BY EDWIN H. WILKINSON. 



103 



Regarding the question of land treat- 

 ment, they agreed with the committee in 

 rejecting it; firstly, on account "of the 

 great initial cost of land, drainage, con- 

 duits, laying out, etc.;" secondly, "of the 

 obvious difficulty of obtaining a sufficient 

 area;" and, thirdly, "of the general un- 

 fiuitability of the land in and around 

 Davyhulme." With respect to this, they 

 instanced the case of Birmingham, which 

 is now feeling the formidable dimensions 

 of its sewage farm to such an extent that 

 other and more compact modes of dealing 

 with the sewage are being undertaken. 



The extension of the sewer to Randall's 

 sluices was condemned from an engineer- 

 ing point of view. 



IJnder their direction, certaia beds were 

 constructed at Davyhulme, and experi- 

 ments were made with them. The filter- 

 ing medium used in the upper bed was 

 clinker. Sin. to Im. gauge; and in the 

 lower bed lin. to iin. gauge. Two other 

 beds of similar size, and a fifth, much 

 smaller, were afterwards added, but the 

 clinkers used were of much smaller mesh, 

 as it was found that the coarser filters al- 

 lowed sludge to get into the body of the 

 bed, and so into the drains below. The 

 material used in the third, fourth, and 

 fifth beds varied from fin. to iin. mesh. 



Settled sewage was first used, the beds 

 being filled once each day for the first 

 week, and twice a day for four weeks. The 

 beds, having acquired a high degree of 

 efficiency at the end of this period, were 

 filled three times a day for a further term. 

 As the application of settled sewage was 

 attended with such satisfactory results, 

 it was decided to apply raw sewage on the 

 same lines. For the first month the raw 

 sewage was applied once each day, and 

 the settled sewage twice. This having 

 proved satisfactory the raw sewage alone 

 was applied three times a day, and was 

 continued for nearly two months, when 

 four fillings per day were tried. After 

 the first week the rough bed showed signs 

 of clogging; and settled was therefore re- 

 sorted to. ' The experiments with tnese 

 beds have extended over a period of two 

 years. The effluent from septic tanks 

 was, instead of settled sewage, ulti- 

 mately passed through the beds. The 

 capacity of the beds was at hrst 

 rapidly reduced, but when the solids in 

 suspension from the raw sewage had pre- 

 viously been removed, by bacterial action 

 in the septic tank, and the beds had got 

 fairly to work, they maintained a capa- 

 city of one - third of the capa- 

 city of the bed without filtering 

 material. When a bed fell below this 

 proportion a short period of rest would be 

 the means of restoring it. The larger 

 beds were constructed to contain 10,000 

 gallons before the clinkers were put in, 

 and when working their capacity was 

 3,333 gallons. 



The beds were treating the effluent from 

 the septic tank at the rate of 6{)0,000gal. 

 per acre, with a resultant degree of purifi- 

 cation of 0.5 grains per gallon oxygen ab- 

 sorption in 4s hours; and 0.04 grains per 

 gallon of albumenoid ammonia. The 

 limits of impurity adopted by the Mersey 

 and Irwell joint committee (the authority 

 which has the responsibility of the con- 

 servation of the rivers in question) is 1 

 grain and .1 grain respectively. 



In their report the experts say: "The 

 results of the treatment of the open septic 



tank effluents have, from the first, 



surpassed our most sanguine expectatian.''' 



It has been found, with the use of the 

 effluent from either open or closed septic 

 tanks, one contact with a bacteria bed lias 

 been sufficient to secure adequate purifica- 

 tion. 



At the end of 1898 an experimental in- 

 stallation of the septic system was got to 

 work. After it had been working about 

 nine months to trv its powers of dissolv- 

 ing solids, garbage was tipped into the 

 tank. After 279 barrow-loads were put 

 in, it was decided to cease. _ Ihe tank 

 was constructed in size sufficient to hold 

 half a day's supply of sewage. If it had 

 been used as a precipitating tanli:, at the 

 end of fourteen months the quantiiy of 

 sludge produced would have been about 

 12,000 tons, but, upon being emptied, it 

 was found to contain 4,000 tons of sludge, 

 and the garbage had been wholly dissolv- 

 ed. The greater portion of this residue 

 was inorganic matter; the proportions 

 were 60 per cent, inorganic and 40 per cent, 

 organic. A large proportion of the in- 

 organic matter, if not the whole, is recog- 

 nised to consist principal'y of silt from 

 the street surfaces, and silt pits are oemg 

 specially constructed to intercept it before 

 the sewage reaches the septic tank. The 

 rapid rate at which the sewage was passed 

 through the tank may account for the 

 comparatively large amount of organic 

 matter, 1,333 tons. Notwithstanding this. 

 It is a very great attainment to have suc- 

 ceeded in destroying two-thirds of the 

 solid matter, and that, too, when passing 

 the sewage through the tanks twice as fast 

 as is usual in other places. Experiments 

 made at other places show that the most 

 perfect bacterial action is obtained by 

 allowing the contact to be twenty-four 

 hours. A closed septic tank was treating 

 sewage during the whole time the sewage 

 was passing through the open septic tank, 

 and samples of the effluent, taken under 

 similar conditions, show that the results 

 for all practical purposes may be regarded 

 as the same. 



The sludge which is not retained in the 

 septic tank passes away in a highly-divid- 

 ed condition in suspension, and by gasi- 

 fication. 

 From samples of the effluent taken from 



