whence S ( a ) = 1 - x l a 2 / K d for a 5 amaxand S ( a ) = 0 for a > amax,where amaxis the particle cutoff size, amax = ( K d / X 1)1’2.
Acknowledgments We are grateful for the assistance of Bernard Au who performed many of the N p distribution experiments. Todd Cheng performed the gel permeation experiments. Literature Cited (1) Rowe, W. D., Holcomb, W. F., Nucl. Tech., 24, 287 (1974). (2) Nishita, H., Hamilton, M., Steen, A. J., Soil Sei. SOC. Am. J., 42, 51 (1978). (3) Moodie, C. D., Koehler, F. E., “Laboratory Manual for Soil Fertility”, 3rd ed., Washington State University, Pullman, Wash., 1975. (4) Bouyoucos, J., Agron. J., 43,434 (1951). (5) Walkley, A., Soil Sei., 63,251 (1974). (6) Peech, M., Soil Sei., 59,25 (1945). (7) Routson, R. C., USAEC Document, BNWL-1464, March 1973. (8) Relyea, J., Brown, D. A., “Mineral Cycling Symposium”, Augusta,
Ga., 1976, in press. (9) Miner, F. J., Dow Chemical Co., Rocky Flats, Colo., 1975, private communication. (10) Unpublished research. (11) Center, B. M., Ruddy, F. H., Anal. Chem., 48,2135 (1976). (12) Cleveland, J. M., Rees, T. F., Enuiron. Sei. Technol., 10, 802 (1976). (13) Rhodes, D. W., Soil Sci. SOC.Am. Proc., 21,389 (1957). (14) Bondietti, E. A., “Agronomy Abstracts”, American Society of Agronomy, 1976, p 126. (15) Wahl, A. C., Bonner, N. A,, “Radioactivity Applied to Chemistry”, Wiley, New York, 1951, p 142. (16) Cunningham, E., Proc. R. Soc. London, Ser. A, 83,357 (1910). (17) Kononova, M. M., “Soil Organic Matter”, Pergamon Press, Headinton Hill, Oxford, 1966, p 103. (18) Myer, G. L., in “Transuranium Nuclides in the Environment”, Publication SM-199/105, International Atomic Energy Agency, Vienna, 1976, p 231. (19) Means, J. L., Crear, D. A,, Science, 200,1477 (1978).
Received for review October 17, 1977. Accepted January 11, 1979. This research was supported b y Department of Energy Grant No. EY-76-S-06-2221,Task 12, Modification 2.
Control of Fouling Organisms in Estuarine Cooling Water Systems by Chlorine and Bromine Chloride Dennis T. Burton” and Stuart L. Margrey Academy of Natural Sciences of Philadelphia, Benedict Estuarine Research Laboratory, Benedict, Md. 20612
T h e relative antifouling effectiveness of chlorine and bromine chloride under intermittent and continuous modes of application in low velocity flow areas was evaluated at an estuarine power plant located on the Chesapeake Bay. No significant difference in the control of fouling organisms was found on the average between similar concentrations of chlorine and bromine chloride. Significant differences in fouling were found between intermittent and continuous halogenation on both clean and prefouled surfaces. Continuous halogenation was more effective over an entire fouling season in controlling primary, secondary, and adventitious fouling communities than intermittent halogenation for periods u p to 2 h per day. Continuous halogenation a t 0.3 mg/L total residual halogen was more effective than 0.1 mg/L total residual halogen during late spring and summer; no difference was found between the two concentrations during the early fall.
Several alternatives to chlorination for control of biological fouling in once-through cooling systems have recently been proposed (1, 2 ) t o satisfy compliance standards set forth in EPA’s Effluent Guidelines and Standards for Steam Electric Generating Source Categories ( 3 ) .Wackenhuth and Levine ( 4 ) and Bongers et al. ( 5 )demonstrated that bromine chloride could be used as an alternative to chlorine in controlling condenser biofouling a t two separate plants. T h e present study was initiated to evaluate the antifouling effectiveness of chlorine and bromine chloride in low velocity flow areas where estuarine waters are used for cooling purposes. T h e objectives of the study were: (a) t o test various intermittent and continuous chlorination and bromochlorination schemes for antifouling control in once-through cooling systems; (b) to determine optimal schemes for control of different fouling communities which occur over a fouling season; and (c) to test the 2-h discharge limitations of EPA’s Effluent Guidelines and Standards for Steam Electric Power Gener684
Environmental Science & Technology
ating Source Categories ( 3 ) .A preliminary report on a portion of the study has been given by Burton (6).
