NATURAL & ARTIFICIAL

SEWAGE TREATMENT

BY

LIEUT.-COL. ALFRED S. JONES, V.C.

ASSOC. M. INST. C.E., FELLOW AND MEMBER OF COUNCIL
OF THE SANITARY INSTITUTE, ETC.

AND

H. ALFRED ROECHLING

M. INST. C.E., F.G.S., FELLOW OF THE SANITARY INSTITUTE, ETC.

London

E. & F. N. SPON, Ltd., 125 STRAND

New York

SPON & CHAMBERLAIN, 123 LIBERTY STREET

1902

PREFACE.

The Authors, some time ago, read before different Societies of professional men, Papers[1] dealing with the Natural and Artificial Purification of Sewage, and as these were favourably received, the thought occurred to them that the time might be opportune for making the information there given available for a wider public.

As, however, a mere republication of the Papers would have been against the rules of the Societies concerned, the Authors decided to re-write entirely the subject matter, and to bring it up to date, so that the present publication is not a mere repetition of their old Papers clothed in a new garb, but an entirely fresh publication, right up to date.

The Authors hope that they have given the information in such a form as to be readily available for District Councillors, Sanitarians, and all interested in this complicated subject.

When considering natural and artificial sewage treatment, it ought to be borne in mind that in the natural treatment we

have to deal with one treatment only, and that, in order to bring the results obtained from artificial processes up to the same standard, the artificial treatment ought to be supplemented by a treatment for the removal of nitrates from the effluent, and another for the removal of pathogenic micro-organisms, which means one treatment in natural, as against three separate treatments in artificial purification.

In addition to this it must be understood that, owing to the great losses by evaporation and by growing plants, which are continually at work on sewage farms, especially during the summer months, when, as a rule, the flow of water in the brook that takes the effluent is smallest, the quantity of the effluent from the natural treatment is probably only from one-half to one-third that resulting from the artificial treatment, which is a point of very great importance.

If it can be proved to them that Nature is not sure and true enough in its methods, the Authors are prepared to assist it with methods and means produced by the inventive brain of man. But if such proof is not forthcoming, they adhere—in preference to groping in the dark—to Nature’s own methods, knowing from experience, that when allowed full scope and fair treatment, it is most sure in all its ways. That will not prevent them, however, from giving in the future, as they have done in the past, the question of sewage treatment in all its aspects their most careful consideration.

ALFRED S. JONES.
H. ALFRED ROECHLING.

London: September 15, 1902.

[1] ‘Sewage Treatment: Science with Practice.’ By Colonel A. S. Jones, V.C., C.E. Read at the International Engineering Congress at Glasgow, 1901. And ‘The Sewage Question during the Last Century.’ Read by H. Alfred Roechling, M. Inst. C.E., F.G.S., F.S.I., etc., on December 2, 1901, before the Society of Engineers, and awarded the Gold Medal of the Society.

CONTENTS.

Part I. By Lieut.-Colonel ALFRED S. JONES, V.C.

NATURAL AND ARTIFICIAL

SEWAGE TREATMENT.

By LIEUT.-COL. ALFRED S. JONES, V.C.
Assoc. M. Inst. C.E., etc.

Introductory remarks.

"How extremely simple it all is!” was the remark of a recent visitor at a sewage farm—which encourages me to venture on publication of the most recent discussions on a “problem” complicated by engineers, chemists, bacteriologists and inventors of systems, who have raised clouds of dust through which it is difficult for ratepayers and district councillors to find their way to “the best practical and available means of sewage disposal.”

I have a belief that publication of all attempts to purify the whole of a town’s sewage, rather than small scale experiments with equations founded on such data, is the desideratum.

1872.

Having begun in the year 1872, with a pamphlet, “Will a Sewage Farm Pay?”[2] I desire to proceed with the present one thirty years later, as my humble contribution to a right understanding of the intelligent Scavenger’s business.

At the earlier date agriculture was prosperous, and ratepayers of Exeter were just as confident that sewage farming would bring large dividends as some of the same

city’s councillors are at present not in the least sceptical that their engineer’s septic system is the true specific for sewage disposal.

In adhering to land as the natural and best agent, I have had the support of the Local Government Board with that of many Royal Commissions, notably the one now sitting, and I have naturally chosen cases where suitable land was accessible when I desired to demonstrate the efficiency and simplicity with which the powers of Nature can be applied for the use and convenience of man.

Nor have I failed to study all “artificial” substitutes for the best means, wherever difficulties of obtaining suitable land presented themselves, e.g. my Canvey Island scheme for dealing with the sewage of London on a relatively small area, and other cases.

Of late years I have welcomed the light thrown on this subject by bacteriologists, but lamented extravagant statements put forward by those who fail to see that the previously unrecognised microbes can do their work, as they have always done it, to most advantage in the upper layers of any porous land.

1902.

An interim report by Lord Iddesleigh’s Royal Commission has, however, awakened such theorists to the fact that land is not to be discarded because it may not bring in a profit or because patentees of systems find it to their interest to contrast neglected or badly managed sewage farms with carefully nursed little experimental installations for artificial treatment of selected samples of sewage.

Recognising the marvellous improvements in arts and manufactures of all kinds due to steam, chemistry and electricity, the public has naturally expected similar results from applied science in artificial sewage treatment,

and there has been no lack of study of every imaginable process during the last thirty years.

1884. Lord Bramwell’s Royal Commission establishes principles.

But the late Lord Bramwell’s Royal Commission on Metropolitan Sewage Discharge established two very important points of general application, namely:—​

1. The principle of separation in works of sewerage and drainage; and

2. The fact that the suspended matters in town sewage can be very effectually removed from its liquid by simple deposition without the aid of any chemical reagent.

1887. The chemist Dibdin discards chemical reagents in favour of M. Pasteur’s aerobic organisms.

And Mr. Dibdin three years later began to demonstrate the mistaken policy of adding lime or any other precipitating agent in any quantity likely to arrest the natural agency of abundant bacterial life, which ultimately disposes of all dead and effete organic matter by forming gases or natural compounds, with more or less offence to human senses, according to the supply of oxygen and rate at which these bacteria can carry out their work.

Leeds and Exeter.

It was soon found that the bacteria of two classes, aerobe and anaerobe, abound in sewage, and the latest Leeds experiment with the continuous or trickling filter show the marvellous rapidity with which the aerobic microbes at any rate, can accomplish their task where air and liquid sewage are sufficiently diffused in the pores of a filter; while Mr. Cameron, C.E., at Exeter has shown rapid evolution of gases and considerable solution of organic solids by anaerobic microbes in a septic tank.

But the enthusiasm of inventors and their converts has made too much of the benefit to the human race supposed to be conferred by the bacterial discovery of M. Pasteur as applied by them to sewage treatment.

Without detracting from the credit due to the great

French savant and other bacteriologists who have followed up his interesting studies of ferments for the last fifteen years, the practical man may well ask how much forwarder have we got in the main and pressing business of purifying our rivers—as a consequence of clearer knowledge of minute forms of life?

Intermittent filtration.

