were not large. Overall, more volatile organic sulfur compounds were found in the experiment under an air atmosphere. This is somewhat surprising since others (3, 7) have reported that aeration reduced the quantity of volatile sulfur compounds. The total quantities of organic volatiles collected upon incubation of fresh poultry manure for 90 days under air and argon are given in Tables I1 and 111, respectively. The total amounts were generally less from the samples with the drying tubes than from those without. This was expected because the CaC12 had decreased the recovery of standards by approximately 2090. The volatiles recovered from the argon incubated samples represented about 1%of the dry matter in the samples. Aeration of manure is generally considered to reduce or eliminate the odor problem; oxidation ditches are one means of handling manure to minimize odor (9).An extremely disagreeable smell arose from the manure under argon shortly after the incubation began, and this odor was maintained throughout the experiment; yet, at no time was the aroma of the manure in air either particularly intense or unpleasant. The data in Tables I1 and I11 do not adequately explain this difference. Sulfur compounds, which have frequently been associated with the odor of manures, were present in the initial stage of the experiments under both argon and air. Carboxylic acids, also odoriferous materials, could have contributed to the smell of the argon-incubated sample during the latter third of the experimental period. The only compounds detected during the bulk of the incubation under argon were alcohols, esters, and ketones, none of which are considered to have an offensive odor individually. It is possible that the mixtures of volatiles detected produced the unpleasant odor. However, some potentially important odor-causing compounds would not have been detected by the methods employed.
The technique used for the collection of volatiles should have wide applicability to the study of gaseous organic compounds. It is a mechanically simple method for the simultaneous collection and concentration of volatiles. Continuous slow flushing of a headspace with a gas stream is a more realistic model of most natural systems than is a sealed vessel. The accumulation or depletion of gases in the headspace is prevented, and disruptions caused by sampling are minimized. It should be possible to study volatiles outside the range detectable in this experiment by employing appropriate trapping materials and GC columns.
Literature Cited (1) Muehling, A. J., J . Anim. Sci., 30,526 (1970). (2) Merkel, J. A., Hazen, T. E., Miner, J. R., Journal Paper No. J 5826, Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, 1968. (3) White, R. K., Taiganides, E. P., Cole, G. D., in “Livestock Waste Management and Pollution Abatement”. D 110. Am. SOC. Aer. ” Ene.. St. Joseph, Mo., 1971. 14) Deibel. R. H.. in “Aericulture and the Qualitv of Our Environment”, N. C. Brady, E>., p 395, Am. Assol Ad;an. Sci., Washington, D.C., 1967. (5) Burnett, W. E., Enuiron. Sci. Technol., 3,744 (1969). (6) Burnett, W. E., Dondero, N. C., in “Animal Waste Management”, Proc. Cornel1 Univ. Conf. on Agr. Waste Management, 1969. (7) Banwart, W. L., Bremner, J . M., Div. of Soil Microbiol. and Biochem., 66th Meeting ASA, Chicago, Ill., Nov. 1974. (8) Adamson, J. A., Francis, A. J.,Duxbury, J. M., Alexander, M., Soil Biol. Biochem., 7,45 (1975). (9) Loehr, R. C., Anderson, D. F., Anthonssen, A. C., in “Livestock Waste Management and Pollution Abatement”, p 204, Am. Soc. Agr. Eng., St. Joseph, Mo., 1971.
,.
I
0
,
Received for review February 9,1976. Accepted J u n e 25,1976. Work supported in p a r t by Grant NGR-33-010-127 from the National Aeronautics a n d Space Administration.
