J
GERARD A. RONLICH Hydraulic & Sunitary Engineering Laboratory, University of Wisconsin, Madison, Wis.
Flotation as a method for the treatment of sewage and industrial wastes has received increased attention during the past several years. In order to evaluate air flotation methods i n removing oil from refinery waste waters a pilot plant was designed to permit operation of three systems-recirculation, split flow, and full pressurization. Results on waste from an API separator, using air input rates of 2.5, 10, and 20 cubic feet per hour indicate that m a x i m u m oil removals are obtained a t 10 cubic feet per hour, using the recirculation method. Comparative studies with and without addition of flocculating chemicals, using the recirculation method a t 10 cubic feet of air input per hour, indicate that with the use of 4 to 12 p.p.m. of alum and 4 p.p.nan. of activated silica, from 15 t o 23% more oil is removed than with air alone. Batch experiments were carried out using a portable flotation kit assembly. The results compare favorably with the continuous flow pilot plant data, indicating that the kit may be used for preliminary survey work in evaluating the air flotation process.
F
LOTATION a8 a methodfoi the treatment of sewage and industrial wastes has received increased attention during the past several years. The use of flotation methods for the concentration of mineral ores, however, has a history extending over almost a century. In mineral flotation highly effective as well a* highly selective separations have been obtained Ji-ith the use of specific flotation reagents. Gaudin (8) summarizes the important steps in the development of the process and presents the basic principles and their application to the flotation of ores in the mineral industry. Early proresses in this industry were based on the use of oils to selectively attach themselves to acidulated ground or pulveiized ore. As early as 1901 the use of gas as the buoyant mpdium was recognized, the gas being produced by chemical reaction between the acid ore and suspended sulfides and carbonates. This development was follon-ed by direct introduction of gas by w e of mechanical mixing or by diffusion of gas through porous media or submerged pipes. The marked progress in the concentration of ores by the flotation process has been made possible by thc use ol chemical flotation reagents which act as frothers and/or collectors. that facilitate the attachment of thr gas bubble to the solid particle. The use of the proper reagcnt has made possible highly selective collection. As might be expected, the principles of flotation have been applied in other industries, such as the paper industry, where recovery of fiber in white water systems is accomplished by flotation methods (4). I n the field of a-ater purification Hopper (11) conducted experimental studies on 34 different raw water supplies. The results showed average reduction in turbidity of 70%, reduction in suspended solids of 79%, and bacterial reductions of 90%. In these experiments Hopper added 20 p.p.m. of a wetting agent (Roccal) to the turbid water, followed by a 10-minute aeration period and skimming off of the foam. These studies weie followed by additional and more extensive work by Hopper and hIcComen (12)
304
uging quaternary ammonium compounds as the suiface active agents. The results substantiated the earlier studies and showed bacterial reductions of 99% and that the removal of particles, measuring 259 microns in diameter, was more than 95% effective, Hansen and Gotaas (109 used a heteropolar laurylamine h j . drochloride (DP 243) as a flotation reagent in studies made on domestic seTTage, paper mill, and textile wades. Removal of suspended solids of 97% or more were obtained using a retention time for clarification of approximately 15 minutes following the addition of the reagent and aeration. The need for additional study to obtain cost data was stressed since the cost of the flotation reagent was a most important factor. Newe, Schmidt, and Szriiolis (f4)have reported studies on sewage treatment by flotation using 28 different detergents They concluded that no positive results were obtained unless the sewage was acidified to about pH 2. Flotation Tith the addition of 10 mg. of detergent per liter of acidified sewage resulted in 90 to 99% reduction of suspended solids, 65% reduction of &day B.O.D., and about 60% reduction in oxygen consumed. Acid treatment alone showed no removal. Excellent results 'imre obtained with alum and without the addition of a detergent in sewage a t a pH of 3.5. The need for further research to find a low cost flotation reagent was considered by the authors to be important. Vacuum flotation (5, 7 , 13) has been used successfully to reniove grease and suspended solids in the treatment of sewage and induetrial wastes. This process takes place in three steps-a short aeration period to saturate the waste with air a t atmosphcria pressure, release of the larger air bubbles, and finally application? of a vacuum of approximately 9 incheB of mercury to the aircharged liquid, I n the latter stage the air in solution is released as finely divided air bubbles, and these with entrained air bubbles iise to the surface nith the solid particles to which they are a& tached. The scum is continuously removed by a suitablr skirnming mechanism. D'Arcy (3) and Ashley (1) discuss the use of a dissolved air O P
