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CORNELL 
 
 UNIVERSITY 
 
 LIBRARY 
 
 FROM 
 
Cornell University Library 
 TD 430.H84 
 
 Water and sewage purification. 
 
 3 1924 005 001 478 
 
Cornell University 
 Library 
 
 The original of tiiis bool< is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924005001478 
 
WATER AND SEWAGE PURIFICATION. 
 
 By Sir Alexander C. Houston, K.B.E., C.V.O., M.B., D.Sc, 
 
 Director of Water Examinations, Metropolitan Water Board, 
 
 London. 
 
 It is impossible to say for a given year how much it has borrowed from 
 the wisdom and experience of previous years, or to try to measure its 
 influence on the years that are to come. Even present-day tangible 
 discoveries may show, tcj.^the far-seeing eye, some of the honourable 
 rust of antiquity, and indeed the extent to which we borrow on the 
 past ill thought and deed is incapable of measurement. Thus it happens 
 that in trpng to sum up the knowledge gained in a particular year 
 we are always trespassing on the past and, conversely, we may be doing 
 the year in question too little credit in relation to its bearing on future 
 progress. Nevertheless, it is desirable to attempt periodically to take 
 stock of current knowledge, to endeavour to show the general trend 
 of events, and to indicate some of the directions in which future progress 
 is likely to, or should, take, place. 
 
 The year 1919 has beetFa>,culminating one in the struggle of expediency 
 over sentimentality, and in new ways of looking at things. Some of 
 the events, which during recent years have brought us to-day to this new 
 jumping-ofE ground for more rapid progress, may be briefly described. 
 
 Water. 
 
 At the very outset of the war, the pioneer work on chlorine sterilisa- 
 tion at Lincoln ^ in 1905 bore full fruit. Giving full credit to all other 
 preventive agencies at work, it may still be said that the health (thanks 
 to Horrocks and his colleagues) of our Armies in the Field all over the 
 world was considerably, if not largely, influenced by efficient chlorine 
 sterilisation processes. 
 
 In 1915 a notable event occurred — Aberdeen^ received the assent 
 
 1 Fifth Report of the Royal Commission on Sewage Disposal, Appendix IV. 
 pp. 99-166 ; also pp. 84-98 ; also 171. Dr. Reeoe's Report to the Local Govern- 
 ment Board on Lincoln epidemic (No. 226), 1906. 
 
 2 Private Legislation Procedure (Scotland) Act, 1899. Aberdeen Corporation 
 Water Provisional Order, Proceedings at Inquiry, October 21-27, 1915 (The Univer- 
 sity Press, Aberdeen). 
 
2 HEPORTS OP THE PBOGEESS OP APPLIED CHEMISTRY, 
 
 of Parliament to a scheme for purifying the River Dee for waterworks 
 purposes by (1) excess-liming, (2) short storage, and (3) rapid filtration, 
 the saving in capital cost on alternative schemes exceeding £100,000. 
 The way towards this event was paved by the discovery that caustic 
 lime present in water, in even the smallest excess, exercised a strong 
 bactericidal action.* 
 
 In 1916 the Metropolitan Water Board* decided to save coal by 
 chlorinating raw Thames River water (70-80 million gallons a day) and 
 allowing the treated water to flow by gravity down the Staines Aque- 
 duct, instead of first pumping it up into Staines Reservoirs. The 
 diSerence between the cost of pumping and the cost of chlorinating 
 is about £1000 a month. The treatment is in successful operation 
 to-day. 
 
 The New River supply* of the Metropolitan Water Board is made up 
 of a variable mixture of New River water (Upper Lea water) and pure 
 well water. During the greater part of the year, owing to the good 
 quality of the well water and the relatively satisfactory state of the 
 river water, the filtered water results are remarkably good, as judged 
 by the ordinary chemical and bacteriological standards, despite the 
 fact that the rate of filtration at the New River works is considerably in 
 excess of that practised at the other works of the Board. During winter 
 fioods, the river water deteriorates so much that the excellent quality 
 of the well water fails to " mask " the deterioration of the mixed filtered 
 water product. The storage reservoirs at Hornsey and Stoke Newing- 
 ton are far too small to afiect the position materially. In 1916 the 
 Metropolitan Water Board started investigations with the object of 
 seeing whether it might not be possible to remedy this state of afEairs 
 by chlorination. It is obvious that to increase materially the filtra- 
 tion area, or to provide adequate storage accommodation, would mean 
 an immense capital outlay in order to improve matters during these 
 transitory periods of deterioration. 
 
 The experiments have been most satisfactory in a bacteriological 
 sense, but the unfortunate fact remains that when the treatment was 
 carried out uninterruptedly for longer than about a fortnight, the water 
 acquired a decidedly objectionable taste. This was partly due to the 
 filters gradually and progressively adsorbing taste-imparting materials, 
 which eventually escaped into the filtered water, so that even when the 
 treatment was perforce stopped the taste remained for some time in 
 
 ' Metropolitan Water Board, Director of Water Exfimination's Eighth Besearch 
 Report (see also Ninth and Tenth Research Reports). 
 
 * Metropolitan Water Board, Director of Water Examination's Twelfth Besearch 
 Beport (see also Eleventh, Twelfth, and Thirteenth Annual Reports). 
 
 ' Metropolitan Water Board, Director of Water Examination's Eleventh, Twelfth, 
 and Thirteenth Annual Beports. 
 
V7ATER AND SEWAGE PtTfttFtCAtlON. 3 
 
 the water as supplied to consumers. It should pertaps be explained 
 that for technical reasons it was impossible to chlorinate the water 
 subsequent to filtration. Although a filtered water may require less 
 chlorine for sterilisation purposes than an unfiltered one, the writer's 
 experience has been that with some waters, at aU events, there is a 
 greater liability to taste troubles if the chlorine is applied subsequent 
 to the filtration process. In 1918 a system of super-chlorination and 
 de-chlorination was adopted, it having been found in the laboratory 
 that even a grossly-super-chlorinated water had no taste after de- 
 chlorination. In practice, however, the results were only moderately 
 successful with regard to absence of taste, although yielding excellent 
 results bacteriologicaUy, nevertheless it did seem as if the kind of taste 
 was considerably modified in character by this method of treatment. 
 The matter is being further investigated, and it is hoped that some 
 satisfactory solution of the difficulty may yet be found. The writer 
 has recently discovered that potassium permanganate in doses of 2-8 
 lb. per million gallons is most effective in preventing or removing the 
 taste' of chlorinated waters whether added before, simultaneously 
 with, or after the chlorine. It appears, however, to be ineffective if 
 the permanganate is added before, and the chlorine after filtration, 
 although the converse plan yields successful results, as does also their 
 joint use either before or after filtration. Sodium manganate may be 
 used successfully instead of permanganate of potassium. The matter 
 has gone beyond mere laboratory experiments. For example, 33 milhon 
 gallons per day flowing down an open channel were treated with 
 chlorine (1 in 1 mUlion). The .water a little way below the point of 
 treatment (about J hour's flow) had, after de-chlorination, a decided 
 " chemist's shop flavour " or " iodoform " taste. Next potassium 
 permanganate (8 lb. per million gallons) was added immediately below 
 the point at which the chlorine entered the water. After a suitable 
 interval it was again, after de-chlorination, tested at the same spot 
 as before, and it no longer gave any taste. The experiment was 
 repeated twice more with exactly the same satisfactory results. By this 
 " see-saw " experiment it was proved conclusively that permanganate 
 under practical out-door conditions can prevent or remove the objec- 
 tionable taste of, at all events, some chlorinated waters. With a longer 
 contact the dose of permanganate may so-metimes be reduced four 
 times. The point that the writer desires to emphasise is that 
 the New Eiver experiments constituted an attempt to tide over 
 economically periods of crisis, and it is difficult to say how 
 far such efiorts may eventually lead us. For example, speaking 
 more particularly of river-derived water supplies, there are 
 normally two periods of the year when the filtered water results 
 are apt to be relatively unsatisfactory. In summer, during very 
 hot weather, the consumption of water may be so materially 
 
