CARBON DIOXIDE USED IN THE DISPOSAL OF WATER SOFTENING-PLANT LIME SLUDGE Thesis for the Degree: of B. S. ~MICHIGAN STATE COLLEGE Robert G. Bottoms 1939 ' THFF'S Carbon Dioxide Used in the Diaposal of Water Softening-Plant Lime Sludge A Thesis Submitted to The Faculty of Michigan State College of Agriculture and Applied Science by Robert Gale Bottoms H Candidate for the Degree of Bachelor of Science June 1959 TF4 FTC” é Acknowledgement This report covers the investigation of lime sludge dis- posal suggested by Mr. H. J. Faust of the Engineering Division of the Michigan Department of Health. I wish to thank Kr. E. F. Eldridge for his helpful crit- icisms and suggestions which he so willingly made during this investigation. I am also indebted to the Civil Engineering Department of Michigan State College and Mr. Eldridge for the use of the laboratory equipement and chemicals used during the investi- gation; and for the samples of lime sludge secured from Ann Arbor and Saginaw by the city of Lansing and the Michigan Department of Health. ] 3 Robert G. Bottoms O a m an C13 :30" Table of Acknowledgement Statement of Problem . . Discussion and Procedure . Illustrations. . . . Explanation of Tables. . Tabulated Data. . . . Graphs. . . . . . Results and Conclusions . Bibliography . . . . Contents Page 10 15 14 18 25 25 Carbon Dioxide Used in the Disposal of Water Softening-Plant Lime Sludge Statement of Problem The lime-soda process of water softening produces a sludge Which is mostly composed of calcium carbonate and mag- nesium hydroxide (CaCO and M8(OH)2). This method of soften- 5 ing is to be used by the City of Lansing in their new treat- ment plant now under construction. Approximately forty tons of lime sludge will be discharg- ed daily from the Lansing water softening plant when it is put in Operation. As yet no provision has been made to dis- pose of this sludge. The Lansing sewage disposal plant will be inadequate to handle it and does not constitute a satisfactory means of dis- posal. Dumping the sludge into the river is also undesirable. Transporting it to some location outside the city would be another undesirable method of disposal because the accumulat- ion of sludge will fill the available land in a short time. Therefore it seems that it would be best to investigate any other means for disposing of the sludge or rendering it so that it might be more easily disposed of. In View of this fact, it has been suggested that this sludge which is largely calcium carbonate be put back into solution by changing to a soluble bi-carbonate by the add- ition of carbon dioxide (002) and discharging it into the l Grand River. An available supply of carbon dioxide is the flue gas from the new Ottawa Street power plant also owned by the City of Lansing. This purpose of this investigation was to determine (1) the feasibility of using carbon dioxide to redissolve lime sludge, (2) the concentration of the lime sludge and its comrd poSition, (3) the amount of dilution necessary, (4) the rate of smlution, (5) the amount of gas necessary, and (6) the depth efficiency for the sludge in tanks where the treatment is to take place. Discussion and Procedure In the lime process of water softening, sufficient lime is added to react with all the bincarbonate present in the water, the magnesium in any form, and to react with the free carbon dioxide. The amount of lime necessary may be determin- ed by laboratory analysis not touched upon by this investiga- tion. ‘ The reactions between the lime and the hardness prOper- ties of the water ace: C8(HCOS)2- + Ca(OH)2 --r 208C05 + BHZO Mg(HCOE)2 + Ca(OH)2 --u--MgCO5 + CaCOs + 2H20 MgCO5 + Ca(OH)2 -->-Mg(OH)2 + 08005 Mg012 + Ca(OH)2 --..Mg(0H)2 + Ca012 Mg(NO5)2 + Ca(OH)2 --v-Ma(OH)2 + Ca(N05)2 MgSO4 + Ca(OH)2 --+-I\‘Ig(OH)2 + CaSO4 002 + Ca(OH)2 -..