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 2
L e t r o l e u r n Wastes“coIloid air” flotation system and give results obtained in the treatment of industrial wastes. I n this process air is introduced into the influent, usually a t the suction side of a centrifugal pump, and dissolved under pressure (25 to 40 pounds per square inch) in a retention tank. The dissolved air is released from solution when the pressure is reduced, essentially to atmospheric pressure, at the inlet to a flotation chamber. The upward rise of the tiny
’
1
PRESSURIZED FLOW
PUMP
CQ
_..__
, Q---i-.-o @.-i-*as. -..---A
VERTICAL FLOW FLOTATION UNIT
EFFLUENT T0 DISCHARGE
SAMPLING POINTS
Figure 1. Flow Diagram Showing Arrangement for Recirculation Flotation System Using Vertical Flow Flotation Chamber
air bubbles carry suspended particles to the surface of the flotation chamber. Mechanical flight scrapers remove the concentrated sludge from the surface. The clarified water is withdrawn from the bottom of the chamber. Flocculating chemicals, USUally aluminum or iron salts, are added if necessary to improve the clarification. It was reported by D’Arcy (3) that a final effluent containing between 5 and 7 p.p.m. of oil was obtained at a California refinery using this process. Barry (8) and Gibbs (9) present information on a diffused air flotation system. In this process the air is introduced through a special type diffuser to a portion of the effluent which is recirculated and mixed with the influent to the system. The mixture of the air laden effluent and the influent flows upward in the central cylindrical section of the flotation tank which is circular in plan. The flow of the liquid is then reversed by a baffle and flows downward. Part of the aerated recirculated effluent is introduced a t the bottom of the tank and rises through the downward flowing liquid to effect additional flotation. The floated sludge i s collected a t the surface of the tank and discharged to a trough by means of a rotating skimming blade. Farrell (6) reports grease removals of 93% and higher with the use of air flotation in the treatment of packing plant wastes and describes combined flotation and clarification equipment. EXPERIMENTAL EQUIPMENT AND PROCEDURE
In order to evaluate air flotation methods on a refinery waste a pilot plant unit mas constructed by the Chain Belt Co. of Milwaukee. The unit consists of a vertical flow chamber, rectangular in plan with the necessary pump, pressure tank, and control valves required to operate the unit as a gravity flow separator or as a flotation chamber. The chamber, proper, is 8.5 feet long, 3.5 feet wide, and has a water depth of 3.1 feet. With a throughput flow of 75 gallons per minute the overflow rate in the chamber is 2.5 gallons per minute per square foot or 3600 gallons per square foot per day. The detention time a t the 75-gallon-per-minute flow is 9.3 minutes. The chamber contains a pair of parallel longitudinal baffles on either side of the tank. The baffle nearest the side wall acts as a scum retention baffle. The waste flow enters a t the bottom of the tank through a distribution manifold, E~OWS upward in the separating zone, over the inside baffles, then under the scum reFebruary 1954
tention baffle and passes over outlet weirs situated a t the sides of the rectangular tank. The weirs extend the full length of the tank The unit was so constructed that the vertical flow baffle and weir inserts could be removed and the unit operated as an API chamber. When operated as an APT unit the dimensions were 8.5 X 4.0 feet, and water depth was 3.5 feet. Under these conditions the overflow rate a t a 75 gallons per minute throughput was 2.2 gallons per minute per square foot and the detention time 12 minutes. The flow of the waste to be treated could be regulated so as to obtain conditions shown in Figures 1 through 4. Figure 1 is a flow diagram of operation as a vertical flow tank and introduction of air and pressurizing of a portion of the effluent which is recirculated and mixed with the raw waste, Figure 2 is a similar arm rangement except that the flotation chamber is an API design. Figure 3 is a flow diagram showing the piping arrangement in which the process consists of aerating a portion of the raw waste, pressurizing, and mixing this with the raw waste. Although not shown, this process could also be operated with the flotation chamber as an API design. Figure 4 is a flow diagram showing the arrangement by which the entire waste flow could be aerated and pressurized. Again the flotation chamber could be converted to a unit conforming to