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Effect of organic compounds on photosynthetic oxygenation—II. Design modification for waste stabilization ponds
Water Research Pergamon Press 1968. Vol. 2, pp. 459--469. Printed in Great Britain
EFFECT OF ORGANIC COMPOUNDS ON PHOTOSYNTHETIC OXYGENATION--II. DESIGN MODIFICATION FOR WASTE STABILIZATION PONDS JU-CHANG HUANG* and EARNEST F. GLOYNA~ The University of Texas, Austin, Texas, U.S.A. (Received 19 February 1968)
AImtraet--This paper describes the potential suppression of dissolved oxygen in ponds and streams due to decreases in photosynthetic oxygenation. Studies involving laboratory waste stabilization ponds, ol~rated under controlled conditions, substantiate th© predicted dccrea~ in dissolved oxygen and treatment efficiency.Designs for waste stabilization ponds can be improved by incorporating a chlorophyll loss factor into commonly used design equations. INTRODUCTION ToE ir~-uamoN of chlorophyll synthesis and the suppression of photosynthetic oxygenation due to the presence of organic compounds have been described in Part I (HuAN6 and GLOVNA, 1968). As a result of numerous laboratory and field observations, it has been recognized that the presence of certain compounds may interfere with photosynthetic processes and thereby reduce the effectiveness of waste stabilization ponds. TmRtrtauRrm and GLOriA (1965) suggested that a factor should be introduced into established design equations to compensate for the reduced oxygenation capacity. Phenolic compounds were chosen as test compounds and laboratory ponds were selected as the treatment system. The applicability of these laboratory units as models for waste stabilization ponds has been verified repeatedly in the authors' laboratory. EXPERIMENTAL PROCEDURE Five laboratory ponds, each 60 cm long, 25 cm wide, and 30 cm deep, were constructed of glass. The capacity of each unit was 45 1. and b a k e s were provided at three positions along the length of the pond. Illumination. Illumination was provided by eight 40W fluorescent and four 40W incandescent lamps. Incident light intensities normal to the pond surfaces ranged from 120 ft-c. to 880 ft-c. with an average value of approximately 500 ft-c. Ponds were uniformly illuminated for 12 hr each day. Wind. Scum consisting of algal cells and floating debris tends to accumulate at the water-air interface of all ponds and this reduces the penetration of light. In full-scale ponds, the formation of scum is greatly inhibited by wind and wave action, and for * Graduate Student, University of Texas, Presently Assistant Professor, Civil Engineering Department, The University of Missouri at Rolla, Rolla, Missouri. t Professor of Environmental Health Engineering, Civil Engineering Department, The University of Texas at Austin, Austin, Texas, U.S.A. 459
460
J u - C H A N G H U A N G a n d EARNEST F . GLOYNA
this reason laboratory units require some artificial wind action. Surface agitation was accomplished by directing small jets of air obliquely on to the surfaces. Temperature. The temperature of the waste water in the model ponds was dependent upon the ambient temperature in the laboratory and absorption of radiant energy
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2 m
/
20 25 30
22
/
/// I / / / ~
23
I l l 24 TEMPERATURE {°C)
i
25
FIG. 1. Temperature profile in model ponds. from the light sources. However, the temperature was similar to that of a nearby industrial pond used to stabilize refinery and petrochemical wastes. A typical daily temperature profile is shown in FIG. 1. Notably, the dissolved oxygen profiles followed a similar pattern, excepting a marked reduction of oxygen was noticeable at the lower depths during periods of darkness. TABLE ] . COMPOSITION OF STARLAC
Food factor Protein Lactose (milk sugar) Milk fat MineraLs Calcium Phosphorus Iron Sodium Potassium Moisture (water)
Dry wt. (%) 36.0 51.0 0.8 8.2 1.3 1.0 0.0006 0.525 1.725 4.0
A synthetic substrate containing non-fat dry milk solids (Starlac), dibasic potassium phosphates and tap water was used. The composition of Starlac is shown in TABLE 1. The BODs at 20°C and COD, respectively, of the Starlac were found to be 460 mg/g and 1100 mg/g. Dibasic potassium phosphate was added in proportion to the ratio
Effect of Organic Compounds on Photosynthetic Oxygenation--II
461
of K2HPO4/Starlac or 93 mg/g. The K2HPO4, besides providing a phosphorus source, helped to buffer the pH and thereby prevent the precipitation of such Starlac constituents as casein. Addition of tap water insured the presence of trace minerals.
EXPERIMENTAL DESIGNS The five ponds, designated as I, II, III, IV, and V, were designed to receive different concentrations of Starlac substrate and varying amounts of phenol. The detention time for each model pond was also designed to meet preselected objectives. Pond I was the control, and received only Starlac substrate. The organic loading of this pond was 180 lb COD per acre per day (83 lb BOD 5 per acre per day or about 93 kg BOD5 per ha per day). The detention time was a relatively short 15 days. Thus, on a daily basis this pond received 3 1. of waste having a COD of 990 mg]l. Pond II was designed to receive the same COD surface organic loading and have the same detention time as Pond I. However, in the influent waste of Pond II, 240 mg]l of COD (equivalent to 100 mg]l dry wt. of phenol) was contributed by phenol while the rest was made up by Starlac substrate. Pond III was designed to receive exactly the same kind of waste as Pond II, excepting a lesser quantity. Theoretically, Pond III was equivalent to an expansion of Pond II. Pond III received only 2 1. of the waste mixture. Thus, this third unit had a detention time of 22.5 days. As reported in Part I, phenol at a concentration of 100 mg/l reduced the chlorophyll to about 75 per cent of its original concentration. On this basis the following equation may be written:
02
Q1 - exp [--KPhen°~ x (C2-C1) ] = exp [ - 2 . 9 9 x 10 -3 x (100-0)] = 0.74 where = quantity of chlorophyll present in the control, = quantity of chlorophyll present in a concentration of 100 mg/1 of 02 phenol, --toxicity constant (algal oxygenation) of phenol, Kphenol C~ and C2 --- concentrations of phenol.
