970
I N D U S T R I A L A N D. E N G IN E E R I N G C H E M I S T R Y
of a line is a necessary part of the operational step, the line and its length are given. These data enable the complete calculation t o be followed in detail on any triangular coordinate paper. All calculations were made on a lO-idch slide rule, and measurements were taken t o the nearest millimeter. The operation described in the example quoted was carried through experimentally, and comparison between actual and calculated results are shown below: Phase Upper layer (point Y ) Actual Calculated Lower layer (point X ) Actual Calculated
--Compn., A
B
weight yo-
s2
3.5 3.8
57.4 57.8
31.6 31.8
20.3 20.2
67.3
2.8
9.6 10.0
3.3
a
solved in less than 3 hours. Three to four days are required to carry out the operation experimentally. A previous publication (3) showed that similar equilibrium relations apply to an oil-binary mixed solvent system, and computations in such a system will be the same as those described here with some slight modifications. Such modified calculations for an oil-single solvent system compared to those for a three-component system have already been discussed (6, 6, 7).
Literature Cited
si
7.5 6.6
66.5
voi. 34, NO.
The time taken in carrying out these computations is not excessive. The above example, for instance, was completely
(1) Bachman, IND. E N G . CHEM.,-4h.i~. E D . , 12, 38 (1940). (2) Brancker, Hunter, and Nash, I N D .E N G .CHEM.,33, 880 (1941). (3) Brancker, Hunter, and Nash. IND. E N G . CHEM.,A N A L .E D . , 12, 35 (1940). (4) Brancker, Hunter, and Nash, J . Phus. Chem., 44, 683 (1940). (5) Hunter, in “The Science of Petroleum”, Vol. 111, p. 1818, Oxford Univ. Press, 1938. (6) Hunter and Nash, IND. E N G .CHEM.,27, 836 (1935). (7) Hunter and Nash, J. Inst. PetToleum Tech., 22, 4 9 (1936). (8) Hunter and Nash, J . SOC.Chem. Ind.,51, 285T (1932). (9) Kurtz, I N D .ENG.CHEM., 27, 846 (1935).
Chemical Treatment of Trade Waste LAUNDRY WASTES FOSTER DEE SNELL AND J. MITCHELL FAIN Foster
D. Snell, Inc., B r o o k l y n , N. Y.
P
ROPOSED treatments for laundry wastes fall broadly into two types, bacterial and chemical. M‘hile bacterial methods are considered the most economical in operating costs, detailed operating procedures are involved and experience with the methods is limited. Difficulties due to alkalinity of the waste could arise. Eldridge (a) estimates the biological oxygen demand (B. 0. D.) of laundry waste a t 400 to 1000 parts per million and recommends an intermittent biological filter a t 1 gallon per square foot per hour. Costs are estimated by analogy t o milk-plant wastes where it would appear that excavation and materials such as concrete, pumps, piping, stone, housing, etc., would average about $100 per thousand gallons, plus $500. Thus a plant to treat 75,000 gallons daily would cost $8000. The cost of operation is small in terms of electricity, but substantial expense in terms of repairs and supervision may be entailed. * Such a plant produces no sludge. Chemical methods for treating laundry wastes have somewhat wider application. References in the technical literature are relatively few, with considerable disagreement among them as to recommended procedures. This is not surprising in view of the diversity of operations in different plants, varying from family laundry in some to industrial overalls in others. Sakers and Zimmerman (6) found the best treatment to be 1200 p. p. m. of lime and 280 p. p. m. of ferrous sulfate, at a cost of 12.3 cents per thousand gallons. After the This is the seventh paper in this series. The first appeared in A m . the third paper was not published. The others were printed in INDUBTRIAL AND ENGINEERINQ CHEMISTRY as follows: 19, 237 (1927); PO, 240 (1928); 21, 210 (1929); 16,580 (1934). 1
D y e s h f Repti-,, 16, 54 (1927);
