Fig. 52.—Pneumatic Chemical Mixer.
Sewage Mixers.—Even after the chemical solution has been added to the sewage, it is necessary to make sure that it is thoroughly mixed with the sewage. The simplest method of doing this is by means of baffle-plates fixed in the channel leading to the tanks. Other methods are by paddle-wheels driven by the sewage itself; by allowing the sewage to drop in a chamber on to a projecting pier or stone; by using power to drive (a) a plunger moving up and down in a sump, (b) a vertical shaft to which horizontal paddles are attached to rotate in the sewage channel, (c) to operate a device similar to the well-known mechanical egg-whisk, (d) or to force compressed air through a perforated pipe laid in the sewage channel. Indeed, there is no end to the various mechanical devices which are used for this purpose.
Fig. 53.—Sludge Press.
Fig. 54.—Sludge Press.