The late civil engineer Bailey-Denton demonstrated, thirty years ago at Merthyr Tydvil, the best conditions of intermittent downward filtration, and his filters there and at Kendal, Abingdon, etc., are still doing their work efficiently to this day, while the coke, coal, clinker, burnt ballast, etc., beds, so popular of late, are clogging up after a few years of more careful treatment than was ever accorded to an acre of land under sewage.

Anaerobic action has also been proceeding in the old sewers of most towns and, as it has now been proved that there is no advantage in the exclusion of air, upon which Mr. Cameron laid so much stress when he brought his Exeter tank to public notice in 1897, there can be no novelty except its name attaching to the anaerobic or septic system, which has thrown many sanitary authorities off their balance of late years.

The whole modern system of self-cleansing sewers having been only rendered possible by public recognition of the horrible nuisance arising from middens, cesspools, and irregularly built sewers of deposit, it is hard for those concerned in the cleanly disposal of sewage to be told that because sewage works are usually remote from populous districts they must there put up with the cesspool nuisance and fancy its old smell changed by the new name, because a preliminary stage in the transmutation of sewage has not taken place, as was formerly the case in the sewerage system of some modern towns, before arrival at the works.

But in this as in other affairs there is force in the old maxim, Medio tutissimus ibis, and a properly constructed open tank, for simple deposition of the solids (frequently washed out), arrests most of the solids and allows fresh liquid sewage, after slight anaerobic action, to pass on to land or filter bed in a perfectly inoffensive condition.

The cleanly and dirty processes for sludge removal.

As an example of this I have, at Aldershot, a pair of tanks close to a public high road, one of which fills with sludge and is emptied every fortnight or so, and as a contrast there is another pair of larger tanks in a remote quarter of the same farm in use for years as septic tanks, from which some sludge is drawn off at long intervals, anaerobic action being allowed its full course as in the Exeter experiments.

It is interesting to compare the results of these preliminary clean, and dirty, processes respectively on similar very fresh domestic sewage which enters the clean depositing, and the septic tanks alike, and my observations are as follows:—

1. The manurial result in growth of crop slightly greater with the septic liquid.

2. Labour increased by the greater deposit carried on to the land under septic liquid.

3. The removal of sludge and washing out the clean tank gives an hour’s work with very little smell ten yards to leeward of the site, but drawing off sludge from the septic tank is a very unpleasant operation, and, at all times, the vicinity of tank and carriers is malodorous for a radius of at least fifty yards from the septic tanks.

Loam on sand and gravel the best medium for aerobic organisms to work in.

Passing now to the aerobic stage of sewage purification we find it universally admitted, that a good loam resting on very porous sand or gravel, affords the best medium for work by the oxygen-loving nitrifying organisms

when they are supplied with constantly moving liquid sewage, and given intermittent periods for the aeration of the pores of the soil.

The proportion of sewage to land is of course as variable as the quality of the land itself, and the best sort of land is rarely available, while the improvement of natural land is not understood by the engineer or chemist, who are usually appealed to by sanitary authorities in their sewage difficulties.

Hence the variety of artificial substitutes of contact beds, costing from 5000l. to 12,000l. per acre, which have been proposed of late years, with the object of purifying a large volume of sewage on a small area.

Leeds experiments.

Mr. Dibdin first startled the world with the formula 1,000,000 gallons per acre, but that has long been cut down to 200,000 gallons, and the life of the contact bed has become the subject of serious concern, as shown in the annexed table of experiment at Leeds.

Others have sought to increase the proportion of sewage to area by arranging for continuous instead of intermittent application; but the difficulty of sprinkling so that every part of a bed may be kept just moist, in order that aeration may be continuous as well as the dropping sewage, is very great, and increases with every gallon and foot from the scale of a laboratory experiment to that of a practical working for a town’s sewage.

There was an article published a few years ago in the Journal Royal Agricultural Society (England) on “The Making of the Land,” showing how nearly all the value of agricultural land in England has been stored up in it by the exertions of our forefathers, through a process of successive improvements from, in many cases, worthless sand and clay, to a condition of the greatest fertility; and I often think that the 12,000l. spent at Birmingham or elsewhere on an acre of contact bed could be expended to better purpose in preparing 100 acres of the worst land to deal, for any number of years, with as much sewage as the contact bed may do for a few years. In the one case we know no limit to the life of the purifier, and that it must be a very short one in the other case.

TABLE SHOWING THE VARIATIONS IN CAPACITY OF CONTACT BEDS.

N.B.—The average duration of the above experiments was 14 months, and average loss of capacity about 70 per cent. original water capacity in that period.—A. S. J.

Wrexham sewage farm.

At Wrexham, in North Wales, I had nineteen years’ management of about 150 acres of good land, with a mixed residential and manufacturing sewage of some 15,000 population, with large breweries and leather works. The owner of this land at the termination of lease asked so exorbitant a price for the improved freehold, that the corporation decided to sacrifice the sewage works on his land, and to carry out a scheme of mine for carrying the outfall sewer two miles further to a site of 200 acres, which they could acquire on reasonable terms in the year 1889.

During my management there was no trouble about the effluent, although it was carefully watched by the authorities of the city of Chester, which takes its water supply from the river Dee, some twelve miles below my late farm; and the fact that the scheme which took the Wrexham sewage two miles nearer to the Chester waterworks intake was carried out unopposed is, I think, strong evidence of well-founded confidence in the efficiency of land treatment where the public have the opportunity of observing such results. It is easy to get up a case with expert evidence against any sewage scheme where the land-owners, clergy and others have no means of properly informing themselves, and have a prejudice against sewage which it is very difficult to overcome except by giving the utmost possible publicity to the truth.

The Camp Farm, Aldershot.

Of late years, while working for the War Department, I have found it expedient to be more reticent, but the Camp Farm restoration has in one way or another become known to the public, and there can be no great harm in my now referring to the circumstances as neither martial law nor a censorship has yet been proclaimed in Hampshire.

When Aldershot Camp was first hutted, soon after the Crimean War, a certain Colonel Ewart, R.E., had imbibed true ideas of the separate system through his association with the work of the late Mr. Menzies, the Deputy Ranger of Windsor Forest, who preached and practised that system in the drainage of Windsor Castle and the town of Eton at a time when every other civil engineer scouted the possibility of keeping rain or subsoil water out of foul sewers—they said it was essential for flushing their big sewers.

Colonel Ewart, at any rate, impressed his corps, and after about 1866 one began to see the word FOUL painted up over gratings into which the soldiers were to pour their slops. A civilian, James Blackburn, also a friend of Menzies, was employed by the War Office to deal with the camp sewage on about 100 acres of rough heather-covered land close by, and he, knowing his business, watched what came down the sewers in wet weather and kept the Royal Engineers up to the Menzies standard.

Mr. Blackburn’s successful management.

Together with this initial advantage of having a regular volume of sewage not much affected by storm water to deal with, Mr. Blackburn had many drawbacks in the “pan,” as it is usually called, of iron conglomerate underlying the very irregular surface which was pitted all over with holes from which gravel or sand had been dug many years ago; but he persevered until he had

got nearly all the area to bear good crops, when he entered the Camp Farm in competition for the Royal Agricultural Society’s 100l. prize in 1879 for the best managed sewage farm in the United Kingdom. The Report of the Judges at that competition is recorded in the Society’s Proceedings 1880, giving full statistics except financial accounts, which Mr. Blackburn withheld because he was then in treaty with the War Office for new terms after fourteen years’ work on the War Department Farm. My impression after reading the judges’ reports and having seen the farm a year or two previously to its date, is that, if the condition as to the production of the financial accounts could have been fulfilled, the first prize would have been awarded to the Camp Farm instead of jointly to those of Bedford and to Wrexham.

