CHEMICAL TREA WHITE W E. G. KOMINEK lnfilco Incoporated, Chicago 16,
!ll~
White water is effectively clarified by chemical treatnient in rapid-rate sedimentation units. Operations in board mills indicate that fiber losses can be reduced to about O.l%, with the value of the recovered fiber defrajing essentially all the operating expenses of the plant. Pilot plant studies have demonstrated that tissue mill wastes
and deinlring wastes can also bc clarified by mheniicali treatment. Sedimentation units are subject to operating difficulties due to entrained air or thermal upsets, which make it necessary to consider the iiistallation of air separation chambers and of an equalization tank in designing n plant €or treating white water.
THE national program for minimizing stream pollution develops, it is becoming more imperative for paper and pulp mills to consider methods of treating t,heir waste waters. Paper mills use large volunies of n-ater in the manufacture of pulp and paper, a large percentage of n-hich is discharged as white water containing the fibers and fillers t h l am not retained on the sheets on the machines. The volunic ailti the suspended solids content of white water discharged per ton of product vary widely. Warrick (3) reported the losscs for various pulp and paper mills in Wisconsin in 1'345and 1946. The results are summarized in Table I. These losses create an objectionable condition in the rivers because the fibers accumulate in unsiyhtlj- deposits in the beds and in the banks of the river, deplete the oxygen cont,cnt of the rivers, kill of" aquatic life, and tend to ruin the rivers for recreational purposes. The volume of white water discharged from a pulp or papcr mill can be reduced by closing up the Pysteni through the reci1,culation of white water to the showers and by returning white water to tlie process whenever possible. However, there is a limitation to the volume of white water that can be returned to the system, because bacteria and slime-producing organisms will grow on the soluble organic matter present in the white water and produce deposits which mould affect the quality of the final product. Chlorine and antislime compounds are used to inhibit organic growths, but it is not possible to close the systems conipletcly. As recirculation does not eliminate thc disposal prohIcm, provisions niust be made for removing the suspended solids and reducing the B.O.D. of tlie water that is discharged froin the plant. Plain sedimentation, filtration, flotation, and chrmical treatment of the xastes are methods of treatment to consider. This paper discusses the operation of chemical precipitation plants to illustrate what can be done by this method of treatment. Rudolfs and Axe (2) have reported their investigation of the chemical trcatment of white water and have indicated doubt as to the value of mechanical flocculation for clarifying paper board mill wastes Their survey also indicated that removal of B.O.D.
by chemical coagulation and settling W:LS little more eAccti~c than plain settling. Homver, the manner of chemical mixin. and flocculating has an important effect upon the results, bcrause considerably better B.O.D. reduction is being obtained b y chemical treatment than could be obtained by plain sdinicstit tion in some installationq.
Type of Product Book paper
Tissue paper Wrapping paper Bond paper Glassine Rag and deinking pulp Kraft pulp Sulfite-pulp Groundwood pulp
CLARIFICATION OF BOARD MILL WASTES
The River Raisin P:iper Coinpany at lIonr&, Mic;!., I i m i'edriced tlx discharge of v\-nst,es to the River Raisin by re-using m:ichine watw and hy cilarifying the white water discharged f'roin the plant. Prior to instn1l:iiion of the i ~ i r c u l a t i n g sppmrim:Ltcly 5000 galloris pci' minutr of waste containiug 3 pounds of suspcnded solids p c r I000 gallons were discti:wgcd t m the river. The volume of \Taste water has bcen reduced to :il)out 1600 gallons poi- minute by rccirculat'ion, and chemical tre:tt ineiit has rctiuccd tlic suspended solids to abut. 0.1pound per 1000 gallons in the effluent. Tlicsc conibincti changes have rctlucctl the discharge of suspended solids from al~out,21,000 to Icss thtm 1000 pounds per day. I n fact, if the suspended solids content ol (,Ire ~ R J Triver n-xter pumped into the plant is taken into acwurit, the mill is :Ldding only ahout 1 j O poiiiid~of suspended solitls to the river per day.
