the last to condense on the particles as they formed. This is probably true for elements such as sulfur, arsenic, and molybdenum. However, there is also the possibility that surface enrichment can occur by diffusion of trace elements from the inside of the particle. Figures 2 and 6 show evidence that ions are mobile enough for this to occur. Individual mullite crystallites shown in Figures 2 and 6 have diameters as large as 1-2 pm. Since Na, Mg, K, and Ca are excluded from these crystals, we have clear proof that they can diffuse over distances greater than 1-2 pm. The attraction of certain elements to the surface from inside the particle can be explained in terms of the Gibbs adsorption isotherm, which states that surface free energies decrease when solutes form surface excesses. We believe that diffusion from the inside of fly ash particles can definitely contribute to surface enrichments, but we cannot account, at this time, for observations that small particles have higher bulk concentrations of trace elements without invoking additional mechanisms that we cannot defend. The authors have plans to perform surface analyses and surface tension measurements on remelted slag and fly ash material in which the molten state will be maintained long enough for equilibrium definitely to be established. If we still observe surface excesses of trace elements, our proposed mechanism of enrichment will be more credible.
Acknowledgment The authors would like to express their gratitude to the Electric Power Research Institute (EPRI), Palo Alto, Calif., for the generous funding and encouragement that they have given to this work. We are especially indebted to Dr. Ralph Perhac of EPRI who has given us valuable technical advice as well as administrative guidance. We are also grateful to our
colleague, W. S.Lyon, the ORNL project manager of this work, for his excellent technical and managerial help. Ralph R. Turner, of the ORNL Environmental Science Division, is conducting a research effort on the leaching of fly ash that is parallel to ours. His expertise in the collection and documentation of our samples is gratefully acknowledged.
Literature Cited (1) Hulett, L. D., Emery, J. F., Dale, J. M., Weinberger, A. J., Dunn, H. W., Feldman, C., Ricci, E., Thomson, J. O., “Proceedings: Advances in Particle Sampling and Measurement”, EPA-600/7-79065, Feb. 1979, p 355. ( 2 ) Hulett, L. D., Weinberger, A. J., Northcutt, K. J., Ferguson, M., Lyon, W. S., EPRI Project RP1061, Final Report, in preparation. ( 3 ) Goldstein, J . I., Yakowitz, H., Ed., “Practical Scanning Electron Microscopy”, Plenum Press, New York. (4) Holt, D. B., Muir, M. D., Grant, P. R., Boswarva, I. M., Ed., “Quantitative Scanning Electron Microscapy”, Academic Press, New York. (5) . . Yakowitz. H.. Mvklebust. R. L.. Heinrich. K. F. J.. Natl. Bur. Stand. ( U . S . )T e c i . Note, No. 796 (1973). ’ (6) Mazdiyasni, K. S., Brown, L. M., J . Am. Ceram. Soc., 55, 548 (1972). (7) Cameron, W. E., Am. Mineral., 62,747-55 (1977). ( 8 ) Cameron, W. E., Ceram. Bull., 56(11), 1003 (1977). (9) Mazdiyasni, K. S., Air Force Materials Laboratory/LLM, Wright-Patterson Air Force Base, Ohio 45433, private communication. (10) Linton, R. W., Williams, P., Evans, C. A,, Natusch, D. F. S., Anal. Chem., 49,1514 (1977). (11) Smith, R. D., Campbell, J. A,, Nielson, K. K., J . Am. Chem. SOC., 13,553-8 (1979).
Received for review July 2, 1979. Accepted April 18,1980,Research sponsored by the Office of Energy Research, U.S. Department of Energy, under Contract W-7405-eng-26 with the Union Carbide Corporation.
