I S D U S T R I A L AND ESGISEERISG CHEMISTRY
March. 1926
23!?
The Treatment of Packing-House Sewage’ Fort Worth, Texas By W. C. Moor2 and W. P.Wayne3 ~ R M O U R&
Co.. F O R T WORTH. TEXAS
L-RISC; this era of rapid progress and growth of cities in which niany people niust live in comparatively rlose quarters, much attention is directed towards sanitation and the sanitary disposal of waste products. The waste products of industry iiiust be included with this material requiring safe aiid sanitary disposal. Municipalities all ol-er t’he country are focusing much attention upon the construction and maintenance of sewage disposal plants. Even cities situat,ed upon streams must, since the passage of stringent ant’ipollution measures by legislatures, treat their sewage before turning it into the rivers. Packing houses are coilfronted with t,he great problem of handling a sewage much heavier and richer than any domestic sewage could possibly be. They have spent large sums of money in experimentation in attempts to find the best treatment to which to subject their sewage. The present is not the first attempt of the Fort Worth packers to treat their waste. The packing plants of A m o u r and Swift were both constructed a t Fort Worth in 1902 and commenced operating that year. I n 1904 an experimental sewage plant was construct’ed. The process of treatment in the first plant) consisted of sedimentation followed by filtration. h large concrete sedimentation basin subdivided into compartments was built. The retention period was from 5 to 10 days, during which time the sewage became very septic. -4 heal-y scum capable of supporting a man TTould form on the surface of the basin. Sludge as settled mas sluiced out through an 18-inch tile into t.he creek. About 13 cubic feet of sludge per million gallons treated was obtained. ileration by air under pressure was also employed. Filtration was accomplished through trickling filters and coke beds. Various sizes of sand were used in the many experiments. However, these beds would become clogged within a week. This plan was di.scontinued, since the cost of such a plant t o handle all the sewage would be prohibitive. An activated sludge plant was constructed upon an experimental scale in 1916. The sewage was first screened through a 30-mesh horizontitl cylinder kept clean by blasts of air. A tank n-as designed v-ith two baffles a t the sewage inlet to give lieary inat’erial a downward accelerat.iori and lighter particles an upward boost. The aeration tank was a reconstructed settling basin of the earlier plant. PI sedimentation tank had a hopper bottom for remora1 of sludge. The sedimentation period was from 2 t.0 2.5 hours. Twenty to 60 gallons per ininute of screened and settled sewage were run through the plant. The screened sewage was aerated about 10 hours before entering the sedimentation compartment. The final effluent was clear aiid possessed a stability of over 90 per cent, but this plan was discontinued because of the exce5sik-e cost of the large quantity of air necessary to accoinplish this aeration.
D
Joint Disposal Plant Units Sewage is brought to the disposal plant from each of the three contributors-namely, the packing plants of Armour 8r Com1
Received Xovember 19, 1926.
: Chief Chemist, Armour & Co., F o r t Worth, Texas. 3 Joint Chemist, Armour & Co., Swift 8r C o . , and F o r t n’orth Stock Yards Co., Fort Wor.th, Texas.