4 REPORTS OF THE PBOGBBSS OF APPLIED CHEMISTRY. 
 
 increased as to lead to considerably increased rates of filtration, and 
 in the winter the water about to be filtered may be much less pure 
 than the normal, and, in addition, there are a variety of circumstances 
 which increase the difficulties — for example, the rate of filtration 
 may have to be increased during exceptionally cold weather, owing to 
 increased consumption of -water consequent upon burst pipes and taps 
 left running overnight. Further, frosty weather may lead to mechani- 
 cal interference with the filtration process, and a seasonal deficiency 
 in the water of those growths which form a skin on the surface of the 
 sand in the filter may also be a factor in influencing the results. It 
 is at times such as these that sterilisation processes seem specially 
 attractive, for the interest on the capital cost and the working costs 
 are inconsiderable, or, at all events, immeasurably small, in comparison 
 with the alternative of an increase of filtration area not really needed 
 except in periods of stress. Developments in the foregoing direction 
 seem likely to attract considerable notice in the near future. There 
 is also the point that consequent upon the war all engineering projects 
 have been greatly delayed and that a considerable time must elapse 
 before new works can be completed. Meanwhile, the consumption 
 of water may be progressively increasing, leading to increased rates of 
 filtration and to a worse water being supplied to consumers. Here 
 again chlorination as a temporary measure may be found extremely 
 useful. 
 
 In 1917 Rotherham decided on the policy of re-using the abandoned 
 and severely censured Ulley gatheri]jg ground, and, subject to the 
 approval of the Local Government Board, to supply water from this 
 source, after being rendered safe by sterilisation processes, to the 
 inhabitants of that town. 
 
 Somewhat later, Cardiff ® determined to adopt a similar course in 
 regard to a portion of their gathering ground, which had been pro- 
 visionally given up as not wholly satisfactory for waterworks purposes. 
 
 The saving involved if these two decisions could be successfully 
 carried out was of a very material kind. 
 
 In 1917 Accra was faced with a very unsatisfactory position as regards 
 its water supply. The water (swamp water, liable to pollution) deterio- 
 rated to a remarkable extent in the relatively large storage reservoirs, 
 absolutely necessary for purposes of quantity. Exhaustive experi- 
 ments were made, and it was found that by applying the " excess 
 lime " method of treatment the water was freed from excremental 
 bacteria [e.g., B. coli) and remained clear, odourless, and free from 
 
 ° C. H. Priestley, " Temporary Sources of Supply in Times of Emergeucy," 
 Water, July, 1919, p. 175. 
 
WATER AND SEWAGE PURIFICATION. 5 
 
 growths under conditions of storage. The saving on alternative puri- 
 fication works represented a large sum of money. This is the first 
 occasion on which the excess-lime method has been used for the express 
 double purpose of destroying " plankton " development and rendering 
 water safe from the epidefniological point of view. 
 
 In the present year Sheffield ' conceived a scheme for the utilisation 
 of river water as compensation water, which, despite its bold and 
 unprecedented character, received, with certain reservations, the 
 assent of Parliament. It is of interest to consider this unique proposal 
 at some length, because its influence on future procedures may be far- 
 reaching. Sheffield was obliged by Act of Parliament to pass about 
 10 million gallons daily of pure moorland water from the Dam-Flask 
 and Rivelin reservoirs down the course of the grossly polluted river 
 Don (which, of course, was not used for drinking purposes) as compen- 
 sation water. The proposal was to reserve this pure water to increase 
 the domestic supply to Sheffield and to abstract from the Don below 
 the point where the sewage effluent from the city, together with many 
 other impurities, entered the river an approximately similar amount 
 of water, to purify and soften it, and to pump the purified river water 
 back about eleven miles up-stream and pass it through the statutory 
 mill gauge in lieu of the unnecessarily pure water discharged from the 
 reservoirs for compensation purposes. The word " unnecessarily " 
 in this connection is used advisedly, for the river Don water was only 
 used for trade purposes and was so heavily polluted with ochre streams, 
 trade effluents, and waste liquors near and below the point of discharge 
 of the compensation water that to " feed " it with water of a high 
 degree of purity was a wasteful procedure. 
 
 Sheffield considered that if they purified and softened the river water 
 abstracted below Sheffield to a standard at least equal to that proposed 
 by the Royal Commission on Sewage Disposal, and softened it as well, 
 they were in no way injuring trade interests, destroying the amenities 
 of the district, or endangering health. Indeed, by utilising a pure 
 moorland water for augmenting the domestic supply of Sheffield, they 
 were greatly contributing to the prosperity and welfare of that import- 
 ant city, and conserving the water and financial resources of the country, 
 inasmuch as any alternative project for providing an equal quantity 
 of potable water would have involved the ratepayers in a capital 
 outlay of approximately 3 million pounds, compared with £350,CC0. 
 
 The proposed method of purification was by lime and soda treat- 
 ment, followed by efficient filtration. 
 
 In proof of ability to purify the water efficiently an experimental 
 plant was erected and elaborate tests made. The following table 
 shows some of the results obtained : 
 
 ' Sheffield Corporation's Bill (1919), Part II.— Waterworks. 
 
b KEPORTS OF THE PROGRESS OF APPLIED CHEMISTRY. 
 
 Analyses of Uiver Analyses of river 
 
 Don water taken at water after 
 
 proposed intake. treatment. 
 
 Parts per 100,000. Parts per 100,000. 
 
 Solids in suspension ... Nil to lO'OO Nil 
 
 Hardness 10-35 to 30-50 3-71 to 8-71 
 
 Oxygen absorbed in 4 tours . 0-32 to 2-38 0-19 to 0-80 
 
 Acidity Nil — 
 
 Total alkalinity — 5-00 to 8-25 
 
 Chlorine 2-00 to 21-60 2-00 to 21-00 
 
 It may be said that Parliament endorsed the wise proposals of 
 Sheffield on all points of principle, but imposed certain reservations 
 and modifications, as a measure of precaution, in view, no doubt, of the 
 unique and unprecedented nature of the project. 
 
 Briefly these were as follows : 
 
 1. The maximum quantity of water which may be abstracted from 
 the Eiver Don and pumped back for use as compensation water is 
 roundly 5 million gallons per day. 
 
 2. The treated water is to be discharged with at least an equal 
 quantity of reservoir water subject to an addition of 10% in the quan- 
 tity of treated water. 
 
 3. The standard of purity and the terms and conditions prescribed 
 by the Act may be varied by the Ministry of Health on the representa- 
 tion of the Corporation, the West Riding Rivers Board, the Associated 
 Millowners, or any other body or person having a substantial interest 
 in the matter, after the expiration of four years from the date when the 
 treated water is first used for Compensation purposes. 
 
