Mr. Hatton. In the middle of 1914. We have been operating it just about two years. We tried out in that experimental station the Imhoff tank, so-called settling tank, sprinkling filters, colloidal tanks, electrolytic processes, chemical precipitation, chlorination, and finally, what we called the activated sludge process, which we have been trying out now for a year this month.
Mr. Magrath. Where did that process originate?
Mr. Hatton. Well, that is a question. Mr. H. W. Clarke, of the Lawrence experimental station of Massachusetts, claims he discovered it. Dr. Gilbert J. Fowler, of Manchester, England, now of India, has assumed the discovery of it and developed it in a laboratory way perhaps further than anybody else up to the time we took care of it in Milwaukee. He started his experiments in 1914, or late in 1913, and we started our experiments in 1914, late in 1914. But it has been developed in Milwaukee to a greater extent than anywhere else, either in Europe or United States. We started with a laboratory investigation. From thence we went to tanks, holding or treating 70,000 gallons a day each, and from thence we have gone to tanks treating 1,600,000 gallons a day, which are now being operated and have been operated since last January. The process, stated briefly, consists of, first, coarse screening the sewage, running it through coarse screens, then into tanks of any depth to suit the conditions and the situation, say from 10 to 20 feet.
Mr. Powell. That is the residue after the first screening?
Mr. Hatton. That is the raw sewage after it has been coarse screened. Then the raw sewage is run into these tanks, which have in the bottom some method of diffusing air which is discharged into the bottom of the tank at low pressure, just sufficient pressure to keep the liquor agitated; while in there this liquor passes through this tank, taking a certain time in accordance with the standard of purification required, from two hours to four hours, during which time it is being agitated and aerated by the air. From these tanks it passes into a sedimentation tank. All of these tanks are practically one tank divided by a wall separating the aerating tanks from the sedimentation tank. After settling in the sedimentation tank from 45 minutes to an hour, or an hour and a half, according to the character of the effluent you require, it then passes out into the point of final discharge. The sludge which settles out of the liquor into the sedimentation tank is then pumped back and discharged into the raw sewage as it enters, or while passing into the beginning of the aerating tank. The surplus sludge which settles in the sedimentation tanks is treated otherwise, which I will describe later. The process is one of aeration and nitrification practically. The sewage does absorb a great deal of oxygen from the air which is forced into it through these diffusing methods. The sludge, however, which we return and keep intimately mixed with the sewage at all times is perhaps the chief medium of purification, because that sludge is filled with microorganisms and nitrifying organisms, which really do the purification work, and that is the reason that it is called activated sludge, because it is so filled with the nitrifying organisms, and the more active the sludge is the more rapid and higher degrees of purification you secure. It is a natural process entirely, simply intensified by artificial means. To show you the activity of that sludge, we got the raw sewage, perhaps a million bacteria per cubic centimeter, in the first aerating tank, within half an hour; the sludge contains anywhere from fifteen to twenty million bacteria per cubic centimeter. In this sludge we give the bacteria the natural environments for their work. We give them food, lodging, and air, and that is just exactly what aerobic bacteria need, and the desire is to have intensified the aerobic bacteria, which we have at all times when the plant is being properly operated. Now, that is a brief description of it.
Mr. Powell. That is the only purpose of aeration?
Mr. Hatton. No; there is another purpose of aeration, and that is the intimate mixture of the sludge with the liquor. That can be done mechanically with a little bit of air put in; but to do it mechanically would increase undoubtedly the cost and the operating expenses. In order to clarify the liquor it is not only necessary to nitrify it, but it is necessary, as we call it, to scrub it, and we remove the colloidal matter by means largely of scrubbing. To describe that in a layman’s way, not in a chemical way, the colloidal matter in sewage rests in the interstices between the globules of water, like water rests in the interstices of the sand at the seashore. Now, if you disturb that sand on the seashore, the water runs out and the sand becomes free of it. If you scrub the globules of water together violently, the colloidal matter is detached from the water and the water becomes clear. That is as near a layman’s description as I can give you, and we have tried the experiment out in our experimental station, to see whether there is any odor in that sewage, and we have thought that there is to a certain extent, not altogether. Now, the question as to how to dispose of this sludge is one of the greatest problems in sewage disposal in the world; and I think if any of you went over to Toronto, which I had the pleasure of visiting three weeks ago, you would see the difficulty that Toronto is up against in getting rid of its sludge, as are all other cities in the United States, whether it be Detroit or Buffalo, Cincinnati, Philadelphia, or New York—well, I will not say New York and Philadelphia, because they are out at the ocean, and they have a chance to get rid of it, but inland cities will have this difficulty.
Mr. Powell. They are taking it up in New York.
Mr. Hatton. Yes; they may be able to discharge the sludge in the sea, but inland cities on the Great Lakes or rivers are going to be up against the proposition as to how to get rid of the sludge. Then any method of sewage disposal which will enable the cities to get rid of the sludge, whether it be at a profit, or whether it be to break even, or whether it be at a loss, and yet to get rid of it to the advantage of the agricultural element of this country and indirectly to ourselves, will be that system of sewage disposal which will undoubtedly meet the conditions of the large cities. That is the proposition which is primarily confronting us in Milwaukee, as I started out to say, and in all of this investigation there has been no doubt evinced in the last three months by the leading consulting sanitary engineers in the United States who have visited our plant that the purification of the sewage has been solved within reasonable cost, but there has been a great deal of doubt in their minds that the disposition of the sludge has been solved, and I have told them that within 90 days——
Mr. Magrath. Did you say that there was a feeling that the problem had not been solved?