Biological Oxidation Parameter Applied to Industrial Wastes E. J. MILLS, jR./
AND
VERNON T. STACK, JR.
Development Department, Carbide a n d Carbon Chemicals Co., Soufh Charleston, W . Vu.
An
e x a m p l e is given wherein unacclimated microorganisms a n d acclimated microorganisms
are found to give different values for biochemical oxygen d e m a n d when determined by a 5d a y incubation period. T h e difference in these two values can l e a d to differences in the calcul a t e d total loading of biochemical oxygen d e m a n d from a given plant. When values a r e calculated using the d a t a obtained with acclimated seed, then the values for the total biochemical o x y g e n d e m a n d loading a r e n e a r e r the actual a n d true value.
H E biochemical oxygen demand (B.O.D.) has been used for Toxidation more than half a century as the parameter for certain biological reactions. A reasonable confidence in B.O.D. data for domestic sewage and polluted streams has been established. The degree of confidence that many analysts place on the standard procedure for the determination of the 5-day B.O.D. is remarkable when it is realized that this procedure is based entirely on assumptions. The assumption is made that the biochemical reaction will follow a unimolecular equation and that essentially the same rate of reaction will exist for all samples. Within reasonable limits these assumptions have been proved adequate when applied to domestic sewage and, in many cases. to industrial wastes. I n more recent years stream pollution resulting from increased quantities of industrial wastes has brought more attention t o analysis for these pollutants. The B.O.D. determination is still the chief analytical tool, and the 5-day procedure remains in service as the parameter for biological oxidation. However, there has been a considerable loss of confidence in the B.O.D. as an analytical method. This situation is not unvarranted because in many instances apparently erratic and doubtful data have been obtained As a result there has been a gram-ing desire among analysts for an analytical procedure to replace the B.O.D. determination. An injustice exists in this attitude, and three papers presented a t meetings of the Purdue Industrial T a s t e Conference (1-3) have been related to this problem. Data in thebe papers shorn- that the B.O.D. determination gives what is asked for, and the assumptions that are applied to the standard B.O.D. procedure can be incorrect frequently.
Discussion For purposes of discussion consider the hypothetical industrial waste from plant X shonm in Table I. The waste contains €our synthetic organic chemicals n-ith a total theoretical oxygen demand of 4000 pounds per day. I n terms of the freqiiently used B.O.D. and population equivalent relationship, this would represent a population equivalent of nearly 16,000 people, if the assumption is made that the ultimate B.O.D. is approximately 4000 pounds per day. Plant X was located on a small stream near a tom-n, which had a sewage treatment plant providing primary and secondary treatment. Studies of stream pollution by the State Stream Pollution Commission showed that the stream was grossly polluted. As plant X dipcharged its industrial wastes directly to
260
the stream, it' was the major source of pollution. Thus, the Stream Pollution Commission ordered the plant to reduce the quantity of B.O.D. discharge from its outfalls to the stream by 80%. However, a B.O.D. reduction of this magnitude could not be accomplished through reduction of pollution a t the source, so t h a t a waste treatment plant was indicated. Management a t plant X approached the officials of the t o m with the proposal that it might be feasible to treat the wastes from plant X in the municipal sewage treatment plant, which had been constructed with adequate allowances for future groxvth in population. Thus, there mas possibly adequate capacity in the plant for treatment of t,he industrial waste. Composited samples of the industrial ivastes were analyzed by the chemist a t the sewage treatment plant over an extended period, and the average 5-day B.O.D. was found to be 760 pound. per day. Based on these data a n agreement was reached that the industrial Taste from plant X would be treated in the municipal sewage treatment plant. The charge for treating the waste was established a t the regular smyage charge with a surcharge of three cents per pound of $day B.O.D. in excess of 300 pounds per day. After a period of a fern months the &day B.O.D. of the industrial waste, as determined by the chemist a t the sewage treatment plant,, had risen to an average value of 2410 pounds per day. Saturally, those in management a t plant X were disturbed. They had expected to pay a surcharge of approximately 14 dollars per day, but they now found that they were paying 63 dollars per day. Suspecting that they mere being overcharged, management a t plant X had one of their chemists determine t,he 5-day B.O.D. of composited samples. Oddly enough, the chemist found the average value to be 760 pounds per day. The widely different averages of B.O.D. values suggest that one set of data has to be n-rong. Thus, to underst'and better the biochemical reactions that produced these results, a loolc a t some basic B.O.D. data for the individual organic materials con-
Table 1.
