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Microbial Population Dynamics on Granular Activated Carbon Used for Treating Surface Impounded Groundwater R. M. D O N L A N and T. L. Y O H E Philadelphia Suburban Water Company, Bryn Mawr, PA 19010
A series of granular activated-carbon (GAC) columns was used to evaluate the microbiological aspects of GAC. Pathogen retention and growth on GAC, types and numbers of microorganisms developing on GAC, and microbial sloughing from GAC into effluents were three areas investigated. Predominant bacteria isolated were similar to previous studies. It was also found that, once established, the numbers of microorganisms in influents and effluents are similar until environmental changes cause fluctuations in the steadystate.
D
URING THE LAST FEW YEARS, an increasing number of groundwaters have
been found to be contaminated with organic chemicals. One affected water is Philadelphia Suburban Water Company's Upper Merion Reservoir, located in King of Prussia, Pa. Upper Merion is a groundwater-fed reservoir, and it is an important source of water for Philadelphia Suburban Water, one of the country's largest investor owned water utilities, supplying water to approximately 850,000 people. Although the source is groundwater, the impoundment takes on some characteristics of a surface supply. Treatment is therefore more extensive than would be the case with "normal" groundwater supply. In the spring of 1979, low levels of trichloroethylene (TCE) were detected in this reservoir by both the EPA and our own laboratory. It was mutually agreed that daily testing should be conducted while laboratory and pilot column studies were performed to find the most cost effective way to remove T C E and other organics from the reservoir water. Both 0065-2393/83/0202-0337$06.00/0 © 1983 American Chemical Society
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granular activated carbon (GAC) and aeration were included in the study. The GAC pilot columns were constructed of glass, stainless steel, and Teflon. They were located in the basement of the treatment building. The feed to these columns was untreated water from the reservoir. The design parameters used for this study are shown in Table I. Three carbon types were evaluated with one column serving as a replicate. The glass columns all had 10-cm (4-in.) inside diameters and were charged to a bed depth of 91 cm (36 in.). The empty bed contact time for this 6-month study was 5 min. During the study, approximately 50,000 bed volumes passed through the columns. Column 4 was taken off-line after 142 days to develop postrun analytical methods. Column 3 was left on-line an additional 4 months to verify data anomalies. Table II provides the actual run parameters of this study. Included in the GAC pilot column study were provisions to evaluate the microbiological aspects of GAC. Specifically, three areas were pursued in these microbiological investigations: 1. Pathogen retention and growth on GAC. 2. Types and numbers of microorganisms developing on GAC. 3. Microbial sloughing from GAC columns into effluents.
Experimental Sampling Procedures. All influent and effluent samples for microbiological analysis were obtained in sterile glass bottles. Of 260 total plate count samples, 42 replicates were collected. These replicates were used to determine confidence intervals for the observed results. Similar replication also was conducted for total coliform and Pseudomonas aeruginosa determinations. Samples were transported immediately to the laboratory where they were refrigerated and analyzed within 24 h. At the completion of the pilot study, G A C columns were disassembled and core samples of each column were taken. Each 91-cm core was divided into six sections. The top 15-cm section was subdivided into a 10-cm lower portion and 5cm upper portion. Each core section was sampled using a sterile spatula, and samples were placed into sterile"whirl-pac" bags. Samples were then transported to the laboratory, refrigerated, and tested within 6 h.
