1921.] Wright.—Chemical Technology of Meat Industry. 163 
and where this is not adopted disposal by broad irrigation or sewage 
farming is carried out. It is not proposed to consider here the methods 
of sewage-disposal as practised, but to indicate the nature of the material 
constituting the sewage from a factory which works up its own products 
and by-products, as is usually done in this country. The figures quoted 
are taken from results obtained in this country, and have been found to 
agree closely with those recorded for Chicago packing-house sewage. No 
figures can be given as regards the volume of sewage discharged from 
New Zealand freezing-works, but it is of interest to note that the volume 
of Chicago packing-house sewage is approximately 50,000,000 gallons a 
day. 
Each 1,000,000 gallons of sewage contains 50,6501b. of total solid 
matter, of which 24,4101b. is organic matter, containing total nitrogen 
2,5601b. and fat 3,7201b. It is thus seen that the normal sewage from a 
freezing-works is composed of approximately \ per cent, of solid matter. 
This solid matter is made up of the undigested food in the alimentary tract of 
the slaughtered animals, the floor-washings of all departments, the washing- 
water contents from fellmongering operations, the lime, and the scudding 
and fleshing residues in pelt washing and curing, the sewage of employees 
on the factory, bath-houses, &c. Before discharge a considerable portion 
is passed through settling-tanks, from which the grease is skimmed. 
Numerous attempts have been made to recover the large amount of 
valuable nitrogenous and fatty matters which daily are lost in the sewage, 
but the initial difficulty—namely, that of the great dilution, and the com¬ 
paratively large amount of water which requires to be treated and handled-— 
has rendered ineffectual most of the attempts to recover the solids profit¬ 
ably. The only successes which have been attained so far have been in the 
direction of handling separately the more concentrated liquids, recovering 
the solids from these alone, and allowing the more dilute portion to be 
discharged in the usual way. 
Recently, however, in connection with the handling of the Chicago 
packing-house sewage, following upon the successful operations which have 
been carried out in the treatment of sewage by what is known as “ treat¬ 
ment by the activated-sludge process,” some hope is given that a solution 
of the problem may be found. The essential principles of activated-sludge 
treatment may be briefly stated as follows : The process involves the forced 
aeration of sewage with a certain volume of previously aerated or activated 
sludge. The result of this treatment is to convert the suspended solids 
into a flocculent and very readily settling form, and to oxidize more or less 
completely both suspended and dissolved organic matters. The effluent 
after the settling-out of its sludge is clear and highly nitrified, and to a large 
extent freed from sewage bacteria. The sludge is high in water content, 
but rich in nitrogen. The Chicago commissioners who investigated the 
process strongly recommend it for the treatment of the packing-house 
wastes, and, as a result of their study of stockyards sewage, recommend 
quiescent settling, which they believe will concentrate the activated sludge 
50 per cent., filter pressing and heat drying to be used after settling. The 
estimated cost of pressing is given at $5-72 per dry ton, and the cost of 
drying $2*45 per dry ton. The figures are based upon the use of Berrigan 
presses (dewatering to 75 per cent, moisture content) and Ruggles-Coles 
direct-heat dryers (drying to 10 per cent, moisture content). They esti¬ 
mate that the dried sludge will average 5 per cent, ammonia, and will be 
worth $12 per ton. 