-Caco5 + H20 The reactions that take place when soda-ash or lime and soda-ash are-added to a hard magnesium water are: 08804 + NaZCOS ---CaCOs + Na2804 Ca012 + NaQCO5 --v-CaCC3 + 2NaCl Ca(N05)2 + Na2003 -—..Caco3 + 2Nauo3 Calcium carbonate has been found to be the main constit- uent of the sludge from a lime or lime soda-ash treatment plant. Other elements which make up the remainder are in much smaller quantities; the main one being magnesiun hydrox- ide which is,with the others,considered of a negligible 5 amount in this investigation. Lime sludge resulting from the removal of hardness from water either by the lime or lime soda-ash process has present- edarproblem ever since the introduction of the process and use of lime in water softening over a century ago. Some investigations have found various methods for dis- posal of this sludge which are used out of necessity rather than from choice, although there may be some choice between two or three methods of disposal. It is with lime sludge dis- posal as it is with the design of water treatment plants; an individual study of the community to be served is necessary in order to determine the most satisfactory yet economical method of handling the problem. Various methods which have been investigated, tried, or used in the past are: l. Discharging into a nearby stream or drainage ditch. 2. Calcining and using again for the softening process. 5. Transporting in wet state to low ground for filling or ponding reclamation. 4. Partial or complete drying for use as a soil sweet- ener. 5. Use as filler for paints, putties, wall boards, etc. In the first case, when the sludge is discharged into the river or drainage ditch, it results in extensive deposits of the insoluble particles, which, when allowed to accumulate, result in a river bed of increased elevation, which in turn affects the drainage of the surrounding land. In various sections of the country today, peOple are having impressed upon their minds the importance of prevention of stream pol- lution and of stream control. While lime sludge, if chem- ‘ically pure, presents no health hazards, it certainly will not improve the beauty of the stream and does reduce the eff- ectiveness of one argument againta stream pollution, which is the appearance of streams and other bodies of water. The second case: It has been suggested by several part- ies that the lime be calcined and reused in the water soften- ing process. However, it was found in Grand Rapids, Michigan that there is an ever increasing amount of other elements in the sludge as it is used over and over again. Due to this fact and that in their case the specifications called for a lime having 85 percent calcium oxide present to work satis- factorily, this possibility was eliminated. The third case is used in the mahoning Valley Sanitary District, Youngstown, Ohio, where lime recovery was consider- ed but did not seem practical. It was decided to adOpt sedi- mentation in ponds. Three ponds were constructed, each of which it was believed would hold the sludge accumulated over the period of one year. It was planned (1953) to fill one pond at a time allow it to dry, and then clean it out and use the sludge for fiilling low land or that it be taken by farmers to apply to soil. This sludge settled to 70 percent moisture very rapidly and to about 60 percent in the pond. 5 The first pond \1935) was approximately 59 percent full at the end of ten months of use and the sludge had a moisture content of 60 percent. It was found possible to dry the sludge in drying beds, in Grand Rapids, to 50 percent moisture, in the summer, and with good drainage they have reduced the moisture content from 85 