Ol
To compensate for this possible photosynthetic suppression, an increased pond volume will be required. Therefore, the modified detention time for this particular set of conditions must be 20.2 days instead of 15 days. Actually, for test purposes the influent was set at 2 1., and this provided a detention time of 22.5 days. Ponds IV and V received 400 mg/1 (dry wt.) of phenol in the influent waste streams. The surface loading of Pond IV was 290 lb COD per acre per day (or 325 kg per ha per day), the detention was 15 days and the waste addition was 3 1. per day. The influent contained 1620 mg/1 of COD. Phenol contributed 960 mg/1 of the COD and Starlac the remainder. Pond V received the same waste as Pond IV, but a lesser volume. Similar to Pond III, the detention for Pond V was increased according to the calculated effect the phenol might have on the chlorophyll:
462
Ju-CHANG t-IUANGand EARNEST F. GLOYNA
Q2
Q, - exp [ - Kv,..o, x (C 2 - - C I ) ] = exp [ - 2 . 9 9 x 10 -3 x ( 4 0 0 - 0 ) ]
= 0.33
Hence a detention of 15/0.33 = 45 days was provided.
t
i ~20
g~15 25 50
I
0
I
r
1 2 3 4 5 6 7 8 9 10 Ir 12 13 DISSOLVED OXYGEN (ms/L)
FIG. 2. Dissolved oxygen profile in model pond I.
EXPERIMENTAL ANALYSES AND RESULTS A p p r o x i m a t e l y 2½ m o n t h s were necessary for the five p o n d s to become r e a s o n a b l y acclimated as reflected by the u n i f o r m removal of b o t h Starlac a n d phenol. Following a t t a i n m e n t of steady-state operations, data were collected for a period of one m o n t h . These results are shown in TABLE 2 a n d FIGS. 2-6. TABLE 2. ANALYTICAL RESULTS Influent
Effluent Total Pond DetenStarlac Phenol COD Starlac Phenol No. tion Drywt. COD Drywt. COD (d)+(f) COD Drywt. COD time (mg/1) (mg/1) (mg/l) (mg/l) (mg/l) (mg/1) (mg/l) (mg/l) (days)
Removals (%) Total Phenol COD (h)+(]) [(e)-(i)] [(g)-(k)] (mg/1) (e) (g) Total COD
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
I II IlI IV V
15 15 22.5 15 45
900 680 680 600 600
990 750 750 660 660
0 100 100 400 400
0 240 240 960 960
990 990 990 1620 1620
210 226 195 207 190
0 38 23 174 106
0 91 55 418 254
210 317 250 625 444
-62 73 57 74
79 68 75 61 73
Phenol and total soluble COD remaining in the effluents. Twice each week the effluents were centrifuged a n d the s u p e r n a t a n t was analyzed for p h e n o l a n d C O D according to Standard Methods for the Examination of Water and Waste Water (1965). The results
Effectof OrganicCompoundson PhotosyntheticOxygenation--II
463
are shown in TABLE2, columns i and k. The percentage removals of both COD and phenol are given in columns l and m. The total soluble COD in the effluent was assumed to be due to the remaining phenol and Stadae substance. The COD contributed by bacterial and algal cells was neglected. Thus,' the portion of COD contributed by the
~L=~/~1 ~1 ~1 ~11~: IO
~o
~
ffJ/
.o
,oh
o
,~
o
25 30 0
I
I I 1 1 1 I, I 3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rng/L)
2
I 12 13
FIG. 3. D i s s o l v e d o x y g e n profile in m o d e l p o n d II.
remaining Starlac in the effluents, column h was calculated by subtracting the COD contributed by phenol, column j, from the total soluble COD in the effluent, column k. As shown in TABLE2, the concentrations of phenol remaining in the effluents of Ponds II, III, IV, and V were, respectively, 38 mg/1, 23 mg/l, 174 mg/l, and 106 mg/l.
°I '1'/''
1''I'71' ~P:l ~1 ~1 ~1 ,.'~Is o
o
b
~
~
0tlf -j -f ? o
o
~
~,
0
~
_
~21
~o 30
I 0
I
I 2
!__I
!
I
I
'
I
I
3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rng/L)
I 12 13
FIG. 4. D i s s o l v e d o x y g e n profile in m o d e l p o n d III.
The corresponding removal efflciencies were 62, 73, 57, and 74 per cent, respectively. The longer detention times and dilution provided by Ponds III and V improved the eftlcieney of phenol removal. The control pond exhibited the lowest concentration of total soluble COD in the
464
Ju-CHANG HUANG and EARNEST F. GLOYNA
effluent (210 mg/l) and the highest COD removal (79 per cent). The toxic effects exhibited by 100 mg/1 (dry wt.) phenol in the influent waste stream of Pond II were demonstrated by a higher COD (317 mg/1) in the effluent and a lower COD removal (68 per cent). However, the portion of the effluent COD contributed by Starlac alone
5
Jy 10
~15 bJ
20
25 3O @
I
2
3 4 5 6 ? 8 9 10 II 01SSOLVED OXYGEN (rag/L)
12 13
Fio. 5. Dissolved oxygen profile in model pond IV.