Vliiic n-aioi. from :i 200-toii inill, using two eoven-c*j.iiiitlei machines is clarified with aluni and activated silica. The t rcatctl water disoh:trgrs l o Mason tributary of the Iliver R&iti, and the underflow is return hydropulpers for re-use. Tlic txeating plant roiisists of :I r 50 feet in diametcr hiving :L capacity of 2100 gxllons pc wjth a 3.0-hp. rotor drive n r i t l L: 0.5-hp. drive on thc scaapcr incc.hanisni. A dry chemical feeder is used to feed alum and :I solution feeder is used for :tclivatc?t s a weir chamber w11e1,et2 silica. The clarified vaier f l o ~ll-irough flow is measured by means of a float-operatcd meter. This molt has electrical controls w1iic.h regulate the feeder openitions anti also control {he sludge blo\voff valves, so that the chemiral feed and the rate of sludge discharged are proportioned to tlic flon. oi waste nTater. The Cgclator : t i the River Raisin Paper Comlmiy is shown in Figure 1. Figure 2 indicates ttic, opvi'alion of the Cyclztlor. Tlic white Rater enters (1 niixing and reaction zone xki(~it ihtb roagulants are applied. Tlir Table I. Losses for Various Types OF Mills in Wisconsin reaction between the r o ~ ~ i i Solids Loss, Pounds uer~ Ton _ of Product _ _ .~~~ _ lants and the white watc~it,iltri R'aete - per Ton of Pvoduct, Gal. Fixcd suspended __ Volatile suspended ~place in the presence of slui i \. 19-16 1945 1046 1016 1946 194Li rontaining previously fornirtl 22.5 13,071 13,093 28.8 31.1 20.3 preci i t a t e s s u s p e n d c d in 80.4 40.6 23,018 27,501 5.7 9.2 lieate! water. Precipii,itiori 31.2 17.9 '30,g 28,432 2F,010 11.3 18.7 57.2 20,461 20,692 24.5 23.6 talics place on these partic.lc\, 32.2 48,727 02,928 4.8 07.0 5.3 therehv increasing their densin 1.57.6 188.2 49,79G 61,600 168.8 168.6 and the rate at which ilic\ 33.6 61.2 64,838 62,385 27.9 41.3 50,470 46,624 3.7 37.6 10.1 erparate from tho treated 36.7 0.2 11.2 2,302 3,900 0.2 19.0 water. The rotor which raiiws mixing and Aocculation a l ~ o 616
April 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
617
c
Figure 1.
Cyclator at River Raisin Paper Company
serves as a low head pump for recirculation. Amount of recirculation is readily adjustable by means of the variable speed drive on the rotor. Under most conditions a recirculation ratio of about 3 to 1 produces the best coagulation of white water. The circulating zone is divided into two concentric compartments, the water rising in the inner zone and flowing downward in the outer zone. The velocity of circulation is controlled to permit air-bound particles to accumulate at the top of the inner zone, where they may be slovr.ly agitated by means of a rotating arm to aid in eliminating entrained air. The flow in the outer zone is directed outward by a baffle, thus permitting the clarified water to separate from the solids. The denser solids which separate from the circulating zone settle to the bottom, while the less densc solids are drawn back into the mixing zone. The settled solids are slowly moved by mechanical scrapers to a sump from which they are continuously removed. This aids in thickening the solids to produce an underflow of masirnum consistency.
