Effect of Upgrading a Municipal Wastewater Effluent on Pollution Indicator and Other Microorganisms in River Water Ernest A. Matson, Sally G. Hornor, and John D. Buck* Marine Research Laboratory, The University of Connecticut, Noank, Conn. 06340
Densities of total and fecal coliforms, fecal streptococci, plate count bacteria, and certain yeasts were monitored in a n eastern Connecticut watershed for 1year prior to upgrading a municipal primary settling treatment plant t o activated sludge and sampling was continued for 19 months afterward. Substantial reductions in densities of indicator and other bacteria and yeasts upstream of the effluent after upgrading were associated with lower annual precipitation and reduced precipitation-associated sampling. The effluent dilution decreased from 0.84 to 1.42% of river volume due to increased daily treatment plant discharge and decreased river discharge. Calculated reductions in effluent discharge of indicators ranged from 10% (total coliforms) to 84% (fecal coliforms), while the discharge of “total plate count bacteria” increased 500%. Chlorination procedures were still required to reduce river total coliform densities below the accepted limit. Within the microbiological perspective, upgrading this treatment plant was of limited value to potential water users.
I km
STUDY AREA?
,-I
Environmental Science & Technology
6 Shetucket River
N
Figure 1. The Shetucket River study area; STP = sewage treatment Dlant
Many municipalities have recently installed activated sludge secondary sewage treatment procedures in an effort t o reduce organic pollution by effluents in receiving waters. Often, the activated sludge process is added to a preexisting primary system, or the secondary treatment facility is installed where no prior treatment existed. The history of domestic wastewater pollution of aquatic systems has been well documented and requires no further elaboration. Installations of or additions to sewage treatment procedures were designed to alleviate some of the biochemical stresses imposed on lentic, lotic, and marine communities and ecosystems. Aside from the main purpose of effluent biological oxygen demand (BOD) reduction, primary sewage treatment removes between 40 and 80% of influent bacteria and the activated sludge process is reported to reduce influent populations by 90 to 98% ( 1 - 3 ) . The exact mechanisms are apparently complex ( 4 ) .Accordingly, a reduction in the concentration of effluent microorganisms by plant upgrading should result in a similar decrease in the receiving waters, assuming no volume changes. There have been numerous reports of the public health microbiology of rivers in which the total and fecal coliforms and fecal streptococci are used as indicators of relatively recent mammalian fec 11 pollution and potential health hazards ( 5 ) . In one of the few studies of its type, Womack et al. ( 6 )used the total coliform group to monitor changes in reservoir water quality Isefore and after a primary settling system was upgraded to activated sludge treatment. They observed significant reductions in total coliform densities after upgrading, but concluded that the observed improvements were “inadequate for today’s needs”. While there are serious problems plaguing the methodology for enumeration (7-1 1 ) and reliability of accepted indicators (12 -24),as well as the supposed significance of the indicated health hazard ( 2 4 ) , many official agencies continue to use some or all of‘these “indicating organisms” (most frequently the total coliforn ) and other limited biological and/or chemical data to classify and restrict the use of water hodies. Nonetheless, these organisms are useful in detecting relative 460
k5
changes in “water quality” under defined circumstances. We have used the total and fecal coliforms, fecal streptococci, total plate count bacteria, and two groups of yeasts t o detect changes in water quality associated with the installation of an activated sludge secondary treatment facility added in conjunction with a preexisting primary settling system. In June of 1973, the city of Willimantic, Conn. (population 17OOO), put its new combined sewage and stormwater runoff activated sludge system into operation and increased capacity from 8300 to 19 000 m 3 day-’ (2.2 to 5.0 mgd). The increased volume included the addition of two textile processing effluents (a total of 25% of mean daily flow), and avoided frequent overflows during high runoff. The purpose of this report is to describe the changes in densities of indicator and other bacteria and yeasts in the water column both up- and downstream of the effluent which occurred between tJune 1972 (1year prior to upgrading) and .January 1975 (19 months afterward), and to relate these changes to upgrading of the sewage treatment procedure.