Materials and Methods Test Conditions. Three 20-day antifouling studies were conducted during the 1976 fouling season a t Baltimore Gas and Electric Company’s Calvert Cliffs Nuclear Power Plant (Calvert Cliffs) located on Chesapeake Bay. Calvert County, Md. T h e studies were conducted in late spring, summer, and early fall to determine optimal schemes for control of different fouling communities which occur over the fouling season. Chlorine and bromine chloride were tested simultaneously under the following conditions: (a) 0.2 mg/L total residual halogen ( T R H ) applied for 15 min every 3 h (average concentration and application duration allowed by EPA); (b) 0.5 mg/L T R H applied for 15 min every 3 h (maximum concentration and application duration allowed by EPA); (c) 0.1 mg/L T R H applied continuously; and (d) 0.3 mg/L applied continuously. T h e antifouling effectiveness of each halogenation scheme was determined by comparing weight change on fouling substrates (115 cm2; 18 in.2) exposed for identical time periods. Total dry weight, organic weight, and inorganic weight were used as measurements of fouling. The experimental apparatus used during the study has been described in detail by Margrey e t al. ( 7 ) . Briefly, the fouling substrates exposed to each test condition were housed in separate troughs which were supplied continuously with 19 (1k0.5) L/min ( 5 gal/min) of unfiltered Bay water a t a flow velocity of approximately 0.3 m/s (1 fth) past t h e fouling substrates. Stock solutions of halogenated water (approximately 40 mg/L T R H ) were continuously made from filtered Bay water in stock head boxes, metered from the boxes a t specific volumes for each experimental concentration and mixed with Bay water before entering each experiniental trough. Timer activated solenoids were used to control the stock solutions entering the fouling troughs receiving intermittent doses.
0013-936X~79/0913-0684$01.00/0@ 1979 American Chemical Society
Table 1. Basic Water Quality of Diluent Water during Biofouling Studiesa parameter
N
temp, O C salinity, ppt dissolved 02, mg/L ammonia N, mg/L
35 35 35
PH CI demand, mg/L
31 35
35
May 3-23. 1976 mean (f-SD)
20.6(k1.52) 7.5(k0.92) 7.6(k1.26) 0.2(kO.10) 7.5(h0.96) 1.3(k0.72)
N
Aug 16-Sepl 5, 1976 mean (f-SD)
36 36 36 36 36 36
a Basic water quality parameters determined by precedures in Standard Methods (8). dark.
T h e chlorine stock solution was made from high purity grade chlorine gas via a venturi activated ejector system. T h e bromine chloride stock solution was made from research grade bromine chloride which was vaporized in a gas evaporator and then mixed with diluent water via a n ejector system. Experimental Procedures. Both clean and prefouled substrates were used to evaluate the antifouling effectiveness of intermittent and continuous halogenation. Sixteen clean fouling substrates were placed in each trough and divided into four serial replicate partitions composed of four substrates per partition tc achieve a balanced block design for proper statistical sampling. One fouling substrate was removed from each partition every 5 days during the 20-day test period. As the fouling substrates were removed every 5 days, clean substrates were placed in their position to eliminate changes in flow patterns around the remaining elements. Four prefouled substrates were placed in each trough a t t h e discharge end. T h e prefouled Substrates were exposed to unfiltered water under t h e same flow conditions described above for 25 days prior to the start of each 20-day study. All prefouled substrates were removed on day 20. Total residual chlorine and bromine chloride concentrations were measured in each fouling trough every 12 h throughout all the studies by the amperometric titration (Fisher and Porter amperometric titrator, Model No. liT1010, Fisher and Porter Co., Warminster, Pa.) procedure (409C) described in Standard Methods ( 8 ) .Total residual bromine chloride was measured as equivalent chlorine and is reported as equivalent chlorine throughout this report. Chlorine demand of the diluent water was determined every 12 h by the above method using a contact time of 5 min in the dark. Other physical and chemical parameters monitored every 12 h included flow rates, temperature, salinity, dissolved oxygen, pH, and ammonia N. All physical and chemical data (with the exception of flow rates) for each study are summarized in Table I. Total dry weight of the fouling material was determined by drying t h e material from each substrate for 24 h a t 90 "C; organic and inorganic weights were determined by ashing for 2 h at 500 to 550 "C. Statistical Analyses. Each 20-day study (excluding the prefoul study data) was analyzed statistically as a three-factor analysis of variance (ANOVA) which included: (a) halogen and reference concentrations, ( b ) replicates nested within each concentration, and (c) days of fouling exposure. Significant ( P < 0.01) day by concentration interactions were found in all studies for the log transformed total, organic, and inorganic data. Scheffes' test (9)and Tukey's multiple range test procedures ( 1 0 ) were used to determine several day by concentration interaction hypotheses which were performed at t h e 1%significance level. T h e prefoul study data were log transformed and analyzed statistically by one-way fixed ANOVA with concentration being the factor considered. Significant ( P < 0.01) concentration interactions were found in both t h e first and third studies. T h e concentration interaction hypotheses were tested
N
24.5(f0.54) 8.5 (f1.30) 7.5(f1.20) 0.2(fO.11) 7.7(f0.37) 2.1( f 0 . 5 0 )
Oct 4-24. 1976 mean (f-SD)
37 37 37 31 37 34
18.7(k2.14) 5.2 (k0.68) 7.3(k1.76) 0.2(fO.11) 7.5(f0.31) 1.6(h0.31)
Chlorine demand was determined by using a 5-min contact time in the
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20
Figure 1. Antifouling effectiveness of intermittent and continuous chlorination (total residual Clp) during the first study May 3-23,1976. Legend: means of reference test total dry weight data ( 0 ) 0.2 ; mg/L applied 15 min every 3 h (A); 0.5 mg/L applied 15 min every 3 h (0); 0.1 mg/L applied continuously (0);and 0.3 mg/L applied continuously (0).See text for details
by Scheffes' (9) and Tukey's (10) test a t the 1%significance level. No prefoul data were available for analysis in the second study because of a power failure which stopped the water flow a t the end of the prefouling period and consequently aborted t h e prefouled substrate portion of the study. T h e third bromine chloride study was lost because the secondary regulator on t h e gas system failed on day 11 of the study.