to 55 percent in seven days. They have also conduct- ed investigations on the use of the centrifuge, which drys the sludge to 66 percent moisture. In the centrifuge, vari- ous strata of the sludge is formed, with practically all of the organic matter in one layer. In connection with the fourth case mentioned, use on the farm, all of the layers would be desirable for soil sweetening, while if used as a filler (case 5), it wouldtbe desirable to have the organic matter removed. After'the centrifugals were used it would be necessary to further dry the sludge in furnaces. Quite a great deal of agricultural lime has been sold to farmers. There is a tendency for the sludge to assist in re- taining moisture when mixed with sandy soil. This in itself could be an important factor if used in advertising to sell the lime to farmers. Use as a filler in plaster and insulating boards is poss- ible and boards made in this way have been found satisfactory according to leading testing laboratories. However to be feasible, the sludge would have to be obtainable close to the 6 base at Operations and at a very lowcost, as would the other materials used in the manufactUre, in order to make it econom- ically sound. A commercial develpqnment of any of the aforementioned possibilities has not been made but has been considered in Grand Rapids and would be possible if a.definite order to cease river pollution with sludge were given.. Lansing's water, which is supplied from wells, has a hardness of 400 p.p.m. according to the State Department of“ Health. It will take 2.8 pounds of lime to treat 1000 gallons of the water. It is planned to treat nine million gallons per day; using 25,200 pounds of lime, which will produce a sludge of 57.8 tons on a dry basis. This will give the reader some idea of the importance of disposal. In this investigation, it was necessary to first use a typical sludge and analyze it. A five gallon sample was obtained from the treatment plant at Saginaw, Michigan, and another from Ann Arbor, Mich- igan. The Saginaw plant has the lime soda-ash process, while Ann Arbor uses solely the lime process. The analysis of the two samples were run in the same man~ ner. For the moisture content, a 25ml. sample of the sludge was weighed, dried in a 105°C oven and the weight of the dry sludge was determined. Approximately 25ml. of the Saginaw sludge weighed 25.8702 grams and the dried sludge weighed 2.4077 grams, thus 25.8702 grams of the sludge sample contained 25.4625 grams of moisture 7 or 90.6 percent. Approximately 25ml: of the Ann Arbor sludge weighed 24. 4570 grams and the residue weighed 0.1557 gram, thus the 24. .4570 grams of the sludge sample contained 24.5015 grams of moisture or 99.2 percent. To determine the calcium present the following method was used: (1) weighed 0.50 gram dry sludge (2) added 50ml. 1—3 hCl ((5) heated to boiling to dissolve (4) filtered through quantitative filter and washed (5) ignited residue in muffle furnace to red heat, cool- ed, and reweighed; gave weight of inertrfiaterial (6) to filtrate from (4) added 20ml. (10% NH4Cl) and made alkaline to litmus with NH40H(conc.) (7) heated to boiling and added 25ml. saturated ammonium oxalate and set in warm place for thirty minutes. (8) filtered on quantitative paper and washed (9) titrated calcium oxalate with KMnO4 (10) to filtrate from (8) added 15ml. NH 0H(conc.) and 20 4 of NagHPO4 (10% solution) and let set for four hours (11) filtered on quantitative paper (12) ignited paper and residue (15) reweighed; gave weight of Mg It was found that a 0.50 gram sample of the Saginaw sludge contained 0.0086 gram of inert material, 0.0254 gram of Mg(0fi)2 and 0.425 gram of CaCOB. On a percentage basis 8 there was 1.7 percent of inert material, 