February 26, 1903] 



NA TURE 



40c 



rapidly as they were introduced by the sewage. But both the grit 

 and the cellulose matters could be separated by sedimentation ; 

 and the cellulose matters might, according to modern research, 

 be slowly resolved by the action of suitable bacteria, if such could 

 be established. Accordingly, it was arranged that the crude 

 sewage should undergo a preliminary settlement in a deep 

 tank, where the sediment should remain undisturbed in the 

 hope that bacterial resolution of the organic matters in the 

 deposit might occur. 



This settling or so-called "septic" tank was found after a 

 time to effect the resolution of the cellulose matters most satis- 

 factory, the necessary bacteria being evidently contained in 

 the sewage. The amount of sediment which should have been 

 found at the bottom of the tank was estimated by carefully 

 gauging the volume of sewage which passed through the tank in 

 the course of six months and determining the amount of suspended 

 ■matter which the sewage contained. When the actual amount 

 of sediment present in the tank at the end of this period was 

 measured, it was found to correspond to about 50 per cent, of 

 the total quantity introduced, and the sediment which remained 

 consisted largely of the grit which had not been previously 

 separated. It was therefore possible to dispose of the trouble- 

 some cellulose matter by long-maintained bacterial action in 

 the settling tank, and to prevent it from clogging the coke-beds. 



The final experimental stage consisted in passing the screened 

 crude sewage through a settling tank, which was of such 

 capacity that the sewage required five hours to pass through it 

 and was so arranged that the sediment was undisturbed by the 

 flow. The effluent from this tank was received successively in a 

 series of coke-beds, in which it was treated in the way already 

 described. After two hours' contact with the coke, it issued as 

 an inoffensive and non-putrescible effluent which readily main- 

 tained the life of fish. The sediment in the settling tank was 

 left entirely undisturbed. As soon as it had become permeated 

 with its suitable bacteria, more than 50 per cent, of it was re- 

 solved into gaseous and soluble substances, and it was certain 

 that a preliminary sedimentation of the grit must have further 

 increased this percentage. 



The sewage capacity of the coke-bed, on the other hand, was 

 carefully gauged at intervals. It was found that the capacity 

 diminished during the formation of the bacterial growth upon 

 the coke surfaces, and that when this was complete the capacity 

 ■of the bed was about 30 per cent, of the whole space which had 

 been filled with coke and with sewage. No permanent alteration 

 in capacity occurred during many months, although the capacity 

 temporarily rose or fell by a few units per cent, from the 

 average. 



It appeared, therefore, that the above method of treatment 

 was applicable to London sewage and that it might now be 

 applied on the large scale. The experimental work was ac- 

 cordingly suspended, and the conclusions arrived at were stated 

 and recommendations were framed in the following words : — 



" Conclusions arrived at by the Experimental Treatment. 



"(1) That by suitable continuous undisturbed sedimentation 

 the raw sewage is deprived of matter which would choke the 

 coke-beds, and the sludge which settles ou ;is reduced in 

 amount by bacterial action to a very considerable extent. This 

 reduction might undoubtedly be increased by the preliminary 

 removal of road detritus. 



"(2) That the coke-beds, after they have developed their full 

 purifying power by use, have an average sewage capacity of 

 about 30 per cent, of the whole space which has been filled with 

 ■coke. 



" (3) That the sewage capacity of the coke-bed, when the bed 

 is fed with settled sewage, fluctuates slightly, but undergoes 

 no permanent reduction. The bed does not choke, and its 

 purifying power undergoes steady improvement for some time. 



" (4) That coke of suitable quality does not disintegrate 

 during use. 



" (5) That the ' bacterial effluent ' of settled sewage from the 

 coke-beds does not undergo offensive putrefaction at all even in 

 summer heat, and can never become offensive. That this 

 effluent satisfactorily supports the respiration of fish. 



" (6) That the use of chemicals is quite unnecessary under any 

 circumstances when the above method of treatment is adopted. 