pany, Swift 8r Company, and the Stock Tards Companythrough 24-inch lines. A line of this size also carries the final sewage to the city main. Sewage from Armour and Swift flows by natural fall to the plant and empties into a basin a t the north end of the plant, wherein is a vertical bar screen, the bars being about 3.5 inches apart. Sewage from the Stock Pards cannot enter directly into this basin, since the end of their line has to be a t a much lower level than the other two sewers. The Stock Yards sewage dumps into a pit beneath the motor pump house, whence it is pumped to the mixing channel t o mingle with the other two raw sewages before entering the screens. SCREENS-The screening system consists of four S o r t h cylindrical revolving screens, 10 feet 6 inches by 5 feet and 8 mesh. Other meshes of 40 and 16 were tried but without success. Two screens are of monel metal and the other two of brass. Monel metal will probably be used exclusively when the brass screens need replacing, as these have proved the most satisfactory. Each screen is fitted with valves so t h a t it may be removed from service a t will by closing the valve and preventing entrance of the mixed raws from the flume. The hay and other large material escaping the bar screens is retained by the mesh, collected on iron ledges or baffles within the screen until each ledge reaches a vertical position at top OF the revolution of the screen, when it drops into a trough in the center of screen. Thence i t is conveyed by small screw conveyors t o a large conveyor, which accommodates the four screens and which carries the screenings t o the ejectors or hoppers, whichever manner i t is t o be handled. The liquid or screened sewage flows out of screen boxes into the large open channel beneath the four screens, thence into a large covered concrete flume leading t o Dorr clarifiers. Clogging of the screens by trash or hay is prevented by constantly spraying a fine stream of water downward upon the revolving screen. This water is taken from Dorr clarifiers and therefore is waste water and sewage. To remove the grease, which collects on the screens and cannot be removed by water stream, live steam under pressure is blown through screens 2 or 3 minutes two t o four times daily. SCREW COXVEYORS-A large screw in a perforated trough carries the screenings from the screens to two ejectors. Sludge from the Dorr clarifiers is generally mixed with the screenings for two reasons: (1) t o facilitate handling of screenings both in conveyor and ejectors, for without the wetting and lubricating effect of the sludge in conveyor, the hay packs in the trough and increases the difficulty of its handling; and ( 2 ) to dispose of the sludge. Trouble was encountered in the ejectors when attempting to blow out the screenings alone, for, instead of being thrust out, the hay would arrange itself about the inner circumference of the ejectors, thus allowing the air to blow through quite futilely. BLOWEROR EJECTOR-An automatic air compressor run by a 32-horsepower motor in the Stock Yards pump house supplies compressed air to the two ejectors. These have a working pressure of 150 pounds, but the pressure used varies according to conditions. The number of loads blown out per day also depends upon the number and class of animals slaughtered. During the latter part of May and early June an average of 140 shots for 8 hours was made, or about 140 shots in day shift and 50 shots from 3 P. :,I. to 11 P. M. Each ejector has a capacity of about 28 cubic feet. There is ample room about the plant to deposit the “blowing.” While this material is a t first slightly odorous, after drying it is not offensive. It can be fired, and smoulders along without bursting into flames. DORR CLARIFIERS~-The liquid sewage from the screens trarels toward the clarifiers in a large covered concrete flume. At exit of this flume is a triangular gate designed to divide the water equally between the two clarifiers. Difficulties were encountered in making an equal division because the curve in the flume tended t o divert water to one side. Concrete slabs were placed where the water ran the fastest t o break the velocity and assist in more equitable distribution. However, some velocity of current is desirable to exert a scouring action on the flume.
INDUSTRIAL AND ENGINEERING CHEXISTRY
240
The water enters the clarifiers through vertical slots which extend from above the water line t o 18 inches below. Each clarifier is 68 feet square. The detention period is about 2 hours in each basin. The settled sewage escapes through underflow slots and over a 24-inch baffle t o the flunie, which conducts the effluent t o the 24-inch sewer leading to the city sewer. GREASESKIMMERS-Mounted on shafts of clarifiers are grease skimmers. Much difficulty was encountered in adjusting the skimmers t o function properly, and they are not yet absolutely satisfactory. They are very bulky and are counterbalanced by concrete and lead blocks. Rubber squeegees could not carry the grease into the launder, as they were not rigid enough and grease would slip back into the clarifiers. These have been replaced by spring brass squeegees. The grease obtained is very gummy and grossly polluted with grass seed and scum of other kinds and does not flow into grease drums without the aid of water or steam. This grease has not been rendered out economically because of the contained impurities, and a t present is blown out of the drums about the grounds. The grease tanks or drums are situated in pits a t the north side of clarifiers.
