Chesapeake Science Vol 12, No. 4, p. 231--239
December, 1971
An Experimental Depuration Plant: Operation and Evaluation1 BOB E. HUNTLEY RICHARD J. HAMMERSTROA4 Gulf Coast Water Hygiene Laboratory ~ Office of Water Quality Division of Water Hygiene Environmental Protection Agency Dauphin Island, Alabama 36528 ABSTRACT: The operation of a prototype (24-bushel capacity) deputation plant for the bacteriological cleansing of oysters was evaluated under prevailing Gulf Coast environmental conditions. Results indicated that with proper plant location and basic engineering design of the system, commercial deputation of shellfish is a feasible method for purifying oysters harvested from restricted waters. Eight trials were conducted over a 15-month period to cover seasonal changes. The depuration tank design permitted three pallets, each holding 16 baskets of one-half bushel capacity, to be stacked in the tank. A fecal coliform MPN of 130 or less/100 g for depurated oysters was established as the maximum level of acceptability for a 72 hour period of deputation. Physical parameters of the sea water which were measured included salinity, temperature, turbidity, pH, and dissolved oxygen. Determinations of the percent wet/dry weight and percent glycogen of depurated oyster meats revealed no adverse effect on quality. Introduction
Since 1925 the U.S. Public Health Service has worked in cooperation with the States and the shellfish industry to assure that raw and frozen shellfish shipped in interstate commerce are safe for human consumption. This cooperative program has operated during more than 40 years with reasonable success in maintaining consumer confidence in shellfish as a food product. However, sanitary control of the growing areas is becoming increasingly difficult. The populations of cities and coastal areas have become vastly larger. Many sewage treatment plants and disposal facilities have been constructed in the coastal regions and recreational uses of estuarine waters have increased tremendously. These factors of population change and economic growth pose a serious threat to shellfish growing areas, and many of these areas have been permanently or intermittently closed to shellfish harvesting.
Depuration of shellfish, while not a new concept, is one method being advanced as an additional step in safeguarding the public's health. Depuration is not a substitute for pollution control. It would, however, allow most of the coastal waters to remain as shellfish harvesting areas and would provide for the continuing utilization of a renewable natural food resource. This paper describes the operation o f a prototype 24-bushel capacity tank for use in depurating the eastern oyster, Crassostrea virginica. The term depuration as used here refers only to the elimination of bacteria. No studies were included to determine th~ presence of viruses or initial content in the oyster o f any trace metals or other toxic materials. The prototype depuration plant is housed in the Gulf Coast Water Hygiene Laboratory which is located on Dauphin Island, Alabama.
Materials and Methods 1Contribution No. 72 from Gulf Coast Water In the planning stage, ten operational test Hygiene Laboratory. 2 Formerly named the Gulf Coast Marine Health trials of the pilot plant were programmed to Sciences Laboratory during the period of this study, cover the normal seasonal changes which would 231
232
B. H. Huntley and R, J. Hammerstrom
be encountered by a commercial plant. Also, a "specific" function description and procedure were prepared to cover each phase of the operation, i.e., handling of sheltstock, sampling schedule, and cleanup. However, with an effort to keep the operation within a practical range, certain procedures strictly enforced during the initial trials were relaxed or altered if proven needlessly restrictive. The operational limits of the environmental factors initially set forth to govern the operation were at no times breached during the course of the study. The seawater flow system into the deputation tank was originally designed so that the ultraviolet irradiated seawater flowed from the UV unit into the tank behind a baffle. The seawater falling to the tank bottom, theoretically was distributed across the bottom, rising to the top and again falling over a baffle to the discharge or effluent port. Two trials, numbers 1 and 2, were completed with this design. The bacteriological results indicated that "dead spots" or "stagnant" pockets developed, making it necessary to modify the flow system. The description of the tank which follows is that of the vertical type flow system resulting from this modification. This modified tank was used to complete the remaining six test trials in the study (Fig. 1). SEAWATER SUPPLY. The incoming seawater was pumped from Dauphin Island Bay into the "wet" laboratory through a system designed to eliminate any contact with metal. The incoming seawater was aerated by the turbulence in and subsequent fall from the constant head tank into the UV unit. ULTRAVIOLET SEAWATER TREATMENT UNIT. A Kelly-Purdy ultraviolet (UV) treatment unit was used in the pilot
