FILTRATION AT VICKSBURG
Experts Report on the Good Results of the American System.
An American filtration plant was recently installed at Vicksburg, Miss., and the Vicksburg Waterworks company had reports made by Dr. R. W. Jones, professor of Chemistry at the University of Mississippi, and Robert E. Milligan, sanitary expert, of Chicago, which show very satisfactory results. Professor Jones says in his report: “In compliance with your request, communicated by S. S. Hudson, attorney, I reported at Vicksburg on July 3, 1903, and remained until the 8th inclusive, to make a thorough examination of the waterworks, with the filter plant, to test the efficiency of the system in supplying an adequate quantity of water, good and wholesome for domestic uses and suitable for technical purposes. I found you had an admirably constructed series of basins for the natural sedimentation of the suspended matter which the Mississippi river water contains in large quantity. These basins increase in depth from north to south, causing the water in them to flow southwards. Two large Worthington pumps force the water from the river to the northernmost basin, which is fifteen feet by 100 feet by eight feet deep, wherein is a large amount of deposit. Between this basin and the second are two vertical walls, with a narrow space between them. The water flows over the top of the first of these two walls into the space between, and passes through some holes left in the second wall into the second basin, 120 feet by 100 feet by ten feet deep. In this basin is an arrangement by which the water is made to move gently along two diagonals, a space of about 350 feet, and this is very effective in causing a large deposit of suspended material. Here the water enters the third basin, fifty feet by 100 feet by twelve feet deep, and by a galvanised iron flume it enters the fourth basin. This flume is two by three feet, and at its entrance the water receives, through a pipe, a constant, small stream of a solution of sulphate of iron. About fifteen feet farther on in this flume a small stream of lime water is added in a regulated flow through another pipe. Weirs and other contrivances effect the commixture of these substances, and of them with the water. Passing across this basin, the water enters the fifth basin, forty-five by too by fourteen feet deep, and from this, by a fivefoot flume, it enters the filter beds, called filter units. Each one of these units is fourteen by twenty by seven and one-half feet deep, and is put in by the New York Continental Jewell Filtration company. The basins and filter units are of strong masonry, built of brick and Portland cement. At the bottom of these units are great numbers of patent bronze screens screwed into the iron pipe manifold. Above these is a layer of crushed white quartz of the size of rice; next above the quartz is a bed of sand (silica) from Horn Island, Mexico, four feet deep. The whole plant acts by gravity. The sulphate of iron and lime are carefully weighed and dissolved in water. These solutions are placed in separate tanks, which work automatically to deliver about one grain and twelve-hundredths of a grain of sulphate of iron to the gallon of water, and thirty-six hundreths of a grain of lime to the gallon of water—in other words, one pound of iron and one-third of a pound of lime to every 7,000 gallons of water. As above explained, the arrangements secure the deposition of a large proportion of the clay and silt suspended in the river water before the addition of these chemical substances. When these are added and distributed throughout the entire volume of water, they react upon each other and upon the matters suspended and dissolved in the water. One of the important results is the formation of ferric hydrate, which hastens and increases sedimentation, acts as a coagulant, bringing together albuminous matter and bacteria in such a way that the filters arrest their passage, whereby the water is purified of the most objectionable content, averaging ninety-eight per cent, efficiency. The water is forced from the clear water basin into the service pipes by two large pumps, each of which has a capacity of 2,500,000 gallons in twenty-four hours. The usual amount of water pumped in twenty-four hours is about 500,000 gallons. The construction of the filter units allows them to be washed clean by forcing the filtered water through the bed from the bottom and discharging the washings into the sewer. This is done daily, and assures not only the cleanness of the filter, but its activity. During the five days I was in Vicksburg I made repeated tests to ascertain if any of the sulphate of iron and lime passed through the filters into the clear water, and 1 did not find at any time the slightest trace of either On the morning of July 4 Mr. R. E. Milligan, of New York, and I began a series of experiments to estimate the number of bacteria in a cubic centimetre of filtered water. We sowed plates of nutrient gelatine morning and evening, for four successive days, and at the end of forty-eight hours after each sowittg^vve counted the resulting bacteria per cubic centifnetre. and calculated the efficiency in the per cent, of bacteria removed by the sedimentation and filtration. The following are the results: July 5, per cent, removed, 99.2; July 6, morning, per cent, removed, 98.8; July 6; evening, per cent, removed. 