2

Click here to load reader

Removal of Ammonia in Water Treatment

  • Upload
    max

  • View
    221

  • Download
    5

Embed Size (px)

Citation preview

Page 1: Removal of Ammonia in Water Treatment

704 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 31, NO. 6

drop in insulation is most undesirable. Experiments and experience have demonstrated that in certain cases an initial drop in dielectric resistance may be observed; then, provided the core is otherwise satisfactory, the improvement will eventually set in, although possibly a t a reduced rate. Addi- tional factors affecting improvement are moisture content of the dielectric and concentration of dissolved salts in the water.

TABLE 111. EFFECT OF CHANGES IN MOISTURE CONTENT Specific Resistance Dielectric

Moisture Content at 75O F. Constant % Ohm-cm. X 1014 4.3 3.3 1.5 0.3 0.1

13.5 13.7 11.3 11.7 14.2

3.2 3.18 3.1 3.05 3.05

Little has been said of the dielectric constant of gutta- percha, balata, and admixtures, in spite of the fact that it is the most important operational constant of a cable. How- ever, it follows more definite laws than the other characteris- tics and may be predicted for a mixture with reasonable certainty by an arithmetical computation from the figures of the components. Nonuniformity in the mixture will almost certainly be reflected in its dielectric constant, and since the moisture content is usually affected by changes in processing, the high dielectric constant of the water will cause changes in the capacity of the finished material.

It might be expected that the dielectric resistance would be more susceptible than the dielectric constant to changes in moisture content; although this is found to be the case, the variations in the former are very irregular, whereas those

of the latter are consistent with theory. Table I11 gives the results obtained in a series of experiments on a mixture of normal proportions in which, as far as possible, the only variable was the moisture content.

Conclusions The satisfactory insulation of a submarine cable core is

fundamentally complicated by the considerable variation in the characteristics of the different types of raw materials. Furthermore, the characteristics of a mixture of components do not bear any known mathematical relation to those of the components. Finally, the considerable variations experi- enced in sample to sample of the same type of raw material, by reason of their jungle origin, causes still further complica- tion.

In these circumstances, it is to be deplored that cable specifications are drawn up in such a way as to cause still further difficulties to a manufacturer endeavoring to supply the best cables commercially possible.

It is to be hoped, therefore, that this paper will throw some light upon what is generally considered an obscure subject and a t the same time cause serious thought by those responsible for drawing up cable specifications.

Acknowledgment Thanks are due to The Telegraph Construction & Main-

tenance Company Limited, for permission to publish the information in this paper.

Literature Cited (1) Dean, J. N., India Rubber J., 82, 853-6 (1931). (2) Kemp, A. R., J. Franklin Inst., 211, 37-57 (1931). PRESENTBID at the 94th Meeting of the American Chemical Society, Rochester, N. Y .

Removal of Ammonia in Water Treatment A. M. BUSWELL AND MAX SUTER State Water Survey Division, Urbana, Ill.

ANY microscopic organisms live and grow in water These organisms are trouble- M some; they often cause odors and unsightly conditions

in the water, although they are nonpathogenic as far as we know. For the latter reason they.have not been subjected to much study by medical bacteriologists. Usually they can- not be grown under artificial conditions and therefore are not attractive material for the general microbiologist. However, increased demands for a more perfect water in any public supply requires that these organisms be eliminated as far as possible from the distribution system.

At present, we have little systematic knowledge of these organisms. Most of them are a true and higher form of bac-

. teria (iron and sulfur bacteria), but protozoa and higher organisms, especially nematodes, are also very common. In general three ways are available to eliminate these organisms: avoidance of contamination, disinfection, and elimination of food supply (starvation).

distribution systems.

Elimination of Organisms Avoidance of contamination requires that the organisms

be kept out by the filter. The efficiency of the filter in this respect is rather low. Even if most bacteria, spores, and cysts are kept back in the filter and are to a great extent re- moved from it in backwashing, a few may pass through. It is also known that nematodes can slowly wiggle through the sand and carry some organishns along. Furthermore, other sources of contamination are possible, such as backsiphoning through plumbing fixtures, and eddy currents a t leaks and through fire hydrant drains.

Disinfection is produced mainly through chlorination, but all organisms found seem to be very resistant to chlorine; a t least they are not affected by a chlorine dosage up to 0.5 p. p. m., to which the water in the distribution system is ordinarily limited because of tastes. Another way of prac- tical disinfection for chlorine-resistant organisms is in the use of the lime softening process. The meager observations made so far seem to show that chlorine-resistant bacteria can re- sist a low pH but not the high pH produced by the lime

Page 2: Removal of Ammonia in Water Treatment

JUNE, 1939 INDUSTRIAL AND ENGINEERING CHEMISTRY 705

treatment. Water softening combined with chlorination gives, therefore, a wide range of active disinfection.

Other means for the limitation of these growths are much needed. It is conceivable that cutting off the food supply will cause their elimination by starvation. All living organ- isms must have available some food supply which furnishes material for bodily growth and which is also capable of yield- ing energy through chemical reactions.