(226 mg/1 )in Pond II was about the same as that in the effluent of the control pond (210 mg/l). The longer detention time provided by Pond III (22.5 days) improved the treatment efficiency (75 per cent) as compared to Pond II. Although the total soluble COD in
0
I
2
3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rag/L)
12 ]3
FIG. 6. Dissolved oxygen profile in model pond V.
the effluent of Pond III was still slightly higher than that of the control. However, the portion of effluent COD contributed by Starlac alone was only 195 mg/1, which was smaller than that in the control. Ponds IV and V provided the same comparison as Ponds II and IIL The amounts of
Effect of Organic Compoundson PhotosyntheticOxygenation--II
465
effluent COD contributed by Staflac in Ponds IV and V were, respectively, 207 mg/l and 190 mg/l. Therefore, similar to Ponds II and III, the presence of 400 mg/l (dry wt.) phenol in the influent did not seem to inhibit the bacterial activity. The efficiencies of removal in Ponds IV and V, were, respectively, 61 and 73 per cent. Dissolved oxygen in the ponds. A dissolved oxygen survey conducted at the end of the experimental effort provided additional information on the operational characteristics, FIGS. 2-6. The dissolved oxygen was monitored at each 5 cm increment of depth near the center of the pond. The measurements were made at 2 hr intervals beginning at 0600 hours and ending at 1800 hours. In the control pond, the dissolved oxygen reached a maximum of 12 mg/1. The levels of dissolved oxygen in Pond II were approximately 0.75 of those in the control unit. These data are comparable to the results of the previously reported test-tube studies which predicted a reduction in the chlorophyll (i.e., a concentration of about 74 per cent of that in the control) for a phenol concentration of 100 mg/l. The phenol content of several grab samples from different locations in Pond II varied from 56 rag/1 to 84 rag/1. Where a longer detention time (22.5 days) was used, the dissolved oxygen in the pond increased to a level which was about 90 per cent of the control unit, FIG. 4. In Pond IV, the maximum dissolved oxygen content was 5 mg/l, which was 41 per cent of that found in the control unit. As a comparison the previous test-tube studies indicated a 33 per cent value when the phenol concentration was 400 mg/l. The phenol concentration in Pond IV ranged from 220 to 320 rag/1. Although the detention in Pond V was three times as much as that provided in Pond IV, the dissolved oxygen in Pond V was only slightly better. The maximum dissolved oxygen measured was only 60 per cent of that in the control unit. The low value of dissolved oxygen in Pond V was attributed to the higher COD in the influent which overloaded the assimilative capacity of the pond. Predominating algae and chlorophyll contents. A microscopic examination of samples taken from each of the five ponds indicated that the predominant algal form was Chlorella. The predominance of Chlorella was partly due to the relatively quiescent conditions. As FOGG (1965) reported, cultures containing more than one species of algae are difficult to maintain in a laboratory, While two or more algal species seem to coexist in equilibrium in a natural water, the same cultures, when brought to the laboratory, will invariably develop into a single culture system. The chlorophyll in the effluents of Ponds I-V, respectively, were 2.4 mg/1, 1.8 rag/l, 2.0 mg/l, 1.2 mg/1, and 1.4 mg/1. The chlorophyll in the effluents of Ponds II-V, as compared to the control unit, were 75, 84, 50, and 59 per cent, respectively. These relative values are comparable to the dissolved oxygen data.
DISCUSSION The assimilative capacities of aerobic and facultative waste stabilization ponds are related to both the algal and bacterial productivity. Toxic compounds present in waste streams may affect the operation of waste stabilization ponds in at least four ways. (a) Compounds may inhibit the photosynthetic processes and hence suppress photosynthetic oxygenation.
466
Ju-C-'nANO HUANG a n d EARNEST F. GLOYNA
(b) Toxic compounds may inhibit bacterial activity, and reduce the rate of biodegradation of organic compounds. Therefore, ponds become less efficient in the treatment of wastes. (c) The biodynamic equilibrium of biological populations in the pond may be upset by the presence of certain toxic compounds. (d) Some industrial wastes are toxic and relatively resistant to biodegradation. These compounds may impose an appreciable COD concentration on the effluents. Consequently, the overall treatment efficiency of the pond is reduced. The studies involving waste stabilization ponds substantiate the predicted decrease in dissolved oxygen as well as reduced COD removals. Consequently, the data as reported in the test-tube study (Part I) can be used to improve existing design equations. For most of the compounds reported herein, the reduction of chlorophyll may be expressed as shown in equation (1). O Fraction of chlorophyll remaining = Qoo= e- ~c
(1)
where
Oo = chlorophyll content if there is no test compound present,
Q K C
= chlorophyll content in the presence of test compound, = chlorophyll inhibition constant of the compound (toxicity), and = concentration of test compound.