Experimental The Study Area. Pertinent data on the Shetucket watershed study area are given in Table I. The Willimantic treatment plant effluent is discharged into the confluence of the Willimantic and Natchaug Rivers where they combine to form the Shetucket River (Figure 1).The Willimantic and Natchaug contribute approximately 64 and 36%, respectively, to annual Shetucket discharge. The effluent discharge ranged from 0.096 to 0.240 m:’s-’, and varied daily and seasonally. Bot,h Stations 2 and 3 on the Willimantic and Natchaug Rivers, respectively, were about 0.5 km upstream of the confluence. Stations 4 through 7 were located 1.1, 1.9,4.5,and 7.5 km downstream of the effluent in the Shetucket River. During low summer flow, the effluent plume was often not mixed with river water a t Station 4, as determined by conductivity measurements. River conductivity and temperature were measured in the field with a Yellow Springs Instrument Co. Model 3 3 SCT meter (Yellow Springs Instrument Co., Yellow Springs, Ohio 45887) and conductivity was expressed as pS cm-I a t 25 “C. Effluent discharge data were obtained from the treatment plant manager and river discharge data were available from the LJ.S.G.S. gaging stations on all three rivers. Precipitation was monitored by the U S . Army Corps of Engineers 9 km
0013-936X/79/09 13-0460$0 1.OO/O @ 1979 American Chemical Society
Table 1. Characteristicsof the Shetucket River Watershed characterlrtlc
area land use (state of Conn.)
river morphometry: depth width substratum channel form gradient river hydrology: discharge (range ’72 to ’74) mean: 1972
1973 1974 velocity flow time (effluent to Sta. 6) river chemistry: PH conductivity oxygen saturation temperature dissolved org carbon precipitation: 45-year average
1972 1973 1974
Table II. Precipitation and Discharge Data before and after Upgrading Sewage Treatment Procedure before
value
1330 km2 75% forested 15 % agricultural 10% residentialhrban 0.1 to 2.5 m 25 m at Stas. 2 and 3 50 m at Stas. 4 to 7 fine silt to large boulders rectangular, steep banks, shoals and cuts at bends 1.33 m km-’
1.2to 204 m3 s-’ (Sta. 5) 30.1 26.9 24.5 0.25 to 1.0m s-’ 20 to 400 min
6 to
a
50 to 150 FS cm-’ 70 to 120% 0 to 27 “C 3 to 10 g m-3
115 cm year-’ 155 cm year-’ 130 cm year-’ 1 la cm year-’
upstream of Station 3. Microbiological Analyses. A biweekly sampling schedule was initiated in June 1972, 1 year before secondary sewage treatment procedures began, and continued for 19 months after upgrading (until January 1975). Subsurface (ca. 10 cm) water samples were taken in sterile, wide-mouthed, 1-L, brown, polyethylene bottles, iced immediately, and returned to the laboratory within 3 h, where enumeration procedures were completed within 6 h. Populations of total (TC) and fecal (FC) coliforms and fecal streptococci (FS) were enumerated in duplicate using accepted procedures (25). Membrane filtration was used exclusively for TC, FC, and FS with presterilized 0.45-wm membranes (HAWG047SO; Millipore Corp., Bedford, Mass. 01730), while “total plate count” bacteria (PC) were enumerated using the spread plate technique (26) with Plate Count agar ( 2 5 ) .Enumeration of yeasts growing a t 20 and 37 “C (Y20 and Y37) was begun in February 1973. Water was filtered through presterilized black 0.80-Fm Millipore membranes (AABG047SO) and incubated on a medium (27) containing 2.3% Bacto Nutrient Agar p H 6.0, 2.0% glucose, 0.1% yeast extract, 0.2% malt extract (Diamalt; Standard Brands Inc., New York, N.Y. 10022) and 30 mg % chloramphenicol. Duplicate plates were incubated a t 20 and 37 “C for up to 5 days. Some Y20 plates were transferred to a 2 to 3 “C refrigerator to prevent overgrowth by filamentous forms and maximize countable yeast colonies. All microbial numbers were expressed as colony forming units (CFU) per unit volume of river water.