.u
values, the mill adds approsimately 0.8 pound of suspended solids and 12 pounds of B.O.D. to the river per ton of pulp. Knack (1)reported that the daily operating cost of the plant is about $108, including $63.35 for chemicals, $18 for power, $18.30 for labor and maintenance, and $8.35 for interest on investment. The waste treatment plant is credited with $72.40 for the recovery of the volatile suspended solids content of the underflow, this credit being based upon the price of mixed waste paper, the lowest priced raw material. Based upon mill capacity, the charge for operation of the waste treatment plant is about 18 cents per ton of pulp. However, it is considered that the over-all changes, with the value of the water recovered in the recirculating system, make the entire pollution control project self-supporting. TREATMENT OF TISSUE MILL WASTES
Operations a t the River Raisin Paper Company require tlie That chemical treatment can have an important effect on full-time service of a n operator. This is largely due t o the fact B.O.D. reduction was demonstrated in pilot plant tests a t a tissue t h a t the mill processes waste paper and the furnish at times conmill. The pilot unit consisted of an Accelator 60 inches in diamtains chemical bags, which add a wide variety of chemicals t o the eter operating at a flow rate of 4 gallons per minute. The pilot water. These chemicals tend t o buffer the waste, and make it plant operated 8 hours per day during most of the tests, alnecessary t o vary the chemical treatment over a wide range to though the operations during the final week were on a 24hourobtain proper coagulation. An average of about 1.6 pounds of per-day basis. Composite samples were obtained for suspended alum plus 0.08 pound of activated silica is used per 1000 gallons solids and B.O.D. determinations (Table 111). for treating this waste, but during the most recent survey, the These tests indicated that a high degree of suspended solids alum dosage averaged 2.9 pounds and the activated silica dosage and B.O.D. reduction can be obtained with a white water of this averaged 0.11 pound per 1000 gallons. type. Alum requirements were about 0.28 pound per 1000 galTable I1 summarizes the rcsults of operation. These tests were made by the Michigan Stream Control Commission. Table 11. Results of Chemical Treatment The survev in 1949 was ninde 7/22/48 7/23/48 7/24/48 3/9/49 3/9/49 3/10/49 %day B.O.D., Raw water 3.0 4.3 3.4 ~ . . ... 3.0 by M c G a t h e n , Munneke, p.p.m. Raw waste 155 135 127 300 200 250 Frost, and Rydland. Their Treated waste 55 50 68 140 76 160 yo removal 64.5 63.0 46.5 53.3 65.4 36.0 survey indicates that the popiiSuspended solids, Raw water 40 24 52 ... ... 42 lation equivalent of the mill p.p.m. Raw *aste 536 556 688 1872 932 1012 Treated waqte 62 33 37 58 46 46 effluent is about 13,800; a n Sludge 13,750 14,230 24,970 .. 14,400 ... average of about 11,960 gallons 7*removal 88.4 94 1 94.6 96.9 95.0 95.1 Suspended volaof water is discharged t o the 16 7 11 .. 10 tile solids, water a w waste 360 388 440 676 768 748 stream per ton of pulp. Fiber p.p.m. T reated waste 34 21 16 36 28 24 Sludge 8,680 9,860 15,510 ... 11,280 ... losses average about 0.1%. If % removal 90.5 94.6 96.4 94.7 96.4 96.8 the suspended solids content Ram water 7.9 7.4 7.9 .. ... 7.6 and the B.O.D. value of the Raw waste 6.9 6.6 7.0 6 9 7.3 7.1 Treated n a b ce 7.1 6.5 6.4 6.4 6 7 6.6 raw water entering the plant Sludge 6.8 6.3 6.2 ... 6.0 ... are deducted from the efflucnt
Vol. 42, No. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
618
Table Ill. Treatment of Tissue Mill Waste Pounds per 1000 Gallons Suspended Solids Activated Calcium BentoInfluent, E a u e n t , % .4!uin silica carbonate nite p.p.m. p.p.m. rcmoyal ... 13 25 0.08 13 ... 0.08 ... 5 14 0.8 11 ... ... 0.08 ... 5 0.08 ... ... 5 ... 0.08 7 ... ... 0.08 12 0.4 ... 12 0.12 6 0.12
...
,
t
.
. . I
.
.
I
lons; and 0.08 pound of activated silica was beneficial in improving clarification and conditioning the sludge. Ground limestone or bentonite also was used with alum, with good results. CLARIFICATION OF DElNKlNG WASTES
Chemical treatment is effective for removing suspended matter from deinking wastes, or mixtures of white water and deinking wastes. These tests were also made in a model 60 inches in di,znieter. The tests indicated that self-coagulation would r(move over 85% of the suspended solids (Table IV). LIMITATIONS OF WHITE WATER CLARIFICATION SYSTEMS
1 .