Total Organic Halogen as a Parameter for the Characterization of Reclaimed Waters: Measurement, Occurrence, Formation, and Removal Martin R. Jekel Engler-Bunte Institute, Department of Water Chemistry, University of Karlsruhe, D-7500 Karlsruhe, West Germany
Paul V. Roberts” Environmental Engineering and Science, Civil Engineering Department, Stanford University, Stanford, Calif. 94305
A modified determination method for total organic halogen (TOX) is described, whereby purgeable and nonpurgeable fractions are measured separately. The detection limits are 0.03 pmol/L halogen for the purgeable fraction and 1.0 pmol/L halogen for the nonpurgeable fraction. The precision is -5%. Data are presented from two water-reclamation facilities in California. The treated wastewater (secondary effluent) contains 1.0 to 10 pmol/L TOX, mostly in the nonpurgeable fraction. The mole ratio of organic halogen to organic carbon is approximately 0.4 to 1.2%. Nonpurgeable halogenated organics are formed during chlorination. The halogenated compounds are removed in several treatment steps: air stripping is effective in decreasing the concentration of the purgeable fraction; activated-carbon and reverse-osmosis treatment substantially reduce the concentration of the nonpurgeable fraction. The halogenated organics remaining after water reclamation appear to be highly mobile in the ground water environment. 970
Environmental Science & Technology
In analyzing organic material in water, two different approaches are possible. The first uses surrogate, collective, or group parameters, such as total organic carbon (TOC), chemical oxygen demand (COD), biological oxygen demand (BOD),total organic halogen (TOX), UV absorbance, or fluorescence, to provide general information about water quality. Group parameters are especially useful in process control since they can be determined within a short time with relatively simple equipment. A disadvantage of this approach is the lack of information concerning the multitude of specific organic substances present. The second approach involves the specific analysis of organic micropollutants, by means of gas chromatography and mass spectrometry (GC/MS). It provides very detailed information on compounds, often permitting inferences as to their sources and fates. The determination procedure starts generally with an enrichment step, sometimes in conjunction with chemical derivatization, and requires sophisticated GC/MS equipment with a data-processing system and skilled personnel.
0013-936X/80/0914-0970$01 .OO/O
@ 1980 American Chemical Society
Application of specific analysis in water characterization has led to the identification and quantification of numerous organics, especially in polluted surface water, drinking water, and wastewaters. Of special interest are halogenated compounds, since they generally do not occur in natural freshwater systems and are therefore indicators of anthropogenic pollution. They are considered to be toxic, mutagenic, and carcinogenic, and hence of health concern. Their importance is reflected in the fact that more than half of all priority pollutants, as designated by the U S . Environmental Protection Agency ( I ), are halogenated organics. By comparing the data from TOX determinations and trace organics analysis by GC/MS with data from river waters (2, 31, it was observed that only minor portions of all halogenated micropollutants were amenable to identification by GC. More polar, nonvolatile, and high molecular weight halogenated compounds presently can be detected conveniently only by the parameter TOX, which was first introduced in German drinking-water research ( 4 , 5 ) . It has not yet been applied widely in wastewater research. The subject of this paper is to evaluate the possible role of TOX as a parameter in wastewater treatment, especially in water reclamation, where quality objectives are similar to those of drinking water treatment. The experimental procedure is described. since it is in part novel. Data are presented from two water reclamation facilities and from one ground water recharge site. Experimental
Background. The methods for determination of total organic chlorine (TOC1) or halogen (TOX) thus far developed for the most part entail: concentrating the organics by adsorption; using nitrate to avoid interference of inorganic chloride by washing to displace chloride (Cl-) from the sample (4-6) and/or by adding to the sample to hinder the adsorption of chloride ( 7 ) ;and converting organic halide to hydrogen halide by pyrohydrolysis ( 4 , s )or controlled combustion (6). T h e adsorption has been achieved by means of small granular carbon filters ( 4 ) ,powdered activated carbon (51, or small packed columns of ground carbon (6). Halogens were detected by titration ( 4 , 5 ) ,specific ion electrodes ( 5 ) ,or microcoulometer (6, 8 ) . On-line coupling of a microcoulometer is advantageous, since it permits sample volumes of 100 mL or less to be used, eliminates the need for collecting a pyrohydrolysate, and directly measures all of the organic halogen adsorbed onto the carbon ( 7 , 8 ) . It was reported that organic bromide was detected only incompletely with pyrohydrolysis ( 6 ) ,whereas in a controlled combustion with diluted oxygen, bromide was quantitatively detected ( 7 ) . Jekel and Reinhard (9) have shown an excellent correlation between a purgeable fraction of organic halogen (POX) and the sum of the amount, of halogen contained in compounds analyzed by gas chromatography. Dressman et al. ( 1 0 ) also have demonstrated the usefulness of relating the quantity of organic halogen that can be inferred from gas chromatographic analysis of water samples to the quantity measured collectively as organic halogen. An alternative procedure for determining TOX has been proposed ( I I ) in which organic constituents are concentrated onto XAD resin rather than activated carbon. The XAD method has been used to characterize the products of water chlorination (12),as well as the halogenated organic constituents of water supplies ( I I). The XAD method was not investigated in the work reported here. Procedure f o r Organic Halogen Determination. Volatile halogenated organics can prove difficult to concentrate onto activated carbon, since they are stripped easily from solution and adsorb poorly. Preliminary tests showed that chloroform a t a concentration of about 120 pg/L in tap water (TOC about