If the chlorophyll inhibition constant is known, the fraction of chlorophyll remaining can be calculated. Now if a waste stream contains organic compounds which exhibit inhibitory effects toward chlorophyll and hence on photosynthetic oxygenation, the volume of a pond must be increased accordingly. However, consideration must be given to the fact that part of the toxic material may be subject to fairly rapid biodegradation. Consequently, under complete mixing and continuous flow conditions, the average concentration of a compound in a pond may be expressed as shown in equation (2) (MARAIS, 1966). oo
C° c = (¢-/-Q)
e -kt' e-(Q/v),, dt' = k ( V / Q ) + 1
(2)
t'=O
where = average concentration of the organic compound remaining in the pond, or equal to the concentration present in the effluent, Co = original concentration of the organic compound present in the influent waste stream, V = volume of pond, Q = quantity of influent flow, = time of exposure (i.e., detention), t' = rate constant of biodegradation of the organic compound. k C
Since V/Q is equal to the detention time, t, equation (2) can be rewritten, C =
~
Co
kt+l
(3)
Effectof OrganicCompoundson PhotosyntheticOxygenation--II
467
As shown in equation (3), the reaction time depends upon the biodegradation rate constant and the degree of treatment desired. The rate constant is in turn dependent upon the temperature, equation (4). t
k,
to
k
0(r,-r)
(4)
where to and t = reaction times required (for a given treatment) at rate constants of k° and k, respectively (i.e., bacteriological action), k, and k = rate constants (bacteriological degradation) at temperatures of To and T, respectively, 0 = temperature coefficient for a specific waste. Noteworthy is the fact that values of ko, k, and 0 are dependent upon the biodegradability of the specific waste. The concentrations can be calculated by substituting equation (4) into (3) and developing a chlorophyll compensation factor,
Is koito+lJ KiCo~.1
= e x p ,~1
(5)
(for photosynthetic reoxygenation suppression) where f = chlorophyll compensation factor, Ks = chlorophyll inhibition constant of the ith compound, k,~ = observed rate constant of biodegradation of the th compound. A general design equation can be developed for determining the volume of an industrial waste stabilization pond. A rational approach can be developed on the basis of knowing the quantity of waste flow, reaction time, biodegradation rate constant, biochemical oxygen demand, and chlorophyll compensation factor. It is recommended that the evaluation of the chlorophyll inhibition constant be based on the waste itself. Furthermore, it is suggested that for calculation purposes the original waste be first diluted to a factor of (koto+l), and that the chlorophyll compensation factor be calculated on the basis of the diluted waste. By substituting equation (5) into a previously developed design formula (H~.MANN and GLOYNA, 1958 and GLOYNA, 1966), it is possible to present a complete formulation.
V= 1.54xlO-StoQY[O(r°-r)]expFK(. C° .~1 L \koto+UJ
(6)
where V a Y
= volume of pond (acre-ft) for a single facultative pond, = quantity of influent flow, gal/day (U.S. gallons), = five-day 20°C BOD (if secondary effluent); ultimate influent BOD, mg/l (if settle solids present), = temperature coefficient, depending upon the specific waste, 0 being 1.085 for a number of biodegradable industrial wastes at 35°C,
468
Ju-CHANG HUANG and EARNEST F. GLOYNA
To T
_
to exp -K =
Co
--
ko
~-
observed maximum operation temperature (based on the maximum monthly water temperature), °C, expected minimum operation temperature (based on the minimum monthly water temperature), 'C, reaction time required for a given treatment at To and ko, base of natural logarithm, chlorophyll inhibition constant of the waste, original concentration of the waste, mg/l dry weight (or mg/1 C O D or mg/l BOD, depending on the unit used in the evaluation of the chlorophyll inhibition constant), observed biodegradation rate constant of the waste at To.
Equation (6) can be rewritten as follows: Co
V : CQY[O~aS-r)]expIK(ko~o+l) 1
(7)
V' = ClQY[O~35-r)]exp K\koto+ l/.]
(8)
or
where = 10.7 x 10-s where temperature fluctuations are large and ponds are designed on a depth of 6 ft and Vis in acre-ft (to = 7.0 days at To = 35°C), C 1 = 3.5 x 10 -5 when depth is 1.82 m and pond volume is in m 3. C
It should be noted that where ponds are built in tropical areas, where temperature fluctuations are minimum and where the solid accumulation is no problem, the depth coefficient C and to in (7) and (8) can be reduced by a factor of two. # CONCLUSIONS Studies involving laboratory waste stabilization ponds substantiate the predicted decrease in dissolved oxygen as well as treatment efficiency. The design standards of waste stabilization ponds can be improved by adding a chlorophyll compensation factor to the previously developed design equation. Equations (6)-(8) are examples for the design of a single facultative waste stabilization pond.
Acknowledgements--Thisstudy was made possible by an initiation grant from the College of Engineering, The University of Texas, and a continuation grant from the Water Supply and Pollution Control Division, U.S. Public Health Service and Federal Water Pollution Control Administration (WP-00688-03). REFERENCES FOaG G. E. (1965) Algal Cultures and Phytoplankton Ecology University of Wisconsin Press, Madison and Milwaukee. GtO~A E. F. (1966) Unpublished Reports. H ~ E. R. and GtO~rNAE. F. (1958) Waste stabilization ponds--III. Formulation of design equations. Sewageind. Wastes30, 963-975. HUANOJ. C. and GLOYNAE. F. (1968) Effect of organic compounds on photosynthetic oxygenation --I. Chlorophyll destruction and suppression of photosynthetic oxygen production. Water Research 2, 347-366.
Effect of Organic Compounds on Photosynthetic Oxygenation--II M~s
469
G. v. R. (1966) Operation and performance of waste stabilization ponds. Bull. Wld Hlth Org.
34, 737-763. Standard Methods for the Examination of Water and Waste Water (1965) 12th Edition. Am. Public Health Association, Inc., New York, N.Y. THmUMURTmD. and GLOYNAE. F. 0965) Relative toxicity of organics to Chlorella pyrenoidosa. University of Texas Report No. 11-6503, Austin, Texas.