waste was sedimented in tanks, the upper layer flowed through a baffled ditch t o a cinder bed to catch any escaping floc. The sludge from the settling was passed t o a drying bed and, on a dry basis, contained 2.6 per cent of grease and 1 per cent of combined nitrogen. Improvements in the treated waste over the raw waste were as follows: turbidity 92.9 per cent, color 64.4, total solids 65.5, suspended solids 96.7, and oxygen consumed 89.3. Daniels (3) adjusted laundry waste with sulfuric acid to pH 2.6 for lime treatment or to pH 7.0 for aluminum sulfate treatment. After settling, the clear supernatant liquor was run off. The settled sludge was dried on beds. Alum treatment after sulfuric acid addition was found cheaper than lime treatment. Tabular data by Pohl (6) show lime to be the poorest coagulant and aluminum sulfate the best. Kline (4) in a report of studies on four laundries found that results varied considerably in each laundry from one part of the day to another. He quotes an average B. 0. D. of 183 p. p. m. and suspended matter of 252 p. p. m., as similar to values for domestic sewage. The oxygen-consumed figure of 196 p. p. m. is higher than the normal for domestic sewage. Boyer (1) found pH adjustment t o 6.4-6.6 with sulfuric acid desirable before treatment. After such adjustment it was necessary to use 240 p. p. m. of ferric sulfate, 160 p. p. m. of ferric chloride, or 200 p. p. m. of aluminum sulfate. The B. 0.D. was reduced by 85-90 per cent; 4 per cent by volume of wet sludge resulted. The laundry whose waste disposal problem is the subject of this paper is situated on an arm of the sea on the south shore of Long Island. A maximum of 75,000 gallons of waste
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1942
waters from family wash is delivered per day. is probably 60,000 gallons, four days a week.
A fair average
Preliminary Work Preliminary tests were made on portions of a 5-gallon sample carefully determined to be representative of the waste produced. These treatments were on 500-ml. quantities. The reagents were fed in 1.2 per cent solution throughout. Each milliliter of this stock solution added to 100 ml. of waste is a factor weight, equivalent to 1 pound of reagent per 100 gallons, or 120 p. p. m. The general results of preliminary treatments were as follows: Ferrous sulfate Aluminum sulfate Mixt. of ferrous and aluminum sulfates iMilk of lime Calcium chloride
911
Generally ineffective Effective at approx. 340 p. pa m . Generally ineffective Generally ineffective Generally ineffective
The “generally ineffective” condition reported consisted either of failure to coagulate or failure to sediment properly without further treatment. The limit of treatment was of the order of 1000 p, p. m. with the thought that, beyond that, costs would become excessive. Undoubtedly some of these treatments, in particular those with calcium chloride and milk of lime, could be made effective with a sufficiently large amount of reagent. A preliminary series of treatments with aluminum sulfate gave the data assembled in Table I.
Laboratory treatment of samples of waste from a laundry delivering a maximum of 75,000 gallons per day, with a fair average of 60,000 gallons four days a week, resulted in addition of 360p.p.m. of commercial aluminum sulfate and 144 p. p. m . of sulfuric acid. This gave a substantially clear effluent. The value for oxygen consumed of the original waste was reduced more than 90 per cent by the treatment. The chemicals are added from a dosage tank inside the building to the waste as it flows from a heat reclaimer into a sewer. The treated waste flows from the sewer into a mixing chamber situated just outside the building, thorough mixing being obtained by passage around baffles. From the mixing chamber the waste flows into a rectangular settling tank of approximately 30,000-gallon capacity, provided with a triple hopper bottom. The lead-in pipe discharges into a delivery box open at the bottom, situated at one corner of the tank. Along the narrow side of the tank, at the opposite end, an overflow basin fitted with a drain provides for removal of the clear effluent. . A self-priming centrifugal pump forces the sludge from the hopper bottoms onto sludge-drying beds. Although some soil drainage is anticipated, removal of most of the water is expected to take place by evaporation.