API design. As shown in the figures the process waste to be treated was pumped to the pilot unit by means of a steam-driven, reciprocating pump. Recirculated effluent or untreated flow was aerated and pressurized using a centrifugal pump. Air was either drawn into the system on the suction side of the pump or introduced under pressure a t the same point or on the discharge side of the pump. The aerated, pressurized flow was then pumped through a 150-gallon holding tank at a pressure of between 50 and 60 pounds per square inch. The pressurized flow was mixed with raw waste or remained as 100% aerated flow and then entered the floeation tank. A vent a t the inlet of the vertical flow tank provided a place of release for the large air bubbles. Air flow was measured with a rotameter and waste flow with an orifice meter. Grab samples a t all sampling points were collected a t intervals of 20 minutes or less and composited. The length of the runs varied from 3 hours to 8 hours with the exception of one 2-hour run. MIXED RAW WASTE AND PRESSURIZED FLOW
7API
CHAMBER
DESIGN
PROCESS
e-
PRESSURE TANK
CENTRlF-dGAL__ PUMP
a
AIRRELIEF
3
S W P L I N G POINTS
I
RECIRCULATED EFFLUENT
Figure 2. Flow Diagram Showing Arrangement for Recirculation Flotation System Using API Chamber Design
The floating oil and solids layer that separated in the unit was skimmed manually during each run as required. Aluminum sulfate and activated silica were used in some of the runs. These chemicals were metered into the mixed influent. RIeasurenient of pH was made a t the flotation tank inlet. Evaluation of the process was based principally upon oil removal efficiency. Additional data such as 5-day B.O.D., suspended solids, and threshold odor number were obtained on some samples. These data, however, indicated extreme variations and no conclusions have been drawn from them. Determinations were made in accordance with “Standard RIethods for the Analysis of Water and Sewage,” with the exception of oil content which
INDUSTRIAL AND ENGINEERING CHEMISTRY
305
In addition to the run8 summarized in Table I, a series of [Pressurization 50-60 poundsjsq. inch g a g e ) runs using recirculation type of treatment, with and without Recirculation Split Flow I’iesiurized Tlow No. of runs II 8 3 4 2 2 2 the aid of flocculating chemiBEours of operation 43.5 48 19 12 G 14 8 cals was made. In t,liis seriw Air applied, cu. f t . / h r . 2.5 10 20 2 5 2.5 7,: 20 the separation chamber conInfluent oil, p.p.in. formed to A Y I design. The Average 167 162 131 166 260 112 91-344 121-133 140-218 238-282 2$-!:22 81-144 Range 125-247 waste f l o ~\vas 50 gallons per Bffluent oil, p.p.rn. minute, and 10 cubic fort of air 36 08 94 50 185 13 I 68 Average Range 71-11? 22-68 45-39 94-112 148--223 111-131 44-93 per hour was added to 25 galOil removal, % lons per minute oi recirculated Average 39 01 58 40 20 ffluent,as in thr prnvious runs. Range 22-62 42-82 55-63 33-40 10-21 27-50 35-45 (2iernical dosqys v:tricd from API design chamber. 4 to 25 p.p.m. of aluminum sulfate, plus 4 p.p.in. of‘ ilctivated silica. In the run in \ \ ~ I i i c ht,lie alum dosage \vas 25 p.p.m. no wtivated s H I X E D RAW AND PRESSURIZED WAS?E I the runs in which chemicals \vex’ used the pH vl’its adjusted to I _ JRIZED approximately 9.0 with sodium hydroxide. llesulti of thi of runs are shown in Table 11. O - - J,__.__ - . - O L O-->--D The range of pH values in those runs in which air w a r wr:d DISCHARGE VERTICAL F L O W F L O T A T I O N U N 1 without’ chemicals, for the data presented in both l’:tbler I and WATER 11, was from 3.3 t’o 10.0 with most of t,he values in a, pH range of from 5 to 7. There was no correlation between @I3values and -PRESSURE TANK oil removals over the pH ranyc encountered. WASTE -CENTRIFUGAL PUMP -1few runs werc made using gravity separation wit,liout ail, or A I R INTAKE chemical addit,ion. As would be expected. since the waste had previously passed through an API separator, the additional deAIR R E L I E F tention time of 9 to 12 rninutep in the pilot plant ~vavnot very SAMPLING POINTS effective in removing addit,ionnl oil. In five rune a t a 50-gtillonsper-minute throughput in thc pilot plant the oil reIIi(Jva1 v:rluc+s Figure 3. Flow Diagram ShoH ing .irrangenieiit for Split Flow Flotation System were 0,6,7, 13, and 16% for ar, average removal of 8.4%. Susceptibility to separation (STS) determinatiorie were m:de on some of thc runs. Results of oil removals hased o n the 8T8 deINfl!PKE PRESSURE TANK terminat,ions for recirculation riinfi using 10 cubic feet of air per hour are shown in Tahle 11. In each case the results indicate that air flotation separates all the separable oil plus an amount th:tt is designated as being not’suweptible to separation. CENTRIFUGAL 9
RESULTS GSISG\*ERTICAII TABLE I. PILOTPLAXT
FLOW
FLor.mo?.I (>H.Z\fBER
‘“4 lz RAw’L%-
^_.__ F-
~
9
PUMP
r
_
_
_
_
v
-
-
-
-
T
IVERTICAL F L O W F L O T A T I O N UNIT
a !%
a
l
O--’*-O o-*-*-
I 1
-
EFFLUENT TO
AIR RELIEF
SAMPLING POINTS
Figure 4.
