792 



NATURE 



[August 19, 1920 



excess water and improvements in mechanical and 

 industrial operations, the air-drying of peat by natural 

 means is the only recognised commercially successful 

 method in use to-day. Reduction of the water-content 

 from 90 to 70 per cent, by pressure alone on the 

 raw peat is considered by the author to be the maxi- 

 mum, and he does not consider that drying by arti- 

 ficial heat becomes a practical proposition until this 

 70 per cent, content is reached, " and even then it 

 is a very doubtful financial proposition." 



For use under boilers the water should be reduced 

 to 30-35 per cent. ; for gas producers it is stated that 

 several leading manufacturers claim successful work- 

 ing with 60-70 per cent., but Prof. Purcell considers 

 that the possibility of using peat with as high a 

 moisture-content as 60 per cent, is doubtful, and 

 quotes the Canadian authority, Haakel, in support. 

 "If it were permissible [to use such wet peat] it 

 would render the industry less dependent on the 

 weather, extend the peat-winning season, and simplify 

 the whole problem." 



Prof. Purcell considers that a clear case for the 

 extended development of the peat deposits exists from 

 an agricultural point of view, for the reclamation of 

 land by removal of the bog and drainage must add 

 to the' food-producing capacities of a country. But 

 labour costs are no small difficultv, for, as Sir George 

 Beilbv Doints out in his introduction, the development 

 of a bog with 20 ft. of good peat is in some respects 

 analogous to the proposal to develop a coalfield of 

 similar area containing a single seam of only 15 in. 

 •thickness. It is true that the peat bog entails only 

 surface working, but the whole depth has to be 

 worked and 10 tons of raw material excavated and 

 handled for i ton of dry peat. J. S. S. B. 



Past and Present Sewage Systems. 



^pWO Chadwick public lectures recently delivered 

 A at Colchester by Mr. A. J. Martin dealt with tne 

 nature and treatment of sewage. Since the very 

 earliest days there have been codes of sanitary laws, 

 but all kinds of readjustments had to be made as 

 soon as men began to congregate in large cities. 

 1 hese crowded conditions seem to be met most satis- 

 factorily by the water-carriage system, by which the 

 clean water supplied to a town returns ultimately to 

 the sewers charged with all manner of pollution. 

 When sewers were first laid the sewage Vv-as dis- 

 charged straight into the rivers. The results were, 

 of course, disastrous, and successive Royal Com- 

 missions were set up to find a remedy. The whole 

 problem of sewage purification was obscure, and 

 very little progress was made for a whole generation. 

 Great hopes were centred in sewage farms as a 

 method of disposing of the sewage, and the various 

 local authorities hoped at the same time to reap a 

 profit from the cheap manuring of the land. Sewage 

 farms, however, rarely pay in a humid climate such 

 as ours, for the land cannot deal with the huge 

 amounts of water brought down from the sewers. 

 Many other methods were tried, but in all of them 

 the investigators failed to recognise the existence of 

 the tiny scavengers .which Nature provides to deal 

 with our waste products. 



The modern method of sewage purification was 

 evolved after Pasteur's discovery of the bacteria 

 which induce fermentation, and, after the work 

 of Warington and of Winogradsky on the 

 nitrifying bacteria in the soil. The purification 

 is carried out in two stages. The first stage 

 is treatment in the "septic tank," through which 

 the sewage passes extremely slowly. The solids sink 



NO. 2651, VOL. 105] 



to the bottom, where they are attacked by anaerobic 

 organisms flourishing there, and ultimately either 

 liquefied or turned into gas. The second .stage of 

 the process consists in the oxidation of the dis- 

 solved polluting matter. This matter has to be 

 brought into contact with a large supply of atmo- 

 spheric oxygen in the presence of certain small 

 organisms which are able to oxidise the organic 

 materials. This contact may be effected in the 

 soil, in a specially constructed filter, or in a large 

 volume of water. When soil forms the contact bed, 

 purification is brought about either by "filtration," 

 when the sewage percolates downwards through the 

 soil, or by "broad irrigation," when the sewage 

 merely passes over the soil surface. The method 

 chosen depends on the openness or otherwise of the 

 soil and subsoil. When suitable land is not available, 

 artificial filters are made of broken clinker, destructor 

 slag, ^tc. These materials provide a home for the 

 nitrifying bacteria. The sewage is allowed to trickle 

 slowly through, and with a good filter a purification 

 of 80-90 per cent, is effected. When purification is 

 allowed to take place in water, the volume of the 

 water into which the sewage flows needs to be about 

 five hundred times greater than the volume of the 

 sewage. 



Engineers had just settled down to the septic 

 tank and trickling filter as the standard method 

 for sewage purification when the "activated sludge" 

 process was introduced by Drs. Fowler and 

 Ardern. In this process the whole purification is 

 completed in a tank provided with particles of acti- 

 vated sludge to serve as homes for the nitrifying 

 bacteria. The sludge {}..e. solid deposit from the 

 sewage) is activated by being submitted to currents 

 of air for several days. It is then placed in the 

 tank with the sewage, and air forced through for 

 some hours until purification is effected. The draw- 

 back of this method is the great bulk of the resultant 

 sludge, and the problem now is to find an economical 

 wav of disposing of the sludge so that the plant-food 

 which is contained in sewage shall not be wasted. 



Experimental Cottage Building. '\ 



N view of the present housing difficulties, con- * 



T IN view 



-^ siderable interest has been centred in the results 

 of the experiments in cottage building which have 

 been carried out on the Ministry of Agriculture's 

 Farm Settlement at Amesbury. These results are 

 published in the Weekly Services for May 15 and 22, 

 where we also learn that on Wednesdays for two 

 or three months competent guides have been avail- 

 able to show visitors the experiments actually in pro- 

 gress. Tha present scheme includes thirty-two cot- 

 tages, sixteen of which are for comparison purposes, 

 and are built of brick on normal lines of construction, 

 while the other sixteen are more directly experi- 

 mental. Each cottage consists of parlour, living- 

 room, scullery, bath-wash-house, larder, fuel store, 

 etc., on the ground floor, with three bedrooms on the Ij' 

 upper floor. Experiments in building in chalk include, •;• 

 a cottage with cavity walls built of blocks made of *'' 

 chalk and cement, one with walls of chalk and cement f; 

 rammed between shuttering, one with walls of chalk '^ 

 alone (chalk pis^), and one with walls of chalk and ■,,!^ 

 straw (chalk cob) built without shuttering. There is ;;: 

 also one cottage of monolithic reinforced concrete and 1 

 two concrete-block cottages with hollow walls. These H 

 two -cottages are being erected under contract by two T j; 

 proprietary firms; for all the other experimental cot- t| 

 tages direct labour is employed. The experiment also H 

 includes a oair of timber-framed cottages faced with ij 



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