depuration plant to disinfect the incoming seawater (Fig. 2). The design of the UV treatment unit limited the usable flow of seawater in the depuration plant to 144 liter: per minute. The unit had been previously tested extensively for its effectiveness in the disinfection of contaminated seawater (Hill, el aL, 1967; Kelly, 1961). The unit was situated approximately two feet above and to the side of the tank. Prior to a test trial, each UV lam F within the unit was metered with a UV intensity meter to determine the output Readings were taken at lamp center and approximately 6 - 8 inches at both sides of the center and the three readings were averaged tc determine the ultraviolet output. Any lamp which did not emit 60% or more of the original rated output was replaced. DEPURATION TANK, OYSTER BASKETS AND PALLETS. The depuration tank wa,, constructed of marine plywood and Douglas fir. The dimensions of the tank were 4'5" H, 10'6" L, and 4'7" W. The bottom of the tank was constructed to slope toward a butterfly valve thus providing a fast drain system which shortened "down time" during each cleanup period and facilitated a more complete removal of oyster feces, sediment, and silt. The interior was painted with an epoxy base paint. A schematic drawing shows the bottom slope and seawater outlet of the depuration tank (Fig. 3). Dye studies were conducted to determine the flow pattern within the tank. The oyster baskets were constructed entirely
~) uv RADIATION CHAWBER (~) LNFLUENT (~) EFFLUENT
7-
Fig. 1. Vertical type flow depuration tank system. Direction of seawater flow is indicated by arrows.
Fig. 2. Ketly-Purdy UV seawater treatment unit. UV bulbs are shown in the top section and the baffles are shown in the b o t t o m section. Direction of flow is from right to left.
An Experimental Depuration Plant
233
Prior to a test trial, the pallets and baskets were placed in the tank which was filled with fresh water containing twenty-five ppm chlorine. The UV unit and pipes leading to the tank were also filled with the chlorine solution. After a 30-minute contact period, all components were flushed with fresh water to remove any detectable concentration of SCHEMATIC OF DEPURATION TANK SHOWING chlorine since any residual chlorine in the BOTTOM SLOPES AND PIPING system would adversely affect oyster pumping (NO SCALE) activity (Kelly et aL, 1960). Initially, this LATERAL SLOPE = 8 . 7 5 ~ chlorination and flushing procedure was L ONGIT UDPNAL ~LOPE=2 75 ~ followed at the end of each 24 hour depuration SEAWATER INLET I ,o'6" ~r i 4'r' period. During subsequent trials, we determined that the initial chlorination period was sufficient to "sterilize" the component parts of the depuration system if at the end of each 24 hour period the component parts of the system were pressure hosed to remove fouling debris, Fig. 3. Schematic of depuration tank showing the UV treatment unit was scrubbed free of accumulated silt, and the UV bulbs and bottom slope and seawater inlet and outlet.
of fiber glass, each having a capacity of approximately one-half bushel of oysters. The pallets, framed of 2 • 6's, were also painted with epoxy paint and each held two rows of eight baskets. A hoist was mounted over the tank for handling the pallets (Fig. 4).
Fig. 4. Depuration tank and component systems-oyster baskets, pallets and UV seawater treatment unit.
234
B. H. Huntley and R. J. Hammerstrom
reflectors were wiped free of encrusting salt. These steps were important to a successful operation. SHELLSTOCK. The polluted shellstock used in the evaluation study were obtained from growing areas closed to commercial harvesting. The oysters were taken with a small dredge during the low tide cycle. After the oysters were harvested, they were hosed, culled and placed in wet burlap bags for transport to the laboratory. Prior to loading the tank, the oysters were hosed and culled again, and transferred into the baskets for placement on the pallets. During the first five trials, polluted shellstock were placed on one side of the tank only. The remainder of the baskets contained "filler" shellstock purchased from a commercial source. The last three trials (numbers 6, 7, and 8) were conducted with a full 24 bushel loading of polluted oysters. DEPURATION. The first 24 hour period began when the oysters were covered with seawater. At the end of each 24 hour depuration period, water samples were collected for bacteriological assay. The depuration process was then temporarily interrupted for draining of the tank, the collection of oyster samples for bacteriological examination, and the cleanup procedure. After each pallet was hoisted from the