EFFECT OF ORGANIC COMPOUNDS ON PHOTOSYNTHETIC OXYGENATION--II. DESIGN MODIFICATION FOR WASTE STABILIZATION PONDS JU-CHANG HUANG* and EARNEST F. GLOYNA~ The University of Texas, Austin, Texas, U.S.A. (Received 19 February 1968)
AImtraet--This paper describes the potential suppression of dissolved oxygen in ponds and streams due to decreases in photosynthetic oxygenation. Studies involving laboratory waste stabilization ponds, ol~rated under controlled conditions, substantiate th© predicted dccrea~ in dissolved oxygen and treatment efficiency.Designs for waste stabilization ponds can be improved by incorporating a chlorophyll loss factor into commonly used design equations. INTRODUCTION ToE ir~-uamoN of chlorophyll synthesis and the suppression of photosynthetic oxygenation due to the presence of organic compounds have been described in Part I (HuAN6 and GLOVNA, 1968). As a result of numerous laboratory and field observations, it has been recognized that the presence of certain compounds may interfere with photosynthetic processes and thereby reduce the effectiveness of waste stabilization ponds. TmRtrtauRrm and GLOriA (1965) suggested that a factor should be introduced into established design equations to compensate for the reduced oxygenation capacity. Phenolic compounds were chosen as test compounds and laboratory ponds were selected as the treatment system. The applicability of these laboratory units as models for waste stabilization ponds has been verified repeatedly in the authors' laboratory. EXPERIMENTAL PROCEDURE Five laboratory ponds, each 60 cm long, 25 cm wide, and 30 cm deep, were constructed of glass. The capacity of each unit was 45 1. and b a k e s were provided at three positions along the length of the pond. Illumination. Illumination was provided by eight 40W fluorescent and four 40W incandescent lamps. Incident light intensities normal to the pond surfaces ranged from 120 ft-c. to 880 ft-c. with an average value of approximately 500 ft-c. Ponds were uniformly illuminated for 12 hr each day. Wind. Scum consisting of algal cells and floating debris tends to accumulate at the water-air interface of all ponds and this reduces the penetration of light. In full-scale ponds, the formation of scum is greatly inhibited by wind and wave action, and for * Graduate Student, University of Texas, Presently Assistant Professor, Civil Engineering Department, The University of Missouri at Rolla, Rolla, Missouri. t Professor of Environmental Health Engineering, Civil Engineering Department, The University of Texas at Austin, Austin, Texas, U.S.A. 459
460
J u - C H A N G H U A N G a n d EARNEST F . GLOYNA
this reason laboratory units require some artificial wind action. Surface agitation was accomplished by directing small jets of air obliquely on to the surfaces. Temperature. The temperature of the waste water in the model ponds was dependent upon the ambient temperature in the laboratory and absorption of radiant energy
(~
..c:
) ~
L~
(3
"¢::
O
C3
2 m
/
20 25 30
22
/
/// I / / / ~
23
I l l 24 TEMPERATURE {°C)
i
25
FIG. 1. Temperature profile in model ponds. from the light sources. However, the temperature was similar to that of a nearby industrial pond used to stabilize refinery and petrochemical wastes. A typical daily temperature profile is shown in FIG. 1. Notably, the dissolved oxygen profiles followed a similar pattern, excepting a marked reduction of oxygen was noticeable at the lower depths during periods of darkness. TABLE ] . COMPOSITION OF STARLAC
Food factor Protein Lactose (milk sugar) Milk fat MineraLs Calcium Phosphorus Iron Sodium Potassium Moisture (water)
Dry wt. (%) 36.0 51.0 0.8 8.2 1.3 1.0 0.0006 0.525 1.725 4.0
A synthetic substrate containing non-fat dry milk solids (Starlac), dibasic potassium phosphates and tap water was used. The composition of Starlac is shown in TABLE 1. The BODs at 20°C and COD, respectively, of the Starlac were found to be 460 mg/g and 1100 mg/g. Dibasic potassium phosphate was added in proportion to the ratio
Effect of Organic Compounds on Photosynthetic Oxygenation--II
461
of K2HPO4/Starlac or 93 mg/g. The K2HPO4, besides providing a phosphorus source, helped to buffer the pH and thereby prevent the precipitation of such Starlac constituents as casein. Addition of tap water insured the presence of trace minerals.
EXPERIMENTAL DESIGNS The five ponds, designated as I, II, III, IV, and V, were designed to receive different concentrations of Starlac substrate and varying amounts of phenol. The detention time for each model pond was also designed to meet preselected objectives. Pond I was the control, and received only Starlac substrate. The organic loading of this pond was 180 lb COD per acre per day (83 lb BOD 5 per acre per day or about 93 kg BOD5 per ha per day). The detention time was a relatively short 15 days. Thus, on a daily basis this pond received 3 1. of waste having a COD of 990 mg]l. Pond II was designed to receive the same COD surface organic loading and have the same detention time as Pond I. However, in the influent waste of Pond II, 240 mg]l of COD (equivalent to 100 mg]l dry wt. of phenol) was contributed by phenol while the rest was made up by Starlac substrate. Pond III was designed to receive exactly the same kind of waste as Pond II, excepting a lesser quantity. Theoretically, Pond III was equivalent to an expansion of Pond II. Pond III received only 2 1. of the waste mixture. Thus, this third unit had a detention time of 22.5 days. As reported in Part I, phenol at a concentration of 100 mg/l reduced the chlorophyll to about 75 per cent of its original concentration. On this basis the following equation may be written:
02
Q1 - exp [--KPhen°~ x (C2-C1) ] = exp [ - 2 . 9 9 x 10 -3 x (100-0)] = 0.74 where = quantity of chlorophyll present in the control, = quantity of chlorophyll present in a concentration of 100 mg/1 of 02 phenol, --toxicity constant (algal oxygenation) of phenol, Kphenol C~ and C2 --- concentrations of phenol.
