Environ. Scl. Technol. 1083, 17, 123-125
above the pavement and is moved to the edge by water and air currents. The airborne lead travels long distances with varying depositions along the way. Once lead gets into the soil it moves slowly in the direction of water flow. The smaller difference between 0.0- and 1.0-m lead concentrations in 1979 than in 1973 indicates that lead is decreasing in these soils by moving toward the 1.0-m positions and the ditch. The increase in median lead concentrations indicates that lead is being moved toward the median with the water flow. The decrease in lead concentrations in soils near the highway is stong evidence that the mandatory use of unleaded gasoline was justified since this ultimately decreased the ingestion by man of lead compounds from the food chain. Registry No. Pb, 7439-92-1.
Literature C i t e d (1) Ryan, J. “Proceedings of National Conference on Disposal of Residuals on Land”; St. Louis, MO, Sept 1976. (2) National Academy of Sciences, National Academy of Engineering, “Water Quality Criteria 1972”;National Academy of Sciences: Washington, DC, EPA-R3-73-033, 1973. (3) Cason, J., Dep&ment of Agriculature, Northeast Louisiana University, private communication, 1972. (4) Code of Federal Regulations, 1975, Title 40, part 80, p 7. (5) Lagerwerff,J. V.; Specht, A. W. Environ. Sci. Technol. 1970, 4 , 583. (6) Oliver, B. G. Environ. Sci. Technol. 1973, 7, 135. (7) Buchauer, M. J. Environ. Sci. Technol. 1973, 7, 131. Received for review April 9,1981. Revised manuscript received March 1, 1982. Accepted October 19, 1982.
Biofouling Control with Ferrate(V1) Joanne Fagan and Thomas D. Walte”
Department of Civil Engineering, University of Miami, Coral Gables, Florida 33 124 Preliminary biofouling control studies were run by utilizing ferrate(VI) as a biocide. Model condenser systems were fabricated and biofilm growth was monitored with time as a function of ferrate(V1) dose and contact time. As ferrate(V1) concentrations of 10-5 M or greater were dosed twice a day for 5 min, biofilm growth was Introduction
The formation of a microbiological film on solid surfaces creates a costly problem for many industries. Although the mechanisms by which microorganisms become attached to solid surfaces are not well understood, the problems created by their attachment have generated a great deal of research, especially in the area of condenser fouling. Traditionally, the most common method of controlling slime growth in electric-generating-plant cooling systems has been to treat cooling waters intermittently or continuously with chlorine. In most cases chlorination has proven to be effective in keeping condenser tubes clean, i.e., maintaining adequate heat-transfer rates and low back-pressure. However, numerous investigators (1, 2) have shown that residual chlorine and its oxidation products are toxiic to organisms in natural waters. Brungs (3) concluded that the safe level of chlorine residual was 0.003 mg/L on a continous basis and 0.04 mg/L if added intermittently. Recognition of the environmental impact of chlorine residual on receiving water ecosystems has led to investigations for alternative ways to maintain condenser cleanliness. Alternative chemicals that have been considered as a replacement for chlorine are also strong oxidants. A detailed review of the nature of these alternatives can be found in Waite et al. (4),and Waite and Fagan (5). All of these oxidants have shortcomings in their ability to control film growth, environmental toxicity, or cost. Previous studies suggest that ferrate(V1) may be effective for fouling control while being environmentally safe. It was, therefore, the objective of this study to investigate the effectiveness of ferrate(V1) for controlling biofilm formation. Materials a n d M e t h o d s
The test apparatus consisted of a closed, 5-gallon continuous-flow system with a Plexiglas test chamber simu0013-936X/83/0917-0123$01.50/0
lating a condenser. The internal dimensions of the test were in. 1.25 in. 35 in. The side walls were designed to hold six in. in, glass slides, At the start of each experiment all systems were enriched with212 mg L-’ of dextrose and 21.2 mg L-l Of nutrient broth, and a culture of naturally occurring microorganisms was added. This inoculum was obtained by enriching a natural water sample with nutrient broth. Preliminary experiments had indicated that the above adjustments to the raw water assisted in developing a secure bacterial film on the slides in 7 days. During all experiments pH ranged from 7.5 to 8.1, and temperature varied between 28 and 35 OC. Except in experiments where velocity was intentionally varied, the reactor velocity was mintained at 1.0 f 0.1 ft/s. Ferrate(V1) was produced and analyzed for purity by using the methods described by Schreyer and Ockerman (6). Only potassium ferrate of greater than 80% purity was used in these experiments. Ferrate was first added after the systems had been operating for 12 h, and dosing then followed a prescribed schedule for each experiment. Starting on day 1.5 and continuing daily, a slide was removed from each chamber, and the film was measured microscopically to determine film thickness. This was done by focusing on the top and bottom of the film and determining the thickness from the vernier on the focus adjustment (accurate to 1 pm). Composition of the film was only described in a qualitative nature, and no taxonomic investigations were undertaken. Results a n d Discussion