Mr. Blackburn had built a big wooden shed and sublet it to a man who bought his ryegrass for some fifty cows (for whose milk there was a great demand in the camp), so this subtenant made a tempting offer to the War Office and got a fourteen years’ lease of the whole farm, while Blackburn retired in disgust.

I wish to write only from knowledge of facts, and will therefore take up my narrative again in 1895, after an interval of some fifteen years.

Neglected state of, in 1895.

In the month of May 1895, I was called upon to visit the Camp Farm and report to Mr. Henry Campbell-Bannerman, the Secretary of State for War at that date.

I found the whole farm in a deplorable condition of neglected nuisance, stagnant lakes of sewage retained here and there by banks of earth, buildings and fences in decay, and the greater part of the camp sewage passing, by pipes laid by its tenant, under a road which

forms the lower boundary of War Department land, to some rough meadows held by their tenant from civilian owners for the purpose of saving him the trouble of spreading the sewage over the sloping surface of the War Department Farm—work which required the use of a land surveyor’s level and staff.

In the ditches of these flat meadows the sewage could go through the septic process to its fullest extent as the level of the river Blackwater kept them nearly full at all times, and the supernatant liquid could spread over the coarse herbage of these meadows only in winter floods, with the result of heavy crops of hay, and sewage disposal conveniently out of sight and outside War Office jurisdiction when a Royal Engineer officer might come to inspect the Camp Farm from time to time.

British Medical Journal’s report.

But before my visit an active Medical Officer of Health (Dr. Seaton), taking an interest in the state of the river bounding his county of Surrey, detected the camp origin of the stagnant sewage, and, concluding that the meadows must form part of the Camp Farm over the road, made a serious report about “Government Sewage Marshes,” which the British Medical Journal took as a text for an article, and the Thames Conservancy attacked the War Department as soon as their 1894 Act gave them jurisdiction in the matter.

Temporary abatement of nuisance.

I was told that the Camp Farm milk and grass had been condemned, and that the tenant had consequently sold his cows and was to give up the farm on June 20, 1895; therefore my report was wanted forthwith, but it was only to take account of anything which could be done temporarily to abate nuisance, as an agreement was pending with the Aldershot District Council for the removal of the camp sewage outfall to some site, at least two miles distant from the camp, at which the District

Council was to become solely responsible for its future disposal, together with their own Aldershot town sewage, and the War Department to be rated for the purpose like any other householder.

I found the Commanding Royal Engineer then in office fully alive to the existing nuisance and prepared to support any efforts I might make to abate it. Accordingly I agreed to become manager in control of such labour and material as was necessary for immediate temporary improvement, and being supplied with army horses, and any necessary buildings, tanks, etc. to be constructed by the Royal Engineers.

1897. The War Office resolve on permanent improvement.

After about two years it became understood that the nuisance could be permanently remedied on the Camp Farm, as I had said from the first, and accordingly the draft agreement, which had then been in discussion for five years, was abandoned. I was asked to prepare a scheme and estimate for such permanent works as would enable the sewage to be effectually disposed of on the Camp Farm.

Recollecting that the sewage had to be at once cut off from Dr. Seaton’s “Sewage Marsh,” and its disposal provided for throughout on War Department land, it will be observed that the improvement work had to proceed piecemeal with some extra care and arrangement; but on the whole I am satisfied that the work has been completed with greater efficiency and economy than would have been the case if the sewage had been turned into the river and the whole site handed over to a contractor for two years in the usual course.

About the same date (end of 1897) about 13 acres of land was handed over to my management with sewage from the Royal Military and Staff Colleges at Sandhurst, about 8 miles distant from the Camp Farm, and, being

somewhat better land to begin with, this part now presents a very pretty example of what a small installation for about 1000 population may accomplish.

But it is worked as part and parcel of the Camp Farm, horses being sent out to Sandhurst from Monday to Saturday when required.

It is, perhaps, worthy of note that the reform of the Camp Farm was initiated in 1895 by the Secretary of State for War in a Liberal Ministry, and that it has weathered for seven years all the storms of Jingoism and the fashionable crazes for artificial sewage treatment.

Sir Buller’s period of command at Aldershot.

But whatever may be the rights or wrongs of General Sir Redvers Buller’s quarrel with the Press and the Government, his reputation as a practical agriculturist is undeniable, and while in command at Aldershot it was his custom to stroll over the Camp Farm on a Sunday afternoon, occasionally leaving a message with cowman or bailiff to warn me of anything he found amiss, for which I was very grateful, living as I do ten miles away. I am proud, therefore, to be able to publish the following letter from one who has shown that he is not to be influenced by complaisance to superior or inferior in expressing or modifying his opinions, and he writes as follows:—​

17 Lowndes Square, S.W.
July 14, 1902.

My dear Jones,

I am delighted to hear that you are publishing a book about sewage treatment.

The sewage farms at Aldershot and the Royal Military College afford ample proof of what a sensible practical man can do. But it is not every one who knows what those farms were before you took charge of them, nor do I think that any one seeing them now could conceive their previous condition. It is to that I can testify; you have turned putrid sewage bogs into fertile fields. You will confer an immense benefit on the

country if, by your book, you can only teach sanitary authorities generally that the crux of the whole question is the necessity for practical commonsense measures against sewage stagnation, and if those measures are taken nature will do the work of purification without the assistance of expensive patents or artificial devices.

Yours very truly,
(Signed) REDVERS BULLER.

To Col. A. S. Jones, V.C., C.E.

It must not be gathered from the foregoing account that the War Office authorities are prejudiced in favour of the natural treatment of sewage, for, like many other sanitary authorities, they have been bewildered of late years by the numerous forms of “artificial” treatment in vogue, and I know of more than one experimental installation for barracks where good available land has been neglected, for I read last summer of ghastly failures among the bacterial arrangements in some of those.

Success mainly due to activity of farm bailiff, foremen and other workers.

I cannot quit the above account of the vicissitudes of the Camp Farm in fourteen years’ growth from a sandy waste to a condition which tempted a tenant to pay a rent of 3l. odd per acre in 1880—its retrogression to its primitive waste during the following fifteen years—and restoration to its present measure of fertility, without expressing the belief that Mr. Blackburn’s success and my own have been mainly due to our good fortune in obtaining the willing services of excellent intelligent foremen and workers who, one and all, have taken a real interest in their several tasks.

Mr. Cameron and other engineers may boast of their labour saving (?) automatic appliances for opening and shutting valves on sewage works, but practical workers, responsible for dealing with a million gallons a day and

upwards average, in hourly varying flow of town sewage, will agree with me in hesitation as to placing entire confidence in the substitution of automatic machines for any large proportion of their manual labour.

Education and encouragement of sewage employees advocated.

I have for many years advocated education of sewage farm managers and watermen, to be selected from the rapidly decreasing class of agricultural labourers by the tender of high wages, houses and good gardens, with other profit-sharing allowances which it will well pay sanitary authorities to hold out to their sewage employees.

