NORTH SYDNEY AND DOUBLE BAY SEWERAGE SCHEMES. XVII. 



as an overflow for the main sewage conduit near the tanks, and 

 relieves the works of any exceptional flow of storm water during 

 continuous heavy weather. The filter beds are protected on 

 the harbour frontage by a rubble dyke, and a jetty has been 

 provided for the purposes of the works. 



Two contracts were let for the construction of the outfall 

 works. One included the preparation of the site for the treat- 

 ment works, and the formation of the filtering areas and the 

 construction of stormwater and effluent channels. The second 

 contract comprised the erection of the tanks and buildings, as 

 well as the supply and installation of the air compressing 

 machinery and fittings. 



The air compressing plant consists of a Tangye horizontal 

 steam engine, type H, which drives a horizontal double-acting 

 air compressor. The air compressing cylinder is 11 in. diameter 

 and 18 in. stroke, with water jacket and all necessary fittings. 

 The inlet valves are opened and the outlet valves closed 

 automatically. 



The sewage upon reaching the treatment works first passes 

 through the screening chambers, which are in duplicate. The 

 screens are of wrought iron bars, and can be lifted alternately 

 and cleaned of the floating solids retained, which are burnt in 

 the destructors. The sewage, after screening, flows along a 

 winding channel, where a concentrated solution of lime, prepared 

 in a mixer in the adjoining room, is admitted into the stream. 

 The supply of lime can be regulated according to the flow of 

 sewage. The quantity to be used, which is at the rate of 1 ton 

 for every 1,000,000 gallons of sewage, is shown by a dial 

 indicating the flow of sewage passing into the works from the 

 main sewer. 



The sewage next passes through a cast iron rotatory agitator, 

 or churn, embedded in the conduit, and the lime is thereby 

 thoroughly incorporated with the sewage. The agitator and 

 lime mixer are driven by shafting and belting from the engine in 

 the basement adjoining. 



