with recirculated effluent. Further, solids to load relationships will be determined, and an antifoam agent will be used if found to be necessary, Evaluation of Results. Pilot plant data are compared with laboratory results in Figures 10 and 11. Figure 10 shows that the agreement of laboratory and pilot plant data is good for variation of B.O.D. removal rate with applied load. The pilot plant produced an effluent mith slightly higher B.O.D. than the laboratory units, Figure 11 demonstrates one of the drawbacks of the process if used as a one-stage treatment method. Data indicate that the B.O.D. of the process waste n-ater can be reduced from 11,000 t o about 200 p.p~m.in a n aeration vessel with a volume equivalent to 4.1 days of waste flow. If an 80-p.p.m. effluent is required, the volume of the aeration vessel must be increased to hold about 8.2 days of flow and to greater than 14 days to produce an effluent with a B.O.D. less than 40 p.p.m. Indications are that for the process to be more econoniical, a two-stage system must be used, where the second stage might use a biological stage similar t o the first or some other method a. chemical treatment.
concluded that formaldehyde was not oxidized in one st,ep, but first rapidly converted to an intermediate or t o intermediates which were oxidized a t a rate slower than that of conversion. 3. Data obtained in continuously fed laboratory activated sludge units having aeration basins of 1000 or 2000 ml. were verified closely by a pilot plant having an aeration chamber of 375 gallons. 4. By returning sludge and by using recirculated effluent) to dilute the raw waste, B.O.D. was removed a t greater than 99% efficiency a t applied loads approaching 200 pounds per day per 1000 cubic feet, and a t about 80% for loads approaching 400 pounds per day per 1000 cubic feet. When the process was operated identically but using tap water instead of recirculated effluent, removal rates were correspondingly less and higher removal rates were unobtainable. It is believed that the recirculated effluent’ contained enzymes or similar materials that were beneficial. Because of its exceptional performance, the process has been named “superact’ivated” sludge process. 5 . Whereas further study is needed to completely est,ablish the hierits of the superactivated sludge process, it offers considerable promise in the treatment of organic wastes and perhaps domestic sewage.
CONCLUSIOKS
(1) American Public Health Association, “Standard Methods fox. The Examination of Water and Seq-age,” 9th ed., 1948. (2) Gellnisn, Issiah, and Heukelekian, €I., Sewage and Ind. Wastea J., 22, 1321-5 (October 1950). (3) LIagfield, F. D., Proc. ThirtpThird Tezas Water Sewage W-oi-ks Short School (March 1951). (4) Moore, W. Allen, Kroner, Robert C., and Ruchhoft, C. C., Anal. Chem., 21, 953-6 (1949). (5) Ragan, 9. L., Chamber of Commerce, Houston, Tex., Proc.
1. When dealing with a toxic organic waste, laboratory batchwise feeding studies are helpful in developing a culture of organisms t h a t will metabolize the waste. And, some idea of the rate a t which B.O.D. can be removed can be determined. However, in this study the time between batchwise feedings had t o be shortened to a matter of hours in order t o obtain B.O.D. removal rates approaching 183 pounds per day per 1000 cubic feet. This type of investigation was very time consuming where continuous feeding was not. 2. I n batchwise feeding studies with pure formaldehyde solutions and process waste water a reduction of the formaldehyde concentration for a given time interval was not accompanied by a corresponding or equivalent decrease of B.O.D. Hence, it was
W. 9. AUSTIN, R’. F. RIEEHAN,
LITERATURE CITED
Fourth Annual Regional Conference on Industrial Healfh, PP. 103-9, 1951.
( 6 ) V d k e r , J. Frederic, “Forinaldehyde,” p . 245, Tow 1-ork,
Reinhold Publishing Corp., 1914. RECEIVED for review April 14, 1953.
ACCEPTED
September 21, 1953.
ANY) J. D. STOCHCHBXI
Research Department, Standard Oil Go. (Inndianu),Whiting, Imd.
