April 1950
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I summarizes extensive performance data based on several years of operating experience. Column 1 shows the usual performance of the Standard Brands yeast plant at Pekin, Ill. The purification amounts to 80% a t a loading of 0.10 pound per cubic foot per day. Since the thirdstage tanks show practically no improvement over the second stage, the effective load is 0.15 pound per cubic foot per day. This plant has been in continuous operation for 10 years. Column 2 shows the performance of digesters operated by the Peoria Sanitary District while digesting the “slops” or “still bottoms” from the Commercial Solvents butanol-acetone plant. The digesters, which have been in operation for about 15 years except for a few periods when the butanol plant was shut down, are accomplishing a 69.8% reduction in B.O.D. at a loading of 0.114 pound per cubic foot per day. Column 3 shows the normal operating results of a plant a t Crystal Lake, Ill,, put into operation in 1944. This plant consists of a two-stage digester for handling wastes from the manufacture of yeast. The waste is slightly more dilute than that .at Pekin and the loading is correspondingly less, a s is the gas yield. The removal of B.O.D. is 70%. The primary digester is equipped with a floating cover and has a capacity of 366,500 gallons. The secondary digester has a fixed cover and a capacity of 264,300gallons. The data in column 4 were obtained on a n installation treating the wasted steep water from a malt manufacturing plant. The steep liquor is free from suspended solids and is discharged directly to a trickling filter. The filter “unloads” continuously and passes to a settling tank which is provided with mechanical sludge removal. This sludge is digested in two 20,000-gallon digesters equipped with floating covers. The effluent from the digesters is returned t o the influent to the trickling- filter. The sludge is di’ gested until i t drains well on sand beds.
607
Although results in column 5 were obtained on a two-stage pilot plant operated for about 4 months, they are believed to be representative of what can be acconipiished under carefully controlled conditions. Ninety per cent purification was obtained with a loading of 0.143 pound per cubic foot. This pilot plant experiment has previously been described in detail (6). ACKNOWLEDGMENT
The author wishes to thank L. 5.Kraus who furnished the performance data on the Commercial Solvents butanol-acetone plant, and M. W. Tatlock of the Ralph L. Wolpert Company, Dayton, Ohio, who furnished the data for the plant a t Crystal Lake, Ill. LITERATURE CITED
Boruff and Buswell. IND. ENG.CHEM.,21, 1181 (1929). Ibid., 22, 931 (1930). Boruff and Buswell, J . Am. Chem. Soc., 56,886 (1934). Buswell, Boruff, and Wiesman, IND.ENG.CHEM.,24, 14-23 (1932). Buswell, et al., Ill. State Water Szirvey BUZZ. 18, 7 (1923). Buswell and LeBosquet, IND. ENG.CHEM.,28, 795 (1936). Buswell and Neave, Ill. State Water Survey Bull. 30 (1930). Buswell, Shive, Bnd Neave, Ibid.,25, 5 (1928). Buswell, Strickhouser, et al., Ibid., 26, 21 (1928). Buswell, White, Symons, et al., Ibid., 29 (1929). Fales, A. A., private communication. Federation of Sewage Works Associations, Comm. sewage works practice, manual No. 1. Johnson, J . Econ. B i d , 9,105-25, 127-63 (1914). . Kimberly, Water Works & Sewerage, 78, 48 (1931). Larson, Boruff, and Buswell, Sewage W o r k s J., 6, 24 (1934). Neave and Buswell,111. State Water Survey Circ. 8 (1930). Neave and Buswell, J . Am. Chem. Soc., 52,3308 (1930). Schlens and Langdon,WuterW o r k s & Sewerage, 88,217-26 (1941). Symons and Buswell, J . Am. Chem. Soc., 55, 2028 (1933). Tarvin and Buswell, Ibid..56, 1751 (1934). RECEIVED January 3, 19.50
SEPARATION OF OIL REFINERY WASTE WATERS ROY F. WESTON The Atlantic Refining Company, Philadelphia 45, Pa.
The probleni of oil removal from oil refinery waste waters is discussed herein. The problem includes the separation, collection, and reconditioning of the oil for recharging to refinery processes, and also the treatment of the waste water to make it satisfactory for disposal. Oil is separated from waste water using gravity differential-type separators. The efficiency of this operation is based on the relative contents of that portion of the oil amenable to separation by gravity differential flotation processes. A n analytical procedure to determine “susceptibility to separation” was devised to determine the nonseparable oil content of
a sample. The efficiencies of the various separators used are presented. After the oil is separated it will contain suspended solids and water. These materials may interfere with efficient processing and so it is necessary to treat slop oils prior to recharging to processing equipment. Typical data on the characteristics of slop oil treatment are given. Operatingdata are given for an automatic backwash sand filter installation that is successfully “polishing” a separatoreffluent. Pilot plant studies using biological filters indicate general improvement of separator effluents includingsubstantial reductionsinoil content.