In this sense I am glad to note the recent formation of “The Association of Managers of Sewage Disposal Works,” Secretary, Charles H. Ball, 5 Fetter Lane, London, E.C., as a Trades Union move from within well calculated to raise the status of the class of men upon whose exertions the community must mainly rely if there is to be any hope of improving the condition of our streams and rivers.

Evidence and Reports of Lord Iddesleigh’s Royal Commission.

Two large Blue Books containing the evidence taken by Lord Iddesleigh’s Royal Commission have been published since the Interim Report, and their contents more than warrant the opinion expressed in the latter; indeed it must surely be admitted that the case for each of the artificial systems was very fully gone into before that Commission expressed the guarded conclusion, “We doubt if any land is entirely useless.”

I do not believe that the surface purification obtained by distribution over even the densest of clay lands was effectively put in evidence, and too much weight was given to the difficulty of increasing the effective top soil on such land; but on the whole I think that the Interim Report is very satisfactory to the reasonable advocates of a preference being given to the adoption of a large area

of land, where available, over any artificial treatment on a small area, other things being equal.

At the time when the Interim Report was issued, however, a very full and careful examination of a select number of sewage farms was still in progress, and Appendix 22, with a casual mention by Dr. M’Gowan, affords the only glimpse to be had in the bulky Blue Books, of any results of that examination having been as yet adduced in evidence.

The Commission’s officers, to my knowledge, were engaged for many months in examining, surveying and taking numerous samples of sewage and effluent at the Camp Farm, and, as they doubtless had equal opportunities of independent observations on the other selected sewage farms, the further reports of Lord Iddesleigh’s Royal Commission cannot fail to be interesting and instructive.

On one point Appendix 22 to the Blue Book abundantly supports an opinion I have so often expressed, namely, that a good strong loamy surface is a more efficient purifier of sewage than many feet of barren sand.

I refer to the curves in Appendix 22, showing the greatly superior purification effected at Nottingham with the best soil as compared to that of the sandy one at Aldershot, which, in its natural character, is about the worst for purification and for producing crops to be found in England.

My experience, however, all points to the extreme importance of studying local conditions from the first inception of plans in each particular case, to their completion with the best available materials.

But when the engineer has done his best, the sanitary authorities, having borrowed the funds to pay for the work, will take no further trouble about its sewage, and

will often engage careless ignorant workpeople at inadequate wages to carry on the hourly varying labour, on efficient performance of which success depends.

Automatic appliances for sewage and effluent discharge.

It may seem idle to complain of boards and their employees showing little interest in the work of sewage disposal, but it is worse to pander to their failings by selling them automatic machines under the pretence that all the thought, and fertility of resource, required for efficient sanitary sewage disposal can be supplied by ingenious applications of hydraulics on the principle that sewage is a fluid, and, as such, will behave like clean water.

Of course, when the aerobic treatment is carried out on a bare level surface of cinders or coke growing only weeds, the lack of interest is very excusable, but in the natural system the growth of crops and contouring a sloping surface with carriers so that every part shall have its trickling water alternating with dry periods for cutting the crops or hoeing out weeds, should be a matter of constant interest to an agricultural worker, and, if he knows his business, good crops and purity of effluent must go together.

Managers should have a free hand.

In order to attain this happy result, a manager must know his business and be given a free hand, not pestered by members of a committee (farmers, butchers, gardeners or town tradesmen) coming to give their advice or orders. The river authority should take samples as often as they like and send the manager as soon as possible the analyses with day and hour of sampling as a guide for future working.

He will then have to explain any defect from average purity of effluent, due to one of the hundred contingencies which may arise in practice, after he and the river authorities have agreed about what that average

analysis should be for his particular farm or works; and it will be for the advantage of all parties not to try and enforce a fixed standard for a whole district, as some river authorities usually attempt to do, because it is easier to lead than to drive a good manager, and nothing at all can be done with a bad one.

It must not be supposed that I think river authorities should be easy going, quite the contrary, but they should trust their inspectors’ reports, and “run in” those sanitary authorities who are careless about the management of their sewage farms and trying to cut down working expenses and capital.

In precipitation or other artificial sewage works it is easy to judge this, but more difficult for any one except the good farm manager to know whether the land is being made the most of for profit or for purification; still the rivers authority ought to get to know if they and their officers take pains.

Purification and profit.

It is a common idea that working a sewage farm for profit, and for purification of the sewage, are two incompatible things, whereas, the good manager with sufficient working capital (double or more what would be enough for the same acreage in ordinary agriculture) and a good market for produce will attain the two together in due proportion in all ordinary seasons, when a fair allowance has been made him for the necessary sanitary work.

It is easy to see how the popular idea of incompatibility has arisen in a case like that above stated of the Camp Farm tenant, eating up year by year all the fertility stored up in the land during the previous period, and letting nearly all the sewage run to waste, because its scientific application would cost much in thought and labour. In much the same way district councils have been, all over the country, stinting their labour bills and

interfering with their managers’ purchases and sales in order to make as small a demand on the rates as they can—each year bringing some change of system—to the end that nobody is responsible or has any confidence in master or man.

With such a state of things up and down the country the way was prepared for preachers of microbe agency to say, why should you buy all that land when a septic tank, a few acres of coke or burnt ballast, and a patent automatic opener and shutter of valves (which you see working so nicely with tap water and model at some exhibition) will give you “no more troublesome sludge,” and a first class effluent with hardly any labour bill? if you only agitate against that arbitrary Local Government Board, which insists upon land!

But those gentlemen neglected the fact, that in a few years’ time their filters would have to be pulled to pieces, washed and put back, while the land remains as efficient as ever, and a valuable asset, in some cases saleable at building value, if it becomes desirable to move the outfall further at some future time.

Sludge treatment.

In the above comparison between natural and artificial treatment reference has been had chiefly to the aerobic branch of the business, but the anaerobic, breaking down some of the solid organic matter and the sanitary disposal of the remainder in the state of sewage sludge (containing fully 90 per cent. of moisture) must not be overlooked or shirked as beneath the attention of the scientific bacteriologists and chemists whose analyses of effluents, and often of what they call crude sewage, are made from the liquid which has passed through a filter paper in their laboratory before their “oxygen absorbed” or “ammonia processes” are proceeded with.

On the contrary, I have always maintained that

sludge, being the foulest part of town sewage, ought to receive primary and earnest attention if we desire to improve the condition of our watercourses.

When town sewage is pumped through a long rising main, it can often be spread on the land in its really crude state, and if the soil is clay ploughed up to receive it the sludge is most beneficial to its texture.

But in every other case we must face the nuisance of extracting the sludge, and its desiccation in one of the following ways.

1. On a farm at some distance from roads and houses, the cheapest plan is to form a bank of earth about 18 inches high, enclosing a rectangular area into which the wet sludge can be run or pumped out of depositing tanks, and left alone until dry enough for cartage, when it can be used on the farm or sold to neighbouring farmers for a shilling or two a load.