 4. Prescribed standard : Solids in suspension, 2 parts per 1G0,C00 ; 
 hardness CaCOj (soap .solution), 8 parts ; oxygen absorbed from 
 N/80 potassium permanganate, in 4 hours, at 80° F., 1 part per 
 lOO.CGO, or on the average of 3 consecutive days not more than G-75 part. 
 
 The Report of the Select Committee on Local Legislation which con- 
 sidered the Sheffield Bill stated : 
 
 " The Sheffield Corporation Bill contained entirely novel proposals 
 with regard to water supply. The Corporation were allowed, after 
 full evidence being given, to substitute for compensation water, which 
 they are now under statutory obligation to discharge into certain 
 rivers, an effiuent from their sewage works purified to a standard 
 required by the Bill, and which standard is based to a considerable 
 extent on the findings of a Royal Commission of some years ago. The 
 urgent need for, and difficulty in obtaining, a further supply of water 
 for domestic purposes, combined with the special circumstances affecting 
 Sheffield, make this case suitable for testing an experiment, which, if as 
 successful as the evidence suggested, would be of incalculable advantage 
 in other cases, where suitable conditions exist for its application." 
 
 In the preparation of these notes the writer is greatly indebted to 
 the courtesy of Mr. Terry. 
 
WATER AND SEWAGE PURIFICATION. 
 
 Within the last few years a great deal of attention has been directed 
 to the suspended matters ^ (particularly the " plankton "^) in river and 
 reservoir waters, owing to their efiect in choking sand filters and some- 
 times in giving the water an ofiensive taste. At the Metropolitan Water 
 Board's Laboratories it is the practice to examine bi-weekly all the 
 samples of pre-filtration water (20-25 in number), river water, all the 
 stored waters, gravel water, etc. The methods adopted are as follows : 
 
 The " resistance to filtration " (by this is meant the degree to which 
 the suspended matters^ — -living and dead — ^in a water interfere with 
 its filtration) is tested in the following manner : A piece of linen of 
 superfine quality (96 meshes to the Unear inch) is folded four times, 
 moistened with water and tied round the end of a glass tube (J in. 
 diameter) by means of a rubber band. It might be conjectured that 
 a layer of sand would be more suitable than linen. The writer has 
 tried it, and it gives a most disappointing range of results, unlike linen, 
 when the results vary from 0"0 to over 300 according to the amount 
 of suspended matter in the water. The tube is passed through a rubber 
 bung which is fitted into a filtering flask, connected with a filter pump. 
 The other projecting end of the glass tube has a piece of rubber tubing 
 attached to it, and into this is inserted the end of a pipette containing 
 100 c.c. of the sample of water to be examined. The water passes 
 through the linen into the flask, and practically all the suspended 
 matter is retained on the inside of the hnen. The rubber bung and 
 glass tube are then detached and fitted on to the additional piece of 
 apparatus. 
 
 This is merely a convenient arrangement for supplying tap water 
 under a constant head (about 5 ft.). The water is filtered through 
 the linen, with its skin of suspended matter derived from 100 c.c. of 
 the original water, for the space of one minute, and the filtrate is then 
 measured. A water having little or no suspended matter will, in these 
 circumstances, give a filtrate of, say, 2C0-3C0 c.c.*'' A water badly 
 affected with algal growths may yield no measurable filtrate, and 
 between these two extremes all kinds of results are obtained (see 
 charts pp. 472-3). 
 
 As regards the microscopical appearances of the suspended matters, 
 the following photographic method of examination is used in order 
 to obtain qualitative and quantitative pictures of the condition of the 
 
 * On pp. 35 and 37 of " Studies in Water Supply " (Messrs. John Bale; Sons & 
 Danielsson, Ltd.) diagrams will be found fuUy illustrating the methods employed. 
 See also Metropolitan Water Board, Director of Water Examination's Twelfth 
 Research Report, and Ninth, Tenth, Eleventh, Twelfth, and Thirteenth Annua 
 Reports. 
 
 ' Photomicrographio illustrations of the various growths in water will be found 
 in "Studies in Water Supply" (Messrs. Macmillan & Co.), "Rivers as Sources 
 of Water Supply " and " Rural Water Supplies and Their Purification " (Messrs. 
 John Bale, Sons & Danielsson, Ltd.), and also in the Director of Water Examina- 
 tion's Reports to the Melropolitan Water Board. 
 
EEPORTS or THE PEOGEESS OF APPLIED CHEMISTKY. 
 
 Eesistance to Filtration 'Experiments. 
 Number of c.o. filtered per minute. 
 
 c.c. JAN. FEB. MAR. APR. MAY. JUNE. JULY. AUG. SEP OCT NOV. DEC. c.c. 
 
 ZOO 
 
 280 
 
 Z6Q„ 
 
 140 
 
 Z20 
 
 ZOO 
 
 ■1'80 
 
 19 
 
 > 
 
 
 
 
 
 .-<•' I 
 
 
 
 /\ 
 
 6-1 
 
 ■■S....A4-W 
 
 X 
 
 >r 1 
 
 Nr 
 
 
 
 I9i6-ia 
 
 \ 
 
 
 / 
 
 r 
 
 *,,' 
 
 \ 
 
 / 
 
 19 O 
 
 
 
 
 \ 
 
 ^ 
 
 / 
 
 
 
 
 1 
 
 r 
 
 
 
 
 
 
 
 \ 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 500 
 
 280 
 
 '=-.,?60 
 
 Z40 
 
 ZZO 
 
 ZOO 
 
 180 
 
 S. AND V. Walton Stoeed Water. 
 JAN. FEB. MAR. APR. MAY JUNE. JULY AUG SEP OCT NOV DEC. 
 
 West Middlesex No. 1. Resebvoie Stoeed Water. 
 
c.c. 
 300 
 
 280 
 260 
 ZW 
 ZZO 
 ZOO 
 180 
 J60 
 JfO 
 
 AV. 
 
 120 
 WO 
 80 
 60 
 40 
 20 
 
 WATER AND SEWAGE PDKLFIOATION. 9 
 
 JAN. FEB. MA R. APR. MAY JUNE. JULY AUG. SEP OCT. NOV. DEC. c.c 
 
 500 
 
 280 
 260 
 2W 
 220 
 200 
 180 
 
 160 
 
 AV. 
 
 120 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 4 
 - ■ 
 
 l^ 
 
 
 
 
 
 
 
 
 
 
 1 
 1 
 1 
 
 \ 
 
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 1 
 1 
 
 
 
 
 
 
 
 
 t 
 1 
 1 
 
 / 
 
 
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 f 
 
 / 
 
 
 
 
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 i/ 
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 If 
 
 
 
 
 ( 
 
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 18 
 
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 \ 
 
 k 
 
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 11919 
 
 
 
 N 
 
 
 
 
 
 
 
 1919 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 100 
 80 
 60 
 
 20 
 
 Raw Thames Water. 
 
 various waters : 20 c.c. of the water are placed in a glass tube and 
 centrifuged, the result being that aU matters in suspension are driven 
 to the bottom of the tube. The contents are then carefully poured 
 ofE to a little above the 0-2 c.c. top mark on the narrower portion of 
 the tube. The pipette is then used to suck out the water to exactly 
 the level of the 0-2 c.c. top mark, care being taken not to disturb the 
 sediment. This water is expelled from the pipette, which latter is then 
 used to mix thoroughly the deposit with the water remaining in the tube. 
 Between the two marks is exactly O-l c.c, and this amount, or one- 
 half of the whole of the suspended matter in 20 c.c. of water, is trans- 
 ferred with the pipette to the small cell. A trace of formalin is added 
 to prevent the movement of any motile organisms that may be pre- 
 sent, and now we have 0-1 c.c. or the suspended matter pertaining to 
 10 O.C. of water, lying in the cell ready to be photographed.^' ' The 
 slide is next centred, so that the middle of the cell hes exactly below 
 the centre of the lens. A magnification of 50 diameters is employed, 
 '• " See footnotes on page 471. 
 
