“Notice is hereby given.“1. That the mayor, aldermen, and burgesses of the borough of,in execution of the powers and authorities given to and vested in them by virtue of the Public Health Act 1875, upon the report of their surveyor, whereby it appears to the said authority to be necessary to enter into, through, or under the lands and premises particularly described in the schedule hereunder written, for the several purposes hereinafter mentioned, the said mayor, aldermen, and burgesses will immediately after theday ofenter into and upon the premises described in the said schedule hereto, and on the plan hereinafter mentioned numbered,for the purpose ofin, through, or under the said lands and premises,and to construct all other necessary works for all or any of the purposes aforesaid.“2. The course of the said sewer is indicated by a line drawn on the said plan from the pointto.“And notice is hereby further given that a plan of the intended works, and of the lands and premises upon which it is intended to enter for the construction of the same, is now open for inspection, between the hours of 10 in the forenoon and 4 in the afternoon, and may then be seen at the offices of the borough surveyor,Street,,and a tracing thereof is hereunto annexed.Dated thisday of18 .________________________________Town Clerk.”[183]
“Notice is hereby given.
“1. That the mayor, aldermen, and burgesses of the borough of,in execution of the powers and authorities given to and vested in them by virtue of the Public Health Act 1875, upon the report of their surveyor, whereby it appears to the said authority to be necessary to enter into, through, or under the lands and premises particularly described in the schedule hereunder written, for the several purposes hereinafter mentioned, the said mayor, aldermen, and burgesses will immediately after theday ofenter into and upon the premises described in the said schedule hereto, and on the plan hereinafter mentioned numbered,for the purpose ofin, through, or under the said lands and premises,and to construct all other necessary works for all or any of the purposes aforesaid.
“2. The course of the said sewer is indicated by a line drawn on the said plan from the pointto.
“And notice is hereby further given that a plan of the intended works, and of the lands and premises upon which it is intended to enter for the construction of the same, is now open for inspection, between the hours of 10 in the forenoon and 4 in the afternoon, and may then be seen at the offices of the borough surveyor,Street,,and a tracing thereof is hereunto annexed.
Dated thisday of18 .
________________________________Town Clerk.”[183]
________________________________Town Clerk.”[183]
The Schedule Referred to.
In carrying out works of sewerage the greatest care is necessary in the materials selected and the manner in which the work is executed. Tunnels and shafts must be most carefully timbered, levels very accurately given and adhered to, and for this purpose sight rails and long boning rods can be used with great advantage. In running sands, or where the line of an old sewer is being followed, or in fact anywhere where a good and quick joint is required, “Stanford’s” patent jointed pipes should be used.
“This joint is made by casting, upon the spigot and in the socket of each pipe, rings of durable material, which, when put together, fit mechanically into each other, as in a bored and turned joint; it needs no skilled labour in fixing, only a little grease, allows of slight settlement of the pipes without injury, and requires neither cement, clay, nor other extraneous material, the pipes containing a perfect joint within themselves.”
Breakages sometimes occur in stoneware pipe sewers afterthey are laid, which generally are found on examination to arise from one of the following causes:
(1.) Laying the pipes on a rigid foundation without recessing the sockets so as to give an even bearing.
(2.) Laying the pipes on foundations which afterwards yield or settle.
(3.) Laying the pipes at too great a depth without protection by concrete or otherwise to resist the pressure of the superincumbent earth, or by not sufficiently punning the filling-in, when a sudden settlement will often crack or crush a pipe.
(4.) Accidental or wilful injuries to pipes which are not noticed before the trench is filled in.
(5.) Laying the pipes at too shallow a depth without protection, when heavy traffic or a falling weight upon the surface will crush or crack a pipe.
(6.) Defective or weak pipes.[184]
The following plates give the different forms of sewerage pipes that are now manufactured in this country, in addition to those of common shapes:
BROOKE’S PATENT SUBSOIL DRAINS AND PIPE-RESTS.
BROOKE’S PATENT SUBSOIL DRAINS AND PIPE-RESTS.
CREEKE’S PATENT CAPPED PIPES.
CREEKE’S PATENT CAPPED PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.
HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.
MAWBEY’S PATENT GROOVED SOCKET-PIPES.
HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
HENRY SHARP, JONES, & CO.’S ROCK-CONCRETE PIPES.
JENNING’S PATENT CHAIR AND SADDLE PIPES.
JENNING’S PATENT CHAIR AND SADDLE PIPES.
The chokage in pipe sewers generally arises from one or more of the followingcauses:—
(1.) Improper gradients.
(2.) Insufficient flush.[185]
(3.) Foreign articles finding their way into and choking the sewer.
(4.) Defective joints through which the liquid runs leaving solid matters behind.