1 mg/L) is removed only to about 85% from a closed system without headspace in a two-step batch adsorption on powdered active carbon. Therefore. a procedure was evaluated to determine the purgeable organic halogen (POX) prior to the carbon-adsorption step, in which the nonpurgeable amount of T O X (NPOX) is measured. Figure 1 is a schematic representation of the laboratory equipment used for these two separate determinations. Water samples of 50 mL are filled by pipet into a gas-wash bottle similar to that used in the closed-loop stripping analysis ( 1 3 ) . A gas mixture of 50% O2 and 50% Ar with a total flow of 200 mL/min is used for stripping. The gas stream containing volatile organics passes directly into a furnace (Lindberg Model 55035 tube furnace) with a quartz tube at 850 "C, where the organics are oxidized. The chloride and bromide are detected on-line by a microcoulometer (Envirotech-Dohrmann, Model C300). The duration of the stripping is 10 min, after which the headspace is blown free of organics by switching the gas flow to the side inlet and the microcoulometer signal reaches the base line within 3 t o 4 min. Tests showed that within this time about 90% of the total POX is detected, while the residual POX of 10% needs extended stripping times. A 40-mL aliquot of the purged sample is transferred to a beaker to which KNO:i is added to establish a concentration of 0.01 N to suppress chloride adsorption. The pH is adjusted to 3 with sulfuric acid to enhance adsorption of organic acids ( 5 ) . Twenty milligrams of activated carbon (Calgon F400, 100-200 mesh) is added by pipetting 2 mL from a well-mixed suspension of 10 g of carbon/L of organic-free water (Milli-Q). Homogenizing is achieved by a n ultra-high-speed mixer (U1traturrax SDT, Janke & Kunkel). The sample is stirred for 45 min. Carbon and suspended solids are filtered off by 0.4-pm membranes (Nuclepore). Twenty milligrams of carbon is added for the second adsorption step and, after 45 min of stirring, is filtered off onto the first carbon cake or onto a fresh membrane for a separate determination. The carbon cakes are washed with 6 to 10 mL of 0.05 N KNO:{solution (pH 3 ) for a t least 15 min to avoid interference of chloride in the pore water. The carbon is transferred to a platinum boat, inserted into the furnace a t 850 "C, and combusted in an atmosphere of 50% 0 2 and 50% Ar a t a total gas flow of 200 mL/min. Halogens are detected on-line by the microcoulometer. Since the freshly ground activated carbon contains some halogens that are not removable by a nitrate wash, a blank determination is necessary. Twenty or forty milligrams of carbon is filtered off from the 10 g/L suspension, washed with nitrate solution, and combusted. The blank contribution with a freshly prepared suspension is approximately 10 nmol of halogen/40 mg of activated carbon. Storage over several weeks led to an increase of the blank to 20 nmol of halogen/40 mg of C, presumably as a result of adsorption of halogenated or-
02/Ar
A BOAT INLET SYSTEM
-7-l
( 850.)
MICROCOULOMETER
PURGING SYSTEM
Figure 1. Laboratory equipment used for determination of POX and NPOX Volume 14, Number 8, August 1980
971
ganics from the laboratory environment. A series of system blank determinations (80 replicates) was conducted in which organic-free water (Milli-Q) was taken through the entire NPOX procedure. The system blank value determined in these experiments was 21.2 f 6.4 pmol of halogen per 40-mL sample (or equivalently per 40 mg of activated carbon). Hence, it is clear that the contribution of activated carbon predominates in determining the system blank value. The detection limits are approximately 0.03 pmol/L halogen for the POX procedure and 1.0 pmol/L halogen for the NPOX determination. The detection limit is taken as that concentration a t which the response is double that of the system blank. Procedure for GC Analysis. Determination of specific volatile compounds was accomplished by gas chromatography analysis (GC),following enrichment of the organic solutes by pentane extraction (14).A 1-mL quantity of analytical grade pentane (Burdick and Jackson Laboratories, Inc.) was injected into each of the sealed 60-mL hypovials (Pierce Chemical Co., Rockford, Ill.) containing the samples, and the displaced water was discarded. A prescribed amount of 1,2-dibromoethane was injected for use as an internal standard. The samples were agitated a t 300 rpm for 30 min on a gyrorotatory agitator. Then the samples were allowed to settle until a clean interface formed between the organic and the water phases. A 5-pL aliquot of the pentane phase was withdrawn with a syringe and injected into the gas-liquid chromatograph (Tracor MT-200). The gas-liquid chromatograph was equipped with a linearized electron capture detector (63Nip source) with a 20-pg detection limit. The GC column consisted of 10% squalane on 80-100 mesh Chromosorb W. Concentrations of organic compounds were quantitated by integrating the respective peak areas (Spectra Physics integrator) and comparing with the peak area of the internal standard. Recovery factors for the individual compounds are determined after each GC column change, and thereafter a t regular intervals. The detection limit of the method was approximately 0.1 pg/L for the compounds reported here.