10 REPORTS OP THE PROGRESS OF APPLIED CHEMISTRY. 
 
 as this, in most cases, is quite large enough for diagnostic purposes, 
 and it gives a reasonably flat and a relatively large field. Of course, 
 the whole of the 0-1 c.c. is not photographed, but it has been found 
 experimentally that about one-twentieth part appears in the picture, 
 which corresponds to the suspended matter in J c.c. of the original 
 water (see plate illustrating some of the growths found in 
 water) . 
 
 The river water usually filters badly in winter, due to the mud, silt, 
 and dirt brought down by the floods, relatively badly in spring and 
 early summer, due to growths {e.g., synedra, -pkurosigma diatoma, 
 navicuta, tabellaria, etc.), but for the remainder of the year the results 
 are usually satisfactory. 
 
 The stored reservoir water varies enormously, some reservoirs yield- 
 ing excellent water all the year round, whilst in other cases the results 
 deteriorate, due to an over-development of growths in the late winter 
 siJid early spring, and again perhaps in the summer and early autumn 
 months. The growths in the reservoir water are usually difierent from 
 those commonly present in the river water, are much more abundant 
 and of more varied character {e.g., jragilaria, asterionella, tabellaria, 
 faidorina, cyclotclla, itejihanodiscus, ceratium, glenodinium, synura, 
 'staurastrum, pediastrum, scenedesmus, eudorina, voloox, oscillaria, etc.). 
 In the absence of any over-development of these growths, stored water 
 filters much better than river water. The further study of the con- 
 ditions which foster the development of these growths is highly import- 
 ant, as they sometimes give water a most objectionable taste and 
 smell, and, apart from this, their choking efiect on filters is often a 
 serious matter. The choking effect may actually lead to a shortage 
 of available water and interfere so markedly with the normal working 
 of the filters that an impure water may be supplied to con- 
 sumers. 
 
 As regards remedial measures, copper sulphate, in doses of 1 in 1 to 
 1 in 5 millions, has been found to be most effective, especially if applied 
 at an early stage of " plankton " development ; and potassium per- 
 manganate (dose 5 lb. per million gallons) has a remarkable influence in 
 removing the objectionable taste produced by excessive development of 
 undesirable growths in water. 
 
 Despite the extension of rapid filtration plants, the advocates of the 
 slow sand filters remain, rightly or wrongly, absolutely unshaken in 
 their belief in the advantages of this well-tried method of purification. 
 The question, however, which is at present receiving considerable 
 attention is this : Is it permissible with, possibly even without, the 
 use of aluminium sulphate as a coagulant to filter at an exceedingly 
 rapid rate, to condone any falling-ofi in the chemical results, and to 
 secure the safety of the consumer by a post-fiJtration clilorination pro- 
 
I 
 
 1 
 
 1*^ io 
 
 1. fedMW^rMm x 400. 2. Pleurosigma X 50. 3. Olenodinium X 150. 
 4. .4s<en'oreeHa X 150. 5. Synedra X 50. 6. Volvox x about 25. 7. Closterium "< 50. 
 8. Dinobryon x 180. 9. Oscillaria X 250. 10. Staurastrum X 50. 11. Fragilaria x 50. 
 12. Ceradiim X 50. 13. TofieHaria x50. 14. Gydotella — ^SiepAajtodiacus group x 400. 
 
 Growths found in River and Stored Water, 
 11 
 
WATEK AND SEWAGE PURIFICATION. 13 
 
 cess ? 1" There are many things which might be urged against sucJi a 
 procedure, but it is, at all events, attractive on economical grounds, and 
 the final sterilisation process, if properly carried out, would ensure 
 epidemiological safety. 
 
 The writer has had so much occasion to deal with the question of 
 accident '^ in connection with waterworks procedure that he approaches 
 the subject with some difi&dence. Yet it is a matter of such importance, 
 and has been, and is being, so seriously neglected that the time seems 
 opportune, despite the, perhaps unduly, tolerant and non-critical 
 attitude adopted by the writer in this article, to utter a word of grave 
 warning. It is extremely difficult to define accident in the sense here 
 suggested. The epidemiologist, bacteriologist, expert in preventive 
 medicine, and men of special knowledge in these matters are so fully 
 aware of the significance of this subject that no words of explanation 
 are needed. Outside certain circles there is room for elucidation. In 
 its simplest form it is obvious that to allow the possibility of any adven- 
 titious water to enter a water supply subsequent to its purification is 
 fraught with potential danger, and danger which even the most astute 
 expert may be powerless to gauge. If filter beds, filter wells, culverts, 
 service reservoirs, etc., are not watertight, it may be impossible for 
 the trained observer to judge imderground sources of pollution in other 
 than a spirit of pure speculation. It might be surmised that, in view 
 of these difficulties, the watertight integrity of waterworks would be 
 taken for granted ; failure indeed in this respect might be regarded 
 as the senseless sacrifice, at all events in a potential sense, of all the 
 money expended on purification. History, however, does not confirm 
 this supposition, nor does experience even show that contaminations 
 of most doubtful origin are absolutely foreign to the final stage of 
 delivery of a reputedly safe water to the consumer. The fact is that 
 waterworks authorities, having purified water to a high standard, are 
 sometimes curiously oblivious to the circumstance that between their 
 piirification processes and the mouth of the consumer there may be a 
 gap of dangerous significance. 
 
 The writer knew of a case where a shed had actually been constructed 
 (it has since been demolished) over the top of a filtered water well, and 
 was used by numeroiis workmen as a shelter and storage place for their 
 tools. The only protection was that the mouth of the well was covered 
 over with loose iron plates. 
 
 " Metropolitan Water Board, Director of Water Examination's Thirteenth 
 Annual Report. 
 
 ** See p. 104, " StvAies in Water Supply " (Messrs. Macmillan & Co.) ; also 
 p. 59, " JRural Water Supplies and Their Purification " (Messrs. John Bale, Sons 
 & Panielsson, Ltd.) ; also heading " Accidental Contamination," Index to 
 Director of Water Examination's Research Reports {Metropolitan Water Board) to 
 be found at end of Eleventh Report on Research Work ; also his Second Annual 
 and succeeding Reports. 
 
14 BBPOBTS OI" THE PROGRESS OP APPLIED CHEMISTRY. 
 
 Another case' within his recollection was one in which a 12-inch irort 
 oipe, jointed in the middle, conveyed unfiltered and polluted water, 
 ised for condensing purposes, over the mouth, of a filtered water welL 
 3ne day a fracture occurred at the joint and a large volume of con- 
 taminated water was swept into the supply. 
 
