sSS MMnup^j City of *X 5~r^ YORK ^QXK sr Sewerage and Sewage Disposal, York. . . . Paper read at a Meeting . . . of the — Incorporated Association of Municipal and County Engineers, . . . held at The Guildhall, on the . . 14th of May, ^ 1904 . % ^ 4 . CJREER, A..M.I.C.E., City Engineer and Surveyor. %0M L Jb7 H Paper read at the District Meeting of the Incorporated Association of Municipal and County Engineers , held at York , May 14, 1904. . ( l-t D R l\ f | — 1 r i vi i i (Tv ('l Br| v li C:t f ; ( SEWERAGE AND SEWAGE DISPOSAL, YORK. By ALFRED CREEK, Assoc. M. Inst. C.E., City Engineer and Surveyor. I The first meeting of the Association held in this city was in February 1882, under the presidency of Mr. Lewis Angell ; when papers were read by the late Mr. George Styan, City Surveyor of York, on “ York and its Public Works,” and by Mr. Escott, until recently Borough Engineer of Halifax, on “ Dwellings for the Labouring Classes in our Large Towns.*’ ^ A second meeting was held in June 1888, when Mr. Mawbey, Borough Surveyor, Leicester, read a paper on “ Municipal Work in York.” The principal public work carried out by the Corporation, since the 1888 meeting, is the sewerage of the city and the dis- posal of the sewage, and it is this subject it is now proposed to refer to. Sewage disposal is the most interesting, and certainly one of the most absorbing problems that we, as municipal engineers, have to consider. It is being studied with care and attention by a number of earnest workers, through whose labours our knowledge on this subject is fast increasing. It is this general interest that promises so well for the future, and leads the writer to think that the time is very near when this difficult and com- plex problem, that has already cost this country many millions of money, may be solved on scientific principles, and when the designing and working of a sewage disposal works may present none of those uncertainties, both in results and in the approval A 95777 2 SEWERAGE AND SEWAGE DISPOSAL, YORK. of the Local Government Board, that now trouble the souls of the great majority of municipalities and their officials. Yarious standards of purification, or rather of impurity, have been sanctioned provisionally by rivers boards and county councils, and tacitly acquiesced in by the Local Government Board. In this district it has been fixed at one grain of oxygen absorbed per gallon, and one-tenth of a grain of albuminoid am- monia per gallon. These varying standards have obviously been fixed by the various rivers boards and county councils to suit the different conditions that obtain in their respective districts. In the Author’s opinion no standard can be a fair and equit- able one, if fixed arbitrarily, and without any reference to local conditions, and to the proportion the volume of effluent bears to the volume of the stream or river into which the effluent dis- charges. It is obviously unfair to fix upon the same standard for an effluent discharging into a river with a minimum flow of fifty volumes of effluent, as for an effluent which forms in itself, the bulk of the volume of the stream into which it is discharged. In the latter case a non-putrescible effluent should be insisted upon, but surely in the former some latitude should be allowed ; if it is allowable to run crude sewage into a tidal river it should surely be allowable to discharge an effluent purified to a limited extent into a river of a greater volume than many a tidal river. What the results of the labour of the Royal Commission on sewage disposal may be it is difficult to forecast. We must possess our souls in patience and hope that it may be a rational solution of the problem, moderate and reasonable in its require- ments, and with a certain amount of elasticity in its working that will commend it to the majority of municipalities. Many towns have during the past twenty years spent vast sums of money on works for the chemical precipitation of sewage, and its attendant evils of sludge pressing and disposal of cake ; they are now in the position of having to begin practically over again and incur additional debt before the loans for the first ex- penditure are liquidated. This is a matter of very serious moment, and one that should be verv seriously considered by SEWERAGE AND SEWAGE DISPOSAL, YORK. 3 the Local Government Board when laying down hard and fast lines for municipalities to follow. The Author has in mind a certain place in Yorkshire where the sewage purification problem has been shelved from time to time by the authority ; they are now in much the same position as they were thirty years ago ; they have incurred little or no expenditure on works, and are now in that happy position of knowing that their policy of letting things slide has resulted in the saving of large sums of money ; while those municipalities, who have honestly tried to deal with the problem regardless of cost, are in the unfortunate position of seeing their works practically con- demned, and, looming in the future, further large expenditure on works that may turn out to be as futile and unsatisfactory as those they had but a few years before carried out under pressure. It is this uncertainty that the Boyal Commission should end. Works carried out with the approval of the Local Government Board, on lines laid down by them, should, if carried out, suffice at least for a period sufficient to enable the authority to pay off the debt incurred in their construction. Statistics. — Year. — Population ...... 1892 67,807 Ditto 1902 79,114 Rateable value 1891 237 , 835Z. Ditto ....... 1901 394,763Z. Death rate per 1000 living 1892 20*9 Average death rate for ten years 1892 to 1901 188 Death rate per 1000 living 1902 15*8 Deaths from zymotic diseases for ten years 1892 to 1901 2-48 Ditto ....... 1902 1*25 4 SEWERAGE AND SEWAGE DISPOSAL, YORK. Sewerage Works and Sewage Disposal. It is proposed to give some particulars as to the cost of the York sewerage works with the cost of pumping, precipita- tion and pressing, and also the results of experimental works carried out during the past five years. The sewerage scheme was designed and carried out by James Mansergh, F.R.S., Past-President of the Institution of Civil Engineers. Mr. James McKie, M. Inst. C.E., acted as Resident Engineer for the construction of the work. The contractors: Sewers and river crossings, Mr. A. Kellett of Ealing; pumping station superstructure, ditto; pumping station foundations, Messrs. Parker and Sharp ; rising main and tanks and buildings, at disposal works, ditto ; pumping ma- chinery, Messrs. Boulton and Watt; pressing machinery Messrs. Goddard, Massey and Warner. The works were commenced in 1890, and with the exception of the house connections were completed in 1894. The actual, cost of the scheme was as under : — £ Construction of main, intercepting and a few subsidiary sewers, including several syphon river crossings . 122,251 Pumping Station 18,830 Pumping machinery ...... 8,938 Rising main and precipitation works, including cottages 28 , 882 Precipitation machinery .*.... 4,555 Land purchase, easements, compensation for damages and engineer’s commission 24,395 Total . . . £207,851 The system for which the works were designed was milk of lime treatment followed by a solution of aluminoferric. The sewage is naturally alkaline. The pumping station, situate on the left bank of the river at the southern boundary of the city, contains : — Two overhead vertical cylinder triple expansion engines, each working three single acting ram pumps. Each engine is capable of lifting and delivering 4,320,000 gallons of sewage per day through the 27-inch rising main to the tanks at Naburn about two miles below the pumping station. Two centrifugal pumps 4 feet diameter, direct driven by two SEWERAGE AND SEWAGE DISPOSAL, YORK. 5 vertical engines. Each pump is capable of lifting and dis- charging into the river 10,000 gallons per minute. There are three Lancashire boilers, each 22 feet long by 6 feet 6 inches diameter, fitted with Vicar’s mechanical stokers. Dynamo for lighting. A workshop for small repairs, screening chamber, etc., etc. The total average quantity lifted per annum (over seven years) has been 1,730,000,000 gallons, viz. 1,239,000,000 gallons a maximum lift of 33 feet increased by friction to about 47 feet, and 491,000,000 gallons a lift of about 16 feet ; in the latter case the pumps not infrequently discharge against a head of water in the river. The average daily flow at the pumping station over this period is 4,739,000 gallons ; the average cost of lifting the 1,730,000,000 gallons has been 20s. 1*30^. per million gallons. The details for 1901, when the figures approximate most nearly to the average, are as under : — Wages s. < 6 d. 5-34 Coal . . 