total precipitation with 24 h of sampling, cm mean precipitation per sampling trip, cm frequency of precipitation within 24 h of sampling, % mean discharge, Sta. 5,m3 s-’ (sampling trips only) mean daily treatment plant effluent discharge, m3 day-’ mean dilution rate, % of Sta. 5 discharge, fl SD
after
% change
16.3
10.4
-28
0.58
0.35
-25
48
27
-23
25.0
21.7
-7.6
a700
11000
+26
0.84 f
1.42 f
4-69
0.49
0.91
Data Analyses. For each sampling trip, the following statistics were calculated: (1)the mean number of CFU per unit volume in each microbial group from duplicate platings, (2) the weighted average of microbial densities a t Stations 2 and 3 after complete water mixing, (3) effluent dilution, (4) the percent increase in microbial densities observed a t Station 5 due to the effluent, ( 5 ) the net effluent concentration of each microbial group (not including die-off or settlement to the benthos over 1.9 km), (6) rate of microbial group transport past Station 5 (CFU.m-:l/(rns.s-l)), (7) the FC/FS ratio, and (8)FC/TC as a percent. Results All sampling trips were prescheduled to coincide with field work of other members of an interdisciplinary study group, and this schedule did not allow us to delay our sampling to avoid precipitation-related events which result in variable densities within short time periods. Also, 1972 and 1973 had much greater total precipitation and subsequent runoff than the period after upgrading (October 1973 through January 1975, Tables I and 11). Before upgrading, 48% of our samples were preceded by precipitation within 24 h ( n = 29), but after upgrading of the treatment plant, only 27% ( n = 31) were associated with precipitation. This coincidence was responsible for part of the high densities of microorganisms a t upstream stations during the study period before upgrading, as discussed below. Treatment Plant Effluent. The effluent accounted for a mean of 0.84 f 0.49% of Station 5 discharge before upgrading and 1.42 f 0.91% afterward (Figure 2 and Table 11) due to a 7.6% decline in total river discharge and a 26% increase in mean daily treatment plant volume (Table 11). Design capacity of the new facility was rarely exceeded, except during a few severe storms. The increase in mean daily plant volume was almost completely accounted for by the two additional industrial effluents (both textile processing wastes). The net result was an increase in the mean relative volume of the effluent in the river of 1.7X after upgrading. Seasonal Changes in Microbial Groups. The data in Figures 3 and 4 have been divided into groups based on the presence or absence of a chlorinated effluent. The treatment plant discharged a chlorinated effluent between May and September, and groups A, C, and E are from these periods. Groups B, D, and F are averages of data collected between October and April. Upstream a t Station 3 (Figure 3), both yeast groups (Y20 and Y37) were most numerous during winter, with higher mean discharge, runoff, and lower temperatures. The TC, FC, and FS organisms were more numerous during the warmer, low-flow summer months. The seasonal group data from Station 5 , downstream of the Volume 13,Number 4,April 1979
461
Table 111. Microbial Group Densities Up- and Downstream of the Treatment Plant before and after Upgrading, and Percent Change In Densities Attributable to the Treatment Plant CFU
m-3 (xio-4) ~~~
up.tresm
PCe TC FC FS
Y20 Y37 a
n
belore a downstreamd
3 x 106 41 000 550 590 1500 120
6X 90 000 3 600 1400 1800 240
lo6
~
% change
+lo0 +120 +550 +140 +20
+loo
after b downstream
upstream
160 X lo6 12000 1300 320 1200 250
0.57 X loe 1000 270 180 770 32
% change
+28 000 +1100 +380 +78 +57 +690
= 29. n = 31. Weighted Stations 2 and 3 averages. Observed at Station 5. *Abbreviations as in Experimental section.