Test of the Procedures for Organic Halogen. Some preliminary investigations were concerned with: a correlation of POX with the halogen content of specific trace organic compounds analyzed by GC; the efficiency of the batch carbon-adsorption procedure; possible interference by inorganic chloride (4-7); and the repeatability of determinations. Table I shows for 10 different reclaimed water samples the concentrations of 8 trace organics commonly found in waters, the theoretical POX calculated from the halogen content of these compounds, and the POX experimentally determined in duplicate samples. The POX data correspond closely to the value predicted by summing the concentrations of compounds determined by GC. This indicates that these trace organics are quantitatively determined by the purging procedure and that the POX value provides useful information about the contribution of volatile organics to the total amount of halogenated organics. Recovery efficiency and possible chloride interferences in the carbon-adsorption procedure were investigated by analyzing solutions of dichlorophenol and bromophenol of adjusted concentrations in the presence of 0,100, and 500 mg/L chloride. Table I1 presents the data from a two-step adsorption procedure. Recoveries of the two phenols were in the range of 94 to 98%, which is considered satisfactory. A third adsorption step perhaps would increase the recovery further. However, minor losses may be inevitable, since carbon grains trapped in the membrane pores during the carbon transfer from the membrane into the combustion boat may be in part responsible for the incomplete recovery of the phenols. Interferences by inorganic chloride, which would lead to recoveries higher than loo%, were not encountered in the concentration range studied. Nitrate addition to the water sample and the wash procedure apparently are sufficient to prevent the adsorption of chloride and to remove it from the pore water. Adsorption efficiency and precision of the NPOX procedure were tested with samples of wastewater that had received activated-sludge treatment. Adsorption was carried out in
Table 1. Comparison of Trace Organics with Purgeable Organic Halogen (POX) sample no.
1 2 3 4
5 6 7
a 9 10 a - signifies
CHC13
C13CCH3
CC14
13.2 13.9 13.9 12.4 16.9
10.6 17.1 13.2 13.1 106
0.15 0.85 0.65
12.9 4.5 3.1 1.2 0.7
34.2 1.2 2.0 0.3 0.5
-a -
specific compounds, pglL CHC12Br CI,$=CHCI
3.6 4.4 3.1 2.4 2.0 1.3 3.0 0.3
I
20.3 8.9
0
-
0.7
-
CHCIBr2
C12C=CCIz
3.6 4.3 2.9 1.8
0.1 0.1 0.2 0.1
0.8
0.5 1.6 0.4
72.7 24.4 0.2 1.2
0.6
-
-
CHBr3
4.7 5.2 4.0 1.o
-
POX, pmol/L calcd found
0.82 1.04 0.87 0.70 5.07 1.92 0.22 0.16 0.06 0.03
0.79 0.82 0.70 0.73 4.79 2.17 0.16 0.14 0.08 0.06
below detection limit, approximately 0.1 bg/L.
Table II. Recoveries and Effect of Chloride Interferences in NPOX Determinations of Halogenated Phenols (Sample Volume 50 mL)
972
organic cornpd
pmol
dichlorophenol bromophenol dichlorophenol bromophenol dichlorophenol bromophenol
0.1419 0.1466 0.1419 0.1446 0.1419 0.1446
Environmental Science & Technology
lnorganlc chlorlde, mglL
0 0 100 100 500 500
NPOX found, prnol step 1 step 2
0.1278 0.1325 0.1 177 0.1318 0.1166 0.1162
0.0108 0.0073 0.0179 0.0087 0.0198 0.0193
sum of steps 1 2, prnol
recovery,
0.1386 0.1398 0.1356 0.1405 0.i364 0.1355
98 97 96 97 96 94
+
Yo
Table 111. Adsorption Efficiency and Repeatability of NPOX Determination in Secondary Effluent sample determ.
