WASTES

April 1950

INDUSTRIAL AND ENGINEERING CHEMISTRY

of about 90 gallons per minute a t 1050 to 1300 pounds per square inch and ran this way until sometime around the middle of September 1948 when during a period of about 4 hours the pressure dropped from about 1300 t o 750 pounds per square inch. Why is not known, but it was presumed t h a t the water must have broken through to a more porous portion of the formation. Operation has continued since then on the basis of 60 to 90 gallons per minute disposal a t pressures of something on the order of 800 pounds per square inch. A second disposal well was drilled and was found t o have substantially the same capacity as the first. Thus, with both wells in service the entire disposal system has been shown to be adequate for the expected requirement of 150 gallons per minute. A complete analysis of the reservoir water was not made because such analyses from other wells in this area were available, but a special determination for barium disclosed the presence of 10 p.p.m. which was not considered high enough to interfere with the use of the well for disposal. Operation has justified this belief, FUTURE O P E R A T I O N

After the black dyes have been leached from all the tower a new jar-test study will be made to determine the best and cheapest chemical dosage. As the blowdown from the tower increases, some of the other wastes can be reduced in quantity. Probably the water from gas cooling can be treated for make-up t o the cooling tower. Now fresh water, amounting to about 25,000 gallons per day, is used for operation of the dry chemical feeders and chlorinator. Probably treated waste water can be used for all of this except the water for the activated silica feeder and reduce

599

the load on the disposal well. Elimination of these lowsolids waters will bring the concentration of the treated water more in line with the calculated results shown in Table I. CONCLUSION

After 18 months’ operation i t has been demonstrated that a treating system in general use in t h e oil fields for disposal of salt water can be used directly for treatment of waste water from a chemical plant. The presence of soluble wood compounds, after proper treatment, appears t o have no deleterious effect on the disposal well, and it is believed that a permanent solution of the waste disposal problem a t this plant has been reached. ACKNOWLEDGMENT

The author wishes to express his appreciation for help rendered by C. V. Edwards, Jr., and E. L. Stovall, Magnolia Petroleum Company, Dallas, Tex.; J. A. Upton and Jerry F. Gleason, Jr., Magnolia Petroleum Company, Premont, Tex.; Cover C. Porter, Southland Paper Mills, Lufkin, Tex.; Joe M. Young, Infilco Inc., Houston, Tex.; and H. B. Gustafson and A. S. Repa, Infilco Inc., Chicago, Ill. LITERATURE CITED

(1) Hess, R. W., Sewage Works J., 21, No. 4, 674 (1949). (2) Pulp and Paper Industry, United States and Canada, Joint Executive Committee on Vocational Education, “Manufacture of Pulp and Paper,” Vol. 3, seo. 7, p. 12, par. 19, 1937 I~BCEIVED January 23, 1980.

NEUTRALIZATION OF ACID WASTES B. W. DICKERSON

AND

R. M. BROOKS

Hercules Powder Company, Wilmington, Del.