4.7 percent magnesium hydroxide, and 85 percent was calcium carbonate. It was found that a 0.50 gram sample of the Ann Arbor sludge contained 0.0015 gram of inert material, 0.0205 gram of Lig(0H)2 and 0.4458 gram of CaCOs. On a percentage basis, there was 0.5 percent of inert material, 4.06 percent magnes- ium hydroxide, and 88.8 percent was calcium carbonate. Theoretically the addition of carbon dioxide would change the calcium carbonate to calcium bi-carbonate, which would be soluble in its own moisture content, for it is an established fact that at 20°C or normal room temperature, 16.6 grams of calciumbtarbmnate is soluble in 100 grams of water. The laboratory work for changing the carbonate to bi-car- bonate was done with apparatus shown in the illustrations, page 10, A Kipp generator using limestone and 1-1 hydrochlor- ic acid was originally attempted, but the limestone gave off a great deal of hydrogen sulphide as well as carbon dioxide. Due to the fact that it wasn't known whether the hydrogrn sul- phide affected the desired dissolving of the calcium carbonate, and that there was the highly disagreeable odor to contend w with, it was decided that som other method should be used. The most satisfactory apparatus found was the one shown, using a separatory funnel, a Erlenmeyer flask, rubber stmpper, rubber tubing, a Y glass tube, two ammonia tubes, and a one liter graduate. Small pieces of a rubber stOpper were placed on the ammonia tubes and used as baffle plates in an attempt to slow down the passage of carbon dioxide through the sludge, 9 Illustrations ’ JVv/ I“ -4" v" Illus. 1 Shows the apparatus used in the laboratory. Two were used to make the best advantage of the time available. 10 Illus. 2 Shows the ammonia tubes, with" rubber tubing attached, also shows the two tubes braced apart with two larger pieces of rubber tubing (note arrows) The slices of rubber step- per used as baffle plates are also shown. giving it more chance to dissolve the carbon dioxide in the water. . Calcium carbonate was placed in the flask and 1-1 hydro- chloric acid was used,being admitted to the flask by the stOp- cock in the funnel. In this way it was possible to obtain carbon dioxide without the hydrogen sulphide and to run the gas through a higher column of water, due to the fact that a higher gas pressure was available and the friction loss through the ammonia tubes was less than through the diffusion disk used with the Kipp generator. This increased height in the column of water, it was believed, would increase the eff- iciency in the Same way as the baffle plates. Due to the fact that Saginaw's sludge was condensed to some extent, it was decided to run all dissolving tests on the Ann Arbor sludge. I Several set-up's of the apparatus were,made and the sus- pended solids tests were made on the sludge before starting and at frecuent intervals during the time that carbon dioxide was bubbling through the sludge. Tests were run three times on the sludge as it was, with- out dilution. Tables I, II, and III show the results obtain- ed. 1 Following these, tests were run on the sludge diluted 1-1 ‘(one part sludge to one part distilled water), 1-5, 1-4, and .1-5. tables IV,_V, VI, and VII. The lengi% of time of run was shortened because it was shown in the first three runs tnat the maximum percent dissolved occurred by the end of the - ll first two hour period. Then it was decided to re-run tests on 1—1 and 1-5 dilutions in order to approximate the length of time from the start in which the major part of the dis- solving took place, tables VIII and IX. The method for determining the suspended solids or the undissolved sludge as it were, was to use« a Gooch crucible with an asbestos mat, dried and weighed, than