PORTABLE FLOTATION TEST K I T
MSCHARGE
Flow Iliagraln Showing iirraiigenient for Fully Pressurized Flotation System
I n order t o make spot, tests on various indust,ria.l \v sewages to determine the effectiveness of the flotation portable test kit was deviwd. A picture of the kit i b ~ho\viiin nt, is a pressurc vessel shown Figure 5, The main piere of cqui is constnictd of a I,ric*ite in thc center of the kit. Tho v
was determined by carbon tetrachloride extractiou and nieasw c-
ment of the optical density of the extract in an infrared spectrome&er. The accuracy of this method is Jsithin =!=IO%.
Flow for i-acli iiin .\ir input rate Pressurization
RESULTS
e used as influent to the For the results show1 the process pilot plant system \vas the effluent from a ta-o-stage API separator. A summary of results obtained on oil removals for the three types of treatment are given in Table I. In this series of runs t h e flotation chamber \vas of vertical flow design. The types of trmtment as indicated in the t,ables are describd as follovs: Recirculation: A waste flow of 50 gallons per minute plus 25 gallom per minute of pressurized effluent making a total flow t,o $he unit of 7 5 gallons per minute. This represents an overflow r a t e in the flotation chamber of 2.5 gallons per minute per square foot. Split Flow: h waste f l o ~of 50 gallons per minute plus 25 gallons per minute of pressurized waste making a total flow of 75 galions per minute. Overflow rate 2.5 gallons per minute per q u a r e foot. Pressurized Flow: -1waste flow of 50 gallons per minute all of which is pressurized. Overflow rate 1.68 gallons per niinute per q u a r e foot.
rn
Opesation, Houss 6 6 6 6 6 6
50 gal./iiiin. waste flow pliis 25 g a l . l i n i n recirrulated effliient 10 o l i . ft.llir, i0-60 l h , , ’ ~ ion35-45 pounds/sq. inch gage Oil Oil Content Content before after Oil TreatTreatReSample Flotation mcnt, ment, moval, Treated Treatment pH P.P.N.a P.P.M. %b 81 46.8 5 5 175 89 GO 34.8 Primary No chemicals 7.2 270 109 54 0 Influent to 5 8 Adi. to 9 0 167 28 80 8 75 p.p.m. alum Adj. to 8.6 175 24 84.7 7.2 270 22 90.3 6.2 89 45 46.5 85 46.8 No chemicals 8.0 7.0 119 175 56 52.2 .4PI 27 67.8 Separator 75 p.p.m. alum j A d j j t ; "0 119 89 33 71.3 6.4 82 61 37.8 103 58 43.7 Final N o chemioala 6.5 7.6 73 47 35.6 Adj. t o 8 . 0 82 19 76.8 103 30 70.8 75 p.p.m. alum Adj to 8 . 0 8.8 103 45 56.3 Before pressiirized effluent was added. .Sllo,.xsed for dihitinp effect caused by adding pressr;rioed effluent
760 n ~ i wa5te . pius 230
id.