N THE manufacture of T h e solution to a difficult waste acid neutralization occurred when the percentproblem is outlined. The acids handled were nitric and nitrocellulose a t the age of sulfuric acid rose Parlin, N. J., plant of sulfuric, and they varied widely in volume, concentration, above 1.3%. This seriously and ratio. Neutralization was accomplished effectively the Hercules Powder Cominhibited t h e r e a c t i o n . pany, large quantities of in a multiple unit reaction chamber provided with twoSince there was no chance water are used which bepoint pH controlled addition of dolomite lime slurry. of providing additional come contaminated with Use of a multicompartment chamber eliminated effect of waste water for dilution, nitric and sulfuric acids. rate of flow. pH controllers employed immersion electhe use of slaked lime was The concentrations of these trodes placed directly in reaction chambers. Design and a necessity. Studies of are low, ranging from 0 to operating data are given. available material in the about 1.50/, as sulfuric acid. North Jersey area revealed The percentage of each acid that a burned dolomite varies widely. The total quantity of acid waste water discharge stone containing about 47.5% calcium oxide, 34.3% magnesium varies with process operations and wide fluctuations are exoxide, and 1.8% calcium carbonate was the most satisfactory and perienced during very short periods of time, from as low as 2000 economical, While the authors did not know it at the time, gallons per minute up to 10,000gallons per minute maximum. this stone provided the additional advantage of holding residual Originally, provision was made for collection of process waste sulfation to a very minimum, an impossibility with any of the waters into one main trunk line sewer, which conveyed them high calcium limes where such concentrations of sulfuric and across the plant property and into the South River, As time nitric acids are t o be neutralized (1). passed other acid wastes from plant operations were connected The original plant was designed for manual control of all into this sewer so t h a t today practically all wastes are carried operations and neutralization was to be accomplished in a in this one line. They are still preponderantly sulfuric and several hundred-foot section of the acid sewer itself. nitric acids. The plant comprised a Dracco vacuum system for unloading During 1941, it became necessary to provide for neutralizathe lime from box cars and delivering it into an elevated storage tion of these acid waters. I n the studies which were made of the bin holding about 50 tons. The matcrial then flowed by gravity problem, it was found that the normal practice’of using crushed from the storage bin into a Hardinge Feedometer having a limestone was not applicable since sulfation of stone particles maximum capacity of 58 tons per day. The measured materia

I

4

INDUSTRIAL AND ENGINEERING CHEMISTRY

600

was discharged into a Dorrco slaker provided with a classifier for mechanical removal of large unburned particles and inerts. The water required for slaking was made up of waste hot water available from a nearby process area and cold plant service water. Steam connections veie provided for manually controlling the temperature in the slaker above 170" F., for there Tvas insufficient hot watcr available a t all timcs. The slurry strength varied betveen 10 and 207,.

Vol. 42, No. 4

the authois found that residual sulfation occurred on leaving the resetion unit. This produced calcium sulfate deposits in the cfflucnt line. The problem TTas solved successfully by adding 17 sste cooling water into the OVerflQTv chamber of the unit equivulcnt to about 570 of the maximum Aom. After this change there lvere never any deposits formed in the effluent lines. Laboratory studies made later indicated that the trouble could have bcen eliminated by the use of dolomitic lime. ilt the Parlin, N. J., plant, dolomitic lime mas in U E ~so that this problem would not arise if this arrangemcnt were used. Ilowever, the ordnance airangcment produced a loss of head of 3 feet which was impractical a t Parlin. Here, the neutralizer had to be fitted into an existing sewer Iine where grades were fixcd anti the ~ o t anllovr l able loss of head ivss 9 inches. PLANT OPERATING D A T A

Figure 1. Division 30 40

Rate of Flow in

Acid Sewer Chart Scale Gallons per Minute

50 60 70 80 90

The slurry was discharged a t a point in the 24-inch acid sev,Ter line which provided about 500 feet for mixing and neutralization before leaving the plant proper. The rate of feed of lime was manual, adjustment being made on the basis of hourly sampling for acid strength. Close control was impossible but major neutralization was accomplished. With more stringent steam standards, this method of manual control was insufficient to provide uniformly complete neutralization of the wastes and so studies were instituted t o develop a more adequate means of neutralizing the acid waters.

The first step in this program was t o study flows and aciditics. The gradient was carefully established between two manholcs several hundred feet apart and in the loa-er one a recording float gage installed so t'hat s chart record could be obtained of the depth of flow in the saver. A rating curve was made up and carefully checked by the use of dye. From this curve water level records could be converted into flow. Figure 1 is a typical chart record of flow to be handled during a 24-hour period. From this i t will be seen t h a t there was wide and frequent variation in rate of flow. The maximum indicated is 9500 and the minimum 3500 gallons per minute. Other chart records indicated maximums of 10,000 and minimums of 2000 gallons pcr minute. With complete shutdown the flow would drop to zero. The problem QI determining acidities wa$ more complex. Samples from the sewer were taken at 2-minute and 15-minute intervals a t different periods during the dag and tit,rated for total acidity. These indicated that the acidity varied from 0 to l,5yo a8 sulfuric acid. An attempt as made to correlate aciditics with flow rates but no correlation existed. Figure 2 s h o m a sample plot and the impossibility of such correlation. In conjunction with fiow and acidity mcasurcments, chcclcs were made on temperature and thcse were found t o range between 75' and 1'70' l?. Here again there was no close correlation, t,he higher temperatures usually coinciding u-ith thc higher fl0K-s. L A B O R A T O R Y AND E N G I N E E R I N G STUDY

With all the field data collected, laboratory studies wcrc instituted to dekrniine reaction rate curves and lime requirements.