 Yet another case presents itself. A consiimer used the ordinary 
 water supply at one part of an hydraulic press and a very impure high- 
 pressure water at another part. A leaky piston allowed the impure 
 BTater to displace the pure water in the supply pipes and probably in 
 :he main itself. The result was that a foul-tasting and polluted water 
 wa,& drawn from any pure water tap in the building. 
 
 There are many persons who believe that no water-borne, or milk, 
 Dr food epidemic has ever residted except as the result of an accident, 
 md these observers explain the comparatively frequent non-occurrence 
 of disease in connection with known pollutions by the absence of some 
 iccidental circumstance, which can convert a contamination of rela- 
 tively small volume into an agency of incalculable danger {i.e., a change 
 Erom non-specific to specific pollution). Concrete instances may be 
 given. A water supply may be contaminated with matters of excre- 
 mental origin, but none of the individuals contributing to the pollution 
 may be suffering from disease, or the eSects of disease. Imagine now 
 that one of these individuals is suffering from typhoid fever, or cholera, 
 or having sufEered from these maladies is in the unfortunate position 
 of being a typhoid or cholera " carrier." Such a person has unhappily 
 become a " human factory of disease," and' may contribute to any 
 pollution myriads of typhoid or cholera germs. Immediately the whole 
 aspect of aSairs is changed, and what was previously a potential danger 
 becomes at once a most dangerous menace, and in all probability the 
 genesis of a widespread epidemic. Again, let us take the case of a dairy, 
 in which the milkers are of unclean habits. No harm may result until 
 perhaps one of the milkers contracts typhoid fever and returns to work 
 as a typhoid carrier, in which event the safety of the milk consumers 
 hangs on so delicate a thread as to be practically non-existent. One 
 could give innumerable instances in support of these contentions, 
 but enough has been said to show the peril surrounding the conduct 
 of a waterworks undertaking if this question of accident is not kept 
 prominently in the foreground. 
 
 Many things have to be considered — the health of workmen, sanitary 
 conveniences on the works and their surroundings, questions of fishing, 
 position of drains, cesspools, etc., watertight character of the whole 
 system of supply (filters, culverts, filter-bed wells, service reservoirs, 
 etc.), penalties attached to nuisance, undesirability of strangers being 
 admitted to any part of the works (from source to consumer), possibili- 
 ties of contamination of the filtered water in the engine wells, " in- 
 suction " into mains owing to diminished pressure, etc., etc. 
 
WATEB AKD SEWAGE PCTRirXCATION. 15 
 
 The writer has had much experience in these matters, and he has seen 
 great fluctuations in the quality of water, as judged by ordinary stan- 
 dards, supplied to consumers, without any serious result. Why should 
 no harm necessarily result under coBditions of obvious deterioration ? 
 The answer is — because of the fortuitous absence of specific pollution. 
 Is the position then always safe, if the ordinary analytical data- are 
 favourable ? The answer unfortunately is — no, if a new factor has 
 arisen, namely, specific pollution, introduced probably by accident, 
 and it is to be feared also in too many cases by avoidable accident. 
 The contamination may be infinitely small in volume and yet almost 
 inconceivably dangerous owing to its specific taint. 
 
 The lesson to be learnt is plain and insistent. The expert, with all 
 his life-long knowledge of pollutions, specific and apparently non-specific, 
 refuses to take any risks, which are foreign to a properly conducted 
 and controlled waterworks undertaking. It remains for others to 
 accept or reject advice based on experience, and, if the latter course 
 be chosen, to accept full responsibility for so doing. 
 
 It may be said — what has all this to do with the year 1919 ? From 
 the consumer's point of view, it has everything to do with 1920 and 
 succeeding years, whether the lesson of avoiding accident is learnt 
 now and security attained as a consequence, or ignored and a policy of 
 danger persisted upon. 
 
 Before passing on to the question of sewage purification, the writer 
 feels that some mention should be made of the mechanical " drifting 
 sand " filtration plant at Toronto. Toronto is splendidly equipped 
 for carrying out important water investigations. There are not only 
 central Public Health Laboratories under the able directorship of Pro- 
 fessor Nasmith, but filtration laboratories under the capable and ex- 
 perienced direction of Mr. Norman J. Howard. A very large number 
 of samples are examined and many valuable researches carried out on 
 water purification, and one can only compare the scale of their opera- 
 tions to that of the Metropolitan Water Board, which have always 
 interpreted Section 25 of the Metropolis Water Act (1902) in the most 
 liberal and imperial spirit, as if indeed their responsibility to humanity 
 was of general and not merely of local significance. Can quite the 
 same be said of all our large water undertakings throughout the United 
 Kingdom ? It is to be feared that this cannot be said, but the fault 
 is not to be found with the Medical Officers of Health, analysts, chem- 
 ists, and bacteriologists concerned, but rather with Waterworks 
 Authorities who, too often, are content with the little rather than the 
 more, and who do not always recognise that applied science has infinite 
 possibilities, not only as regards safeguarding health, but in respect of 
 saving unnecessary expenditure, and that these matters should be- 
 looked upon in a national and not a parochial spirit. 
 
]6 REPORTS Of THE PROGRESS OF APPLIED CHEMISTRY. 
 
 It is true, however, that in very many cases the water supply is 
 so pure that numerous analyses and comprehensive investigations 
 may seem to be uncalled for, and, no doubt, this has influenced water- 
 works policy in the past. Nevertheless, a great deal can be learnt 
 from the study of even pure water, and there can be but few waterworks 
 which possess no problems awaiting solution by the trained observer. 
 
 The water supply for the city of Toronto is drawn from Lake Ontario, 
 which is apparently being polluted to a progressively increasing extent 
 (62% increase within the last five years, as judged by the B. coU test). 
 Here we have an example of what a scientifically controlled and uni- 
 formly exercised' supervision can do in the way of warning. Continuity 
 of records can alone achieve such results, and Toronto is to be con- 
 gratulated on this enlightened policy as regards the work of water 
 examination. The late Theodore Eoosevelt is said to have remarked 
 several years ago that the people of Canada and the United States 
 should be sufficiently civilised to be able to get rid of their sewage in 
 some other manner than by dumping it into their drinking water. 
 
 Two filtration systems are used — the slow sand and. " rapid drifting 
 sand " types, and in describing briefly the results obtained the writer 
 draws all his information from two interesting papers by N. J. 
 Howard.^^ 
 
 As regards the former (slow sand), excellent results were obtained 
 in 1918. The average number of bacteria (agar at 37° C.) per c.c. 
 in the raw water' was 356-3, and in the filtered water 2-2 (reduction 
 ^9-1%). The average number of excremental bacteria (rebipelagar 
 at 37° C.) per c.c. in the raw water was 26-5, and in the filtered water 
 0-25 (reduction 99%). The average indicated number of B. coli pre- 
 sent in the raw water was 11-36 per c.c, whilst the filtered water con- 
 tained 0-027 per c.c. The total percentage removal of the colon 
 bacillus in the filtered water was 99-7. 
 