2. A wall of farmyard long manure may be used instead of earth, and trench 5 feet wide dug on each side of the longer sides of the rectangle, leaving 3 feet of ground between the wall and trench, on which men can stand to scoop the sludge over the wall when it has consolidated a little in the trench; the latter is then ready to receive the sludge from another tank emptying, which is again scooped over the wall on to a thin coating of farmyard manure, which has been scattered over the last layer of sludge in the rectangle; and thus in a year’s time a solid mass of the mixture is raised four or five feet high, and is in capital order for putting in drills for a crop of mangold wurtzel.

This is the plan in use at the Camp Farm; it occupies little ground and smells only like rotten dung does during the few days carting to the mangold field.

3. Pressing by compressed air forcing a liquid mixture

of sludge and lime into the interstices between cloths supported by vertical iron plates on a horizontal frame; and such pressing is a very expensive process, only resorted to when the sewage works are in a confined populated district where no accumulation of sludge can be tolerated.

Expert examination of neighbourhood a very necessary preliminary to any sewage scheme.

Before any sewage scheme is conceived a very careful survey of the neighbourhood ought to be made by a person who knows the requisites of a site for sewage disposal, especially if land irrigation is intended, because natural advantages of site both for tanks, main carriers, roads, etc., may make all the difference in the world in expense and efficiency not only in first cost of works but also in their use afterwards.

And if land is to be acquired for sewage farming it will be very desirable to include in the purchase some neighbouring high lying area, not required for sewage disposal but for growing straw crops to be used on the farm.

Cropping a Sewage Farm.

Vegetation of some kind, useful or weeds, will grow from sewage, and must be frequently removed from land or contact bed.

This is a matter of vital importance, because when sewage is intermittently applied to land of any kind or to coke beds, vegetation of some kind or other must result and must be removed in order to leave a clear course for the next dose of sewage; the cost of removal and destruction of weeds will be found very great when contact beds are tried on any working scale and would be quite prohibitive if allowed to grow on irrigated land.

Hence we must crowd out the weeds as much as possible by useful plants which will bring something towards the cost of their removal; and as that return from perishable greenstuff is dependent upon its

immediate sale or consumption on the farm, the manager must cast about for demands for his abundant supply; but as both the sunshine (in this climate) and markets are very capricious factors in the problem, he has no easy task always to make both ends meet.

Theoretically the town which yields the sewage ought to provide an abundant demand, but in practice it can rarely be depended upon, Edinburgh being the only exception, where the Craigentinny sewage meadows are rented at a very high figure by the cow-keepers of a city situated in the heart of an arable district.

Alternative destinations for vegetation thus removed. Milk (everywhere in demand) or a destructor furnace.

Fortunately, however, there is always an unlimited demand for milk, and if he has the means of keeping a herd of cows on the farm, or can arrange with a neighbouring cow-keeper to take all the grass and roots he can supply at a low rate, it is about the best course a manager can adopt.

If he maintains a herd of cows, tied up in good, well ventilated stables, and has them daily brushed and groomed like horses, they require no exercise and produce milk in perfection for an average period of fifteen months from date of purchase after their third or fourth calving.

Such a herd will consume rye-grass carted from the field from April to November, and mangolds, kohl-rabi, and rye-grass hay during the winter, thus securing a uniform demand for produce of the sewage land throughout the year, and such cows will only require a little cotton cake and oat straw bedding (of which latter they eat a good deal) to fit them for sale to the butcher as soon as they become dry.

The advantage of such a steady demand is so great when rye-grass and mangolds, etc., are indicated as the

main crops of the farm, owing to the large volume of sewage per acre, that the system of cow-keeping is forced upon managers, however reluctant their sanitary authorities may be to provide the necessary working capital, unless they can find a reliable contractor to receive at a fixed price any quantity of grass and roots the authority may grow and deliver.

Permanent pasture grazed and for hay available in certain cases.

When a town has more land in proportion to its sewage, permanent pasture may take the place of Italian rye-grass, and, with proper precautions, a part of the permanent pasture may be grazed; but the saving of labour, thus supposed to result from letting animals bite and carry their food, is expended in making up, in a necessarily imperfect manner, the carriers trodden in by the cattle.

Importance of neat tidy contour carriers, correctly levelled.

And here I would observe that most of the bad odour into which sewage farming has fallen of late years is distinctly traceable to the common absence of sufficient regularly contoured and neatly cut distribution carriers resulting from parsimony about wages bills natural to the ratepayers’ representatives in Council, and often to the manager’s dependence on a borough surveyor’s coming to the farm with his level and staff for great measures, or on his own guesses for smaller works, instead of using an instrument to peg out every distribution carrier at the right moment.

Attract good labour.

There is another important outlay of capital to be provided for in every complete sewage scheme, which should embrace sufficient good labourers’ houses and gardens in order to attract and retain on the spot the best class of workers.

Summary of the experience of a lifetime.

To sum up the general conclusions to which my experience points, and which I trust may prove useful to district councillors, they are as follows:—​

1. In works of sewerage, limit and regulate, as far as possible, the volume of sewage by excluding subsoil water and clean surface water.

2. Where the outfall sewage enters the disposal works provide a pair of open catch-pits (or grit-chambers), each twice as wide as, and 2 feet deeper than the sewer, with sluices allowing the sewage to pass through one pit at a time in its free course, while the other pit is being dried and the deposited detritus dug out. The depth below sewer invert may be more than 2 feet, and length of catch-pit is immaterial, but I confine its width to twice that of the sewer in order to conserve sufficient velocity in the current to carry forward organic matter, paper, etc., and leave only clean sand and gravel in these catch-pits.

Continuing the course by open channel (of same width as outfall sewer), it should expand to five or six times its width, forming the screening chamber, and thence discharge into the

3. Depositing tanks. These are best formed in concrete with smooth surface, with a semicircular level weir from which the liquid overflows into a semicircular collecting open carrier leading to the aerobic process on land or contact bed.

The semicircles above referred to are struck from centre of the inlet to depositing tank with a radius of 50 feet or more.

The weir level should be at least 1 inch below that of invert of inlet, and the depth of tank immediately under this point should be governed by consideration of the facility of drawing off the sludge by valve at that depth to the sludge drying beds by gravitation if possible, or pump if necessary, and

from this sludge emptying valve the smooth concrete bottom of tank slopes up to the semicircular weir above described.

The bottom and sides of such a tank should be made with the best Portland cement and finest granite chippings wrought to a smooth surface, so that the sludge may be easily swept clean away with a squeegee to its outlet valve, as it is very necessary to have the tank thoroughly washed after each emptying if my view of the clean mode of sewage disposal is to be carried out.

But with the dirty mode, on the contrary, some of the sludge only should be drawn off and the septic anaerobic action preserved continuously in the tank itself, whereas I prefer that action to have its early and less offensive course in the tank and its completion in a drying bed mixed if possible with farm-yard manure.

4. The aerobic process. The one essential point in this final process, whether in land or “contact beds,” is sufficient aeration (excess as by blowing has no result commensurate with cost of its introduction), and it can be attained by intermittence of sewage and rest, or by continuous passage of sewage through a bed of coarse medium kept always just moist in all its atoms by a rain-like dropping on the surface so carefully adjusted as to moisten all parts and not to form a water-seal in any part of the bed. Intermittence is easily arranged on any scale of working, and continuous filtration, on the contrary, is difficult even for a few thousand gallons a day.