" Recommendations founded on the above Conclusions. 

 "It would appear desirable, therefore, without delay, to com- 

 mence the "treatment of the London sewage by the above 

 bacterial method. The construction of the necessary works will 



NO. -1739, VOL. 67] 



take time and will involve expenditure, but'unless it is taken 

 in hand, all considerations tend to show that owing to the 

 increased abstraction of water by the water companies, both at 

 their existing intakes and at the newly constructed reservoirs 

 for storm water at Staines, a large portion of the lower river 

 will continuously deteriorate. This deterioration would arise 

 from the increase in the amount of the discharge of sewage 

 effluent and the decrease in the upper river flush. Possible 

 trouble arising from these causes will be absolutely prevented 

 by adopting, under proper conditions and on a large scale, the 

 treatment which has been strikingly successful on the experi- 

 mental scale. It must be remembered that the condition of the 

 river cannot be improved by any suddenly adopted action. 



" If the treatment is introduced without delay and is gradually 

 extended it may reasonably be expected that the increasing de- 

 terioration in the lower river water will first be checked and 

 will ultimately be prevented : while the gradual development of 

 the treatment will cause the expenditure to be spread over a 

 period of years, and will prevent it from being unduly burden- 

 some. 



"It must be remembered that the present settling channels 

 would serve, as at present, for settling purposes, but by the 

 altered method of working them they would also act as sludge 

 destroyers. They should, however, undoubtedly be preceded by 

 grit chambers. 



" It must be further borne in mind that the expense 

 involved in the purchase and application of chemicals would 

 be dispensed with." 



Other conclusions, which were incidentally arrived at during 

 the above experimental work, may be mentioned. The material 

 used for filling the bacteria bed seems to exert no considerable 

 influence on the purification obtained ; coke proved to be the 

 most efficient, ragstone containing calcium carbonate was less 

 efficient, but the difference in efficiency was not of serious 

 amount. 



The depth of the coke-bed did not materially affect its 

 efficiency between the limits tried, which ranged from four feet 

 to twelve feet. In the interspaces of the coke, even in the 

 deepest bed, a satisfactory proportion of oxygen was present in 

 the air; the bed was able to aerate itself without mechanical 

 aid. 



The amount of sewage dealt with satisfactorily by the system 

 of intermittent filling of the coke-bed described above was greater 

 than that which could be similarly purified by a continuous 

 supply furnished by sprinkling or by other methods of dis- 

 tribution. 



The report concludes with detailed information concerning 

 the bacterial treatment of their sewage by the authorities in 

 forty-eight of the principal centres of population in this country. 

 This information has been supplied by the responsible officers 

 from the centres concerned and has been brought up to date of 

 April 30,1902. 



A consideration of this information in conjunction with that 

 supplied concerning the London experimental work will probably 

 be felt to justify the opinion "that the process (of bacterial 

 treatment of sewage) has been uniformly successful when the 

 construction and use of the necessary plant has been reasonably 

 and properly carried out," and that the metropolis may now 

 safely adopt this "natural" method of sewage disposal. 



Frank Clowes. 



SILICA GLASS. 



A FEW weeks ago we described some of the excellent 

 ■^ results obtained by Messrs. Heraeus, of Hanau, in 

 their attempts to produce apparatus of " silica glass," and 

 Prof. Dewar has added point to our remarks by exhibit- 

 ing at the Royal Institution a " liquid air holder " made 

 of silica, which had been made to order and sent by return 

 of post, almost, from Hanau to London a few days before. 

 Similar apparatus could have been made in England, it is 

 true, but it could not have been produced by any means so 

 quickly as at Hanau. Now we receive from America an 

 account of an animated discussion on the subject of " silica 

 glass " which lately took place at a meeting of the Ameri- 

 can Electrochemical Society at Niagara Falls on the 

 occasion of the reading of a paper, by Mr. R. S. Hutton, 

 of Manchester, on his method of casting silica tubes in the 

 electric furnace, which shows that our American cousins 



