Sewage disposal . al was nonputrescible and the cost of operation materiallyless. Thus the operation of a bed mainly of j—|-inch materialwith 1 foot of |-|-inch material on top and feet of l|-2|-inchmaterial below cost $ per million United States gallonsagainst $ for a bed of l|-2|-inch material. The average rateof operation is 900,000 United States gallons per acre per is effected by means of the fixed sprinkler describedon page 339. A general view of one of the beds is shown inFig. 108, and another view in winter in Fig. 109. After filtration the trickling effl
Sewage disposal . al was nonputrescible and the cost of operation materiallyless. Thus the operation of a bed mainly of j—|-inch materialwith 1 foot of |-|-inch material on top and feet of l|-2|-inchmaterial below cost $ per million United States gallonsagainst $ for a bed of l|-2|-inch material. The average rateof operation is 900,000 United States gallons per acre per is effected by means of the fixed sprinkler describedon page 339. A general view of one of the beds is shown inFig. 108, and another view in winter in Fig. 109. After filtration the trickling effluent contains about 125 partsper million of solids. This is treated in separator tanks at a costof 28 cents per million United States gallons to eliminate solids;pumping sludge from these tanks and digging it into the landcosts ten cents more (Watson, 1907). Analytical results for the various parts of the Birminghamplant, in 1909, are given in the table on page 364. 364 TREATMENT IN TRICKLING OR PERCOLATING BEDS. Fig. 109. View of Birmingham Beds in Winter (courtesy of J. D. Watson). TABLE XCIII COMPOSITION OF SEWAGE AND EFFLUENTS AT BIRMINGHAMAnalyses of average weekly samples collected every half-hour during the 24 hours, in the year per million. Separa-tor tankeffluent. Oxygen consumed in 4 hours unfiltered Albuminoid nitrogen Nitrogen as nitrates and nitrites Suspended solids Septicefflu-ent. Silt Trick- Crude tank ling sewage. efflu- efflu- ent. ent. 9 408 194 98 128 21. 1. 15. 15 The average capital cost of the last eighteen beds built atBirmingham was about $35,000 and the total cost of treatmenttaking the larger beds with their appurtenant tanks, etc., as abasis, and including all interest charges and operating expensesaverages about $, per million U. S. gallons. Important investigations of the trickling process have beenmade at many other English cities besides Birmingham, themost notable of which, perhaps, are
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