Iron organisms gain a t least part of the energy needed from the oxidation of ferrous to ferric iron. Similarly, sulfur bac- teria use the oxidation of sulfur to sulfate ions

replace calcium and magnesium ions in the water by sodium ions), carbonaceous zeolites have the property of hydrogen- ion exchange. They are able to replace any metallic ion by hydrogen ions and thus form acids in the treated water. Ammonia is included in the ions that are removed by carbo- naceous zeolites.

Tests were made with the tap water of the University of Illinois. This water is aerated and filtered to remove iron and then chlorinated. It is practically a pure carbonate water, free of sulfates, but after heavy chlorination it contains about 5

or of hydrogen sulfide to water and elemen- tary sulfur. However, in some cases it is w found that these organisms or similar ones persist even in the absence of sulfur and with

4 400% very complete removal of the iron. In such 0 % cases attention may be called to the possi-

bility that the organisms may gain energy r I-

from ammonia which is present in many 3 300 well waters. oxidation of ammonia depends on the prod-

z - 5 0 v)

2

UI

The energy available from the Q

uct formed, as shown by the equations: 2 200 g I B

NH4+ + 202 = 2H+ + NOa- + NH4+ + ' / 2 0 ~

NH4+ + ' /~OZ

HzO - 81,230 cal. I 100 2H+ + NOS- + H+ + l/zNz + H20 - 63,230 cal.

S/2H20 - 86,670 cal. GALLONS PASSED - The existence of the process in the second of REMOVAL OF AMMONIA 8Y CARBONACEOUS ZEOLITE

these equations is confirmed by the fact that in many distribution systems nitrites can be found, although the raw water contains only ammonia. Calcu- lations from energy relations show that the energy in the ammonia in a million gallons of the University of Illinois water SUPPlY would be sufficient to Produce 40 Pounds of baaterial growth (dry weight). This material would Yield 800 Pounds of wet sludge of 95 per cent moisture content and contains only about 12 per cent of the nitrogen of the ammonia in the original water. Evenif we do not anticipate that the biological reaction uses all the ammonia available, we can nevertheless assume that the m~monia Will furnish energy and nitrogen for a great amount of organic sludge. Elimination of the m~monia from the distribution system will therefore help to reduce considerably the after-growth in pipe lines.

p. p, m. chlorine ions. On an average, the water contains the following metallic ions in parts per million: calcium, 60.6; magnesium, 28.2; sodium, 56.5; ammonium, 2.7. In a long run the carbonaceous zeolite (Zeo-Karb, provided by the Permutit Company) shows two cycles with this type of water: first an acid cycle in which 811 metallic ions are re- moved, then a sodium cycle in which the carbonaceous zeolite acts as a noma1 zeolite, removes only the hardness produe- ing metals, and replaces them with the sodium extracted dur- ing the acid cycle. The boundaries between the cycles are not sharp, and there is somewhat a gradual change from one action to the other. This can also be found relative to the re- moval of ammonia.

In the acid cycle practically all the ammonia is removed, In the effluent an average is found of only 4.4 per cent of the ammonia in the raw water. At the end of the acid cycle, when the total solids increase, the ammonia content increases also to an average of 13.2 per cent of that in the raw water. Dur- ing the sodium cycle very little ammonia is removed, the effluent containing on an average 77.8 per cent of that of the raw water. At the end of the sodium cycle as soon as the hardness increases, the carbonaceous zeolite seems to be un- able to retain the ammonia; at least an increase in ammonia was found then, the content of the effluent averaging 120 per cent of that of the raw water.

Carbonaceous zeolites, if regenerated with sodium chloride, act like siliceous zeolite in removing the hardness from the water. Probably in this case they will also remove ammonia during the sodium cycle, a t least a t the beginning of the cycle. But to obtain full benefit of the special properties of the car- bonaceous zeolites they should be used only in the acid cycle- i. e., after regeneration with an acid. It is during this acid cycle that the carbonaceous zeolites form an excellent and re- liable means for reducing the ammonia content of the water to a very low amount, averaging in these tests 0.12 p. p. m.

waukee. wis.

Elimination of Ammonia It was first thought that the ammonia could be eliminated

by the formation of ammonium magnesium phosphate. To study this possibility, two series of experiments were run on &liter samples with trisodium phosphate as the source of phos- phate ions. Since trisodium phosphate is also used as a water softener, lime was employed to soften the water and to aid the phosphate to react with the ammonia. Neither the tri- sodium phosphate nor the lime alone had any effect on the am- monia. Even if the trisodium phosphate and lime were intro- duced a t practically the same time, no effect on the ammonium content could be found within experimental error (actual re- duction from 1.6 to 1.52 p. p. m. ammonia nitrogen). If the lime was introduced first and, after 20 minutes of reaction time for the lime softening, twice the necessary amount of tri- sodium phosphate was added to bind the ammonia, a slight reduction of the ammonia from 2.0 to 1.3 p. p. m. was found as the best result. Apparently trisodium phosphate reacts too easily with calcium to be effective for the removal of ammonia.

The recent development of carbonaceous zeolites offers a

silica zeolites have the property of base exchange (that is, they possibility for the Of ammonia' Ordinary PRESENTED at the 96th Meeting of the American Chemical Society, Mil-