Industrial W a s t e s from Plant X
Organic Materiale Discharged t o Sewer
Lb. of Material Discharged per Day
Lb. of Theoretical Oxygen Demand
Acrylonitrile Ethylene glycol Carbitol Acetone Total
500 1000 600
900 1300 1140
300 2400
INDUSTRIAL AND ENGINEERING CHEMISTRY
660
4000
Vol. 48, No. 2
STREAM POLLUTION PROBLEMS
Figure 1. -
B.O.D. of acetone at 20" C. with unacclimated microorganisms
Ultimate B.O.D., 80.270 of theoretical oxygen demand Velocity constant, 0.1 02
Figure 2. A. 6.
B.O.D. of ethylene glycol at 20' C.
Acclimated microorganisms Ultimate B.O.D., 90% of theoretical oxygen demand Velocity constant, 0.1 45 Unacclimated microorganisms
data was obtained with unacclimated microorganisms from dotained in the industrial waste will be helpful. The B.O.D. mestic sewage, and the low value of 760 pounds of 5-day B.O.D. curve for acetone is shown in Figure 1. These data conform per day resulted. After the industrial waste had been admitted nicely with the general idea of B.O.D. The B.O.D. developto the treatment plant, the biological growth in the biological ment follows the unimolecular equation, and the velocity conoxidation unit became acclimated t o the waste. The analyst a t stant is approximately 0.10. A completely different situation is the treatment plant employed these acclimated microorganisms shown in the B.O.D. data for ethylene glycol in Figure 2. The in the B.O.D. analyses of the waste from plant X, and the higher one set of data, where the microorganisms had not been acclimated average of 2410 pounds of 5-day B.O.D. per day resulted. The to ethylene glycol, show a lag period of several days. The 5-day chemist a t plant X was not aware that acclimation of microB.O.D. value is approximately 20% of the ultimate B.O.D., organisms was the reason for the differences in B.O.D. data. and obviously does not meet the assumptions t h a t are made Therefore, he obtained seed for the B.O.D. determinations from when the 5-day B.O.D. is employed as a n analytical tool. The a conveniently located sewer carrying domestic sewage. The B.O.D. development with acclimated microorganisms is different. The lag period has been eliminated, and the B.O.D. curve conmicroorganisms were unacclimated, and the results compared forms to approximately normal B.O.D. development. closely with the initial data obtained by the analyst a t the treatThe acclimation of microorganisms to particular materials is ment plant. not something which occurs in a few hours. I n some cases acThe data in Figure 5 show t h a t the 5-day B.O.D. obtained climation might be accomplished in a few days, and in other cases with unacclimated microorganisms is not a suitable parameter several months might be required. Nevertheless, the acclimation for the industrial wastes from plant X. The same is true of the ultimate B.O.D. obtained with unacclimated microorganisms of microorganisms expressed in the data in this paper is the result because acrylonitrile is not oxidized. The alternative is the use of allowing nature t o take its course. The possibilities with acclimated cultures are more thoroughly illustrated in a paper on of acclimated microorganisms in the B.O.D. determination. acclimation of microorganisms presented a t the ninth Purdue But, how should the parameter be employed? The data in Industrial Waste Conference ( 8 ) . Table I1 show the per cent of the ultimate B.O.D. developed by The B. 0. D. of carbitol as shown in Figure 3 is another exthe standard 5-day procedure. This relationship is influenced ample of improved biological oxidation with acclimated microby lag periods and variations in the rate of biological oxidation. organisms. A rather long lag period in the development of The basic assumptions in the standard 5-day B.O.D. procedure B.O.D. exists with unacclimated microorganisms. The developrequire t h a t the ratio of 5-day B.O.D. t o ultimate B.O.D. be essentially constant. To employ effectively any fixed incubation ment of an acclimated culture shortened the lag period significantly, but did not eliminate it entirely. Acrylonitrile, the period this assumption would have to be made, but the relationfourth component of the industrial waste, does not exert a B.O.D. ship of 5-day B.O.D. to ultimate B.O.D. for the individual when seeded with unacclimated microorganisms. The B.O.D. organic components of the waste from plant X varies widely. data of Figure 4 are the results obtained with a n acclimated culture which oxidized acrylonitrile a,t an extremely fast rate. This is a n example of the vastly different biochemical reactions that Table 11. Tabulation of Biochemical Oxygen Demand of Industrial mav be obtained with acclimated and unacWastes from Plant X climated cultures of microorganisms. Unscclimated Microorganisms Acclimated Microorganisms Organic &Day, 20' C. 5-Day, 20' C. The knowledge of the biological oxidation of Materials Diacharged Ultimate, Ultimate, Ultimate, Ultimate, the organic components of the waste from plant to Sewer Lb./daya yo lb./day Lb./day % lb./day X with acclimated and unacclimated micro615 97 635 nil Acrylonitrile nil 980 84 1170 1170 Ethylene glycol 325 ik organisms enables better understanding of the 445 47 940 940 Csrbitol 65 7 discrepancies in 5-day B.O.D. data. Figure 5 530 370 70 530 Acetone 3LO 70 Totals 760 29 2640 2410 74 3275 shows B.O.D. data for the waste when accliPounds of biochemical oxygen demand based on pounds of organic material in Table I. mated and unacclimated microorganisms are employed. The initial average of 5-day B.O.D. February 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
26 1
I
/
I
,
I
I
I
*
.:i 7-I
;
I
~
0
Figure 3. A.