Results Significant differences in t h e control of estuarine fouling organisms were found between intermittent and continuous halogenation on both the clean (see Figures 1-6) and prefouled (see Table 11) substrates. Greater fouling occurred on all substrates exposed to intermittent concentrations relative t o continuous halogenation. Both application schemes reduced fouling relative to the references. No significant difference in fouling control was found on the average between similar concentrations of chlorine and bromine chloride. Differences between total, organic, and inorganic weights on a particular day of a study were similar in most cases. T h e organic portion of t h e total weight composition was approximately 20 to 25; t h e inorganic fraction was approximately 7 5 to 80%. Curves for t h e organic and inorganic weight changes were not included in Figures 1-6 because the shapes of the curves for both halogens were similar to the total dry weight curves. Discussion Predominant Components of Fouling Communities. T h e differences in antifouling effectiveness between interVolume 13,Number 6,June 1979 685
Table II. Mean Total Dry Weight, Organic Weight, and Inorganic Weight of the Prefoul Substrate Studies Conducted from May 3 to 23, 1976 and October 4 to 24, 1976 test concn, mg/L TRH, a and duratlon 01 application
May study ow wt, mg
total wt I mg
227.28
O.OOb
43.31 no datad 294.53 207.33 85.75 31.47 251.54 248.43 69.12 53.83 510.10 no datad
O.OOb
1714.10 1233.65 634.86 228.28 1409.84 1203.89 450.22 397.97 2965.60
0.20 Ci2, 15 min every 3 h 0.50 C12, 15 min every 3 h 0.10 Cl2, continuous 0.30 GI2, continuous 0.20 BrCI, 15 min every 3 h 0.50 BrCI. 15 min every 3 h 0.10 BrCI, continuous 0.30 BrCI, continuous 0.00 = 0.ooc
October study total
lnorg wt, mg
183.97 1419.57 1026.32 549.1 1 196.81 1158.30 955.46 381.10 344.14 2455.50
inorg
273.92 261.85 424.38 470.36 294.32 213.26
59.51 60.62 94.56 99.94 47.77 35.77
214.41 201.23 329.82 370.42 246.55 177.49
442.59 640.68
no data e no data e no data e no data e 117.81 149.11
324.78 491.57
a Bromine chloride expressed as equivalent chlorine. Prestudy references; substrates prefouled for 25 days and then processed at day 0 of the regular 20-day study. Study references: substrates prefouled for 25 days and then exposed for 20 days to the test conditions (45 days total fouling). Replicates were not run during the first study. e Secondary regulator on bromine chloride gas system failed on day 11; days 15 and 20 bromine chloride data were lost.