1
sei:$$z
1
{
1
i
'
I n each of the tests shown in the table final effluent was used as the pressurized liquid. A 750-ml. sample of the waste to be treated was poured into a 1-liter graduate. To this was added 250 ml. of the pressurized cffluent. The t a o were then mixed and the flotation allowed to take p l a c ~ . At the end of 15 minutes a sample n-as withdrawn from below the floated scum and analyzed. Data given for the oil contents bcfore treatment refer to the samples before the pressurized effluent \%-asadded. The data shown for "Oil Removal, '%" were calculated allowing for the adjustment to oil content caused by adding the pressurized effluent. I n the tests a pressure of 35 pounds per square inch Rage was used. DISCUSSION
The results of the pilot plant study indicate that all three air flotation methods used were substantially more effective than addit'ional gravity separation in removing oil from an .&PIseparator effluent.
February 1954
Figure 5 . Portable Flotation Test Kit
Mofit of the data were obtained with the a,pparatus arranged to perform as a recirculation unit in which the effluent, from the unit was aerat'ed, pressurized, and mixed with the influent waste undergoing treatment. In the comparative studies using 50 gallons of feed pcr minute plus 25 gallons of recirculat'ed and pressurized effluent per minute at air rates of 2.5, 10, and 20 cubic feet per hour, without chemical addit,ion, the results indicate that there i8 a marked improvement (25% increase) in oil removal when the air input is increased from 2.5 t,o 10 cubic feet per hour. As shown in Table I incrcasing the air rate from 10 to 20 cubic feet per hour resulted in a decrease in oil removal indicating that the increased air to the '20cubic-feet-par-hour level had a11 :tdwrse effect. In comparing the three mcthods used a t 2.5 cubic Feet, of air input per hour, the recirculation and split flow treatments showed about the same percentage oil removal (39 and 4OOj, respectively), whereas pressurization of all the flax showed a removal of 20%. Increasing air input from 2.5 to 7.5 cubic feet per hour a t a flow of 50 gallons per minute increased oil rem0va.l from a value of 20% to a value of 39% for 100% flow pressurization. A further increase in air input to 20 cubic feet, per hour showed no significant increase in oil removal. Table I1 s h o w the resulte of an additional series of six runs, each of 6 hours duration using recirculation of 25 gallons of effluent per minute, 50 gallons of feed per minute and 10 cubic feet of air input per hour. The results compare favorably with the result's from those runs made under the same operating conditions as given in Table I. An average oil removal of 62% v a s noted. K i t h the addition of chemicals an improvement in performance is notc,d, the oil removal averaging about 80%. The data indicate that there is no significant difference in oil removal with variation in chemical feed for the three chemical dosages of 4, 6, and 12 p.p.m. of alum which were used. In these three runs the alum feed was supplemented with 4 p.p.m. of activated silica. A single run of 5 hours duration using a chemical dosage of 25 p.p.m. of
INDUSTRIAL A N D ENGINEERING CHEMISTRY
307
alum gave an oil removal of 94%, the final effluent from the recirculation unit containing 12 p.p.m. oil. The results given in Table I1 were obtained using an APT chamber design for flotation, while the results given in Table I were obtained using a vertical flow chamber. A comparison between the recirculation runs with 10 cubic feet of air input per hour indicate no significant difference, the vertical flow chamber showing removals of 64% and the API chamber removals of 62% for the averages. No correlation between PI-I and oil removal mas indicated in the runs in which air was used without chemicals. As shown in Table I1 the data indicate that the unit will separate considerable more oil than is considered separable as determined by the susceptibility to separation (STS) test B.ATCII TESTS
