[Illustration: FIG. 79.—“CLOSED” TYPE, CANDY-WHITTAKER SPRINKLER.]
_Automatic Revolving Distributors._—One of the first, if not the
first, of the revolving distributors for percolating filters was the
“Candy-Whittaker” sprinkler in its original form. This is supplied
by the Patent Automatic Sewage Distributors, Ltd. It is now made in
three different forms: the “Open” type, the “Enclosed” type, and the
“Buoyant” distributor, as shown in Figs. 78, 79, and 80. The most
prominent feature of these sprinklers is the mercury seal joint,
for which it is claimed that it gives an absolutely watertight and
frictionless joint, that it cannot freeze, and that no renewal of
the mercury is required. It is stated that the use of the patent
“check-ring” in combination with the mercury seal prevents any loss of
the mercury, no matter what the head may be. Another feature is that
the ball-bearings are moisture-proof, due to the special methods of
construction. In addition to the above, the makers point to the special
value of their compensating arms system, by means of which their
distributors will work continuously with a very small volume of sewage
and still be capable of dealing with any larger volume of sewage that
may be required. The names of the “Open” and “Enclosed” types are
self-explanatory, but the “Buoyant” type is specially designed to
reduce the friction on the bearings. The revolving portion is supported
by a float or buoy in the form of a cylindrical tank, which floats in a
small chamber at the centre of the filter. The removal of all weight
friction on this distributor reduces the power required to rotate it to
the minimum.
[Illustration: FIG. 80.—“BUOYANT” TYPE, CANDY-WHITTAKER SPRINKLER.]
Another make of revolving distributor is well-known as the “Cresset.”
This is manufactured by Messrs. Adams Hydraulics, Ltd., and is
illustrated in Fig. 81. In this case the special feature is the joint
between the revolving and fixed portions of the apparatus. It consists
of a simple air-lock, formed by a cushion of air between two water
columns. This is clearly seen in the illustration. It is obvious that
this is an absolutely frictionless joint, so that there is no loss
of head. It also has the effect of removing the strain to which the
overhead ball-bearings are generally subject, so that the revolving
body swings freely in the true vertical line from the cross head above.
Another point is that no expense is involved, and very little trouble
is incurred, in renewing this joint whenever it may be found necessary,
but it has been maintained in perfect condition without requiring
renewal for very long periods. Special means are provided for removing
and replacing the ball-bearings in the cross-head without dismantling
the distributor.
Another type of distributor manufactured by Messrs. Adams Hydraulics,
Ltd., is their “Sypho-Jet,” as shown in Fig. 82. As its name implies,
it is siphonic in action, and combines the functions of a sprinkler
and intermitting valve in one apparatus. It may either be used in
connection with a dosing tank or connected direct to the settling tank,
from which it draws off a certain depth of water every time it fills to
a certain height.
[Illustration: FIG. 81.—“CRESSET” REVOLVING DISTRIBUTOR.]
[Illustration: FIG. 82.—“SYPHO-JET” REVOLVING DISTRIBUTOR.]
Two types of revolving sprinklers are manufactured by Messrs. Mather
and Platt, Ltd. These are illustrated in Figs. 83 and 84. The special
feature claimed for the “Pipe Arm” distributor is the overflow centre,
as this eliminates the use of joints or seals. Another point of
interest in connection with this apparatus is that there are two sets
of ball-bearings at the head, one to take the weight of the revolving
portion, the other to take lateral movement. In addition there is a set
of roller-bearings at the centre, which are arranged to prevent lateral
movement, and they can be adjusted to take up any wear that may occur.
The “Open-trough” type, Fig. 84, is provided with a special turbine
arrangement at the centre, which it is claimed gives an immediate
motion when the sewage is turned on. The distributing troughs being
open assist in aerating the liquid, and as it is possible to provide
holes in the bottom of the troughs these are able to drain completely
dry, and can also easily be cleaned. This apparatus is provided with
ball and roller bearings, as described in connection with the “Pipe
Arm” type mentioned above.
[Illustration: FIG. 83.—PIPE-ARM DISTRIBUTOR.]
[Illustration: FIG. 84.—TROUGH-ARM DISTRIBUTOR.]
Messrs. George Jennings, Ltd., manufacture a revolving distributor,
the special feature of which is that the sewage is delivered from the
central fixed column to the revolving tank, to which the arms are
attached, by means of a syphon formed in the central column itself,
but this syphon is disconnected from the supply pipe by a fixed
cylinder and port-holes, which make the syphon independent of the
pressure at the inlet to the supply pipe outside the filter bed. The
pressure acting upon the syphon is therefore the atmospheric pressure
applied direct to the surface of the liquid in the fixed cylinder,
thus operating without any loss of head. In addition to the ordinary
overhead ball-bearings, a gun-metal bearing is provided to check any
excessive lateral movement. The syphon described above when once
started remains sealed, as the outlets are trapped by the liquid at the
bottom of the revolving cylinder, and as the top lip of the revolving
cylinder is arranged to be 6 inches above the top water level in the
tanks, any flooding at the centre of the bed by the liquid overflowing
at this point is impossible (see Fig. 85). When required to deal with
fluctuating flows this sprinkler can be fitted with compensating arms.
Messrs. Whitehead and Poole manufacture a revolving sprinkler, as
shown in Fig. 86, in which a float is used to carry the weight of the
rotating parts, so that wear and tear and friction are reduced to the
minimum. The chamber containing the float is completely closed, and
this is below the surface of the filtering material, so that they are
not affected by frost. In this sprinkler the joint between the fixed
and rotating parts is made by utilising a little of the buoyancy of the
float to form an upward bearing at the neck of the float chamber. It is
claimed that this joint is perfectly watertight, with the minimum of
friction.
[Illustration: FIG. 85.—REVOLVING DISTRIBUTOR.]
[Illustration: FIG. 86.—BUOYANT REVOLVING SPRINKLER.]
[Illustration: FIG. 87.—REVOLVING DISTRIBUTOR.]
The revolving distributor manufactured by Messrs. Ham, Baker and
Co., Ltd., shown in Fig. 87, consists of a revolving trough to which
the distributing pipes are connected. The trough is supported upon
ball bearings carried upon a pillar, and the special feature of the
apparatus is that the incoming sewage is delivered into the central
trough in such a way that it strikes upon blades fixed in this trough,
and it is claimed that in this way full advantage of the initial head
of sewage is obtained. By this means also no special joint is required
between the fixed and revolving parts. A special method of gaining
access to the ball-bearings for inspection and cleaning is provided.
In connection with this distributor the makers supply an automatic
cleaning gear for the spray holes, Fig. 88. This consists of a rocking
bar attached to each arm of the distributor and provided with a number
of small fingers or pickers, one opposite to each hole. An arm or a
lever attached to the rocking bar, and suspended from same to within
a short distance of the surface of the filter, comes into contact
with a block of wood or other material fixed in the filter itself at
each revolution, and thus causes a movement of the rocking bar which
actuates the finger points and causes them to pass in and out of the
spray holes in the arms. By this means any obstruction is removed and
forced out by the pressure of water within the arm, and the holes are
kept free.
[Illustration: FIG. 88.—CLEANING GEAR FOR SPRAY HOLES.]
The “Facile” rotary distributor shown in Fig. 89 is manufactured by
Messrs. W. E. Farrer, Ltd. The special advantage claimed for this
distributor is that it has no joint, so that there is no friction to
overcome beyond that in the ball-race, upon which the whole weight of
the revolving portion is supported. It is provided with a syphonic
attachment to the central column, and thus acts as a self-dosing
distributor, and, if desired, can be connected direct to the septic
tank. A patent gauging tube is fitted, so that the volume of the dose
may be gauged whether it is fed from the dosing chamber in the ordinary
way or direct from the septic tank. Access is provided to all parts,
and the ball-race can be removed without dismantling the apparatus.
[Illustration: FIG. 89.—“FACILE” REVOLVING DISTRIBUTOR.]
[Illustration: FIG. 90.—THE “CARLTON ROTOR” DISTRIBUTOR.]
Among the later types of revolving sprinklers is the “Carlton Rotor”
distributor, Fig. 90, manufactured by the Carlton Engineering Company.