the 50ml. sam- ple taken in each case was filtered with the suction filter and aspirator, and dried in a 10500 oven and weighed. The difference in the weight represented the smount of suspended solids. In this way it was possible to determine the percent- age dissolved in a certain length of time. Explanation of Tables The tables have several columns and need some explanation in order to eliminate a lengthy heading for each column: Time, is the length of time that the carbon dioxide had bubbled through the sludge before the test for suspended sol-' ids was made. In the case of "0" tine, it is for the amount of suspended solids in the sludge before the gas generator was started. Cruc. Ident., is the identifying mark on the crucible used. That is, several crucibles used in this experiment were used and in the oven at the same time as well as for the cruc- ibles used in other eXperiments being conducted in the labora- tory. Dry Wt., is the weight of the crucible with the asbestos mat in the crucible used for filtering. Dry Wt. and 801., is the weight of the crucible with the asbestos plus the suspended solids from the sample after it has been dried. Wt. Sol.,is the weight of the suspended solids in the sample taken. At "0” time it is the total amount of suspended solids in the sludge in order to give a basis for figuring the amount of the solids dissmlved in a certain length of time. ’ Per. Dis., is the percent of the original suspended sol- ids in the sludge that has been dissolved in the particular length of time given. 15 Time 0303t¥>O <1 0'1 ion-2 CE (0 Cruc. Ident. Cruc. Ident. Tables Table NO..I Undiluted Sludge Dry Dry Wt. Wt. & Sol. 16.0054 16.2566 16.4154 16.6104 15.5485 15.7449 16.5084 16.4944 Table NO. II Undiluted Sludge Dry 9W, t 0 16.0054 18.0118 16.4440 15.9555 16.5966 16.4650 18.0518 14 Dry Wt. 8C SOJ. 0 16.2566 1811845 16.6500 16.1182 16.5681 16.6458 18.2426 Wt. Sol. 0.2512 0.1950 0.2066 0.1869 W t o Sol. 0.2512 0.1725 0.1869 0.1827 0.1715 0.1828 0.1908 Per. Dis. 0000 Time ()3 Time Cruc. Ident. 4 R G I‘I’I Cruc. Ident. Table No. III Undiluted Sludge Dry Wt. 16.0054 14.4621 15.8651 16.4249 15.4887 Dry Wt. & Sol. 16.2566 14.6654 16.0854 16.6556 15.6960 Table No. IV Sludge Diluted 1-1 Dry )6; t 0 15.7248 16.5522 14.4628 16.4915 15 Dry Wait 0 & Sol. 15.8476 15.4515 14.5459 16.5665 12'! 3' Q Sol. 0.2512 0.2015 0.2005 0.2107 0.2075 W t . Sol. 0.1228 0.0795 0.0811 0.0750 Per. Dis. 00.0 19.8 20.2 16.1 17.4 Per. Dis. 00.0 55.0 34.0 59.0 Table No. V Sludge Diluted 1—5 Time Cruc. Dry Dry Vt. Wt. Per. Ident. Wt. & Sol. Sol. Dis. 0 61 18.0542 18.1160 0.0618 00.0 2 52 15.925 15.9557 0.0298 51.7 4 02 16.6448 15.6749 0.0501 49.7 Table No VI Sludge Diluted 1-4 Time Cruc. Dry Dry Wt. Wt. Per. Ident. Wt. & Sol. 801. Dis. 0 4 16.0595 16.0906 0.0515 00 1 61 18.0558 18.0780 0.0222 57 2 28 15.4955 15.5182 0.0229 55 4 HGM 14.5490 14.5717 _0.0227 56 16 Time 15101-40 Time Time Cruc. Ident o 26 _ '71 5.. Ca 82 Cruc. Ident. 4 28 82 Cruc. Ident 0 Table No. VII Sludge Diluted 1-5 Dry Dry Wt. Wt. 8c Sol. 16.4506 16.4795 16.4558 16.4680 15.9150 15.9505 16.5226 16.5549 Table he. VIII Sludge Diluted 1-1 Dry Wt. 16.0562 15.4748 16.5688 Dry Wt. & Sol. 16.1520 15.5698 16.4552 Table No. IX Sludge Diluted 1-5 Dry 1N t 0 18.0405 15.8065 15.9455 17 Dry Wt. & Sol. 18.1040 15.8415 18.9740 Wt. Sol. 0.0489 0.0142 0.0155 0.0125 Wt . Sol. 6.1158 0.0950 0.0844 Wt. 801. 0.0657 0.0550 0.0285 Per. Dis. 00 71 69 75 Per. Dis. 00.0 18.0 27.2 Per. Dis. 00.0 45.0 42.7 0) 000% D K :1 4} .Q wtmbkvq . _ a-— ‘.\|‘HIL‘|.|.' nr(l(fl . u. ‘I I . I - II l’ll III I'll I'll Y’ -L- v—rt-b P, 0 L y L, V3 1 ,. p‘rr 9 v c f a > ' T‘ s—3— 0 .I.¥LL,¢2 .1 (fr A‘. II. £11 .L . . .v. -11.! ‘klo‘v'. 75:91. 91.. .1)» . rill. 1 r-5.l?*.¢ ‘t ————-.___4 4-. —< - —— 4.1. .4 .