T H E J O U R N A L OF IiVDUSTRIAL A N D ENGINEERING C H E M I S T R Y
Vol. 9, No.
I
LABORATORY AND PLANT ARTIFICIAL ALKALINITY IN WATER FOR FILTRATION By A. WAYNECLARK Received November 1, 1916
The very clear a n d interesting paper b y W. Lee Lewis in t h e October, 1916,issue of THISJ O U R N A L , p. 914,entitled “Some Features of Swimming Pool Control” is a valuable addition t o t h e literature of t h e subject of swimming pool waters both from t h e chemical a n d bacteriological viewpoint. T h e writer notes with interest t h e discussion of t h e problem of “conserving t h e alkaline life” of water t h a t is treated over a n d over again with alum as is done with t h a t in swimming pools. The conclusion of t h e author of t h e above paper may be summed up b y saying t h a t he has shown b y his work just how long t h e alkalinity can be conserved or, in other words, how long t h e hour of exhaustion of alkalinity can be ppstponed. With t h e water of t h e Great Lakes having a carbonate content of 118 parts per million, it is shown t o be possible t o postpone this exhaustion long enough t o satisfy t h e requirements of this particular case. T h e relatively high carbonate content of t h e water of these lakes is a fortunate circumstance not met with in many other waters which have t o be taken care of by filtration plants a n d by those in charge of their operation. As t h e writer of this is one of those so situated i t is thought t h a t a few words on t h e subject will be of interest a n d assistance t o those in control of filter plants as well as of swimming pools. The writer is in charge of t h e control work of t h e water filtration plant of t h e Company named below a n d t h e plant is operating at t h e r a t e of somewhat over a million gallons of water per day of 2 4 hours a n d running practically 24 hours per day, so t h a t t h e successful application of t h e “artificial alkalinity” is a matter of practical large-scale experience covering periods of many weeks of uninterrupted operation. T h e raw water scarcely ever contains more t h a n 5 0 parts per million of carbonates. The pinch comes in periods of heavy rainfall a n d practically all winter t h e flood period in t h e river t h a t is t h e source of supply, causes t h e carbonate content t o drop so close t o zero t h a t there is n o reaction with aluminum sulfate a n d consequently no “floc.” It fell t o the writer’s lot t o wrestle with this problem some years ago a n d no practical solution of t h e question of added alkalinity has ever come t o his notice in the literature. Moreover, talks with practical filter men have been almost equally barren of definite information. The whole question seems t o be in a n uncertain a n d very unsatisfactory condition. Evidently lime is sometimes used b u t t h e objections t o i t are so great as t o make i t almost prohibitive. On account of its low solubility i t must be added as a “milk” which means using a continuous stirrer and all kinds of trouble in regulating valves a n d pipes from sedimentation of t h e lime after learing t h e mixer.
Again, i t seems t o be a tradition among filter men t h a t soda ash (carbonate) is t h e thing t o use. Theoretically, this would seem t o be correct. The writer has experimented with i t in t h e laboratory and has personally tried t o operate t h e filtration plant using it, having tried every imaginable combination of proportions of aluminum sulfate a n d soda ash. It will not work because a n y excess of soda ash will redissolve the “floc” of aluminum hydroxide. As also a n y excess of aluminum sulfate will redissolve t h e “floc” i t is not hard t o understand t h a t although there may be a theoretical combining proportion, yet t h e thing is impossible from a practical standpoint. I n repeated long-time runs with t h e writer present a n d himself adjusting t h e feed valves, no continuous coagulation could be produced. The redissolved “floc” produced colored water sooner or later. I n casting about for a possible substitute for natural carbonate alkalinity i t was thought advisable t o t r y sodium bicarbonate, because i t is cheap and is a bicarbonate t h a t might produce a n effect similar t o t h e natural calcium bicarbonate of water. T h e immediate complete success of this procedure a n d its successful continued use has frequently made t h e writer desire t o publish t h e results believing t h a t there is sore need for such knowledge among filter men. T h e above-mentioned paper on swimming-pool control brought t h e subject t o mind in a forcible way. The bicarbonate may be added in a n y excess. I t is of course harmless in a n y needed amounts t o t h e stomach, eyes, throat, a n d nose. It can be added t o t h e water in bulk b y hand or fed in measured quantity by a regulating valve from a solution. It is easily dissolved although not extremely soluble, can be purchased in a high s t a t e of purity, in quantity, almost anywhere. Th.e result of t h e reaction with aluminum sulfate is of course sodium sulfate. This also is harmless in t h e quantities under consideration. Approximately equal weights of bicarbonate a n d commercial aluminum sulfate react well, t h e bicarbonate being practically anhydrous a n d t h e sulfate carrying about 5 0 per cent water. N o care need be taken t o avoid a n excess of bicarbonate. As for swimming pools, this of course prolongs t h e alkaline life almost indefinitely or until a taste develops t o a n objectionable degree. I n filtration plants for industrial or municipal use t h e old troublesome question of almost complete absence of reaction in cold water stays with US in winter when using bicarbonate of soda, just as without it. I n t h e plant under t h e writer’s control there is one feature t h a t it is believed could be copied advantageously b y some others. Here t h e water from jet condensers f r o m t h e power plant is used t o supply t h e filtration plant. This water is kept at 60 t o 7 0 ’ F.
