Section YORK, 1886. President. SIR SPENCER WELLS, BART, Presidents of Sections. L-PROF. F. DE CHAUMONT, M.D., F.R.S. II. BALDWIN LATHAM, MINST.C.E., F.R.MST.Soc. Honorary Local Secretary-S W. NORTH, M.R.C.S. BOLTON, 1887. President.-RIGHT HON. LORD BASING, F.R.S. Section I. PROF. J. RUSSELL REYNOLDS, M.D., F.R.S. Conference of M.O.H.-PROF. W. H. CORFIELD, M.A., M.D. Honorary Local Secretaries-R. G. HINNELL, E. SERGEANT, L.R.C.P. M.R.C.S., and MARSHALL ROBINSON, Section 99 WORCESTER, 1889. President.-G. W. HASTINGS, M.P., J.P. I.-GEORGE WILSON, M.A., M.D. II.-HENRY J. MARTEN, M.INST.C.E. III.-J. W. TRIPE, M.D., F.R.C.P. F.R.MET,Soc. Conference of M.O.H.-PROF. W. H. CORFIELD, M.A., M.D. Honorary Local Secretaries-W. STRANGE, M.D., and HORACK SWETE, M.D. BRIGHTON, 1890. President.-SIR THOMAS CRAWFORD, K.C.B., M.D. Section 99 99 Presidents of Sections. I.-G. VIVIAN POORE, M.D., F.R.C.P. PROF. T. ROGER SMITH, F.R.I.B.A. Conference of M.O.H.-ARTHUR NEWSHOLME, M.D., D.P.H. Conference of Inspectors of Nuisances-ALFRED CARPENTER, M.D., M.R.C.P., D.P.H. Honorary Local Secretary-A. NEWSHOLME, M.D. PORTSMOUTH, 1892. President.-SIR CHARLES CAMERON, M.D., F.R.C.S.I., D.P.H. Presidents of Sections. Section I.-PROF. J. LANE NOTTER, M.D. II. JAMES LEMON, M.INST.C.E., F.R.I.B.A. Conference of Naval and Military Hygienists-INSPECTOR-GENERAL J. D. Conference of Medical Officers of Health-PROF. C. KELLY, M.D. Conference of Municipal and County Engineers-H. PERCY BOULNOIS, M.INST.C.E. Conference of Sanitary Inspectors-PROF. A. WYNTER BLYTH. Conference on Domestic Hygiene-LADY DOUGLAS GALTON. Honorary Local Secretaries—ALEXANDER HELLARD and B. H. MUMBY, M.D., D.P.H. LIVERPOOL, 1894. President.—SIR FRANCIS SHARP POWELL, Bart., M.P. III.-THOMAS STEVENSON, M.D., F.R.C.P. Conference of Mercantile Marine-SIR W. B. FORWOOD. Conference of Medical Officers of Health-CHARLES E. PAGET, M.R.C.S., M.O.H. Salford. Conference of Municipal and County Engineers-A. M. FoWLER, M.INST.C.E. Conference of Sanitary Inspectors-FRANCIS VACHER, F.R.C.S. Conference of Ladies on Domestic Hygiene-THE LADY MAYORESS OF LIVERPOOL. Honorary Local Secretaries-H. PERCY BOULNOIS, M.INST.C.E., and E. W. HOPE, M.D. NEWCASTLE-UPON-TYNE, 1896. Section 99 I. PROF. W. H. CORFIELD, M.A., M.D. Conference of Port Sanitary Authorities-A. HOLT BARBER. Conference of Medical Officers of Health-ALFRED HILL, M.D., F.R.S.E., F.I.C. Conference of Municipal and County Engineers-F. J. C. MAY, M.INST.C.E. Conference of Sanitary Inspectors-G. REID, M.D., D.P.H. Conference on Domestic Hygiene, THE MAYORESS OF NEwcastle. Honorary Local Secretaries-H .E. ARMSTRONG, D.HY., and J. W. HEMBROUGH, M.D. JOURNAL OF THE SANITARY INSTITUTE. THE LESSONS TO BE LEARNT FROM THE EXPERIMENTAL INVESTIGATIONS BY THE STATE BOARD OF HEALTH OF MASSACHUSETTS UPON THE PURIFICATION OF SEWAGE. BY CAPTAIN SIR DOUGLAS GALTON, K.C.B., D.C.L., LL.D., F.R.S., Late R.E., HON. M.Inst.C.E. (FELLOW.) Read at a Sessional Meeting, December 11th, 1895. I HAVE been requested to open a discussion upon some of the general conclusions which may be drawn from the Massachusetts experiments. These have been published for some time, and they have been elaborated by further efforts of engineers both in this country and in America. My task is to endeavour to give you a brief account of the various experiments which have been made, and to present to you the conclusions to which these various experiments point. My remarks are only intended to open out what we hope may be a valuable discussion on this important subject. It has practically only been in comparatively recent times that the growth of our population has compelled the public to recognise the necessity for the disinfection, purification, or destruction of refuse matter. A sparse population could afford to allow the refuse to purify itself gradually in the soil, or in ditches, streams, and rivers; but as the population and proximity of habitations increase, careful attention must be given to methods of dealing with the refuse to prevent the injurious effects which arise VOL. XVII. PART I. from decaying organic matter in the neighbourhood of dwellings, or from the use of polluted water in our streams and wells. As a result of the epidemics of cholera between 1830 and 1850, the removal of excreta by water carriage obtained a great development, and during the discussions which took place upon the problem of Metropolitan Drainage before 1858, the utilization of sewage and its purification by application to land received much consideration. The problem was in the hands of the engineer and the chemist, and the conclusions at which experts in sewage then arrived may be generally summed up as follows: 1st. The direct application of sewage to land is thoroughly effective as a means of purification. There is no sanitary objection whatever to the system of sewage disposal by agricultural irrigation, and no nuisance or offence can arise in connection with it, save as a result of gross neglect or mismanagement. But it entails difficulties in thickly settled districts, owing to the extent of land required. 