This is specially designed to obviate the use of a dosing tank, to
work satisfactorily with any variation of flow, and to prevent all
possibility of choking. It is claimed that these advantages are
secured by the use of a special water-wheel which rotates round the
central column on an inclined plane. The sewage is delivered to this
water-wheel by means of a bend connected to the central column. As
each section of the water-wheel is filled, it rotates and delivers its
contents into an annular trough, to which the distributing arms are
attached. These are, however, not perforated with spray holes, but
are provided with small bends on the top of the arms, which deliver
the sewage into distributing troughs fitted with baffle plates. These
baffle plates are so arranged that the sewage is delivered on to the
surface of the filter in a thin film and at a uniform rate over the
whole surface.
[Illustration: FIG. 91.]
[Illustration: FIG. 92.—THE “CARLTON” DISTRIBUTOR.]
A novel apparatus for the purpose of providing an automatic method
of cleaning the orifices of the arms of revolving or travelling
distributors is shown in Fig. 91. This is supplied by the Carlton
Engineering Company, in connection with their ordinary type of
revolving distributor, also shown in Fig. 92. In the distributing arm B
apertures are made in the form of elongated slots A, each slot having a
brass cleaning blade E inserted. These blades are carried on brackets
fixed by a set-screw D, on to a reciprocating rod or tube C, mounted
on runners F. Two bevel wheels G are strapped on to the arm, and are
connected by an eccentric rod to the reciprocating rod C. At every
revolution which the distributing arm makes, the bevel gearing G
comes in contact with the stop H, causing a partial revolution of the
gearing. This in turn causes the backward and forward motion of the
cleaning blades in the apertures. The apertures are thus kept entirely
free from grit or any other solid matter, and the flow is broken up
into a fine spray.
[Illustration: FIG. 93.—“SIMPLEX” REVOLVING DISTRIBUTOR.]
The “Simplex” revolving distributor is manufactured by the Ames Crosta
Sanitary Engineering Company, Ltd., and illustrated in Fig. 93. This
sprinkler revolves on a ball-bearing which runs in a bath of solid
grease, and is protected from moisture and dust by means of special
washers. The whole of the weight is carried from the top of the pillar,
no bearing being submerged in the sewage. The seal is arranged by
means of two gun-metal rings with special annular grooves turned in
them; the top ring is carried from the revolving bucket by means of a
rubber or copper washer, thus the ring carries no part of the weight of
the apparatus, and is free to compensate for any oscillation. Rollers
running on ball-bearings are placed under the bucket, and these take
up side movement due to wind and other causes. The revolving arms are
provided with a special cap at the ends, which can be removed by a
quarter turn to enable the arms to be cleaned. There is no head lost,
as the level of water in the bucket is equal to the head in the supply
chamber or channel. The apparatus is not affected by frost, and is
remarkably sensitive, as 2 inch head of water above the holes in the
arms will start the apparatus in motion.
[Illustration: FIG. 94.—REVOLVING SPRINKLER (Burn and Brown’s
patent).]
Messrs. Burn Bros. manufacture a revolving sprinkler, “Burn and Brown’s
Patent,” shown in Fig. 94, which has one or two special features. These
consist of a self-regulating apparatus for dealing with the variation
of the flow of sewage and at the same time cleaning the orifices. A
shaft carried on each of the arms, and mounted on suitable bearings, is
provided with tapered fingers fixed in a position corresponding to the
holes in the arms. By means of a float in the circular revolving tank
connected to a simple lever the shafts on the arms are given a slight
movement, which causes the fingers to enter the orifices in the arms
as the flow decreases, and to be withdrawn as the flow increases. The
result is that the orifices are enlarged or reduced as the flow varies,
and the movement of the tapered fingers tends to make the orifices
self-cleansing. It is claimed for this distributor, that it can be made
to deal with any variation in flow of sewage up to 6 volumes, with a
maximum head of less than 18 inches above the surface of the material
of the filter.
A new type of automatic revolving sprinkler is the “Hodgson” overflow
type, manufactured by Messrs. George Kent, Ltd. As will be seen
from the illustration, Fig. 95, the sewage passes first into a feed
chamber attached to the central column, from which it flows into the
distributing chamber D, to which the arms are attached. It is claimed
that by use of the weirs W in the distributing chamber, a uniform speed
of rotation and consequently a uniform distribution, is secured. The
ball-bearing upon which the rotating portion is carried is stated to
take both the side and end friction.
The revolving distributors previously described are all constructed
on the Barker’s Mill principle, to some extent if not entirely. The
Fiddian type of distributor, supplied by Messrs. Birch Killon and
Co., and illustrated Fig. 96, is based upon an entirely different
principle. It consists of an elongated water-wheel, which revolves
around a circular filter. It is pivoted at the centre of the filter
upon the supply pipe, and the outer end of the distributor is carried
upon a rail track. In the case of large filters, from 70 feet to 110
feet diameter, two rail tracks are used. The liquid passes through the
supply pipe and is delivered into the buckets of the water-wheel, from
which it falls in the form of a film, so that the water-wheel not only
drives itself over the filter by means of the weight of the liquid, but
it also distributes the liquid which drives it. A very small quantity
is sufficient to start the distributor and keep it in motion, the head
required, measured from the surface of the filter, being about 18
inches. The buckets are provided with graduated weirs, the width of
which is proportionate to its distance from the centre of the filter.
By this means uniformity of distribution is secured. It is claimed that
as there are no small holes to be choked, the apparatus can be employed
for all kinds of liquid with the minimum of attention, and that it does
not require any dosing apparatus.
[Illustration: FIG. 95.—“HODGSON” REVOLVING SPRINKLER.]
[Illustration: FIG. 96.—FIDDIAN REVOLVING DISTRIBUTOR.]
_Power-driven Revolving Distributors._—One of the first revolving
distributors in which it was decided to adopt power to drive it
independent of the sewage, was the “Scott-Moncrieff and Alliott”
distributor, manufactured by Messrs. Manlove, Alliott and Co., Ltd.,
and erected at the Birmingham Sewage Farm for Mr. J. D. Watson. In this
case a horizontal arm is attached to and pivoted upon the vertical
stand-pipe in the centre of the filter which is connected to the supply
pipe. The outer end of the horizontal arm is carried by a rail, and
is fitted with an oil engine which travels along on the outer rail
on the end of the arm. The rotating arm consists of a large main
trough or carrier into which the sewage from the central stand-pipe is
delivered, and on one side of the main trough is fitted a row of small
troughs, each of which is supplied with sewage from the main carrier
through a porthole specially proportioned to the volume of sewage to
be discharged from the trough and to its distance from the centre of
the bed. By this means uniform distribution is secured over the whole
area of the filter. From each of the small troughs the sewage flows
over the edges of the trough, and thence, trickling down the outside
of the trough, is discharged in a row of fine rain-like columns upon
the filter. It is claimed for this distributor that absolute uniformity
of distribution is secured, that it will work equally well with any
volume, that there are no holes to become choked, that it requires the
minimum of supervision, and that it will deal with any variation up to
3 times D.W.F. without attention (Fig. 97).
[Illustration: FIG. 97.—SCOTT-MONCRIEFF POWER-DRIVEN REVOLVING
DISTRIBUTOR.]
In the “Hartley” circular power-driven distributor, the apparatus
(manufactured by Messrs. Hartley, Causton and Richmond, and shown in
Fig. 98), is arranged in a form similar to that used in connection with
the Barker’s mill type of distributor, with this difference, that it
is driven by an electric motor attached to the end of one of the arms,
which is used as the distributing arm; and the arm on the opposite side
is the balancing arm to counteract the dead weight of the distributing
arm and act as a balance against wind pressure. The current is brought
to the distributor by an overhead cable, connected to a revolving
contact at the top of the central standard. The method of distribution
from the distributing arm is different from the usual type, as it takes
place through a number of sectional distributing pipes C (Fig. 99),
which are connected to the main tube H. These are arranged in echelon,
so that by opening the covers P P a cap or cleaning rod may be passed
through each tube from end to end. Each sectional distributing tube,
C, is suspended from the main tube by an attachment D. This attachment
carries a screw, G, by which is regulated a valve shown open at E and
closed at E_{2}. The flow may be increased or decreased to any extent,
or stopped altogether, by this valve. Each space between the dotted
lines on the plan is covered by one sectional tube, and the sewage flow
can be increased or decreased, or stopped upon each section. The spray
nozzles are of a special type, and by use of the deflection or spray
plates M, a smaller number of spray holes or jets are required, so
that they can be made larger, and they are thus not so easily choked.