(5.) An excess of road detritus or of ashes, through the house closets of the poor, finding their way into the sewer.
(6.) Improper bends in the line of sewer.
(7.) Right-angle or improper junctions being formed with the sewer.
(8.) A collapse of the sewer.
A temporary chokage in a small-sized sewer which does not arise from any structural defect can be speedily and effectually remedied by the use of Ben Reed’s patent drain-cleaning rods, which are probably too well known to every town surveyor to need any description, but in conjuction with man- or lamp-holes and straight lines of sewers they are very valuable.
Before closing this chapter, a few words upon what is called the “separate system of sewerage” may be of use.
The mistake hitherto made has been to try to absolutely separate all rainfall from the sewers, and there is no doubt that a partial separation of the rain-water from the sewage proper has many advantages; but it must be understood that a great deal of the rain-water that falls upon roofs of buildings and in back yards and small back streets must of necessity be carried into the sewers, as well as liquid refuse from manufactories. A partial separation thus carried out has the following advantages:
(1.) It is not necessary to have sewers of enormous diameter.
(2.) The depth of the surface water conduits need not be so great as that which is necessary for sewers.
(3.) The avoidance of road detritus being washed into the sewers.
(4.) Where the sewage has to be pumped or treated chemically or put on the land, the combined system causes an immense unwieldy bulk of liquid to be at times dealt with.[186]
(5.) The sewers may be placed at the back of the houses, a great advantage which cannot be carried out under the combined system.
(6.) The regularity in the amount of flow of sewage.
(7.) The accuracy with which the quantity of sewage may be calculated and the sizes of sewers apportioned.
(8.) Economy both to the general rates and also to individuals in carrying out their connections.
(9.) Where old and defective sewers exist they are often fitted to carry surface water, but are quite inappropriate as sewers.
No rules, however, can be laid down with regard to this question, as each town or district must be treated as the case requires.
In conclusion, I will mention the different methods at present in vogue for the sewerage of towns.
(1.) The combined system, where all sewage, surface water, manufacturers’ refuse, and subsoil waters are carried in the same sewer.
(2.) Similar to the above, the subsoil water, however, being carefully excluded.
(3.) The partially separate system.
(4.) The absolutely separate system, where there are three sets of sewers, one for sewage proper, one for surface water, and one for subsoil water.
(5.) The “Lieurner” system, which professes to remove all sewage by exhausting the air in the sewers and drains.
(6.) “Shone’s” pneumatic ejector system, which is described asfollows:—
“The ejectors are cast-iron receivers of a suitable form, placed underground at depths to suit the locality, into which ejectors the sewage flows through the ordinary pipe drains from the houses. As the liquid rises in the interior of the ejector, and when full, it lifts a valve and admits compressed air from an engine which supplies the entire district. The ejectors are thus emptied of their contents, which are blown out in about eighty seconds of time, and the sewage passes through cast-iron main pipes of suitable diameters to the land, or other outlet provided to receive it, or it may be distributed upon the waste land as it passes through.”
(7.) The dry systems, which consistof—
(a.) Earth closets;
(b.) Tubs, as the Goux, &c.;
(c.) Pails, as the Rochdale;
(d.) Middens.
But all these dry systems require some system of sewers to carry off rain-water, slop-water, &c., and in my opinion are not suitable for very large communities.