,
T w o of Wmte lTllite Mi11 2 4Illl 3
R a t e of Flow, Gal./Min. 8 7.5 7.5 8 8 12 12
12 12 7.5 7.5 9.0
12.7 12.7 7.5 7.5 7.8 7.5 7.5 Combined white water and deinking
6.0 6.0 6.0
G.0 6.0 6.0
I
.
This unit is 25 feet in diameter and has a capacity of 300 gilllons per minute of white imter. The rotor has a 0.5-hp. variable-spcetl drive and the scraper mechanism has a 0.25-hp. drive. Alum and activated silica are used for treatment,. Alum requirements range from 0.7 t'o 1.7 pounds per 1000 gallons and the silica Gosage averages about 0.25 pound pcr 1000 gallons. These vsrixt,ions i n chemicals depend largely upon the amount of filler in the white water . Excellent clarification w a s usually obtained, but occasionally the presence of entrained air caused some of the fibers to float
Table
Any system of white water t r e a t m e n t has limitations which are dependent upon the physical characteristics of the suspended solids. Flotation systems lack the ability to remove the heavier filler along with the colloidal material, while sedimentation systems are susceptibk to air entrainment and to thermal upsets caused by temperaturc fluctuations. In many paper mills the method of collection of the white water affords a sufficient degree of air separation t o make sedimentation effective. Rowever, if the system does not permit air separation before treat-
ment, effective solids removal will not be obtained unless B.O.D. some means are provided foi influent, Effluent. '3% releasing the air ahcad of the P . P . ~ . p.p.m. removal clarification unit. This can .. ... ... 93 180 48.3 sometimes be done by install.. ... ... ing a water seal in thc scvcr 50 67.8 155 .. ... line. Jn other instances, the 39 77.7 175 , . , . . ... installation of an air-sc.paiation ... chamber will release the cn... .. ,.. ... trained air that adheics to tlic 21 8 1 . 4 113 34 67.6 105 hhers. Init,ial operation of t,lie Cyclator at the Acme Papcr Honrd Company a t Reading, Pa., indicnt,ed the need for releasing air prior to the treating unit.
IV. Lime
Clarification
Cheinioale, P.P.M. _______ Alum Silira
2ki 240 ...
200
125 125 125 125
...
...
220 240 240 240 240 240 240 240
i5Q 250 300 300
of Deinking Wastes
... '
34 34
..
76 125 KO chemicals
5 ,.
.. ..
I0 10
IO
.. ..
Suspended Solids, P.P.M. Influent Effluent -&%di? 1160 1190 564 510 410 880 800 915 1290
...
... ...
40 3; 182 20 70 60 40 40 240
27,180 42,360 11,200 15,600 24,600 21,900 10,700 21,840 24,600
No ciietnicals 68
... 60 60
No chemicals 57 155 80 80
80
20 20 20
.. .. .. .. ..
1630 670 1728 1770 1880 1400
200 70 50 100 2 10 190
50,000 36,000 32,800 21,600 31,000
April 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
and increased the suspended solids content of the effluent. A Cascade aerator was installed t o eliminate the carry-over caused by air entrainment. Temperature fluctuations have an important effect on sedimentation, particularly in the tieatment of white water, because the fibers are light and therefore susceptible to thermal disturbances. Although the average temperature rise that can be tolerated depends to some extent upon the characteristics of the suspended solids, in general an average rise of 3 e F.per hour will not affect the clarity of the effluent if slurry recirculation is used to equalize the temperature before the water reaches the zone when solids separation takes place. With a greater rate of temperature increase, coagulation of white wastes becomes critical, and the installation of an equalization tank should be considered.
