of the farm, owing to
the large volume of sewage per acre, that the system of cow-keeping is
forced upon managers, however reluctant their sanitary authorities may
be to provide the necessary working capital, unless they can find a
reliable contractor to receive at a fixed price any quantity of grass
and roots the authority may grow and deliver.
[Sidenote: Permanent pasture grazed and for hay available in certain
cases.]
When a town has more land in proportion to its sewage, permanent
pasture may take the place of Italian rye-grass, and, with proper
precautions, a part of the permanent pasture may be grazed; but the
saving of labour, thus supposed to result from letting animals bite
and carry their food, is expended in making up, in a necessarily
imperfect manner, the carriers trodden in by the cattle.
[Sidenote: Importance of neat tidy contour carriers, correctly
levelled.]
And here I would observe that most of the bad odour into which sewage
farming has fallen of late years is distinctly traceable to the common
absence of sufficient regularly contoured and neatly cut distribution
carriers resulting from parsimony about wages bills natural to the
ratepayers’ representatives in Council, and often to the manager’s
dependence on a borough surveyor’s coming to the farm with his level
and staff for great measures, or on his own guesses for smaller works,
instead of using an instrument to peg out every distribution carrier
at the right moment.
[Sidenote: Attract good labour.]
There is another important outlay of capital to be provided for in
every complete sewage scheme, which should embrace sufficient good
labourers’ houses and gardens in order to attract and retain on the
spot the best class of workers.
[Sidenote: Summary of the experience of a lifetime.]
To sum up the general conclusions to which my experience points, and
which I trust may prove useful to district councillors, they are as
follows:—
1. In works of sewerage, limit and regulate, as far as
possible, the volume of sewage by excluding subsoil
water and clean surface water.
2. Where the outfall sewage enters the disposal works
provide a pair of open catch-pits (or grit-chambers), each
twice as wide as, and 2 feet deeper than the sewer, with
sluices allowing the sewage to pass through one pit at a
time in its free course, while the other pit is being dried
and the deposited detritus dug out. The depth below sewer
invert may be more than 2 feet, and length of catch-pit is
immaterial, but I confine its width to twice that of the
sewer in order to conserve sufficient velocity in the
current to carry forward organic matter, paper, etc., and
leave only clean sand and gravel in these catch-pits.
Continuing the course by open channel (of same width as
outfall sewer), it should expand to five or six times its
width, forming the screening chamber, and thence discharge
into the
3. Depositing tanks. These are best formed in concrete with
smooth surface, with a semicircular level weir from which
the liquid overflows into a semicircular collecting open
carrier leading to the aerobic process on land or contact
bed.
The semicircles above referred to are struck from centre of
the inlet to depositing tank with a radius of 50 feet or
more.
The weir level should be at least 1 inch below that of
invert of inlet, and the depth of tank immediately under
this point should be governed by consideration of the
facility of drawing off the sludge by valve at that depth to
the sludge drying beds by gravitation if possible, or pump
if necessary, and from this sludge emptying valve the smooth
concrete bottom of tank slopes up to the semicircular weir
above described.
The bottom and sides of such a tank should be made with the
best Portland cement and finest granite chippings wrought to
a smooth surface, so that the sludge may be easily swept
clean away with a squeegee to its outlet valve, as it is
very necessary to have the tank thoroughly washed after each
emptying if my view of the _clean_ mode of sewage disposal
is to be carried out.
But with the dirty mode, on the contrary, some of the sludge
only should be drawn off and the septic anaerobic action
preserved continuously in the tank itself, whereas I prefer
that action to have its early and less offensive course in
the tank and its completion in a drying bed mixed if
possible with farm-yard manure.
4. The aerobic process. The one essential point in this
final process, whether in land or “contact beds,” is
_sufficient_ aeration (excess as by blowing has no result
commensurate with cost of its introduction), and it can be
attained by intermittence of sewage and rest, or by
continuous passage of sewage through a bed of coarse medium
_kept always just moist in all its atoms_ by a rain-like
dropping on the surface so carefully adjusted as to moisten
all parts and not to form a water-seal in any part of the
bed. Intermittence is easily arranged on any scale of
working, and continuous filtration, on the contrary, is
difficult even for a few thousand gallons a day.
[Sidenote: Anticipation of a coming reaction against “fads” and
overpressure in sanitation.]
Since the above was written our grand old philosopher Herbert Spencer
has published a volume of “Facts and Comments”[3] containing a chapter
on “Sanitation in Theory and Practice,” which points to a coming
reaction against the movement begun, some fifty years ago, by the late
Sir Edwin Chadwick and followed up by many enthusiastic exploiters of
the popular dread of “germs,” which he associated with bad smells.
Of course the professor’s practical acquaintance with Chadwick’s hobby
is, as he says, very limited, and his argument, that because sewage
and manure smells are harmless in the open air of the country, they
should be equally innocuous in a town, falls to the ground when
brought to the test of experience, and I trust that Mr. Spencer will
forgive me for pointing out that sewer-gas, drawn into a dwelling
room, in town or country, through scullery waste pipe or other
connection with a sewer in which the air is of lower temperature than
that of the dwelling room, is really prejudicial to health whether
accompanied or not by disease germs.
And although, as one of the experts to whom Chadwick appealed and
whose moderate testimony was cast aside because it did not come up to
the standard desired by his enthusiasm, I fully endorse Mr. Spencer’s
caution with regard to the mass of Blue Book evidence on sanitation, I
venture to express my regret that the dear old man has had an
unfortunate experience of sewage treatment, and my surprise that so
deep a reasoner should have published his judgment in this chapter
without having taken the pains to extend his acquaintance with sewage
treatment in other places than the single instance of Burton-on-Trent.
In thus despising an unsavoury subject Mr. Spencer is not alone, and I
am sorry to have to say that general indifference is answerable for
the waste of much public health and money, because it need not be
surprising if those following a _despised_ trade are sometimes ready
to take advantage of the prejudice and ignorance of their employers.
In this sense I beg to quote Professor Spencer as follows in
justification of the reflection with which I began the above essay:—
“New sanitary appliances are continually being devised,
sanctioned by authority, and required by surveyors; and
surveyors may have and certainly sometimes do have, personal
interests in pushing the use of them; either as being
shareholders in the companies they are manufactured by or as
receiving percentages on the numbers sold through their
recommendation.”
[2]: Published by Longmans, London, 1874. Third edition
published by R. Potter, Wrexham, 1885.
[3]: ‘Facts and Comments,’ by Herbert Spencer. Williams and
Norgate, London, 1902.