Anticipation of a coming reaction against “fads” and overpressure in sanitation.

Since the above was written our grand old philosopher Herbert Spencer has published a volume of

“Facts and Comments”[3] containing a chapter on “Sanitation in Theory and Practice,” which points to a coming reaction against the movement begun, some fifty years ago, by the late Sir Edwin Chadwick and followed up by many enthusiastic exploiters of the popular dread of “germs,” which he associated with bad smells.

Of course the professor’s practical acquaintance with Chadwick’s hobby is, as he says, very limited, and his argument, that because sewage and manure smells are harmless in the open air of the country, they should be equally innocuous in a town, falls to the ground when brought to the test of experience, and I trust that Mr. Spencer will forgive me for pointing out that sewer-gas, drawn into a dwelling room, in town or country, through scullery waste pipe or other connection with a sewer in which the air is of lower temperature than that of the dwelling room, is really prejudicial to health whether accompanied or not by disease germs.

And although, as one of the experts to whom Chadwick appealed and whose moderate testimony was cast aside because it did not come up to the standard desired by his enthusiasm, I fully endorse Mr. Spencer’s caution with regard to the mass of Blue Book evidence on sanitation, I venture to express my regret that the dear old man has had an unfortunate experience of sewage treatment, and my surprise that so deep a reasoner should have published his judgment in this chapter without having taken the pains to extend his acquaintance with sewage treatment in other places than the single instance of Burton-on-Trent.

In thus despising an unsavoury subject Mr. Spencer is not alone, and I am sorry to have to say that general

indifference is answerable for the waste of much public health and money, because it need not be surprising if those following a despised trade are sometimes ready to take advantage of the prejudice and ignorance of their employers.

In this sense I beg to quote Professor Spencer as follows in justification of the reflection with which I began the above essay:—​

"New sanitary appliances are continually being devised, sanctioned by authority, and required by surveyors; and surveyors may have and certainly sometimes do have, personal interests in pushing the use of them; either as being shareholders in the companies they are manufactured by or as receiving percentages on the numbers sold through their recommendation.”

[2] Published by Longmans, London, 1874. Third edition published by R. Potter, Wrexham, 1885.

[3] ‘Facts and Comments,’ by Herbert Spencer. Williams and Norgate, London, 1902.

NATURAL AND ARTIFICIAL

SEWAGE TREATMENT.

By H. ALFRED ROECHLING,
M. Inst. C.E., etc.

I. INTRODUCTORY REMARKS.

At the request of Lieut.-Colonel A. S. Jones, V.C., Assoc. M. Inst. C.E., who has done yeoman service in this matter, I have great pleasure in putting down some observations on this old but ever controversial question of sewage treatment.

Colonel Jones has done more than anyone else living to establish correct views on sewage farming, and he has lately changed the Government sewage marshes at Aldershot into a veritable “Garden of Eden,” watered by the waters from Aldershot Camp, growing healthy crops, and causing not the slightest nuisance. After many struggles, even the milk from the dairy cows is now recognised as good and supplied to the military hospitals. This is an achievement of which anyone might be proud; and all those who have been over the farm during the time of the “deluge,” and can now study the order and system evolved out of chaos by Colonel Jones will testify to this! It is pleasant to record that the War Office have recognised Colonel Jones’ work for them by having appointed

him quite recently to manage all the sewage disposal works in the Aldershot district. This will involve the laying out of irrigation works in eight separate places, in some of which artificial methods of sewage purification have been tried and found wanting.

Before commencing with my task proper it may not be out of place to describe here very shortly the various stages through which the sewage question has passed during the century just closed. Such a retrospect is of general interest and may throw some further light upon our subject; it must of necessity be short, otherwise it would absorb more time and space than is at my disposal, and any shortcomings in this respect that the reader may discover, I trust he will kindly put down to this cause.

"The man in the street” seems year after year more called upon to form an important element in settling questions even of a scientific nature, and if what I am going to say should prove of some service to him my labours will be well repaid.

II. THE SEWAGE QUESTION DURING THE LAST CENTURY.

A Short Retrospect.

In dealing with the sewage question during the last century, it will be an advantage to distinguish between the theory and practice of sewage purification, as such a division of the subject will render it less complicated and will tend to avoid misconceptions.

Dealing first with the theoretical side of the question, it is very doubtful whether at the dawn of the century even a working hypothesis existed to explain the process

of sewage irrigation which was then adopted in one or two instances, notably at Edinburgh, where the town sewage was very successfully purified on the Craigentinny meadows. It is more than likely, that at this time instinct took the place of theory, and that sewage irrigation was an instinctive imitation of irrigation with river water employed for many centuries in some eastern countries.

Later on it is on record, that Cagniard de la Tour in France, about the year 1825, and Schwann in Germany, about the year 1836, expressed the view, that organised substances—micro-organisms—played some role in fermentative and putrefactive changes. Almost diametrically opposed to this were the views authoritatively laid down by the then star in the chemical horizon, Justus von Liebig, who, about the year 1845, maintained that these changes were brought about by the dead inert matter itself—by molecular movements in the same—and not by organised substances, the presence of which in fermenting or putrefying substances was purely accidental. So great was Liebig’s authority then, that many almost blindly adopted his views, and the strife that commenced around these opposing views was fought with the greatest bitterness. But the stronghold of old ideas, which were gradually but surely being supplanted by new ones, could not hold out for ever against combined attacks, however stoutly it was defended by its designer, and its final downfall came about the year 1860, when a young Frenchman, Pasteur, established beyond doubt by his ever classical researches, that fermentation and putrefaction were, in the first instance, due to living organisms and not to dead matter. Pasteur further demonstrated that living organisms were also the cause of some and probably of all zymotic diseases.

So far, so good! But unfortunately the methods of biological research employed by M. Pasteur were very cumbersome and left otherwise much to be desired, so that his discoveries could not be fully utilised and extended, until in 1882 Robert Koch of Berlin published his new methods of investigation. This was the signal of raising the floodgates of biological (bacteriological) research throughout the world with this result, that the flood waters pent up until then inundated practically other branches of scientific investigation and drowned their individual life for some time to come.

During this interval, 1860 to 1882, investigators who wished to study the organised impurities in sewage had to proceed by indirect methods. They had no means of ascertaining by direct biological experiment the number and character of the micro-organisms contained in sewage: all they could do, was to determine chemically the dangerous nature of the sewage by the amount and origin of organic matter it contained, which would probably act as food to the germs; and the greater this amount was, so it was inferred, the greater would be the number of germs it harboured and the more dangerous its character.

This was the condition of things at the time the second Rivers Pollution Commission carried out its investigations, which in many respects, and rightly too, are still considered standard investigations. It cannot be surprising, therefore, that, being without proper means of biological examination, and having to rely chiefly on chemical methods only, the Commissioners came to the conclusion that the changes brought about in sewage purification were due to mechanical and chemical agencies!

It is frequently a matter of the utmost difficulty to

ascribe, after the lapse of half-a-century, a new theory to one special author, as several investigators may have been trending the same way quite independently of each other, but may not have been equally successful in the matter of their publications becoming generally known. Theories, as a rule, do not drop out of the clouds like meteorites, they force themselves gradually upon men’s minds and are elaborated by them until ripe.