Application of Weak Base Ion-Exchange Resins for Removal of Proteins David H. Foster*’, Richard S. Engelbrecht, and Vernon L. Snoeyink Department of Civil Engineering, University of Illinois, Urbana, 111. 61801
The increasing demands being placed on our water resources have resulted in a need for continually upgrading the quality of treated wastewater effluents before discharge into receiving waters. The organic matter portion of effluents is of concern because of the potential damage it may cause to the environment and the public health dangers it may present. These substances may be present because of their resistance to conventional biological waste treatment methods or may be metabolic end products. As a result, biological treatment should be regarded as only a partial solution to the problem of removal of organic matter from wastewater. The various treatment schemes for removal of residual organic matter from secondary water treatment plant effluents have focused principally on adsorption processes such as activated carbon adsorption. Activated carbon treatment may fail to remove large organic molecules, such as protein, which are unable to penetrate the carbon pores to take advantage of the large surface area carbon provides. In addition, carbon must generally be thermally regenerated. Recently, interest in the use of synthetic resins for complete or partial replace~~
Present address, Department of Civil and Architectural Engineering, University of Wyoming, Laramie, Wyo. 82071
ment of activated carbon treatment of wastewater has increased since the capacities of many of the resins for some substances are high and thermal regeneration is avoided. A large portion of the organic compounds in secondary effluents is thought to be high-molecular-weight organic anionic fractions which may contain up to 509/0of the organic nitrogen in the effluent ( I , 2 ) . Proteins and nucleic acids are present in high-molecular-weight fractions and may account for much of the total nitrogen present. Since many of the organic compounds present in wastewater in the normal operating range of pH values are anionic, this study focused on anion exchange resins as potential replacements for activated carbon in the treatment of wastewater from biological treatment units. The proteinaceous fraction of residual organic matter which would be removed by resin treatment is important from several standpoints. Treated wastewater effluents contain 2-8 mgh. of organic nitrogen, much of which is proteinaceous in nature ( 3 ) .Removal of organic nitrogen from effluents would be beneficial to the environment since its presence may contribute to oxygen depletion in receiving waters and may also provide a source of nutrients for algae and thus contribute to algal blooms. In addition, wastewater effluents contain viruses which are a special class of proteinaceous material. The virus particle is comprised of a nucleic acid core covered with a Volume 11, Number 1, January 1977
55
The applicability of resinous sorbents to the treatment of waste streams containing complex organic molecules was determined. Proteins, principally bovine serum albumin, and a bacterial virus, MS2, were used as model materials in conjunction with selected resinous sorbents and activated carbon. Batch studies indicated that the capacity of a weak base, phenol-formaldehyde resin, showed superior sorption capacity to that of activated carbon. Sorption was pH dependent with little removal at extreme pH values, suggesting that Donnan
exclusion of the molecules occurred. When protein carboxyl groups were esterified, sorption was significantly reduced, whereas blocking protein amino groups had little effect on sorption except to increase it a t low pH values. The influence of pH on sorption was confirmed in continuous flow studies. Wastewater organic compounds reduced the capacity of the resin for virus due to competitive effects. Greater than 90% recovery of sorbed protein could be obtained by caustic regeneration.
protein coat; therefore, much of the surface chemistry of viruses is due to its behavior as a protein. Removal of viruses from municipal wastewater effluents by resin treatment would serve the public health by protecting water supplies which might be contaminated by treated wastewater effluents. Specific industrial processes, such as in the dairy industry, produce wastes which contain large quantities of proteins which could be removed by treatment with resin, recovered, and sold as feed supplements for livestock. The range of potential application of resins in waste treatment is large and should be exploited to the fullest to achieve maximum environmental, public health, and economic benefits.