 The rate of filtration for the year was 3-27 million imperial gallons 
 per acre per day. The total amount of water filtered was 11,470 million 
 imperial gallons. The water is subjected to a final chlorination process 
 before delivery to the consumers. The average daily consumption 
 per capita was 128 imperial gallons. To those not familiar with 
 €anada and the United States this figure is an amazing one. The 
 abundant sources of supply, the intensely cold climate, the comparative 
 non-control of waste, and many other factors influence the position. 
 Yet, when a water, however illimitable in bulk quantity, has to be 
 purified, it does seem at first sight that a curtailed consumption niight 
 be cheaper than increased purification works. On the other hand 
 there is the fact that the purification of water forms but a small pro- 
 portion of the total cost of a waterworks undertaking. 
 
 I'' '' Contract Record and Engineering Review'' (Toronto), 1919, Sept. 17, No. 
 38, p.' 871 ; No. 41, Oct. 8, p. 937. 
 
WATER AND SEWAGE PTJBIPICATION. 
 
 17 
 
 The meclianical " drifting sand " filtration plant deals with 60 million 
 gallons a day at a rate of 150 million gallons per acre per day (see fig. 2). 
 The purification is brought about by the use of alum (average 1 grain 
 per gallon) without previous sedimentation ; " drifting sand," which is 
 constantly being washed and automatically replaced (by patented 
 devices) ; a stationary eSective cone of sand, which is only back- 
 washed and cleaned when the loss of head becomes a material factor ; 
 and a final post-filtration chlorination process (0-2 part per million). 
 The initial loss of head in the filters is 6 ft., and in the process of opera- 
 tion this gradually increases to lift, when the filter is back-washed. The 
 life of the filters ranges between 
 one and seven days, according 
 to the physical condition of the 
 water being treated and the 
 amount of coagulant being 
 used. Is it permissible to con- 
 clude, without being supercri- 
 tical, that the advantages of 
 the " drifting automatically 
 washed and replaced sand " is, 
 after all, only relative 1 Wash- 
 ing apparently takes 20 min- 
 utes and then the filter is run 
 to waste for another 20 minutes. 
 Assuming that the washing is 
 reasonably perfect and the 
 final sterilisation process really 
 eSective, the waste of 20 min- 
 utes' flow of water seems to be 
 hardly warrantable, unless on 
 the score of added security. 
 The amount of dirty waste 
 water passing through the sand washer is stated to be 2%, whilst an 
 additional 1-2% is used for backwashing and waste purposes. This 
 is an appreciable proportion of the total supply, but when water is 
 superabundant the matter becomes of small importance. 
 
 The dose of alum was on the average only 1-027 grains per gallon, 
 but during periods of high pollution as much as 2-5 grains had to be 
 applied. 
 
 Excluding three abnormal records, the bacteriological results were 
 as follows : The average numbers of bacteria (agar at 37° C.) per c.c. 
 in the raw and filtered waters were 3C3-6 and 34-7 respectively X88-4% 
 reduction). The raw water contained 6-( 8 B. coli per 1 c.c, and the 
 filtered water C-22 per c.c. (964% reduction). The chlorinated water 
 showed an average bacterial count of 1-72 per c.c, whilst only two 
 
 Fig. 2. 
 
18 REPORTS OF THB PROGRESS OP APPLIED CHEMISTRY. 
 
 samples out of 19(0 samples examined showed the presence of B. coli 
 in 1 c.c. (99-9% reduction). 
 
 The writer cannot trace in Howard's interesting paper any precise 
 reference to B. coli tests on ICO and 10 c.c. of liquid. It would be of 
 interest to learn how far the filtration and chlorination processes 
 removed B. coli from these amounts of water, because, obviously, it 
 is one thing to get excellent results on a 1 c.c. basis and quite another 
 thing to obtain similar " findings " when dealing with larger volumes 
 of water. 
 
 A comparison of the results with those previously given would seem 
 to show that the " drifting sand " filtration system did not, generally _ 
 speaking, yield such good bacteriological results as the slow sand 
 filtration process. 
 
 An interesting practical conclusion is revealed in the paper, namely, 
 that experiments showed that the time element is apparently not of 
 vital importance in the administration of the alum, that is, that there 
 is no great, if any, advantage in allowing a long, if any, time to elapse 
 between the addition of the alum to the water and the filtration process. 
 
 Race, an observer of rare merit, had previously obtained similar 
 results at Ottawa. 
 
 It would be of interest to know Howard's opinion of the relative 
 advantages of the two processes of treatment (slow sand and rapid 
 drifting sand), and how they compare with each other when judged 
 on engineering and financial grounds ; and also how the latter compares 
 with other types of rapid filters. The writer has had ample experience 
 of the working of all the well-known rapid filters used in this country, 
 but cannot speak from personal knowledge as regards the rapid " drift- 
 ing sand " filters. 
 
 Sewage. 
 
 Progress in sewage purification has been necessarily delayed during 
 the last few years, but the most extraordinary ingenuity was shown 
 during the war in disposing of sewage and refuse matter under the 
 most adverse conditions at many of the camps. It would seem that 
 not only are our sanitary experts second to none in initiative, but 
 that those who previously had had no experience in sanitation were 
 able to adapt themselves in the most remarkable manner to meet the 
 sanitary needs of all the complex situations arising out of the war. 
 The imagination, initiative, and ingenuity displayed in sanitary matters 
 during this period should in peace time bear rich fruit, and the writer 
 believes that as a nation we shall again occupy a premier position in 
 connection with all matters pertaining to public health. 
 
 Experiments in the purification of sewage by means of activated 
 sludge continue to attract wide interest, and Mr. Haworth's highly 
 ingenious notion of obtaining aeration by stirring instead of " air 
 blowing " operations is the latest development in this line of investiga- 
 
WATEK AND SEWAGE PUBIFIOATION. 19 
 
 "tion. At the moment of writing, Sheffield is putting down a unit 
 ■capable of dealing with one million gallons a day, and the results will 
 be eagerly awaited. Mr. Haworth (to whom the writer is much in- 
 ■debted for valuable information) prefers the word " bio-aeration " 
 to " activated sludge " in describing this method of sewage treatment, 
 and it certainly is a more scientific and apt description of what really 
 takes place. 
 
 The following extract from Mr. Haworth's report to the Sewage 
 Disposal Department of the City of Sheffield for the two years ended 
 March 25, 1919, is full of interest : 
 
 " In a previous Report experiments have been described in which 
 crude sewage was being treated by means of activated sludge. These 
 experiments have been continued and developed, and two tanks on a 
 working scale have been constructed recently, which are treating 
 50,C(X) to 60,CC0 gallons of trade sewage per day. 
 
 " Early in 1916 a tank of 800 gallons capacity was fitted with a 
 paddle stirrer, and with an apparatus for inducing air mechanically. 
 -After this tank had been in use for some time it was found that by 
 suitably regulating the revolutions of the paddle, purification could be 
 obtained satisfactorily to the extent of at least three fillings of the 
 tank per day, without the use of the aerator. The tank has been 
 operated during the last two years in this manner. The following 
 table indicates the character of the results obtained : 
 
 " Analysis of Samples from Experimental Aeration Plant, Sheffield 
 
 Sewage Works. 
 
 From November 27, 1918, to January 31, 1919. Number of 
 
 Samples, 45. Eesults in parts per ICO.CCO. 
 
 Effluent. 
 
 Best. Worst. Aver. Best. 
 