8 10*35 Oil and waste . 1 7-85 General repairs . . 0 11-95 Water . 0 2-21 Rates, taxes and insurance . . 1 0-44 Sundries . , 1 5-98 Total cost per million gallons * 20 8*12 The annual cost of precipitation and pressing during the same period has averaged 2Z. 4s. 11 d. per million gallons treated at the works. Taking the year 1901-2 as being the nearest to the average, the following are the details for that year : — Quantity treated . . . 1 , 324 , 000 , 000 gallons. Precipitation . Wages — Engineers and stokers Alum mixing Cleaning tanks . Materials — Aluminoferric Sundries Cost per million gallons. s. d. s. d . i. d. 0 5*89 1 3*90 1 0 17 2 9*96 15 0*71 0 042 15 113 Total for precipitation . 17 1109 6 SEWERAGE AND SEWAGE DISPOSAL, YORK. Pressing. Cost per million gallon*. Wages — s. d. t. d . Engineers and stokers . 2 1*54 Lime mixing 1 5*83 Pressing .... 4 8*08 Maintenance, cleaning down, etc 0 11*72 9 3*17 Materials — Coal . . . r 4 9*03 Oil and Waste 0 4*18 Lime 6 2*86 Press cloths 1 11*95 Maintenance of plant and machinery 0 3*66 13 7*68 Total for pressing 22 10*85 General. Including rates and taxes and maintenance of buildings 5 1*27 Total cost per million gallons exclusive of interest and sinking fund . . . 45 11*21 From February to December 1896, the sewage was chemi- cally treated with lime and aluminoferric, the quantity used varying with the quantity of sewage delivered at the works, and to some extent with its strength ; the average was about five grains per gallon of lime, and of five grains per gallon of aluminoferric. During this period eleven analyses of the sewage and effluent were made, the average results were as under : — — Oxygen absorbed three hours at 80°. Albuminoid Ammonia. Parts per 100,000. Sewage 4*92 0*469 Effluent 1*58 0*111 On these figures the purification works out at 67’ 8 per cent, for oxygen, and 76 per cent, albuminoid ammonia. The strongest sewage analysed in this period was by oxygen absorbed 9*71, and the weakest 1*74. The strongest by albu- minoid ammonia 1*406, and the weakest 0*380. As the sewage was naturally alkaline, and complaints were made as to the action of lime on the fish in the river, its use as a precipitant was discontinued for a certain period, and the sewage treated with aluminoferric only, the average quantity SEWERAGE AND SEWAGE DISPOSAL, YORK. 7 used being 6 grains per gallon. From December 1896 to December 1897, twelve analyses were made of the sewage and effluent, the average results were as follows : — — Oxygen absorbed three hours. Albuminoid Ammonia. Parts per 100,000. Sewage 7*95 1-212 Effluent 2' 36 0-266 On these figures the purification works out at 70 per cent, oxygen absorbed, and 78 per cent, albuminoid ammonia. The strongest sewage analysed during this period was by oxygen absorbed 12*06, and the weakest 3*51 ; the strongest by albuminoid ammonia 1*406, and the weakest 0 * 540. The reason why the sewage was so much stronger in the second period was that, during the intervening time, old sewers in the city were being connected to the intercepting sewers, and as these had been waterlogged from the time of their construc- tion, and at the time of connecting up were lying full of foul matter, it was not surprising to find this marked increase in the foulness of the sewage. An examination of these results shows the fallacy of adopt- ing a percentage of purification for comparison, here we have an increase of 4*3 in the percentage of purification, while the result shows the effluent to be 33 per cent, worse according to the oxygen absorbed, and 55 per cent, worse according to the albuminoid ammonia. A curious feature in the case was that during the whole of these two periods, samples of the river water were taken and analysed at the same time as the sewage, one from half-a-mile above the outlet from the disposal works, and one from half-a- mile below. The results showed an average of 0*258 oxygen absorbed in the twenty-three samples above the outlet, and an average of 0*270 oxygen absorbed below the works. On ten occasions the river below the outlet was better than that above, and on the remaining thirteen occasions worse. The greatest difference in impurity was found in the river water above the outlet, although on the average it was less, thus demonstrating as clearly as analyses can that the flow of sewage effluent into this river 8 SEWERAGE AND SEWAGE DISPOSAL, YORK. (rarely flowing at a less rate than 150,000,000 gallons a day) was not perceptible half-a-mile below the outlet. In consequence of a number of dead fish being found in the river strong complaints were made by the fishery board, and the West Eiding Eivers Board ; they attributed the destruction of fish to the effluent from the works, notwithstanding that the same epidemic in fish life was to be found in other rivers tributary to the Ouse, where no chemically treated sewage effluent was dis- charged ; dead fish have frequently been noticed in the river, especially in a very dry summer. The Author presumes there are epidemics in fish life as in animal and bird life. However, the Corporation have never shown any desire to shirk their responsibilities, and with the view of ascertaining if they could in any way improve the effluent, empowered the writer to experiment in bacteriological and other methods of sewage purification. Accordingly, a series of experiments were put in hand in April 1899, and the results reported fully to the Corporation in October 1901. As this report was reprinted in the technical papers circulating amongst the members, it is proposed only to give a brief summary of the results obtained up to that date so as to furnish continuity in this paper. Experiment No. 1. COVERED SEPTIC TANK AND SINGLE CONTACT. Tank 40,000 gallons capacity. Four filters each 40 feet by 20 feet by 3 feet deep. Cycles 8 hours. Medium, clinker | inch to lj inch. First Period of Working, April 24, 1899, to October 28, 1900. Average of 7 Analyses. Grains per Gallon. — Oxygen Absorbed. Albuminoid Ammonia. iCalcium Nitrate. Gallons per Square Yard per 24 Hours. Gallons per Acre per 24 Hours. Sewage . . 2*430 0-377 Nil .. .. Effluent . . 0-805 0*190 Nil 42-89 207,580 Percentage of 1 purification / 66-80 49-60 •• •• - » & SEWERAGE AND SEWAGE DISPOSAL, YORK. 9 Second Period, December 10, 1900, to August 1, 1901. Average of 7 Analyses. Grains per gallon. — Oxygen Absorbed. Albuminoid Ammonia. Calcium Nitrate. Gallons per Square Yard per 24 Hours. Gallons per Acre per 24 Hours. Sewage Effluent . Percentage of I purification / 3*007 1*075 64* 15 0*501 0*128 74*35 Nil Slight tra- ces on two occasions 121*54 588,225 This experiment was continued until 1902, but no better results were obtained, and considerable trouble arose in conse- quence of the sludging up of the filter surface. Experiment No. 2. CRUDE SEWAGE AND DOUBLE CONTACT BEDS. No. 1 bed 90 feet by 30 feet by 2 feet 9 inches. Medium, clinker 1^ inch to 3 inch. No. 2 bed 90 feet by 30 feet by 2 feet 9 inches. Medium, clinker § inch to f inch. Cycle 8 hours principally. August 1, 1899, to October 13, 1900. Average of 9 Analyses. Grains per gallon. ■ Oxygen Absorbed. Albuminoid Ammouia. Calcium Nitrate. Gallons per Square Yard per 24 Hours. Gallons per Acre per 24 Hours. Sewage 2*341 0*450 Nil , , Effluent . 0*362 0*101 0*59 31*57 152,815 Percentage of I purification j 80 72 •• •• •• 10 SEWERAGE AND SEWAGE DISPOSAL, YORK. Experiment No. 3. LADDER-FILTER — CRUDE SEWAGE AND MULTIPLE CONTACT. Filter 10 compartments, each 4 feet by 3 feet 5 inches by 2 feet deep. Medium, clinker | inch to f inch. The 10 chambers were arranged in steps each 6 inches below that above, the sewage passed down through the material in the first chamber, up through the second, and so on. June 8, 1899, to September 15, 1900. Average of 3 Analyses . Grains per gallon. — Oxygen Absorbed. Albuminoid Ammonia. Calcium Nitrate. Gallons per Acre per 24 Hours. Gallons per Square Yard per 24 Hours. Sewage 2-365 0-347 Nil .. .. Effluent . 