IL originating from leaks, spills, tank drawoffs, processing
satisfactory oil content probably will be b u t one phase of the general problem of providing a satisfactory plant effluent. However, it is an important and universally used phase of treatment. Because other aspects of the problems of oil refinery waste disposal have been discussed elsewhere (2-6’) the3e discussions will be confined to the problem of oil removal. I n all known cases, oil is separated from waste water using gravity differential-type separators. During this process oil rises to the surface, sediment settles to the bottom, and relatively small concentrations of oil and suspended solids pass
0
operations, and maintenance and repair activities may find access t o the plant sewers in almost every part of a refinery. Therefore, the economical and adequate separation of oil from waste water is a problem of considerable importance to the refiner. The problem is that of the separation, collection, and reconditioning of oil for recharging to refinery processes and that of the treatment of the waste water to make it satisfactory for disposal. The treatment of refinery waste waters t o produce effluents of
INDUSTRIAL AND ENGINEERING CHEMISTRY
608
Separator d
S o . of Runs
'rotillfioT7-, million gal. II day
c
7 7
4.8-5.9 2.2-3.0 t.2-8.0
Orcrflow ratch, ft./min. 0.027-0.03:3
I.
Separator Operation Data Most I+oh,zLle Ogersri~l- l&ngc"----
Velocity, ft./niin. 1.1-1,35 O.CI8-1.19 3.34-3,YS 2.45-2,7G
Specific xssx-itsr 0 . 7 4 6 - 0 . 707 0.786-0.828 0.856-0.901 0.Q8: 0.93 0.836-0.001
.-
-
.. -
-
.S.< 40-150
3 -21
~~
~~
1:fflnent 14-47 12-37 21-41 26-52 21-40 105-210 108-163
~
~
s
65-92 0.047-0.037 39-63 7-15 40-80 37-70 14-24 0.025-0.020 33-.7!) 50-97 lij-38 60-98 0.140-0.15s 19 4.2-4.8 D-ld 50-107 18--39 7B-100 0.137-0.149 2.40-2.62 19 4.2-4.5 D-2J 335-540 47 -82 57-8:: 0.433 2.98 20 0.144 EO 220-3.50 60 -100 0.836-0.001 57 -88 0.217 1.49 E 19 0.072 T h e most probable operating ranwe includes the central 50% of tlie d a t a . An overflow rate of 0.1 ft./min. & m l s 10SO gal./sq. ft./day. S.T.S., susceptibility t o separation, is expressed as t h e p.p.111. of oil reliiiiiriiw a f t r s 30 sr-in. or lol~gerquiescent settling in a rallon or smaller conl:iiiier. d D-1, conventional %stage A.P.I. separator. e Design basis. I 0 - 2 ,A.P.I. separator of same size as D-1with the second stage inlet device rerilaccd with strcanrlincd vertical guide wmes. E, exporimentai singlc-stage A.I'.I.-type separator, 1.5 ft. wide, 3.0 it. deep, and 20.5 ft. lonr. 13
13
Table
Vol. 42, No. 4
Figure 1 t,lirough the separator, OT'PY the' effluent weir, ant1 out t o the receiving natural viaters. In evaluating the efficicncj- of opcratiou of the gravity diffcrcntial-type separator, the results canriot be based on the relative total oil content in the influent and thc offfucnt, but must be based on the relative contents of that portion of the oil amenable to separation by gravity differential flotation proccsses. This is the case because oil may be present in the form of emulsion or in combination wit,h suspended matter so that it cannot be scparated by gravity differential nieans in rensonnhly-sized separators. For this reason, an analytical procedurc t'o determine "susceptibility to separation" has been devised to deterniine the nonseparable oil content of a sample. Thc msccl)tibility t o separntioii (S.T.S.) numbci is equal t o tlie oil concentration, eupressed pa1 ts per niilliori (p.13.m.) picsent in the centiul layer o1 a settled saniplc. Typical susceptibility to separation data for vaiious separators is hewn i n Tablc I. The efficicncy of oil removals :is shown is based on tlie rclative removal of thc separable oil-i.c., the relative rcmoval of that fraction of oil in cuccss of tlie suxcptibility to separation value. I t should be pointcd out a t this tinie that tlic oil contcnt t o a waste water influent to a separator is composed of t15-o fractions. One fraction is carried in suspension in the form of sinal1 droplets or small suspciidcd solids-oil agglomerates and the other fraction floats on the surface of the mater as free oil. The fraction of oil referred to in Table I as the influent sample contains suspended
oil onl)-. Thcrt~forc,in general, the actual emeicncy ol a sqmrator lor retaining oil will be aoincirhat higher than the ~ a l i i c ? shown on Tablc I and Figurc 1.. The efficiencies of removing separable oil, using t h e various separators as shon.11 in Figurc 2, are shown in Table I and Figui,c> 1. separators A , B , and C arc of the ancient type macle up oi' E: series o E r el a t ivcly sinal1 e onip art iiicnt s . Water flows fro 111 compartment to coinpartmerit through ports, archways, or g : ~ t ( : ~ provided for that. purposc. Tkic direction of flow for cac:li separator is shown on Figure 2 . Separators D-1 and 0 - 2 :ire o i modern American Petroleum Institute, A.P.I., design :tritl c o ~ i tain sludge-collect'ing mei:hanisin. Separator E is :j sirid 1 euperimental unit of the A.P.I. type. It is interesting to notc that the d.l'.T.-type separators ;ircx more efficient than the othcr scparators, cveri though t,hc ovci~.. flon- rates are considerably highcr; also that a separator rnay bcrcasonably cffieient but, nevertheless, ma,y produce a n offliiei, t of uiisat,isfactory quality bcciiuso of the nonseparable oil content, ---Le., a high susceptibility to separation value. The emulsifying influence of punipiiig is shown by tht! rcl:llivc wsccpt.ibility t,o separation valucs for separators t' and E. IVaste water for scparator E wns punipcd froin thc inlet of mtor C. Theoretical considerations, using the principles enunciatctl hy Camp ( I ) , indicate t,liat' the efficiencies of separable oil rcmov:tP o all the separators referred t o ticrcin ii' should be 08 to 1 0 0 ~ for the oil droplcts existed as 0.02-em. dianictcr or larger. The 0.02em. diameter is the s i x suggested by thc Commit,tcc on t,lic~ Disposal of Itcfincry Wastcs of the American l'etrolcurn Iiistituic for use in separator design. Tlie reason for relatively low separation officiencies for selxtr:it,nrs A , B , and C is probably- that the nunierous ch:tngcs in
SEPARATOR
C
Figure 2.
SEPARATOR 0-1
Plan Views of Various Separators
April 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY Table
Bcparator A
B c
II.
Slop
No. of Samples 10 10 49 13 57 7
1 1
a
b C
d
Based Based Based Based
on on on on
Oil Characteristics Most Probable Operating Range Specifio Solids, Water, gravity % ’ b y wt. % b y wt. 0 . 7 4 6 -0.767 0.24a 35.3a 49. Ba 0.766 -0.828 0.5a 0.856b-0.901 1.44-6.4 5.2-22.0 12.2-58.0 0.858 -0.885 1.52-4 . 9 18.2-38.2 0.866c-0.903 1.08-6 .o 0 92lgi-0.916 0 948 0 929
2.7-3.68 21.8 4.7
58.5-68.0 66.3 59.0
1 case. 16 cases. 9 cases. 3 cases.