J a n . , 1917
T H E J O U R N A L OF I N D G S T R I A L A N D ENGINEE R I NG CHEMIST R Y
in winter. It contains only a few per cent of condensed water, I t seems as if in building filtration plants, in conjunction with pumping stations, some of t h e heat from exhaust steam could, either by t h e above method or some other, be used t o raise t h e temperat u r e of t h e water t o be filtered, even if only a few degrees. T h e striking advantage of warming t h e water supply is well known, but, of course, coal cannot be burnt solely t o heat t h e water. Where swimming pools are t o be supplied with water t h a t is originally of such low alkalinity as t o give practically no reaction with alum, i t is of course difficult t o devise a way t o fill them t h e first time. If t h e raw water supply could be first fed into a pair of capacious tanks a n d there treated with bicarbonate using alternate tanks, i t would solve t h e problem easily. This could be done except for t h e probability t h a t so much space could rarely be provided. IThere t h e city water supply is of sufficient purity a n d clearness t o be used without filtration for t h e first filling of t h e pool, this trouble is eliminated. Where alum a n d bicarbonate solutions can be fed into t h e running feed water b y gravity from tanks with regulating valves as is done in larger filtration plants, there would be no question a t all, b u t as far as t h e writer knows, swimming pools are usually supplied with alum-Eeeding devices and filters all under city water pressure. This works fairly well with waters of high enough alkalinity a n d also will be satisfactory for refiltering water from t h e swimming pool because t h e bicarbonate can be added t o t h e pool before refiltration. Such plants use potash alum in large crystals which are packed in a closed t a n k under water pressure a n d t h e water, i n slowly passing through t h e t a n k full of alum, becomes a saturated solution. T h e undissolved alum retains its massive condition on account of its relatively slight solubility. T h e t a n k therefore does not choke up. Sodium bicarbonate cannot be used in a n y such device because of its solubility a n d fineness. &4 solution of i t in such a pressure t a n k would be constantly changing in strength b y progressive dilution a n d any undissolved bicarbonate would pack tightly in t h e t a n k so as t o stop t h e flow. For t h e same reason aluminum sulfate cannot be used in such pressure-filtration systems. It is a strange fact t h a t makers of pressure filters will contract t o provide filtration plants for swimming pools in t h e face of t h e above difficulties a n d make n o provision whatever for supplying artificial alkalinity, They must know very well t h a t t h e alkalinity mill be exhausted after a definite number of refiltrations and t h a t raw water with low alkalinity will not react a t all. It is generally conceded among filter men t h a t one grain of aluminum sulfate per gallon of water is t h e minimum and t h a t each grain per gallon removes 7 parts carbonate per million. On this basis i t would require in t h e neighborhood of I O pounds of bicarbonate for each turn-over of a 70,000 gallon pool. JOHNSON
&
JOHNSON
LABORATORIES
NEWBRUNSWICK, NEWJERSEY.
57
SOME LABORATORY CONVENIENCES By A. E. PERKINS Received Xovember 27. 1916
Fig. I illustrates a flat bottomed Kjeldahl flask used t o replace t h e special flask described in connection with t h e writer's extraction apparatus.l I n these days when all kinds of hand-made and special glass apparatus is so expensive and so difficult t o obtain, t h e advent of a n y simple b u t efficient homemade substitute should be welcome. Fig. I is selfexplanatory. The coiled spring D may' be satisfactorily made from KO.2 0 brass spring wire. We make use of alundum extraction capsules, C, b u t there would seem to be no good reason why other forms could not be used equally well. We are also now making use oE t h e regular stock size test tube I O in. X I in.> for t h e condensers B instead of t h e special size specified in t h e original description referred t o above. Fig. I 1 illustrates a simple, convenient, and very satisfactory home-made burette support. T h e support is attached t o t h e overhead shelf E , on which t h e bottles l , , ,@ ,#
"
B
'
y
@
,
I
FIG.I1
of standard solutions are kept. This arrangement leaves t h e table t o p free from encumbrance. The novel feature of t h e support as here described may be briefly stated as follows: A , t h e rod t o which t h e burette clamps are attached, is of 3/8 in. diameter and may be of any convenient length. It is threaded for about 6 in. on t h e upper end. B , B are hardwood strips 18 in. X 2'/2 in. X '/B in. bored a t a suitable distance from t h e end t o permit the p a s a g e of the rod A . B is their vertical projection. A burr and washer are provided above and below each of the strips B . B , as shown a t A'. These when tightened hold the rod a n d strips securely in place. t h e distance between B , B , being adjusted according t o t h e thickness of t h e shelf. -4 slit or groove G, in. wide and as long as desired, is cut beginning near t h e other end of each of the strips B , B; a 3/s in. bolt of proper length is prorided with a washer; and a burr with attached lever, or t h u m b n u t as shown at C,D ,grips t h e support firmly to the shelf. T H I S JOURNAL. 6
(1913). 148.