1-320 0-220 Nil 72-47 350,737 Percentage of I purification / 44-2 36-6 •• •• •• Experiment No. 4. OPEN SEPTIC TANK AND CONTINUOUS FILTRATION. This filter (No. 1) is circular, 67 feet 6 inches in diameter, the floor of Portland cement concrete with radial grooves on the surface 1£ inch deep and 1J inch wide, beginning about 3 feet from the centre and terminating at the outer edge, where they are about 6 inches apart. From the centre to the circumference the floor has a fall of about 6 inches. Around the floor and forming part of the same construction is a shallow channel 2 feet 6 inches wide to receive the filtrate as it leaves the filter. On the concrete floor, about 6 inches from the channel, a 9-inch brick wall is carried up, built in pigeon-hole work 8 feet 9 inches in height. The space inside this wall is filled up with clinker and cinder to a depth of 6£ feet. It would have SEWERAGE AND SEWAGE DISPOSAL, YORK. 11 been desirable to use only a clean hard material not likely to fall or become disintegrated by exposure to the atmosphere, or con- tinuous saturation, but as this class of material could not be obtained at a reasonable figure such material as was easily obtainable had to be used. Part of the clinker was of fairly good quality, but a large proportion of it was insufficiently burnt, and easily disintegrated with moisture. As the clinker was put in and levelled, perforated unglazed pipes 4 inches and 6 inches diameter were laid radially at three different levels at intervals of 2 feet in height from the floor ; in all 24 lengths of these air ducts were laid, allowing a free access of air to all parts of the filter, to these in a large measure the Author attributes the successful results obtained. They have been invaluable in facilitating the regular observation of tempera- tures in the filter. 8-inch cast-iron pipes are laid from the end of the open septic tank down to and under the floor of the filter, then carried up vertically above the surface level of the filtering material. On the top of the last pipe the distributor is fixed, and as the tank effluent enters this, it is spread or distributed equally over the whole area of the filter in the form of small jets. It trickles down through the filter, emerging at the floor level as a clear and bright liquid, totally devoid of smell and purified to a greater degree than in any of the other experiments. July 5, 1900, to August 19, 1901. Average of 40 Analyses. Grains per gallon. — Oxygen Absorbed. Albuminoid Ammonia, Calcium Nitrate, Gallons per Square Yard per 24 Hours. Gallons per Acre per 24 Hours. Sewage 3 024 0-511 Nil .. .. Effluent . 0-468 0-049 8-09 440 2,129,600 Percentage of 1 84-5 90-0 purification / The worst results obtained during this period were : — Oxygen absorbed ...... 0 896 Albuminoid ammonia, . . . . . 0 090 Calcium nitrate . . . . . . . 104 A 4 12 SEWERAGE AND SEWAGE DISPOSAL, YORK. The best result obtained was : — Oxygen absorbed . Albuminoid ammonia Calcium nitrate . . 4 0-114 0 021 20-51 Experiment No. 5. OPEN SEPTIC TANK EFFLUENT AND DOUBLE CONTACT. Tank 160 feet by 40 feet by 6 feet 6 inches (part of flow used for this experiment). November, 1900, to April 25, 1901. Average of 16 Analyses, Grains per gallon. — Oxygen Absorbed. Albuminoid Ammonia. Calcium Nitrate. Gallons per Square Yard per 24 Hours. Gallons per Acre per 24 Hours. Sewage 3 031 0-551 Nil .. .. Effluent . 0-647 0-068 1-97 37 04 179,298 Percentage of 1 purification / 78-6 87-6 V •• •• This disposes of the results obtained up to the end of August 1901. It is not surprising under the circumstances that it was decided to discontinue experiments Nos. 1, 2, 3 and 5, while experiment No. 4 was continued on the same lines ; on March 12, 1902, the filter was stopped to allow of the construc- tion of a grit chamber at the entrance to the open septic tank. Continuing the record of results given under No. 4 (see above) the following are the figures up to the stopping of the filter on March 12, 1902. Up to this date the crude sewage had, after rough screening, been run into the open septic tank and no attempt made to inter- cept grit ; it was therefore decided to wall off part of the tank 10 feet 6 inches by 39 feet 6 inches by 7 feet at the inlet end, so as to form a chamber for the deposition of grit and other SEWERAGE AND SEWAGE DISPOSAL, YORK. 13 Date of Analyses. Gallons per Square Yard per 24 hours. Sewage. Effluent. Calcium N itrate. Oxygen. Albuminoid. Ammonia. Oxygen Abso bed. Albuminoid. Ammonia. 1901 Sept. 10 . 390 3*23 0*65 0*40 0*05 7-93 „ 18 . 390 3*43 1*20 0*43 0*09 8*19 „ 26 . 475 2*45 0*41 0*47 003 9*84 Oct. 1 . 475 5*78 0*32 0*31 004 8*20 » 8 . 475 5-49 0*33 0*34 0*05 8*20 „ 23 . 475 1*82 0*65 0*32 0*08 8*61 Not. 6 . 475 3-01 0*52 0-36 008 2*46 „ 27 . 475 3*90 0*45 0*35 0*08 3*69 Dec. 11 . 475 2*38 0*58 0*20 0*06 6*97 27 . 475 2*82 0*50 0*28 006 5*33 1902 Jan. 8 . 475 .. .. 0*65 0*07 3*85 » 13 . 475 5*95 043 062 005 8*20 Mar. 6 . 475 2-05 0-42 0*43 0*06 •• Average 3*53 0*54 0*32 0*06 6*79 heavy substances. This, and other works hereafter referred to, occupied until May 7, 1902, when the working of the continuous filter was resumed. Up to this date (March 7, 1902) the tank and filter had passed 105,000,000 gallons of sewage, equal to 464 gallons per square yard per twenty-four hours over the actual days working, or 426 gallons per yard per day over the whole period. This quantity represents over thirty days’ normal flow from the en- tire city. In the interval between stopping the filter on March 12, for the formation of a grit chamber and the restarting on May 7 (fifty-six days), the sewage in the tank was drawn off, when the sludge was found to average a depth of 20 inches over the whole tank, or about 390 cubic yards, representing 1 cubic yard to about 270,000 gallons of sewage, whereas with chemical precipi- tation the sludge would have been about 3570 cubic yards, or 1 cubic yard to say 30,000 gallons. The sludge was cleared out and the grit chamber wall constructed. 14 SEWERAGE AND SEWAGE DISPOSAL, YORK. During the same period one-half of the circular filter was opened into, the material was found to be quite clean, the gela- tinous substance that under working conditions surrounds each piece of clinker had disappeared leaving a thin covering of grit adhering to the surfaces of the material ; the only smell observ- able was that of newly-turned earth. The opening into the material was continued over the whole of the eastern half of the filter, down to the concrete floor, and the material turned over. With the exception of the bottom 9 inches, the whole of the material in that half of the filter disturbed was similar to that already described ; the bottom 9 inches resting on the floor was found to be composed of fine gritty ashes, the result of the dis- integration of the filtering medium ; this was cleared away and the half of the floor exposed, covered with old pan tiles placed on old bricks laid radially between the grooves in the floor. All the old filtering material with the exception of the very fine was then replaced and sufficient new clinker added to make up the deficiency. The old bricks and pan tiles left a space of about 4 inches between the concrete floor and the underside of the pan tiles, forming so many open ducts for the access of air to the bottom of the filter, in addition to the perforated pipes laid in the body of the filter. On May 7, 1902, the filter was restarted, the westerly half remaining undisturbed as put in April and May 1900. Up to the 20th of the month about 288 gallons per square yard per day were passed through the filter ; from the 20th to the 29th, 315 gallons; and from the 29th to June 14, 341 gallons, the effluent being bright and clear. The suspended matter from the east side had the appearance of white ash and was sufficiently heavy to lie in the channel surrounding the filter ; the suspended matter from the west or undisturbed side was more flocculent. That from the east side of the filter averaged 2*26 grains per gallon of suspended matter, while that from the west side averaged 4*62 grains, this was from July to November 1902. At the close of this period, the analyses of the two approximated so closely that further separate analyses were not considered necessary. From the restarting of the filter to November 4, samples for analysis were taken from each side of the filter, and the results are given in detail for the purpose of comparison. SEWERAGE AND SEWAGE DISPOSAL, YORK. 15 The quantities passed through the filter varied from 288 gallons to 515 gallons per square yard per twenty-four hours as per the following table, together with the results in grains per gallon. Date. Gallons per Square Sewage. East, or Disturbed Side. West, or Undisturbed Side. Yard per 24 Hours. Oxygen. Albu- minoid. Oxygen. Albu- minoid. Oxygen. Albu- minoid. 