In a discussion before the Iowa Section of the American Waterworks Association Dr. Edward Bartow commended activated sludge for its value as a fertilizer. This has been proved, he said, by its chemical composition, by its reaction with various solids and by its effect on the growth of plants. Pot cultures and garden experiments have shown that the nitrogen is in a very available form.
E. E. Sands, City Engineer of Houston, Texas, bases this statement on results of experiments conducted for a year: “Our investigation has demonstrated that sewage can be disposed of anywhere that there is a vacant tract of land in the city without creating a nuisance and without any objectionable feature.” The total estimated cost for treatment will be about $9.14 per million gallons when the plant is run at the rate of 18,900,000 gallons per day. He estimates that the total cost for treatment by the Imhoff tanks and the sprinkling filters would be not less than $11 per million gallons.
After an extended investigation by their sanitary engineers, Armour & Company have concluded that the activated sludge method will satisfactorily purify the industrial wastes from their Packingtown factories. Assistant Superintendent, M. D. Harding, estimates that from data now available the cost per million gallons exclusive of depreciation, interest and repairs, will be $3.
When considering the applicability of this process to conditions in any city consideration should be given to the following points. The process requires competent supervision, which Mr. Hatton claims may be a blessing in disguise in view of the experiences of cities which, after having built disposal plants of various kinds, have left their operation to the kind mercies of Providence with disastrous results. This process also requires the expenditure for constant power. The cheaper the power the more adaptable the process is commercially; but if the unit is small and the power cost high, the operating cost may be too great. The sludge must be constantly treated to avoid nuisance. The process produces a high degree of purification. If the local conditions do not demand this the process might be too expensive in comparison with some other process which will produce a satisfactory effluent.