Ol
To compensate for this possible photosynthetic suppression, an increased pond volume will be required. Therefore, the modified detention time for this particular set of conditions must be 20.2 days instead of 15 days. Actually, for test purposes the influent was set at 2 1., and this provided a detention time of 22.5 days. Ponds IV and V received 400 mg/1 (dry wt.) of phenol in the influent waste streams. The surface loading of Pond IV was 290 lb COD per acre per day (or 325 kg per ha per day), the detention was 15 days and the waste addition was 3 1. per day. The influent contained 1620 mg/1 of COD. Phenol contributed 960 mg/1 of the COD and Starlac the remainder. Pond V received the same waste as Pond IV, but a lesser volume. Similar to Pond III, the detention for Pond V was increased according to the calculated effect the phenol might have on the chlorophyll:
462
Ju-CHANG t-IUANGand EARNEST F. GLOYNA
Q2
Q, - exp [ - Kv,..o, x (C 2 - - C I ) ] = exp [ - 2 . 9 9 x 10 -3 x ( 4 0 0 - 0 ) ]
= 0.33
Hence a detention of 15/0.33 = 45 days was provided.
t
i ~20
g~15 25 50
I
0
I
r
1 2 3 4 5 6 7 8 9 10 Ir 12 13 DISSOLVED OXYGEN (ms/L)
FIG. 2. Dissolved oxygen profile in model pond I.
EXPERIMENTAL ANALYSES AND RESULTS A p p r o x i m a t e l y 2½ m o n t h s were necessary for the five p o n d s to become r e a s o n a b l y acclimated as reflected by the u n i f o r m removal of b o t h Starlac a n d phenol. Following a t t a i n m e n t of steady-state operations, data were collected for a period of one m o n t h . These results are shown in TABLE 2 a n d FIGS. 2-6. TABLE 2. ANALYTICAL RESULTS Influent
Effluent Total Pond DetenStarlac Phenol COD Starlac Phenol No. tion Drywt. COD Drywt. COD (d)+(f) COD Drywt. COD time (mg/1) (mg/1) (mg/l) (mg/l) (mg/l) (mg/1) (mg/l) (mg/l) (days)
Removals (%) Total Phenol COD (h)+(]) [(e)-(i)] [(g)-(k)] (mg/1) (e) (g) Total COD
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
I II IlI IV V
15 15 22.5 15 45
900 680 680 600 600
990 750 750 660 660
0 100 100 400 400
0 240 240 960 960
990 990 990 1620 1620
210 226 195 207 190
0 38 23 174 106
0 91 55 418 254
210 317 250 625 444
-62 73 57 74
79 68 75 61 73
Phenol and total soluble COD remaining in the effluents. Twice each week the effluents were centrifuged a n d the s u p e r n a t a n t was analyzed for p h e n o l a n d C O D according to Standard Methods for the Examination of Water and Waste Water (1965). The results
Effectof OrganicCompoundson PhotosyntheticOxygenation--II
463
are shown in TABLE2, columns i and k. The percentage removals of both COD and phenol are given in columns l and m. The total soluble COD in the effluent was assumed to be due to the remaining phenol and Stadae substance. The COD contributed by bacterial and algal cells was neglected. Thus,' the portion of COD contributed by the
~L=~/~1 ~1 ~1 ~11~: IO
~o
~
ffJ/
.o
,oh
o
,~
o
25 30 0
I
I I 1 1 1 I, I 3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rng/L)
2
I 12 13
FIG. 3. D i s s o l v e d o x y g e n profile in m o d e l p o n d II.
remaining Starlac in the effluents, column h was calculated by subtracting the COD contributed by phenol, column j, from the total soluble COD in the effluent, column k. As shown in TABLE2, the concentrations of phenol remaining in the effluents of Ponds II, III, IV, and V were, respectively, 38 mg/1, 23 mg/l, 174 mg/l, and 106 mg/l.
°I '1'/''
1''I'71' ~P:l ~1 ~1 ~1 ,.'~Is o
o
b
~
~
0tlf -j -f ? o
o
~
~,
0
~
_
~21
~o 30
I 0
I
I 2
!__I
!
I
I
'
I
I
3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rng/L)
I 12 13
FIG. 4. D i s s o l v e d o x y g e n profile in m o d e l p o n d III.
The corresponding removal efflciencies were 62, 73, 57, and 74 per cent, respectively. The longer detention times and dilution provided by Ponds III and V improved the eftlcieney of phenol removal. The control pond exhibited the lowest concentration of total soluble COD in the
464
Ju-CHANG HUANG and EARNEST F. GLOYNA
effluent (210 mg/l) and the highest COD removal (79 per cent). The toxic effects exhibited by 100 mg/1 (dry wt.) phenol in the influent waste stream of Pond II were demonstrated by a higher COD (317 mg/1) in the effluent and a lower COD removal (68 per cent). However, the portion of the effluent COD contributed by Starlac alone
5
Jy 10
~15 bJ
20
25 3O @
I
2
3 4 5 6 ? 8 9 10 II 01SSOLVED OXYGEN (rag/L)
12 13
Fio. 5. Dissolved oxygen profile in model pond IV.
