Fig. 143.—Contact Bed Apparatus.
Fig. 143a.—Contact Bed Apparatus.
Another apparatus which has been used largely in the past is that supplied by the Septic Tank Company, Ltd. This apparatus is made in two forms, illustrated in [Figs. 141] and [142]. The chief difference between the two types is that in the one case, [Fig. 141], the period of contact is controlled by the filling of the next bed, and is thus dependent upon the rate of flow of the sewage, while in the other case, [Fig. 142], the period of contact is “timed” for from one to two hours, and is independent of the rate of flow of the sewage. In both cases each set of gear is built up on its own bed-plate, and comprises the inlet and outlet valves and the connecting pipes to and from the same. The valves are of the simple spindle-type, and are connected by rods to rocking levers and actuated by buckets or floats, working in chambers or pits which are in communication with the different beds. By means of overflows from the beds to the buckets, and other devices, the various portions of the gear are actuated in such a manner that they automatically fill the several beds in each set in regular rotation, hold them full for contact, and eventually discharge the treated liquid to the effluent drain. Full details of the method of operation can be obtained from the manufacturers, who claim that the gear will work satisfactorily without attention other than the oiling of the bearings and joints every few weeks.
Another type of automatic apparatus for contact beds is that manufactured by Messrs. J. Blakeborough and Sons, as used in the Triple Tank System of sewage treatment, [Fig. 143]. In this case the beds are arranged in sets of three, and the filling of each is effected by the overflow from the last bed filled, the discharge being effected by the rising of the liquid in the last bed filled. The apparatus consists broadly of a slide-valve controlling the outlet-pipe, and connected by levers to floating cylinders located in separate chambers. One chamber controls the opening and the other the closing of the valve. The outlet is provided with a rising and falling arm, which is connected by a lever to a balance float fixed in a chamber, and coupled by means of a pipe to the float-chamber of another bed. The method of operation is us follows:—The tank effluent flows by gravitation to bed A, the filtered effluent thus rising in outlet chamber A, and also in the overflow chamber which is connected by pipes to outlet chamber A. As soon as bed A becomes full, the filtered effluent overflows into closing chamber A, which is coupled by a pipe to opening chamber B, and the floating cylinders in each case are raised, with the result that the valve of bed A closes and the valve of bed B opens, the liquid thus commencing to run on to bed B. The same action as above is repeated when bed B is full, and bed C is to be filled, whilst bed C in turn is coupled to bed B, so that the triple action is repeated over and over again so long as sewage continues to flow to the beds. As bed A fills, the liquid rises in outlet chamber A, and, this being coupled to float chamber C, the liquid rises to a corresponding height in float chamber C. Some time elapses before the liquid rises to such a height in the float chamber as to sink the mouth of the outlet pipe below the surface of the liquid in the outlet chamber, this space of time (which can be regulated as desired) representing the length of time that the bed is allowed to stand full before commencing to empty. When the liquid has risen to a given height in float chamber C, the balance float is raised, this action tipping the lever and lowering the rising and falling outlet pipe in outlet chamber C, thus drawing off the effluent from the top slowly, and without disturbing the whole contents of the bed. (Note: Bed C is assumed to be full). After the liquid in the bed has been drawn off, the rising and falling outlet pipe remains stationary at the bottom of the chamber until the next action takes place, which is as follows:—When bed A becomes full, it is allowed to stand full until the liquid in bed B (now filling) has risen to a given height, when it raises the balance float in the float chamber A in a similar manner as described above, and thus empties the bed A, at the same time emptying the float chamber C, in which is fixed the balance float connected to the rising and falling outlet pipe of the bed C (now standing empty), thus raising the outlet pipe and rendering the bed again ready for use.