The
biological oxidation of refinery waste waters has been investigated ing filters at feed rates of 8,500,000 to ~ ~ ~ Qgal~ 0 ~ 0 0 ~ means of pilot scale tri lons per acre per day. movals of oil, phencpls, biochemical oxygen demand., and odor were used as criteria o%per€ormance. As filter loadings were increased, the reniovalis cpf pollutants effected per unit of bed volume increased; however,, per cent removals decreased and concentrations of undesirable constituen t s in ecpclinag a portion of the filter e uent improved the efHuent increased. removal of oil and phenols but was ineffective in improving removal of odor and biochemical oxygen demand. %containing Taste waters from petroleum refineries are normally discharged through gravity-type oil-n-ater separators ( 3 ) . Under many conditions, however, oil-water mixtures contain emulsions and solids that retard gravity separation, and minute particles of oil and solids remain in suspension in the discharge from the separator. Oil itself is slightly soluble in mater. These suspended and dissolved materials impart tastes and odors to the discharge and are responsible for the oxygen demand. Studies have been undertaken to develop treatment processes that
316
will economically remove the materials producing tastes and odors and will reduce the oxygen demand of refinery Taste waters. Such biological processes as the trickling-filter and the activated-sludge process have proved effective in the treatment uf many industrial waste waters ( 7 ) . Both of these proccsws provide an aeration or oxidizing zone, where the waste water 2nd mcroorganisms are brought into contact, and clarifiers or final settling tanks. Trickling filters employ a stationary biological system, the microorganisms being contained in the slime that en-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 2
L e t r o l e u r n Wastesline leading to the spray nozzles; one filter was operated without recycle. The remainder of the filtered water was discarded. The initial raw-feed rate to the filters was 8,500,000 gallons per acre per day (m.g.a.d.). The feed rate was increased stepwise a t intervals of 4 or 5 weeks to 17,000,000, 28,000,000 and 42,000,000 gallons per acre per day. Recycle ratios of 0.5 to 1, 1 to 1, and 2 to 1 Bere employed in the three units equipped for recycle operation. The settlers were operated a t an overflow rate of 180 gallons per square foot per day with a retention time of 1.2 hours. During the investigation, the ambient temperature varied between 42' and 101' F The minimum and maximum waste water temperatures were 82" and 102" F. Treatment accomplished was followed by collecting duplicate, 24-hour composite samples of the filter charge and of the effluents from each settler, One sample was used for the determination of oil EFFLUEKT EFFLUENT EFFLUEUT content and the second for all other analyses. EFFLUENT The latter sample was refrigerated during the Figure 1. Diagram of Trickling Filter Pilot Plant collection period to inhibit biological action. 3. Sump 1. Sampler The analytical methods employed and the fre4. Settler 2. Flowmeter quency with which they were performed are listed in Table I. Conventional methods were used except for the measurement of oil content. The infrared method, velopes the filter medium. The activated-sludge process employs used for this determination, involves the extraction of oil from a circulating biological system, the sludge acting as the carrier the sample with carbon tetrachloride and the measurement of the for the microorganisms. The activated sludge is separated from absorbance of the extract a t 3.43 and 3.51 microns in an infrared the treated waste water in the settlers and all or a suitable portion is returned to the oxidizing zone, where it is mixed with the incoming waste water. I n both processes, the decomposable organic FEED R A T E , m g a d matter in a waste is oxidized or metabolized in the aeration zone, 8.5 17 28 42 I I and the insoluble matter generated as a result of biological reactions is removed in the settlers. IO0 I n the present study, the trickling filter was chosen for the 75 treatment of gravity separated refinery process water because of E n its stability and low operating costs. The effectiveness was inn 50 vestigated in pilot scale equipment over a test period of 17 con2 o 25 secutive weeks. The criteria of performance were reductions in the four major characteristics of this water: oil content, biochemical oxygen demand (B.O.D.), phenol content, and threshold odor number. d 75 (
n
a
DESCRIPTION OF EQUIPMENT
The pilot plant consisted of a pH controller, four circular trickling filters with individual settlers, and five sample-compositing devices. A schematic diagram of the arrangement of the units is shown in Figure 1. Each filter was 45 inches in diameter (11 s feet of area) and 6 feet deep (66 cu. feet of volume). Broken%mestone, 2.5 to 3 inches in size, was used for the filter medium. Stationary spray nozzles were situated 1 foot above the filter surfaces. The filters were preconditioned by operation on waste water discharged from a separator for several months before the tests were started. This treatment was considered adequate to adapt the biological gron-ths to the feed. A sump a t the base of each filter served as a reservoir for a recycle pump and a settler-feed pump. The settlers were 30-gallon rectangular vessels with hopper bottoms to permit sludge drawoff. Each sampler consisted of two metering units that permitted the collection of essentially identical samples. PROCEDURE
Waste water, pumped continuously from the separator outlet channel, was adjusted to a minimum pH of 6.5 by the addition of 5 % sodium hydroxide solution. The water was then charged to the filters through individual flowmeters and distributed uniformly over the surface by the spray nozzles. The filtered water drained into the sump, from which a portion was pumped to the settlers, I n three of the four units, a second portion was recycled through a flowmeter and mixed with raw feed in the February 1954
50 0
25
6 n
3
n
iY 2 a
t
ms x
pw 1
I5
5 8
10
9
5
$ (L
I-
WEEKS
Figure 2. Characteristics of Feed and Effliieiits Weekly averages Solid black. Feed Cross-hatched. Effluent, once-through operation Dotted. Effluent, 2-to-1 recycle operation
INDUSTRIAL AND ENGINEERING CHEMISTRY
317
OtL
t‘;. 80 D
93 I
I
xI
I_L_I_I_L_J 20 60
0 GALS
40
/M Cf d
Figure 3.