tank, the oysters, baskets, and pallets were hosed with fresh water to remove marine silt. The tank was hosed free of debris and marine sediment, the seawater feed and drain pipes were flushed free of silt, and the reflectors and bulbs were wiped free of salt encrustations and rinsed with fresh water. During the cleanup period, the oysters were culled to remove obviously dead animals ("gapers"). In our pilot plant, four men could accomplish the culling and the cleanup procedure in approximately 30 minutes. Depuration time for the second and third 24-hour periods began when the oysters were again covered with seawater. SAMPLE COLLECTION AND ASSAY. Seawater samples were taken at the influent end of the tank, and hydrometers were used to measure salinity. A minimum salinity of 10 o/oo was the lowest limit established for plant o p erations. Seawater temperature was monitored at the influent and effluent ends of the depuration tank by constant recording
instruments. The temperature range for optimal Gulf Coast oyster activity is 15-28 C (Galtsoff, 1964a). The temperature limits for the deputation plant trials were set at not less than 12 C or more than 31 C. Seawater samples for determination of pH were collected at the influent end, center, and effluent end of the depuration tank. Turbidity measurements were made of the incoming seawater. The possible adverse effect of high turbidities on ultraviolet disinfection of seawater is well documented (Furfari, 1966; Phillips and Hanel, 1960). A Spectronic 20 Colorimeter was used to obtain readings on the seawater, and the results were expressed in Jackson Turbidity Units (JTU). Seawater samples were collected from the influent end, midcenter, bottom, and the effluent of the depuration tank for determinations of dissolved oxygen (DO) using the Alsterberg modification of the Winkler method (Alsterberg, 1960). Two measurements were taken to observe possible changes in oyster quality due to the artificial plant environment. Random samples were taken prior to 0 hour of the shellstock (filler and polluted) to determine base line percent wet/dry weight and percent glycogen of the oyster meats. Additional random samples of shellstock were also collected at the end of each 24 hour depuration period for determinations of these parameters. For each trial, samples were collected of the raw seawater, the UV treated seawater, and the seawater at the influent and effluent ends of the depuration tank at 0 hour and at the beginning of each subsequent 24 hour depuration period. A 0 hour oyster sample, consisting of a composite of 24 polluted oysters taken at random from the shellstock, was assayed to determine the initial level of coliform and fecal coliform organisms. Additional oyster samples consisting of 12 animals were collected from each single or set of numbered test baskets at the end of each 24 hour depuration period for bacteriological assay. The numbered test baskets were designated by location within the tank to provide for representative samples of oysters for bacteriological examination (Fig. 5). A composite sample of the "filler" shellstock, when used, was collected for bacteriological assay at the end of each 24 hour depuration
An Experimental Depuration Plant
period. The bacteriological examinations of the seawater and oyster samples were conducted in accord with APHA "Recommended Procedures for the Bacteriological Examination of Sea Water and Shellfish" (Third Edition, 1962).
Fig. 5. Schematic of operational layout of the depuration tank system. Numbers indicate designations and locations of baskets to provide for representative oyster samples for bacteriological assay.
235
Results and Discussion E N V I R O N M E N T A L FACTORS. The data compiled from the environmental factors during the eight trials were within the operational limits set in the preliminary planning of the pilot depuration plant study (Table 1), During the eight trials, the salinity of the seawater ranged from 10.8 to 28 o/oo and the temperature ranged from 18.0 to 31.0 C. Temperature changes can and do occur as quickly as changes in salinity and can cause critical levels in the oxygen content of the seawater. The pH ranged from a low o f 7.60 to a m a x i m u m of 8.05, turbidity ranged from 6 to
TABLE 1. Data on environmental factors. Dissolved oxygen ppm
Turbidity JTU Trial no.
Timehours
Salinity o/oo
Temperature C Inf/Eff
1
0 24 48 72 0 24 48 72 0 24 48 72 0 24 48 72 0 24 48 72 0 24 48 72 0 24 48 72 0 24 48 72
18.0 20.1 21.2 19.3 21.0 22.2 22.5 20.6 23.5 22.1 21.3 21.8 27.0 21.0 16.7 10.8 17.9 19.0 17.5 19.0 24.8 24.4 24.1 24.7 18.3 19.4 19.7 18.6 28.0 26.9 26.4 -
30.0 '29.5 28.9 '29.0 30.0 '30.0 29.2 '29.3 24.9 '24.5 29.4 '28.0 26.8 '25.5 18.8 '18.8 24.0 '18.0 18.5 '18.5 23.1 ~19.6 25.7 '16.0 22.7 23.2 23.7 26.6 29.0 29.0 29.0 27.3 27.9 29.9 30.5 31.0 25.1 24.6 23.9 24.1 18.5 18.4 18.4 -
2
3
4
5
6
7
8
Inf.