619
that is required. I n general, an alum dosage of less than 2.0 pounds per 1000 gallons will be effective for removing the fibers, but more alum will be needed if the waste contains finely divided filler which must also be removed. Sedimentation units are affected by entrained air in the white water, b u t operating difficulties due to entrained air can be avoided by the installation of an air-separation unit. Slurry recirculation eliminates thermal upsets caused by temperature variations of less than 3’ F. per hour. Greater rates of change will increase the suspended solids content of the clarified water. Chemical treatment is particularly applicable to board mills where the recovered fibers can be returned directly t o the process in a concentrated form, as the value of the recovered fibers defrays essentially all operating expenses for the treating plant, LITERATURE CITED
CONCLUSIONS a
White water can be effectively clarified by chemical treatment if effective mixing and slurry recirculation are used; removal of better than 95% suspended solids is obtained by treatment with alum and activated silica. The amount of coagulants needed for effective treatment depends upon the characteristics of the white water and on the degree of clarification and B.O.D. reduction
(1) Knack, M. F., “River Raisin Paper Company’s Approach to
Treatment of Board Mill Wastes,” Fourth Industrial Waste Conference, Purdue University, Sept. 22, 1948. (2) Rudolfs, W., and Axe, E. J., Wuter and Sewage Works, 95,No.6, 21’9 (1948).
(3) Warrick, L. F.,IND. ENG.CHEM.,39,673 (1947). RECEIVED October 8. 1949
TREATMENT OF COTTONFINISHING WASTE LIQUORS GEORGE G. BOGREN Weston & Sampson, Consulting Engineers, Boston, Mass.
2. TRICKLING FILTER. T h e pilot plant expeniments described were conducted This unit is 0.25 acre in area as a step in a program to abate the pollution of a small thesc experiments had and consists of a IO-foot stream receiving the wastes from a large cotton finishing their origin in caustic depth of coarse crushed and peroxide kiers, bleachplant. The finishing plant has a dual sewerage systemstone within a n earth embankment. Wastes are aplight wastes are discharged to the stream without treating, dyeing, mercerizing, plied intermittently by a ment, and the heavier wastes are pumped to a treatment and sundry special finishing dosing siphon through a grid plant. Wastes are now receiving primary and partial processes, together with the of fixed nozzles. The aver~ a 5 hwaters which form secondary treatment. Complete secondary treatment is age daily rate of dosage is 1,100,000 gallons per acre necessary in the planned stream pollution abatement the bulk of the wasteliquors, per day, and the rate durand a small amount of program. The wastes vary widely in alkalinity from hour ing the period 7:OO A x . t o to hour. For this reason, and for economic reasons. highdomestic sewage. 5:OO P.M. is 1,600,000galrate trickling filters seemed the most promising method of Table I shows the comlons per acre per day. The average B.O.D. loading is position of the waste liquors treatment. Pilot plant experiments showed that B.O.D. 0.15 pound per cubic yard removal of at least 60% was possible at a rate of filtration duiing the period of these of filter media. of 10,000,000 gallons per acre per day. experiments. 3. INTERMITTENT FINE The volume of wastes CINDERFILTER.This unit amoun’ s to about 2,000,000 is 1acre in area and consists of a depth of 4 feet of screened cinders varying from 2 inches at gallons per 24 hours, and 60 to 90% of this flow is discharged the bottom t o about 0.3 mm. at the top, underdrained. Trickling between the hours of 7:00 A.M. and 5:00 P.M. Normally the finishfilter effluent is applied intermittently by a pump, through ing plant is in operation 5.5days weekly. wooden distributing troughs. The average rate of dosage is 285,000 gallons per acre per 24 hours.
HE wastes treated in
T
PRESENT T R E A T M E N T M E T H O D S
All the wastes are treated by subsidence, and about 15% by subsequent trickling filtration through crushed stone and intermittent filtration through a fine cinder filter, which may be described briefly as follows:
1. SUBSIDING BASINS. There are three rectangular horizontal-flow basins, each 32 X 64 feet in area, with an average depth of 17 feet. The period of detention a t average flow is 9.5 hours and during the period 7:OO A.M. to 5:OO P.M., 4.3 hours. The overflow rate at average daily flow is 325 gallons per square foot per 24 hours, and during the period of maximum flow 700 gallons per square foot per 24 hours.
EFFICIENCY O F PRESENT T R E A T M E N T P L A N T
Table I1 shows the average chemical composition of the wastes a t various stages of treatment during the period of operation of the pilot plant. The percentage removal of the significant constituents by various units of the treatment plant during the period of these experiments is shown in Table 111. P I L O T P L A N T STUDIES
Abatement of stream pollution requires that more complete treatment of the entire volume of wastes be undertaken. En-