SECONDARY 1REATMENT
PRIMARY TREATMENT
Figure 2. Shetucket River discharge and treatment plant effluent dilution
PRIMARY TREATMENT
SECONWRY TREATMENT
CI'
Cl'
-' SAMPLE GROUP
Figure 4. Seasonal densities of indicator bacteria and 20 and 37 O C grown yeasts at downstream Station 5.Sampling groups as in Figure 3;abbreviations as in Experimental section
SAMPLE GROUP
Figure 3. Seasonal densities of indicator bacteria and 20 and 37 O C grown yeasts at upstream control Station 3. Sampling group A = June-September, 1972;B = October-April, 1972-1973; C = MaySeptember, 1973;D = October-April, 1973-1974;E = May-September, 1974;F = October-January, 1974-1975. Abbreviations are as in Experimental section
effluent, are shown in Figure 4 and were statistically similar ( P < 0.05) to the other downstream Stations 4 6 , and 7 (data 462
EnvironmentalScience & Technology
not shown). The effect of summer chlorination procedures was evident during sampling periods A, C, and E. During chlorination periods, microbial group densities downstream of the effluent were rarely greater than the weighted upstream average of Stations 2 and 3, except for the PC organisms. High densities of T C organisms were reduced substantially throughout the watershed after upgrading as a result of (1) lower precipitation-associated sampling, and (2) lower runoff rates. Comparisons before and after Upgrading. In Table 111, mean microbial group densities are compared up- and downstream of the effluent, and all data are included from winter and summer sampling. The upstream value for densities was obtained by taking the weighted average of Stations 2 and 3 for each sampling trip (microbial group density multiplied by the relative volume of each tributary river), and this statistic was compared with the densities observed at Station 5, 1.9 km downstream of the effluent. The maximum percent increase before upgrading was in the FC group, which increased 550% over upstream values. After upgrading, the FC and FS groups were the only ones in which there was a decrease in the relative effect of the effluent. The percent increase in group densities downstream of the effluent increased
Table IV. Microbial Group Transport Rate, Up- and Downstream of the Treatment Plant before and after Upgrading, and Percent Change in Transport Attributable to the Treatment Plant mean CFU 5-1 ( x 1 0 - 4 ) a
-
mlcroblal group
upstreamd
before downstream e
PC’ TC FC FS Y20 Y37
250 000 3 400 47 50 130 10
240 000 3 600 150 56 73 10
a Calculated individually after each trip (CFU.m-3/m-3.s-’). as in Experimental section.
70 change
-4
4-6 +220 +12 -44 0 n = 29.
upstream
after downstream
% change
52 000 46 25 18 74 3
7 500 000 560 61 15 57 12
+14300 +1120 4-61 4-17 -23 +300
n = 31. Weighted Stations 2 and 3 averages. e Observed at Station 5. Abbreviations ~
Table V. Effluent Contributions to Microbial Group Densities and Changes in Treatment Plant Discharge of Microbial Groups during Nonchlorination Periods mlcroblal group
PC = TC FC FS Y 20 Y37
Yo occurrlng at Sta. 5 due to effluenta before after
68 87 96 93 24 67
99 97 90 83 49 80
calcd effluent concn a before after
12 000 33 25 7.5 2.4 1.5
55 000 24 3.2 0.99 1.1 0.20
calcd effluent discharge before after
100 000 290 220 65 21 13
600 000 260 35 11 12 2.2
% change in mean dally discharge
4-500 -10 -84 -83 -43 -83
a Calculated from the weighted averages of densities upstream at Stations 2 and 3 compared with those densities observed at Station 5 downstream; in CFU m-3 X lo-’ (during October-April nonchlorinationperiods only). Obtained from calculated concentrationdata (footnote a, above), and mean daily effluent discharge of 8700 m3 day-’ before, and 11 000 m3 day-’ after upgrading (CFUday-’ X lo-’*). Abbreviations as in Experimental section.