N E U T R A L I Z A T I O N EXPERIENCE IN O R D N A N C E P L A N T S

During the war, the authors had had similar problems in the ordnance plants manufacturing smokeless powder. There, extremely large quantities of these same acids, a t about the same concentration, had to be neutralized before being discharged into the receiving streams. The problem had been solved satisfactorily by the use of single-stage reaction chambers employing recirculation with ratios of from 10 t o 30. Ten per cent lime slurry was used and its feed controlled by means of Leeds & Northrup p H controllers. I n order to compensate for the variations in rate of flow into the units, a Parshal flume was constructed ahead of the reaction chamber. A flowmeter was installed on this and connected electrically into the lime controller. By this arrangement the feed of lime was controlled both by pH demand and rate of flow. Good control was obtained. High calcium burned lime was used for neutralization and

0 3000

I

!

4

!

I

4000

5000

6000

7000

8000

F L O W IN G . P M

Figure

2.

Flow vs,

Acidity in Waste A c i d Sewer

Dl K)

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

April 1950

TION CHAMBER

CLAS~IFIER e

4

CIRCUL~ATING Figure

LIME SLURRY LINE

3. Flow Diagram

These requirements indicated t h a t a retention period of about 5 minutes was necessary for complete reaction of the lime. They also showed t h a t the total quantity of lime necessary t o bring the p H t o 4.5 varied between 101 and 108% of theoretical. Of this, about 95% was necessary t o bring the p H up to 2.0 and the remaining 6 t o 13% from 2.0 to 4.5. Thus, in the design of the slurry feeding equipment at the reaction chamber, a single control valve had to be large enough to pass 108% of maximum theoretical, and if two stages of feed were employed the first had to be of this same size while the second should have a capacity 20y0 of this. The selection of the reaction chamber was the number one problem. Past experience had indicated the need for both p H and flow control on lime feed. The authors were limited in total head loss below t h a t necessary for a n y type of primary metering. Therefore, some other arrangement for control was necessary. The possibility of a multiunit reaction chamber was studied. I n investigating the multiunit reaction chamber a control analysis was set u p on the basis of 1-minute retentions at normal flow in well-agitated tanks. A unit of four tanks in series was selected. It was considered possible for the raw influent to change from a pH of 6.0 t o a maximum acidity of 1.274 in a period of 5 minutes. The computations showed t h a t under this condition the PI-I would be 1.8 in the first, 2.3 in the second, 2.7 in the third, and 3.1 in the fourth, at the end of a 1-minute period, respectively, and would go lower in time. A similar analysis was made on flow considering a variation from 5500 to 9500 gallons per minute in 5 minutes. The authors found that the p H in the first would be 1.0, in the second 2.0, in the third 2.6, and in the fourth 3.0. Their computations were based on unbuffered solutions and, since the wastes t o be handled would be buffered, the magnitude of change should be considerably less. It was concluded t h a t by placing control in the third tank the effects of flow could be eliminated and control made by pH alone, I n order to improve the over-all control i t was decided to apply two-point application with the major share of the lime in the third chamber. The design was established so t h a t the fourth chamber would be used for averaging the initial control and a fifth tank was added for final trimming with a small quantity of lime. The unit was thus established with five chambers each provided with good agitation. This problem was discussed in detail with the engineers of the k e d s & Northrup Company and their calculations confirmed the authors' studies. The multiunit reaction chamber was established. G E N E R A L ENGINEERING DESIGN

The ordnance plant experience had been with electrical operation of the controllers and lime feed valves. Here there was

