102 



SEWAGE PURIFICATION AND DISPOSAL, 



perforated plate was a layer of flint, 

 through ■which the liquid portion ro?e un- 

 til it reached the level of the outlet drain. 

 The mean depth of the filtering material 

 was 14in,, and the space underneath the 

 plate 5 cubic feet. 



Mr. Scott-Moncrieft' states that the in- 

 variable result, where he put down instal- 

 lations of these tanks, based upon an al- 

 lowance of 3 or 4 cubic feet for each in- 

 habitant served, has been the almost com- 

 plete liquefaction cif the solid matter, and 

 the sludge in everj'^ case was a negligible 

 quantity. His next step was to pass the 

 effluent from the cultivation tank through 

 shallow, open earthenware drains filled 

 with coke, but it appears that this treat- 

 ment had very little effect upon the efflu- 

 ent. However, it was observed that when 

 it passed into an almost stagnant, but 

 bacterially very active, ditch, m the pro- 

 portion of one to three respectively, the 

 effluent purified what was before a pol- 

 luted stream. This fact (which to many 

 may be hard to believe) will again be de- 

 monstrated further on in this paper, when 

 dealing with experiments carried out with 

 the Manchestei sewage. 



Using Mr. Scott-Mon Crieff's own words, 

 he states that this proves two things: — 

 •'First, that the ditch was a very active 

 oxidising agent; and, secondly, that the 

 organic matter coming from the 'cultiva- 

 tion tank" was in a condition highly sus- 

 ceptible to further oxidising changes, and 

 was in a much more unstable molecular 

 condition than the raw sewage, which had 

 seriously polluted the stream when un- 

 treated. """ 



He next devised a highly oxidising ap- 

 paratus consisting of nine wooden boxes 

 (perforated). Tin. deep, and each having an 

 area of 1 square foot, which he placed 2in. 

 apart and above each other. These he 

 filled with coke about the size of beans. 

 In utilising the filtering material for re- 

 storing oxygen to the sewage to the fullest 

 extent, he used V-shaped tipping chan- 

 nels, so that the liquid would be evenly 

 distributed. 



Installations have been carried out on 

 this plan in several places, notably at 

 Birmingham, at Chelmsford, and at Ca- 

 terham, under the sanction and authority 

 of the War Department. At the latter 

 place there is exceedingly strong sewage 

 from the barracks, which accommodate 

 1,200 persons. 



Dr. E.ideal, who was asked by the War 

 Department to report on the efficiency of 

 the installation at Caterham, states the 

 results are satisfactory, and that "the 

 process has been successful in destroying 

 completely four-fifths of the total organic 

 matter present in raw sewage." 



Septic Tanks. 



Under the septic tank system the larg-i 

 est installation as yet carried out is atj 

 Barrhead, where the works are designed' 

 to serve a population of 10,000, and to puri- 

 fy a maximum flow of sewage and storm 

 water of 400,000 gallons per day. 



The works consist of two grit chambers, 

 four septic tanks, and eight bacteria beds, 

 all of which are built with concrete. The 

 sewerage main discharges into the grit 

 chambers, from which the sewage passes, 

 without screening, into the septic tank. 



When the septic tank system was first 

 introduced it was thought that it was ne- 

 cessary to exclude all light and air. It 

 is now found by experience that the results 

 obtained from raw sewage are the sanie 

 whether the tanks in which the anserobic 

 microbes are active, is covered or open. 

 This may be due, perhaps, to the coating 

 of hard scum which is formed in the tank, 

 and which would tend to exclude the light 

 and air. 



There may be cases, however, where, for 

 various reasons, it would be advisable to 

 cover the tanks. For all practical pur- 

 poses it is settled beyond dispute that the 

 open is as efficient as the closed tank. 



Manchester Sewerage. 



To prevent the pollution of the Man- 

 chester Ship Canal, in 1896 proceedings 

 were instituted against the Corporation 

 at the County Police Court, and an order 

 made calling upon the Council to do what 

 was necessary within 12 months. Thig 

 period has had to be extended, as it was 

 found impossible to make the necessary 

 experiments to enable » conclusion to be 

 arrived at in the time given. 



Eventually a scheme was prepared for 

 conveying the effluent from Davyhulme to 

 the tidal Rivftr Mersey at Randall's 

 sluices. When this scheme was referred 

 to a poll of the ratepayers it was rejected 

 bv a large majority. Messrs. Latham, 

 Frankland, and Perkins, experts, who 

 were called in to advise the Council upon 

 the question, supported the ratepayers in 

 their decision. 



The Council thereupon decided to ap- 

 point the three experts already named to 

 advise them and report on the whole ques- 

 tion of sewage purification and disposal. 



Up to this time no adequate experience 

 had been gained in the use of bacteria beds 

 with sewage diluted with trade refuse. 



Upon getting to work the experts named 

 confined their attention to t"he three me- 

 thods which had been already before the 

 Council : — 



1. Treatment by land. 



2. Conveying the effluent into tlie tidal 

 portion of the rivei. 



3. Bacterial treatment. 