direction of flow and changes in velocity in passing through the gates and ports between the various compartments cause short circuiting and high velocities that interfere with separation. T h e influence of remixing of the waste water in lowering separation efficiencies is brought out by comparing the data of D-1 and 0 - 2 (see footnotes in Table I ) as shown on Figure 1. The fact that separators D-2 and E, which are of the best design knolvn t o date, did not give efficiencies as high as the theoretical may be due t o one or more of several causes. It could be due t o normal variations in rate of flow, temperature, specific gravity of the oil, etc. ; but theoretical considerations indicatc that the variations found would not account for such discrepancies. Another cause might be that the specific gravity of the oil separated from the water is not the same as that of the oil which remains i n the water. If oil is associated with suspended matter it is entirely conceivable that oil-suspended solids agglomerates could have specific gravities equal t o or either lighter or heavier than water. Still another cause could be that the 0.02-em. droplet diameter is not representative of actual conditions. If the “effective” droplet diameters were about 0.013 cm., the range of theoretical efficiencies would coincide with the actual range in efficiencies for both separator D-2 and the 0.144-million gallons per day flow to separator E. The term “effective” is used advisedly in reference t o oil droplet diameters because of the probable effect of suspended solids on specific gravity. The study of a large number of well-designed separators might indicate an average effective diameter that would provide a practical basis for separator design. The use of the theories of Camp make such a study ~casiblc. Earlier theories were not adequate for this purpose. FILTRATION
609
ide) or emulsion-breaking organic chemicals for resolving slop oil emulsions. The addition of 2 to 15 barrels of waste caustic per 1000 barrels of slop oil in conjunction with heat treatment has aided in resolving some slop oil emulsions. The characteristics of the water layer when using waste caustic and heat are shown in Table 111. I n such cases the treatment and disposal of this material presents a definite problem. Typical data on the characteristics of slop oil treatment bottoms are shown in Table 11. The quantity of bottoms varies appreciably, depending on the solids content of the slop oil. The volume is excessively large a t those localities troubled with biological growths in the sewerage system or separation facilities. The characteristics of slop oil treatment bottoms at such a location are’shown in Table I1 for plant C. Pilot plant experiences using a 0.5-square foot Oliver precoat vacuum filter indicate t h a t slop oil emulsions may be successfully resolved by filtration through diatomaceous earth. Filtration rates of 2.3 to 6.8 gallons per square foot per hour (the range in numerical values shown includes the central 50% of the data) were obtained when filtering at about 170” F. The solids removed by filtration varied from 0.043 to 0.182 pound per square foot per hour. The cake obtained averaged about 21% moisture and %yooil. The fuel value of the cake was 12,700 B.t.u. per pound. The water layer separating from the clean oil has characteristics as shown in Table 111. It should be noted that the pollution load is much less than t h a t from caustic and heat treatment.
SPARATOR B
SEPI\RATOR D-l
Figure 3. Typical Data Showing Relationship between Suspended Solids and Oil Content of Separator Effluents
The fact that filtration will resolve slop oil emulsions indicates that the suspended solids present are probably the stabilizing The separated oil will contain suspended solids and water as indicated by the typical analyses shown in Table 11. Since agents. combined bottom sediment (suspended solids) and water contents in excess of about 1.0% may interfere with efficient Table 111. Characteristics of Water Layer from Slop Oil Treatment processing, may create accident hazards, and may shorten “on-stream” running Suspended NO. Oil, ’ solids, C.O.D., B.O.D., time, i t is necessary to treat slop oils Source Cases p.p.m. pain. p.p.m. p.p.m. P 15 prior to recharging t o processing equip30-130 500-1,360 Vacuum filtration experiments 3? 37-130 77-153 6.9-7.7 ment. I n most cases the emulsions are D 4900-10,300 60-940 22,000-56,000 5660-14,440 10.0-10.2 Plant samples rather easily resolved by heating to a T h e range shown includes 50% of t h e cases. 190” F., retaining a t this temperature for 4 to 6 hours, and then settling for 12 to Table IV. Sludge Characteristics 24 hours. At the end of the settling Lb. Sludge Most Probable Operating Range Produced/ period, 3 definite layers of material will Specific Million Gal. B.t.u./lb. Solids, Water, Oil, No. of Sepagravity % b y wt. % b y wt. d r y solids by wt. Runs of Flow rator exist. The top layer will be clean oil; the A 7 380 5500-10,800 1.0-1.06 54-79 6.4-13.5 4.8-10.6 middle layer will be water containing B 4 710 7405-7590 1.0-1.01 74-75 2.4-5.0 19-20 soluble components, suspended solids, C 7 119 6213a 1.02-1.08 13.5-18 80-85 0.29-1.1 E 18 84 ... 2.1-6.0 78-94 2.7-9.6 and oil; and the bottom layer will be an F 2 748 8645 l:Oib 38.6 49.6 11.8 oily sludge. a Average of 3 results. b Based on 1 result. I n some cases it is advantageous or necessary t o use caustic (sodium hydrox-
INDUSTRIAL AND ENGINEERING CHEMISTRY
610
Vol. 42, No. 4
Table V. Typical Operation Data of Automatic Backwash Sand Filtera
Date 8/23/49 8/24/49 8/25/49 8/26/49 8/27/49 8/28/49 8/29/49 8/30/49 9/1/49 9/2/49 9/3/49 9/4/49 9/6/49 9/7/49 9/8/49 9/9/49 8/17/49 8/17/49 8/18/49 8/19/49 8/23/49 8/24/49 8/25/49 8/29/49 8/30/49 8/31/49 8/1/49 9/2/49 9/19/49 9/20/49 9/21/49 9/22/49
Influent Characteristics, P.P.M. Tursolids bidity Oil B.O.D. C.0.D.b 15 25 101.0 89.0 8 1i:o 87.0 28 104.0 15 24 96.5 107.0 27 9:6 28 84.0 112.0 10 89.0 .. ... 27 218 11 46.0 3 2i:2 123:o 99 100.0 19 100.0 31 106.0 26 24 112.0 109.0 1rj: 1 92.2 610 197.0 44 80.5 31 38 ... 87.5 14 39 2 60.0 59.0 33 F5.0 7 24 95.0 71.0 6 29 iii:o 40.5 7 20 .. ... 8 .. ... .. .,. 16 .. ... .. 13 .. , . . .. 15 .. ... ... 12 .. ... 14 .. ... ... 21 .. ... ... 8 .. ... .. ... 24 .. ... 6 .. .. ... 17 .. ... 22 .. ... .. .,. 2480 ., ... . . . . . 620 .. ... .. ,.. 440 .. .. .. ., 164 , . ... Sus.