601

too much lag for best control. Experience on p H control at another plant wherein air operation was used indicated much quicker response than with the electric type. From this it was decided to use air-artuated p H control units and those manufactured by Leeds & Northrup were selected. It had also been found from past work t h a t the butterfly valve was best suited for control of lime slurry feed since large variation in capacity could be controlled with small movement. This lent itself admirably to t h e diaphragm motor for air actuation and this arrangement was selected. Thenext point investigated was the lime facilities. The authors already had lime storage, fceding and slurry producing equipment, but these were limited as to the quantity t h a t could be produced in any given intcrval of time. Furthcrmore, they Were not amenable to quick change necessitated by the widely fluctuating flows and acidities. Some other arrangement washecessary t o providc for this. I n the authors' studies they had determined t h a t the existing equipment had sufficient capacity to handle the maximum acid discharged over 24 hours on a n average basis. It was necessary, therefore, t o determine peak requirements. These were established as average acidity and maximum flow and as peak acidity and average flow, each over a 20-minute period. The largest quantity of lime was required during periods of peak acidity and average flow. At this time the demand rose t o 7600 pounds of lime above the maximum average rate of slaking. Converted to 10% slurry volume this meant t h a t 1100 cubic feet of working storage facilities would be required. This storage would need t o be installed between the slaker and points of lime application in the reaction chamber. I n order t o control under all conditions there had to be sufficient lime available so t h a t when the demand came, t h e butterfly valves could open and the proper amount of lime be discharged. Furthermore, t o eliminate lag to a minimum, this lime had t o b e always available at the valve ready for use. To provide for this a slurry circulating system of ample capacity for peak drmands was considered necessary. The excess lime would be returned t o the slurry storage tank. I n addition, provision had t o be made to hold as nearly constant a head as possible on the control valves, in order t h a t their discharge capacity would be constant. Thcse points were carcfully considered in the lime feed system. FIELD C O N S T R U C T I O N

The invert of the main sewer was approximately 6 feet below ground level. Thus in the design of the reaction chamber, all retention volumes had t o be computed below this point. I n the h a 1 construction of the multiunit reaction chamber, serious consideration was given to protection of the concrete surfaces against acid corrosion. Past experience had indicated t h a t for maximum protection of concrete from acid corrosion, the proper procedure was to apply a primer coat and then a triple-layer membrane covering directly against the surface of the concrete tank. This was covered with two courses of acidproof brick for a total thickness of 8 inches. Membrane and brick were bonded with acidproof cement. All openings through the concrete walls and brick lining were made through 316 stainless steel sleeves set in the concrete and bonded into the wall and brick lining with acidproof cement. Terra cotta pipes were carried through these sleeves and bonded in place with acidproof cement. The new reaction chamber was located parallel with the acid sewer and about 150 feet away from t h e lime slaking building (Figure 3).

INDUSTRIAL AND ENGINEERING CHEMISTRY

602

Figure

4.