This joint disposal plant is designed principally to reduce the suspended solids and grease. Just how well this is accomplished may be seen from the tabulated results and averages which follow: CHARaCTER OF COMBINED RAws-The combined raw sewages consist of the raw sewages from the two packing houses and from the Stock Yards, and are mixed in the channel before entering the screens. Samples m-ere taken half hourly from 8 A . M. to 3 or 3 : 30 P. M. and placed in galvanized pails packed in ice to compose the day sample. A sample was taken from this bucket and the solids determinations immediately begun every afternoon. Table I-Average
Solids Contents of Packing-House Waste Settleable Settleable Nonsettlesusb y volume able (Imhoff (Imhoff tube) tube) Dissolved pended Total P.P.~. P . P . ~ . Cc. p.p.m. P,p.m. P.p.m. Raw Sewage 2241 1360 30.9 1874 7390 5039 March 2003 1238 33.3 765 6566 4567 April 8390 6030 2369 1474 30.6 .. 2565 46.2 7364 3224 10588 July 10292 .. .. .. 55.0 .. (fixed 5778, volatile 47651 Screened Sewape 1876 890 20 3 1554 7136 5087 March 900 21 2 703 4669 1603 6277 April 1107 21.6 5475 1707 7182 May 2181 1662 28 0 8889 6708 Tune 8994 .. .. 28.5 July (fixed 5300, volatile 3982: Dory Efluent 0.9 697 March 5853 0.54 225 April 5389 0.36 May 6099 0.4 June 7993 0.46 , 7330 (fixed 4466, volatile 2703) Biochemical Oxygen Demand (on Dorr E B u e n t Only) 1Dav 5 Davs 140; March 786 1373 April 820 M a y and June ll28 July 7;3 Sludge f r o m Dorr Clarifiers Grease, d r y basis Nitrogen, d r y basis Moisture
dkt
f”Uz
..
%
March April July
12.06 9.57
Stock Yards sewage flows intermittently during the day, while from the packing houses there is a continuous flow. The strength of the raw sewage varies during the day, week, and season, depending upon the time and number of animals killed, The average flows are as follows: Armour
70
2.64
%
91.27 91.81 91.35
Table I shows average of solids determinations for each month in which they were run. The figures for June include a few days more than half the month, as this report was begun before the close of the month. The sewages from Armour and Swift are similar in character and quantity, but that from the Stock Yards is less in amount and strength and from a different source. The
Gallons 856,000 264,000 1,120,000 840,000 291,000 1,131,000 400,000
Day Night Total Day Night Total
Swift Stock Yards
The total solids in raw samples is greater in May and June than for the two preceding months, as the kill increased about 50 per cent. Table 11-Average
Results
Vol. 18, No. 3
March April May June Tulv Average first 4months 5months
Reductions i n Solids i n Packing-House Waste Sus-
Total
Dissolved
pended
76
70
70
3.44 4.34 14.39 16.04 12.61 9.565 10.18
March
20.80
April May June
17.89 27.30 24.51
July 28.78 Average first 4 m o n t h s 25.125 5 m o n t h s 25.86
B y Screens 0.95(inc.) 16.29 2.19 19.97 9.02 27.92 8.90 32.35
Settleable Settleable by volume by (Imhoff tube) melght
%
70
26.93. 35.21
...
...
34.30 36.34 29.41 39.31 48.2
1.600
24.13
34.38
.. ,
...
2.43
. ..
... 74.52 ...
,
,
~~
...
B y Entire Process q.26 62.12 97.09 finc.) 3.92 66.10 98.60 0.00 83.20 97.4 2.70 86.66 99.13 (inc.) 99.18
...
,
98.13
...
32.02 35.79
Grease
76 27.21 26.73
... ... ...
26.97
...
.. ,
77.55
...
74.26
97.4 96.02
... ,
..,
...
96.71 98.26
75.91
,,
,
..
