water from the Scioto River to a hardness of between 35 and 50 p. p. m. without resorting to excess treatment with lime and soda ash. Without the use of aluminum compounds the limit seems to be somewhere between 80 and 100 p. p. m. SUBSTITUTION OF ZEOLITES FOR SODAASH TO REMOVE NON-CARBONATE HARDNESS-It has already been mentioned that the addition of soda ash to remove the non-carbonate hardness is conducive to the formation of soluble hardness salts. We now know that it is not necessary and in many cases not advisable to use soda ash to remove permanent or non-carbonate hardness from water because in communities where salt may be obtained a t a fair cost it is cheaper to remove non-carbonate hardness by means of the zeolite process than by means of soda ash. The operation of a lime-softening plant followed by zeolite treatment is about as follows: The water is first treated with sufficient lime to reduce the temporary or carbonate hardness to the lowest possible figure, then, after settling, it is carbonated with carbon dioxide to convert the normal carbonates to bicarbonates, thus preventing the deposition of normal carbonates on the zeolite sand and also preventing the formation of normal sodium carbonate in the softened water. The presence of sodium bicarbonate in the zeolite-softened water makes it possible to mix it with water containing non-carbonate hardness and not get a precipitation or an after-reaction. After settling and carbonation, the lime-softened water flows to the filters and, if desirable to reduce the hardness of the water to zero, all the water is passed through zeolite filters. If it is desirable to leave some residual hardness in the water then of course it is only necessary to filter a portion of the water through zeolite filters. At the Columbus plant it is believed that it will be possible to reduce the hardness of the water from 300 p. p. m. to 160 p. p. m. by lime treatment alone, and that, in order to produce a softened water with a total hardness of, say, 80 p, p. m., it will be necessary to filter only half of i t through zeolite filters, reducing the hardness of this portion to zero, and then mixing it with the other portion having a hardness of 160 p. p. m. The resultant product will have a hardness of 80 p. p. m. and no after-reactions are expected because the residual sodium salts in the zeolite softened water are present as bicarbonates. M o d e r n Applications of L i m e T r e a t m e n t
Two modern applications of lime treatment have recently been described by Waring?
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Vol. 19, No. 5
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
570
EXP~RIENCB AT YOUNGSTOWN, Omo-Several years ago the City of Youngstown instituted the excess lime treatment for the badly polluted Mahoning River water used as a source of supply at t h a t plant. That the treatment has been a success is demonstrated by the experience of the last few years. The raw water pollution load a t Youngstown is probably the greatest of any water treatment plant in the country. The yearly average B. coli index exceeds 20,000 per 100 cc. and it is not possible t o use chlorine a t this plant because of interference by phenol-bearing wastes. The final effluent during the past year has not shown a single positive presumptive B. coli test in any of the five 10-CC. portions tested daily. EXPERIENCE AT IRONTON, OHIO-Following the unsuccessful attempt at Ironton t o relieve the bacterial load in the Ohio River a t that point, a change of treatment was made beginning in December, 1925. The experience of Youngstown has been made use of a t Ironton in the following schedule: The plant has double coagulation facilities; accordingly, lime was applied t o a primary basin in an amount to produce causticity, therefore sterilizing the supply. Alum was applied at the secondary basin t o coagulate the turbid Ohio River water. It was noted that considerable alum was required if the influent water t o the filters was t o be kept in a condition to prevent carbonate scale forming 4
1. Am. Wafn Works AEEOC.,16 (1926).
on the sand grains as a result of the excess lime used. In order t o economize on alum, the pH value of the water is being reduced by the use of carbon dioxide gas applied a t the mixing chamber of the secondary basin. A saving of more than two grains of alum per gallon seems to be promised and the water coming to the filters contains no monocarbonate alkalinity that would incrust filters or piping beyond the plant. By means of the practice above related it will be possible to produce excellent filtered water without the use of any chlorine; without increasing the cost of the water treatment over previous practice; and having as reserve processes, or factors of safety in the treatment, both the coagulation in the secondary basin and the rapid sand filtration.
EXPERIEXCE AT COLUMBUS, OHro-At the Columbus plant it is customary to omit the chlorine treatment during flood periods when the organic matter is high and the water has a n unpleasant taste or odor, and to substitute the excess lime treatment, about 20 p. p. m. caustic alkalinity being carried in the filtered water. This amount of caustic alkalinity is not noticeable to the consumer. SOFTENING A HARDWELL-WATERSupmy-One city in Ohio is now building a water-softening plant to soften a hard well-water supply. The water contains much objectionable iron which will also be removed in the softening process. This plant will be unique in that the softened water will not be filtered, and no after-troubles from deposits in the distribution system are anticipated because it is expected that the softened settled water will be sparkling clear and it will be carbonated, thus eliminating the possibility of incrustation in the mains. The softening chemicals will be agitated with the water for one hour and a settling period of 24 hours will be allowed, with a velocity through the settling basins of less than 7 feet per hour. On account of its low cost of construction, this type of plant, made available for municipal water softening on account of the successful development of recarbonation, should prove attractive to communities wanting to soften and improve the quality of their already clear but hard water.
A Laboratory Aspirator Reported by M a r t i n Meyer C O L L B COF ~ TAB CITY OF N s w YORE,NEWYORECITY
4 air
THE laboratory aspirator shown
in the accompanying diagram was invented by a student in The College of the City of New York, Isaac Singer, in his second year of chemistry. Although i t operates upon the familiar principle, it seems to be essentially new. It is so simple of construction, ingenious, and useful that it deserves notice. The following materials are required: one 8-inch (20-cm.) Pyrex test tube, glass tubing, one two-hole rubber stopper, and one solid rubber stopper into which three holes have been drilled. It is better to drill these than to use a three-hole stopper in order to be sure that the holes are properly placed. One hole of the lower stopper has been slightly enlarged. The other features of construction and operation are easily seen from the diagram. All the materials required are found in the kit of the general chemistry student and its construction is well within his ability.