Table I. Pilot Column Design Parameter Specification Carbon types
Diameter Bed depth EBCT Run time Bed volumes
WV-G(2) F-400 ICI HD-1030 10 cm (4 in.) 94 cm (37 in.) 5 min 6 months 50,000
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Table II. Pilot Study Run Parameters
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Parameter
Col 1 WV-G
Col 2 WV-G
Col 3 F-400
a
Col 4 HD-1030 b
Run length (days) Bed volumes treated
176 50,100
176 49,600
300 85,000
142 39,900
Liters Empty bed contact time (min)
371,000 5.0
368,000 5.1
630,000
296,000 5.1
Surface loading (gpm/sq. ft.) Head loss (feet of water)
4.5 50
4.4 55
4.4
PH average range
influent average 7.48, range 7.20-7.65 7.54 7.52 7.53 7.2-8.8 7.2-8.8 7.2-8.8
7.47 7.2-7.7
influent average 156, range 152-166 161 161 161 155-172 156-175 155-177
160 155-166
Alkalinity (as C a C 0 ) average range 3
Dissolved oxygen (mg/L) average range
5.1 56
4.4 16
influent average 4.0, range 0.5-8.2 3.4 0.1-7.5
3.3 0.2-7.5
3.3 0.1-7.6
4.2 0.2-7.7
Turbidity F T U units average range
0.46 0.27-0.60
influent average 0.7, range 0.2-1.18 0.47 0.46 0.20-0.62 0.17-0.60
0.50 0.20-0.74
Total organic carbon (mg/L) average range
influent average 0.67, range 0.5-1.24 0.42 0.43 0.45 0.18-1.33 0.22-0.98 0.2-1.18
0.48 0.24-0.84
Temperature °C
influent average 13.0, range 9.5-21.0
"Chemical values reported only for 176-day period. "All values represent only 142 days of sampling.
Influent and Effluent Analyses. For total plate count analyses, samples were diluted in sterile buffered water. Two plates of standard plate count agar (Difco Laboratories, Detroit, MI) were planted for each dilution. The pour plate procedure was used. Plates were incubated at room temperature for either 6 or 15 days. Colonies of predominant organisms on total plate counts were isolated on standard plate count agar (spc). Isolates were identified according to the methods of Shayegani et al. (i). Other sources also were consulted to aid in identification
(2-15).
Total coliforms were enumerated with the membrane filter procedure (6), and verification was performed on both typical and atypical colonies (7). Verification results indicated that only typical (green sheen forming) colonies were coliforms. P. aeruginosa also was enumerated with the membrane filter procedure (6). All colonies were verified on milk agar (6). Two media were tested for their efficacy in enumerating total enteric bacteria: MacConkey's agar (Difco) and Tergitol-7 agar (Difco) supplemented
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with 1% triphenyltetrazolium chloride. For each, 10 mL of sample was filtered through a 0.45-/xm filter which was then placed on the agar medium. MacConkey s agar plates were incubated at 35°C for 24 h; Tergitol-7 agar plates were incubated at room temperature for 48 h. After incubation, all colony types were counted. Verification of colonies on both media was performed by isolating colonies on standard plate count (spc) agar and identifying through the API-20E system (Analytab Products, Plainview, NY). Enteric pathogens were enumerated according to the procedures of the "Microbiological Methods for Monitoring the Environment" (7). This procedure is shown in Figure 1. Two liters of each sample was filtered through a 0.45-/mi membrane filter. The filter was then divided in half and each half placed into a separate flask of selenite broth (Difco). Oneflaskwas incubated at 35°C for 4 days,
SAMPLE
CONCENTRATION OF
SAMPLE
Membrane Filter
ENRICHMENT
ISOLATION PLATING
Xylose Lysine Desoxycholate Agar
Brilliant Green Agar
BIOCHEMICAL IDENTIFICATION (Primary Screening) I Figure 1. Procedure for enumerating enteric pathogens.
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and one was incubated at 41.5°C for 4 days. After 48 h and again after 4 days, a subculture from each selenite broth was streaked onto two xylose lysine desoxycholate (XLD) agar plates (Difco) and two brilliant green lactose bile (BGLB) agar plates (Difco). One X L D plate and one BGLB plate were incubated at 35°C, and one X L D plate and one BGLB plate were incubated for at 41.5°C. BGLB plates were incubated for 48 h, and X L D plates were incubated for 24 h. Suspect colonies were then picked, isolated on spc agar, and identified through the API-20E System. Core Analyses. Total plate counts of cores were performed by placing a 0.5g core sample into a sterile Pyrex tissue grinder, adding 1.0 mL of sterile buffered water, and grinding to a fine consistency. To this was added 4.0 mL of sterile buffered water. The diluted sample was then drawn out of the tissue grinder with a pipet and placed into a sterile tube. The subsample, now a 1:10 dilution of the original sample, was mixed on a Thermolyne maxi-mix for 5 min. The subsample was then diluted out in sterile buffered water and planted on agar in duplicate. Plates were incubated for 6 days and counted. Predominant isolates on total plate counts were identified as described previously. Biological activity ( C 0 production) was determined by a modification of the technique of Stotzky (
