A.
ppm) but contained 36% of the total zinc and was the major reservoir of zinc in the sediment. Conclusion
I 80 -
8.
LEAD DISTRIBUTION E S 35
Acknowledgment The authors thank Dr. K. G. Tiller for collecting the sediment samples and Dr. J. D. G. Hamilton for assisting with the mineralogical analyses.
-?
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.-
c
2
2
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The heavy liquid density gradient technique has been shown to be suitable for the separation of the mineral components of near-shore sediments as a basis for the assessment of the concentration and distribution of heavy metals. Adequate sensitivity for the determination of lead, cadmium, and zinc in the density subfractions was obtained using either direct flame or graphite furnace atomic absorption spectrometry. The technique avoids the problem of nonselective dissolution encountered with chemical methods of determining metal distributions, and, as the present work has shown, provided that the sediments contain only a small proportion of discrete ultrafine particles, accurate and reproducible data can be obtained. The concentration and distribution patterns revealed should be useful in evaluating the environmental significance of contaminated sediments.
40-
Literature Cited (1) Piper, C. S., “Soil and Plant Analysis”, University of Adelaide, Adelaide, S. Australia, 1950. (2) Agemian, H., Chau, A. S. Y., Analyst (London), 101, 761-7 (1976). (3) Schmidt, R. L., Garland, T. R., Wildung, R. E., “Copper in Sequim Bay Sediments”, Battelle Pacific Northwest Laboratory Annual Report, Part 2, p 136, 1975. (4) Malo, B. A., Enuiron. Sci Technol., 11,277-82 (1977). (5) Subramanian, V., Experientia, 31 ( I ) ,12-3 (1975). (6) Muller, L. D., Burton, C. J., “The Heavy Liquid Density Gradient and Its Applications in Ore Dressing Mineralogy”, Proceedings of the Eighth Commonwealth Mining and Metallurgical Congress, Melbourne, Australia, Vol. 6, pp 1151-63, 1965. (7) Francis, C. W., Bonner, W. P., Tamura, T., Soil Sci SOC.4 m . Proc., 36 (21, 366-76 (1972). (8) Francis, C. W., Brinkley, F. S., Nature (London),260, 511-13 (1976).
0
x
d
20-
Figure 5. (A) Lead concentrations in the density subfractions of sediment ES 35 (-1000 10 pm). (B) Distribution of lead between the density subfractions of sediment ES 35 (-1000 10 pm). See Table I1 for a description of the subfractions
+
+
reduced still further if it could be shown that it was present as insoluble particulate matter. A different concentration-distribution relationship was observed for zinc in sample ES 26, where the organics subfraction had not only the highest concentration of zinc (490
Received for review June 2,1978. Accepted September 1,1978.
Coagulation and Direct Filtration of Humic Substances with Polyethylenimine Harold T. Glaser’ and James K. Edzwald” Department of Civil and Environmental Engineering, Clarkson College of Technology, Potsdam, N.Y. 13676
The National Organics Reconnaissance Survey by EPA indicated that the presence of trihalomethanes in drinking water is widespread in the U.S. ( 1 ) . The presence of these organics constitutes a public health problem since the occurrence of chloroform in potable water has been statistically associated as a cancer risk (2, 3 ) ; consequently, EPA has proposed a Primary Drinking Water Standard of 100 Fg/L for total trihalomethanes. Several investigators have shown that the chlorination of waters containing humic substances results in trihalomethane formation (4-7); Le., humic substances are Present address, James M. Montgomery, Consulting Engineers, Inc., 1990 N. California Blvd., Walnut Creek, Calif. 94596.
precursors in this reaction. Humic materials are also responsible for the natural color imparted to waters and are usually removed by coagulation with alum followed by sedimentation and filtration. Humic substances are amorphous, acidic, predominantly aromatic, hydrophilic, chemically complex polyelectrolytes or macromolecules. The substances exist in a range of molecular weights, from a few hundred to tens of thousands (€49)with a size estimated in the range of 3.5-10 nm (10). Humic substances are negatively charged macromolecules for the pH conditions of most natural waters and can be classified as colloidal matter due to their colloidal dimensions. pH will affect both the charge density and configuration of the humic macromolecules in solution. As the pH
0013-936X/79/0913-0299$01.00/0 @ 1979 American Chemical Society
Volume 13, Number 3, March 1979
299
A series of polyethylenimine polymers (cationic) with molecular weights from 600 to 50 000-100 000 was used in coagulation and direct filtration studies of humic acid at pH 5.5-6. Destabilization of humic acid is achieved where the optimum polymer dosage is independent of molecular weight; however, solidbiquid separation of floc in the jar tests is poor due to poor particle contact opportunities. The direct filtration of humic acid is an effective treatment process with
continuous polymer feed. The filter aid dosage can be selected from jar tests as coagulation and filtration are analogous. Polymer dosages which produce under- and overdosing in the jar test also produce identical effects in direct filtration. Greater head loss was observed for direct filtration without flocculation. A brief flocculation period results in particle aggregation, an increase in the mean size of the particles being applied to the filter bed, and lower head loss development.