(226 mg/1 )in Pond II was about the same as that in the effluent of the control pond (210 mg/l). The longer detention time provided by Pond III (22.5 days) improved the treatment efficiency (75 per cent) as compared to Pond II. Although the total soluble COD in
0
I
2
3 4 5 6 7 8 9 I0 II DISSOLVED OXYGEN (rag/L)
12 ]3
FIG. 6. Dissolved oxygen profile in model pond V.
the effluent of Pond III was still slightly higher than that of the control. However, the portion of effluent COD contributed by Starlac alone was only 195 mg/1, which was smaller than that in the control. Ponds IV and V provided the same comparison as Ponds II and IIL The amounts of
Effect of Organic Compoundson PhotosyntheticOxygenation--II
465
effluent COD contributed by Staflac in Ponds IV and V were, respectively, 207 mg/l and 190 mg/l. Therefore, similar to Ponds II and III, the presence of 400 mg/l (dry wt.) phenol in the influent did not seem to inhibit the bacterial activity. The efficiencies of removal in Ponds IV and V, were, respectively, 61 and 73 per cent. Dissolved oxygen in the ponds. A dissolved oxygen survey conducted at the end of the experimental effort provided additional information on the operational characteristics, FIGS. 2-6. The dissolved oxygen was monitored at each 5 cm increment of depth near the center of the pond. The measurements were made at 2 hr intervals beginning at 0600 hours and ending at 1800 hours. In the control pond, the dissolved oxygen reached a maximum of 12 mg/1. The levels of dissolved oxygen in Pond II were approximately 0.75 of those in the control unit. These data are comparable to the results of the previously reported test-tube studies which predicted a reduction in the chlorophyll (i.e., a concentration of about 74 per cent of that in the control) for a phenol concentration of 100 mg/l. The phenol content of several grab samples from different locations in Pond II varied from 56 rag/1 to 84 rag/1. Where a longer detention time (22.5 days) was used, the dissolved oxygen in the pond increased to a level which was about 90 per cent of the control unit, FIG. 4. In Pond IV, the maximum dissolved oxygen content was 5 mg/l, which was 41 per cent of that found in the control unit. As a comparison the previous test-tube studies indicated a 33 per cent value when the phenol concentration was 400 mg/l. The phenol concentration in Pond IV ranged from 220 to 320 rag/1. Although the detention in Pond V was three times as much as that provided in Pond IV, the dissolved oxygen in Pond V was only slightly better. The maximum dissolved oxygen measured was only 60 per cent of that in the control unit. The low value of dissolved oxygen in Pond V was attributed to the higher COD in the influent which overloaded the assimilative capacity of the pond. Predominating algae and chlorophyll contents. A microscopic examination of samples taken from each of the five ponds indicated that the predominant algal form was Chlorella. The predominance of Chlorella was partly due to the relatively quiescent conditions. As FOGG (1965) reported, cultures containing more than one species of algae are difficult to maintain in a laboratory, While two or more algal species seem to coexist in equilibrium in a natural water, the same cultures, when brought to the laboratory, will invariably develop into a single culture system. The chlorophyll in the effluents of Ponds I-V, respectively, were 2.4 mg/1, 1.8 rag/l, 2.0 mg/l, 1.2 mg/1, and 1.4 mg/1. The chlorophyll in the effluents of Ponds II-V, as compared to the control unit, were 75, 84, 50, and 59 per cent, respectively. These relative values are comparable to the dissolved oxygen data.
DISCUSSION The assimilative capacities of aerobic and facultative waste stabilization ponds are related to both the algal and bacterial productivity. Toxic compounds present in waste streams may affect the operation of waste stabilization ponds in at least four ways. (a) Compounds may inhibit the photosynthetic processes and hence suppress photosynthetic oxygenation.
466
Ju-C-'nANO HUANG a n d EARNEST F. GLOYNA
(b) Toxic compounds may inhibit bacterial activity, and reduce the rate of biodegradation of organic compounds. Therefore, ponds become less efficient in the treatment of wastes. (c) The biodynamic equilibrium of biological populations in the pond may be upset by the presence of certain toxic compounds. (d) Some industrial wastes are toxic and relatively resistant to biodegradation. These compounds may impose an appreciable COD concentration on the effluents. Consequently, the overall treatment efficiency of the pond is reduced. The studies involving waste stabilization ponds substantiate the predicted decrease in dissolved oxygen as well as reduced COD removals. Consequently, the data as reported in the test-tube study (Part I) can be used to improve existing design equations. For most of the compounds reported herein, the reduction of chlorophyll may be expressed as shown in equation (1). O Fraction of chlorophyll remaining = Qoo= e- ~c
(1)
where
Oo = chlorophyll content if there is no test compound present,
Q K C
= chlorophyll content in the presence of test compound, = chlorophyll inhibition constant of the compound (toxicity), and = concentration of test compound.