90
100
LBS I H c f d
LBS / M C f d
Effect of Loading and Recycle on Performance Recycle Ratio
lCIillion Gal. 1 Acre /Day 8.5
None
2 to 1
t?a
tA
17
28 42
x
spectrometer. An average absorptivity value obtained from several refinery oils vas used as a standard. The method is applicable over a wide range of concentration, is accurate to n-ithin IO%, and can detect as little as 1 p.p.m. of oil. RESULTS
Analyses of the 2 i h o u r composite samples of the feed t o the pilot plant are shown in Table 11. The average oil content was belo\T the reported tolerance level of 100 p.p.m. for satisfactory biological oxidation (8),but the range of variation encompasses this limit. Relatively low averages for B.O.D. and chemicnl oxygrn demand (C.O.D.) indicat,e low concentrations of decomposable organic matter in thc wiste vi-ater. The phenol concentration was low enough to present no problem from the viewpoint of toxicity. The average B.0.D.-ammonia nitrogen ratio of thr feed n-as 16.5 to 1 and the B.0.D.-phosphate phosphorus ratio was 860 to 1. Weekly averages of the composite data for both the feed and effluent characteristics were used in evaluating the performance of the filters a t the different flow rates and recycle ratios. A summary of these data is shown in Figure 2 . The beat effluents were produced a t the raw feed rate of 8,500,000 gallons per acre per day. Performance a t 2-to-1 recycle ratio was usually better than once-through operation; eflluent oil contents were lower in all instances except’ one. Thp B.O.D. reductions were not signifi-
TABLE 1.
h A L Y T I C d L LICTHODS 4XD
Characteristic n,i GY0.D. C.O.D. Piienol Threshold odor number Susnended solids Aminonia
FREQUENCY OB ANALYSES Analysis per We&
Method (Reference)
_... _-._TnfrlrPrl
&day, 20’ C. ( 2 ) 3 Iodate oxi,datipn (5) 2 Aminoantlpyrine (6) ? Dilution, 20’ C. (4) Am. Petroleum Inst. ( 1 ) 1 Xesslerization ( 2 ) 1 Stannous chloride ( 2 ) 1 Electrometric ( Z ) 5 This niethod is currently bein- considered by both the American Petroleum Institute and the American Society of Testing Materials.
210Bphate
TABLE 11. CHARACTERIRTICS O F PILOT Charrtcteriutic Oil, p.p in. B.O.D., p.p.m. C.O.D.. p.p.m. Phenol, p.p.m. Threshold odor number Suspended solids, p.p.m. Ammonia, p.p.m. Phosphate, 9.p.m. pH, after adjustment
Average 79
PLANT
Maximum 125
FEED Xlinimiim 22 2s
56
101
99 2 2 8,800
30,000
71 1 1 800
1: 3.4 0.2 7.1
3‘4 7.7 0.7 11.3
2.1 0.02 6.5
126 5 9
3
cantly different for the two types of operation. Phenol reduction did not appear to be affected by recycle a t the lower feed rates, but the recycle operation wus superior at the higher rates. Odor reductions ~vrreinfluenced more by feed iates than b)- the amount of recycle. There was a degradation of the effluents, odorwise, nhen the feed rate 75-as increased from 8,500,000 to li,OOO.000 gallons per acre per day. -4further dcgradation occurred after operating for 2 rveelre nt 28,000,000 gallons per acre per day. Z-Ioxever, the over-all average a t 42,000,000 gallons about equaled that for the 28,000,000-gallon period. Data for the 0.5-to-1 and 1-to-1 recycle operations fell betiyeen or near the values shopn.