..
...
...
..
I
.
.
. . I
,
.
Effluent Characteristics, P.P.M. Tursolids bidity Oilc B.0.D. C.0.D.b 5 3 61.0 T 7' 1 15 60.0 6 .. 71.0 2 10 5.7 93.0 'r 11 .. 150 3 54 1s: 9 9i:o 5 7 .. 76.0 3 9 88.0 11 7' 13.8 59.2 T 9 .. .. 12 T .. 0 16 .. 3i: 0 12 0 72.0 T 14 1 7 83:O , . .. 1' .. .. .. .. T , ,. ., 3 .. ,. T .. .. , . T , . .. Sus.
..
..
.. I
.
..
..
I
.. .,
'r 'r
.. ..
..
T
..
..
, .
..
,.
..
..
4
..
.
Backwash Characteristics, Oil, P.P. M 480 620
.
9/7/49 9/7/49
..
As t,he separator skimmings contain solids, so the bottoiii scdiments (sludges) contain oil. Dat'a on the quantities and characteristics of sludges that accumulate are shown in Table ITr. These sludges may be disposed of irito lagoons located in isolated and/or protected areas. Thc sludges will air dry and the oil contents will evaporate, oxidize, or otherwise lose their identity as such. Relatively large areas are required for such disposal, and so other methods must be investigated when land is at, a premium. Pilot plant investigations using a precoat vacuum filter indicate the possibility of dewatering the sludges by filtration t,lirough diatomaceous earth. The voluniet,ric filtration rates arc, loir in t'his case in that they varied from only 0.6 to 1.45 gallons pcr square foot per hour. The quantity of solids removed by filtration varied from 0.233 to 0.323 pound per square foot per hour. However, the sludge cake contained only 21 water and averaged about 24% oil. The fuel value of the cake was about 10,500 B.t.u. per pound, so that the cake may be burned with the production of heat in excess of that required to sustain combustion. The ash is suitable for disposal as fill. Since solid matter rises to the surface of the separator wit,h the oil, oil settles to the bottom with the sludge, and both oil and solid matter are carried out of t.he separat'or in the effluent; it is apparent that the suspended solids content of the effluent may influence the oil concentration. In Figure 3 two typical sets of dat'a are shown to illustrate the variations between suspended solids41 concentrst,ion relationships that may be expected from sample to sample and separator t,o separator. For those cases in which oil content is iufluenced by suspended solids concentrations, substantial oil removals may be obtained by filtration. The results of small-scale field experiments are shown in Figure 4. It is evident that suspended solids and oil were closely associated for the separator effluent used in this study. As a result of extensive experiments conducted in 1939 and 1940 to determine the effectiveness of shallow filters (3- to 8-inch depth) using granular mediums (magnetite) for removing oil from separator effluents, it was concluded that filters using magnetite, sand, or possibly other granular mediums, could be effective devices for effluent "polishing." Consequently, a Hardinge auto-
Sus. solids
Turbidity
80.0 46.4 75.0 64.3 69.3 31.2 45.4 77.4 62.6 75.1 76.3 69.2 pl.6 s o .0
39.6 46.0 37.3 38.7 42.7 43.4 55.5 34.0 52.7 47.4 54.1 51.6 43.4 60.0
66.0
51.7
60.6 61 3
,.