2nd. The chemical treatment of sewage produces an effluent harmless only after having been passed over land, or if turned into a large and rapid stream or into a tidal estuary, and it leaves behind a large amount of sludge to be dealt with. 3rd. Hence it was long contended that the simplest plan in favourable localities was to turn the sewage into the sea, and that the consequent loss to the land of the manurial value in the sewage would be recouped by the increase in fish life. Purification was originally supposed to be due to the oxidising effect of the air, but the researches of Schloessing, in France, and Frankland and Warrington, in England, brought the biological element into consideration. Schloessing found that when sewage was passed through baked sand and marbles, no purification was produced at first, but that later the effluent became clear and free from organic matter. He found that this purification was arrested by the presence of chloroform in the sand, and that it began again when the chloroform was washed out. This confirmed him in the conclusion that purification requires the co-operation of living organisms. Warrington believed that nitrification was due to living organisms chiefly confined to the surface soil. And Frankland concluded that purification is a process of oxidation, producing carbonic acid and nitric acid, and that a continual aeration of the soil is necessary. The conclusion was thus reached that in the direct application of sewage to land, the loam on the surface at once supplies nitrifying organisms ready to convert the sewage into a form suited for food for the plants which are on the land. Dr. Frankland, many years ago, suggested the intermittent filtration of sewage through a thickness of five or six feet of material; and Mr. Bailey Denton and Mr. Baldwin Latham were among the earlier engineers who adopted the method. The simplest theory of the working of any filter is that its action is mechanical, indeed the word "filter" has come to mean ordinarily a more or less perfect strainer. In this aspect the working of the filter is continuous, but it soon chokes and must be cleaned. The intermittent filter on the other hand presents quite different conditions. It is no longer a mere mechanical strainer. No doubt when first established there may be a period at the outset when it effects little more than a mechanical purification; but, under the best conditions, there speedily begins a change of the profoundest significance. The filter becomes a method of developing the conditions which favour the action of bacteria by the exposure of the sewage in the presence of air. The Massachusetts experiments may be said to have taken. up the question at this point. The experiments show that a sand filter does not effect the nitrification when first used. Time is necessary for it to accumulate a suitable colony of bacteria. Furthermore, the colony adjusts itself to the work it has to do. If, then, the amount of sewage is suddenly increased, and is continued at the larger amount, the nitrification will at first be incomplete, but the bacteria will soon multiply and purification will again become satisfactory, often amounting to the destruction of 99 per cent. of the nitrogenous matters in the sewage, and all but a fraction of one per cent. of the bacteria. Nitrification is affected by the season and by temperature. It is most active in the growing months of May and Juneeven more so than in the hotter months of July and August. With this exception the amount of nitrification varies with the amount of the sum of the ammonias in the sewage, so that, in the winter months of 1888-89, while the nitrates of the effluent were lower than at other times, it was found that the sum of the ammonias in the sewage was also lower, and that nitrification at that time was quite as complete as in the previous months. The general conclusions were thus summed up in the report of the chemist to the experiments, Mr. Hazen : "The purification of sewage by intermittent filtration depends upon oxygen and time; all other conditions are secondary. Temperature has only a minor influence; the organisms necessary for purification are sure to establish themselves in a filter |