VOI,
no.
mL
pmol of NPOX found in step 1 step 2 step 3
1 2 3 4
50 50 50 50
0.172 0.159 0.168 0.173
0.030 0.024 0.021 0.016
0.008 0.008 0.009 0.006
av std deviation
NPOX, pmol/L
4.20 3.82 3.96 3.90 3.97 f O .16
three sequential steps, each with 20 mg of powdered activated carbon. The water sample contained less than 0.1 pmol/L POX; therefore, the purging procedure was not applied before the adsorption. Results are presented in Table 111. A third adsorption step leads to only a minor increase in observed NPOX, generally less than 5% of the sum total for the three steps. The standard deviation was -4% for four replicates. The two-step adsorption procedure was considered sufficient for the detection of about 95% of halogenated organics determinable with the method described. In tests with activated sludge effluents and reclaimed water samples, -85% of the TOC was adsorbed using this procedure. Hence, we believe that the method described offers a useful approximation of the amount of organically bound halogen present in reclaimed water samples. However, it cannot be stated unequivocally what fraction of the total organic halogen is recovered, for the obvious reason that the true concentration is unknown. Problems might be encountered with heavily polluted waters, where higher carbon dosages are necessary, or waters with considerable amounts of poorly adsorbing constituents. Description of Field Sites. The occurrence and removal of TOX were investigated a t two water-reclamation facilities in California. The first of these is Water Factory 21, operated by the Orange County Water District. The treatment-plant influent is secondary effluent from activated-sludge treatment. Reclamation treatment consists of high-lime treatment, ammonia stripping, recarbonation, chlorination (6-10 mg/L), dual-media filtration, and granular activated-carbon adsorption. One-third of the carbon effluent undergoes reverse osmosis to meet the standards for TDS; the rest is disinfected with chlorine (25ppm). The facility and its performance are described by McCarty and Argo (16) and Reinhard et al. (17). The second advanced wastewater-treatment plant investigated here is the Palo Alto Reclamation Facility operated
by the Santa Clara Valley Water District (SCVWD). As in Orange County, reclaimed water is used for direct well injection into a confined aquifer, as a remedy for saltwater intrusion. The influent has been treated in a conventional activated-sludge process. The advanced-treatment sequence consists of chlorination, high-lime treatment, ammonia stripping, recarbonation, ozonation, filtration, activatedcarbon adsorption, and final disinfection with chlorine. The reclamation facilities have been described elsewhere (18). The tertiary effluent of the Palo Alto reclamation plant is directly injected into a confined aquifer. Hydrologic conditions and water quality transformations have been reported elsewhere (19). The experimental injection site consisted of an injection well (11) and several surrounding observation wells a t different distances from 11. Results from the observation wells P 5 (10 m from 11) and P7 (40 m from 11) are presented. The water reaches the observation wells from the injection well by flow horizontally through an aquifer consisting of silty sand. The aquifer material has an organic carbon content of 0.25%, a clay content of 2%, and a total cation-exchange capacity of 0.12 mequiv/g dry weight. The approximate retention time of the water in the aquifer was 17 h for well P 5 and 270 h for well P7. Results a n d Discussion Water Factory 21. Data are summarized in Table IV for POX, NPOX, TOX, and TOC for the period February to June 1979, determined in 6 to 13 samples from different treatment steps at water Factory 21. In addition, the percent molar ratio of total organic halogen to total organic carbon is given as a measure of the degree of halogenation of organics. Apparently, most of the halogenated organics in the samples from Water Factory 21 are not purgeable, since the NPOX category accounts for more than 90% of the TOX. The purgeable organics obviously are removed effectively during stripping processes and to a lesser extent by activated carbon. The POX reduction by the reverse-osmosis plant is due to volatilization in a stripping tower used for decarbonation. Both chlorination steps, with a dose insufficient to reach the breakpoint, increase POX by formation of trihalomethanes (THM),known byproducts of chlorination (20).The increase of the NPOX concentration during chlorination reveals that much more, up to 10-fold, of these substances are formed. In terms of quantity, the THMs obviously are only minor contributors to the TOX formed in chlorination. Similar ratios of formation of nonvolatile halogenated organics previously have been observed in studying the chlorination of river water (21) and of deionized water containing humic acids ( 2 2 ) . Substantial removal of NPOX occurs in lime treatment, activated-carbon adsorption, and in reverse osmosis (RO) a t
Table IV. Organic Carbon and Organic Halogen Concentrations in Water Reclamation at Orange County Water Factory 21 concentratlonsa wmol/L
TOXITOC, mol of halogen/
treatment
TOC,
effluent
mg/L
POX
NPOX
TOX
mol of C
POX
NPOX
n
secondary effluent lime treatment
12.4 10.0
n.a.= n.a.