Reaction Chamber and

Control House

T o provide for bypassing the flow from the 24-inch sewer into the neutralizer, diversion manholes 1%ere installed in this ,line. These were constructed of reinforced concrete and provided wit'h acidproof brick lining. The diversion gates were fabricat,ed of 316 stainless steel and rode in guides fabricated of the same material. These manholes were built around the existing sewer line and, after completion of all constivction work, the terra cotta pipe between the inlet and outlet was broken out, the gates dropped in place, and diversion was under control. The reaction chamber was rectangular in shape and designed to have a normal working capacity of 38,000 gallons. It was constructed of reinforced concrete. The unit was divided into five chambers by means of wood baffles set in grooves in the walls and floor. These grooves were made by a selected arrangement of the brick lining. The baffles were held from floating by chrome iron rods bonded into the brick work. BafRing was arranged for under- and overflow and openings were dosigned for minimum losses. In the fift,h chamber an additional baffle directed the incoming flow downward. The agitation in each chamber was provided by a 42-inch diameter turbo mixer driven by a 7.5 hp. motor. These agitators mere designed by the Turbo Miser Corporation and provided not only good agitation but also excellent dispersion of the lime slurry. They were constructed of 316 shinless steel. They were supported on a structural timber framework becausc it provided greater resistance to corrosion from the vapors than one of all steel. Figures 4 and 5 show the general arrangemcril; and turbo mixer drives and supports. The lime slurry storage tank was of necessit)y located as close to the lime control building as possible t o keep piping to a minimum, Figure 6 shows the building and slurry storage tank. I n the design of the lime slurry tank the need for good agitation t o hold the lime in suspension \vas kept, in mind. A rectangular tank was constructed with a central cross baffle extending partway down from the top, making two equal-sized chambers. A 34-inch turbo mixer of cast iron Construction, driven by a 5 hp. motor, F a s installed in each chamber. The floor was sloped toward the end, away from the slurry inlet. The tank was arranged for a normal working volume of 1100 cubic feet. Ii had a total available capacity of approximately 1600 cubic feet. The tank was connected to the slaker by a steel line of welded construct,ion and provided ivith smooth curves where changes in direction were necessary. Lime requirements for maximum peak neutralization were computed t o be 550 gallons per minute based on 10% slurry. The minimum would of course be zero. It was felt t h a t 10% excess capacity in the circulating pumps should be adequate and accordingly they were selected for GOO gallons per minute.

Vol. 42, No. 4

During the ordnance work t,he authors Iiad used standard sump-type sewage pumps for handling lime. They were all iron construction and stood up fairly well. However, their general construction was not ideally suited for long life and so it was decided that a better constructed pump was required. Thtx pumps selected were to be able to withstand temperatures of 210 ' F. as it was planned to operate the slaking equipment a t not less than 200" F. The final selection was a modified tloep well-type unit constructed for a short sett.ing. The pump bowvl design had bearings a t each end so that there mas no overhang of the impeller. Intermediate hearings provided stability of the shafting. The bowl and impeller were of cast iron construction provided with a baked-on enamel finish. Thc customary oil column and bronze hearings were redesigned for cutless rubber bearings, and the head and t,ailshaft bearings were made of the same material. Provision \vas made to allow €or wat,er lubrication in the so-called oil column and tail bearing. Only a few gallons per minute were requircci for each. n l t h t.his arrangement the cutless rubber bearings were lubricated adequately and partially cooled. Furthermorr, since the lubricating water was under pressure, there was 110 chance for lime to n-ork into any OF tho bearings. The impcller side seals were eliminated and a cutlces rubber bottom seal T ~ employed, S thus holding \vc:tr t o one point. Provision was made in shaft adjustment to allo\\- for compensa tion for wear t h a t might occur a t this point. Two pumps were installed in the tloc~pchncl of the slurry storage chambers, and provided with ahvegrouiid discliarge. One was for normal use, the other a spare. Figure i shows t,hc top of the lime slurry storage tank with cleni,ric conti.ols, turbo mixer drivcs, and circulating pumps.

Figure 5.

Reaction Chamber Showing Agitators

The necessary piping to connect the pumps Mith the reaction chamber was installed underground. It was constructed of steel with standard cast iron flanged fittings. In the design of the piping system, main line velocities were held to a minimum of 5 feet per second and maximum of 7 . Lubricated plug cocks, with full body opening, suitable for lime slurry service were used in place of gate valves. No check valves nere installed , I n each pump-bearing v a t e r supply line, a pressure ewitcli

April 1950

INDUSTRIAL AND ENGINEERING CHEMISTRY

603

motors which controlled the movement of the valve vane through linkage. They were seleckd on the basis of discharge capacity a t 5 pounds per square inch. The No. 3 valve was 4 inches in size, the No. 5 was 2 inches in size. They were connected to cast iron flanged tees in the circulating line with a plug cock in between t o allow for isolation.

Figure 6.