The total thickness that the biofilm attains must be limited by shear forces and diffusion properties within the film. At least within the velocities tested in this study total filmthickness does not appear to decrease with an increase in velocity. It may do the opposite, i.e., increase with increase in velocity due to increased oxygen diffusion through the film, keeping the inner layers from becoming anaerobic and sloughing as in a trickling filter. However, it seems probable that there is some value of shear stress beyond which the film can no longer remain attached, hence there will be a maximum film thickness possible for a given shear stress. Both changes in velocity and nutrient concentration caused changes in appearance of the biofilm
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looI 0
1
o
M Fe 0 4 0 CONTROL
M K z F e 0,
A F e 04,2 TIMES/DAY, 5 MINUTES
M K z Fe O4
An
*Fe04,2 TIMES/ DAK 2 0 M I N U T E t
/
i601
70
z Y
-IV,
TIME ( DAYS 1
TIME (DAYS)
Flgure 1. Effect of different ferrate(V1) concentrations on film development. Ferrate(V1) dosed every 12 h for 20-min contact.
in our test systems. An increase in velocity caused the film to appear more dense and to have a lower water content. A 5-10-fold increase in nutrient concentration caused the film to grow more rapidly and weaken the strength of attachment. Figure 1shows film thickness vs. time when dosed with three different concentrations of ferrate(V1) with 20-min contact every 12 h. The control represents an average of all controls from the individual experiments. It can be seen that at concentrations of and M, ferrate(V1) inhibited film development; however, at lo* M film growth rate was not significantly retarded. The finding that the necessary concentration for retarding film growth was between lo4 and 10" M is especially interesting because that is also the concentration of ferrate necessary to achieve effective kill of enteric bacteria in suspended systems (7). A 20-min contact period in these tests was chosen because it is typical of the duration of chlorination treatment in power plants. On the basis of results from previous disinfection experiments it seemed probable that there would be little ferrate remaining after the first 5 min; however, most of the significant disinfection occurs within that time in suspended systems. Both ferrate decomposition experiments and residual purple color suggested that some ferrate residual was still present in the water after a 20-min contact in these systems. Therefore a shorter duration of exposure was tested. There was no significant difference in the activity of ferrate against biofilm when the duration of exposure was decreased from 20 to 5 min per treatment (see Figure 2). These results are consistent with the observation that most of the inactivation in suspended systems occurred in the first 5 min. However, because there was less surface area for the ferrate to react with the attached film, one might have expected a slightly longer period of inactivation, especially in light of the fact that there was residual iron(V1) remaining in the system after 5 min. These observations suggest that the concentration or frequency of 124
Environ. Scl. Technol., Voi. 17, No. 2, 1983
Flgure 2. Effect of variable contact time on film development for a constant ferrate(V1) dose. I
100-
A 0
-
0
0
M KZFeO4
M K2Fe 04,2 T I M E S A DAY
IO-' M K 2 F e 04,1 T I M E / l D A Y 2x1Cj5M KzFe04,t TIME/lDAY
IOs5 M K z F e 04,ITIME/2DAY~ 80-
-
i
-
TIME ( D A Y S )
Flgure 3. Effect of ferrate(V1) concentration and frequency of treatment on film development.,
application could have been decreased further and still have accomplished adequate antifouling control by utilizing a 20-min contact period. The effect of frequency of treatment was considered in two different manners. In the first case the total concentration of ferrate per day was held constant while the number of treatments per day was varied. In the first experiments ferrate was added twice per day at M, and in second case 2 X M ferrate was added once a day. Both schemes appeared to be effective for preventing
Environ. Sci. Technol. 1883, 17, 125-127