substantially for all other groups. Thus, since upstream water quality improved after upgrading (especially PC, TC, and Y37, Table 111), and the effluent was relatively larger, there was a more pronounced relative increase in densities downstream of the effluent, even though absolute downstream concentrations decreased throughout (except PC and Y37). In Table IV, we describe the rate a t which numbers of organisms pass a given point in the river, as it approaches and passes the effluent. In a river system, this characteristic is equally important as concentration data, since it describes the rate a t which water users will be exposed to indicators of potential health hazards. Total discharge of microorganisms past Station 5 decreased significantly after upgrading ( P < 0.001) for all groups except PC and Y37, and part of this decrease can be explained by improvements in upstream water quality (Tables I11 and IV, Figure 3). There were 4.8-, 74-, 1.9-, 2.8-, 1.8-,and 3.3-fold reductions in PC, TC, FC, FS, Y20, and Y37 group transport, respectively, from upstream sources after upgrading. This is in comparison to 6.4-, 2 5 , 3.7-, and 1.3-fold reductions in TC, FC, FS, and Y20 transport and 31- and 1.2-fold increases in PC and Y37 group transport past downstream Station 5 . There are a t least two possible explanations for this observation: (1) either there were significant changes in effluent concentrations, and (2) discharge-associated removal rates of organisms from the water column between Stations 2 and 4 were different between study periods. In Table V, we have estimated the changes in effluent quality and quantity using treatment plant volume data obtained from the plant manager and our microbiological and discharge data. These estimates are low net figures since we have limited data on effluent concentrations (extremely variable densities depending upon influent and processing rates) and removal of indicator and other microorganisms from the water column is related to changes in river dischargez8 (those relationships are not used in these calculations). Nonetheless, a good first-order estimate can be made
of the net effect of the effluent on Station 5 water quality as a comparison before and after upgrading. The effluent supplied most of the microorganisms isolated from Station 5 during both study periods (except for the Y20 group) (Table V). The percent occurring a t Station 5 due to the effluent increased for all groups after upgrading, except for the FC and FS group. This is a result of the combined effects of (1)variable decreases in net calculated effluent concentrations of microorganisms, and (2) an increase in mean daily treatment plant discharge. For example, net calculated effluent TC densities decreased only 27% (from 33 to 24 X loy CFU m-:3),probably as a result of decreased urban stormwater runoff into the combined treatment system, whereas the FC and FS groups decreased 87% (from 25 to 3.2 and 7.5 to 0.99 X lo9 CFU m-j, respectively). When changes in effluent discharge between study periods are included, there were net decreases in daily effluent discharge ranging from 10 to 84% (TC and FC, respectively) and a net increase in daily discharge of PC bacteria of 500% (Table V). These overall changes were also reflected in the frequency of the FC/FS ratio distribution (Table VI). Upstream, the frequency of ratios less than 1.0 (predominant livestock pollution in the presence of mixed pollution (29)) was reduced from 35 to 21% a t Station 2 and from 42 to 39% a t Station 3. There were similar moderate increases in the frequency of ratios greater than 2.0 (predominantly human pollution in the presence of mixed pollution (29) upstream. Downstream, however, the relative effect of the effluent after upgrading increased significantly since (1) the frequency of ratios less than 1.0 decreased a t least twofold at Stations 4 , 5 , and 6, and (2) the frequency greater than 2.0 increased 1.3- to 1.6-fold. This change in ratio distribution can be attributed to, in part, reductions in agricultural runoff, reductions in the frequency of sampling during such runoff, decreased stormwater runoff into the treatment plant, increased travel time of organisms in the river due to lower river discharge resulting in disproportionate die-off of FC and FS, as well as the observed Volume 13, Number 4, April 1979
463
BEFORE IMPROVEMENT N:26
50
0
AFTER IMPROVEMENT N, 3o
51a.3 I
Table VI. Distribution of the FWFS Ratio at All Sampling Stations before and after Upgrading Sewage Treatment Procedure a % < 1.00 % > 1.0 < 2.0b % > 2.0b slatlon
before
after
before
after
before
aftor
2
34 42
21 39 7 14
25 21 17 16 13 21
34 11 14 14 6 16
42
3 4 5 6 7
44 4a 79 72 73 67
34 28 37 17
ia 16
38 4a 56 49 63
a Before. n = 24; after, n = 30. Categories described in Geldreich and Kenner (29)combined into: < 1.0, probably livestock in the presence of mixed pollution; > 1.0 < 2.0, unsure; and > 2.0, probably human in the presence of mixed pollution. Percent occurrence within each interval.