Among the advantages claimed for this distributor are the following.
That it can be regulated to work with any variation in the volume, from
the smallest quantity to 2 million gallons per acre per day, without
increasing the consumption of power. Separate sections of the filter
may be removed or rested entirely by adjusting the valves G. The
distributor can work with any head of sewage from 6 inches to 6 feet,
or more if desired. It is not affected in any way by wind pressure; and
as the balancing arm empties at the same time as the distributing arm,
it is always in balance. The horse-power required to drive it is very
little, less than half horse-power per acre. The rate of distribution
on any of the sections of the filter can be varied from 50 to 400
gallons per yard per day.
[Illustration: FIG. 98.—POWER-DRIVEN REVOLVING DISTRIBUTOR.]
[Illustration: FIG. 99.—DETAILS OF DISTRIBUTING ARM.
(See FIG. 98.)]
This type of distributor was first erected at the Hanley Sewage
Works in 1902, in order to comply with Messrs. Willcox and Raikes’
specification fora power-driven distributor suitable for a large
circular filter, on which a Scott-Moncrieff distributor was previously
employed.
[Illustration: FIG. 99A.—VIEW OF HARTLEY CAUSTON AND RICHMOND’S
POWER-DRIVEN REVOLVING DISTRIBUTOR IN OPERATION.]
A somewhat similar type of distributor is the “Adams-Cutler” Fig.
100, manufactured by Messrs. Adams Hydraulics, Ltd. In this case the
distribution is from spray holes in the pipe arms in the same way as
the ordinary Barker’s Mill type of distributor, but instead of relying
upon the motive power due to the head of sewage, the distributor is
operated by a rope drive; and where there are a number of distributors
in one installation, each of them is operated by a cross-drive taken
from a main drive rope, so that any one or more can be cut out of the
circuit or controlled, or the speed varied as may be required. It is
claimed that a very small amount of power is required to operate a
revolving distributor, and the ease with which it is carried upon a
central column, are arguments in favour of the revolving over the
rectangular types where absolute control is essential and a natural
working head is not available.
[Illustration: FIG. 100.—“ADAMS-CUTLER” POWER-DRIVEN REVOLVING
DISTRIBUTOR.]
Messrs. Mather and Platt, Ltd., also manufacture an electrically-driven
revolving distributor of the Open Trough type, as shown in Fig. 101.
This machine is of special design, and particularly suited for large
diameter beds. The troughs are similar to those of the ordinary type
of distributor previously mentioned, but are supported on the Warren
Girder principle. There are four pipe arms, the end of each being
fitted with a special carriage running on rails fixed outside the bed
at the floor level. On one of the carriages an electric motor is fixed
and connected to the rail wheels by means of chain drives. The current
is transferred to the motor from the main at the top of the central,
pole of the distributor by means of slip rings.
[Illustration: FIG. 101.—POWER-DRIVEN REVOLVING DISTRIBUTOR.]
_Automatic Travelling Distributors._—There are several types of these
on the market at present. The first is manufactured by Messrs. Birch
Killon and Co., Fig. 102, and is constructed on the Fiddian water-wheel
principle. The design is similar to that described in connection
with the automatic revolving distributor, but it involves two rail
tracks supported on walls or piers on each side of the filter. The
head required for this type is about 2 feet from the surface of the
filter to the top water level in the carrier, and the distributor is
fitted with a syphon which feeds it from the carrier or trough. In
large schemes the trough is placed along the centre of the filter, and
supplies a separate distributor on each side.
[Illustration: FIG. 102.—FIDDIAN TRAVELLING DISTRIBUTOR.]
Another type is manufactured by Messrs. Ames Crosta Sanitary
Engineering Company, as shown in Fig. 103. This sprinkler can be
adapted to existing contact beds. It is carried from the walls of the
central channel in cantilever form, no other bearing or rails being
required. On each side of the machine a hopper is carried in which
water-wheels revolve. The water in its passage from the feed channel to
the distributing arms is conveyed on to the water-wheels, and the
power generated there is transmitted by means of a chain drive to the
wheels of the carriage, and thus the whole apparatus is moved along
the beds. When the machine nears the end of the bed a reversing lever
comes in contact with a buffer, and by this means the direction of
motion is changed, and the machine travels backwards along the bed.
Two distributing arms are carried on each side of the apparatus,
one feeding half the bed in one direction and the other feeding the
remaining portion of the bed in the opposite direction, thus giving a
regular intermittent feed to the bed. A great advantage of this class
of machine is that the whole of the machine is supported from the
central channel, and as the wheels are close together, the long lengths
of shafts with their risk of twisting, retarding and wearing are
dispensed with.
[Illustration: FIG. 103.—TRAVELLING DISTRIBUTOR.]
Messrs. Ham, Baker and Co., Ltd., have for some time supplied an
automatic travelling distributor. This is illustrated in Fig. 104, from
which it will be seen that it consists of a water-wheel mounted on
rollers and divided into sections composed of a number of buckets.
The sewage is delivered through a syphon and patent reversing
valve, in such a way that alternate sections only of the filter bed
receive sewage in each direction of travel, thereby insuring equal
inter-delivery periods.
[Illustration: FIG. 104.-TRAVELLING DISTRIBUTOR.]
[Illustration: FIG. 105.—“HANLEY” POWER-DRIVEN TRAVELLING
DISTRIBUTOR.]
_Power Driven Travelling Distributors._—The well-known Hanley
Distributor was specially designed by Messrs. Wilcox and Raikes, Civil
Engineers, for use on their schemes at Hanley, Fenton, Ilkeston and
elsewhere, as illustrated, Fig. 105. The object of this distributor
is to ensure intermittent discharge at regular intervals, and at a
predetermined rate, in the form of a thin film over the surface of fine
grade material, and in order to secure these results it was decided to
drive the distributor by electric power rather than depend upon the
variable and limited amount of power obtainable from the head of the
sewage itself. The distributor consists of a pipe extending across
the whole width of the bed and supported on wheels, so that it may be
drawn backwards and forwards by means of the wire rope attached to the
centre. The distributing pipe tapers towards the end farthest from the
supply trough, and the sewage is discharged by means of nozzle pipes
attached to the flat side of the distributor about 3 inches apart, and
connected with it near the top so that the main pipe always remains
full. The discharge of the sewage commences and stops along the whole
length of the pipe almost simultaneously, and any sediment lies in the
bottom of the main pipe where it cannot obstruct the outlets of the
nozzles. The nozzles are about ⅝ inches in diameter, and provision
is made for cleaning them by removing a plug in the top of each. In
order to secure a uniform interval of time between each dose of sewage
discharged on to any part of the filter, the distributors are arranged
to discharge when travelling in one direction only, the valves on the
outlets of the feed syphons being automatically turned off and on by
means of a lever, which is actuated by stops fixed at each end of the
iron trough or at any intermediate point desired. In this way it is
possible to arrange for any portion of the filter to be thrown out of
action when necessary for cleaning or repairs. The speed at which the
distributor travels may be varied by adjusting the gear wheels attached
to the electric motor. At Hanley it has been found that the best
results are obtained when the distributors occupy about 7 minutes in
making one complete journey, the filters being 200 feet long, so that
when the filters are working at the normal rate of 1,000,000 gallons
per acre per day, each dose represents one gallon per square yard. In
other words, the film one-fifth of an inch in thickness is applied
200 times per day, and thus a total depth of 40 inches of sewage is
distributed over every portion of the filters in operation in 24 hours.
The power required to drive the distributors is about 1½ B.H.P. per
acre of filter. Electric motors are usually adopted, but small oil or
gas engines may be substituted when electric current is not available.
The winding drums for the wire ropes are driven by belt gear of the
usual type with fast and loose pulleys. The reversal of the drum when
the distributor reaches either end of the filter is accomplished by
an automatic belt striking gear, and a float in the supply trough is
used to cut out a distributor, or continue in action at a reduced rate,
when the supply of sewage becomes insufficient to maintain the normal
rate of distribution. These distributors are manufactured by Messrs.