film development. There did not appear to be a quantitative or qualitative difference in film development under either of these treatment regimes (Figure 3). In another series of experiments the concentration of ferrate was held constant, but the frequency of application was varied. In this case as treatment frequency varied, differences in the rate of film development were noted. Further, there appeared to be a different ferrate-film reaction depending on dosing frequency. In the case where ferrate was added every 12 h no observable film developed, and the few cells that were attached to the surface were atypical of cells in control film. When ferrate was added only once every 24 or 48 h, some film developed initially, and the cell types and organization were typical of that for control films. However, these films were weakly attached, and hence sloughed so that there remained little or no slime growth on any of the experimental slides by the end of the experiment. Control chambers from some of the experiments described above received a or M dose of ferrate for 20 min to test the ability of ferrate to detach an established film. it was noted that in all cases established films on slides prior to ferrate treatment were greater than 60 pm thickness. At concentrations of lo4 and lo6 M, potassium ferrate was unable to detach these established films, and after 24 h following treatment there was no significant difference between slides exposed to ferrate and controls. The optimal dose of ferrate(V1) appears to be slightly less than M when added every 1 2 h for these test systems. A contact time of 5 min was adequate and would be expected to be similar in waters with a lower pH and less buffering capacity as more of the oxidizing power
would be released in a shorter period of time. In waters containing high BOD it would probably be necessary to increase ferrate dose in proportion to the increase in BOD. However, in the model condenser system utilized for this study ferrate(V1) ion appears to be an effective antifoulant, as only short contact times are required for ferrate concentraions of M to maintain condenser cleanliness. Registry No. K2Fe0,, 13718-66-6. L i t e r a t u r e Cited (1) Mattice, J. S.; Zittel, H. E. J . Water. Pollut. Control Fed. 1976,48, 2284-2304. (2) Arthur, J. W.; et al. “Comparative Toxicity of Sewage Effluent Disinfection to Freshwater Aquatic Life”; USEPA Ecological Res. Series, 1975, 600/3-75-012. (3) Brungs, W. A. “Effects of Wastewater and Cooling Water Chlorination on Aquatic Life”; USEPA Ecological Res. Series, 1976, 600/3-76-098. (4) Waite, T. D.; Jorden, R.; Kawaratani, R. In ”Water Chlorination: Environmental Impacts and Health Effects”; Jolley, R. L., Ed.; Ann Arbor Science: MI, 1978; Chapter 59. (5) Waite, T. D.; Fagan, J. In “Condenser Biofouling Control”; Garey, J., Ed.; Ann Arbor Science: MI, 1980; Chapter 30. (6) Schreyer, J. M.; Ockerman, L. T. Anal. Chem. 1951,23, 1412. (7) Waite, T. D. J . Environ. Eng. Diu. (ASCE) 1979,105, No. EE6. Received for review February 8,1982. Revised manuscript received September 23,1982. Accepted October 22,1982. This work was supported by Grant RP-RP61-3 from the Electric Power Research Institute.
Cross-Contamination of Water Samples Taken for Analysis of Purgeable Organic Compounds Steven P. Levine” and Mark A. Puskar Department of Environmentaland Industrial Health, School of Public Health-I Michigan 48109
I, The Unlverslty of Michigan, Ann Arbor,
Paul P. Dymerski Analytics, Inc., Richmond, Virginia 23260
Beverly J. Warner and Charles S. Friedman Monsanto Research Corporation, Dayton, Ohio 4541 8
Analysis of volatile organic compounds in water, including chlorinated and aromatic species, is usually performed with U.S. EPA methods 601 and 602. The high sensitivity of the method combined with the use of a permeable cap liner and a screw cap with a center hole results in a potential for contamination and/or crosscontamination of samples. Results indicate that contamination and/or cross-contamination can occur through the silicone-Teflon cap of a vial but that this contamination will be low for the case of proximal storage of certain highand low-concentration samples. Introduction
Analysis of volatile organic compounds in water, including chlorinated and aromatic species, is usually performed with US.EPA methods 601 and 602 ( 1 , 2 ) . The 0013-936X/83/0917-0125$01.50/0
methods call for purge and trap concentration of the analytes prior to analysis by gas chromatography (GC) with electrolytic conductivity or photoionization detection or by mass spectrometric detection (MS) (3-6). This results in a limit of detection on the order of 1 pg of analyte/L of water (3). Samples are taken in headspace-free vi& that are fitted with center-hole screw caps and Teflon-lined silicone cap liners. The high sensitivity of the method combined with the use of a permeable cap liner and a screw cap with a center hole results in a potential for contamination and/or cross-contamination of samples. This was recognized in the original publication of the proposed methods 601 and 602 in which the following statement was made: “Samples can be contaminated by diffusion of volatile organics through the septum seal into the sample during their shipment and storage” (1,2). Up to now, no study has been made to quantitate this potential for con-
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