-_.._.__....J 0 . 1 _ h . . _ 1 1 . 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V. a. .v. .1 . ~ . T .i .. . .. ... v1 . . l. .1 .. 1 .. a .. i. .r .. 1 t. . w. . . _ . F _ . . . . e . . . I . _ . 1 . . . . . 1 . . . . . . . > . y. .l .. . ...... . _. . . S . . ,. . :1 . I L I. .‘I . . . . n 1 u. . .eV. ... on. .v o 1 e - b . IV . . f‘. . _. 1 . . .. .. . .. . . . . . . ... . .1 .. . .... . ... . — qv . e r w n. u.- . v.‘ e: u . .. . .. .1 - 1 1 ,1? _ . .. .. .. , 1 . .... . .. .1 . . . .. . ... . 1. s u. .0 qt 6...; .. u. . .40. v... . . v. . a . . . . i. . . .... ...... .. . . ....- .. . r .. .. . . . _ P . . .1 . . _ . . . . . .. . 1 .‘. .. v. - . . .. ~.1 H a t r r > .!1|f . t {.17 9|.. ..‘|1. wlYo .L .0 ols| . ‘4’. A . . 1 L1 .I? 6. 1 I pl. 1 .1. f «L 11-17;; 1 >LV.O141$111? 1... . VIP] . I «L11. 1. T. o. Results and Conclusions As may be seen from the tables (I - IX) and the graphs (1 - 9), there was little change in the amount of sludge dis- solved after the first one or two hour period, and the maxi- mum was dissolved when the sludge was diluted 1-5. The 1-5 dilution showed from 70 to 75 percent of the sludge to he dis- solved in the first two hours. On the basis of the moisture content of the Ann Arbor sludge of 99.2 percent and the fact that the plant will dis- charge 57.8 tons of sludge on a dry basis daily, it would mean that the undiluted sludge discharged from the plant would am- ount to 4725 tons, 9,450,000 pounds, or 1,152,000 gallons per day, and, when diluted 1-5 and subjected to dissolving by the carbon dioxide process, there would be 6,792,000 gallons of water wasted into the river and in addition there would still be 9.45 tons of sludge left undissolved to be deposited on the river bed. On the basis of the graph (no.10) showing the effect of dilution on the percentage dissolved at the end of a two hour period, and assuming that hhere is a straight line relation- ship between the amount dissolved and that 95 percent dis- solved would be satisfactory, a dilution of 1-8 would be neces- sary to waste into the river each day 10,188,000 gallons,of water, wnich is more than the anticipated amount of water to be treated by the plant daily. Another fact, whose effect on the result is doubtful, is 25 that distilled water was used in the laboratory experiments. This might mean that the dilution would have to be still great- er. Therefore it is evident that the treatment of lime—sludge with Carbon dioxide and disposal in the river would be unsat- isfactory, which contradicts the assumption that was based on the fact that the lime-sludge should have dissolved in its own moisture content. There is no apparent reason found in the experiments to. explain the fact that calcium carbonate did not dissolve in the presence of carbon dioxide. It is possible that the rate of formation of Galcium bi-carbonate is very slow and beyond the limits of the practical application of the process. How- ever, no explanation can be given for the first reduction in solids followed by no apparent reaction after the first hour 01" CWO o Champion, H. T. Dittoe, w. H. Eldflidge, E. F. Hoover, C. P. BibliOgraphy "Lime Sludge and Its Disposal" JAWWA Vol. 26, 1954 "Disposal of Lime Sludge at Water Soften- ing Plants." 'Vol. 80, 1955 "The Disposal-or Water Sortening Plant Sludge at Sewage Treatment Plant, Grand Rapids, Michigan, Michigan Engineering Ex- periment Station Bulletin Number 40. Water Supply and Treatment. Johnson, Alfred M. F. A Study of the Mechanism of Water Soft- Steel, Ernest W. Theroux, Eldridge, and Mallman ening with Lime. Water Supply and Sewerage. Analysis of Water and Sewage. g, If. 1} 11m... ”11 .1 t . .. . ' C. H IG A N M S E P A 1 R B L . V. T S 1 R H E V N M U E Tl A VI? 1.: