Mr. Tawney. What is this process called?
Mr. Hatton. Activated sludge. We tried out the Imhoff tank process with chlorination in this same sewage, and found the cost a little bit less than the cost of this process, without finally disposing of the sludge. We also tried out Imhoff tank, followed by sprinkling filters, and found the cost much more than this process. We also found, in our climate of Milwaukee, that, instead of averaging two and a half million gallons, or getting two and a half million gallons per acre per day through sprinkling filters in wintertime, there were three months that we could not get more than a million and a half. We also found that up to the present date we have not been able to dry sludge in the open air coming from the Imhoff tank from the first of last November up to the present day, and in making our estimates, we do not believe we could get three months in the whole year in this climate—I am speaking of Milwaukee—when we could dry sludge effectually from the Imhoff tank or any other sedimentation process. We have too much rain in June to dry sludge, and the only way we could possibly dry Imhoff tank sludge was by covering with glass, heating the place, as suggested by a gentleman in Cleveland, Ohio.
Mr. Mignault. How long does the drying process last?
Mr. Hatton. Well, that is all according to the weather. If the weather is very nice and warm, and we have the sun, and not too damp, it will dry out in about two weeks; it will dry into a spadable condition in five to six days in good dry weather, but if there is a little bit of rain comes along overnight, or if it is alongside a lake, and there is considerable moisture or damp, it may take two or three days longer.
Mr. Powell. How do you dry the sludge?
Mr. Hatton. In a drier, an industrial drier, just the same as they use in the packing houses in Chicago and many of the breweries and many other places throughout the United States in industrial works.
Mr. Mignault. Does it require much space?
Mr. Hatton. No; the amount of land which we have laid out to treat a hundred million gallons a day, which is the quantity we will have to treat, is 20 acres; that is, including our pumping stations, our ministration houses, sludge-disposal houses, and everything concerned. In fact, to be distinct, this system can treat from ten to twelve million gallons of sewage per acre per day.
Mr. Tawney. What does it cost?
Mr. Hatton. The cost of the treatment?