plate filter with a 0.45-pm pore size membrane filter and a glass fiber prefilter. Membranes were changed frequently to minimize the formation of a gel layer on the surface of the membrane which might alter its pore size and filtration properties. The resins used in the study represented a variety of types (Table I). Both charged and uncharged resins were studied to determine the importance of the type of functional groups and resin matrix in sorption of proteins. Phenol-formaldehyde resins were preconditioned for study by cyclic treatment with acid and base followed by thorough washing with distilled water. Absolute ethanol extraction of the resins was carried out prior to the last acid-base cycle to remove any organic residues remaining from the manufacturing process. XAD-8 was preconditioned by extraction with methanol and hydration with water. Resins were brought to equilibrium with the particular fluid to be studied in an experiment by passing the fluid without the sorbate at a slow rate through a column of preconditioned resin until an identical influent and effluent pH was obtained. An additional 500 bed volumes (BV) of fluid were passed through the resin bed to assure that equilibrium had been achieved. Resins were prepared for weighing in batch studies by centrifugal dewatering. The moist resin was weighed rapidly and then immediately dispensed into the appropriate sample bottle containing the particular fluid under investigation. Generally 15 samples were used to determine an isotherm using three concentrations of proteins. Controls containing protein but no resin were employed at each protein concentration. A portion of the dewatered resin was weighed in triplicate in a tared weighing dish and dried for three days a t 103 "C. The average percentage weight loss was used to calculate the dry weight for experimental resin samples. Activated carbon (Filtrasorb 400, Calgon Corp., Pittsburgh, Pa.) was sieved to a 177-250-pm size range, washed thoroughly with deionized water to remove dust and fines, and dried a t 103 "C to a constant weight and stored in a desiccator. The carbon was conditioned for a particular experiment by bringing it to equilibrium with the particular fluid to be studied in the same manner as used for the resins. Batch studies were conducted using 8-02 square flint glass bottles which had been prepared by treatment with detergent solution followed by thorough rinsing with deionized water to reduce solute sorption to the glass and by ultraviolet radiation to reduce bacterial contamination. The bottles were agitated on a rotary shaker at 120 rpm. Both batch and continuous flow studies were conducted at 4 "C to avoid thermal denaturation of the protein and to reduce the rate of virus inactivation. Continuous flow studies were conducted with Duolite A-7 at 4 "C in columns 19.8 cm in length and 1.474 cm in diameter with a length to diameter ratio of 13.4 (aspect ratio). The ratio between column diameter and resin diameter was 35.1 for the largest mesh size of resin used. These conditions were felt to be sufficient to allow establishment of uniform flow conditions in the column and to avoid wall effects. Flow rates of ap-
Materials and Methods This study focused on the use of weak base resins as adsorbents in wastewater treatment. Strong base resins generally bind organic molecules so strongly that they are difficult to regenerate. As a result, the resins become "fouled"; that is, they lose some of their capacity to remove organic molecules with each successive cycle. As a rule, the adsorption or exchange of organic molecules by weak base resins is more easily reversed, and they are, therefore, less subject to the organic fouling observed with strong base resins ( 4 ) . In this study, bovine serum albumin (BSA) was used as the principal model protein. BSA has a molecular weight of 69 000 and an isoelectric point (IEP) of 5.15. Pepsin, with a molecular weight of 36 000, was also studied. A modified version of the Lowry method was used for analysis of the proteins (5). Bacterial virus MS2 against Escherichia coli strain A-19 was used as the model virus in the continuous flow study in wastewater. MS2 is an icosahedral virus, 25 nm in diameter, with a single stranded RNA core. The isoelectric p H of the virus is 3.9, indicating an acidic protein coat composition. In terms of size and shape, MS2 is quite similar to members of the enterovirus group such as poliovirus. The assay procedure for MS2 was the agar overlay method described by Overby et al. ( 6 ) . Secondary effluent was obtained from the activated sludge units of the Urbana-Champaign Sanitary District East Side Plant. The effluent was centrifuged in a continuous flow centrifuge at 13 500 rpm a t a flow rate of 6 l./h and then filtered into a sterile collection bottle through a sterile 142-mm
Table 1. Properties of Synthetic Resinous Sorbents
56
Resin
Source
Matrix
XAD-8 ES-33
Rohm and Haas Diamond Shamrock
Acrylic ester Phenoiformaldehyde
S-30
Diamond Shamrock
A-7
Diamond Shamrock
Phenolformaldehyde Phenolformaldehyde
Environmental Science 8 Technology
Principal functional groups
None Predominantly tertiary amine None Predominantly secondary amine
/
Figure 1. Batch sorption of bovine serum albumin by selected resinous
sorbents
-3-01
I 0-
IO'
I 0Ceq i g / P
Figure 2.
