NA TURE 



THURSDAY, DECEMBER 12, 1901. 



THE BACTERIAL PURIFICATION OF 

 SEWAGE. 

 Sewage and the Bacterial Purification of Sewage. By 

 Dr. S. Rideal. Pp. iii + 308. (London : Sanitary 

 Publishing Co., 1901.) Price 14^. net. 



THE practicability of effecting the purification of town 

 sewage on the large scale by bacterial agency has 

 now been abundantly proved. The process has passed 

 beyond the e.xperitnental stage, and must now be ac- 

 knowledged as the only method which can convert the 

 putrescible matter of sewage on the large scale into 

 inoffensive and harmless substances. Accordingly all trust- 

 worthy information respecting the results which have been 

 arrived at from the lengthy experimental trials, and from 

 the application of these results on the large scale, will be 

 welcome to public sanitary authorities, and perhaps even 

 still more acceptable to the professional advisers of these 

 bodies. The treatise under review has been written by 

 one who has carefully watched the progress, and who 

 has had a long and varied e.xperience, of bacterial treat- 

 ment. The book is, therefore, undoubtedly worthy of 

 careful perusal and consideration by those who are 

 responsible for disposing of the sewage from houses, 

 villages or towns. 



The author covers a wide ground. He treats of the 

 general character of sewage, and gives an historical 

 sketch of the processes which have been resorted to for 

 disposing of it. He also enters fully into the modern 

 methods which have been recommended for the chemical 

 examination of sewage and of sewage effluents, and states 

 the standards of purity which have been suggested. 

 Probably his description of the methods of collecting and 

 examining these liquids will be of special value, since no 

 such general description seems to be at present available. 

 The summary of Dr. Houston's work on the identification 

 of the bacteria present in raw sewage, a detailed account 

 of which has appeared in the reports published by the 

 London County Council, will also be useful, together with 

 the account of the most important chemical changes which 

 are brought about by bacteria. Naturally, also, some 

 account is given of the treatment of sewage by irrigation 

 and by chemicals, and of the " sterilisation " processes — 

 processes which appear in the light of present knowledge 

 of doubtful advantage, since they destroy the vast number 

 of bacteria which effect or complete the purification of 

 sewage, in order to make sure that a small minority of 

 possibly injurious bacteria are disposed of. 



The latter portion of the book will undoubtedly com- 

 mand most general attention, since here the author 

 deals with bacterial purification. This is treated of in 

 some detail, and the information which is given has been 

 collected from the most trustworthy sources generally 

 available. One can only regret that the large amount of 

 useful matter accumulated has not been somewhat more 

 systematically arranged and carefully summarised and 

 compared ; and, above all, that the author has not stated 

 very clearly and emphatically the conclusions which he 

 himself has arrived at from its careful consideration. The 

 author h-as, however, apparently not been willing gener- 

 NO. 1676, VOL. 65] 



ally to act as assessor of the relative value of the different 

 bacterial methods and apparatus, and due acknowledg- 

 ment should be made of the time and trouble which he 

 has expended in bringing together important informa- 

 tion much of which, until now, has existed only in the 

 form of scattered reports and papers. That the work 

 which he has done in this direction is really valued 

 is shown by the fact that a second edition of the 

 book has been issued twelve months after the original 

 publication ; and it may be stated that the author has, 

 as far as possible, availed himself of the opportunity 

 which a new edition afforded him of bringing the matter 

 up to date. 



The author speaks in his preface "of the experiments 

 on bacterial purification, which have now been carried 

 out on a sufficiently large scale to establish the safety of 

 embarking on the treatment of sewage on bacterial lines 

 for even the largest centres of population." This state- 

 ment proves that he is in touch with the recent experi- 

 mental trials of the method at the sewage outfalls of 

 our great towns. And it cannot be too emphatically 

 stated that the near future is to see the adoption on the 

 large as well as the small scale of this most rational 

 process of " self-purification " of sewage. For after all 

 bacterial purification is natural purification. It simply 

 amounts to allowing the living agents of purification, 

 which are present in the raw sewage in immense 

 numbers, to carry out their useful function under the 

 most favourable conditions. This adoption of natural 

 methods must surely commend itself; and no one who 

 looks at sewage treatment from a disinterested point 

 of view will regret the approaching general relinquish- 

 ment of artificial chemical or electrical treatment in 

 favour of allowing natural agencies to have free course, 

 provided only that reasonable efficiency and economy can 

 be assured in making the change. This natural treat- 

 ment may in some localities be effected on sewage farms 

 by the development of bacteria in a suitable soil ; but 

 in most localities great advantage is obtained by sub- 

 stituting for the soil properly constructed bacteria beds, 

 in which the treatment can be carried out on a smaller 

 area and under more complete control than by means of 

 the bacteria in the soil. 



The experience and knowledge derived from several 

 years' natural purification of sewage on the small scale in 

 coke bacteria beds at the London and Manchester out- 

 falls should suffice to give satisfactory assurance in these 

 respects. After varied and continued trials it has been 

 found independently at both these important centres that 

 the raw sewage on its arrival at the outfalls should be 

 roughly screened and then subjected to sedimentation 

 without previous admixture with any chemicals. It has 

 been shown that sedimentation may be appropriately 

 allowed to take place in open tanks or channels in two 

 stages. Much sand, road detritus and cellulose matter 

 can thus be first removed, and this may be simply thrown 

 out upon the land or dealt with in destructors without 

 causing offence ; while in the second sedimentation 

 "sludge" consisting of f^cal and putrescible matter 

 subsides. If the substances which are separated out 

 by the latter sedimentation are simply left in contact 

 with the sewage, which constantly flows over them, at 

 least 40 per cent, of the solid sediment disappears 



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