NA TURE 



73 



TREATMENT AND UTILISATION OF 

 SEWAGE. 

 Treatment and Utilisation of Sewage. By W. H. Cor- 

 field, M.A., M.D. (Oxon.). Third Edition, Revised 

 and Enlarged by the Author and Louis C. Parkes, 

 M.D., Cert. Public Health (Lend.). (London: Mac- 

 millan and Co., 1887.) 



OF late years, discussions about sewage have occupied 

 a large share of the proceedings of many of the 

 Societies concerned with the practical application of 

 science, and recent scientific discoveries have as yet done 

 little to modify the conclusions of the last ten or fifteen 

 years. Dr. Farr's Report on Vital Statistics proves that 

 increased density of population (if sanitary conditions 

 remain constant) is itself a cause of increased ill-health 

 and death, which can only be counteracted by increased 

 precaution. And the prominent position occupied by 

 England in sanitation must be ascribed to the constant 

 efforts which have been made to cope with the increasing 

 density of the population. A danger to health arises 

 from density of population mainly because of the retention 

 in our midst of the impurities which are the necessary 

 accompaniments of the act of living, that is to say, the 

 retention of those substances which putrefy, and from 

 the products of the putrefaction of which various matters, 

 or, it may be, organisms, inimical to life, become dis- 

 seminated through the air. 



The new, a third, edition of Dr. Corfield's record of 

 the treatment and utilisation of sewage is a valuable con- 

 tribution to the history of the development of the 

 methods by which some of these evils have been coun- 

 teracted. The first edition was the practical outcome of 

 researches and experiments made by a Committee of the 

 British Association, which was appointed to consider the 

 evils arising from the unsystematic arrangements which 

 prevailed at the inception of the water-carriage system 

 for sewage. Before the introduction of the water-carriage 

 system, refuse polluted the soil under and around the 

 houses, the wells, and the air : when water-carriage was 

 resorted to, it was thought sufficient to allow the dirtied 

 water to flow to the nearest outfall, and the result was 

 the pollution of our ditches, streams, rivers, and sea- 

 shores. Our experience of the way in which these evils 

 can be overcome has been gained slowly and tentatively : 

 and Dr. Corfield's record of the various processes which 

 have been tried and abandoned is not only useful as a 

 means of preventing those methods that have been found 

 unsuccessful from being brought forward again, but the 

 account he gives of the causes of failure teaches im- 

 portant lessons to the sanitarian — lessons that may 

 enable him to combat the insanitary conditions which 

 a dense population is coiitinually developing under new 

 and unforeseen aspects. 



Much as the subject of sewage disposal has been dis- 

 cussed, the varying conditions under which towns have to 

 dispose of their sewage make it impossible that there 

 should be any uniform method of disposal. It is abund- 

 antly certain that sewage contains elements of value. 

 Vol. XXXVI. — No. 917. 



Dr. Tidy values the sewage at %s. or 95. per annum per 

 head of the population, of which the solid part is worth 

 \s. 2d. Dr. Corfield estimates the sewage of London 

 alone at between ^1,000,000 and ^1,500,000. Dr. Liebig 

 estimated it at ^4,000,000. But Dr. Hoffman, in 1857, 

 summed up this question in the statement that the value in 

 London sewage was like the gold in the sands of the Rhine 

 — it amounted to millions, but it would not repay the cost 

 of recovering it. Some of our first authorities on the sub- 

 ject, indeed, having most strongly advocated the com- 

 mercial value of sewage, have ended, after years of labour, 

 by saying, " Get rid of it in the cheapest manner ; throw 

 it into the sea if you can." The assumption that, because 

 sewage has within it manurial value, therefore its removal 

 ought to produce a profit, has had a most unfortunate 

 effect on the treatment of this question. The search 

 after the philosopher's stone of profit in sewage-disposal 

 retarded the sanitary movement for years. 



But, whilst it is easy to say, " Throw your sewage into 

 the sea," it is rarely that we can so deal with it without 

 injuring foreshores or tidal estuaries, and many sea- 

 side resorts are suffering from such a method of disposal. 

 A tidal river can only be safely resorted to under excep- 

 tional conditions. The discharge of crude sewage into 

 a river, or, for the matter of that, on to land, is not satis- 

 factory. For instance, the metropolitan sewage is poured 

 into the tidal estuary of the Thames, where there is an 

 enormous volume of water. Notwithstanding the purify- 

 ing power of water, the sewage has seriously polluted the 

 river beyond its capacity for purification in dry weather. 

 On the other hand, it has been shown that the Barking and 

 Halfway Reaches of the Thames, where the sewage is 

 poured in, are really now better for navigation than they 

 were before the metropolitan drainage outfalls were 

 opened. 



Independently, however, of the evils of the pollution 

 of the tidal estuary of the Thames by the metropolitan 

 sewage, we cannot conceal from ourselves that if some 

 method of utilisation were feasible, even though it cost 

 as much as we now pay for disposing of the sewage 

 without utilisation, the resulting agricultural produce 

 would be a gain to the nation. But there is not at 

 present any generally-accepted plan for converting the 

 metropolitan sewage into food, nor does it seem very 

 probable that any metliod of treating the London sewage 

 as a combined whole will enable us to do so usefully. 

 The Metropolitan Board of Works, indeed, appear to 

 consider it more prudent to submit to the known cost 

 of loss than to embark on the more speculative course of 

 endeavouring to rescue the valuable contents. 



The most important question for the nation at the 

 present time relates to other towns in the kingdom — that 

 is to say, the question how, in the case especially of 

 inland towns, can the sewage be purified so as to pre- 

 vent it from damaging neighbouring properties, and make 

 it fit to be passed into rivers. The best authorities 

 are agreed on one point, viz. that it must not be sent 

 crude into the rivers ; and the preliminary straining off 

 of the suspended matters is only a httle less objection- 

 able. Precipitation alone will not render the effluent 

 water sufficiently pure ; but if you let that effluent, 

 after precipitation, flow over a small area of land, you 

 will give the effluent the finishing touches towards 



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