I
Sorption of bovine serum albumin by carbon and resin
proximately 11.5 BV/h were used in all cases. Flow rate was maintained by air pressure on the influent supply reservoir using a single-stage regulator and by flow meters placed between supply reservoir and columns. The influent concentration of sorbate was 200 mg/l. in the protein experiments, corresponding to a chemical oxygen demand (COD) value of 440 mg/l. For virus experiments, an influent concentration of approximately 109 PFU/ml was maintained. While the protein COD values are typical of COD'S normally encountered in domestic wastewater, the organic nitrogen concentration is atypical for wastewaters in that the COD is made up entirely of protein. The virus concentration used was much higher than reported values of virus in wastewater effluents (7). However, use of concentrated virus suspensions allowed a more thorough characterization of the breakthrough curves than would have been possible otherwise. Results and Discussion
Relative Batch Sorption Capacities. A comparison of selected resins using Freundlich isotherms indicated that Duolite A-7 possessed the highest batch BSA sorption capacity of the resins studied (Figure 1).The capacity of the tertiary amine resin ES-33 was essentially equal to that of an uncharged phenol-formaldehyde resin (S-30) over the equilibrium concentration (Ceq)range studied. It is not possible at this point to determine if the functional groups of ES-33 participate in the sorption of protein, since other factors such as pore size may explain the lower capacity of ES-33 compared to A-7. In addition, the anion exchange capacity of ES-33 was less than that for A-7, indicating a lower density of functional groups. The percentage cross-linking between the two resins may differ also and could influence the ability of the protein
to utilize the theoretically available capacity. The resin matrix was capable of sorbing a substantial amount of protein. Since the phenol-formaldehyde resins demonstrated superior sorption capacity compared to the acrylic resin XAD-8, it may be hypothesized that a portion of the sorption capacity in the phenolic resins was due to specific sorbate interactions with the resin matrix, possibly through the x electrons in the aromatic portions of the sorbate and sorbent. The batch sorption capacity of A-7 for BSA was also substantially greater than that of activated carbon at neutral pH as shown by the isotherm in Figure 2. Activated carbons have a large specific surface area which, in the case of Filtrasorb 400, amounts to approximately 1000 sq m/g. However, much of the surface area is inside the pores which are apparently not large enough to admit large protein molecules. More than 60% of the pore volume of Filtrasorb 400 is in pores which are less than 30 nm in diameter (8),which would not readily allow the diffusion of protein into the carbon interior. The relative amounts of pore volumes in A-7 and Filtrasorb 400, which may be reached by diffusion, cannot be readily determined. The resins, being hydrophilic gel structures, change considerably in dimensions upon drying. Thus, the methods available for determination of surface area and pore size distribution are not reliable when applied to resins. Abrams (9) reported that pores visible in scanning electron micrographs of phenol-formaldehyde resins ranged from a few Angstrom units to over 10 000 nm. Average pore diameters in dried gels were in the range of 20-30 nm but could be considerably larger in fully hydrated resins. The activated carbon surface is partially oxidized and contains lactone and carboxyl groups (IO),and BSA sorption onto carbon could be hindered a t neutral pH since both the sorbate and sorbent would be negatively charged and electrostatic repulsion would result. Thus, despite the large surface area of a coal base activated carbon such as Filtrasorb 400, it would be expected that the protein sorption capacity of carbon would be small. Several studies have compared the removal of viruses by activated carbon and provide some insight into the adsorption onto carbon of proteinaceous materials such as viral coat proteins. The viruses examined represent a range of physical and chemical types. Sproul et al. (11)examined the removal of bacterial virus T2 and poliovirus I by activated carbon from wastewater effluents and concluded that carbon adsorption should not be relied on as a fundamental removal process since high effluent concentrations may occur. In batch systems using four powdered carbons, the maximum ,virus removal achieved was 75%,while removals as low as 29% were observed. At flow rates greater than 1 gal/min/ft* of filter surface in continuous flow studies, removals of T2 virus were less than 10%.Continuous flow experiments using poliovirus I showed a mean removal efficiency of 26.7% and indicated that virus was displaced from the carbon surface by wastewater organics as the bed exhaustion capacity was approached. Drewry (12) compared the removal of bacterial virus f 2 by activated carbon and an anion exchange resin. At the same bed depths the resin proved to be the most efficient adsorbent. Selectivity of the resin and the presence of organic matter were thought to influence removal. Recently, Gerba et al. (13)examined the removal of poliovirus I on activated carbon and concluded that adsorption of virus was reduced in proportion to the concentration of organics present and that removal was strongly influenced by solution pH. Treatment of secondary effluents by lime precipitation significantly reduced interference of the adsorption of viral coat proteins onto carbon compared to samples which were treated by filtration alone. Removal in the presence of organics varied from less than 1 up to 70%. In general then, for virus removal at neutral pH values prevailing in most wastewaters, sorption onto activated Volume 11, Number 1, January