1902. May 28. 288 6*22 0-35 0*47 June 11. 515 4*48 0-50 0*39 004 0*34 003 July 1. 515 1*86 0*63 042 0-06 0*40 0*05 » 8. 515 2*17 0*42 0-47 0-04 0*32 0*03 Aug. 5 . 515 365 0*81 0-47 0-04 043 0*06 » 12. 515 6-50 0*55 0*41 0*06 0*34 0*06 „ 26. 515 2-84 0-56 0*49 0-06 0*52 0*05 Sept. 23. 515 2*54 0*52 0*45 0-06 0-53 0-07 Oct. 9. 515 7*92 0-39 0-33 0*07 0-26 0*07 „ 21. 490 4*07 0*66 0*51 014 0*44 0*11 Nov. 4 . 450 3-71 0-03 0*51 0-07 0*51 006 Average • 468 4-09 054 0-45 0*06 037 0-05 Percentage of purifica-j tion / •• •• 89 89 91 91 Up to this date both sewage and effluent had been allowed to settle before analysing. The reason why this course was adopted was that Dr. Smith, the medical officer for the City and and analyst to the Sewerage Committee, considered it the fairest course to adopt ; he is of opinion that the mineral matter in the liquid takes up a certain portion of permanganate, and conse- quently shows on analysis an excessive absorption of oxygen, not due to organic matter in the sewage. An additional reason was that on enquiry from ten analysts it was found that five analysed after shaking up the effluent, so as to obtain part of the solid impurities, and five analysed after settlement of the solids. To be on the right side therefore, it was decided from this date to shake up all samples at the time of analysis. The further results from this filter between November 4, 16 SEWERAGE AND SEWAGE DISPOSAL, YORK. 1902, and the end of March 1904, show pretty much the same results as those already referred to. The Author does not wish to overburden the paper with figures ; he therefore gives the average of the (30) analyses made during this period. November 18, 1902, to March 22, 1904. Average of 30 Analyses. Grains per gallon. — Oxygen Absorbed. Albuminoid Ammonia Calcium Nitrate. Gallons per Square Yard per 24 Hours. Sewage 540 117 .. .. Effluent 0-57 Oil 9*48 380 From June 1903, the samples were tested after incubation for five days at 80 degrees, and in all cases the effluent was found to be non-putreseible. This filter has, up to the end of March, been at work for three years and nine months ; it was built on economical lines, the walls of common local bricks and the filtering medium of a very poor description ; it has nevertheless done excellent work during this period in having passed 209,808,000 gallons of sewage and along with the septic tank effected such a purification that on leaving the filter it contains only half the impurity allowed by the West Eiding Rivers Board, and is absolutely non-putrescible. From May 7 to August 1, 1902, 2 feet 6 inches of sediment had accumulated in the grit chamber, there was, at the latter date an entire absence of scum both on the grit chamber, and on the open septic tank, the average depth of sludge in the bottom of the open septic tank was 3 inches. The grit was cleaned out for the first time on September 4, at this date a 2-inch scum covered the surface of both the grit chamber and the open septic tank. (See Diagram No. 2, show- ing depth of sludge after one and two years respectively.) The depth of sludge was 4 feet 10 inches, and occupied about 2000 cubic feet of the chamber. As 21^ million gallons of sewage had passed through, this would be equal to 1 cubic yard to 290,000 gallons of sewage ; of course it will be under- stood that this sludge was not all mineral matter. Dr. E. Smith, analyst to the Sewerage Committee, says, “ The organic, volatile SEWERAGE AND SEWAGE DISPOSAL, YORK. 17 and combustible matters (including numerous bits of wood and woody fibre, hair, stalks, etc.) amounted to 45 per cent, of the dry residue, leaving 55 per cent, non-volatile, non-combustible, mineral matter. I made rough tests for nitrogen and phosphates ; there was a large amount of organic nitrogen, the residue was also rich in phosphates, so that the residue would make a very good manure, although the large amount of woody fibre would probably prove inconvenient in a manure.” From observation since made, the writer has come to the con- clusion that, under the circumstances that obtain in this experi- ment, the chamber should be cleaned out once in every two or three weeks. The very satisfactory results obtained from the open septic tank and continuous filter induced the Sewerage Committee to construct a second continuous filter on somewhat similar lines, endeavouring in the new work to ascertain what kind of filtering media would give the best results ; accordingly the adjoining precipitation tank No. 5, 160 feet by 40 feet by 7 feet, was con- verted into an additional open septic tank, and a new filter 100 feet internal diameter constructed. This work necessitated some little interruption in the work of No. 1 tank and filter, but with the exception of about two days, the old plant was kept at work during the alterations. With the additional tank, a total capacity of 478,650 gallons is provided for septicising the sewage. The cubic capacity of the open septic tank provision is 2836 cubic yards. The filter contents : Cnbic yards. No. 1 . . . . 900 No. 2 . . . . 2182 Total . . 3082 or 0 * 9 of tank capacity to 1 of filter contents. At present we have an excess of tank capacity, but this will be remedied when a third filter is constructed. The second tank is not used separately as distinct from No. 1. The crude sewage flows in at the top level of the grit chamber, over a weir wall, into and through No. 1 open septic tank, over a second weir, into and through No. 2 open septic tank, and from thence to the filters. In no case does the sewage flow through submerged openings. 18 SEWERAGE AND SEWAGE DISPOSAL, YORK. From the outlet end of No. 2 tank the tank effluent flows into two channels, one for each filter, and in so doing passes over two notch gauges, these are proportionate to the area of the filters, so that under ordinary conditions each filter receives the proportion due to its area. Valves are provided for increasing or reducing the quantity passing to each filter when required for experimental purposes. The average depth of sludge in tanks at various dates is shown on Diagram No. 3. The new filter (No. 2) is of somewhat different construction from No. 1. The floor falls from the outside rim to the centre, the object of this is to retain as far as possible any disintegrated material that may fall to the bottom, and the suspended matter in the filtrate. This can be removed when a sufficient quantity has accumulated, by means of pipes communicating with a trench in the land adjoining the filter. The floor is formed of 8 inches of concrete with old railway rails embedded in it ; on the floor are built 4^-inch pigeon-hole dwarf walls radiating from the centre, varying from 6 inches to 15 inches apart, and carried to a uniform height of 7 inches above the level of the floor at its circumference ; expanded metal is laid on these walls over the whole area, and on this the filter- ing material is placed ; this method of construction gives a clear space of 7 inches between the filtering material and the filtrate lying on the concave floor. The filter is surrounded by a channel which collects the filtrate and conducts it to the outlet on the outer rim of the floor, a 9-inch pigeon-hole wall of blue Staffordshire bricks is built in cement, and carried up to a height of 7 feet 6 inches above the expanded metal floor. This filter is filled with four different classes of material, viz. : clinker, hard broken bricks, honeycomb slag, and gas coke. These were filled in separately and form four distinct vertical sections in the filter, the cubic contents of each section of the filter is as follows : 1492 cubic yards clinker, 312 cubic yards hard broken bricks, 189 cubic yards honeycomb slab, and 189 cubic yards gas coke. This arrangement was adopted with the view of ascertaining the value of each material as a filtering medium, both as to its suitability as a habitat for nitrifying bacteria and also as to its lasting properties. It is perhaps rather early yet to state definitely which SEWERAGE AND SEWAGE DISPOSAL, YORK. 19 