Mid.
Eft.
Inf.
Mid.
Eft.
36 8 16 12 36 18 18 24 54 32 36 24 *
47 8 12 10 41 8 14 14 56 31 31 21
47 6 10 8 49 14 14 18 54 51 29 21
5.6 5.0 5.3 6.2 6.5 5.3 6.4 7.5 6.8 6~7 6.5 7.8 4.3
5.6 5.4 5.4 6.2 5.2 3.4 5.9 7.6 7.1 6.8 6.4 7,4 3.6
4.3 3.6 4.0 4.6 5.7 3.8 5.4 7.9 6.8 6.7 5.8 7.2 2.8
5.7 2.8 4.6 4.1 4.8 4.6 5.2 3.8 4.9 4.9 4.3 3.4 4.8 6.4 6.7 5.3 6.7
4.5 5.0 4.3 4.7 4.3 5.6 4.8 3.6 4.1 4.3 4.5 3.4 3.4 4.7 5.8 5.9 6.6
5.0 3.4 4,6 4.3 4.6 5.2 5.7 3.7 3.9 4.0 5.0 3.3 3.4 4.7 6.0 6.5 6.5
22 30 56
47 41 39
41 38 35
* The omission of data is the result of temporary failure in the recording equipment.
236
B. H. Huntley and R. J. Hammerstrom
56 JTUs, and dissolved oxygen content ranged 72 hours of deputation. Considering glycogen from 2.8 to 7.9 ppm. The flow rate of 144 as a measure of oyster quality, the data liters/rain was sufficient to maintain the oxygen indicated that depuration did not alter the level in the water above the critical level of 2.5 quality of oyster meats. ppm. According to Galtsoff (1964b), the oyster The culling of the oysters in each basket will stop pumping below this level. F!.ow rate is during cleanup procedures was originally one of the environmental factors which will intended to determine if the artificial require careful attention in a commercial environment had an adverse effect on the depuration plant located along the Gulf Coast oysters. Recorded results of the "gapers" at to insure the oysters an adequate oxygen each 24 hour period during trials 3 - 8 gave evidence that the mortality rate of the oysters supply. Table 2 presents data on the condition index did not approach 1.0%. From these data, we of the oysters based on percent wet/dry weight assume that the environmental conditions and percent glycogen content of the oyster within our tank were not adverse to the survival meats. Percent wet/dry weight was not altered of the oysters. BACTERIOLOGICAL QUALITY OF to any significant extent. This implies that AND OYSTERS. The deputation did not affect the oyster as regards S E A W A T E R weight. The glycogen content of the oysters in bacteriological quality of the raw seawater for each trial was greater to some extent after 48 to coliform and fecal coliform organisms is presented in Table 3. The raw seawater was effectively purified to an acceptable quality in nearly all trials. Exceptions are noted in trial TABLE 2. Data on condition indices of oysters. number two at the 72 hour period and trial number four in which elevated levels of % Wet/Dry coliform organisms were detected in all periods Trial No. Time-hours weight % Glycogen except at 72 hours. We have no explanation of this elevated coliform MPN in trial number 2. 1 0 12.7 2.5 24 14.2 9.1 During the 4 days when trial number 2 was 48 15.5 9.3 conducted, winds from 14 to 25 mph prevailed 72 14.8 6.3 with showers, and tornado warnings were issued 2 0 12.5 11.0 for the area. We were unable to monitor 24 13.4 9.5 turbidity during this trial, and the possibility 48 12.9 7.5 72 12.9 12.0 exists that due to silt caused by wind agitation 3 0 15.0 21.0 of the seawater in the bay, the turbidity was 24 17.0 27.0 above the effective range of the UV seawater 48 17.0 23.0 treatment unit. 72 16.0 23.0 The bacteriological data on the oysters art 4 0 16.6 25.0 24 21.6 33.0 shown in Table 4. Only those data which were 48 19.6 33.0 concerned with the confirmed fecal coliform 72 16.7 38.0 (EC positive) results on depurated oysters are 5 0 15.8 38.0 presented. The data were obtained from 24 17.6 26.0 48 17.2 33.0 analyses of the oyster samples taken from the 72 16.9 40.0 pilot depuration plant