[174]If the sewers vested in and belonging to a local authority are allowed by their negligence to get out of repair, they are liable to an action for damages (Vide‘Fitzgerald’s Public Health Act,’ 3rd edition, p. 19). Keeping in repair does not, however, include construction of entirely new works. (Ibid.)[175]The sewers provided by a local authority must be sufficient to carry off the ordinary sewage and rainfall of the district, but they need not be sufficient to carry off an extraordinary flow of water caused by a storm; damage caused by that comes under the definition of damage caused by the act of God, for which there is no individual responsibility (Ibid.p. 20). This clause seems to insist upon sewers carrying the rainfall.[176]See chapter on “Ventilation of Sewers.”[177]A local authority is not to be held liable for not keeping their sewers cleansed at all events and under all circumstances, but only where by the exercise of reasonable care and skill they can be kept cleansed. They are, however, liable, in case they make default in observing the requirements, to have an injunction filed against them and to be restrained by injunction from allowing the continuance of the nuisance. (Ibid.p. 23.)[178]For the legal definition of “drain,” see the chapter on “House Drainage.”[179]Facilities must be given to enable manufacturers to send the liquids proceeding from their works into the public sewers, provided the sewers are more than sufficient for the requirements of the district, or if the liquids would not prejudicially affect the sewers, or from their temperature or otherwise be injurious in a sanitary point of view.VideRivers Pollution Act 1876 (39 & 40 Vic. c. 75, s. 7). But this question is often greatly disputed, and has led to much litigation.[180]If everything has to be carried in a sewer, the following provisions must bemade:—(a) The house sewage which may be calculated from the water supply.(b) Manufacturers’ refuse.(c) Rainfall, which is a very uncertain quantity.(d) The subsoil water should certainly be dealt with, but it should on no account be permitted to enter the sewers themselves; separate provision under the main sewers should be provided for this purpose.[181]Messrs. Sharp, Jones and Co., of Bournemouth, make most excellent concrete pipes up to 36 inches in diameter, which can be economically and advantageously used in many instances, and are gaining every day in popularity with engineers.[182]The definition of “lands” as given in the Public Health Act 1875, is as follows:—“‘lands’ and ‘premises’ include messuages, buildings, lands, easements, and hereditaments of any tenure” (38 & 39 Vic. c. 55, s. 4).[183]Notices may be signed either by the clerk to the local authority or their surveyor (38 & 39 Vic. c. 55, s. 266).[184]The thickness of stoneware pipe sewers should be as follows:Internaldiameterof pipe.Thicknessofmaterial.in.in.3¹⁄₂4⁵⁄₈6³⁄₄91121¹⁄₈151¹⁄₄181³⁄₈The thickness of fire clay or earthenware pipes should be slightly in excess of those given for stoneware.[185]The patent automatic flushing arrangement by Mr. Rogers Field, C.E., is an excellent apparatus for lessening the chances of a sewer becoming choked from this cause.[186]It is necessary in many towns where the combined system is in force, and the sewage has to be pumped when heavy rains commence, to put temporary clay dams round the street gratings to prevent the surface water from entering the sewers, thus at once showing the inability of the system to deal with flood waters.
[174]If the sewers vested in and belonging to a local authority are allowed by their negligence to get out of repair, they are liable to an action for damages (Vide‘Fitzgerald’s Public Health Act,’ 3rd edition, p. 19). Keeping in repair does not, however, include construction of entirely new works. (Ibid.)
[175]The sewers provided by a local authority must be sufficient to carry off the ordinary sewage and rainfall of the district, but they need not be sufficient to carry off an extraordinary flow of water caused by a storm; damage caused by that comes under the definition of damage caused by the act of God, for which there is no individual responsibility (Ibid.p. 20). This clause seems to insist upon sewers carrying the rainfall.
[176]See chapter on “Ventilation of Sewers.”
[177]A local authority is not to be held liable for not keeping their sewers cleansed at all events and under all circumstances, but only where by the exercise of reasonable care and skill they can be kept cleansed. They are, however, liable, in case they make default in observing the requirements, to have an injunction filed against them and to be restrained by injunction from allowing the continuance of the nuisance. (Ibid.p. 23.)
[178]For the legal definition of “drain,” see the chapter on “House Drainage.”
[179]Facilities must be given to enable manufacturers to send the liquids proceeding from their works into the public sewers, provided the sewers are more than sufficient for the requirements of the district, or if the liquids would not prejudicially affect the sewers, or from their temperature or otherwise be injurious in a sanitary point of view.VideRivers Pollution Act 1876 (39 & 40 Vic. c. 75, s. 7). But this question is often greatly disputed, and has led to much litigation.
[180]If everything has to be carried in a sewer, the following provisions must bemade:—
(a) The house sewage which may be calculated from the water supply.
(b) Manufacturers’ refuse.
(c) Rainfall, which is a very uncertain quantity.
(d) The subsoil water should certainly be dealt with, but it should on no account be permitted to enter the sewers themselves; separate provision under the main sewers should be provided for this purpose.
[181]Messrs. Sharp, Jones and Co., of Bournemouth, make most excellent concrete pipes up to 36 inches in diameter, which can be economically and advantageously used in many instances, and are gaining every day in popularity with engineers.
[182]The definition of “lands” as given in the Public Health Act 1875, is as follows:—“‘lands’ and ‘premises’ include messuages, buildings, lands, easements, and hereditaments of any tenure” (38 & 39 Vic. c. 55, s. 4).
[183]Notices may be signed either by the clerk to the local authority or their surveyor (38 & 39 Vic. c. 55, s. 266).
[184]The thickness of stoneware pipe sewers should be as follows:
The thickness of fire clay or earthenware pipes should be slightly in excess of those given for stoneware.
[185]The patent automatic flushing arrangement by Mr. Rogers Field, C.E., is an excellent apparatus for lessening the chances of a sewer becoming choked from this cause.
[186]It is necessary in many towns where the combined system is in force, and the sewage has to be pumped when heavy rains commence, to put temporary clay dams round the street gratings to prevent the surface water from entering the sewers, thus at once showing the inability of the system to deal with flood waters.