,.
..
..
Oil
C 11
B.O.D. C.0.D.b
80.0 D8.8
31.5 42.3 38.6
, . .
02.6
17.0
..
99.0
72.8
...
30:3
73.7 88.5
24.0
19.3 70. 1
9 9 . $1 99 7
99.3 100.0 100.0 08.0 85.7 08.8 '39.3 77.0 99.3 '39.2 99.3 ?9,5 00.0 09 r, 98.4 99.5 99.6 100.0 99.8 90.5 D!L4
b
A v . Filtra-
__ tion Rate,
yo RedLir&oiis
..
40.7 24.2 27: 8
Gal./Min./ Sy. F t ,
Rcniarksd
0.31 0,3!) 0.45 0.35 0.33 0.29 0.36 0.40 0.42 0.37 0.35 0.31 0.24 0.36 0.35 0.31
., , .
.. .. ..
Filter area 296 sq. ft: filter backwash rate, 100 iral./min C.O.D. = 'chemical o;ygen deliland nsing iodic arid. T = trace. C = 24-hr. coiiiposite sample; S = s p o t sample.
matic backwash sand fi1tc.r \\'as installed in 1048 for ' ~ p o l i d i i ~ i g ' ~ the effluent of an oil separator receiving oil of high specific gravity from a loading and storage area. The effluent is normally of good quality but is intermittently of sufficiently poor quality that effluent treatment was indicated. A photograph of this installation is shown in Figure 5 . The filter is nominally 12 X 25 feet and contains about 10 inches of sand supported on porous p1:ttes. At the time of construction, filter sand mccting the specifications of the American Water Works Association for rapid sand filters was placed immediately on lop of the porous plates. A few weelrs after starting operation, difficulty was experienced with derailing of the backwash carriage. After some investigation it was determined that the cause of derailing was excessive drag by the backwash pump shoe, the excessive drag being due to high friction caused by accumulations of sand and the warping of the plank providing the inlet ports to, and the cover of, the backwash manifold. When the unit was shut down for inspection after 6 months' operation, it was found that sand leaks into the various cffluent
F f U T M EMOW. OF ML
Figure 4. Effect of Filtration through Granular Mediums on Relative Removal of Suspended Solids and Oil
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1950 Table
61 1
‘ flotation is demonstrated by the accuniulation of oil on top of the filter. In the ca8e of this filter, a 3-inch sltirnniiiig Oil Concn., P.P.M. opening to the wash water trough was InEfReduc Lpadprovided a t each end of the filter. These fluent fluentb tion, % ’ 1ng two openings do not provide satisfactory means for skimming accumulated oil, and 95.7 1.92 96 4 73.1 0.56 so future installations will be provided 26 7 67.8 0.60 28 9 with skimming troughs, Most filters arc 76 7 90.8 1.66 32 5 84.5 0.73 provided with an emergency overfloiv. .. ..3 Obviously, a baffle must be placed ahead 0:49 22 86:5 28 2 93.0 0.65 of the overflow weir for oily waste ivatev 17 2 88.3 0.37 26 1 96.1 0.58 fitration services. The results of an investigation to de.. 6 termine t.he influence of backwashing on 22 5 77:3 0:47 effluent quality are shown in Figure 6. 17 2 88.3 6.36 This study indicates that there is no sig17 8 52.8 0.39 0.49 23 3 87.0 66.7 0.06 3 T nificant change in effluent quality during 93.0 0.30 14 T the backwash operation. However, the 42 3 93.0 0.95 29 4 86.2 0.64 return of backwash water to the sepa26 1 96.1 0.58 rator influent does affect the quality of day (1610 Ib. per acre it. equals 1 Ib. per effluent from the separator. This adverse change in filter influent quality has but a minor influence on effluent quality. Although minor mechanical difficulties associated with the reversal of the backwash mechanism have been encountered, 9 months’ operating experience with the unit has demonstrated that the process is highly successful for this service and that the mechanical problems should continue to be minor in nature. About 1man-hour per day is required for routine operation duties. Routine inspections to check on operation are made once per 8hour shift.
VI. Typical Operating Data for BioRltration of Refinery Wastes
Date
8/1/49 8/2/49 8/3/49 8/4/49 8/5/49 8/7/49 8/8/49 8/9/49 8/10/49 8/11/49
Biochemical Oxygen Demand Concn., P.P.M. InEfReducLoadfluent fluent tion, % inga
123 92.1 165 188
12.9 13.3 36.6 37.0
Filter No. 1 2.48 89.5 1.97 85.9 3.56 77.8 80.4 4.10
155 118 72.8 149 100
26:5 19.2 12.0 25.6
82.9 83.9 85.0 82.8
...
