BACTERIAL PURIFICATION 257 



Under the microscope it showed aquatic larva cases, frag- 

 ments of winged insects, numerous anguillulse, Crustacea 

 (Daphnia), rotifers, infusoria (monas, paramoecium, vorticella), 

 algae (cladophora and species of conferva), cladothrix, beg- 

 giatoa, fungus-mycelium, black particles, probably coke, brown 

 amorphous matter, silicious particles, vegetable hairs and fibre.^ 



Humous matter is favourable and even necessary for subse- 

 quent nitrification (p. 123). Humic acid in presence of water 

 absorbs large quantities of ammonia.^ 



Dibdin and Thudichum found that the suspended solids in 

 the tank effluent averaged nearly 20 parts per 100,000 less than 

 those in the sewage, equivalent to 24*6 tons of solid matter 

 removed by the tank in a year. In August, 1897, one year 

 after the tank had been started, the solid matter in it was found 

 to be 5 tons, therefore the difference, nearly 20 tons, had dis- 

 solved and in great part disappeared as gas. This result has 

 been confirmed in other cases : Mr. Fowler found that in the 

 experimental tank at Manchester about two-thirds of the sus- 

 pended solids were removed with the production of little sludge. 



At Oldham it was estimated that 15*63 grains per gallon of 

 suspended solids were equal to i ton of sludge per million 

 gallons : the quantity of sludge entering the septic tank in 1901 

 was 278, and the amount leaving 117 tons, the difference, 

 161 tons, " having been either left in the tank, converted into 

 gas, or liquefied." After 12 months' working the water in the 

 tank was lowered, and there was found to be not more than 

 2 ft. of sludge at the bottom, in a very liquid condition. " The 

 smell from the sludge was not so objectionable as in the case 

 of ordinary sludge from a fresh tank." It readily dried, and 

 then had an earthy odour and the appearance of garden mould.^ 



Evidence before the R. Commission on Sev/age confirmed 

 this digestion of organic matter and showed its variations.* 



The flow through the tank is continuous, and requires no 

 attention, while the submergence of inlet and outlet minimises 

 disturbance of the contents. At the far end, a transverse iron 

 pipe, about a foot below the level of the liquid, with a slot on 

 the under surface extending its length, forms an exit for the 

 effluent, which passes into a small cistern with a V-gauge, and 



^ Trans. Soc. Engineers, 1900, p. 247. 



'^ Oesterr. Chem. Zeit., 1900, iii., 516. 



3 Report by Dr. Wilkinson, M.O.H. to County Borough of Oldham. 



^ Interim Report, vol. ii., 1902. 



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