Prof. Phelps. That is $6?
Mr. Hatton. Yes.
Prof. Phelps. Would you tell us the cost of the aeration in preparing the sludge?
Mr. Powell. That would be taken into account as against some other system.
Mr. Hatton. I think I have that. I will read to you from a copy of the Second Annual Report of the Sewage Commission of the City of Milwaukee of 1915:
The cost of the activated sludge, continuous flow, with a removal of 95.5 per cent bacteria—
I say that because the cost of the operation and the plant depends entirely upon the character of effluents you want to secure. A lower grade of effluents lowers the first cost and operating cost, so this is based on a removal of 95.5 per cent, which is our standard——
The disposal of sludge in cost per million gallons, $3. The interest and depreciation on the cost of the plant, based at 7½ per cent, $2.81. Cost of operation, exclusive of sludge, $2, making a total cost of $7.81 per million gallons treated.
From this $7.81 must be taken the value of the recoverable sludge, which, as I stated to you, so far in our investigations has been $3 per million gallons, or making a total net cost of $4.81 per million gallons, which includes overhead charges.
Mr. Tawney. What was the cost of your Milwaukee plant?