..
..
..
3:ie 2.61 1.68 3.27
..
Filter h-0. 2 84.3 2.44 49.0 1.97 49.2 2.61 79.4 2.57 78:7 2:52 85.2 2.22 88.5 1.55 86.2 3.00
8/1/49 115 17.7 8/2/49C 89.7 45.7 114 58.0 8/3/49C 120 8/4/49 24.7 ... 8/5/49 115 24:s 8/7/49 8/8/49 104 18.4 68.6 7.9 8/9/49 8/10/49 136 18.9 .. .. 8/11/49 ... e Loading is given in thousands of Ib. per acre ft. per 24-hr. c u . yd.). b T 3 trace. Sodium sulfide feed to No. 2. I
.
BIOLOGICAL TREATMENT
Although the sand filter is a satisfactory device for removing suspended solids and oil, it is not a highly efficient device for removing constituents causing B.O.D., taste and odor, toxicity, etc. Probably the most satisfactory process for removing such constituents is that of biological treatment. Because numerous refinery wastes contain such constituents as well as oil, pilot plant experiments have been conducted to determine the effectiveness of biofiltration in improving effluent quality. Although three difFigure 5.
Hardinge Automatic Backwash Sand Filter
channels were responsible for inactivating about two thirds of the filter area. Fortunately, the porous plates were clean and the sand in the active are= appeared to be clean. An analysis of the sand showed an oil content of about 0.5% by weight. When the unit was returned to service the possibility of further trouble due to sand leaks was guarded against by placing about 5 inches of torpedo sand (approximately l/le- to 3/i8-inch diameter) immediately on top of the plates and then placing about 5 inches of clean filter sand on top of that. Three months’ additional operating time has indicated no sand leaks. Typical operating results based on %hour composite and spot samples are shown in Table V. Excellent oil removals are indicated. I n this case the relative oil removals are somewhat higher than the relative suspended solids removals. This could be expected for a service involving oils of high specific gravity. Also, as would be expected, the B.O.D. and C.O.D. (chemical oxygen demand) removals are low. I t should be mentioned a t this point that experimental investigations indicate that filters of this type will not remove appreciable quantities of emulsified oil. The filter appears to remove oil by mechanical straining and by flotation. The fact that the filter backwash contains suspended matter and several hundred parts per million of oil illustrates the part that mechanical straining plays in oil removal. The part of
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Vol. 42, No. 4
CONCLUSION
Table
VI!.
Data Relative to Operation and Maintenance of a Refinery's Sewerage System"
(Oil separation facilities and slop oil treatment equipment) Slop oil handled % of crude oil charge 2.00 Waste water trebted, gal. per barrel of crude oil charge 260 Sources of slop oil handled 29.5 Tank cleaning8 and bottoms, %, 44.0 Tank drawoffs t o the sewers, % Miscellaneous known sources drawn t o sewera, % 19.7 Miscellaneous unknown sources escaping to sewers, % 6.8 Distribution of operation and maintenance costs Operation labor, % 43.2 Maintenance and repair (labor and materials), % 20.0 Utilities, 9% 11.6 2.5, a Overhead and depreciation, 7; a All d a t a are based on t h e 1945 annual average. The costs of waste treatment research, development, and process engineering equaled 37.0% of the total of the operating department's budget.
ferent pilot plant investigations Imve bcwi carried on from 1!1-10 t u date, t,he current investigations are providing the most interesting and the most promising results. Typicai data from the operation of duplicate, single-stage, 6-inch di:amcter., &foot deep filters Iieing doused at. a rate of 15 million gallons pt:r a,cre per clay and bciiig followed by 2 hours' sediinent,atioii, are shown in Tahle 1'1. Plant wvastes from a fluid catnlyat cracking unit are being used :is t h e feed stock. Although no nutrient materials are being added, file efficiencies obtained are comp:ii.al)lc with those From sewagetreatment filters. It is interesting to note that the oil removnl .efficiencies are of the same order of magnitude as those for B.O.D. T o this date, there is no indioat,ion that oil contents up to and including 100 p.p.m. will iiavc any rctariling effect on B.O.D. removal. There is evidenrc that the prcsence of sulfides d l reduce R .O.D. efficiencies. Data obtained to datc show t1i:it :L significant part' of tlie oil feed t,o the filter is not osidieed. Tlie sludge accumulating in the effluent settling t,ank contains oil equivalent to about 31 7 0 of the oil-free solids content.. The data of Table V I indica hat the biological filter may have practical application as a tlcvice for improving thc qualit'y or refinery effluents.