 ■Suspended solids . . 11-6 69-8 34-20 _ _ _ 
 
 ■Oxygen absorbed in 4 hrs. 3-32 13-38 7-10 0-15 0-60 0-32 
 
 Free and saline ammonia 1-224 6-41 3-34 0-039 2-275 0-424 
 
 Albuminoid ammonia . 0-304 1-74 0-751 0-022 0-129 0-05 
 
 •ehlorine 6-7 16-8 9-8 6-4 16-0 9-29 
 
 Nitric nitrogen ... — — — 1-55 0-16 0-75 
 
 Dissolved oxygen taken in 
 
 5 days at 65° F. . . — — — 0-013 0-389 0-153 
 
 " The results of this and other experiments led to the conclusion that 
 given suitable agitation, to obtain thorough intermixing of the acti- 
 vated sludge with the sewage, and to prevent settlement, the necessary 
 air requixed to maintain the biological activity might be obtained by 
 ■surface aerd,tion. To accomplish this it was found necessary to produce 
 -constant change of surface of the liquid. 
 
 " The question also suggested itself, and is worthy of investigation, 
 whether in the case of systems where air is blown through the sewage. 
 
20 BEP0BT3 OF THE PROGRESS OP APPLIED CHEMISTRY. 
 
 the aeration is not largely brought about by solution at the surface, 
 by reason of the large disturbance and change of surface exposed by 
 the rising bubbles, rather than by solution of oxygen from the bubbles 
 themselves. It was evident that, except in the case of small tanks, 
 the horizontal paddle type of agitator would not be quite suitable, 
 and two tanks of a different type have recently been designed and 
 put into operation. 
 
 " The tanks are 30 ft. by 14 ft. by 4 ft. deep, with level floors. Divi- 
 sion walls have been constructed to form a continuous channel, approxi- 
 mately 3 ft. 3 in. wide, along which the sewage can circulate and return 
 to an agitator placed at one end of the tank. The agitator consists of 
 two vertical pistons of the Root's blower type. On rotating the, 
 agitators, the sewage is circulated at a velocity sufficient to prevent 
 settlement of the sludge. A velocity of 1^ ft. to 2 ft. per second haa 
 been found ample to accomplish this result. The mechanical aerator 
 was fixed in one of the tanks, in case additional air was required, but 
 it has been found unnecessary. By means of the agitators and the 
 special construction of the tanks constant change of surface occurs^ 
 One tank was put into regular use in October, 1918. Humus, washed 
 from material taken from a contact bed, was put in to a depth of about 
 6 in., and the tank filled with sewage. 
 
 " After ten days' agitation the sludge was completely coagulated 
 and flocculent, and found to be sufficiently activated to allow the- 
 experiment to proceed. The tank was then worked on the fiU-and-draw 
 principle, and has purified sewage satisfactorily and continuously 
 during the last three months, three fillings of the tank per day being 
 dealt with. The liquid treated is an industrial sewage, containing at 
 times a large proportion of iron liquors, soaps, etc. These at times have- 
 required extended periods of treatment. 
 
 " The following table indicates the character of the sewage dealt with 
 and the results obtained : 
 
 Analysis of Samfles from Experimental Aeration Plant, Tiniley Sewage 
 
 Work;, Tank No. 1. 
 From November '29, 1918, to January 31, 1919. Number of 
 Samples, 62. Results, in parts per 1C0,CC0. 
 
 Sewage. Effluent. 
 
 Best. 
 
 Suspended solids 
 Oxygen absorbed in 4 hrs. 
 Free and saline ammonia 
 Albuminoid ammonia . 
 Chlorine ... 
 Nitric nitrogen . 
 Dissolved oxygen taken 
 in 5 days at 65° F. . — — -- 0-017 0-912 0-277' 
 
 * Agitators stopped for two periods. 
 
 Best. Worst. 
 
 9-8 119-6 
 
 Aver. 
 
 44-7 
 
 Best. 
 
 Worst. 
 
 Aver. 
 
 1-88 17-26 
 
 5-84 
 
 0-26 
 
 1-45* 
 
 0-76 
 
 1-208 5-632 
 
 2-525 
 
 0-110 
 
 3-024 
 
 1-249 
 
 0-364 3-560 
 
 M31 
 
 0-062 
 
 0-277 
 
 0-13 
 
 4-1 14-7 
 
 8-5 
 
 5-8 
 
 12-1 
 
 8-6 
 
 — — 
 
 — 
 
 1-15 
 
 0-03 
 
 0-325 
 
WATER AND SEWAGE PtTBlPlOATlON. 21 
 
 " The power absorbed by the process described is calculated at 20 
 horse-power per million gallons, but there appears no doubt that 
 the agitators employed could operate a much larger tank with only a 
 slight additional power consumption. There is no doubt that a variety 
 of types of agitator might be devised to operate such a process, probably 
 with greater efficiency. Several types are at present under considera- 
 tion. The Committee have already authorised the extension of the 
 experiments to deal with the whole of the flow of their Tinsley works 
 as soon as suitable plant can be obtained." 
 
 The great practical and scientific importance of W. D. Adeney's re- 
 searches on the rate of solution of gases by water is attracting the 
 attention of all those interested in the purification of water and sewage. 
 His latest contribution (jointly with H. G. Becker) on the subject will 
 be found in Vol. XV. (N.S.), No. 44 (Sept. 1919), of the Scientific Pro- 
 ceedings of the Royal Dublin Society. In their " Statement of Results " 
 the authors say : 
 
 " From the figures given in the previous section it is possible to 
 calculate the rate of solution of the gases dealt with, for any conditions 
 of area exposed, depth or degree of saturation, provided that the water 
 is kept uniformly mixed. 
 
 " The expression can be put either in the form 
 
 dw , 
 
 Tr-=a — ow 
 dt 
 
 which gives the rate of solution at any instant, or in the form w— 
 (Wg — Wi) (1 — e"'*), which gives the amount dissolved at the end of any 
 given time when »„= saturation value and Wi= amount of gas in solu- 
 tion initially. For 3)ractical purposes it is most convenient to work in 
 percentages of saturation ; hence the latter equation becomes w= 
 (100 — Wi) (1 — e"*'), and since 
 
 'V 
 
 by substitution 
 
 m;=(100-m;0 (l-e-'P) 
 
 as the general equation for any given temperature, and since / varies 
 with temperature according to the equations 
 
 Oxygen /=0-0096 (T - 237) 
 Nitrogen /=0-0103 (T - 240) 
 Air /=0-0099 (T - 239) 
 
 the corresponding general equation for each gas by substituting these 
 expressions in the formulae is obtained, thus : 
 
22 BBPOBTS OF THE tBOGfeESS OF APPLIED CHEMISTB*. 
 
 For oxygen w=(100 -Wj) ri-e-ooossiT-a^"?*! 
 For nitrogen m)=(100 ~Wj) i _ g-ooio3(T-240)^( I 
 
 For air «)=(100— Wi) ^ _ g-o'0099(T— 239)^1 
 
 " As an example of the use of these formulse, consider the question of 
 the dissolved oxygen in 1000 c.o. of water, area exposed being 100 
 sq. cms., temperature 2"5°C., and initial gas content:=40% of satura- 
 tion. How much gas will be dissolved in an hour ? 
 i = 60 minutes, 
 w = 60(1 -e-o-o^'s') = 60(1 - e-o'222) = 60(1 - 0-8C09)= 60 X 0-1991 
 
 =11-8% of saturation. 
 