material will ultimately prove most efficient in these respects, but for the general information the Author appends the results obtained up to date. This filter (No. 2) was started on April 29, 1903, and up to February 23, had passed on the average 362 gallons per square yard per twenty-four hours, or 1,752,000 gallons per acre per day. With this quantity the following results were obtained. Analyses of effluents from No. 2 filter showing results from different filtering media. Average of five analyses in grains per gallon. — Sewage. Broken Bricks. Honeycomb Slag. Coke. Clinker. Oxygen absorbed 4 j hours at 80° . \ 5-80 0*697 88 p.c. 0*668 88-5 p.c. 0-497 91*6 p.c. 0*481 91-7 p.c. Albuminoid am-f monia . . . \ 1-18 0*122 89 *6 p.c. 0-103 90-4 p.c. 0-078 93*4 p.c. 0*084 92-8 p.c. Calcium nitrate Nil 7*53 7*69 9-43 9*00 In comparing the results obtained, it should be borne in mind that this is a comparatively new filter, that had only been working for a few months. In addition to the samples taken from the various filtering media other samples of the combined flow from all four materials were taken on eight occasions between September 15, 1903, and March 22, 1904 ; the following is the average in grains per gallon : — Oxygen Absorbed. Albuminoid Ammonia. Calcium Nitrate. Sewage . . 5*74 1*24 .. Effluent 0*54 0*096 7-945 The average flow per square yard per twenty-four hours during this period has been 398 gallons. Another point of considerable importance is the durability of the various materials under the conditions that obtain in the filter. This is not a subject on which it is possible to get very reliable information over a short period, i.e. November 20, 1903, to March 30, 1904. The Author has however, ascertained that 20 SEWERAGE AND SEWAGE DISPOSAL, YORK. fine grit has come away from the different sections in the following proportions : Without going into details, it can only be said at present that during the period the filter (No. 2) was under observation for this purpose, i.e. from November 1903 to March 1904, there does not appear to have been any degradation of the filtering materials, or if there has been, the filter has retained the result of the breaking down of the material ; on the other hand, of the total quantity of mineral matter carried on to the filter by the tank effluent, certain portions have been retained : the broken bricks retained 61 per cent., the slag 61 per cent., the coke 47 per cent., and the clinker 62 per cent. There are a great many points in connection with the bacterial system of sewage purification on which it is desirable that we should have definite and reliable information, so that in design- ing a scheme the different parts should be so proportioned that the best results may be obtained at the least possible outlay. It has occurred to the writer and doubtless to most of those present that the most efficient length for a septic tank is a factor that it would be desirable to have definitely settled ; there are, however so many conditions to consider that it is only by contributions to a common stock of knowledge that we can hope to arrive at a safe conclusion. As a small contribution on the subject the following infor- mation may be useful. Two tanks, each 164 feet long by 40 feet wide have been used as open septic tanks, the flow from the first passing through the second ; the velocity of the flow for some days before and after the observations to be referred to was 0*28 feet per minute, or 16f feet per hour, and the quantity passing, 628,000 gallons per twenty-four hours. Samples of the flow were taken at the inlet (raw sewage) and at various distances between the inlet and the outlet, whence it passed to the continuous filters. The results are given in the tcble on page 21. _ It would appear with a sewage of the composition given, with a velocity of 0*28 feet per minute, that no adequate progress in purification was effected after flowing through the tank for a distance of 225 feet ; the items of oxygen absorbed and albu- minoid ammonia remaining stationary during the further flow of 100 feet. It will be observed that there was a continued reduc- SEWERAGE AND SEWAGE DISPOSAL, YQRK. 21 Analysis of Septic Tank Contents taken on March 15 , 1904 . Grains per gallon . Distance from Sewage Inlet. Free Ammonia. Albuminoid Ammonia. Oxygen Absorbed. Total Suspended Solids. Mineral Suspended Solids. Organic Suspended Solids. feet. 0 2 555 0-665 3160 34-3 8-4 25-9 18 1-435 0-595 2-673 30-1 8-4 21 *7 72 1-400 0-560 2-43 28-0 7-7 20-3 102 1-085 0-420 2-43 25-9 70 18-9 132 1-260 0-420 2-31 22-4 6-3 161 195 1-575 0-385 1-944 21-0 4-9 161 225 1-575 0-315 1-6 20-3 4-9 15-4 255 1-260 0-315 1-6 17*5 4-9 12-6 308 M 90 0-315 1-6 14-7 3-85 10-85 326 1-190 0-315 1-6 14-35 3-85 10-5 tion in the free ammonia and solids, both mineral and organic, but this reduction would not be sufficient to warrant the con- struction of a longer tank. (See Table above.) It is evident that this tank does something more than liquefy the organic solids, as the sewage on this occasion was purified during its progress through the tank to the extent of about 50 per cent, both in oxygen absorbed and albuminoid, and it is evident that this improvement is not confined to the later period of its flow through the tank. As the percentage of purification is greatest in the first 18 feet of flow, gradually diminishing as it proceeds until it reaches a point when a further flow of 100 feet fails to effect any further improvement in the sewage, the in- ference is that both anaerobic and aerobic bacteria are working throughout the whole effective length of the tank, and that when a certain stage of purification has been reached a different pro- cess is required to carry on the work. The difference in the extent and rapidity of the purifying process is very marked when passing through the filter. In the last 100 feet of flow through the tank the sewage has evidently remained in a comparatively stable condition ; no purification took place, whereas in the fifteen minutes taken to pass through a depth of 6 feet 9 inches of filter, the purification increased to 72 per 22 SEWERAGE AND SEWAGE DISPOSAL, YORK. cent., bringing up the total purification by tank and filter to 86 per cent. The strength of the sewage on this occasion was very much below what usually obtained. The average strength of the sewage during the past six months has been 6*44 grains per gallon oxygen absorbed. The action on the suspended solids is very interesting ; of the total quantity entering the tank with the sewage 75 per cent, was organic and 25 per cent, mineral. On leaving the tank the suspended solids had been reduced to 58 per cent., and this was composed of 73 per cent, of organic suspended matter, and 27 per cent, mineral, this approximates very closely to the proportions in the raw sewage. (See Table, p. 21.) Similar observations taken over ten hours on October 6, 1903, when the sewage showed 9 • 73 grains per gallon oxygen absorbed, tend generally to confirm the results above described so far as the purification is concerned. The velocity was 0*105 feet per minute, or 6 * 3 feet per hour, and the quantity passing through, 238,000 gallons per 24 hours. As in the former case, there was no reduction in oxygen absorbed during the last 100 feet of flow. With this velocity 92 per cent, of total suspended solids were deposited in the first 18 feet, i.e. in the grit chamber, while in the former case with a velocity of 0*28 feet per minute only 58 per cent, of the suspended solids were so deposited. The suspended solids in the sewage on this occasion comprised 52 per cent, organic and 48 per cent, mineral. The total solids were reduced during the flow through the tank to 8 per cent., and this was composed of 75 per cent, organic and 25 per cent, mineral, so that notwithstanding that the sewage in the latter case contained nearly three times the quantity of suspended solids and a velocity through the tank of only 6 * 3 feet per hour, as against 16| feet in the former case. The proportionate results on leaving the filter were practically identical. Temperatures. A large number of observations have been taken of the temperature of the sewage, filter bed, filtrate and atmosphere during the past three years. Shortly the results are as follows : SEWERAGE AND SEWAGE DISPOSAL, YORK. 23 In the winter the sewage averaged 8 degrees above the atmosphere, the