B.
B.O.D. of Carbitol at 20"
C.
Acclimated microorganisms Ultimated B.O.D., 82.5% of theoretical oxygen demond Velocity constant, 0.1 26 Lag period, 2.4 days Unacclirnated microorganisms
35001
I
I
i
2
4
Figure 4.
~
--
l
8
6
10
12
14
I
B.O.D. of acrylonitrile at 20' C.
Acclimated microorganisms Ultimate B.O.D., 70% of theoretical oxygen demand Velocity constant, 0.32
eration of the biological oxidation unit, but for any comparative purpose all data would have t o be expressed in terms of the ultimate B.O.D. Conclusions
DAYS OF INCUBATION
Figure A. 6.
5. B.O.D. of industrial wastes from plant X Acclimated microorganisms Ultimate B.O.D., 3275 Ib. per day Velocity constant, 0.1 0 8 Unacclimated microorganisms Ultimate B.O.D., 2 6 4 0 Ib. per day Velocity constant, 0.084 Lag period, 4.25 days
Therefore, the only reliable parameter that can be applied to t,he industrial waste from plant X is the ultimate B.O.D. obtained with acclimated microorganisms. The fact that the ultimate B.O.D. is the basic value has aln-ays been true of B.O.D. evaluations. The salient points indicated by the dat, in this paper are: The biological oxidation of industrial wastes can be evaluated more accurately when acolimated microorganism are employed. There are no valid assumptions that can be made which will allow the standard use of a fixed incubation period for evaluating the B.O.D. of industrial wastes. The authors do not contend that a fixed incubation period should never be employed, but believe that the incubation period should be determined by the analyst, and that he should base his decision on the actual manner in which the B.O.D. is exerted. The particular circumstances might dictate an extended incubation period. Data obtained for some fixed incubation period could be employed in the calculation of efficiencies and the op-
262
There is a serious need for investigators t o follow a more flexible approach when evaluating the biological oxidation of industrial wastes. The continued use of the &day B.O.D. as the standard measure of oxygen demand has definitely become a limiting factor. Even the determination of ultimate B.O.D. values is not always a completely satisfactory procedure. To achieve a more complete understanding of the biochemical reactions that can occur during the hiological oxidation of certain materials, acclimated cultures of microorganisms should be used. Results obtained with acclimated microorganisms are indicative of what will occur naturally in a biological oxidation system when sufficient time for acclimat,ionis provided. At the present time the folloviing procedure is employed for the evaluat,ion of the B.O.D. of synthetic organic chemicals in this laboratory. The long term B.O.D. curve is determined employing a source of unacclimated microorgariisnis as seed. If this is not satisfactory, the acclimation of microorganisms for the particular material is attempted ( 8 ) ) and the long term B.O.D. curve is determined employing the acclimated culture of microorganisms as seed. The procedure is time-consuming, but it ensures that a reawnable interpretation of the biochemical reactions can be ninde. It is the opinion of the authors that the ultimate B.O.D. developed with acclimated microorganisms is the only reliahle B.O.D. value for industrial vastes. Once this value is obtained by the above procedure, the biological oxidation characteristics of the particular waste are revealed clearly. Literature Cited (1) Lamb, C. B., and Jenkins, G. F., "B.O.D. of Synthetic Organic Chemicals," Proceedings of Seventh Industrial Waste Confer-. ence, Purdue University, Lafayette, Ind., 1952. ( 2 ) AIills, F,. J., Jr.. and Stack, V. T., Jr., ".lcclimation of Micro-
organisms for the Oxidation of Pure Organic Chemicals," Proceedings of Sinth Industrial Waste Conference, Purdue Univeraity, Lafayette, Ind., 1954. (3) XIills, E. J., Jr., and Stack, V. T., Jr., "Biological Oxidation of Synthetic Organic Chemicals," Proceedings of Eighth Indiistrial Waste Conference, Purdue University, Lafayette, I d . , 1953. R E C E I V Ef D o r review April 2 5 , 195.5.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTEDSeptember 20, 1955.
Vol. 48, No. 2