For the batch tests using the portable flotation kit the results can be considered qualitative since the air input could not be measured. The principal purpose in presen ting these data is to show that the kit can be used to make exploratory tests to determine the effectiveness of flotation as a method of tieating industrial wastes. In the data s h o m in Table I11 the removals obtained on the tests using the final effluent from an iiPI separator were somewhat lower than those obtained in the continuous flow pilot plant even with the much higher chemical dosage that was used, The best results, using the batch method with chemical addition, were obtained rThen the waste undergoing treatment was primary influent to an AU'I separator. The samples for these tests were taken as the waste was discharged over the influent weir to the separatoi. In this case oil removals of about 85% were indicated. The results of this preliminary investigation of the application of air flotation to refinery waste waters indicate that the flotation process warrants consideration. The pilot plant data show that considerably more oil removal can be obtained in flotation treatment of a separator effluent than is indicated by susceptibility to separation tests, One of the prinripal advantages of the process is the relatively short detention time (15 minutes) required in
the flotation chamber to effect separation. Variations in chemical composition of wastes from different refineries and even within one refinery are proof that there is no such thing as a typical refinery waste, but use can be made of a portable flotation kit, similar to the one described, for survey purposes a t a particular refinery. The results of such surveys n-ill form a basis for further study of pilot plant or prototype operation and design. ACKNQWLEDG3PENT
The author wishes to acknowledge the cooperation of Roy N. Giles, Robert J. Auatin, and George M. Brooks of the Standard Oil Co., Whiting, Ind., in providing facilities for conducting these studies, and in making the analytical determinations. Acknowledgment is made, also, to Leo Schumann, Oliver Tucker, Carlton rind, Weld Conky, and William Throop of the Chain Belt Co., bIilTvaukee, \Vis., who participated in the design of the pilot plant and portable flot,ation equipment', and who assisted in the operation of these units. LITERATURE CITED
( I ) =Ishley, J. H., Wuter & Sewage W o r k s , 97, 297 (19.50). (2) Barry, A. I., Chem. Eng., 58, 107 (1951). (3) D'Arcy, N. A, Jr., Proc. Am. Petroleum Inst., 31M (111) (1951). (4) Easton, P., and Baum, R., T a p p i , 33, 301 (1950). (5) Eliassen, R., and Schulhoff, H. R., Sewage W o r k s J . , 16, 287 (1 944) (6) Farrell, L. S.,Water 6: Sewage Works, 100, 171 (1953). (7) Fisher, A. J., Food Inds., 15, 87 (July 1943). (8) Gaudin, A. bI.,"Flotation," 1 s t ed., New York, McGraw-Hill Book Co., 1932. (9) Gibbs, F. S., Water 6: Sewage Works, 97, 241 (1950). (10) Hansen, C. A , and Gotaas, H. B., Sewage Works J . , 15, 242 (1943). (11) Hopper, 6 . H., J . Am. Water Works Assoc., 37, 302 (1945). (12) Hopper, S. H., arid McCowen, M. C., Ibid., 44, 719 (1952). (13) Logan, R. P., Sewage W o r k s J . , 21, 799 (1949). (14) Newe, >I., Schmidt, J., and Szniolis, d.,Gaz, Woda i Tech. S a n k (Poland) 25, 176 (June 1961): abstract Sewage and Ind. Wastes, 24, 1203 (1952). ~
RECEIVED €or review April 16, 1953.
Treatment of Petroc eractivated Slu
ACCEPTEDJuly 3 , 1953
ical
J
E. R. STRONG AND RICHARD HATFIELD Southwest Research Institzhte, Sun Antonio, Xes.
SI"""
3 the summer of 1948, Southwst Research Institute has cooperated with the Celanese Corp. of America in a study of the waste waters discharged by their Chemcel plant a t Bishop, Tex. The plant produces by diiect oxidation of petroleum hydrocarbons such synthetic organic chemicals as acetic acid, acetone, acetaldehyde, formaldehyde, pa1 nformaldehyde, methanol, propanol, butanols, and propylene glycol. As a result of this method of operation, vmtei contaminated by the process is discharged a t a rate of flow of 400 to 700 gallons per minute. This process waste water has an organic fraction which is composed of traces of the compounds produced by Chemcel as well as intermediates and other by-products resulting from side reactions A typical analysis is presented heren ith. At present process waste is being disposed of by solar evaporation i n carefully constructed ponds that cover 375 acres (3). Celanese has studied numerous treatment methods in an effort to find one
308
that might require less land and yet be as economical as solar evaporation. I n 1949 they began a pilot plant study to investigate the ability of the trickling filter in treating the process waste water, and Ragan (6) published a progress report on the results obtained. SouthFest Research Institute joined Celanese Corp. of America in the filter study after it was already in progress, first to perform the necessary biochemical analyses and later t o
TYPICAL AXALYSIS g-%ay biological oxygen demand, ZOO
Chemical oxygen demand, p . p . m . Immediate oxygen demand Total suspended solids Formaldehyde, p.p.in. Other orgmic compounds
INDUSTRIAL AND ENGINEERING CHEMISTRY
C., p . p . m .
4.5 11,000 30,000 nil nil 6000 traces
Vol. 46, No. 2
