Land Treatment of Sewagre. 



The test might have to be taken in conjunction with 

 the permanganate ' oxygen absorbed ' test, to pro- 

 vide against the (unlikely) contingency of an effluent 

 being a sterilised one ; and in the present state of 

 our knowledge it might also be advisable to safe- 

 guard it further as regards a maximum of nitro- 

 genous organic matter to be allowed in any effluent 

 at any time (measured, say, by the albuminoid 

 nitrogen), though this additional precaution might 

 in the end be found unnecessary. We think there 

 can be no doubt that, if it could be satisfactorily and 

 easily worked out in practice, a standard based upon 

 the above principles would deal equably between 

 effluents from strong and weak sewages, not favour- 

 ing the one at the expense of the other." (Part I., 

 page 65.) 



The following extract from Mr. Dibdin's book 

 (which has already been mentioned) agrees very 

 closely with the above suggestion. " The exact 

 degree o'^ aeration which an effluent thus kept 

 should maintain is a matter for further experience 

 to determine ; but if it does not fall below 60 per 

 cent of the maximum possible, no evil results need 

 be apprehended. Whenever the aeration of the 

 water of the Thames was found to exceed this 

 minimum there was no suggestion of nuisance, and 

 fish appeared in the areas which maintained this 

 degree of aeration. If, then, an effluent be added to 

 water in quantity exceeding that which would 

 actually be the case in practice, and the degree of 

 aeration at no time falls below the point indicated, 

 fish-life would be in no way interfered with. Further, 

 the power of a river to purify itself depends upon 

 the degree of aeration maintained ; and when this 

 exceeds the figure above mentioned there is not 

 the least fear of putrefactive processes intervening, 

 but aerobic purification continues, and all remaining 

 organic matter is rapidly oxidised. A most valuable 

 standard of purity might be arrived at by these 

 means. Suppose, for example, that a mixture of 

 one part of effluent and one part of fully aerated 

 water be allowed to stand in an open vessel of 

 diameter equal to the depth of the liquid, and that 

 the degree of aeration, ascertained daily for a certain 

 number of days, does not fall below an agreed figure 

 to be determined, then such effluent may be safely 

 admitted into any ordinary stream. In extreme 

 cases, when the only water in the brook is derived 

 in summer time solely from the sewage works, the 

 effluent must of course stand the test without any 

 dilution." (Pages 297 and 298.) 

 Baotario- I^''- Houston gives the following summary (Part 

 suml^. in., pages 187 and 188) : " Some diffidence is felt in 

 briefly summarising the foregoing conclusions. It 



is assumed that what follows in the way of summary 

 will be interpreted in the light of my more detailed 

 and guarded statements, and only accepted as valid 

 subject to the qualifying remarks and reservations 

 that have been previously brought forward. 



(1) The treatment of sewage on land (with the 

 apparent rather than real exception of Nottingham) 

 does not so modify the biological qualities of sewage 

 as safely to admit of the direct discharge of the 

 effluents from land processes into drinking-water 

 streams. 



(2) The bacterial flora of the soil on sewage farms 

 is apt to resemble that of sewage plus in a greater 

 or less degree the microbes characteristic of soil. 



(3) With regard to the ultimate fate of sewage 

 microbes sown broadcast on soil, a gradual destruc- 

 tion (relative, if not absolute) of the bacteria of non- 

 Bporing and adventitious sort seems to ensue when 

 the application of sewage to the soil is discontinued. 



(4) The bacterial flora of effluents from land pro- 

 cesses of sewage treatment is characteristic of the 

 bacterial flora of sewage, not of soil. 



(5) The average percentage reduction in the total 

 number of bacteria and in the number of B. coli 

 and spores of B. enteriditis sporogenes in the land 

 effluents as compared with the sewage is striking. 



(6) The best effluents from the different sewage 

 farms were remarkably modified in the direction of 

 purity, and easily satisfied my suggested bacterio- 

 logical standards for effluents destined to discharge 

 into non-drinking-water streams. 



(7) The average biological quality of the effluents 

 from the sewage farms, excluding Nottingham, was 

 not entirely satisfactory according to my bacterio- 

 logical standards (non- drinking -water streams). 

 Nevertheless, generally speaking, the effluents 

 came within measurable distance of ' passing ' the 

 primary and nearly always passed successfully 

 the secondary standards which have been provision- 

 ally adopted for working and comparative purposes. 



(8) It is extremely difficult for many reasons to 

 compare either (a) land filtration with ' surface 

 irrigation' or (6) land eminently well suited for 

 sewage purification processes with land less suitable 

 or of unsuitable sort. Thus as regards (a), surface 

 irrigation is commonly combined with some filtra- 

 tion, and in respect of (i) suitable land is usually 

 sewaged to a much greater extent than unsuitable 

 land ; consequently in the resultant effluent differ- 

 ences are masked which otherwise might be very 

 apparent. Of course, in point of fact, (1) filtration 

 and suitable land, and (2) surface irrigation and 

 unsuitable land, are usually correlated conditions. 

 There was no comparison between the effluents from 



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