Fig. 108.—Fixed Distributor.
A different type of fixed distributor is that manufactured by Messrs. J. Blakeborough and Sons. This apparatus, patented by Messrs. Haller and Machell, Civil Engineers, is used in the triple tank system of sewage treatment. [Fig. 109] illustrates the “Aerat” type, which consists of cast-iron channels supported on wrought-iron joists carried upon piers. Each length has six orifices on each side, through which the sewage passes on to small trays provided with radiating grooves on the top and dripping points on the under side at the edge. As the distributors may be fixed within a few inches of the surface of the filter, very little head is required to operate them.
Fig. 109.—Fixed Distributor.
A very ingenious form of fixed distributor, [Fig. 110], is supplied by the Septic Tank Company, Ltd. From its name, “Capillary Trough Distributor,” it will be observed that during normal and minimum rates of flow, capillary attraction is utilised to deliver the sewage on the filter in the form of drops. The tank effluent is delivered to each trough distributor over brass V-notches, set in the side of the main channel, into which the tanks discharge. These V-notches are adjustable, and are set so as to prevent their being tampered with subsequently. The trough distributors are of artificial stone, true from end to end, and set level. Over both their edges copper wires are fixed, at intervals of a few inches, each wire extending from within a short distance of the bottom of the trough channel over the edge and down to the underside of the trough. On a trough being filled the liquid overflows right along the edge, and is attracted by and runs down the wires, so that if the flow is at all excessive a little stream will run down each; on the flow subsiding to the ordinary, a drop-by-drop delivery commences; should the flow of sewage cease altogether for any length of time, the wires will go on dripping until they have drawn off the contents of the trough, almost to the end of the wires. On a fresh supply of sewage arriving at the installation, and the troughs refilling to a higher level, the rate of delivery from the wires will increase until it keeps pace with the flow, thus ensuring an even distribution on the filter throughout the day. There is no loss of head in connection with this apparatus beyond the depth of the distributing troughs themselves.
Fig. 110.—Capillary Trough Distributor.
Spray Jets.—This type of distribution is not used in many installations in this country, but it has been adopted in large schemes in the U.S.A. There are a number of different types, including those in which the sewage is forced upwards through a nozzle and falls back on the surface of the filter, and others in which the sewage flows through inverted nozzles, and each jet impinges upon a fixed cup or disc of metal, or other material, and is thus spread out on to the filter. Among the former, one of the simplest types is that manufactured by Messrs. Adams Hydraulics, Ltd., [Fig. 111], in which, by means of a square baffle plate, provided with suitable grooves, the spray is forced out in such a manner that it covers a square area of the filter. It is claimed for this that it covers the whole surface and no portion of the filter is wasted, as in the case of round jets which cover circular areas. The same firm also supply several other types of fixed sprays, as shown in the illustration.