The magnitude of the question of “sewage disposal” almost decided me to refrain from making any remarks upon it, but on reconsideration I thought a few might be serviceable.
Sewage disposal means the getting rid of the foul water contained in the sewerage system of any community.
Where a dry method is in force for the collection of the excrementitious matters it is called “interception”; the following are some of the systems which effectit:—
Privies, ashpits, middens, cesspools, pails, troughs, the “Rochdale,” the “Eureka,” the “Goux,” Fosses Permanentes, Fosses Mobiles, and Moule’s, Taylor’s, and Phillip’s earth closets.
The collection and disposal of the mass of excrement under these dry systems is found to be a very troublesome matter, and they are at their best but inferior substitutes for water carriage, nor must it be forgotten that sewers and drains are necessary even if a good interception process is in force. I shall therefore confine my remarks to the disposal of water-carried sewage.
Many books have been written, many valuable reports have been prepared and issued, lengthy papers and discussions have been frequent at the meetings of scientific societies, and almost innumerable pamphlets have been published upon this important sanitary subject. Some millions of money have also been spent in trying to deal satisfactorily with this question, not only with a view to the purification of the effluent of the sewage, but also to endeavour to make a profit out of theresiduals.[187]The result of this literature, discussion, and experiment has led to the following conclusions:
No hard and fast lines can be laid down as to the best method to be adopted for the disposal of the sewage of any town, but the peculiar circumstances of each case must be considered before advice could be given on the subject: geographical position, physical arrangement, habits of the population, and the character and quantity of the sewage of the town being some of the most important.
In any case it is necessary that the transmission of the sewage to the outfall should be effected as speedily as possible, and that the position of this outfall should be such as to cause no nuisance. The contents of the sewers should, if possible, be emptied by gravitation, as pumping is a constant expense, and economy with efficiency must of course be studied.
Up to the present time the following are the methods adopted in this country for the disposal of sewage:
(1.) Passing the sewage in its crude state into the sea or tidal river.
(2.) Passing the sewage in its crude state over large tracts of land; this is called broad irrigation.
(3.) Passing the sewage in its crude state on to small tracts of land previously prepared by deep drainage; this is called intermittent downward filtration.
(4.) Mechanical subsidence of the sewage in large tanks, the effluent passing on to land or into a river.
(5.) Mechanical filtration of the sewage, the effluent passing on to land or into a river.
(6.) The introduction of lime or other precipitant into the sewage, which is allowed to settle in tanks, the effluent passing on to land or into a river.
Very little need be said upon the first of these methods. Many engineers of high standing contend that, where practicable,the sea or the tidal estuary of a river is the right place for the sewage, as no costly works are necessary, and an abominable nuisance is thus got rid of at once and for ever. To ensure this, however, great care must be exercised in the selection of the site for the outfall. Float observations should be made, not only of the surface tides and currents, but also of those at different depths, and the effect upon the sewage by its different specific gravity from that of the salt water must be allowed for, as well as the difference of level of the tides and the configuration of the adjoining coast line.
The second method, that of broad irrigation, is one that finds considerable favour with a large number of engineers and agriculturists. The great sewage-disposal cry has always been, “Put back on the land what you have taken from it, or some day there will be no beef and no bread.” The difficulty is to always find land in sufficient quantity and so situated as to be available for this purpose. Almost any soil is, however, suitable for irrigation, provided it is well and properly drained. The quantity of sewage which should be used for this purpose per acre of land varies considerably, as will be seen on reference to a table prepared by Mr. Henry Robinson,[188]where the number of inhabitants to each acre irrigated is in one case (Leamington) stated to be 55, in another (Blackburn) 208,[189]the average being 137, the number of gallons per head of population per diem being 38.
It may be useful to state here that a hundred tons of sewage will cover an acre of land 1 inch in depth, and that the value of sewage as a manure is said to vary from ¹⁄₂d.to 2d.per ton, or, calculated in another manner, about 10d.per head of population per annum.
The best crops for a sewage farm (in addition to nearly all kinds of market-garden produce) are rye-grass, mangolds, beetroot, cabbages, carrots, potatoes, turnips, rabi, parsnips,lucerne, beans, wheat, oats, and barley; the cereals, however, are apt to run rather to straw, and some care is also necessary not to oversewage potatoes and some other root crops. Grazing cattle or cows can also be carried on with advantage, the presence of sewage having no effect either on the milk or flesh of animals fed on sewage farms.
The third method, that of intermittent downward filtration, is really irrigation of land to such an extent as the land will filter or purify the sewage, the effluent passing off pure, irrespective of any effect upon the crops which may be growing upon the land.