98.75; July 7, per cent, removed. 97-5; July 8. morning, per cent, removed, 99; July 8. evening, per cent, removed, 99.2. This shows an average efficiency of 98.74. The two samples of July 8 were taken from the Hotel Carroll and the Piazza. T collected two gallons of the filtered water from the clear water basin, which I analysed on my return to my laboratory in the university, with the following results, expressed in parts per 1.000.000. Chemical analysis of filtered water of the Vicksburg Waterworks company supplied to the people of that city: Parts per 1,000,000—Appearance clear, transparent, colorless, free of turbidity; odor, none; reaction alkaline; total solids in solution dried at no degrees. 166.000: loss on ignition. 58.000; chlorine, 8,620; free ammonia. 0.015; albuminoid ammonia. 0.100; nitrites, 0.000; nitrates, 0.021; oxygen consumed, 2.100. From careful examination and inspection, as well as from painstaking bacterial and chemical analysis, I conclude as follows: 1.—The waterworks are excellent in all their parts. 2.—The filter units do their work with approved efficiency. 3.—According to the highest and strictest standards the water should be pronounced pure and wholesome for domestic purposes and good for industrial uses.”
The report of Mr. Milligan says: “Following your request. T have made a complete investigation of the conditions surrounding the water supply of vour comnany. as it is pumped to the city of Vicksburg. After the water is elevated by means of lowservice pump to the settling reservoir, it then passes by gravity slowly from one reservoir to another, these reservoirs being baffled to increase the period of time in which the water is subjected to this preliminary subsidence or settlement. The effect of this part of the process is to remove the heavier, grosser matters in suspension before the water flows to the coagulating, settling basins. In fact about thirty-five per cent, of all the matter in suspension is removed from the water in this preliminary settling basin. After this partial purification, the settled water flows slowly to the coagulating basin, and is conducted there hv certain flumes or aoueducts. As the water passe« through these flumes, it is met by a small stream of the solution of the sulphate of iron, which flows bv gravity and has a strength, which, when added to the flowing raw water, adds about one grain to the gallon of the sulphate of iron salt and which is eoual to 234-1000 of a grain of metallic iron to each gallon of raw water. The raw water containing this minute amount of iron flows onwards about t wen tv feet, when it is met by a weak solution of lime or lime water, and the amount of lime added to the raw water here is equivalent to 36-7000 of a grain of slacked lime to the gallon. It will be seen that the raw water now contains 22-1000 of a grain of iron and 36-1000 of a grain of lime to every gallon, and a reaction immediately occurs between these ele ments, producing a result called ‘coagulation;’ the final reaction being the formation of an insoluble hydrate of iron in the water, which is itself gelatinous and bulky, and aggregates together the final particles of suspended matter and bacteria which have escaped the preliminary settlement alreadv mentioned: and the coagulation with these adhering impurities precipitates to the bottom of the settling tank, through which it is slowly passing on its way to the filters. The filters finally remove any portion which has not settled in the sedimentation basins Such, briefly, is a description of the process of purification employed: and the object of the investigation was to establish the fact of the removal of bacteria and growths, and, also, to demonstrate beyond contention that no portion of the added lime or iron remains in the filtered water. After a series of bacterial examinations lasting from Tilly 1 to July 8. supplemented by chemical analysis. I am able to state positively, that the filtered water as pumped to the city is pure in a bacterial sense—the removal being equivalent to ninety-eight per cent, average The number of bacteria remaining in the filtered water is so few as to classify the water as very pure in a sanitary sense. Furthermore, samples were drawn from the taps at the hotel Carroll and the hotel Piazza in the city, and these samnles showed equal purity with the water as it is discharged from the filters. Searching chemical tests during the en tire time of the examination was made each day, with the result that at no time was there either iron or lime found to remain in the filtered water. The filtered water is freer of iron than the raw water from which it is derived. To sum up: The fil tered water contains no added iron or lime. The turbidity is entirely removed. The water contains neither color nor odor, and is free of bacteria to the extent of ninety-eight per cent, removed, and, in every sense of the word, is a sanitary, potable water of excellent quality.”