514 SECTIONAL TRANSACTIONS.—G. 
By the extraction and analysis of the gases occurring in polluted waters 
undergoing oxidation it has been possible to study the changes accompany- 
ing the destruction of impurities occurring in true and colloidal solution in 
such waters. Thus it has been established, within the limits of experi- 
mental error, that equal volumes of the same polluted water undergoing 
aerobic fermentation consume equal quantities of oxygen and give rise to 
products which are constant in quantity, provided always that dissolved 
oxygen be present in excess. 
The rates of solution of oxygen and nitrogen by fresh and salt waters 
have been determined and a well-defined mathematical equation obtained 
connecting rate of solution, surface exposed, volume of water, temperature 
and degree of saturation. 
Air dissolved by water at its surface does not remain concentrated in the 
surface liquid but sinks more or less rapidly, causing aeration to depths of 
at least 10 ft., a process for which the term ‘ streaming ’ has been adopted. 
Mr. JouN Hawortu, M.B.E.—Bio-aeration or activated sludge 
(10.40). 
Mr. Frank C. Voxes.—The treatment and utilisation of sludge 
(10.55). 
Toward. the middle of the last century the frequent epidemics, which 
attacked urban populations, aroused public opinion, and gave rise to the 
gradual development of pure water supplies, water carriage of the excreta, 
the removal of the settleable solids from the sewage, and the oxidation of 
the foul water. 
Anticipations of a rich financial return from the general application of 
the settled solids to the land have not been realised. In many cases it is 
necessary to dispose of this offensive matter or sludge on site. Its character 
can be completely altered by subjecting it to a process of digestion. 
At the works of the Birmingham Tame and Rea District Drainage Board 
is treated the sewage from a population of 1,200,000. The watery mass of 
highly odorous material known as sewage sludge is digested in separate 
tanks in two stages, pumped on to drying beds, lifted and dumped. There 
is no nuisance from smell. 
The size of the works required for carrying out this process has been 
materially decreased recently by utilising the gaseous products of the 
digestion process. The power required for other purposes has been 
supplied continuously by consuming the sludge gas in engines having 
a total of 1,000 horse power, the waste heat abstracted from the engine 
cylinders and from the exhaust gases being used to raise the temperature 
of the digesting sludge. 
The rate at which digestion occurs depends very largely upon temperature, 
and the provision of means for maintaining the digesting sludge at a uniform 
temperature enables a sewage works to be independent of any outside source 
of power. 
Mr. H. R. Lupton.—Machinery for dealing with sewage (11.10). 
The paper is intended primarily as an appendix to those dealing with 
sewage treatment. It deals only with the mechanical appliances involved, 
not with constructional and civil works. 
The mechanical appliances are divided into four categories according -as 
they deal with (a) crude sewage, (b) sewage liquor, (c) sludge, (d) screenings. 