Blakeborough and Sons, and have now been in regular use since 1902 on
the Hanley Sewage Disposal Works, where the remarkably satisfactory
results obtained are largely due to the highly efficient system of
distribution on the filters.
[Illustration: FIG. 106.—“STODDART” DISTRIBUTOR.]
[Illustration: FIG. 107.—“STODDART” DISTRIBUTOR.]
_Fixed Distributors. Trays and Troughs._—One of the best known of the
fixed distributors is the “Stoddart,” as illustrated in Figs. 106 and
107. It will be seen that it consists of trays of galvanized sheet
iron, formed into a number of V-shaped troughs. The ridges between
the troughs are provided with diamond-shaped perforations at frequent
intervals, and in the bottom of the troughs drip points are inserted
through holes to project on the under side. The distributing trays are
bolted to specially designed supply channels, connected to a common
channel, and the whole of the troughs are mounted on adjustable chairs
(F, Fig. 106) carried on tees, which are in turn supported
on concrete or brick piers. As the liquid passes into the V-shaped
troughs, it fills them and overflows through the diamond-shaped slots
in the ridges and thence trickles down on the under side of each
trough and drops off from the drip points on the filter below in the
form of rain. It is claimed for this method of distribution that the
whole of the available fall is utilised; that it adapts itself without
adjustment to all rates of flow, however varied, that the sewage and
storm-water may all be treated on the same area, and that there is a
total absence of moving parts. This distributor is supplied by the
patentee, Mr. F. W. Stoddart, of the Western Counties Laboratories,
Bristol.
Another type of fixed distributor is fixed only so far as actual
distributing channels are concerned. This is manufactured by Messrs.
W. E. Farrer, Ltd., and illustrated in Fig. 108. The fixed troughs
or channels are laid directly over the filter-bed, and fitted at the
inlet end with concentrating chutes which receive the discharges from
a double-acting tipping trough, which is supported at its extreme
ends by heavy gun-metal bearings. If it is over 10 feet in length, an
additional support is provided at the centre in the form of a specially
designed rocker. The chutes and the channels are provided at the bottom
with ¼-inch holes at 3-inch centres, through which the sewage is
spread on to the surface of the filter, which is below the underside
of the trough. The channels are arranged at 1-foot centres, so as to
distribute the sewage over the whole area of the bed. By means of the
double-acting tipper each half of the filter is dosed alternately,
and suitable periods of aeration are thus provided. This apparatus is
suitable for a single small house with 4 or 5 inmates, and for larger
filters of 600 square feet in area and upwards.
The Ducat filter is provided with what may be termed a fixed
distributor. It consists of a series of small tipping troughs fixed
across the filter, each of which when full tips its contents on to the
filter below. The liquid is thus discharged at the same point each
time, but intermittently in small doses. As, however, the distributor
does not move it is included under this heading.
[Illustration: FIG. 108.—FIXED DISTRIBUTOR.]
A different type of fixed distributor is that manufactured by Messrs.
J. Blakeborough and Sons. This apparatus, patented by Messrs. Haller
and Machell, Civil Engineers, is used in the triple tank system of
sewage treatment. Fig. 109 illustrates the “Aerat” type, which consists
of cast-iron channels supported on wrought-iron joists carried upon
piers. Each length has six orifices on each side, through which the
sewage passes on to small trays provided with radiating grooves on
the top and dripping points on the under side at the edge. As the
distributors may be fixed within a few inches of the surface of the
filter, very little head is required to operate them.
[Illustration: FIG. 109.—FIXED DISTRIBUTOR.]
A very ingenious form of fixed distributor, Fig. 110, is supplied
by the Septic Tank Company, Ltd. From its name, “Capillary Trough
Distributor,” it will be observed that during normal and minimum rates
of flow, capillary attraction is utilised to deliver the sewage on
the filter in the form of drops. The tank effluent is delivered to
each trough distributor over brass V-notches, set in the side of the
main channel, into which the tanks discharge. These V-notches are
adjustable, and are set so as to prevent their being tampered with
subsequently. The trough distributors are of artificial stone, true
from end to end, and set level. Over both their edges copper wires are
fixed, at intervals of a few inches, each wire extending from within
a short distance of the bottom of the trough channel over the edge
and down to the underside of the trough. On a trough being filled the
liquid overflows right along the edge, and is attracted by and runs
down the wires, so that if the flow is at all excessive a little
stream will run down each; on the flow subsiding to the ordinary,
a drop-by-drop delivery commences; should the flow of sewage cease
altogether for any length of time, the wires will go on dripping until
they have drawn off the contents of the trough, almost to the end of
the wires. On a fresh supply of sewage arriving at the installation,
and the troughs refilling to a higher level, the rate of delivery
from the wires will increase until it keeps pace with the flow, thus
ensuring an even distribution on the filter throughout the day. There
is no loss of head in connection with this apparatus beyond the depth
of the distributing troughs themselves.
[Illustration: FIG. 110.—CAPILLARY TROUGH DISTRIBUTOR.]
_Spray Jets._—This type of distribution is not used in many
installations in this country, but it has been adopted in large schemes
in the U.S.A. There are a number of different types, including those in
which the sewage is forced upwards through a nozzle and falls back on
the surface of the filter, and others in which the sewage flows through
inverted nozzles, and each jet impinges upon a fixed cup or disc of
metal, or other material, and is thus spread out on to the filter.
Among the former, one of the simplest types is that manufactured by
Messrs. Adams Hydraulics, Ltd., Fig. 111, in which, by means of a
square baffle plate, provided with suitable grooves, the spray is
forced out in such a manner that it covers a square area of the filter.
It is claimed for this that it covers the whole surface and no portion
of the filter is wasted, as in the case of round jets which cover
circular areas. The same firm also supply several other types of fixed
sprays, as shown in the illustration.
[Illustration: FIG. 111.—FIXED SPRAYS.]
Another type is manufactured by Messrs. Ham, Baker and Co. This is
shown in Fig. 112, from which it will be seen that it can be adapted to
any existing installation, and to standard spigot pipes. Each jet being
in the form of a stop-valve, any individual spray may be put out of
action when necessary.
Messrs. W. E. Farrer, Ltd., manufacture a type shown in Fig. 113.
The special feature of this is a loose disc inside the nozzle, which
oscillates as the sewage passes through, and so tends to clear away any
flocculent matter which may accumulate in the orifice of the nozzle.
The sewage itself is delivered from the nozzle in the form of a very
fine film, and it is claimed that by this means any nuisance from smell
is reduced to the minimum.
[Illustration: FIG. 112.—FIXED SPRAY NOZZLE.]
[Illustration: FIG. 113.—FIXED SPRAY NOZZLE.]
Messrs. Burn Brothers also manufacture a fixed spray, Fig. 114, called
the Burn and Brown’s Patent “Whirl” Spray. The special feature of this
is that it consists of an inverted conical spreader, provided with
vanes revolving on a spindle. The sewage, as it leaves the nozzle,
impinges upon the face of the cone, causing it to revolve rapidly and
spread the sewage in the form of fine drops. Owing to the special
construction of the serrated edges of the cone, the sewage is well
distributed over the whole area covered by the spray.
[Illustration: FIG. 114.—“WHIRL” SPRAY NOZZLE.]
[Illustration: FIG. 115.—“ACME” SPRAY NOZZLE.]
The “Acme” type of fixed spray, manufactured by the Ames Crosta
Sanitary Engineering Company, is shown in Fig. 115. The special feature
of this spray is that it has a loose metallic cone, which is provided
with a helical groove, inside the nozzle. This cone rotates as the
sewage passes through the nozzle, and thus gives a maximum spray with a
small head. These sprays have a free waterway, and the rotation of the
cone tends to prevent the choking of the orifice.
[Illustration: FIG. 116.—FIXED SPRAY JET.]
A simple form of fixed spray consists of perforated pipes arranged at
suitable intervals over the surface of a filter, and provided with
dosing apparatus to give intermittent supply under pressure, and thus
deliver the sewage in the form of jets from the perforations in the
pipes. An improved form of this type of distribution is supplied by
the Septic Tank Company. This is illustrated in Fig. 116, from which
it will be seen that orifices in the top of the distributing pipes
are fitted with nozzles, set at an angle of about 45 degrees to the
vertical. The discharge from these nozzles, it is claimed, gives the
maximum efficiency of distribution.