Great discussions have arisen (the principal battle-ground being Merthyr Tydvil) as to the maximum quantity of sewage which an acre of properly prepared land will treat, some of the champions of this system contending that a good porous soil properly drained to a depth of six feet will purify the sewage of 6000 persons per acre, others that only the sewage of 250 persons can be so treated.[190]
There can be no doubt that earth has a most powerful deodorising power. Laboratory experiments have shown that as much as eight gallons of sewage can be filtered through a cubic yard of loamy soil in twenty-four hours, the soil being drained at a depth of six feet, the effluent therefrom having obtained a wonderful degree of purity. Much, however, must depend upon the character of the soil of the filtering area and the strength of the sewage which is being operated upon.
The following description of the manner in which the earth acts upon sewage will be of interest:
“The fæcal matters and other impurities attached themselves to the surfaces of the particles of earth by a kind of cohesive attraction, and in this state were readily attacked bythe oxygen of the air. Their organic carbon became carbonic acid, their nitrogen was converted into nitrous or nitric acid, which united with the lime, magnesia, and other basic matters present. Mechanically suspended impurities were arrested as by a sieve, and the water issued from beneath—not indeed fit for dietetic or domestic purposes, but at any rate in a fair state of purity and quite inoffensive to the senses.” (VideW. Crookes in the discussion on the Sewage Question by Norman Bazalgette, ‘Min. of Proceedings of the Institution of Civil Engineers,’ vol. xlviii. p. 164.)
The land thus used as a sewage filter requires constant aëration by being dug over or ploughed, and if this precaution is taken, it is surprising to what a wonderful extent the land will take sewage without becoming what is called “sewage sick.” Clay soils are, however, stated to be ill-adapted for this purpose.
The next method, that of mechanical subsidence of the sewage in large tanks, has been attempted in conjunction with irrigation and filtration without much benefit, nor has the fifth method I have mentioned, viz., that of mechanical filtration of the sewage, met with any better result. Artificial filters have been constructed of burnt clay, cinders, coke, charcoal, peat, chalk, gravel, broken stone, sand, spongy iron (this is now being applied very successfully for the purification of water), straw, cocoa-nut matting, wicker-work, and wire gauze of different degrees of fineness of mesh.
The late Mr. Odams spent a considerable sum in endeavouring to strain sewage through revolving screens of wire gauze with but little success, and Mr. Bannehr has striven to achieve the same object by passing sewage over oscillating screens of the like material.
In all these cases of mechanical filtration, however, the effluent has either not been sufficiently pure or the screens and filters have become clogged and refused to act.[191]
The last method that I have mentioned for the disposal of sewage is that of precipitation, or what may be more properly called the chemical treatment of sewage.
Precipitation means the production, by the introduction of chemical substances within the body of the sewage, of certain solid compounds, which, in settling, drag down with them the suspended matters in the sewage, together with a small proportion of the polluting matters which are in solution in the sewage, this proportion varying with the quantity of solid matters deposited. The effluent from the tanks in which this precipitation takes place is then allowed to flow direct into a river or stream, or is still further purified by being passed over land or filtered through deep-drained soils.
Chemical treatment of sewage was first tried in Paris in the year 1740, and since then every effort has been made to extract a valuable and commercial manure from sewage and purify the effluent. Between the years 1865 and 1875 more than 400 patents were taken out in respect of these and other matters in connection with the sewage question.
It is almost needless to say that but few of these patents were of any practical value. Those processes which have some merit and are now best known are, I believe, included in the followinglist:—
List of Chemical Processes forthe Treatment of Town Sewage.
The A. B. C. (or Sillar’s) processAnderson’s processBird’s„Blyth’s„Campbell’s„Collin’s„Forbes and Price’s processFulda’s processGoodall’s„Hanson’s„Higg’s„Hille’s„Holden’s„Lenk’s„Lundy’s„Manning’s„Scott’s„Smith’s„Spence’s„Stothert’s„Suvern’s„Whitthread’s processWickstead’s„
Space will not permit me to describe these processes, andprobably most of them, if not all, are familiar to my readers. Suffice it to say that in nearly all cases themodus operandiis that of mixing certain chemicals with the sewage by mechanical agitation, or by passing the sewage over “salmon ladders,” &c., then allowing the sewage to remain perfectly still whilst the solids are gravitating, and then dealing with the effluent in different manners.
Amongst the numerous chemical ingredients which are used for this purpose may be mentioned thefollowing:—
Alum, animal charcoal, ashes, blood, bone ash, carbolic acid, chalk, chloride of lime, chloride of zinc, chloride of iron, clay, creosote, hæmatite, hydrate of lime, lead nitrate, magnesian salts, oxide of manganese, perchloride of iron, salt, soda, sulphate of zinc, sulphate of iron, sulphuric acid, and tar.
