Land Treatment of Sewage. 



colour. Nos. 267 and 274 showed this more par- 

 ticularly ; in No. 66 it is noted that the colour 

 was due to iron and not to peaty matter, and this 

 no doubt applies to the others also. After being 

 filtered some of the effluents were just tinged, but 

 others were still very brown. They had either no 

 smell at all or an iron smell; in one or two in- 

 stances the odour was so strong as to be suspicious, 

 but the presence of so much iron necessarily made 

 the characterisation of the smell more difficult than 

 usual. There was much lime and much sulphate 

 in solution, and also — as stated above — very con- 

 siderable quantities of iron, mostly in the state of 

 ferric hydroxide, partly in suspension and partly 

 in solution ; in the worse effluents some ferrous iron 



far enough in relation to the total nitrogenous 

 matter present. The effluents from the uncropped 

 arable land were the least nitrated. The results 

 showed that at the time of our observations the 

 land was getting rather too much to do, but they 

 also showed that it was capable of turning out good 

 effluents. It should not be forgotten, in connec- 

 tion with this criticism, that at Altrincham some 

 (though not much) storm water is also treated, 

 and that the whole of the sludge from tank or 

 lagoon is dug into the soil. . . . The rate of 

 filtration at Altrincham is probably fairly rapid." 

 (Part II., page 51.) 



The Bacteriological figures may be summarised 

 as follows : — 



BACTERIOLOGICAL ANALYSES (TOTAL NUMBER OF BACTERIA PER CO.). 



Sevrajre. 

 (9 samples.) 



Efflaent.* 

 (15 samples.) 



Streara.t 

 (1 sample.) 



(1) Gelatine at 20 deg.C 



(2) Agar at 37 deg. C 



(3) B. coli or closely allied forms (sayat least)... 



(4) B. enteriditis sporogenes (spores— say at 

 least) 



13,820,000 

 1,570,222 



50,000 

 70 



363,400 

 7,275 



400 



f 97 per cent 1 



( reduction ) 



(99 per cent^ 



(. reduction 3 



C Varied from ^ 



) at least 100 t 



I to 1,000, not \ 



t^ 10,000 -' 



f Varied from 1 



none in 1 c.c. I 



to at least 10, !■ 



but less than I 



100 J 



53,000 

 6,700 



At least 100 



rAt least 10, 

 ] but less than 

 (. 100 



• Satisfactory (1) 6, (2) 10, (3) 9 and (4) 11 out of 15 effluents in each case. 



t Volume of brook water to effluent was about 6 to 1 when sample was drawn, but normally the ratio is about 3 to 1. 



was also present. Strictly speaking, they would 

 have been the better for being strained or settled 

 before being run into a brook. Besides affecting 

 the smell, the presence of so much iron accounts 

 for the comparatively small quantity of dissolved 

 oxygen found in those effluents; under ordinary 

 conditions effluents of this class ought to have con- 

 tained more oxygen, although, on the other hand, 

 it must be remembered that the Altrincham efflu- 

 ents come from a weak sewage, and would there- 

 fore tend to take up oxygen more rapidly than 

 effluents of apparently the same chemical composi- 

 tion derived from a strong sewage. The dissolved 

 oxygen test is therefore to a great extent dis- 

 counted here." (Part II., page 50.) "The Altrin- 

 cham effluents were fairly satisfactory on the 

 whole, but the nitrification was not carried quite 



"Judged as a whole the results were certainly 

 good, since the majority of the effluents passed the 

 suggested standard for non-drinking-water streams. 

 From Mr. Kershaw's report it appears that although 

 part of the farm is peat land, this land is not used 

 for irrigation purposes. The area actually irri- 

 gated, although containing some peat, is of a 

 sandier character. It is possible that the peat 

 land, although considered unsuitable for sewage 

 purification purposes, may exercise some restrain- 

 ing influence on the multiplication of the bacteria. 

 But the satisfactory results are probably to be 

 ascribed to the porosity of the surface soil, and 

 the fine, white sand and gravel which Mr. Ker- 

 shaw describes as immediately subjacent to it. 

 Moreover, the sewage was in some respects not 

 very strong, and was doubtless diluted by subsoil 



20 