TABLEI. PRELIMINARY SERIESOF ALUMCOAQULATIONS OF REPRESENTATIVE SAMPLE 824-1 Experiment Number 824A-2A 824A-2B 824A-2C 824A-2D 824A-2E 824A-2F 824A-2G
Alum Added P. P. M. 120 240 288 336 384 432 480
3 Hr. after Treatment Depth Condition of of upper sludge, % layer 2.0 Cloudy 7.2 Cloudy 7.2 Cloudy Clear 8.0 8.0 Clear 9.2 Clear 10.0 Clear
24 Hr. after Treatment Depth Condition of of sludge, upper % layer 3.2 Cloudy Cloudy 6.8 6.4 Cloudy Clear 7.6 Clear 7.6 Clem 7.6 Clear 8.0
TABLE11. ALUMCOAGULATIONP OF REPRESENTATIVE SAMPLE 824-1 WITH VARIOUS AMOUNTS OF SULFURIC ACID Experiment Number 824A-3A 824A-3B 824A-3C 824A-3D 824A-3E 824A-3F 824A-3G 824A-3H 824A-31 824A-35 824A-3K a 360
66’BB. HzSOr Added P. P. hi. 0
48 96 144 192 240 288 336 384 432 480
3 Hr. after Treatment De th Condition of of upper sludge, % rayer 8.0 Clear 8.8 Clear 8.8 Clear Clear 7.2 6.0 Cloudy 5.6 Cloudy 5.2 Cloudy 3.2 Cloudy 4.0 Cloudy 5.2 Cloudy 4.4 Cloudy
24 Hr. after Treatment Depth Condition of of sludge, upper % layer Clear 4.6 Clear 4.8 Clear 4.0 Clear 4.4 Cloudy 4.0
acid. The results (Table 11) indicated that the most economical treatment was 360 p. p. m. of aluminum sulfate and 96 p. p. m. of sulfuric acid. These tests were confirmed on a second composite sample taken over a period of two days; the treatments are shown in Table 111. The net result was an indication that treatment with 360 p. p. m. of commercial aluminum sulfate and 96 p. p. m. of 66” BB. sulfuric acid should prove satisfactory as regards coagulation and clarity. EFFECTOF TREATMENT. A substantially clear effluent was obtained. Results of analyses of the original effluents as submitted, together with those obtained after treatm,ent, are compared in Table IV. Treated samples are designated by the numbers assigned in the preceding tables. Values for oxygen consumed are used rather than those for B. 0. D., because the oxygen-consumed value is a measure of the total organic matter present and is therefore more inclusive. As the figures in Table IV indicate, more than 90 per cent reduction in the oxygen-consumed value resulted with all three treatments on which analytical data were obtained.
p. p. m. of alum added in each oase.
T ~ B L111. E CONFIRMATORY SERIESOF ALUMAND SULFURIC ACID COAQWLATIONSOF SECOND SAMPLE 824-2
Treatment with Aluminum Sulfate and Sulfuric Acid The sludge volumes obtained in Table I when coagulation was complete were obviously too great. Sludge volume is normally associated with electrical charge on the particles which, in turn, is related to pH. Therefore the next series consisted of 500-mi. portions of the sample of waste treated with 360 p. p. m. of alum and varying amounts of sulfuric
Experiment Number 824A-4A 824A-4B 824A-4C 824A-4D 824A-4E 824A-4F 824A-4G 824A-4H
Alum Added P. P. hi. 360 360 360 360 288 336 384 432
%io”,”*
Added P. P. hi. 0 48 96 144 96 96
96 96
% Sludge per under Layer Clear after: Up3 hr. 5.2 5.6 4.4 3.6 5.6 6.4 6.4 6.6
24 hr. 4.8 4.8 3.6 3.6 4.4 4.8 4.0
4.0
972
INDUSTRIAL AND ENGINEERING CHEMISTRY RESULTS OF COAGULATION IN TERMS OF ANALYTICAL DATA
TABLE IV. Sam le Numier 824-1 824-1 824-2 824-2 824-2
Treatment Number Untreated 824A-3C Untreated 824A-4A 824A-4C
~~~~l Residue, P.P.M. 903 546 822 449 696
Alteration b y Treatment P.P.M. %
---I54
Vol. 34, No. 8
Fixed Residue, P.P.M. 3 59 438 370 370 464
. . . . . .