One of the great difficulties in connection with the precipitation of sewage is the disposal of the sludge which is left behind in the tanks.
This sludge contains about 90 per cent. of moisture, and if left to dry atmospherically, a thin crust forms over it, thus protecting that which is underneath, and it will not dry for many months. In some cases it is sought to dispose of the accumulations of sludge by digging it into the land; in others it is mixed with house ashes, &c., and sold as manure. Its bulk, however, in proportion to its manurial value is so excessive as to render it almost valueless, and it is difficult to get rid of it for this purpose even when fortified with ammonia or other chemical. A frequent practice now adopted is to reduce its bulk by exposure or by presses to a semi-dried condition; in other cases it is dried to a powder by heat, and General Scott has patented a method where, in connection with the lime process, it is burned and manufactured into cement. Sometimes it is squeezed in presses, such as Needham and Kite’s or Johnson’s, or it is filtered by Milburn’s or Weare’s apparatus. For drying the sludge by heat, Borwick’s or Forrest’s machines have been used with some success, butthere is no doubt that the slimy, glutinous, albuminous, offensive mixture technically known as sludge is a difficult matter to dispose of in all sewage works.
In connection with the chemical treatment of sewage, it is of advantage to pass the effluent over land filters on the intermittent downward filtration principle. Another very effective plan is to pass the effluent (or even crude sewage) through land which is thickly planted with the Anacharis or American weed, duckweed, sedges, rushes, reeds, &c., or through beds of osiers or alder trees. An acre of land thus planted is said to purify more than three million gallons of sewage per diem.[192]
There is no doubt that plants of this description have a powerful action in purifying sewage or foul water of any kind, and where land is scarce this method has many advantages.
It is almost unnecessary to add that where sewage is treated in any other manner than that of throwing it into the sea or river, bulk is a great objection, especially if it has to be pumped.
To obviate this bulk the separate system is of great advantage, and Isaac Shone’s new method for ejecting sewage along pipes seems also to be a most desirable invention in connection with this subject.
[187]It is computed that every ton of liquid sewage which is treated chemically costs about three-quarters of a farthing.[188]Vide‘Sewage Disposal,’ by Henry Robinson, C.E., &c., 2nd edition, p. 79.[189]I purposely omit (Kendal) 856, as this is, properly speaking, “filtration.”[190]For much interesting information upon this and other subjects in connection with sewage disposal, see ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. xlviii. p. 105 et seq. Also the report of a committee of the Local Government Board on Modes of Treating Town Sewage, 1876. ‘Sewage Disposal,’ by Henry Robinson, C.E., and other works on the subject.[191]Under the Rivers Pollution Act, no effluent is allowed to enter a stream &c., if it contains more than three parts of suspended inorganic matter, and one part organic matter for every 100,000 parts of liquid.[192]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. xlviii. p. 179.
[187]It is computed that every ton of liquid sewage which is treated chemically costs about three-quarters of a farthing.
[188]Vide‘Sewage Disposal,’ by Henry Robinson, C.E., &c., 2nd edition, p. 79.
[189]I purposely omit (Kendal) 856, as this is, properly speaking, “filtration.”
[190]For much interesting information upon this and other subjects in connection with sewage disposal, see ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. xlviii. p. 105 et seq. Also the report of a committee of the Local Government Board on Modes of Treating Town Sewage, 1876. ‘Sewage Disposal,’ by Henry Robinson, C.E., and other works on the subject.
[191]Under the Rivers Pollution Act, no effluent is allowed to enter a stream &c., if it contains more than three parts of suspended inorganic matter, and one part organic matter for every 100,000 parts of liquid.
[192]Vide‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. xlviii. p. 179.
The necessity for some manner of dealing with the noxious vapours emanating from sewage other than that of letting it find its way from the sewers into the house drains and thence into dwelling houses, has induced the legislature of this country to introduce the following clause in the Public Health Act 1875, which imposes on every local authority the duty of causing their sewers to be ventilated so as not to be a nuisance or injurious to health.
“Every local authority shall cause the sewers belonging to them to be constructed, covered, ventilated and kept, so as not to be a nuisance, or injurious to health, and to be properly cleansed and emptied” (38 & 39 Vic. c. 55, s. 19).
The result of this compulsion upon local authorities to ventilate their sewers has been the introduction of many methods to effect the purpose, the great difficulty being to “ventilate so as not to be a nuisance or injurious to health,” the advocates of open ventilation contending that this is effected by having a sufficient number of openings in a sewer to dilute and safely disseminate the foul gas with atmospheric air so that no nuisance is caused.[193]
Many other methods have been from time to time suggested, some of which have been carried into effect, and I will now proceed to give them in detail, discussing their merits and objections in each case.