[Illustration: FIG. 117.—“CARLTON” ADJUSTABLE FIXED SPRAY.]
A self-cleansing spray jet has been brought out by the Carlton
Engineering Co. From the illustration, Fig. 117, it will be seen that a
plug B is fitted into the orifice and supported upon a spindle, which
is attached at its lower end to a lever connected to an automatic
tipper on the outside of the nozzle. The tipper is fed by the spray
from the nozzle, and as it falls alternately on one side and on the
other it raises and lowers the plug B in the orifice, which tends to
prevent any clogging, and also varies the area of the orifice and the
rate of discharge, as well as the area of the filter-surface covered by
the spray.
A simple type of fixed spray is supplied by Messrs. George Kent, Ltd.,
and is shown in Fig. 118. In this case the liquid issuing from the
nozzle impinges upon a curved surface or cone, by which it is deflected
and spread out, leaving the surface at an angle of 45 degrees to the
vertical. One of the advantages claimed for this type is that it has no
small holes to become clogged.
[Illustration: FIG. 118.—FIXED SPRAY NOZZLE.]
A novel form of this type of apparatus is manufactured by Messrs.
Daniel Adamson and Co. Above the orifice in the nozzle is suspended
a revolving deflecting plate (Fig. 119). The vanes of this plate are
shaped in such a way that, as it revolves, the jet impinges against a
different angle every instant. None of the energy is wasted in churning
or throttling, as the plate merely directs the water in such a way that
no two drops ever fall twice on exactly the same spot. It is stated
that the diameter of the wetted area of the filter surface is more than
double the head.
[Illustration: FIG. 119.—ADAMSON’S FIXED SPRAY.]
There are a considerable number of other types of nozzles used for
fixed sprays. Several of these are illustrated in Fig. 120, where A is
the type in use at Salford; B, the type used at Birmingham; C, a nozzle
with a double spreader in use at Waterbury, Conn., U.S.A.; D shows
another type in use at Waterbury, with a single spreader, but this is
so arranged that it can be adjusted to give a smaller or larger area of
orifice. E shows the type adopted at Columbus, Ohio, U.S.A.
In connection with some elaborate studies of methods of distribution
for percolating filters, which were carried out for the Sanitary
Research Laboratory and Sewage Experiment Station of the Massachusetts
Institute of Technology, by Messrs. Winslow, Phelps, Storey and McRae,
a special series of investigations were made into the value of what
is referred to as the “gravity method of spraying.” This consists in
supplying the sewage from troughs or pipes supported above the filter,
and discharging it through orifices on the under side of the pipes
or troughs in the form of solid jets, which are made to impinge upon
concave discs fixed near to the surface of the filter. The effect of
this impingement is to cause the liquid to splash upwards and outwards
in the form of a fine spray, and, as a result of a long series of tests
with various forms of discs and various heads, it was found that the
best average results were obtained with a concave metal disc 3 inches
in diameter having a curvature corresponding to a radius of 2 inches.
With a total head of 4 feet and a head of 3 feet from disc to the pipe
above, it gave the best results obtained with that total head. With a
total head of 6 feet and a head of 4 feet from disc to supply pipe,
it gave the best results obtained by any of the forms of this type of
distribution that were tested.
[Illustration: FIG. 120.—FIXED SPRAY NOZZLES.]
A method of distribution similar to this type of gravity disc spray is
manufactured by Messrs. Glenfield and Kennedy, Ltd. The details of this
disc, with the methods of supporting same and the method of supplying
the sewage from an overhead pipe, are shown in Fig. 121.
[Illustration: FIG. 121.—GRAVITY DISC SPRAY.]
In connection with sewage disposal works where chemical precipitation
has been adopted for preliminary treatment, the tank effluent has been
distributed over fine-grained percolating filters, by means of dosing
tanks discharging comparatively large volumes intermittently over the
surface of the filter. In such cases the aim has been to deliver the
liquid at such a rate that it would flood the entire surface of the
filter in a very short space of time, and then percolate through and
leave the surface free to aerate for as long a period as possible
before the next discharge took place. This process involved the use
of small filters, in order that the area to be flooded should not be
too large for the liquid to spread over it rapidly, and the use of
very fine material to prevent the liquid from passing through too
quickly. Among the difficulties encountered by this method were the
displacement of the surface layer of the material, due to the high
rate of delivery; and the labour involved in cleaning the surface of
the filter. A further trouble which arises when effluents from septic
tanks are treated by this process is the evolution of evil-smelling
gases, which are certain to cause a nuisance if there are any houses
in the vicinity. Efforts have been made to obviate this difficulty by
distributing the sewage through open-jointed or perforated pipes laid
a few inches beneath the surface of the filter, as described later in
connection with contact beds (page 200). While this is satisfactory to
a certain extent, especially where the volume to be treated is small,
and the filter capacity is comparatively large, neither this method,
nor that of flooding the surface of the filter, can be said to comply
with “the desideratum in the application of sewage to percolating
filters,” quoted previously (page 106), nor do they avoid the
difficulties encountered in securing uniform distribution dealt with
in the following pages. The defects of these methods of distribution
may also have been aggravated by the very optimistic anticipations on
the part of the designers of the schemes as to the volume of sewage
which could be satisfactorily purified under such conditions. It is,
therefore, desirable to point out that, in the event of either of these
methods of distribution being adopted, care should be taken to secure a
very high degree of clarification (reduction of matters in suspension)
in the preliminary tank treatment, and to provide filters of ample
cubic capacity.
_Methods of Feeding Percolating Filters._—Under the heading “Methods
of Distribution” (page 106), reference is made to some experiments,
from the results of which the conclusion was drawn that “a high
efficiency in sub-surface distribution is fostered by a slow continuous
rate of application rather than by an intermittent application at
a higher rate.” This agrees in every respect with the author’s own
experience, and confirms his opinion that intermittent discharges
to percolating filters should only be resorted to in cases where it
is absolutely necessary in order to assist in securing uniformity
of distribution, or to ensure a sufficient volume for the operation
of the appliances adopted for distribution. Among the former may be
cited fixed spray nozzles and jets from fixed pipes, in which cases an
intermittent supply is useful in causing a regular variation of the
head upon the orifices, thus varying the distance to which the jets or
sprays are thrown, and producing greater uniformity of distribution
per unit of area covered. Examples of cases, where intermittent supply
is necessary in order to discharge the volume required to operate the
appliances adopted for distribution, are found in connection with
most types of fixed distributors and nearly all types of automatic
revolving distributors. In the case of the latter, it is well known
that a certain minimum head is necessary to overcome the friction due
to the resistance of the air and to the weight of the apparatus itself
on its bearings. However small this friction may be, it needs a volume
of sewage slightly in excess of that required to fill the spray-holes,
which must be large enough to take the maximum flow of sewage when
working under the maximum head. It frequently occurs, especially
in small schemes, and in schemes where the percolating filters are
preceded by contact beds or slate beds, that the rate of flow of the
sewage is at times so low that it is not equal to the minimum volume
required to operate the distributor, and, in the absence of any
arrangement to overcome the difficulty, the distributor would cease to
revolve and the sewage would trickle through the spray-holes without
proper distribution. The same difficulty arises in connection with many
of the fixed methods of distribution, and it is most readily overcome
by the use of a dosing tank fitted with an automatic syphon or valve,
by means of which the sewage is held-up in the tank until it reaches a
certain predetermined level, and is then discharged at a given rate to
the filter. When the tank is empty the discharge ceases, and the sewage
is again held-up as before.
In the case of large installations, or schemes where the whole of the
sewage is pumped and the rate of flow to the filters is thus under
control, it is not necessary to use a dosing tank for the purpose of
providing the rate of discharge to the filters necessary to keep the
distributor in motion. It is, however, maintained in some quarters
that intermittent supply is desirable in any case, in order to secure
alternate periods of work and rest for aeration. There is one obvious
disadvantage in this method of working. Assuming that during the
maximum rate of flow of the sewage the volume which comes down in 5
minutes is stored in a dosing tank, and discharged to the filters in 2½
minutes, it is clear that the rate of distribution is twice as great as
it would be if the distribution were continuous over the whole period
of 5 minutes. It is claimed that the disadvantage of the higher rate of
distribution is counteracted by the 2½ minutes of rest and aeration,
but on this point there is room for doubt, especially when the
conditions which come into play during the average and minimum rates
of flow of the sewage are taken into consideration. Taking the average
rate as equal to one-half the maximum rate, it will be seen that the
dosing tank will discharge every 10 minutes, but the time in which
its contents are delivered to the filter will still be 2½ minutes,
so that under these circumstances the rate of distribution on the
filter will be four times as much as it would be if the distribution
were continuous. During the minimum rate of flow of the sewage the
conditions are still worse, and it is difficult to accept the theory
that periods of rest for 7½ minutes will compensate for excessive rates
of distribution at four times the rate under continuous operation for
periods of 2½ min. at a time.