SCREENED SEwAGE-Tables 1 and 11 show average solids contents of the three sewage samples, the reductions accomplished by the screens for each month, and a n average for the 4 and 5 months. The largest reductions are for suspended solids and settleable solids both by Teight and by volume. This is as might be expected, since the larger part of the total solids is present in a dissolved state, and since the dissolved matter is hardly affected by the mechanical treatment undergone by the sewage. The reduction of suspended matter when included with dissolved solids does not appear SO large a figure as when shown for the suspended matter alone. Dissolved solids show an increase through screens one month and a decrease the following month; hence i t is best to state they are not materially affected. There is a reduction of grease through the screens. Grease becomes mixed with the hay and floating material and is removed with this material. DORR EFFLUENT OR FINAL-TREATMENT LIQuID-This is the final product or effluent from the joint disposal plant and is furthermore the sewage sent to the city disposal plant mixed with domestic sewage for further purification. As evidenced by the reduction table, which shows reduction by screens, then reduction by entire process, the Dorr clarifiers perform excellent work reducing settleable suspended matter. To obtain results of the clarifiers alone it is necessary to deduct the figures for the screens from those shown under the heading “By Entire Process.” An average of the monthly averages shows a decrease in suspended matter by weight of 74.52 per cent. These figures are obtained by filtering through a Gooch crucible a known volume of the sewage samples and weighing for the increase in weight of the crucible. The figures for “settleable by volume” are obtained by
INDUSTRIAL A N D ENGINEERING CHE.MISTRY
March, 1926
taking readings of material settled in Imhoff tribes a t the end of 2-hour periods. “Settleable by weight” figures are calculated hy weighing this deposit in Imhoff tubes after washing with water to remove liquid sewage, which is rich in dissolved matter, and drying thoroughly. The latter determination was made only in hlay and June and greases were run only in the first 2 months. An average reduction of grease of 75.91 per cent for these 2 months was realized.
City Disposal Plant Units SCREEm-one screen, 6 feet by 11 feet 8 inches. The bars are 0.5 by 2.5 inches with a n opening of 1 inch i n the clear. The submerged area is 44 feet square. GRIT C ~ x n i ~ ~ ~ s - T l i eare r e two rectangular grit chambers, 4 feet 6 inches wide, 3 feet deep, and 60 feet long. ~\/IAIN PLMPIXGSTA’rIoN-This station, 25 by 6.3 feet, contains three Gould’s centrifugal single-stage, dolble-suction pumps, having a capacity of 3900 gallons per minute each. There is also one Worthington, size 5, humus pump with a capacity of 230 gallons per minute. EIIERGESCP Punip HousE--This is 20 by 24 feet and contains two lG-inch Worthington pumps, driven by two Sterling gas cngines. IMHOFF Txxxs-Four rectangular tanks containing doubleflow, double-sludge chambers, 95 feet 6 inches long, and the single-flow chambers 16 feet wide. The total retention based on complete displacement is 1.8 hours. DIVERSIOXOR RECEIVING WELLS-TWO, each 23 Feet 6 inches deep, one a t each end OF the Imhoff tanks a t center. SPRIKKLING FILTERS-Three, each 384 by 120 feet, and the stone 8.2 feet deep. SLVDCEPUMPHous:G--This is 16 by 24 feet, equipped with Gould single-acting Triplex plunger stuff pump, capacity 6.52 gallons displacement per revolution of crankshaft. SLUDGE DRYING BEDS-Eighteen, 240 by 14 feet each. DORRCLARIFIERS-TWO,circular, 80 feet in diameter. L A B O R A T O R Y - T ~ ~ laboratory, 25 by 25 feet, completely equipped for sewage work.