 " Hence after an hour the water will have risen to 51-8% of satu- 
 ration. 
 
 " These equations can also be used to calculate curves showing the 
 rate of solution in water of the different gases under different con- 
 ditions, and as an example the curves for oxygen between 0° C. and 30° 
 C. have been calculated in percentages of saturation. It is note- 
 worthy that when expressed in percentages of saturation the curves 
 for the three gases lie very close to each other, those for oxygen and 
 nitrogen being practically identical." 
 
 Some years have passed since the Royal Commission on Sewage 
 Disposal ^* issued their final report, but it is really only now that the 
 full force and significance of their recommendations are beginning to 
 be adequately recognised, and the writer ventures to prophesy, on 
 evidence much more valuable than his own experience, that the year 
 1919 marks •the dawn of a growing appreciation of the great practical 
 value of the Commission's labours. 
 
 The war, of course, has been partly responsible for this transitory 
 period of relative stagnation of thought and action, but also it takes 
 time to assimilate new ideas, especially when the questions dealt with 
 cover a wide field of observation, are treated in an imaginative as well 
 as a courageous and novel spirit, and embrace circumstances concerning 
 which little was known, or if known, was open to controversial inter- 
 pretation. 
 
 Much has been written about the Commission's work, but the writer 
 agrees with those who think that the novel as well as the common-sense 
 and logical basis of all their investigations and conclusions has been 
 the keynote of their successful deliberations and is bound to attract 
 
 '' Eeferenoe may be made to Mr. Kershaw's " Chiide to the Report of the Royal 
 Commission on Sewage Disposal " (Messrs. P. S. King & Son, Ltd.). 
 
WATER AND SEWAGE PURIFICATION. 23 
 
 to a progressively increasing extent the favourable comment of all 
 Students of true progress. 
 
 After laboriously investigating the bacteriological qualities of all 
 liquors and effluents from sewage purification processes, and coming 
 to the conclusion that the methods of treatment failed to free these 
 liquids from undesirable excremental bacteria, the Commissioners did 
 not either advocate bacteriological standards, or suggest the necessity 
 for sterilisation. On the contrary, they proceeded to take the bold 
 line of judging effluents on a physical, chemical, and biological (ex- 
 clusive of bacteria) basis. In doing so, they pointed out to waterworks 
 authorities abstracting water for domestic use from polluted rivers 
 the measure of their responsibilities,, and warned them that even if the 
 danger from these liquids could be economically (a large assumption) 
 removed, there would still remain the countless unavoidable contamina- 
 tions which affect rivers flowing through, and draining, inhabited 
 areas, which, in practice, can only be dealt with by.purifying adequately 
 the water after abstraction. In this connection it must always be 
 remembered that even assuming the practicability of sterilising the dry- 
 weather flow of sewage, it would be quite impracticable to deal with the 
 whole volume of liquid which reaches a sewage works or escapes ante- 
 cedently by overflows into rivers during periods of very wet weather. 
 
 As regards their suggested chemical standard (general standard for 
 non-drinking water streams), this was based chiefly on two factors : 
 (1) the desirability of preventing the accumulation of solid putrescible 
 matter in the bed of rivers (not more than 3 parts of suspended matter 
 in 100,000 parts of effluent is suggested), and (2) the importance of 
 judging organic matter (in solution and in suspension) on the rational 
 basis of its " decomposition value " (hence the standard of not more 
 than 2 parts of dissolved oxygen used up in 5 days at 65° F. in the 
 " whole " liquid, i-e., including the sediment, is suggested). This is 
 not a standard of the amount of organic matter in an effluent, but of 
 that proportion of the total organic matter which alone really counts 
 in its polluting effect on rivers. Without in the least criticising the 
 value of other and perhaps simpler tests, the writer thinks the estima- 
 tion of the amount of oxygen used up by an effluent is the truest crite- 
 rion, scientifically and practically, of its behaviour when discharged into 
 a stream. In framing their general and special standards the Com- 
 missioners took the opportune course of studying the quality of river 
 waters and the effect as regards silting, growths, de-aeration, nuisance, 
 etc., on river waters of the discharge into them of effluents of variable 
 quality and volume. Far from being satisfied with mere laboratory 
 " findings " they subjected them to the crucial test of field observation. 
 In this way they arrived at the important criterion figure of 04 part 
 of dissolved oxygen taken up in 5 days as, generally speaking, the non- 
 nuisance limit in the case of rivers. Rivers infringing this standard 
 
24 REPORTS OF THE PBOGBBSS OP APPLIED OHBMISTEY. 
 
 were liable to become de-aerated, to show accumulations of black mal- 
 odorous mud and to encourage the development of unsightly grey 
 fungoid growths. On the other hand, rivers which did not exceed the 
 criterion figure were, on the whole, sweet, clean, and satisfactory in 
 the above respects. It should be noted that the general standard 
 (conveniently referred to as the 3/2 standard), which has been proved 
 to be attainable in practice, would not clash with this criterion figure 
 of 04, provided that the dilution of the efiiuent with river water was 
 at least 8 times and the river water fer se did not absorb more than 0-2 
 part of dissolved oxygen in 5 days, both of which circumstances had 
 been shown by the Commissioners to be true in practice in the great 
 majority of instances. The foregoing by no means exhausts the fair 
 and common-sense (if the writer may say so with great respect) attitude 
 adopted by the Commission, for they recognised that no single figure, 
 no matter how carefuUy chosen, could possibly be suitable in exceptional 
 circumstances. Thejr recognised that in a few cases the 3/2 standard 
 might not be sufficiently drastic, and in the others (the larger number) 
 quite unnecessarily severe in view of the local conditions. In the latter 
 cases they suggested special relaxed standards, based on the suspended 
 solids only, which may be designated as follows : 
 
 General Standard. — 3/2. Not less than 8 dilutions. 
 
 Special Standards.— 6/0 ; 150—300 dilutions. 15/0; 300—500 
 dilutions. 0/0 ; over 500 dilutions. 
 
 The suggested machinery for giving efEect to these recommendations 
 was a Central Authority controlling, co-operating with, and advising 
 Local Authorities. 
 
 Only one aspect of the Commission's work has been dealt with here, 
 but enough perhaps has been said to show that we shall at once be in a 
 position to make rapid progress in the purification of rivers without 
 imposing unnecessary hardships on sewage authorities, irrimediately 
 legislative efEect is given to the recommendations of the Eoyal Com- 
 mission in regard to standards. 
 
 The writer calls attention in conclusion to the excellent Bibliographia 
 contained in the Supplemental Circular of the British Waterworks 
 Association. It aims at and succeeds in drawing attention to profes- 
 sional and technical papers and articles dealing with water supply and 
 cognate subjects. In the last Quarterly Circular (No. 26, Nov. 1919) of 
 the British Waterworks Association, the Secretary, Mr. Warner Terry, 
 gives under the heading " National Control of Water Sources " a most 
 valuable Digest of References to and Reports and Recommendations 
 of Royal Commissions, Special Committees of Parliament, Proceedings 
 of learned Societies and professional Institutions, and the opinions 
 of experts, on the subject of the National Control of Water Sources, the 
 establishment of Watershed Conservancy Authorities under a central 
 Government Authority, etc. 
 
 Printed in Great Britain by Butler & Fanner, Frame and London 
 
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