Those who advocate intermittent supply under all circumstances would
appear to have lost sight of the fact that very ample periods of rest
are already provided by all revolving distributors. When working at the
rate of one revolution per minute, the average time taken by each arm
to pass over any one point on the surface of the filter may be taken as
0·5 second. Before the succeeding arm reaches the same point a period
of 15 seconds will have elapsed, so that under these conditions the
ratio of the periods of work to periods of rest is as 1 to 30. In other
words, even during continuous distribution, the time allowed for rest
and aeration is thirty times as much as that during which the sewage
is actually being delivered to the filter, and there would thus appear
to be no reason for unnecessarily adding to the periods of rest by
means of dosing tanks, especially as such a course involves a greatly
increased rate of distribution at all times when the discharge actually
takes place.
There is, of course, the possibility of adopting the happy medium,
which would consist of a dosing apparatus of such a type that it would
provide a continuous supply during the maximum flow of the sewage, and
only act as an intermitting appliance during the minimum rate of flow.
This is probably the best arrangement to adopt in all cases where a
dosing apparatus is absolutely essential.
As previously stated, however, there are many cases where the
conditions render the use of a dosing tank absolutely necessary to
prevent the stopping of the distributor, and these have brought about
the introduction of several types of automatic syphons and valves, all
arranged specially for the purpose of giving intermittent discharges
to filters, contact beds, areas of lands, and so forth. There are
various methods of constructing dosing tanks, all dependent upon the
arrangement of the preliminary processes and the filters which follow
them. In nearly all cases, however, it is found necessary to reduce
the fall taken up by the dosing tank to the minimum, and the different
syphons and valves have thus been designed to work with the least
possible head. One point in the construction of dosing tanks should not
be overlooked, i.e. the provision of a washout valve for use when it
becomes necessary to clean out the tank. It may be noticed here that
neither the Fiddian type of distributor, on the water-wheel principle,
nor the power-driven distributors, require any dosing tank to keep
them in motion during the periods of minimum flow of the sewage. In
the case of the Fiddian distributor the apparatus remains standing
until the buckets are filled, and each time these discharge their
contents the distributor is moved forward a short distance. Under these
conditions, however, the disadvantage of long intervals of rest between
comparatively large discharges of sewage still remains. Undoubtedly the
most even rate of distribution under all conditions is secured by the
use of power-driven distributors, whether of the rotary or travelling
type, but these can only be economically adapted for use in large
installations or where power is available at a very low cost.
[Illustration: FIG. 121_a_.
T = tank. C = carrier.
P = supply pipe. F = filter.
E = effluent channel. H = humus tank.]
[Illustration: FIG. 121_b_.
T = tank. C = carrier.
P = main supply pipe. P_{1} = branch supply pipe.
V = regulating valve. W = washout valve.
F = filter. E = effluent channel.
H = humus tank.]
Apart from the question of continuous _versus_ intermittent methods
of feeding percolating filters, there still remains the problem of
deciding whether the actual connections between the tanks and the
filters shall be in the form of channels (carriers) or pipes. For fixed
sprays and revolving distributors, which involve the use of pressure
due to a column of liquid, the actual connection to the apparatus must
be in the form of a pipe extending at any rate to the outside of the
filter. Whether it should be continued beyond this point in pipe form
or in a channel depends entirely upon local conditions, such as the
slope of the ground, the planning of the filters, and the relative cost
of the two methods. There is one thing to be said in favour of pipes,
i.e. that there is less chance of a nuisance being created by the
evolution of foul gases from the sewage than in the case of open
channels. On the other hand, channels may be, and frequently are,
covered in. Whichever method is adopted, care should be taken to
provide a valve or penstock on the connection to each separate filter,
in order to be in a position not only to throw any filter out of work
when desired, but also to regulate the rate of supply to each filter
independently of the others. Washout valves should also be provided on
the channels or pipes, in suitable positions. Where the filters are
arranged in groups, as suggested in Figs. 75 and 77, the intervening
spaces may be used to accommodate a simple receiving tank, or a dosing
tank, to which the sewage or tank effluent may be conveyed by an
elevated channel or by a pipe under pressure. The connections to the
adjacent filters may then be provided in the form of pipes leading
from this central tank direct to the distributor at the centre of each
filter. If the receiving tank or dosing tank in such cases is built
upon piers, the floor of the tank will come above the level of the
surface of the filters, and the space below may be utilised for an
effluent receiving chamber or even for a settling tank to arrest the
solids in suspension in the effluent. There are many ways in which the
supply to filters may be arranged, and the preceding notes are merely
intended as suggestions, which may be elaborated as found desirable to
suit conditions which vary almost in every case.
[Illustration: FIG. 121_c_.
T = tank. D = dosing tank.
P = supply pipe. F = filter.
E = effluent channel. H = humus tank.]
Figs. 121_a_ and 121_b_ have been prepared to show conditions under
which channels and pipes respectively would be suitable for supplying
the tank effluent to the filters. Fig. 121_c_ is the plan of a works
where a dosing tank is used to deliver the tank effluent intermittently
through separate supply pipes to each of the filters. If the valves on
the supply pipes are properly adjusted, each filter will receive an
equal proportion of each discharge from the dosing tank. An alternative
method is to provide an apparatus by means of which each separate
discharge from the dosing tank is delivered in rotation to each of the
filters.
In cases where the appearance of the works must be taken into
consideration, the method of arranging the tanks and filters suggested
in Fig. 121_d_ may be adopted. By this means the space covered by the
works is utilised to the utmost, and the tanks are of the form by which
uniformity of distribution and the maximum reduction of velocity is
secured. On the other hand, it is probable that the slope of the site
will only rarely suit this arrangement.
[Illustration: FIG. 121_d_.
O = outfall sewer. S = screen chamber.
D = detritus tank. T = settlement tank.
C = carrier. P = supply pipe.
F = filter. E = effluent channel.
H = humus tank.]
_Dosing Apparatus._—Various methods of providing intermittent supply
are in use. Among these one of the first was a simple form of balanced
valve with float. This, however, has been superseded by other types,
among which the syphons are the simplest form. One of the first of
this type specially designed for the purpose in question was the
low-draught syphon, manufactured by Messrs. Adams Hydraulics, Ltd.,
and shown in Fig. 122. The special feature of this apparatus is that
it can be arranged for a small depth of sewage in the dosing tank.
It will work with any depth from 6 inches upwards. These syphons can
also be arranged to work singly, in pairs, each one coming into action
alternately, or in numbers of three and upwards, when they can be
adjusted to work in sequence or simultaneously.
[Illustration: FIG. 122.—LOW-DRAUGHT DOSING SYPHON.]
Another type of syphonic dosing apparatus is that supplied by the
Patent Automatic Sewage Distributors, Ltd., and shown in Fig. 123. In
this case a syphon is combined with a mechanical valve operated by
floats, hence the name “auto-mechanical syphon.”
A further type of syphonic dosing apparatus is manufactured by Messrs.
George Jennings, Ltd., as shown in Fig. 124. These syphons are arranged
to work in regular sequence, and are operated by means of air valves,
which are shown mounted on a frame and connected by means of air pipes
to the syphons. The sequence is obtained by means of cams, fixed in
different positions on a shaft, which is rotated by means of a float
actuated by the rise and fall of the liquid in the dosing tank.
[Illustration: FIG. 123.—DOSING SYPHON.]
A different type of dosing apparatus is the “Coleman” valve,
manufactured by The Ames Crosta Sanitary Engineering Company, Fig. 125.