4.03 3.07 2.96 5.97
4.42 3.46 3.02 6.27
0.0043 0.0042
NH3 stripping
0.39 0.39 0.06 0.30
2.02 2.32 1.12 1.73
1.15 1.16 1.17 1.36
13 12 7 13
0.18 0.34 0.07
3.83 4.37 0.87
4.01 4.71 0.94
0.0078
1.31 1.79 1.70
1.52 1.11 1.40
10 6 10
recarbonation, chlorination
n.a. ma.
spread factor S b
(6-10 mg/L C12),
filtration activated carbon disinfection (25 mg/L CI2) reverse osmosis and decarbonation a
Geometric mean of
6.2
ma. 2.6
ma. 0.0043
n samples. Spread factor is the antilog of the logarithmic standard deviation (base 10). n.a. = not analyzed.
Volume 14, Number 8, August 1980
973
Table V. Halogenated Organics in the Santa Clara Valley Water District Reclamation Facility at Palo Alto treatment
effluent
activated sludge chlorination (14 mg/L CI2) lime treatment, ammonia stripping, recarbonation, ozonation, and filtration activated carbon chlorination (4 mg/L CI2) a
TOXrrOC, mol of halogen/
concentratlonsa pmollL
TOC, mg/L
POX
NPOX
TOX
mol of C
POX
NPOX
n
11.2 10.8 8.1
3.00 3.34 1.23
3.20 4.80 4.18
6.20 8.14 5.41
0.0066 0.0090 0.0080
1.69 1.52 2.26
1.53 1.12 1.40
6 6 6
2.3 2.2
0.39 0.39
1.55 1.94
1.94 2.33
0.0101 0.0127
1.30 1.53
1.41 2.65
6 6
spread lactor S b
Geometric mean of n samples. Spread factor is the antilog of the logarithmic standard deviation (base 10).
Water Factory 21. Without the final RO treatment, designed for desalination, the tertiary treatment system is not capable of reducing NPOX compared to the plant influent, since the TOX formation in chlorination steps outweighs the elimination in lime treatment, air stripping, and GAC treatment. The molar ratio of TOX/TOC indicates that nevertheless only small amounts of organic carbon bear chlorine or bromine atoms. But it is apparent that this ratio increases during the treatment sequence because of chlorination. I t can be anticipated that the overall performance of the tertiary treatment system with respect to TOX would be improved if the chlorine dose could be reduced or eliminated. Palo Alto Reclamation Facility. Data obtained a t the Palo Alto Reclamation Facility during the period April to June 1979 are presented in Table V. Fresh activated carbon had been filled into the contactors immediately prior to the sample series, explaining their good performance. Ammonia was present a t a concentration of about 20 mg/L. Therefore, it can be inferred that the chlorine residual was in combined form, principally as monochloramine. The Palo Alto secondary effluent contains considerable amounts of volatile halogenated organics, since the POX represents about 50% of the TOX. The major contributors to the POX are chemical solvents, such as trichloroethane, trichloroethylene, or tetrachloroethylene. Within the treatment sequence the TOX increases during both chlorination steps. Most of the rise is due to formation of high molecular weight compounds, as indicated by the change in NPOX. The ratio of nonpurgeable to purgeable organics formed during the first chlorination step is ANP0X:APOX = 51. In the second chlorination step, a significant increase was observed in NPOX, but not in POX. While the volatile organics are effectively removed by purging in the processes of ammonia stripping, recarbonation, and ozonation, the nonpurgeable compounds are eliminated poorly. Only the fresh activated carbon is capable of substantially reducing the concentration of NPOX as well as of POX. Overall organics (TOC) are, however, removed better than halogenated compounds, as indicated by the increase in the TOX/TOC ratio during the treatment sequence. The results of TOX determinations of ground-water samples influenced by recharge with reclaimed water are presented in Figure 2. At the start of the TOX measurement period, the injection well I1 had been operating for about 5 months. The concentration of organics measured as TOC decreased from I1 to P 5 by about 25% and from I1 to P7 by about 50%,presumably by biodegradation (19).The significant drop in TOX concentration a t I1 during the observation period is attributed to the change from exhausted to fresh granular activated carbon in the treatment plant. The concentrations a t both wells P5 and P7 respond rapidly following 974
EnvironmentalScience 8 Technology