I975
Figure 5. Percent of total coliforms which were of fecal origin (FC/TC X 100) at all stations before and after upgrading sewage treatment
procedures. Each data point represents the mean of a 3-month sampling period. The mean percent is given for each station before and after upgrading changes in effluent microbiology. Figure 5 displays the substantial increase in the percent of coliforms which were of fecal origin after upgrading. Runoff (30) and aftergrowth of terrestrial coliforms (31) were significantly lower (98% reduction) throughout the upstream watershed (Figure 3), while the FC group was reduced by only 51% (see also Table 111). Downstream of the effluent, the disproportionate decreases in effluent TC and FC organisms (Table V), combined with the increase in relative effluent volume (Table 11),resulted in smaller increases in the FC/TC ratio.
Discussion In contrast with other predictions (1), the discharge of total bacteria (as measured by PC) increased significantly ( P < 0.001) after upgrading, and reductions in other groups (Table V) were not as high as anticipated. There are several possible explanations for these observations, including (1) unrepresentative sampling, (2) toxicity of the industrial effluents, (3) improper operation and/or construction of the new facility, and (4) conceptual flaws in the plant design. Apparently, discrepancies between predicted and observed improvements in effluent quality are not uncommon (6,32),but there are few follow-up reports of this type from which to draw firm conclusions. With respect to the possible explanations for inadequate effluent reductions, all are problems of varying severity. In response to (1)above, Glantz (33)found seasonal river TC and FC trends similar to those reported here, but also encountered 5-min variations of up to 900-fold under stable flow conditions using accepted procedures (25).We have no time-dependent data, but since there were no statistically significant differences ( P < 0.05) among any of the means from all downstream stations (data from Stations 4,6, and 7 not given), we do not consider this variability a factor in our study. No data are available on the effects of the two industrial effluents, so the possibility of toxicity in this treatment plant cannot be evaluated. Combinations of industrial effluents with domestic 464
Environmental Science & Technology
sewage in activated sludge treatment plants have apparently led to problems elsewhere ( 6 ) .In response to explanation 3, several different problems were encountered in optimizing treatment plant operation after upgrading. Further, we question the predictive capability involved in activated sludge processing, since many unresolved questions on the microbial ecology of sewage were being actively studied a t a time when many similar treatment plants were under construction (34-37). Microbial ecologists have had limited input in the conceptual design of these facilities (38). We conclude, as others have (21),that the TC group is an inadequate indicator of the potential presence of possible health hazards. Too many of the commonly encountered coliforms are of nonfecal origin (Figure 5), and are often difficult to enumerate on a plate containing other mixed IMViC-reacting organisms. Many of this group may be from the same geographical source (39),but few, in this study, were from the same biological source. Chlorination procedures are apparently not absolute for eliminating potential health hazards. Silvey et al. (20) isolated Salmonella spp. equally as often before and after chlorination, and all bacteria showed signs of rejuvenation after removal from chlorination contact. Engelbrecht et al. (40) demonstrated that coliforms have a lower resistance to chlorine than enteric viruses, protozoan cysts, some yeasts, and acid-fast bacilli. Another conceptual and methodological problem exists in the study of any of these microbial groups in some types of river systems. Until recently, few studies (14, 15,17,28,31,41) examined the role of indicator organisms in the sediment community, and there is evidence that the planktonic community of indicators is a minor component of the pollution indicator microbiology of shallow water rivers (28, 42). Thus, studies of die-off rates based on mathematical models of indicator survival with time downstream (32,43)may be inadequate in estimating the true health hazard potential (regardless of indicator used) if sediment studies are not included. Within the limits of the microbiological perspective, we can conclude that upgrading this treatment plant to activated sludge processing was of limited value, since chlorination procedures are still required to meet existing indicator standards based on TC densities. Variable densities of indicators upstream of the effluent resulted from agricultural runoff and nonpoint sources of human pollution (Table VI), for which there are, as yet, no satisfactory controls. Even if modest human population densities increase within the watershed (and solely a t the expense of agricultural land), and all dwellings become sewered, chlorination or other procedures will still be required to meet indicator standards, regardless of the level of domestic sewage treatment. Further, improve-
ments in the chemical quality of the Shetucket River due to upgrading have not been demonstrated; dissolved oxygen concentrations remained the same as before upgrading (70 to 120% saturation) (44, 4 5 ) , and mean annual BOD5 was less than 2.0 ppm in all three rivers prior to upgrading ( 4 4 )and for several months afterward ( 4 6 ) . Upgrading this treatment plant had no observable effect on fish ( 4 7 ) or aquatic macrophytes ( 4 8 ) .