This consists of a balanced valve, suspended from a hollow lever which
contains mercury, and has a branch provided with a float actuated by
the rise and fall of the liquid in the tank. As the sewage rises in the
tank, the float overcomes the resistance of the balance weight on the
lever, which is lifted, and the mercury falls to the lower end of the
lever. The combined action of the float and the mercury opens the
valve, and the sewage is discharged. When the tank is emptied, the
apparatus resumes its former position ready for the next dose.
[Illustration: FIG. 124.—DOSING SYPHONS.]
Another type of dosing apparatus is manufactured by Messrs. Mather and
Platt, Ltd. This consists primarily of a flap valve, counterbalanced
weights, and a balance vessel or drum, which is filled gradually with
liquid, the whole being pivoted about a horizontal axle. When the
measuring chamber and balance drum are both empty, the counterbalance
weights raise the latter and allow the flap valve to close, the
balance drum then being in its highest position. As the measuring
chamber fills, a portion of the sewage is allowed to pass from it
into the balance drum, which is thus gradually filled, and at a given
level its weight will suffice to overcome the counterbalance weights
and the pressure of the sewage on the flap valve, and will open the
latter, thus allowing a measured quantity of sewage to be discharged
into the troughs or pipes for spreading over the filter. The balance
drum discharges its contents meanwhile, and thus, when the measuring
chamber is empty, the flap valve closes again by the action of the
counterweights, and the chamber is ready to receive another quantity of
sewage (Fig. 126).
[Illustration: FIG. 125.—“COLEMAN” DOSING VALVE.]
Messrs. George Kent, Ltd., have introduced several different types of
dosing apparatus, which can be arranged to draw off less than 6 inches
head of water and any greater depth. In one case the apparatus, Fig.
127, consists essentially of a seating S, through which the liquid
discharges, a valve-cap C, attached to arms which rotate about the pin
P and nearly balanced by the weights W, also by floats F F attached
to a frame, also rotating about P and carrying two adjusting weights
A A. The apparatus is actuated by the rise of the liquid, raising the
floats and lifting the cap C, which returns to its position after the
discharge has taken place. For greater depths a different type is used,
as shown in Fig. 128. In this case the apparatus consists of a valve
seating S, through which the liquid discharges, two floats A and B, a
controlled device for giving a sudden release and for regulating the
levels at which the valve is opened or closed, and an alternating gear
G, which is fitted with two or more valves placed in the chamber and
operated in rotation. The action of the apparatus is as follows: When
the liquid in the dosing chamber reaches the top level, the float A has
acquired sufficient buoyancy to cause the shoulders of the plate K to
suddenly push aside the rollers at the ends of the weighted levers L L
of the control device. The lugs T T then come in contact with the
collar R, and the valve-cap C and the float B are lifted. The tank
discharges until the floats A and B have lost sufficient buoyancy to
cause the bottom shoulders of the plate to push aside the rollers and
allow the valve to close.
[Illustration: FIG. 126.—DOSING VALVE.]
[Illustration: FIG. 127.—DOSING VALVE.]
This apparatus is applied in various ways for different
purposes in connection with sewage works, and the same
firm also manufacture special valves for giving a measured
discharge under various heads.
[Illustration: FIG. 128.—DOSING VALVE.]
[Illustration: FIG. 129.—DISTRIBUTING AND DOSING APPARATUS.]
The Ames Crosta Sanitary Engineering Company, Ltd., also supply a very
ingenious method of providing intermittent supply to filters, as shown
in Fig. 129, which is equally suitable for percolating filters, for
contact beds, or for intermittent filtration on land. This machine is
arranged to give any desired timed discharge to the beds in rotation,
or to discharge measured volumes to the beds in rotation. By means of
valves or weirs, the machine is arranged so that additional beds in
the series are automatically brought into operation as the increase
in flow demands, and the additional beds brought into action go out
of action as the flow decreases. The illustration shows a machine for
delivering timed volumes on a series of six beds. The square chamber is
divided into six divisions by means of iron plates; each division is
connected to one of the six beds by means of a pipe. A circular dish or
vessel is suspended over these divisions, and revolves on ball-bearings
carried on the bridge. The circular dish is provided with a weir at
its circumference, and the sewage or tank effluent which enters the
dish from the pipe in the centre is diverted by means of the weir or
outlet to one of the divisions supplying the beds. The upright shaft
from which the revolving dish is suspended is fitted with a six-toothed
ratchet wheel, and, by the rise and fall of a float in the liquid of
the actuating tank, a pawl is moved along until it engages with the
next tooth of the ratchet wheel. When the pawl has caught the tooth of
the ratchet wheel the outlet valve in the actuating tank is opened,
and as the liquid flows out of the tank the float descends, and by
means of levers the pawl is moved one-sixth of a revolution; the pawl
being engaged with the ratchet wheel, the dish is revolved one-sixth
of a revolution, and the weir is thus brought over the next division,
and consequently the next bed receives the flow. Extra weirs can be
arranged at various levels, so that if more sewage is coming than that
required for one bed, a portion of the liquid would flow over one or
more of the weirs, and so on, to the respective beds. The flow to the
actuating tank is taken from the feed channel, and can be set to fill
the actuating tank in any desired period of time. The discharge from
the actuating tank can be conveyed either to a special plot of land, or
into the revolving dish. An ingenious device is arranged so that
any bed in the series can be instantly shut out of action should it
become overworked. In an apparatus for feeding revolving sprinklers,
arrangements are made for bringing the extra beds into operation by
means of valves controlled by the flow of sewage.
[Illustration: FIG. 130.—BALANCE-VALVE DOSING APPARATUS.]
Messrs. Glenfield and Kennedy also manufacture a balance-valve type of
dosing apparatus operated by means of floats and buckets. This is shown
in Fig. 130.
[Illustration: FIG. 131.—DISTRIBUTING AND MEASURING
APPARATUS.]
The “Uniform” automatic distributor, manufactured by Messrs. Whitehead
and Poole, is designed for the automatic distribution of measured
volumes of liquid to filters or other areas in regular rotation. This
is shown in Fig. 131, and the principles on which it is constructed
involve rotating arms carried on a float operated in a closed central
chamber. The arms are rotated by the reaction of the discharge of the
liquid, but are locked so as to remain stationary in one position,
continuing to feed one filter until the head of liquid actuating a
regulating cock and tipper releases the locking device and permits the
rotation of the arms to the next bed, where the process is repeated,
and so on to all the filters in rotation.
The “Ponding or Intermitting Valve,” supplied by the Septic Tank
Co., is shown in Fig. 132. The essential features of this apparatus
are two cylindrical vessels of cast-iron or other suitable material,
approximately of the same shape, weight and displacement. One vessel is
used as a bucket and the other as a bell. They are suspended from two
equal arms of a pivoted lever at approximately the same distance from
the standard carrying the lever. On the same end of the lever to which
the bell is hung, an ordinary lift-up valve is attached, the seat of
which is at or below the low-water level in the ponding chamber. This
valve is connected with the lever by means of a linked rod, chain, or
other suitable arrangement. The cubical content of the bell and bucket
is sufficient to ensure the displacement of the liquid, in excess of
that required to lift the valve from its seat, by rocking the lever to
which it is attached. In the bottom of the bucket a draw-off valve is
provided for the purpose of emptying same. This valve is constructed
so as to prevent the liquid passing through it into the bucket as
it rises in the chamber, and to open and allow the contents of the
bucket to escape when the water in the ponding chamber has almost been
discharged. The operation of the apparatus is as follows. The ponding
valve being closed, and the supply of liquid being turned into the
ponding chamber, the liquid will rise. On reaching the small ball in
the bottom of the valve of the bucket, the ball will float and close
this bucket valve, so as to prevent the entrance of the liquid through
and into the bucket. The liquid continuing to rise, will gradually and
simultaneously submerge the bell and the bucket. The upper edge of the
bucket is fixed at the predetermined height to which the liquid is to
rise in the ponding chamber. The bell and bucket being of the same size
and weight, and being hung so that the one is level with the other, the
displacement of both will be equal up to the time the liquid reaches
the upper edge of the bucket, and consequently no movement of the lever
will take place. On the liquid rising above the top edge of and filling
the bucket, it will cause the displacement of the bucket to be reduced
to much less than the displacement of the bell, and this difference is
sufficient to lift the valve from its seat, and discharge the contents
of the ponding chamber. As the liquid in the chamber recedes, the
bucket and the bell will both be gradually left suspended in the air.