1977
57
carbon is not high and is considerably reduced by the presence of competing organic substances. Since the comparative data for resins and carbon indicated that Duolite A-7 had the greatest affinity for BSA of the sorbents studied, a detailed investigation of this resin was conducted to determine the mechanisms of protein sorption on the resin surface and to delineate some of the factors influencing sorption. Variation of Sorption with pH. Duolite A-7 contains principally secondary amine functional groups with a probable pK range of 5-6.5 (14). The sorption of BSA onto A-7 resin which had previously been brought to equilibrium with phosphate buffer showed a variation with pH with the sorption maxima occurring above p H 5 (Figure 3). Below pH 5 the resin is largely in the acid form, and the BSA amine and carboxyl groups are largely protonated. This reduces the opportunity for uptake by the ion exchange mechanism and could explain why BSA sorption decreased sharply as the pH decreased below 5. Also, the cationic protein is excluded from the resin by Donnan exclusion which causes a further decrease in uptake. Similar events occur a t high p H where the resin phenolic hydroxide groups become ionized (pK approximately 8.5) ( 1 5 ) and where the protein is anionic. In the pH region between pH 5 and 8, the mechanism of protein uptake could be due to an exchange occurring between the phosphate form or resin and the anionic protein:
R R, N: Hf H,PO,-
+ BSA-
H
R
Ri N: Hf BSA-
+ H,PO,-
(1)
H
Alternately, the mechanism could also be due to hydrogen bonding through a BSA amine group:
R R, N: H,PO,
+ H,N
BSA
H
R R, N: H-N H
BSA
+ H3P0,
I H
The former mechanism would be consistent with a shift to lower solution pH values which were consistently observed when BSA was sorbed onto the resins. In addition, above p H 5 the resin acid groups are converted to the free base form while the protein is becoming increasingly anionic. The presence of both the acid form of the functional groups and the anionic protein would be necessary for an exchange to occur by the mechanism of Equation 1. Since acid resin groups are decreasing as pH increases in the region of pH 5 and the BSA is becoming more anionic, a sorption maximum results. Donnan exclusion a t extreme pH values would tend to reinforce the tendency toward a sorption maximum a t pH 5 . The pepsin data of Figure 3 tend to support the proposed mechanism of Equation 1. Pepsin (IEP < 1.0) (16) which is principally anionic at pH values above 1showed a considerable amount of sorption in the region of pH 2-5 consistent with an exchange mechanism and where BSA failed to sorb. The factors governing the shape of the curves are complex and would depend on properties other than charge, such as charge distribution with pH, steric factors affecting the charged groups, and molecular size. Pepsin, for example, is the smaller of the molecules and may be affected by differences between solution pH and the internal pH of the resin more than BSA since it 58
Environmental Science 8 Technology
I
2
4
6
8
IO
1
12
14
pH Vc ,e
Figure 3. Influence of bulk pH on sorption of pepsin and albumin on Duolite A-7
would be expected that more of the pepsin would be able to enter the resin than would be the case with the albumin. An exchange of the type proposed in Equation 1would require the presence of deprotonated carboxyl groups on the protein. If the protein carboxyl or amino groups are blocked, then the active sorption site on the protein could be determined and the sorption mechanism clarified. When BSA carboxyl groups were esterified according to the method of Hoare and Koshland (17),sorption of BSA was reduced two orders of magnitude a t both pH 5 and 7 in comparison to untreated BSA (Table 11). On the other hand, when BSA amino groups were diazotized by the method of Tabachnick and Sabotka (18, 19),BSA sorption was unaffected, thus ruling out Equation 2 as a mechanism. At pH 2.5, however, sorption of diazotized BSA was increased over untreated BSA. This was possibly due to a reduction in Donnan exclusion and sorption to the matrix. In summary then, the protein carboxyl groups appear to be the active protein sorption site. Ionic Strength. The ionic strength of the suspending medium had a dramatic influence on the ability of the A-7 resin to sorb BSA (Figure 4).While the data in the figure are for nitrate only, similar trends were observed for various concentrations of sodium salts of phosphate and sulfate. The increased sorption of BSA a t decreasing ionic strength was also accompanied by a downward shift in bulk phase pH as sorption took place, indicating that sorption of BSA resulted in a release of hydrogen ions from the resin. The influence of ionic strength on sorption was felt to be due to several factors. If ion exchange is in fact the dominant mechanism by which proteins are sorbed onto weak base resins, then the law of mass action must be taken into account. An increase in the concentration of the bulk phase inorganic anion in Equation 1 would cause the reaction to shift to the left, indicating a decrease in the amount of protein which could be removed by exchange. Thus, by mass action, one would expect an increase in ionic strength to result in a reduction of protein sorption. In addition, the presence of organic molecules in water is believed to cause an increase in the Table II. Functional Group Modification and Protein Adsorption a Untreated BSA
PH 5 PH 7 a
x Wg).
