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PURIFICATION OF SEWAGE AND WATER
LAWRENCE EXPERIMENT STATION,
Nov. 1, 1889, to Dec. 31, 1891.
EXPERIMENTS UPON THE PURIFICATION OF SEWAGE AND WATER AT THE LAWRENCE EXPERIMENT STATION,
NOV. 1, 1889, TO DEC. 31, 1891.
The experimental work of the Lawrence Experiment Station is still under the active direction of Hiram F. Mills, C.E., member of the Board, who originally designed the station and planned its work. Mr. Allen Hazen is chemist in charge of the station, and Mr. George W. Fuller is in charge of the biological department. Mr. Harry W. Clark is assistant chemist. The compiling of the records and the preparation of the tables and diagrams have been the work of Mr. F. L. Fales. Professors T. M. Drown and W. T. Sedgwick of the Massachusetts Institute of Technology are respectively consulting chemist and biologist with a general oversight of the chemical and biological investigations.
The following detailed account of the work of the station has been prepared by Mr. Allen Hazen, chemist in charge :
The special report of the board upon the Purification of Sewage and Water, 1890, contains a full account of the work at the Lawrence Experiment Station during the first two years up to Nov. 1, 1889, and also a summary of the results for 1890.
During the past two years investigations have been continued upon purification by filtration along the same general lines, but in such a way as to throw additional light upon numerous points of great practical importance. Most of the filters described in the previous report have been continued in use to obtain information as to their permanence, while many others have been started to investigate special points connected with sewage purification and the filtration of water.
Filter Tank No. 1, which is one of the original filters and has been in use four years, has filtered sewage during the past two years, 1890 and 1891, at an average rate of 85,920 gallons per acre daily for every day in that time, and with a removal of 94 per cent. of the organic matters, as shown by the albuminoid ammonia, and 98 per cent. of the bacteria. Filter Tank No. 2, also one of the original filters, has filtered for the same period, at an average rate of 49,360 gallons per acre daily, and has removed 97.5 per cent. of the organic matters and at least 99.99 per cent. of the bacteria of the applied sewage. With many other filters correspondingly good results have been obtained.
The purity of the effluents obtained by intermittent filtration was thoroughly discussed in the report on the Purification of Sewage and Water, and it will suffice to say in this connection that there is no other method of sewage purification which yields results at all comparable to those obtained by intermittent filtration under favorable conditions.
One of the most important results of the past two years' work is the fact that, by systematically breaking the scum which forms on the surface of filters, a very much larger quantity of sewage can be purified without any deterioration in the quality of the effluent.
We had found that different materials require different treatments for the best results ; that a system of applying sewage best adapted to a fine material fails to yield the best results when applied to a coarse sand, and vice versa. By studying the performance of our different filters under various conditions, in connection with the mechanical composition of their materials, we have discovered many of the causes of these differences, and have secured data which will enable us to determine, in advance, the general line of treatment required by different sands. In a similar way we can form an approximate estimate of the quantity of sewage which can be successfully applied to various materials under known conditions. *
We have continued the study of the effect of winter weather upon filtration, and have found that even with unprotected filters good results are possible in our climate under some conditions to be discussed in the following pages. The effluents obtained in winter, while less perfect than those of the warmer months, were still good, - much better than could be obtained by other processes, as,
for instance, chemical precipitation.
An excessive quantity of acid in the sewage prevents satisfactory purification, but our experiments have shown that if, for the treatment of such sewage, a filter containing limestone is employed, the acid is neutralized, and a good result is obtained. This is a most important demonstration, as it assures the successful use of sewage
The reader should bear in mind that the results given in this paper were obtained at the Experiment Station where all of the work is under scientific supervision, and the sewage is applied to small areas with uniformity and in definitely measured doses. In applying these results to actual work on the large scale some allowance may have to be made for less farorable conditions.