Acknowledgments This paper is Contribution No. 119 from the University of Connecticut, Marine Research Laboratory. We wish to thank Patricia Bubucis, Susan Coleman, Mark Hines, Janice Ibbison, Mark Rogers, and Robert DeGoursey for expert technical assistance throughout.
Literature C i t e d (1) LVarren, C . W., “Biology and Water Pollution Control”, W. B. Saunders, Philadelphia, 1971, ( 2 ) Kabler, P., Sewage Ind. Wastes, 31, 1:173-82 (1359). ( 3 ) Kampelmacher, E. H., van Noorle Jansen, L. M.. J . Water Poilut. Control Fed., 42, 2069-73 (1970). (4) van der Drift, C., van Seggelen, E., S t u m m , C., Hol, W., Tuinte. J., A p p i . Enoiron. Microbiol., 34, 315-9 (1978). ( 5 ) Geldreich, E. E., in “Water Pollution Microbiology”, Mitchell, R., Ed., LViley-Interscience, Kew York, pp 207-41, 1972. (6) Womack, J . D., Burdick, cJ. C . 111, Larson, F. D., Water Res. Huli., 9, 100-1.5 (1973). ( 7 ) Stuart, D. G., McFeters. G. A,, Schillinger, J . E., A p p l . Enciron. Microbioi., 34,42-6 (1977). (8) Bissonnette, G. K., Jezeski, J. J., McFeters, G. A,, Stuart, D. G., A p p l . Enuiron. Microbiol., 33,590-5 (1977). (9) Braswell, J. R., Hoadley, A. W., A p p l . Microbiol., 28, 328-9 (1974). (10) Hufham, J . B., A p p l . Microbioi., 27, 771-6 (1974). (11) Presswood, W.G., Brown, L. R., Appi. Microbioi., 26, (1973). ( 1 2 ) Geldreich, E. E., Clarke, H. A,, A p p i . ,kfiCrfJbio/., 14, 429-37 (1966). (13) Gallagher, T . P., Spino, D. E., W a t e r Res., 2, 169-75 (1968). (14) Hendricks, C . W., Can. J . Microbiol., 17,551-6 (1971). (15) Hendricks, C. W., A p p l . Microbiol., 24, 168-74 (1972). (16) McFeters, G. A., Stuart, D. G., Appl. Microbiol., 24, 805-11 (1972). (17) Cohen, J., Shuval, H . I., W a t e r Soil Air Pollut., 2, 85-95 (1973). (18) Johnstone, D. L., Kubinski, A. M., Report No. 14, State of Washington Water Research Center, Pullman, Wash., 1973. (19) Smith, R. J., Twedt, R. M., Flanigan, L. K., J . W a t e r Pollut. Control Fed., 45,1736-45 (1973). (20) Silvey, J. K. G., Abshire, R. L., Nunez, W. J., 111, J . Water Pollut. Control Fed., 46,21%-62 (1974).
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Receiued /or recieu March YO, 1978. Accepted Nouember 16, 1978. This work was supported in part by a grant from t h e I n s t i t u t e of W a t e r R i w u r c e s , 1 ‘niuersity o/ Connecticut, u’ith federai f u n d s prot’ided b ) t h e O//icr o/ W a t e r Resources, OWRR Project N o . A 0.52-(‘0.V.Y.
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