1.36X 1.06X
lo-’
lo-’
Esterifled BSA
Dlazotlzed BSA
1.27X 2.95x 10-3
1.50X lo-’ 1.47X lo-’
C,; 0 :I2 20105 6 mq/l bv/hr
I: ob
lb
20
310
40
20 Bed Yolimes
60
70
so
90
Id0
Figure 5. Breakthrough of bovine serum albumin with Duolite A-7 at pH 2.77 10
Figure 4. Effect of ionic strength on bovine serum albumin sorption
proportion of water molecules involved in orderly liquid crystalline structures (20).That is, organic compounds tend to reduce the overall entropy of the fluid. An increase of ionic strength, on the other hand, reduces the ability of organic molecules to organize water into crystals (20). In systems where ionic strength is high, the large entropy changes which accompany the adsorption of organic molecules from solution would be reduced since the water molecules would be less organized to begin with. As a result, sorption of organic molecules from high ionic strength aqueous solution would be less favorable from a thermodynamic standpoint than from a dilute ionic solution. The effect of ionic strength is logarithmic, meaning that the effect of ionic strength in reducing BSA sorption becomes intensified exponentially as the ionic strength is increased. The sorption of macromolecules may be viewed as being due to sorption of segments of the molecule a t a number of sites along the polymer chain (21). Any interference with the sorption of individual segments of the chain would weaken sorption of the entire molecule. Increasing the degree of interference would eventually result in “blockage” of sufficient sites on the resin or protein so that sorption could be prevented. While the exact nature of the site “blocking” has not been delineated, ion competition or ion pair formation with carboxylate groups and inorganic cations could reduce the effective number of sites on the protein. With increased ionic strength, more protein functional groups would be involved in ion-ion interactions and the probability of exchange with the resin would become increasingly unlikely. Continuous Flow Column Studies. The breakthrough of M phosphate buffer with Duolite A-7 BSA at pH 2.77 in as the column media was immediate with the ratio between effluent and influent concentration (c/co) reaching 0.99 after 2.01 BV (Figure 5). Since the first BV was the displacement volume of the solution originally contained in the column which contained no protein, the breakthrough to saturation of the column occurred rapidly, and no observable sorption of BSA occurred. Sorption a t this p H was not possible due t o Donnan exclusion of the positively charged protein and the protonated resin surface. Therefore, the continuous flow study confirmed the findings in batch systems. At p H 5.68, with the same system, breakthrough did not begin until after approximately 30 BV (Figure 6). The breakthrough capacity was 2.20 x 10-2 g/g a t a flow rate of
? 05
0
0
Bed Volumes
Figure 6. Breakthrough of bovine serum albumin with Duolite A-7 at pH 5.68
11.40 BV/h. In this investigation the breakthrough point was defined as the point where a concentration of sorbate which could be reliably detected first appeared in the column effluent and the breakthrough capacity as the column capacity to the breakthrough point. At pH 5.68, column saturation was reached a t 456 BV. Experimentally, the observed batch capacity was greater than the observed column saturation cag/g, which is not surprising in view of the pacity of 8.9 X relatively slow kinetics observed in the batch studies. The elapsed time-to-column saturation a t a flow rate of 11.40 BV/h was only 40 h, while the batch equilibrium time was over 190 h. The protein may not have had the opportunity to come to equilibrium in the retention time provided in the column and a lower capacity resulted. As previously noted, viruses possess protein coats which serve to protect the nucleic acid core which contains the genetic information necessary for virus replication. Viruses are of considerable public health importance and have been detected in raw wastewaters a t levels up to 500 000 plaque forming units (PFU) per liter and, as a result, may be discharged to the environment via effluents receiving conventional treatment (7). In addition, viruses may be detected a t relatively low levels in wastewater by direct measurement, while protein determination in wastewater is subject to a number of interferences. The sorption behavior of viruses in wastewater in continuous flow systems could give a reasonable indication of the potential usefulness of resinous sorbents for removing viruses and other proteinaceous materials from waste effluents, since competition with other organic solutes and with ions a t levels expected to occur in full scale operations could be studied. The breakthrough curve for virus in wastewater indicated that competitive effects have a strong influence on virus sorption (Figure 7). The breakthrough virus sorption capacity of A-7 in p H 7.86 wastewater was only 12.83% of the breakthrough capacity of A-7 for virus in phosphate buffer in the Volume 11, Number 1, January 1977