the change in input. There is no significant change or lag in concentration between the injection and observation points. Hence, we infer that the organic halogen in the injected water must be associated for the most part with compounds that are poorly degraded and poorly adsorbed. The molar concentration of TOX was approximately five times higher than the purgeable fraction, indicating that the bulk of the organically bound chlorine and bromine is incorporated into nonvolatile compounds, sufficiently polar or high in molecular weight so that they are difficult to analyze and are poorly retained by sorbents such as activated carbon or aquifer material. Ratio of NP0X:POX. The ratios of NP0X:POX found in this work ranged from approximately 1 to 50, depending on the sampling point. The lowest value (approximately unity) was found in Palo Alto secondary effluent; the highest value (50) was observed after air stripping at Water Factory 21. The ratio of NP0X:POX formed during the first chlorination step was approximately 12 a t Water Factory 21 and 5 a t Palo Alto. In previous studies of organic halogen formation during chlorination (21, 2 2 ) , ratios of nonvolatile to GC-analyzed volatile products had been reported in the range of 5 to 10 on an equivalent basis. When XAD resin is used for concentrating organics in the NPOX procedure, the amount of nonvolatile organic halogen formed during chlorination is approximately equal to the amount of volatile organic halogen (12). This
TOTAL ORGANIC HAUGEN TTOX)
FRESH WIC AT RELAMdTIOt. F p u L i w
0
60
70
80
90
100
110
120
I?;O
INJECTED VOLUME ( IO’rn’)
Figure 2. The breakthrough of total organic halogen (TOX) at observation wells P5 and P7 at the Palo Alto groundwater recharge site
suggests that recovery of substances containing organic halogen is less complete when XAD resin rather than activated carbon is used as the adsorbent in determining organic halogen ( 2 3 ) .
Conclusions The effects of physical-chemical treatment on the behavior of TOX were studied a t two water reclamation plants. The addition of chlorine for disinfection purposes was identified as the main problem in the treatment sequence, where chloramines as biocides were formed. Considerable increases in organic halogen were observed, especially in the nonpurgeable fraction. The TOX increases were higher in chlorination steps prior to activated carbon treatment, since the concentration of precursor material was much higher there. The addition of chlorine was also mainly responsible for the general increase in the degree of halogenation, expressed as the molar ratio of TOX/TOC. This ratio was generally in the range of 0.4 to 1.2% in the cases studied. Halogenated organics were partially removed in several treatment processes. Volatile compounds (POX) were effectively purged in processes such as ammonia stripping or decarbonation, and are adsorbed onto activated carbon to some extent. Significant reductions in NPOX were observed in lime treatment, activated-carbon adsorption, and reverse osmosis. The high removal efficiency of reverse osmosis is believed to be explainable in terms of the presumed high molecular weight of the nonvolatile compounds contributing to NPOX. The removals achieved in such processes are offset by the formation of chlorinated byproducts, especially NPOX, in chlorination. This is observed even where the chlorination breakpoint is not reached. Undesired formation of halogenated organics presumably can be mitigated by: reducing chlorine dose; shifting chlorination to points where precursor concentrations are lower; or using alternative disinfectants, such as ozone or chlorine dioxide. Further study is needed to evaluate the efficacy of such measures. Study of the transport and fate of halogenated organics in a ground-water recharge system reveals that these compounds in the aggregate are transported through the aquifer rapidly and with little change in overall concentration. It is inferred that the substances behaving in that manner are poorly biodegradable and weakly adsorbed on aquifer material. Considering the potential health effects of halogenated organics in drinking water, their removal should be considered a major treatment objective in water reclamation. I t appears that the halogenated organics occurring in treated wastewater effluents are for the most part difficult to analyze as individual compounds using methods that rely on purging or solvent extraction for enrichment prior to gas chromatography. A t present, the most promising possibility for comprehensive, quantitative measurement is to determine collective parameters such as POX, NPOX, and TOX. Additional research is needed to ascertain the accuracy of organic halogen measurements, and to elucidate the nature of the substances that contribute to the overall quantity.
