TRADE EFFLUENTS 341 



. Hops in large quantities are particularly difficult to deal with, 

 and may be easily intercepted at the breweries. 



At many places, as for example Dorchester, when brewery 

 refuse is present in the sewage in large quantities, a '* pig-pen " 

 odour is noticed at the septic tanks and sprinklers, and the 

 author has suggested in order to obviate this aerial nuisance, a 

 partial treatment with chlorine. When the works are far 

 removed from habitations, bacterial treatment of such sewage, 

 as shown by Dr. Barwise at Burton, and Dr. Maclean Wilson 

 in the West Riding of Yorkshire, can be accomplished without 

 any difficulty. 



The treatment of " burnt ale," or " pot ale," from distilleries 

 has received much attention in Scotland : it contains about 

 45 times as much total solids as ordinary sewage, and when 

 precipitated by lime it gave a manure worth about 70s. per ton, 

 but the liquor that was left was quite unfitted to be turned into 

 any stream without further purification. Evaporation, and 

 blowing into furnaces or smoke stacks in spray, have presented 

 difficulties owing to its stickiness and corrosive action on metals. 

 At Mortlach distillery, according to Dr. Cowie, it had been 

 treated successfully by tanks, coke beds, and coarse sand filters. ^ 

 But by themselves brewery and distillery wastes are treated 

 with difficulty on bacterial filters directly, owing to the forma- 

 tion of acids. The Hook Norton Brewery Company in 1900, 

 according to Naylor, impounded the strong liquor in a settling 

 tank for not less than 24 hours in contact with putrid sludge 

 from sewage, and when the putridity had once been established 

 throughout the liquid, sewage-sludge was no longer necessary. 

 The contents of this tank, which may be termed an " anti- 

 souring" rather than a septic tank, are pumped continually on 

 to a coal filter; the little suspended matter present after the 

 first filtration is intercepted by shallow sand filters, and the 

 effluent is clear, neutral, colourless, sweet, contains nitrates, 

 and about o'l part per 100,000 of albuminoid ammonia. The 

 diminution of dissolved oxygen after saturation is less than 

 30 per cent. Naylor states that a number of works in the 

 north of England now use a septic tank holding not less than 

 3 days' flow, started by old sewage sludge, and fed with a 

 mixture of waste liquors with not less than 5% of domestic 

 sewage. He finds that the species of bacteria so introduced 

 have the effect, partly by generating ammonia and so neutraliz- 



^ /. R. San. Inst., igoo. 