Until the liquid in the chamber drops below the bottom of the bucket,
the latter will remain full; on the water continuing to fall, the ball
in the small valve at the bottom of the bucket will drop, allowing the
contents of the bucket to escape. On the bucket being emptied of its
contents, the weight of the bell, together with the valve and chain or
rod, will overcome that of the bucket, the valve will close, and the
liquid commence to pond in the chamber again.
[Illustration: FIG. 132.—THE SEPTIC TANK CO.’S PONDING VALVE.]
[Illustration: FIG. 133.—AUTO-MECHANICAL DOSING SYPHON.]
The special syphons manufactured by Messrs. Burn Bros., described under
contact bed apparatus, are also suitable for use as dosing syphons, and
work singly or in sequence, and give intermittent discharge to filters
or to land (see Fig. 145, page 218).
An auto-mechanical type of syphon for dosing tanks is supplied by the
Carlton Engineering Co., and is illustrated in Fig. 133.
_EFFLUENT SETTLING TANKS OR HUMUS PITS._
Reference has already been made, under the heading “Grading of
Filtering Material,” to the advisability of using coarse material, for
the reason that the converted organic matter will in that case readily
pass away in the effluent, and thus prevent the choking of the filter.
Even with finer material, a certain amount of solids in suspension will
be found in the effluent, and, in order to produce a final effluent
suitable for discharge into any stream or watercourse, it is necessary
to arrest and remove these suspended solids. This fact has been
recognised by the Royal Commission on Sewage Disposal, who recommend
the adoption of effluent settling tanks with a capacity equal to two
hours’ flow of the sewage, and provided with means for removing the
deposit.
The solids in effluents from percolating filters are rather difficult
to arrest, as they are in the form of very finely divided matters in
suspension. Many methods have been tried in various places, but in the
author’s experience he has found that the chief factor in securing
a satisfactory settlement of these solids, is the reduction to the
minimum of the velocity of the effluent in its passage through the
settling tank. If this principle is adopted, the simplest form of
tank is similar in construction to that suggested for detritus tanks,
so long as the outlet end is constructed in the form of a weir of
the greatest possible length under the circumstances. Such a tank is
illustrated in Fig. 134. By this means the rate of flow over the weir
may be reduced to the minimum; and if, in addition to this, the outlet
at the bottom of the tank is arranged in the form of a plug valve fixed
in a pocket below the lowest point of the floor proper, near to the
inlet end, and the floor is laid with a sharp slope towards this
outlet, it will be found possible, as a rule, to draw off the deposit
without discharging the entire contents of the tank, as long as it
is done at frequent intervals. As there is a tendency for a scum to
form on the surface of the liquid in these tanks, it is desirable to
provide a scum-plate of wood, slate, or other material, as shown in
the illustration, and in all cases, except the smallest schemes, these
tanks should be constructed in duplicate. It may be mentioned here that
the hydrolytic tank, Fig. 34, page 52, and the separator of the Septic
Tank Co., Ltd., Fig. 47, page 65, have both been adopted for use as
effluent settling tanks.
[Illustration: FIG. 134.—EFFLUENT SETTLING TANK.]
The deposit from effluent settling tanks, as a rule, rapidly dries
without creating a nuisance when it is spread out in a thin layer
upon a suitable draining bed similar to that suggested for dealing
with sludge from settling tanks (Fig. 58, page 83). Under favourable
conditions as to fall, the draining bed can be constructed below the
level of the sludge outlet from the effluent settling tank, and the
deposit can then be drawn off by gravitation. There is, however, still
the problem of disposing of the liquid flowing from the bed, and as
this should have a free outlet, it usually happens that the levels do
not permit of the discharge of the deposit by gravitation. Under these
circumstances the outlet should still be arranged as shown, Fig. 58,
but it should be connected to a sludge well fitted with a chain-pump,
or other means of raising the deposit to the draining bed, which may
thus possibly be situated at the same level as the similar beds for the
sludge from the settling tanks. When dry, this deposit may be spread
out on the land, or used in gardens and on farms as a manure.
_SAND FILTERS._
It would probably be more correct to use the term “fine-grain filters”
to describe the alternative methods occasionally adopted to deal with
the effluents from percolating filters, as they do not always consist
of sand. Fine clinker, ashes, broken saggars, and similar material, is
equally suitable so long as it is of a gritty nature and not wholly
dust. The term “sand-filters” is, however, used here, as it is well
known in connection with the filtration of drinking water, and the
method of construction is practically the same.
Although primarily designed for the purpose of arresting the suspended
solids in final effluents, and thus required to act simply as
mechanical strainers, sand filters have the additional advantage of
increasing the degree of purification, especially from a bacterial
point of view. The most important factor to be considered in
constructing these filters is the grading of the material. It must
not be too fine or contain too great a proportion of dust, or it will
rapidly become clogged and involve much labour and expense in cleaning
the surface layer. The nearest approach to perfection in material for
this purpose is the coarse Leighton Buzzard filter sand. As in the
case of the best material for the percolating filters themselves, it
may cost a little more than other less satisfactory kinds, but it will
generally be found to be the cheapest in the end.
In constructing filters of this type, whether composed of sand or other
material, it is essential that the bottom layer should be of a coarser
grade, in order to provide free drainage. In a general way it will be
found satisfactory to have a series of 2-inch agricultural drain pipes
laid on the floor and converging towards the outlet. Over the whole
floor should then be laid a layer 6 inches deep of gravel, broken
bricks or stones of the size of walnuts, upon this a layer 3 inches
deep of pea gravel, and at the top a layer not less than 9 inches deep
of suitable sand or other fine grade material. The surface of the
filter should be well below the level of the inlet, in order to allow
the liquid to pond up on the surface 6 inches to 9 inches in depth
without backing up to the level of the floor of the percolating filter.
One of the difficulties encountered in operating filters of this type
is to secure even distribution over the whole area. The means to be
adopted for this purpose should be simple and easily cleaned, and it is
usual to find troughs of wood or iron, glazed ware channel-pipes and
similar arrangements in use. Unfortunately these do not effectively
cover the whole area until the sand has been saturated and the surface
slightly coated, thus preventing the liquid from passing through as
fast as it comes in. When this occurs, however, the time for cleaning
the surface is not far distant, and when the filter is brought into
use again the whole preliminary process has to be repeated. The best
way of avoiding these difficulties would appear to be to arrange the
filter in such a way that the liquid must cover the whole area from
the very beginning. This can be accomplished by fixing the normal
outlet _above_ the level of the surface of the filter as suggested,
Fig. 135, where the final effluent discharge is normally from the end
of the swivel-jointed pipe when in its vertical position. When it
becomes necessary to clean the filter and drain it for purposes of
aeration, the swivel-jointed pipe is simply lowered to the floor of the
outlet-chamber, as shown in plan, and raised again when the filter is
brought into operation.
[Illustration: FIG. 135.—SAND FILTER.]
Filters of this type should never be less than two in number, so that
one may be in work while the other is being cleaned. It would probably
be advisable to have even three or four filters for schemes of moderate
size, so as to provide longer or more frequent intervals of rest for
aeration. It will be obvious from the preceding observations that
these filters must be substantially constructed and made absolutely
watertight. When dealing with a good effluent from percolating filters
or contact beds, these final sand filters may be provided at the rate
of 1 square yard for every 500 gallons of the daily dry weather flow.
Where ample fall is available, careful consideration should be given
to the advisability of operating these sand filters in the same manner
as percolating filters, i.e. by using revolving sprinklers for the
purpose of distribution without submerging the filtering material. This
applies particularly in cases where it is desirable to secure a very
high degree of bacterial purification. Recent investigations have shown
that sand filters for drinking-water, when operated in this manner, are
highly efficient and involve less expense for maintenance. In addition
to this they require less cleaning, so that a much smaller area is
thrown out of work during cleaning operations, and a smaller total
area of filter surface is needed than in the case of similar filters
operated on the submerged system. The additional fall required for the
revolving sprinklers will usually be a serious difficulty in the case
of sewage disposal works, but where it is available, and the extra cost
entailed is not of great importance, the idea deserves consideration.
Filters of this type should be preceded by an effluent settling tank as
previously described.