Sewage Irrigation at Bishop's Stortford 



373 



settle to the bottom, and consequently there 

 are no horizontal screws or ascending and 

 descending dredging buckets for clearing out 

 the sludge. There are no extensive and costly 

 filter beds to arrest the particles held in 

 suspension by the sewage percolating through 

 them and requiring renewal after a certain 

 period of use. Neither is any elaborate con- 

 struction of revolving screens, or indeed, any 

 machinery whatever, adopted for straining 

 the turbid sewer water. Hence, it is quite 

 possible that the ingenious plan found effec- 

 tual for its purpose at Bishop's Stort. 

 ford may not be viewed with much favour 

 by Sanitary Engineers whose ideas are 

 prone to run upon complicated con- 

 trivances, clever mechanism, massive erec- 

 tions, and so on. Economizing space and 

 time, the principle followed is to intercept 

 the thick matter in the stream of sewage, 

 not when quiescent, but while it flows ; and 

 the merit of the invention lies in the dis- 

 covery of a screen which allows the liquid to 

 pour rapidly through, yet detains nearly the 

 whole of the suspended particles. Embankers 

 of salt marshes know well enough that a 

 faggot staked upon the surface flooded by 

 the tide will collect in its interstices the slimy 

 mud which is carried in the turbid current ; 

 and accommodating to a different use this 

 method of accelerating disposition, the Stort- 

 ford plan essentially consists in passing the 

 sewage horizontally through a vertical screen 

 or wall of faggots. In one of the small 

 receiving tanks (from which the sewage passes 

 through iron gratings to the pumps), Mr 

 Odams has placed an upright wall of osier- 

 bunches about 1 8 inches in thickness, and 

 extending 5 feet across the current of sewage 

 which flows through it. Perhaps common 

 thorn faggots would have been still better, and 

 the thickness as well as minimum surface area of 

 the screen must depend upon the volume and 

 velocity of the current of foul water to be 

 cleared by passing through. At Bishop's 

 Stortford the faggot-screen at 5 feet breadth 

 and standing some 4 feet into the water 

 presents a surface area of about 20 square 

 feet; and this is found sufiicient for the 

 screening or filtering of filthy sewage passing 



through at the rate of about 700 gallons per 

 minute. Large solids, bits of paper, &c., 

 together with a portion of the slime deposited 

 upon the obstructing face of the faggot wall, 

 fall to the bottom of the tank, which for this 

 purpose is made deeper than the lowest part 

 of the screen. The sediment which collects 

 upon the interstitial superficies of the faggot 

 bundles has to be extracted, say twice a week, 

 in order to preserve, or, rather, continually to 

 renew their straining capacity ; and this clear- 

 ance is accomplished in the easiest manner 

 imaginable. The faggots being raised out 

 of the tank, there is directed upon them a jet 

 of the clarified sewage issuing under pressure 

 from a flexible tube and hose, when they are 

 washed clean almost instantaneously. The jet 

 of course is drawn from the main pipe which 

 conducts the sewage from the pumps up to 

 the farm. Immediately behind the faggot 

 wall is a flat vertical screen of copper wire 

 gauze, of fifty meshes to the linear inch ; 

 so that very fine scum which may find 

 its way through the apertures of the 

 faggots is caught upon its surface. The 

 gauze, stretched upon rectangular frames 

 sliding in grooves, can be withdrawn in 

 sections, for the purpose of being occasionally 

 (perhaps daily) cleansed by a douche, in the 

 same way as with the faggots. This arrange- 

 ment is the invention of Mr Isaac Brown, of 

 Edinburgh. While the unscreened sewage 

 has a very offensive odour, the sewage after 

 flowing through the screen is comparatively 

 sweet : it can be applied in irrigation with 

 scarcely any perceptible smell, and as it is 

 so far clarified as to be but very slightly 

 cloudy, it is free from liability to deposit 

 noxious sediment in carriers and gutters, or 

 upon the blades and leaves of plants. It will 

 be observed that the solid matter of the 

 sewage is obtained in mass without the 

 addition of lime, clay, or any chemical in- 

 gredient whatever; so that the weight of 

 sludge to be dealt with is only that originally 

 present in the discharge from the town drains. 

 Mr Odams' proposal is to mix with the 

 sludge (after removal with the tank) an 

 equivalent of dry eartli, loam, clay, or what- 

 ever soil is readiest to hand, the necessary 