filtrate 3 degrees below the sewage. The filter itself averaged from 2 degrees below the sewage to 1 degree above, the lower temperature being in that part of the filter nearest to the outside wall. Aeration. There can be little doubt that this form of filter wholly above ground lends itself admirably to thorough aeration. Observations have been taken at the openings in the pigeon-hole wall at the termination of the perforated pipes by means of an anemometer ; the results show that notwithstanding the numerous openings for the admission of air into the filter the velocity on the windward side varied from 350 to 1050 feet per minute, while on the lee side it varied from 550 to 1240 feet per minute from the filter, sufficient to satisfy the most voracious microbe. Fish Life. There is on the table a photo of a fifty minutes’ catch of roach and dace at the outlet from the continuous filters, the few fishermen who try their luck at this place rarely have reason to complain of a poor catch. Explanation of Diagrams. No. 1 Diagram represents the quantities in grains per gallon of oxygen absorbed in four hours at 80° F. by sewage and No. 1 filter effluent between July 1900 and March 1904, also the number of gallons put on to the filter per square yard per twenty-four hours during the same period. The sewage is shown by a full line, the effluent by a dotted line, and the volume per square yard by a dot and dash line. The figures on the left hand side of the diagram represent grains in their reference to the sewage and effluent, and hun- dreds of gallons in their reference to the quantities put on to the filter. No. 2 Diagram show6 the depth of sludge in the open septic tank after one year's use by a dotted line, and the depth of sludge alter two years' use, when an additional tank had been added, 24 SEWERAGE AND SEWAGE DISPOSAL, YORK. by a full line. The horizontal lines represent depths in inches, and the vertical lines length in feet from the sewage inlet. No. 3 Diagram represents by vertical lines the average depth of sludge in inches over the whole area of the tanks at the dates given at bottom of diagram. The tanks have been in use from May 7, 1902. The diagram, it will be seen, commences on January 21, 1903, so that the 7 inches shown on the latter date represents the accumulated deposit of sludge over the whole area between those two dates. DISCUSSION. Mr. J. T. Eayrs : I quite agree with the Author of the paper when he says you cannot fix any arbitrary standard for sewage effluent. It is a point which some people, and some county councils insist on, but it is very obvious that it is quite a fallacy to insist upon a certain percentage of purification when one does not know the strength and quality of the sewage one is dealing with. In smaller towns the sewage may not be one-fifth of the strength of the sewage in larger places having trades waste to deal with, and when you speak of 90 per cent, of purification, the effluent may really be worse than the crude sewage of a smaller town. That shows the fallacy of taking a percentage of purification as the basis. I am very glad Mr. Creer has referred to the question of fish caught at the sewage outfall, because I think it was on my suggestion when here some time ago that the practice was adopted of having the fish weighed when taken. I was very much struck when at the works by seeing anglers fishing nowhere along the river but at the sewage outfall. I then suggested to Mr. Creer that he should keep a record of the names of the fishermen and the quantities of fish taken, because the information might be useful in any ulterior proceedings by the County Council or the River Board. These records come in very handy when required. I would suggest if the diagrams shown on the walls are published in our Proceedings, that a few more explanatory notes will add to their value. The quality of the river water above the intake appears to be practically the same as the quality at the sewage outfall, where the effluent is discharged into it, and after the river has passed through the entire city. That indicates to me two things : DISCUSSION. 25 one that there is very little if any pollution going on as the river passes through the city— a great deal, if not all the sewage has been diverted from the river and turned into the sewers — and the second point shows that the effluent, although not quite so good as the river water, still after it enters the river there is no appreciable effect on the quality. As to experiments 4 and 5, No. 4 is an experiment which has been carried out now on a larger scale — open septic tanks and continuous filtration ; No. 5 is open septic tank effluent and double contact. Although the depth of filtration with the double contact is exactly the same as with continuous filtration, it only passed about one-twelfth of the quantity per square yard, or gallons, per acre, and the effluent was not nearly so good. That is very conclusive as regards the sewage of York. Whether it applies to other places I am not prepared to say, but so far as York is concerned it shows the great superiority of continuous filtration over the double contact system. Mr. A. M. Fowler : Municipal engineers know that in towns of a similar character to York where they have few manufactories, large sums of money are now being spent in schemes of this character. But to apply this system so admirably worked as in York to other towns it is desirable to have all the facts bear- ing upon it, the number of manufactories and the quantity of manufacturing refuse. In Leeds, Manchester and towns of that class, the manufacturing refuse turned into the sewers creates an enormous difficulty in the purification of the sewage, whereas at Exeter and other places similar to York, there is practically no difficulty whatever, and you can get a splendid effluent. There- fore, if we could get statistics bearing upon this — giving the number of water-closets, privies, ashpits, the number of manu- factories, the quantity of trade effluents and the trades carried on — it would be very useful to us. As to fish living at the outfall of a sewage effluent, Prussian carp will live in almost any water. In 1872 when I designed the works at Leeds, where we had the A. B. C. process in operation, I had fish living there in globes for five months, some in the town’s water and others in the effluent water from the sewage tanks ; one died in the town’s water three days before the fish in the sewage effluent. So you can get an effluent sufficiently good for fish to live in, but in doing so you are going to a very great expense. Mr. J. P. Spencer: Mr. Creer has placed before us the 26 SEWERAGE AND SEWAGE DISPOSAL, YORK. development and change from one system to another, and I think he has made it demonstrable that for a city like York the open septic tank with continuous filtration is the best. I knew York long ago, and I have been in it in more recent times, and it seems to me, judging from the two periods, that the river is in a much better state now than formerly, notwithstanding the greater volume of sewage effluent put into it. Mr. A. D. Greatorex : I should like to propose a very hearty vote of thanks to Mr. Creer for his valuable paper. As regards Mr. Creeps statement as to the proportion the volume of effluent bears to the volume of the stream into which the effluent discharges, that is a very important point. In my own case the volume of the effluent is one-thirtieth of the stream into which it discharges, and from analysis the river is really worse than the crude sewage of the town, owing to the sewage discharge higher up the stream. To make a standard for a place like this would be grossly unfair. Dr. Wilson, Chief Inspector of the West Eiding Eivers Board : I am really glad of the opportunity of thanking Mr. Creer for giving me the chance to be present to hear his interesting paper. There are several points in the paper I should like to refer to. First as to standard of purification. I quite agree with Mr. Creer that an arbitrary chemical standard is not one to be advocated. Several times — very frequently indeed — the Eivers Board have been asked to fix a chemical standard ; it would, as you can easily see, make easier the work of the Board ; but they have no legal power to do so. It would be absurd to fix the same standard for an effluent which discharges into a navigable river like the Ouse and an effluent which discharges into a small stream which is afterwards used for drinking purposes. Mr. Creer has pointed out the fallacy of adopting a percentage of purification as a standard. The sewage in the West Eiding differs enormously, and a purification of 90 per cent, at York would produce an effluent much better than, say, at Bradford, which has one of the worst sewages in the Eiding. Mr. Creer has mentioned the pressure exercised by the Eivers Board and the complaints of the Eivers Board as to the state of the Ouse. He rather gives himself away in a previous paragraph, when he says the effect is perceptible half a mile below the outlet from the sewage works, and that on many occasions the chemical analysis of the water was worse below DISCUSSION. 