Data relativc to the operation and maintenance ol a refinery's sewerage system, oil separation facilities, and slop oil treatment equipment are shown in Table VII. This table shows thc quantity and sources of slop oil that are handled and the relative costs of operating and maintaining the system. Operating personnel arc on duty around the clock every day of the year. They operate 8 separators draining directly to the Schuylkill River and 3 separators draining t,o plant sev,Ters. They also operate the slop oil treatment facilities, maintain the sewerage system, and keep abreast of activities in the rcfinery that may influence waste wvatcr quality. The foregoing discussions have dwelt on the problem of oil removal from refinery wast,es but have inferred that otlier problems of pollution abatement may esist. Ot,her problems do esist and in some cases may be of n greater magnitude and may bc more difficult and costly to solve than those of oil removal. However, tlie ot'her problems are generally susceptible to local solution, and so the satisfact,ory removal of oil from general plant effluents will continue t o be the industry's major pollution abatement prohlcni for some time to come. Oil removal is becoming more rlifficult continuously as new processes conducive to the formation of emulsions and nonseparnl)le suspensions continue t o be irist~nllrtlinside the refinery fenoc.. LITERATURE
CITED
(1) C a m p , T. R.. Pioc. Am. Soc. Civil Ilingrs., 71, S o . 4, 445-86 (1945). (2) Hart, SV. B., Sewuye W o r k s J . , 17, No. 2, 307-19, (1945). (3) W e s t o n , R. F., Proc. Ind. Waste Utilizetion Conj., P u d u e Unia., 1, 98-425 (1944). (4) V e s t o n , R. I?., ancl Hart, IT'. B., Water Works & S e w e m y e , 88, 208-17 (1941). (5) W e s t o n , R. F., M e r m a n , R. G., a n d D e M a n n , J. G., Proc. Arm, Water Conf., Engrs. SOC.West. Penn., 9, 151-70 (1948). (6) W e s t o n , R. F., M e r m a n R. G., a n d D e h l a n n , J. G . , Scu:ogr; W o r k s J., 21, SO.2,274-85 (1949). ~IECEIV Dccemher ED 12, 1040.
TREATMENT OF COMPRESSED YEAST WASTES WILLEM RUDOLFS ASTES from the imnufacture of nozeies a t the bottom and flow upof compressed Yeast a~ Cornward through a sludge blanket to peRutgers University, N e w Brunswick, N. J. posed predominantly of highly ripheral overflov weirs; a circular EUGENE H. TRUBNICK hopper-bottomed settling tank for reputrescible dissolved organic substances which require oxygen for slabiliaation tention and return of digester sludgcs; Anheuser-Busch, Inc., Old Bridge, N. J. in much the same manner as docs two 4-foot deer, trickling filters enuinncd domestic sewage. Spent nutrient, which with recirculating pumps; and a final settling tank for the collertion of filter sludge. comprises 15yoof the total volume of the IT astcs a t the ;InlieuscxrB.O.D. reductions of as high as 957% were obtaincd with t h o Husch yeast plant, has a biochemical oxygen demand (B.O.D.) digesters and 75yo with the trickling filters. The degree of value of 2000 t o 15,000 parts prr million (p.p.m.) and acpurification accomplished by each of the units could be contiolled counts for 70% of the pollution load of the combined wastes by varying operating conditions. Operating results indicate These wastes, which are typical of a great variety of soluble that certain factois influence the puiification processes signifiorganic industrial wastes, have bwn wcceisfull~treated for mol c cantly and that control of these factors can be utilized to achirvr than 5 years by a combination of anaerobic digestion ancl any desired degree of treatment. trickling filters. Tlic plant (Figure l), designed for flexibility of opwation, ronsists essentially of: two equalization tanks, one for the conDIGESTION centrated portions of the wastr and one for the dilute portions, Thc ripe sludge used as seed in the digesters has remained such as wash waters and cooling ~ a t e r s ~, h i c hprovide for conviable throughout the 5 years of operation; during this time not tinuous uniform flow to the treatment units; two steam heated only has it not been necessary to replenish sludge, but an average digrstrrs jn series, into whjeh the TI astcs arc introduced by means
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