Lime Storage and Slacker Building and Slurry Tank

was installed. It was set to make contact when the pressure dropped below 15 pounds. This actuated a relay which rang a bell and tripped out the pump motor. This arrangement eliminated any possibility of damage to the pump through low water pressure of the bearings. Figure 7. Top of Slurry Storage Tank with Agitators and I n the earlier installation steam was used a considerable porCirculating Pumps tion of the time in order to hold slaking temperatures to a t least 180" F. In the new system it was felt that maximum The valves discharged through stainless pipe into the cye of efficiency of the slaker would be obtained by holding the temthe turbo mixers. perature in the unit nearer 200" F. A study of the source of A supplemental line was installed adjacent t o each valve to hot water showed that contaminated condensate under some allow for manual dosing should the automatic control be down. pressure was obtainable. By the installation of storage facilities Figure 8 shows the butterfly valves, by-pass valves, discharge and cold water to condense the flashed steam, ample hot water lines from valves into the eye of the impellers, also slurry cira t about 200" F. could be provided. A storage tank was inculating lines. stalled and provided with the necessary steam and cold water In order to provide for a constant back pressure on the butterfly blending arrangement. Two pumps were provided, one to be a valves, the recirculation line was carried up to 12 feet in the air spare. Temperature of the water ranges above 190" F. and and allowed to discharge into an open-top tubular chamber which slaker temperatures run consistently above 200 F. discharged into the return line to the slurry storage tank. This Leeds & Northrup Micromax, p H recording, pneumatic conis shown projecting above the control house roof in Figures 4 trollers with automatic reset and rate action were selected. and 7 . These were of the strip chart type with a scale range, 0 to 8 O P E R A T I N G EXPERIENCE pH. Two units were installed, one t o control the admission of slurry at the No. 3 chamber and the second to control the adWhen the plant was first placed in operation, trouble was experienced with both sample pumps. It was found that vapor mission to the No. 5 chamber. These units were actuated from would collect in the priming chamber and gradually seal off t h e the standard glass electrode flow cells, which were housed in a pump suction. I n the case of the No. 1 unit taking its suction tile control house adjacent t o the reaction chamber. This building also held all electric controls as well as p H electrode from No. 3 chamber, the trouble was due to entrained air from. the agitation in the reaction chamber. The installation of a j e t sample pumps. Figure 4 shows the control house and its relation on the chamber greatly reduced the trouble. I n the case of t h e t o the reaction tank. No. 2 unit, the trouble was due to reaction of the fine unburned The sample pumps were of acid-resisting construction and were carbonate particles. This final reaction liberated carbon single suction centrifugal units, each having a capacity of 10 gallons per minute. They dioxide in t h e suction were provided with a sucline to the sample pump tion priming tank so that in and in the pump itself. V a r i o u s arrangements of case of power failure they jets for removing this vapor would prime t h e m s e l v e s were tried but to no avail. upon restarting. All piping Even tapping into the eye and valves from the reacof the impeller failed to help tion chambers to the pumps m a t e r i a l l y . Satisfactory and electrode a s s e m b l i e s were of stainless steel. operation was obtained for The control valves for anywhere from 15 minutes t o 5 hours, and then i t admission of the lime slurry to the reaction chambers would become necessary t o were of the butterfly type reprime. of cast iron construction. I n s t u d y i n g methods They were provided with of e l i m i n a t i n g t h i s Figure 8. Primary (/eft) and Secondary (right) Lime Slurry p r o b l e m , t h e f i r s t that air operated d i a p h r a g m Control Valve and Piping O

INDUSTRIAL AND ENGINEERING CHEMISTRY

604

came to mind I\ as the use of sump pumps constructed of stainless steel. D e l i v e r y o n these was extremelv long. The second rn a< the possibility of immersion e l e c t r o d r s placed directly in the reaction chambers. T h e a u t h o r s obtained an i m m e r s i o n electrode from Leeds &. Northrup and had i t installed to replace the S o . 2 samplc pump and electrode assembly. The immers i o n cxlcctrode w a s attached to a piece of chrome pipe and placrd in the same location as the original suction line in the fifth chamber. The original pumping arrangement was designed for a. maAimum lag of 20 seconds from tank to electrodes. With the new immersion unit this was m a t c r i a l l y reduced. The immersion elcctrodc aswmbly coniprised a plastic housing about 3 inches in diFigure 9. Immersion p H Electrode ameter and 3 inches long with one end rounded. This end n a b piovidcd n i t h a recess tapped to receive 0.75-inch pipe. The other cnd \Tas provided with lhrcc tapped openings to ieceive the t n o glass electrodes and temperature electrode. The electlodes were held firmly in place by soft plastic bushings VCI J similar t o gaskets which fitted between the collars on the electiorles and the housing. A stainless steel screen was fitted arountl the outside of the main housing for piotection of the electrocks Figuie 0 shows one of the units. I