Bearing this in mind, and subject to further research, it would appear as if Alexander Müller had been the first to apply Pasteur’s general theories as to decomposition, fermentation and putrefaction to the problem of the self-purification of sewage. He made his experiments in 1869 and published them in 1873. Since that date a very large number of investigators have been at work on similar lines, and whilst it would lead too far to deal with them minutely, it ought to be stated that the results of their labour confirmed the view of living organisms playing a very important part in the decomposition of sewage. Among the many names prominent in this respect are those of Schloesing, Müntz, Hatton, Warrington, Sorby, Winogradsky, Percy Frankland, Dupré, Emich and Dibdin. That set of researches, however, which has done more than any other to consolidate the theory of bio-chemical changes taking place in the self-purification of sewage are the investigations of the Massachusetts State Board of Health, which were commenced in November 1887, and are still being continued.

Since 1895 a large number of additional experiments have been made, which will be dealt with more in detail later on, but speaking generally they have not materially increased our knowledge of the processes taking place in sewage purification.

Summarising the remarks on the theoretical aspect of this question, it may be said that, as to the agencies at work, we know now they are of a mechanical, chemical and biological nature; but as to the processes and products brought about by these agencies we know very little beyond the initial and terminal stages, as will be pointed out in some of the subsequent observations.

Directing now attention to the practical side of the question, it has already been stated that the only known sewage treatment at the commencement of last century was land irrigation. Then about the middle of the century chemistry seems to have taken the matter in hand and tried to make a lucrative business out of it. It is on record, however, that it did not succeed in this attempt, and the financial loss which this endeavour has caused is a dismal subject to investigate.

There is before my mind’s eye the case of a gallant officer of His Majesty’s land forces who, after having reached very near the summit of his career, retired and employed his time in trying to make a fortune out of sewage. So enamoured was he of the subject, that—so the story goes—he commuted his pension to have all the more ready money; but fortune did not smile on him, and his last days were spent under the lengthening shadows of the sorrow of financial difficulties, having practically lost all he possessed.

The emphatic verdict of the first Sewage Commission of 1857, the first and second Rivers Pollution Commission, and, indeed, of all other authoritative investigations, was in favour of land treatment; and it cannot, therefore, be surprising to find that the Local Government Board insisted, save in exceptional cases, that “any scheme of sewage disposal, for which money is to be borrowed with

their sanction, should provide for the application of the sewage or effluent to an adequate area of suitable land before it is discharged into a stream.” Indeed, had this body taken any different view and neglected the findings of practically all authoritative inquiries, it would have been singularly deficient in the discharge of its duties to the ratepayers of this country.

But the best of land cannot go on for ever doing its duty if by systematic neglect and ignorance the essential conditions for successful purification are year after year violated; and the great pity is that the Local Government Board, after deciding in favour of land treatment, did not systematically superintend this operation. It may not have had the power, but it is quite evident that had it done so, things would not have drifted from bad to worse, until local authorities, driven to despair by the apparent failure of land and not discerning the right cause, refused altogether to be ruled by what seemed to them a very unfair and absurd restriction.

It was at this time that Mr. Dibdin, who, on behalf of the London County Council, had been carrying out a set of valuable experiments, came forward with his application of well known theories to sewage operations on a large scale. As I pointed out at the time, Mr. Dibdin’s experiments proved beyond a doubt that the application of sewage to suitable land was right in principle and that the failures were brought about by the non-observance of the rules laid down by this gentleman—that, in fact, sewage irrigation was the only natural method of sewage purification and that all the other methods were artificial. I described land treatment as the natural self-purification of sewage and the oxidation or contact bed system as the artificial self-purification of sewage.

But the swift current of public opinion had set very strongly against sewage farms, and nothing but the contact bed treatment would do. A large number of experimental plants on this system grew up like mushrooms all over the country, and the waves of enthusiasm seemed at one time to engulf even the Local Government Board itself with its “antiquated notions,” until Parliament came to the rescue and appointed on May 7, 1898, a new Royal Commission to study the question of sewage purification.

This Commission consists of nine members,[4] i.e. six professional men and three laymen. Of the professional men, one is a biologist, one a chemist, two are medical men in administrative positions, and two are engineers likewise in administrative positions. Of the laymen two are members of special boards for the prevention of the pollution of rivers.

So far the Commissioners have issued an Interim Report dated July 12, 1901, a volume of evidence and a volume of appendices. Quite lately, it is stated, they have issued a further Interim Report, to which are attached separate reports on some special subjects by their officers, but this report has not yet come to hand.[5]

At the time of their first Interim Report, July 12, 1901, the Commissioners had held altogether thirty-five sittings, the first of which was on June 22, 1898, and the last on May 22, 1901. The period thus covered is nearly two years, and out of the thirty-five sittings thirty took place in London, and five in the provinces, viz. at Leeds, Ripon, Manchester, Accrington and Reigate.

On these occasions, all in all, fifty-eight witnesses were examined, who may be grouped as follows:

Out of this number twenty-five were officials, viz. five lawyers, six medical men, six chemists and eight engineers. Four officials were further managers of artificial sewage purification works, but not one single manager of natural purification works, i.e. a sewage farm manager, was called, the term “sewage farm manager” being used here to indicate an official whose sole duty it is to manage a sewage farm.

The entire absence of this latter class of official is so striking that it cannot be due to accident, but must be the outcome of a settled policy not to reopen questions conclusively settled by previous inquiries.

Another point that strikes the observer is that the Commission only called one zoologist and one botanist, as it is to these scientists that belongs in the first instance the question of studying the fauna and flora of sewage before the subject is taken up by other branches of natural science.

Speaking on the whole, the evidence taken by the Commissioners forms very interesting reading, and ought to be carefully studied by those who have to deal with the subject. When now and again opinions are expressed, which seem directly opposed to each other, it must be borne in mind that here, as in other things human, unanimity of opinion, though much desired, is apparently unobtainable.

To understand the conclusions fully, at which the Commissioners in their Interim Report have arrived, it ought to be pointed out that they had either to accept the recommendations in favour of land passed by all previous Royal Commissions and authoritative inquiries, or they had to show by incontestable evidence that their predecessors had made grievous mistakes, and where!

Of these two courses, the present Commissioners have adopted, no doubt for very good reasons of their own, the first, and they have started therefore, in the conclusions to which they have come, at the point where previous inquiries had left off, viz. that land treatment is a very proper method of sewage purification.

But before referring more in particular to their observations on land treatment, it will be necessary to point out that the Commissioners evidently divide all methods of sewage purification into two main classes, viz. natural and artificial methods. Into the former they only place land treatment, whilst they call all other methods artificial.

This division seems to have given a great deal of offence to all those who have expressed decided and frequently very one-sided views in favour of the “bacterial” treatment of sewage; but on closer examination it cannot be denied that the Commissioners were quite right in forming this view, as the following remarks will show.

For main divisions of all methods of sewage treatment two factors seem to be of primary importance, viz. the agencies which bring about this purification, and the way in which these agencies are employed. Now, it will not be denied that all agencies are natural ones, whether the process employed is a purely chemical one, a purely “bacterial” one, land treatment pure and simple, or a combination of these, and, at the present time no such

thing as an artificial agency is known; indeed, it is perhaps not too much to say that there cannot be such a thing as an artificial agency. Hence it is impossible to divide sewage purification methods in this respect by the agencies employed, and one is bound to fall back upon the way in which these agencies are employed. Here it is no longer open to argument whether a chemical process or the contact bed system—oxidation bed system—is artificial, or whether the land treatment is natural! For who would deny that masonry or concrete tanks and the materials contained in the same are artificial products—i.e. products formed by man—and that land is a natural product—i.e. formed by nature—and that further the soil is the natural home of bacteria. Hence it must be perfectly clear, even to a casual observer, that the line of demarcation drawn by the Commissioners between all known systems of sewage purification is a correct and legitimate one, and that all objections to such a division are based on misconceptions.

Concerning land treatment, the Commissioners observe, “We doubt if any land is entirely useless,” but further on they observe that peat and stiff clay lands are generally unsuitable for the purification of sewage. Concerning peat, nobody acquainted with the subject would probably differ from their conclusions owing to the great amount of moisture contained in this material; but as to clay soils, the Commissioners when making this statement must have known that there are several successful sewage farms on this kind of land in existence, such as the sewage farms at South Norwood, Wimbledon, Warwick and Leicester, not to mention others. In the case of Leicester, although the land is a very dense boulder clay, the Corporation of this town have just purchased the freehold of the farm for about 160,000l.

Dealing with the artificial processes from a chemical point of view, the Commissioners are of opinion that it is practicable to produce by these processes alone, either from sewage or from certain mixtures of sewage and trade refuse, effluents which might be discharged without fear of creating a nuisance, and that in consequence the Local Government Board would be justified in modifying, under proper safeguards, the present rule as regards the application of sewage to land.

The artificial processes referred to in the observations appear to be the following:—​

Closed septic tanks and contact beds.
Open septic tanks and contact beds.
Chemical treatment, subsidence[6] tanks and contact beds.
Subsidence tanks and contact beds.
Contact beds alone.
Closed septic tank followed by continuous filtration.
Open septic tank followed by continuous filtration.
Chemical treatment, subsidence tanks, and continuous filtration.
Subsidence tanks followed by continuous filtration.
Continuous filtration alone.

The Commissioners do not say what these safeguards are, in fact they state that no general rules concerning them can be laid down, and that in the case of these artificial processes it is necessary to consider every case on its own merits.

The next point dealt with is the bacteriological quality of effluents, and here the Commissioners observe: “We find that, while in the case of effluents from land of a kind suitable for the purification of sewage there are

fewer micro-organisms than in the effluents from most artificial processes, yet both classes of effluents usually contain large numbers of organisms, many of which appear to be of intestinal derivation, and some of which are of a kind liable under certain circumstances at least to give rise to disease.”

No particulars of effluents from sewage farms are given, and later on it will be shown that this conclusion of the Commissioners is not in accord with the results published up to now and available concerning the bacterial purity of effluents from land treatment.

The report concludes with some remarks on rivers pollution. The Commissioners state that it is of the utmost importance to provide the simplest possible means for adequately protecting all rivers, and they think that this subject is of such grave importance “as to demand the creation of a separate Commission or a new department of the Local Government Board, which shall be a supreme Rivers Authority, dealing with matters relating to rivers and their purification, and which, when appeal is made to them, shall have power to take action in cases where the local authorities have failed to do so.”

Summing up the observations on the practice of sewage treatment, it may be said that as a result of their extended inquiries, the present Royal Commissioners have at the end of the century re-established land in its position as the first and only natural method of sewage purification, beside which they have recognised artificial (biological) treatments as being under proper safeguards admissible for the purification of sewage.

Before concluding this portion of the observations, it is necessary to mention the valuable work done by Mr. Scott-Moncrieff and Mr. Cameron, who, contemporaneous with Mr. Dibdin, but quite independently, had

experimented with sewage and evolved their own artificial methods of sewage treatment.

These remarks must suffice for the more historic portion of the subject, viz. the progress of sewage purification during the last century, and it is time now to direct attention first to natural and afterwards to artificial sewage treatments.

[4] Two of these have since retired.

[5] This report has just been issued (August 18, 1902), and although the special reports it contains are of the greatest interest, it is not necessary to refer to it again in these observations.

[6] The expression “subsidence tanks” is intended to denote tanks which are used in such way that little or no septic action is produced.

III. THE SUBSOIL.

General remarks on subsoil and its properties.

Before dealing more in detail with the processes taking place in the pores of the subsoil of sewage farms, it may not be out of place to make here a few general observations on the mechanical structure of soil, its permeability, water capacity, retentive power, the capillary movements in the same, its temperature, the subsoil air, the movement of water in and through the same, the micro-organic life in soil, and its absorbing powers.

1. Mechanical Structure of Soil.

Size of grain and pores.

Here is of interest the size of the grains or particles composing the soil, the size of the pores and their collective capacity.

According to the character of the soil, its grains or particles will vary from very large in coarse gravel to very fine in fine sand and clay.

Variable size of pores.
Surface attraction.

The size of the pores will vary as the size of its grains from large to small, but frequently a certain kind of soil will contain a mixture of large and small pores. The finer the pores the more energetic will, as a rule, be the surface attraction of the grains composing the soil.

Pore-volume.

With particles of equal size pore-volume amounts to about 38 per cent. of the total space, and sinks down to 10 or 15 per cent. with particles of unequal size.
With equally sized particles the pore-volume is the same whether the particles are small or large.

The collective capacity of the pores or the pore-volume mainly depends on the equal or unequal sizes of the particles. When the same are of equal size the pore-volume amounts to about 38 per cent. of the total space occupied by the soil, but when this is not the case it may sink to as low as from 10 to 15 per cent. of this space. With equally sized particles the pore-volume is the same whether the individual particles are large or small. In nature it will be the exception to find all the particles of equal size, such a condition of things prevails only when careful sorting by sifting or riddling has taken place, and in the majority of cases the larger pores will be partly filled up by the smaller particles of the soil.

2. Permeability of Soil.

Permeability depends first on the size of the pores, and secondly on the pore-volume.

The permeability of a soil for the passage of air and water depends, in the first instance, on the size of the pores, and is further to some extent influenced by the pore-volume.

Effect of large and small pores.

Soil with large pores will offer but little resistance to the passage of air and water, but when the pores are small these movements will be greatly impeded.

Permeability is proportional to the fourth power of the pore-diameter.

It has been ascertained that the permeability of soils is proportional to the fourth power of the diameter of the pores, so that it decreases very rapidly with the diminishing size of the pores.

In frozen soil permeability decreases rapidly.

In subsoil with small pores all movements of air practically cease when it is half full of water, and in frozen soil the decrease of the permeability is still more marked.

3. Water Capacity of Soil.

Water capacity is equal to the pore-volume.
Air can never be wholly driven out of the pores.

The water capacity of a soil is that quantity of water which can be stored in its pores; it is therefore equal to

the pore-volume. For very accurate measurements allowance must be made for a small amount of air, which even after filling remains in the pores and cannot be dislodged, but for practical purposes this can be overlooked.

1 cubic yard of soil with particles of equal size will hold about 85 gallons of water.