1
q I500
c
i
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15001 I
E
i
I
I P
0
t-
/
300M Oo
5
15
10
TIME
20
(Days)
TIME
(Days)
Figure 2. Antifouling effectiveness of intermittent and continuous bromochiorination (total residual BrCl as equivalent CI2)during the first study May 3-23, 1976. Legend: means of reference test total dry weight data ( 0 ) 0.2 ; mg/L applied 15 min every 3 h (A);0.5 mg/L applied 15 min every 3 h (0); 0.1 mg/L applied continuously (0); and 0.3 mg/L applied continuously (0).See text for details
Figure 3. Antifouling effectiveness of intermittent and continuous chlorination (total residual CI2)during the second study Aug 16 to Sept 5, 1976. Legend: means of reference test total dry weight data ( 0 )0.2 ; mg/L applied 15 min every 3 h ( A ) ;0.5 mg/L applied 15 min every 3 h (0);0.1 mg/L applied continuously (0); and 0.3 mg/L applied continuously (0).See text for details
mittent and continuous modes of application in low velocity flow fields may possibly be explained by changes in biotic succession on surfaces exposed to estuarine fouling. Although the exact mechanisms of biofouling on clean surfaces are not completely understood, it is known t h a t substrates exposed t o estuarine waters are initially covered by slime-forming microorganisms such as bacteria and protozoa ( 1I , 12).This tightly adherent deposit has the ability to t r a p inorganic particulate matter which builds into the original slime layer and subsequently serves as an attachment layer for higher organisms (13, 1 4 ) . Primary fouling organisms, such as barnacles, bryozoans, and hydroids, follow almost immediately after t h e development of the slime film ( 1 3 ) .These are later joined by secondary fouling organisms, such as anemones, ascidians, and mussels. T h e primary foulers appear to alter the conditions of the surface (as do the slime-forming microorganisms), so t h a t it is more suitable for t h e settlement of t h e secondary foulers (15).T h e primary and, to a gieater extent, the secon-
dary foulers reduce the free flow of water over t h e surface, which in turn may result in large accumulations of sediment on substrates located in water with high turbidity. Adventitious organisms, such as ostracods, amphipods, and worms, follow the secondary invaders. Approximately 75% of t h e total fouling material t h a t accumulated on the fouling substrates in this study was found t o be nonbiological. T h e large inorganic portion of fouling material is, without question, a function of t h e processes described above; however, it is also the result of certain forms of scaling and nonbiological fouling (16, 17). Water-formed scaling, which is the crystalline growth of insoluble salts and/or oxides, may occur as well as scaling from the oxidation of soluble ions and compounds in water by strong oxidizing agents (such as chlorine and bromine chloride), which form insoluble precipitates (18).Nonbiological fouling may include loose, porous, or gelatinous accumulations of insoluble salts, hydrous oxides, and extraneous materials such as sediment, vegetative materials, and debris ( 17 ) .
686
Environmental Science & Technology
1800
m
r
1800
I5O0l
1500
+
1200
-
z - 1200. C
-
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I
/
I
I
2
s
900
> n
$
600
F
0
+ 300
0
3
5
IO
TIME
I5
0
20
0
5
(Days)
Figure 4. Antifouling effectiveness of intermittent and continuous bromochlorination (total residual BrCl as equivalent CI2) during the second study Aug 1 6 to Sept 5, 1976. Legend: means of reference test total dry weight data ( 0 ) 0.2 ; mg/L applied 15 rnin every 3 h (A);0.5 mg/L applied 15 rnin every 3 h (0);0.1 mg/L applied continuously ( 0 ) ; and 0.3 mg/L applied continuously (0).See text for details
E f f e c t s of H a l o g e n a t i o n o n the S t u d y of F o u l i n g Communities. An initial deposition of fouling material occurred on all substrates by day 5 in this study. No significant difference in fouling was found between the intermittent and continuous modes of application during t h e early phases of the first and third study. This may be attributed to the fouling community present on the substrates a t t h a t time. T h e predominant community was probably composed of t h e slimeforming organisms and/or immature primary foulers, which are more susceptible to intermittent halogenation than more mature primary and secondary organisms. I t has been shown t h a t intermittent chlorination will control slime film development, whereas low level continuous chlorination is more effective in coni rolling primary and secondary fouling communities (18, 151). T h e difference between initial fouling control during t h e first and third study compared to the second study which had significantly higher initial fouling under intermittent halogenation than under continuous halogenation may be the result of higher ambient temperatures during August and early September. Higher temperatures would stimulate slime film development, which in turn would induce primary fouling organisms to attach and grow more rapidly than those a t lower temperatures. Fouling generally increased on the reference substrates and those exposed to intermittent halogenation between 5 and 10 days. This was probably due t o the succession of biota from slime forming organisms to primary, secondary, and adventitious organisnis, which are not controlled as effectively by intermittent halogenation as by continuous halogenation. Significant increases in fouling occurred by day 20 on some of the substrates exposed to 0.1 m g L continuous halogenation in the first and second studies; none occurred in t h e third study. Continu'ous halogenation a t 0.3 mg/L inhibited all fouling from day 5 forward in t h e first and third study; however, significant increases occurred by day 20 in t h e second study. These differences in fouling control by continuous low level halogenation are most likely related to t h e biocide tolerance of different organisms within the fouling communities which change over t h e fouling season from early May to October. T h e predominant component of t h e macroinvertebrate fouling community a t Calvert Cliffs during the first study was t h e barnacle B