under the conditions 6 0 17.0 11.0 existing during each trial. The cutoff point for 24 19.0 23.0 depurated oysters was arbitrarily set as a fecal 48 16.0 20.0 coliform MPN of (equal to or less than) 72 17.0 21.0 7 0 11.9 7.0 130/100 g oyster meats for each single or set of 24 13.6 13.0 numbered test baskets within the tank. The 48 13.1 13.0 initial level of bacterial pollution (EC 72 13.0 20.0 positive-MPN) at 0 hour is shown under the 8 0 14.5 8.0 24 15.3 20.0 column heading "Composite of SheUstock" in 48 13.6 14.0 Table 4. As can be observed in trial number 5 72 (0 hour MPN of 49,000/100 g), at the end of
An Experimental Depuration Plant
48 hours of depuration, three baskets (Nos. 1, 3, and 7) were above the MPN limit for depurated oysters and at 72 hours all baskets were within an acceptable level. By contrast, trial number 3, with an initial fecal coliform MPN of 1,700/100 g, had one basket (No. 2) which was below the cutoff MPN at 48 hours but was above an acceptable level at 72 hours. Rapid elimination of the bacteria by the oyster is demonstrated in trial number 8. With an initial fecal coliform MPN of 1,100/100 g at 0 hour, all baskets, with one exception (No. 8) were below the cutoff MPN at the end of 24 hours o f depuration. Comparing trial number 8 with trial number 6, the initial MPN o f the latter trial was 790/100 g and yet the feeding activity of the oysters was not sufficient, in most cases, to rid the animals of the bacteria to an acceptable level in less than 48 hours.
237
It is very difficult to account for such variation. However, it is conceivable that one oyster with a relatively high bacterial load in a pool o f 12 animals could result in an elevated count for the total sample. There is little doubt that continued progress in the study of depuration will provide for predictability well within acceptable confidence limits for large scale commercial operations. There is, however, a need for further scientific and technical inquiry. More engineering studies are desirable to determine the best possible design of the tank and seawater feed systems. These studies should also be concerned n o t only with the most feasible methods o f loading and unloading the tank, but should also inquire into the "stacking" of oysters in the depuration tank. The use o f heat exchangers for temperature control and the storage o f the
TABLE 3. Bacteriological data on seawater coliform and fecal coliform MPN/100 ml. Time-Hours Trial No. 1
2
3
4
5
6
7
8
Sea Water Treat.
0
24
48
72
Colif.
F.C.
Colif.
F.C.
Colif.
F.C.
Colif.
F.C.
Raw UV Inf. Eff. Raw UV Inf. Eft. Raw UV Inf. Eft. Raw UV Inf. Eff. Raw UV. Inf. Eft. Raw UV Inf. Eft. Raw UV. Inf. Eft. Raw UV Inf. Eff.
17 <1.8 4 <1.8 11 <1.8 <1.8 >16,000 4.5 <1.8 >16,000 2,000 49 2.0 1,100 790 23 <1.8 920 920 4.5 <1.8 4.5 2,300 17 <1.8 110 350 23 <1.8 3,500 2,800
2.0 <1.8 <1.8 <1.8 <1.8 <1.8 <1,8 >1,600 <1.8 <1.8 1,600 1,700 4.5 <1.8 27 17 23 <1.8 79 130 4.5 <1.8 230 9.3 <1.8 110 17 13 <1.8 17 33
4.5 <1.8 <1,8 13 45 <1.8 <1.8 540 17 <1.8 130 350 170 2,0 1.8 170 27 <1.8 33 18 4.0 <1,8 170 130 230 <1,8 33 33 13 <1.8 49 330
<1.8 <1.8 <1.8 <1.8 9.3 <1.8 <1.8 33 7.8 <1.8 49 220 7.8 <1.8 <1.8 7.8 4.0 <1.8 4.5 <1.8 <1.8 <1.8 4.0 7.8 <1.8 <1.8 6.8 130 4.5 <1.8 <1.8 2.0
7.4 <1.8 5.9 <1,8 4.5 <1.8 <1.8 84 32 <1.8 7.8 33 79 2.0 49 33 23 <1.8 13 <1.8 6,8 <1.8 6.8 17 46 <1.8 23 9.3 6.8 <1.8 33 33
2.0 <1.8 <1.8 <1.8 <1.8 <1.8 <1.8 24 4.5 <1.8 <1.8 <1.8 1.8 <1.8 2.0 <1.8 7.8 <1.8 <1.8 <1.8 4.0 <1.8 <1.8 2.0 7.8 <1.8 2.0 <1.8 4.5 <1.8 2.0 <1.8
12 <1.8 14 1,600 52 12 <1.8 17 79 <1.8 70 22 79 <1.8 70 23 49 <1.8 7.8 33 4.5 <1.8 7.8 13 49 <1.8 4.5 4.5 14 <1.8 7.8 11