27 than it was above the outfall. Mr. Creer does not state the real ground of the complaint of the Rivers Board, and this I mention to show the difference between a bacterial effluent and a chemical effluent. In 1901, a warm and dry year, the whole of the weir on the river below the sewage works was covered with sewage fungus, and the death of large numbers of fish was due to this sewage fungus. That was the effect of a chemical effluent dis- charged without filtration into the river. An effluent, such as that Mr. Creer is now producing from the sprinkling filters, has just the opposite effect. The effluent is in such a condition that it improves after being discharged into the river, instead of, like a chemical effluent, undergoing reaction and deterioration. There are one or two points on which I would like to warn some of the members present as to the making of loose deduc- tions from the results obtained by Mr. Creer. The strength of the sewage is given in the paper. The amount of sewage per head of the population shows that a good deal of subsoil water is mixed with the sewage of York, and the results of analysis show it is a weak sewage. There are sewages in Yorkshire which give twelve times the oxygen absorbed of that of York, and the engineers must not expect the same results with such sewages as Mr. Creer is able to obtain at York. Then mention is made in the paper of the suspended matter in the filter effluent. In the case of the filters at Leeds and many other places throughout the West Riding, the amount of suspended matter is a drawback to these percolating filters, and the effluents require after-treatment for its removal. It accounts for about 50 per cent, of the impurity of the effluents. It is not an offensive matter — in fact, it is much like garden mould in appearance, but still it is an impurity which should be removed before discharge into a stream. Again, later on in the paper, where Mr. Creer gives a table of analyses of the effluents from different materials which he is using, I think it should be mentioned that the sizes of the materials used are very different, and to my mind the difference in results between clinker and broken bricks is due more to the sizes of the materials than to their nature. This question of bacterial purification is now quite out of the hands of the chemists and the biologists, and wholly in the hands of you engineers, and I am glad to know that so many able men are working at the details of these methods of the bacterial purification of sewage. We have not yet, however, 28 SEWERAGE AND SEWAGE DISPOSAL, YORK. quite got rid of chemical methods. There are many places where trade refuse is mixed with domestic sewage where chemicals are still used with advantage. Mr. C. F. Wike : Unfortunately I have not had time to go thoroughly into the statistics contained in Mr. Creeps valuable paper, which embodies the results of great thought and experi- ence in connection with the sewage question. Mr. Creer’s conclusions are not theories only, and whether they are right or wrong we know they have been carefully and honestly thought out. With respect to the standard of purity required by the Eivers Board and its application to rivers of different volume — it does seem reasonable that some distinction should be made between tidal rivers and those which are canalised, where in times of drought the effluent from a sewage works may be the only feeder. Naturally, in the latter case, the effluent should be a very good one. I thoroughly agree with Mr. Creeps para- graph as to the position of towns which, during the last fifteen or twenty years, have honestly tried to purify their sewage, and have spent large sums of money in this way. In Sheffield we some time ago spent 150,000Z. to 200,000Z. on the works and outfall sewers, and now the Local Government Board and the Eivers Board tell us it is necessary to begin all over again, so far as the works are concerned. Seeing that we have a Sewage Commission sitting, whose final report may shortly be expected, we have not thought it unreasonable to hasten slowly, but the Eivers Board are of different opinion, and consequently it has been necessary to prepare a scheme which will involve an ex- penditure of possibly 300, 000£. to 400, 000£., and this is now under the consideration of the Local Government Board. It is shown by Mr. Creeps summaries that he has got very satisfac- tory results by treating the sewage in an open septic tank and passing the effluent through a continuous filter, but of course, as has already been stated, there is a difference between the sewage of various towns. In Sheffield, after very careful analysis, we have come to the conclusion that the best effluent is obtained by passing the crude sewage through a settling tank, and after- wards through the double contact beds. We take samples every hour which are mixed at the end of the day, so that we get a correct average, and these are then analysed. We get a purifica- tion of from 95 to 97 per cent, by this means, and it is upon this basis that we are proposing to extend our works. DISCUSSION. 29 Mr. E. P. Hirst: I should like to add my thanks to Mr. Creer for the very valuable paper which has been placed in our hands. The time appears to be arriving when with other seaside towns we at Southport may have to clarify, if not purify, our sewage. I notice that Mr. Creer states that 1,730,000,000 gallons were lifted per annum. Now that, with a population of 80,000, gives about 60 gallons per head per day. I should like to know how much Mr. Creer considers sewage proper, and how much subsoil water. Then again, speaking of albuminoid ammonia, he gives it in parts per 100,000. I should like to know if the percentages of oxygen absorbed are given in grains per gallon, or whether they are also given in parts per 100,000. It would materially help us to know how the strength of the York sewage compares with that of our own localities. Mr. Creer states in experiment No. 1 that the gallons per square yard treated were 42*89. This I take it was in the three fillings of the bed. Now, as the capacity of the bed appears to be something like 60,000 gallons, or rather, let me put it in another way, as a cubic yard would contain about 168 gallons, and Mr. Creer only put on 14 gallons per square yard per filling, is only about one-twelfth of the total capacity of the bed, and inasmuch as the filtering medium would probably not take up more than two-fifths or one-third of the total capacity of the bed, I cannot quite understand the small quantity which appears to be treated. Either the beds could not have been filled, or there must have been a considerable silting up in them. In regard to experiment No. 4, I do not know, but I presume that the septic tank that was used in this experiment was the same as the one which was used in experiment No. 5. I merely want to be quite sure that I understand that aright, and if so, I should like to know (as I see there are two tanks), whether the sewage is allowed to stand in one of these septic tanks, or whether there is a continuous flow through it. I should be glad also to know the cost of the circular filters, and the sizes of the materials used in their construction. Alderman Sir Joseph Sykes Kymer: In former times we had a very easy system of disposal. We just turned the sewage into the river. We stuck to that system as long as we could, because we knew when we departed from it that it would be a very expensive process. We only departed from it under pressure. Mr. J. Lobley : I beg to second the vote of thanks. In some 30 SEWERAGE AND SEWAGE DISPOSAL, YORK. respects there is the most remarkable