, “Rlanual 011 thc Dis(1) American Petroleui posal of Refinery Wastes,” Yol. I V , “Sampling and Tcstinp of Liquid Wastes,” 1953. ( 2 ) .Im. Pub. Health Assoc., New Toik, “Standard Methodr f o r the Examination of Water and Sewage,” 9th ed., 1946. (3) Giles, R. N., Scheineman, F. W,, Nicholson, C. T., and .\nstin, R.J.,Sewage and Ind. Wastps, 23, 281 (1951). (4) J . Am. Water W o ~ -48soc., h 30, 1133 (1938). (5) Johnson, D. W,, Tsuchiya, H. lI.,and Halverson, 1%. stracts of papers Presented a t 109th Meeting of -1 CHEMICAL SocIrrY. p. 2-S, 1946. (6) Martin, R. W., Anal. Chem., 21, 1419 (1949). (7) Rudolfs, W., and Ileukelekian, H , Chem. Eng. Prorf., 48, 449 (1952). (8) Weston, R. F., ISD. KSG. CHEY.,42, 607 (1950). RECEIVED for remew April 1, 1963.
318
DISCUSSION
The effect of loading and recycle on trickling X filter performance is shown in Figure 3. Percentage reniovals are based on the differencee in Concentrations between the raw feed to the filters and effluents from the settlers. Loadings are based on concentrations of the components in the raw feed to the filters and are expressed as gallons or pounds per 1000 cubic feet of bed volume per day (gal./blcfd, lb./Mcfd). Percentage removals declined with increased loadings of oil, B.O.D., and phenol. Higher prrcentage removals of oil and phenol xwre obtained with rrcyc,le operation than with once-through operation, but B.O.D. removals did not follow this pattern. Recycle was advantageous in effecting oil removal over the entire range of loadings studied. +it low loading, phenol removals were equal for the two types of operation, but, with inueased loading, removal declined rapidly with once-through operation a t 17,000,000 and 42,000,000 gallons per acre per day. At 28,000,000 gallons, however, removals were almost equal for the t n o types of opcration. B.O.D. and phenol removals showed the same trends at 8,500,000 and 17,000000 gallons. At 28,000,000 gallons, however, phenol removals improved and B O.D. removals underwent an unexplaina1)le drop. At 42,000,000 gallons per acre per day, there was a wide divergence in phenol removals, recycle performance reinaining a t a high level and oncethrough operation falling to about 50%. In this period of opeiation, B.O.D. removals TOR to a level higher than that eliperienced a t 28,000,000 gallons. From Figure 2, it will be noted that feed oil concentrations were 100 p.p m. or more for the entire 28,000,000-gallon period. These high oil concentrations coincide with the period of loaest B.O.D. removals. I n the succeeding period, feed oil concentrations dropped to less than 90 p.p.m. and B.O.D. removal rose to a level that might have been predicted by extrapolating data for the 8,500,000- and 17,000 000-gallon period*. Phenol removal was unaffected by the high oil concentrations. The suspended-bolids content of the settler effluents v a s a t times greater than that of the filter feed and at other timcs less. Surface scum and Pludge accumulations that collected in the settler were combined for analysis. The combined material, on the average, consisted of about 50% oil and 50y0 solids (chloroform RTashed), on a dry basis. The amount of sludge resulting from once-through operation ranged lrom 75 to 157 pounds per million gallons of filter feed, while that for 240-1 recycle operation ranged from 74 to 200 pounds per million gallone. Sludge accumulation was independent of the filter feed rates.
INDUSTRIAL AND ENGINEERING CHEMISTRY
~ C C E P T E DJ,ine
2Qj 1953.
VoI. 46,No. 2