< 1.8 <1.8 1.8 230 <1.8 <1.8 <1.8 <1.8 <1.8 <1.8 4.5 <1.8 <1.8 <1.8 4.5 <1.8 13 <1.8 20 2.0 2.0 <1.8 <1.8 <1.8 33 <1.8 <1.8 <1.8 2.0 <1.8 <1.8 <1.8
B . H . H u n t l e y and R. J. H a m m e r s t r o m
238
R ~
R ~
~
V
~
~%~
~ VV
~V
V
V ~
~V
A
z
~
V
~V
V ~
~
V
VVV
~
~
V
VV
%
V
VV
A
~
~R~
~
%%%
~VV
~
~%~
% ~
~VV
~
~
VV
V
. ~
~ - -
~E
~V
~
~
~
~
~
V
~
~
V
V
~V
~
V
~
~
~ V
~VV
VVV
~
V
~
V
~ V
VVV
~
V
~V
VV
g A 9 o
"5 e 9
~6
~z
<
A
~
~
VVV
An Experimental Depuration Plant
oysters prior to and after depuration, if necessary, are additional subjects for further study. Methods to maintain proper salinities in certain areas of the Gulf Coast during winter months will be required if a low salinity problem exists in the seawater at the selected building site of the deputation plant. From the i n f o r m a t i o n presented it may be concluded that the need exists for additional inquiry into the operation and evaluation of shellfish deputation plants. However, the results presented show that the concept of depuration is a feasible procedure for bacteriologically purifying Gulf Coast oysters and a method whereby such shellfish from restricted harvesting areas can be made a marketable product. ACKNOWLEDGMENTS The evaluation of the depuration system described in this paper was undertaken as a "team" effort, involving each Unit in the Gulf Coast Marine Health Sciences Laboratory. The project would not have been completed without the full cooperation from many personnel in the Bacteriology, Chemistry, Marine Biology, Virology, and Field Investigations Units as well as the vital support from the Maintenance Unit personnel. Special thanks are due Mr. John C. Bugg, Jr., for his design, developmental, and investigational activities in the initial phases of the study; Mr. Jack L. Gaines for field collection of polluted oysters; Mr. Maynard W. Presnell and Mr. John J. Miescier for their assistance in conducting bacteriological analyses; Mr. Eric A. Robertson, Jr., for the condition index data;
239
Mr. Abner C. Jones, III for salinity, turbidity, and temperature data; and Mr. Jack Mayer for the dissolved oxygen and glycogen information. LITERATURE CITED FURFARI, S. A. 1966. Deputation plant design. Environmental Health Series, Food Protection, Public Health Service, U.S. DHEW, PHS 999-FP-7:7. GALTSOFF, P. S. 1964a. The American oyster. Fishery Bulletin of the Fish and Wildlife Service, U.S. Department of the Interior, Vol. 64:407-408. - - - . 1964b. The American oyster. Fishery Bulletin of the Fish and WildlifeService, U.S. Department of the Interior, Vol. 64:213. HILL, W. F., Jr., F. E. HAMBLET, and E. W. AKIN. 1967. Inactivation of poliovirus type 1 by the Kelly-Purdy ultraviolet seawater treatment unit. Appl. Micro. 17(1): 1-6. KELLY, C. B. 1961. Disinfection of seawater by ultraviolet radiation. Amer. J. Pub. Health 51:1670-1680. - - - , W. ARCISZ, M. W. PRESNELL, and E. K. HARRIS. 1960. Bacterial accumulation by the oyster, Crassostrea virginica, on the Gulf Coast. U.S. DHEW Public Health Service Tech. Rep. F60-4, pp. 9. PHILLIPS, G. B., and E. J. HANEL. 1960. Use of ultraviolet radiation in microbiological laboratories. Tech. Report BL-28, U.S. Army Chem. Corps Bio. Labs., Ft. Detrick, Md., p 57. Recommended procedures for the bacteriological examination of sea water and shellfish, p. 17-37. 1962. 3rd edition, American Pub. Health Assoc., Inc., New York. Standard methods for the examination of water and wastewater, p. 309-311. Alsterberg (Azide) modification of Winkler method. 1960. 1lth edition, Amer. Pub. Health Assoc., Inc., New York.