(1.) Open shafts are carried up from the crown of the sewer to the centre or side of the roadway, and there protected by an open iron grid or grating at the level of the street surface.
This is the system which has hitherto found most favour with town surveyors, and is sometimes modified or worked in conjunction with the practice of untrapping all the gully pits and buddle holes at the sides of the roadway, which is an excellent plan if the theory of the atmospheric air dilution at which this system aims is a correct one; in fact, if this dilution by air is all that is necessary to render the foul air in a sewer innocuous and inoffensive, there cannot be too many openings into it.
The objections to this system are as follows:
(a.) The foul air escaping into the public streets is often very injurious to persons passing a ventilator, and sewers are buried out of sight, but they are not out of mind so long as we are constantly and unpleasantly reminded of their existence.
(b.) It is found that a change of temperature either of the atmosphere, or of the air in a sewer, will seriously affect the action of a shaft, causing it sometimes to have upcast currents of air, sometimes downcast; the effect of this latter action, especially when it arises from the direction of the wind blowing over or into the shaft, is frequently to drive the impure gases contained in the sewer into the house drains, and from thence into the houses, unless they are so trapped and ventilated as to prevent it.
(c.) They are also affected by the fluctuations of the flow of sewage in the sewer, or by barometric changes in the atmosphere.
(d.) The situation of the open grids in the street is sometimes somewhat awkward for traffic, and horses will frequently shy at them, they also admit solid road detritus into the sewer unless they are protected by a catch plate of some description.
(e.) They are tempting places for children to play over, with what results may be imagined.
(2.) Open shafts are carried up the sides (gable ends if possible) of buildings in the neighbourhood of the sewer; these shafts may be either open at the top, or be furnished with exhaust cowls. This system is sometimes employed in conjunction with inlet shafts at the sides of the street, in the manner shown by the drawing which follows:
Ventilation
This method has the advantage over the first system I have mentioned of carrying the smells further from our reach, but it also has the following disadvantages:
(a.) The distance and the number of bends and elbows the gases have to traverse before reaching the external air.
(b.) The difficulty of fixing them just at the points where they are most required with reference to the gradients of the sewer, especially if they are to be constructed of such an internal diameter as will ensure their efficiency.
(c.) The great objection raised by occupiers and owners ofpremises against having them fixed on their premises, both on sanitary and legal grounds.
(d.) Their great expense.
(e.) The effect of weather upon their currents.
(3.) By making use of the rain-water pipes from adjoining buildings.
This method commends itself as being very economical, and the opportunities thus given for ventilation are so numerous. If sewers are to be ventilated at all[194]it would seem at first sight that there could not be too many openings from and into them, but this system has the following serious objections:
(a.) When raining, little or no ventilation can take place, and this is the very time, owing to the rising of the water in the sewer, that the gases should be allowed free egress if such is considered the best manner of dealing with them.
(b.) The position of the head of the rain-water pipe is generally the worst that could be chosen for the egress of the gases, both on sanitary and pneumatic grounds.
(c.) The joints of a rain-water pipe are usually none of the best.
(d.) The objections persons naturally have to allow the rain-water pipes of their houses to be used for such a purpose.
(4.) By utilising the lamp posts or columns adjacent to the sewer.
The objects of this system are first to obtain a constant upward current from the sewer, and secondly to secure that the foul gases and air shall be consumed and rendered innocuous by being burnt. The objections to this systemare—
(a.) The lamps are only lit at night, consequently little or no ventilation would be going on during the day.
(b.) The number and diameter of the lamps are generallytoo small to make any appreciable effect upon the ventilation of the sewer.
(5.) By passing or filtering the foul air through charcoal placed in trays or other receptacles in shafts.
The theory of this method is admirable, as the charcoal would arrest all the impurities and flocculent organic matters contained in the foul air, and allow only the pure filtered air to pass into the atmosphere.
It has been found, however, where this method has been adopted, that the charcoal very soon becomes so caked and consolidated from damp and the vibration of the traffic, that it will neither allow the air to filter through, nor absorb the impurities contained in it; these objections and the amount of attention this system requires, has not rendered it very popular with town surveyors, although it has much to recommend it.
(6.) By making use of ordinary chimney shafts.
This method and the one which follows have some merits, the principle being that an upward current is established as an exhaust from the sewer, and also that the foul air is purified by being passed through fire, but both these advantages are only gained when the fires are actually burning; the objections to this systemare—
(a.) Structural difficulties must often be encountered and overcome.
(b.) Possibility of explosion arising from leaks of gas mains into sewers (a by no means uncommon occurrence, as all who have charge of sewers frequently find to their cost).