contrast between my own town and York, but there is one similarity in the enormous amount of water to be dealt with at the sewage disposal works. I gather from Mr. Creer’s paper that he has to deal with the very large volume of sewage of 60 gallons per head per day. In my case I have had a good deal of mine water coming into the sewers, and the Local Government Board insist upon multi- plying that mine water by six. In order to provide bacteria beds for that means an enormous expense. The vote of thanks having been unanimously passed, Mr. A. Creer, in reply, said : I must express my hearty thanks for the reception you have given to my paper, and the interesting discussion that has followed the perusal of it. I dare say some of you will feel with me that this question of sewage disposal is a most fascinating one, and if once you begin to take an interest in the subject, it seems to absorb all one’s spare time. I think it quite likely that if the works had been seen before the paper was discussed, there would have been no necessity to ask some of the questions. I do not propose to answer all the questions now. If it is found that there is not time for further discussion after visiting the works I shall be pleased to answer any questions sent to me in writing, so that the replies may appear in the Proceedings. Dr. Wilson made some remarks as to the filtering media. It is quite likely that the difference in grade of the material may have had something to do with the results obtained. But, of course, you cannot get definite results from one experiment. It is quite possible that in the further extension of the filtering provision we may try different materials and different sizes. The curious thing is, that the clinker is very much smaller than the other three materials ; the coke is as large or larger than the broken brick, but is not larger than the honeycomb slag. The slag is a very tough ma- terial and difficult to break. You will see that the coke which is as large as the slag, and larger than the other materials, gives us the best results. That gives you an idea of the value of coke as a filtering material as apart from size. I would like to say, in regard to Mr. Hirst's question as to the analyses, that the earlier analyses referred to were taken very early on in the history of sewage disposal at York. They were made by a Leeds chemist, and he gave us the results in parts per 100,000. All the other results are in grains per gallon. The volume of sewage to quantity of water pumped into the city averages DISCUSSION. 31 35 gallons per head per day. The quantity pumped by the Corporation at the pumping station is about 41 gallons per head per day. We have many sewers that are below the level of the two rivers — the Ouse and the Foss — and some of them are very old, practically centuries old, and you will understand the difficulty of tracing these out and cutting them off from the intercepting sewers which take the sewage down to the works. I hope the Local Government Board and the Rivers Board will give consideration to the fact that the water we treat is practically double what we ought to legitimately treat in the city of York. A cordial vote of thanks to the Lord Mayor and Corporation for the use of the Council Chamber for the meeting was passed unanimously. Communicated Discussion. Mr. E. J. Silcock : I wish to direct special attention to the comparative results obtained in the new continuous filter with the different materials used as the filtering medium. These results are set out in the table given. It has long been my opinion that the materials which were utilised in nearly all the earlier experiments, i. e. coke and clinkers, are of much too soft a nature to be used as part of a permanent works, especially where these works are being carried out by money for which loans have been obtained, and I have strongly urged the desirability of using harder materials, such as slag, lava, granite, etc. Holding these views, it is disappointing to find that the results of Mr. Creer’s experiments extending over a considerable period show that the degree of purification obtained by using broken bricks and slag, although satisfactory in themselves, are yet sensibly inferior to those obtained by using coke and clinkers. Before finally accepting these results I should be glad if the Author would give full particulars as to the size to which the various materials were graded, as this point may explain to some extent the difference in the results obtained. If the broken bricks and slag are larger than the coke and clinker they will permit more solids to be washed through the bed, and this may cause the analyses to show the results in favour of coke and clinkers. However this may be I would urge upon those Members who have the opportunity of comparing results ob- tained by various materials to take every opportunity of doing so and of putting on record their experience. I may say that in 32 SEWERAGE AND SEWAGE DISPOSAL, YORK. the Leeds experiments this question has been carefully gone into, and it has not been found that there was any variation worth considering in the degree of purification obtained from various filtering media, and I have therefore considered that the greater stability of the material was the most important factor in selecting the material which should be used. Communicated Reply, Mr. Creer : In reference to Dr. Wilson's remarks on the quality of the river water half-a-mile below the works, it will be seen on reference to the paper that the river water below the works was on the average 4 • 5 per cent, worse by the oxygen absorbed test than above, and as this percentage was on a very low figure, viz. 0*270 grains per gallon, it will be seen that the effect of the effluent from the chemically treated sewage was trifling. The replies to Mr. Hirst's questions are given hereunder. The 1730 millions include storm water. The normal daily flow is about 46 gallons per head per day ; of this quantity about 10 gallons is due to subsoil water. The question as to capacity of bed I cannot follow ; each of the two beds had a cubic capacity equal to 46,426 gallons, not 60,000, and the effluent from the first bed passed through the second. Probably Mr. Hirst has had in his mind a single contact system, whereas the experiment referred to double contact when the quantity treated was passed through two filters, thus doubling the area required for filtration. The septic tank used for No. 4 experiment was the same as used for No. 5 ; but in the former case the whole flow was used in the experiment, while in the latter only part, the balance passing to other experimental plant. Full particulars are given in the paper as to the method of working the tanks. The cost of the 100 feet diameter filter was about 1500£. ; it is obvious that a number of filters could be put up at a very much less cost per unit. Dr. Wilson asked a question on the same lines as Mr. Silcock, this was answered at the Meeting and appears in the Report. LONDON: PRTNTKD BY WILLIAM CLOWES AND SONS. LIMITED, GREAT WINDMILL STREET, W., AND DU E E STREET, STAMFORD STREET, 8.E. DIAGRAM No. 1 Oxygen Absorbed in 4 Hours at 80° Fah. (Grains Per Gallon). Gallons passing per Sq . Yard per 24 Hours. CITY OF YORK- SEWAGE DISPOSAL DIAGRAM No. 2. Diagram shewing the depth of sludge in the Open Septic Tank after one and two years use. DIAGRAM No 3. Diagram shewing the average depth of sludge in Open Septic Tank. CITY OF YORK SEWAGE DISPOSAL. s jrj Jp 2 i: i. li N 9, ft n i QL or n lJj i M 3 il V 1, d •i: 3 tJD < £ m * 3 a > 1 N i ; 5 n ba j i 3 L A \ a 3 £ 12 1. .1 1 j "i > * 12 J Y / A c 12 \i 1: IJ 1 1: II 4f i It o jL 2 i: 1. V 1 ft \ * 2 ft 1 i ; K Hj K) CJ 4 ’Noinvo a3d SNivao ni 6 asaaosav n3oaxo Z s < £ a < a Diagram shewing the various stages of fouling and purifying that the water passes through during its passage from the Water Works Intake to its return to the River at the Effluent Sewage Outlet. N0T1V0 U3d SNIVaO 0 18 72 102 132 195 225 255 308 326 Diagram shewing the purification effected in the sewage during its flow through the Open Septic Tank, the figures along the bottom of the diagram shewing the distances from the tank inlet where the various samples were taken for analysis. Diagram shewing the gradual deposition of suspended solids in Open Septic Tank as the sewage flows through the whole length of the Tank. Q1T Y o F YORK SEWAGE DISPOSA L .