-357
-39
-226
-27
. . . .-45 . . -373
Alteration b y Treatment P.P.M. %
...
DIAGRAMMATIC PROFILE DOSAGE TANK
GROUND LINE'.
FIGURE 1. WASTEDISPOSAL PLANT
COST. Based on a daily discharge of 60,000 gallons, the cost of treatment is estimated to be $3.30 a day as follows: 180 lb. aluminum sulfate at $1.35/100lb. $ 2 . 4 3 4 8 lb. 66' BB. sulfuric acid at 1.80/100 Ib. 0.87 Total
$3.30
Plant Design After the method of treatment had been determined by laboratory experiment, a plant was designed to put the process into operation. The layout of the waste disposal plant is shown in Figure 1. The waste water leaving the heat reclaimer flows into a sewer. The chemicals are added from a lead-lined dosage tank inside the building, also connected to the sewer. The 250-gallon dosage tank holds sufficient mixed aluminum sulfate and sulfuric acid, in the form of a 5 per cent solution, to treat 75,000 gallons-the maximum daily waste. The outlet from the dosage tank is adjusted manually so that rate of
+22
+94
+25
...0
FT 5 IN
1
...
+79
...0
organic
Alteration by Solids, Treatment P.P.rl.1. P . P . M . 70' 554 ... 108 -436 -80 452 79 -sf3 -83 132 -320 -71
oxygen Alteration b y Consumed, Treatment P.P.M. P.P.M. % 1590 . . . . . . 83 -1507 -95 1110
75 95
. . . . . .
-1035 -1015
-93 -92
addition of the chemicals is proportioned to the quantity of the waste water. This becomes a little under 3 gallons of the mixture of commercial aluminum sulfate and 5 per cent sulfuric acid per 1000 gallons of waste water. The treated waste water flows into the mixing chamber situated just outside the building. Thorough mixing is obtained by passage around baffles. From the mixing chamber the waste flows into a rectangular settling tank of approximately 30,000-gallon capacity provided with a triple hopper bottom. The treated waste discharges into a delivery box open a t the bottom and situated a t one corner of the tank. Along the narrow side of the tank a t the opposite end, an overflow basin fitted with a drain receives the clear effluent. Sludge pipes coming from a manifold, each fitted with a valve which can be operated from the top of the tank along the side by a valve-handle extension, withdraw sludge from the centers of the hopper bottoms. The expected maximum volume of sludge, after allowing for some dilution in handling, is 5 per cent of 75,000 gallons or 3750 gallons per maximum day. A self-priming centrifugal pump, located on the ground and sheltered in a pumphouse which is 6 feet from the tank, pumps the sludge onto the sludge-drying beds. When desirable, the settling tank can be emptied by pumping the contents through a by-pass into the drain which leads from the overflow basin attached to the tank. Return to the 1 overflow basin is prevented by a valve located in the drain pipe between the by-pass and the overflow basin. The sludge-drying beds are located on the mound. Although some soil drainage is anticipated, removal of most of-the water takes place by evaporation. The four sections of the sludge beds occupy practically all the available space on the other side of the pond from the laundry. The dried sludge from one or more of the sections may be removed while a t the same time sludge is being accumulated in the others.
Literature Cited (1) Boyer, J. A., Texas Eng. Expt. Sta., Bull. 42 (1933). (2) Daniels, F. E., Public Works, 54,190-1 (1923). (3) Eldridge, E. F., Mich. Eng. Expt. Sta., Bull. 82, 73 (1930); "Industrial Waste Treatment Practice", p. 283, New York, McGraw-Hill Book Co., 1942. (4) Kline, H. S., Ohio Cons. Sewage Treatment, 20th Ann. Rept., 1936, 67-71 (pub. 1937). (5) Pohl, ,M.V., Gesundh. Ing., 60,422-3 (1937). (6) Sakers, L. E., and Zimmerman, F. hL., M d . Water Sewerage Assoc., Proc. 8 n d Ann. Conf., 1928,70-3. PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry a t the 103rd Meeting of the AVERICANCHEIICALSOCIETY, Memphis, Tenn