is increased, increasing stability will result due to dissociation of carboxyl and phenolic functional groups. An extended configuration would be expected with increasing pH due to repulsion between charged functional groups. A reexamination of water treatment technology is needed to improve existing processes and to develop new processes for the removal of humic substances (trihalomethane precursors) from water supplies. The research reported here is a laboratory scale feasibility study of the direct filtration process for removing humic substances from water including an examination of the physical and chemical parameters which affect it. Specific objectives are: to examine the destabilization of humic acid by polyethylenimine; to determine if the filter aid dosage can be selected by a laboratory jar test; to examine the effect of flocculation on filter efficiency and head loss; and to examine the effect of polymer molecular weight on filter efficiency and head loss.
lowing molecular weight fractions (number average) were used: 600 (PEI-6), 1200 (PEI-12), 1800 (PEI-18), 40 00060 000 (PEI-6001, 50 000-100 000 (PEI-1000), and 60 00080 000 (PEI-1090). Humic acid concentrations were determined by measuring absorbance using a Bausch and Lomb Spectronic 710 spectrophotometer (420 nm, 5-cm cells) and comparing with a standard curve. Apparent color measurements were made at pH 6 with no pretreatment; true color measurements were made by filtering samples through a glass fiber filter and adjusting the pH to 11 prior to reading absorbance. Residual turbidity was measured with a Hach Model 2100A turbidimeter. A bench scale laboratory pilot filter was designed and constructed from 2.54 cm (1in.) i.d. plexiglass columns. This was a conventional downflow rapid sand filter operating a t 5 m/h (2 gal min-' f F ) . Sieved and washed Ottawa sand was used as the filter media with a geometric mean size of 0.6 mm, a bed porosity of 0.4, and a bed depth of 14 cm (5.5 in.). Color removal by direct filtration was investigated with and without flocculation prior to filtration as shown by the schematic diagrams in Figure 1. Flocculation time was varied using different size reaction vessels which were completely mixed to prevent particulate removal during the flocculation step. Prior to each run, the filter bed was precoated with concentrated polymer solution (1 g/L) and rinsed with distilled water to remove excess polymer. During the filter run, polymer was fed continuously at the desired dose. The effluent was analyzed for apparent color, turbidity, and pH. Head loss through the bed was monitored by a mercury manometer from taps on the filter column. A detailed explanation of these procedures is available elsewhere (11).
Methods The coagulation process was modeled by the standard laboratory jar test procedure. A synthetic colored water was prepared with 5 mg/L humic acid (Aldrich Chemical Co.) and 2 X 10-3 M NaHC03 for alkalinity and ionic strength. The pH was adjusted to 5.5-6 with 1N HC1 which was constant for all experiments. The PEI (polyethylenimine) series of polymers (Dow Chemical Co.) was used which permitted examination of the effect of molecular weight. Polyethylenimine is a highly branched polyamine produced by the acid-catalyzed polymerization of the monomer, ethylenimine ((22"s). The fol-
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Results and Discussion Destabilization of Humic Acid with PEI. Figure 2 shows
Polymer, Reservoir
Synthetic Water
No Flocculation Provided
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i
Polymer
n
Manometer Ta P Sand Bed Synthetic Water
Floccu iati on Reactor
1Monometer
Flocculation Periods of 73,13, and 30minutes Figure 1. Schematics of
filtration apparatus used for experiments with
0-, 7.3-, 13-, and 30-min flocculation time
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Environmental Science & Technology
results of jar tests performed on synthetic water with PEI-6 and -1000. The optimum dose for PEI-6 is 0.8-1.0 mg/L and for PEI-1000 it is approximately 3 mg/L. Over- and underdosing are observed in both cases. At the optimum dose, apparent color removal is about 50% for PEI-6 and nonexistent for PEI-1000. Turbidity removal is also poor. Visual inspection of the jars indicated formation of small unsettleable floc. The removal of true color indicates that destabilization of the humic acid has occurred, but sedimentation is not effective. This can be explained as follows. Initially, perikinetic flocculation is rapid due to a large number of submicron humic particles; however, as the particles are aggregated to the micron size range, the particle number decreases and the formation of large aggregates by orthokinetic flocculation is limited due to low rates of particle contacts. Therefore, the jar test is a satisfactory model for determining the optimum polymer dosage for destabilization but for these colloidal systems good solid/liquid separation is not achieved. A stoichiometry between the initial humic acid concentration and the optimum dose is shown by the results in Figure 3 for two PEI polymers of widely different molecular weights. These stoichiometric results are summarized in Table I. In addition, other jar test experiments involving 5 mg/L humic acid showed the optimum polymer dosages to be 0.8-1.0 mg/L
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Initial Humic Acid Concentrotion IOrng/1 5mg// A 2 5mgN True Color
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