152 SEWAGE AND ITS PURIFICATION 



tion and dissolving may occur. Pumping causes some of the 

 organic matter in suspension to disintegrate, and thus renders 

 it more easily soluble. Agitation with pulverization of the 

 organic solids has been the subject of many patents. 



At Manchester up to 1897 the heavy insoluble matter brought 

 down with the sewage (sometimes as much as 300 tons after a 

 flood) was deposited in the precipitation tanks, from which it had 

 to be removed by manual labour at considerable cost. Catch- 

 pits were then interposed " to intercept large solids which might 

 cause damage to the machinery," with movable coarse screens 

 balanced by weights so that they could be raised for cleaning. 

 Finer screens, with mechanical rakes, were fixed at the outlet. 



London sewage is screened through iron gratings, and in 

 1897 it was stated that the weight of the screenings was 

 between 80 and 100 tons per week. A destructor furnace 

 built close by was used for destruction of the refuse. Screening 

 is also mentioned at Friern Barnet, Oldham, Swinton (''strainer 

 with cleaning rakes attached"), Glasgow (" wrought-iron grid 

 to catch heavy and floating matter "), Accrington (*' screening 

 chamber where detritus is deposited, with wrought-iron grid to 

 prevent floating and large substances from passing into the 

 precipitation tanks. A revolving fork arrangement cleans the 

 screen by lifting the deposited material to the surface. 

 The chamber has also a hopper-dredger for removing the 

 detritus that accumulates at the bottom"), Kingston ("Native 

 Guano process"), Launceston (" ferrozone and polarite ") ; in 

 fact, all places and systems except those with a preliminary 

 hydrolysing tank find it necessary to separate the coarser organic 

 matters mechanically. 



At Melbourne, Victoria, the city sewage is pumped into 

 *' straining-cages," and the material caught in them is subjected 

 to steam at 292° F. (45 pounds pressure), "which should 

 effectually render the material innoxious." The dry result is 

 destroyed in a furnace, as of no manurial value. In 1899-1900 

 it amounted to 961 tons, or 141 tons after drying.^ 



Roughing Filters.— In Colonel Waring's, used in the first stage 

 of his system in the United States, a lo-inch suction - pump 

 delivered the solids and liquids on to a shallow bed of broken 

 stone, divided by a vertical partition ; when one side became 

 choked the other was used. From this it passed into "strainers" 



^ Report by W. Thwaites, Chief Engineer to Melbourne Board of Works, 

 April, 1 90 1. 