(c.) The objections of owners and occupiers to allow their premises to be thus made use of to carry off a public nuisance for which they as individuals are in no way responsible.
(7.) By lofty shafts erected at convenient positions which are either in connection with furnaces or are simply open to the air.
For a long outfall sewer with no connections this method has many advantages, notably so in the large furnace and shaft erected on the Brighton outfall sewer by the borough surveyor, Mr. Lockwood. But in a general system of sewerage, it was found by experiments made by Sir Joseph Bazalgette, C.B. that the effect of trying to reduce the gases by the action of furnaces was but very small, and that the area over which the effect extended was but very limited: in fact, a sewer may be compared to a perforated tube, the house drains, gully drains, &c., representing the perforations; the effect of an exhaustion by the action of the furnace is simply to suck fresh air into the sewer at all these points instead of removing the foul air for any distance.
High shafts at different points effect a partial clearance of sewer gases, but they are very costly, and the reasons I have previously given against the system of open shafts are practically the same in this and all other modifications of the principle.
Many other methods have been tried from time to time, either to prevent the formation of gases in the sewers, or neutralize or destroy them, some of which are as follows:
By giving a quick velocity of discharge in a sewer; by placing materials within sewers which would absorb the gases as fast as they were generated; by passing deodorants or disinfectants into sewers; by deodorizing or disinfecting all materials before they are allowed to enter a drain or sewer; by placing chemical agents within sewers to give off certain gases which would then, it was conjectured, destroy the noxious properties of the sewer gases; by introducing charcoal into sewers to absorb the foul gases; by laying pipes within the sewers for the purpose of discharging chlorine into the sewer; by employing galvanic agency to disengage or to produce ozone from the sewer gas; by passing the foul air through shafts into which water was constantly injected,and by endeavouring to extract the foul air by fans driven by machinery.
I have myself patented a plan for “annihilating sewer gases” by allowing them to be absorbed into dry earth, and have tried the system with some very marked and successful results.[195]
Having thus far considered all the known methods for dealing with the noxious emanations which proceed from sewers, the next point to consider is what these noxious emanations are, and whether they exist in all sewers.
It has been found that even in sewers of the best and most modern construction what is called “sewer gas” is generated in more or less quantity; this arises even from fresh sewage, but is far more noxious and dangerous to health when the sewage has begun to decompose. Even where the sewers are so constructed as to remove all the sewage to the outfall within 24 hours (which has been decided to be the maximum time it should take), there is still an accumulation of slime on the inner periphery of the sewers, owing to the rise and fall of the sewage line, which is constantly manufacturing gases of decomposition.
It is no doubt true that the more perfect the system of sewerage is the less foul air there is in the sewers, but in very few towns will there be found no sewers or drains where temporary obstructions of the sewage do not occur, and where gases are generated, which then find their way into other parts of the sewage system unless they are dealt with in some effective manner.
As to what is the actual composition of this foul air in a sewer little or nothing seems to be known, except that it ishighly dangerous to health if breathed, and is also very offensive to the smell.
The “fœtid organic vapour,” or sewer gas proper, has for its companions in a sewer, sulphuretted hydrogen, a most poisonous as well as unpleasant smelling gas, carburetted hydrogen, due very often to leaky gas mains or services, or to decomposing vegetable matters, carbonic acid gas or carbonic anhydride (choke damp), and some ammoniacal compounds.
The actual component parts, however, of any gases in a sewer must vary considerably with its conditions and locality, &c., in the same manner as they would in any public building or room, and it is impossible to tell, without costly experiments, what gases may be prevalent in any particular portion of a sewer. But whatever may be the analysis of this foul air, there can be but little doubt that it contains organic matter floating about in it as solids, and that it is excessively injurious and even dangerous to breathe, and that it should be caught and destroyed or rendered innocuous, and not be permitted to pass into and contaminate and poison the air we breathe.
Some engineers are of opinion that this foul air always finds its way to the upper portions of the sewerage system, but my investigations into this subject have led me to believe that no rule of this kind can be laid down, for with quick velocities of flow, in some sewers, the gases are carried by friction in the direction of the flow of the sewage, and do not ascend as has been imagined.
Whatever system of ventilation of the main sewers in any town may be adopted, it is imperative that the house drains connected with them should be properly trapped and ventilated, and this is in my judgment of even greater importance than the ventilation of the main sewers. On this point I have given more explanations in the chapter upon “House Drainage.”
In conclusion, let me refer my readers to a most exhaustive discussion, and very valuable information contained in the chapter entitled “Ventilation of Sewers and Drains” in Mr. Baldwin Latham’s ‘Sanitary Engineering,’ in which may be found almost everything that is at present known upon this important subject.