If the chlorophyll inhibition constant is known, the fraction of chlorophyll remaining can be calculated. Now if a waste stream contains organic compounds which exhibit inhibitory effects toward chlorophyll and hence on photosynthetic oxygenation, the volume of a pond must be increased accordingly. However, consideration must be given to the fact that part of the toxic material may be subject to fairly rapid biodegradation. Consequently, under complete mixing and continuous flow conditions, the average concentration of a compound in a pond may be expressed as shown in equation (2) (MARAIS, 1966). oo
C° c = (¢-/-Q)
e -kt' e-(Q/v),, dt' = k ( V / Q ) + 1
(2)
t'=O
where = average concentration of the organic compound remaining in the pond, or equal to the concentration present in the effluent, Co = original concentration of the organic compound present in the influent waste stream, V = volume of pond, Q = quantity of influent flow, = time of exposure (i.e., detention), t' = rate constant of biodegradation of the organic compound. k C
Since V/Q is equal to the detention time, t, equation (2) can be rewritten, C =
~
Co
kt+l
(3)
Effectof OrganicCompoundson PhotosyntheticOxygenation--II
467
As shown in equation (3), the reaction time depends upon the biodegradation rate constant and the degree of treatment desired. The rate constant is in turn dependent upon the temperature, equation (4). t
k,
to
k
0(r,-r)
(4)
where to and t = reaction times required (for a given treatment) at rate constants of k° and k, respectively (i.e., bacteriological action), k, and k = rate constants (bacteriological degradation) at temperatures of To and T, respectively, 0 = temperature coefficient for a specific waste. Noteworthy is the fact that values of ko, k, and 0 are dependent upon the biodegradability of the specific waste. The concentrations can be calculated by substituting equation (4) into (3) and developing a chlorophyll compensation factor,
Is koito+lJ KiCo~.1
= e x p ,~1
(5)
(for photosynthetic reoxygenation suppression) where f = chlorophyll compensation factor, Ks = chlorophyll inhibition constant of the ith compound, k,~ = observed rate constant of biodegradation of the th compound. A general design equation can be developed for determining the volume of an industrial waste stabilization pond. A rational approach can be developed on the basis of knowing the quantity of waste flow, reaction time, biodegradation rate constant, biochemical oxygen demand, and chlorophyll compensation factor. It is recommended that the evaluation of the chlorophyll inhibition constant be based on the waste itself. Furthermore, it is suggested that for calculation purposes the original waste be first diluted to a factor of (koto+l), and that the chlorophyll compensation factor be calculated on the basis of the diluted waste. By substituting equation (5) into a previously developed design formula (H~.MANN and GLOYNA, 1958 and GLOYNA, 1966), it is possible to present a complete formulation.
V= 1.54xlO-StoQY[O(r°-r)]expFK(. C° .~1 L \koto+UJ
(6)
where V a Y
= volume of pond (acre-ft) for a single facultative pond, = quantity of influent flow, gal/day (U.S. gallons), = five-day 20°C BOD (if secondary effluent); ultimate influent BOD, mg/l (if settle solids present), = temperature coefficient, depending upon the specific waste, 0 being 1.085 for a number of biodegradable industrial wastes at 35°C,
468
Ju-CHANG HUANG and EARNEST F. GLOYNA
To T
_
to exp -K =
Co
--
ko
~-
observed maximum operation temperature (based on the maximum monthly water temperature), °C, expected minimum operation temperature (based on the minimum monthly water temperature), 'C, reaction time required for a given treatment at To and ko, base of natural logarithm, chlorophyll inhibition constant of the waste, original concentration of the waste, mg/l dry weight (or mg/1 C O D or mg/l BOD, depending on the unit used in the evaluation of the chlorophyll inhibition constant), observed biodegradation rate constant of the waste at To.
Equation (6) can be rewritten as follows: Co
V : CQY[O~aS-r)]expIK(ko~o+l) 1
(7)
V' = ClQY[O~35-r)]exp K\koto+ l/.]
(8)
or
where = 10.7 x 10-s where temperature fluctuations are large and ponds are designed on a depth of 6 ft and Vis in acre-ft (to = 7.0 days at To = 35°C), C 1 = 3.5 x 10 -5 when depth is 1.82 m and pond volume is in m 3. C
It should be noted that where ponds are built in tropical areas, where temperature fluctuations are minimum and where the solid accumulation is no problem, the depth coefficient C and to in (7) and (8) can be reduced by a factor of two. # CONCLUSIONS Studies involving laboratory waste stabilization ponds substantiate the predicted decrease in dissolved oxygen as well as treatment efficiency. The design standards of waste stabilization ponds can be improved by adding a chlorophyll compensation factor to the previously developed design equation. Equations (6)-(8) are examples for the design of a single facultative waste stabilization pond.
Acknowledgements--Thisstudy was made possible by an initiation grant from the College of Engineering, The University of Texas, and a continuation grant from the Water Supply and Pollution Control Division, U.S. Public Health Service and Federal Water Pollution Control Administration (WP-00688-03). REFERENCES FOaG G. E. (1965) Algal Cultures and Phytoplankton Ecology University of Wisconsin Press, Madison and Milwaukee. GtO~A E. F. (1966) Unpublished Reports. H ~ E. R. and GtO~rNAE. F. (1958) Waste stabilization ponds--III. Formulation of design equations. Sewageind. Wastes30, 963-975. HUANOJ. C. and GLOYNAE. F. (1968) Effect of organic compounds on photosynthetic oxygenation --I. Chlorophyll destruction and suppression of photosynthetic oxygen production. Water Research 2, 347-366.
Effect of Organic Compounds on Photosynthetic Oxygenation--II M~s
469
G. v. R. (1966) Operation and performance of waste stabilization ponds. Bull. Wld Hlth Org.
34, 737-763. Standard Methods for the Examination of Water and Waste Water (1965) 12th Edition. Am. Public Health Association, Inc., New York, N.Y. THmUMURTmD. and GLOYNAE. F. 0965) Relative toxicity of organics to Chlorella pyrenoidosa. University of Texas Report No. 11-6503, Austin, Texas.