Difficulties Encountered
The disposal plant (of Fort Worth was placed in operat,ion the latter part of April, 1624. As with any new ventureand this was a new venture, for although there: are other plants of the same ‘type, each presents its onm peculiar problems-numerous difficulties had to be overcome. At the time the plant commenced operation there was much heavy rainfall, and the emergency pumps had t,o be used against the pressure of the river. The main pumps nere not in proper alignment at first. The nozzle,s on filter beds became clogged over easily. Filter No. 1 did not function properly, but would run continuously instead of cutting off and on. There was found to be a difference in size of t.he dosing chamber of this bed, the chamber was rebuilt, and this bed is now the best of the three. There was insufficient head on nozzles for their spray to cover more than one-quarter of the bed. The head was increased 1 foot by installing angle irons and adjustable weirs in dosing chambers, and the spray then covered practically all the beds. At one time, the Dorr basins became septic, because the squeegees a t bottom were not revolving, as the key had been left out of the shaft. The Imhoff tanks became septic in December, 1924. An examination revertled that the sludge completely filled the tanks t o above the slots. The drying beds were insufficient to provide for the large withdrawal of sludge immediately and urgently necessary. This situation was met by running a 6-inch line over the south levee and pumping sludge onto the flat plot of land between the plant and t,he river.
Results of Tests
T a b l e I11 gives a v e r a g e results of tests since the beginning of operation of the plant. These are c o m p i l e d f o r only the raw sewage a n d f i n a l effluent, since this report is intended to show the disposition of t h e packers’ waste when mixed w i t h t h e domestic sewage of the city. Results of samples of Imhoff and filters are thus o m i t t e d . An attempt was made to show the effects of packing waste upon the domestic sewage by averages for the m o n t h s w h e n no packing-house seu*age entered the plant and comparing with ayerage3 for the months when a mixture v a s t r e a t e d . AccorLlingly, an average for May, 1924, to Fehruary, 1925, inclusive, gives the character of straight domestic sewage. A separate average for May and June, 1925, represents the c h a r a c t e r of the mixture. d third average for July also indicates the mixture, but differs in t h a t d u r i n g this m o n t h on1.v one pump mas run, thus handling less of the mixture. March and April are not included in any of these averages because they cannot be classified as purely “mixture” or “domestic” months. On hfarch 12, 1 9 2 5 , s e w a g e f r o m t h e packing houses came down in the early afternoon. Three pumps were used for the 12th and 13th; then only one was run until the 18th, when
24 1
242
19DUSTRIAL A Y D ESGIA17EERISGCHEMISTRY
the plant was shut don-ii completely for several days. On the 17th the bottom of Imhoff unit KO. 2 was discovered to be broken. Large slabs of concrete had fallen into the sludge compartments. On March 29 the plant was started, using only one Imhoff tank. Unit No. 2 was out of service until April 11. The cause of the damage was laid to excess sludge in the tank, with accompanying formation of excess gas which could not easily escape owing to presence of considerable oil on surface of vente. Sewage from packers was again turned in on kpril 17. The tables show large increases in total solids for both raTT sewage and final effluent at the city plant. This increase is due almost entirely to the large amount of dissolved solids added toethis raw sewage from the Dorr effluent from the joint disposal plant. Although much of this dissolved matter is organic, artesian water used a t the packing houses has a very high content of dissolved salts. Suspended matter in r a x sewage shows a decrease of 5.86 per cent due to the dilution by the Dorr effluent of the joint plant containing less suspended matter than the normal domestic raw sewage. Dissolved solids are affected little by a plant of this type, but appear in the final effluent, giving i t a high total solid content, although it will contain little settleable suspended solids. The effects of packing waste are felt chiefly by the filters, which attempt to remove some of the colloidal and semicolloidal material. The Imhoff tanks are not given an extra load, since there are fewer parts per million, or a t least no more of settleable matter, in the mixture than in the straight domestic sewage. Stability for May shows an average of 90.4 per cent but during the latter part of June many samples lost their color immediately or several days after being set up. During the latter part of June and early July the stability was practically nil; in the latter part of July and early August i t had risen to nearly 80 per cent. The final effluent from this plant is yellow to brown, especially in the afternoons. This color is not believed to be of serious consequence, but is attributed to the presence
Vol. 18, No. 3