Figure 10.

pH Control Chart for No. 3 Reaction Chamber

Vol. 42, No. 4

This new in5tallation produced very good control in the instrument. After 2 months' operation, the No. 1 sample pump and electrode assembly was also replaced with an immersion electrode. In this installation the electrode TTBS al)out 9 feet below the surfare. With these units in service the pump troubles were ended and maximum response was had in the controllers. To date the new electrodes have given very satisfactory service. The slurry circulating pumps were installed without strainers on the suction openings. I n finishing some minor changes to the slaker building small pieces of wood about 2 inches in diameter accidentally got into the lime feedei and from there found their way into the slurry storage tank. They were drawn into the impellers, causing loss of capacity. However, in shutting cio~~rn the pump and closing the discharge plug cock, there was enough backflow through the unit to release the ~ o o dpieces. The pump on being restarted, developed full capacity until the blocks finally wedged themselves again to obstruct the flow. This took from one half hour to several hours. In investigating this trouble, the slurry tank was emptied as the authors felt there might have been a heavy build-up around the pumps. Inspection on the tank showed the floor and corners free of any deposits of lime, reflecting thc excellent agitation provided by the turbo mixers. Since the tank was clean, the pumps were pulled and when the suction bell was removed the cause of the trouble was revealed. I n order t o eliminale a recurrence of this trouble and provide protection for the pumps, basket strainers were installed on each suction inlet. These were constructed with 0.5-inch free spaces between the wires. TVhile these rolved the main problem they produced another in that they became completely incz us1 ed n ith calcium carbonate and had to he abandoned. The problem was solved for good by the installation of a basket strainer on the outlet from the slalier. This is removed once a week and a spare basket installed in its place. The original basket is cleaned and is rcady for installa tion the following week. Only a small amount of build-up has been found which is easily Iemoved. Wood splinters arid misccllaneous debris from the lime boy car3 are held in the strainer. This arrangemrnt has proved very satisfactory and cleaning has becwne a routine operation. I n the operation of the slurry circulating system, the authors had home concrrn for possible deposits in the return line. To date there has been no trouble expericncrd and an investigation of the lines has shown no deposits. The plug cocks on the by-pass lines into KO. 3 and S o . 5 chambers became caked and plugged between the tee on the circulating

Figure 11.

p H Control Chart for No. 5 Reaction Chamber

April 1950

h

&

INDUSTRIAL AND ENGINEERING CHEMISTRY

line and the cock. By simply opening and closing these twice a week, the build-up is flushed out before i t has had a chance to cake. Initial operation was instituted with controls set at 2.3 and 3.5 pH. It was found t h a t the initial dosage was too high and that there was a wide spread in the secondary control varying from 3.0 t o 8.0 pH. However, duo t o poor operation of the secondary sanipling pump, it was never certain whether this spread was due to control or sample. I n time the authors gradually adjusted both control points downward and found t h a t 2.0 and 3.0 were about right. Sample pump troubles still clouded the issue and, for a time, it was necessary to run with only the control in the third chamber. With this method of operation, this control had to be set at about 3 and the effluent values had to be checked a t the end of the sewer. The control was not too good and a spread of about 1.5points below and 5 above was noted. With the installation of the first immersion electrode, the control in the fifth chamber was brought into line and the only troubles were pump outages in the No. 3 chamber. When the second immersion electrode was installed, pump troubles vanished and the controllers began t o function properly. Figures 10 and 11 are portions of chart records which show the typical effect of the pH control with rate action. Here the average band width at the first control is 0.3 p H unit wide (Figure 10) and the second 0.2 p H unit wide (Figure 11). The authors feel that this equipment is providing excellent control and that they are obtaining complete neutralization of thc effluent. While the p H value of the effluent leaving the reaction chamher is about 3, the pH