Acknowledgments The authors thank the Orange County Water District and the Santa Clara Valley Water District for their cooperation in sampling, and Martin Reinhard, Gary Hopkins, John Kissel, and ,James Graydon for providing data used in this paper. Literature Cited (1) U S . Environmental Protection Agency, “Recommended List of
Prioritv Pollutants”. Washineton. D.C. Effluents Guidelines Division,i97’i (2) Stieglitz, L., Roth, W., Kuhn, W., Leger, W., Vom Waaser, 47, 347-77 (1976). ( 3 ) Stieglitz, L:, Roth, W., Prepr. Pap. N a t l . Meet. Diu.Enuiron. Chem. Am. Chem. SOC.,19(1), 330-2 (1979). (4) Kuhn, W., Ph.11. Thesis, University of Karlsruhe, West Germany, 1974. (5) Kuhn, W., Fuchs, F., Sontheimer, H., 2. Wasser Abumser Forsch., 10(6), 162 (1977). (6) Takahashi, Y.. paper presented at the proceedings of the EPA/ NATO-CCMS Conference on Adsorption Techniques, Reston, Va., May 1979. ( 7 ) Dressman, R. C., McFarren, E. F., Symons, J. M., paper presented at the Proceedings of the American Water Works Association Water Quality Technology Conference, Kansas City, Mo., Ilec 1977. (8)Coulson, D. M., Cavanagh, I,. A., Anal. (‘hem., 32, 1245-7 (1960). (9) Jekel, M. R., Rpinhard, M., paper presented a t the Pacific Conference on Chemistry and Spectroscopy, Pasadena, Calif’., Oct 10-12,1979, (10) Dressman, R., Najar, R., Redzikowski, R., paper presented a t the Proceedings of the American Water Works Association Water Quality Technology Conference, Philadelphia, Dec 7 979. (11) Glaze, N. H., Peyton, G. R., Rawley, R., Enuiron. S c i . T e c h n ~ ~ l . 11,68.5-90 (1977). (12) Oliver, €3. G., Can. R e s . 11(6), 21L2 (1978). (13) Groh, K., Zurcher, F., J . Chromatop., 117, 285-94 (1976). (14) Henderson, J . E., Peyton, G. R., Glaze, W. H., in “Identification and Analysis of Organic Pollutants in Water”, Keith, L. H., Ed., Ann Arbor Science Publishers, Ann Arbor, Mich.. 1976, p p 10511. (15) Trussell, A. R., Uinphres. M. D., Leong, I,. Y. C., Trussell, R. R., J . Am. Water Works Aasoc., 71, 385--9 (1979). (16) McCarty, P. L., Argo, D., “Water Factory 21. Reclaimed Water, Volatile Organics, Virus and Treatment Performance”, KTISPB-285Ot58/5U‘P, Stanford University. June 1978. (17) Reinhard, M., Dolce, C. .J., McCarty, P. L., Argo, I). G., J . Enuiron. Eng. Diu.. Ani. SOC.c‘iu. Eng:.,105, 676-93 11979). (18) Roberts, P. V., McCarty, P. I,., Roman, W. M., J . Eniliron. Eng. Diu.,Am. SOC.Civ. Eng., 104,938-49 (1978). (19) Roberts, P. V., Schreiner, .J., Hopkins, G. D., paper presented at the Proceedings of the Symposium on Wastewater Reuse for Groundwater Recharge, Pomona, Calif., Sept 6-7, 1979. (20) Bellar, T . A., Lichtenberg, J . J., Kroner, R. C., J . Am. Water Works As.\oc., 66(12), 703-6 (1974). (21) Sontheimer, H., Heilker, E., Jekel, M. R., Nolte, H., Vollmer, F. H., J . Ani. Water Works Assoc., 70(7), 393-6 (1978). (22) Sander, R.. Kuhn, W., Sontheimer, H., 2.Wasser Abu.asser Forsch. 10(5), 155 (1977), (23) Glaze, W.H., Kinstley, W , , Saleh, F. Y., paper presented a t the Third Conference on Water Chlorination, Colorado Springs, Colo., Oct 28-Nov 2, 1979. Received for reuieu November 5, 1979. Accepted April 21, 1980. The investigations presented were performed under grants from the Ministry of Research and Techndory. Federal ReDublic, of Germany (02-W T 863), and the U S . E n u h n m e n t a i Protection AgencY (EPA-R-804431).
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