of vegetable dyes from the paunches of animals. Especially a t this time of year would the content of their paunches produce such a discoloration. This color can no doubt be removed by proper filtration. There is a decrease in suspended solids, both total and settleable, in the raw sewage when mixed with effluent from the joint plant. On the other hand, there is a large increase in total suspended matter and a small increase in settleable matter by volume in the final effluent for the mixture months. Solids, other than dissolved, in final effluent depend upon the amount of material thrown out by the filter beds. These beds have been unloading heavily material which was not removed by clarifiers. At the time of running but one pump a clear, stable effluent was turned out. When two pumps were used and the rated capacity of the plant greatly overrun, the filters refused to operate effectively and hence the effluent was poor. The plant is rated to handle 7.5 million gallons of straight domestic sewage daily, but had been attempting to purify 7 to 8 million gallons of the rich mixture. One pump was cut out again, leaving one operating. After a month’s run the average of tests showed little difference from those of May and June, but the stability had risen. One pump puts through about 5 million gallons daily. The city officials are considering building additional units to this plant. It is hoped that the addition will be adequate to handle all of the sewage. The average flow is estimated at 10 to 12 million gallons per 24 hours. The plant should be large enough to take care of the peak flow. If adequate additions are made, the work done should warrant the statement that such a sewage disposal plant will purify the sewage to the satisfaction of all concerned. Acknowledgment
Inasmuch as most of these tests were made in the laboratory of the city sewage disposal plant, the writers wish to express their appreciation to W. S. Jlahlie, city chemist, who has charge of this plant, for the many courtesies shown them during the past year.
Research in Electrodeposition IVith the exception of silverware and certain types of builders’ hardware, the electrodeposition of metals is incidental t o the main problems of manufacturing. At any rate, i t is regarded as incidental by manufacturers, although there are frequent examples of the success or failure of a metal part due t o the perfection of the electroplating employed to impart desirable characteristics or provide a protective coating. There are instances of manufacturing losses due to the failure of the deposited metal film in the assembled article, and numerous experiences could be cited to show t h a t electrodeposition is more important than the brief attention ordinarily given to i t would indicate. Present methods in electroplating have largely been evolved by empirical methods in the hands of men without adequate technical training and this field still suffers from a scarcity of scientifically trained men. Some of the most constructive work on the physical and chemical characteristics of electroplating solutions has been done under the direction of William Blum at the Bureau of Standards. The fundamental data established have been applied to great advantage by industry, particularly in the deposition of copper, zinc, lead, bright nickel, black nickel, and chromium. Evidences of this activity are to be found in the bureau’s publications on the subject. These have appeared as contributions to the technical press, bulletins, technical publications, and circular letters of the bureau. There have been seven general communications, three on copper deposition, two on zinc, two on lead plating, sixteen on nickel deposition, two on black nickel plating, two on chromium plating, and a number on miscellaneous topics. One indication of the readiness with which the plater of today avails himself of such scientific knodedge as may be established
is the extent to which the hydrogen-ion concentration of plating solutions is now being measured as one method of controlling the acidity of nickel depositing solutions. Afore than one hundred plants are now following the recommendation made for the measurement of hydrogen-ion concentration and the interpretation of the results. Another major contribution has been the design of a simple device to aid in the measurement of the conductivity of nickel depositing solutions. N u c h of the research work undertaken a t the Bureau of Standards on the subject of electrodeposition was initiated t o meet the needs of the government departments themselves, such as electroplating for the \Tar and Navy Departments, the manufacture of copper map plates for the Coast Service and Hydrographic Office, and the manufacture of printing plates used a t the Bureau of Engraving and Printing. The results achieved here have resulted in the saving of thousands of dollars x i t h the possibility of even greater savings in future. Appreciating the importance of such research, the American Electroplaters’ Society now proposes t o secure the support of two hundred manufacturers to provide a fund of %10,000 per year for three years, this fund to be held in trust by the society and expended for salary and expenses of research associates to be placed a t the Bureau of Standards. The efforts of the electroplaters may come to the attention of chemists in the various organizations, who would do well t o familiarize themselves with the character of work done on electrodeposition a t the Bureau of Standards and be in position to recommend favorable action in supporting this type of fundamental work, the results of which can scarcely fail to make substantial returns on the modest investment.