605

+

value has risen to 4.5 leaving the plant proper, and is 5.0 entering South River. This is due t o the lower reaction rate of the dolomitic lime and thus necessitates the lower control setting. This control assures that all mineral acidity has been neutralized. These values have been obtained by adequate sampling at both these points and correlating with the chart records. As a further check on the operation of the equipment, titration of residual acid has been made on many samples of the effluent from the reaction chamber and thesc havc varied from 0 t o 200 parts per million (p.p.m.) as sulfuric acid, indicative of good control. The operation of the whole trcating system, including labor for unloading of the burned lime from box car t o storage bin, is adequately handled by one man per shift. It is not felt t h a t t h e labor required is excessive considering the magnitude of the installation. CONCLUSION

The authors believe that they have evolved a satisfactory and economical method for ncutralizing a widely fluctuating acid waste. They have been able to hold the effluent a t a satisfactory p H level so t h a t its effect on the receiving stream is negligible, and a one time source of aggressive pollution has been eliminated completely. LITERATURE CITED

(1) Jacobs, H. L., Chem. Eng. Progress, 43, 247 (1947). RECIOIVED December 12, 1949.

OPERATION OF ANAEROBIC FERMENTATION PLANTS A R T H U R M. BUSWELL Illinois State Water Survey Urbana, Ill. H E term “tradewastes” Anaerobic fermentation plants for the reduction of solids from the carbon in as ordinarily used apB.O.D. of organic wastes are capable of continuous operathe organic matter. These plies to the watertion for indefinite periqds. Loadings of 0.14 pound per processes might be classificd carried wastes discharged cubic foot per day of organic wastes have been found feasias fermentative or gas proby manufacturing plants. ble in many pilot plant studies. Existing plants built ducing and precipitating The purpose of this paper with a large safety factor are loaded to 0.1 pound per cubic (bioprecipitation), respecis to discuss certain biofoot per day and regularly produce a 70 to 80Yo improvetively. A more common logical processes which, ment in the quality of the waste. classification of the procbroadly speaking, are appliosses for biological stabilicable to the stabilization of zation is made on t h e all organic wastes. A few of these waste liquors carry mineral basis of the classes of bacteria and other microorganisms which salts or acids which are responsible for more or less damage to the are responsible for the results produced. This classification distream. By far, the larger number discharge organic material of vides the stabilizing processes into the aerobic and anaerobic a biological origin which on decomposing causes putrefactive groups-that is, those produced by organisms requiring air o r odors and a depletion of the oxygen of the stream below the reoxygen and those carried on in the absence of oxygen, quirements of normal fauna and flora. It is obviously this latter Except in the case of very simple substances like acetic acid o r class of wastes which are of primary concern in a discussion of the glucose, aerobic and anaerobic action both yield solid and gaseous biological process in industrial waste treatment. end products under practicable conditions. When carried t o t h e The primary object of treatment processes is to prevent oxygen extreme, thc solids may be almost if not quite completely gasified deficiency in streams. Oxygen deficiency is the basic cause of by both processes. nuisance and destruction of fish and other aquatic life, including The character of the solids and gases is distinctly different in normal vegetable life. The elements carbon and hydrogen and, the two cases. The aerobic process naturally yields carbon dioxto a small extent, nitrogen are the chemical factors responsible for ide, the hydrogen forming water. The solids produced are largely consumption of dissolved oxygen; so the problem is to remove microbial protoplasm together with colloidal and suspended matsubstances containing unoxidized compounds of these elements. ter (6, 8, 9, I S ) caught by the biological jelly. The solids amount Bacteria of various sorts are capable of accomplishing this in to 60 to 70% of the original material, the remainder being carbon two ways-namely, to form either relatively insoluble ga..qes or dioxide and water.

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