59
0
I
I
I
I
100
200
300
400
5 00
Bad Volumes
Figure 7. Breakthrough of MS2 bacterial virus with Duolite A-7 in wastewater same range of pH values. In both cases, the resin was brought to equilibrium with M pH 7 phosphate buffer prior to use. The column effluent in the wastewater experiment contained virus in all BV except the initial displacement volume. However, virus removal was 99% or more for 30 BV, and the removal efficiency did not decrease to 95% until 53 BV had passed through the column during 5 h of column operation. Overall virus removal to saturation at 410 BV was 32.31% of influent values. Organic substances removed from the wastewater, in addition to viruses, could occupy sites on the resin surface and make them unavailable for virus sorption, thus reducing virus sorption capacity through competition. Total organic carbon was removed by the resin but in a somewhat erratic fashion which did not exhibit a typical breakthrough curve (Figure 8). However, the TOC removal curves were similar to those observed for removal of chemical oxygen demand (COD) substances by weak base resins reported by Rebhun and Kaufman (22) and Schnack and Kaufman (23).The average removal was 39% of influent values with the effluent TOC averaging 7.0 mgh. A sufficient quantity of organic matter was sorbed by the resin to considerably reduce the effectiveness of the resin for virus removal. The carbohydrate data (Figure 8) indicate that this component of wastewater was not effectively removed by the resin and could not compete with virus for resin sorption sites. Gerba et al. (13) observed 20-26% removal of poliovirus from filtered secondary effluents on activated carbon columns of similar lengths and comparable operating conditions. Since Gerba used UV absorbance rather than the more conventional total organic carbon (TOC) to express organic concentration, a direct comparison of results is not possible. However, it may be inferred that the organic concentrations in Gerba's study were relatively lower since biologically treated rather than raw wastewater was employed as the feed to the column. When the pH of the wastewater was adjusted to pH 3.5, removal of virus 14.
I
0 30 2
I
r
J I00
! 2w
!
!
300
400
5x
Bed V o l ~ m e ~
Figure 8.
60
Removal of wastewater components by Duolite A-7
Environmental Science & Technology
by carbon exceeded 50% for approximately 60 BV. However, when the pH was unadjusted, removals decreased to 25% or less after only 10 BV had passed. In contrast, removal of MS2 by Duolite A-7 did not decrease to 25% until 215 BV had passed through the column (Figure 7 ) . It should be pointed out that exhaustion, in terms of overall organic removal from treated wastewater effluents with resin beds, generally is not reached until more than 1000 BV have been passed (23,24). As a result, the capacity of a resin for removal of virus and other proteinaceous materials could be exceeded well before the capacity of the resin to sorb other organics is reached. The pH of the influent during the period of column operation was consistently higher than the column effluent by 0.4-0.9 pH units. The inorganic carbon data (Figure 8) gave a typical breakthrough curve, indicating that a portion of the decrease in pH could have been due to removal of alkalinity by the resin. Since the most likely explanation for the removal of alkalinity in this case is by exchange of the bicarbonate for phosphate ions, the data strongly suggest that even at pH values above neutrality, functional groups in the acid form are present on the resin surface in significant quantities. The mechanism proposed for exchange of virus and protein would require the presence of groups in the acid form on the resin; thus, the data indicate that an exchange mechanism is possible even a t pH values well above the resin pK value. Desorption. The column used in the pH 5.68 study of BSA sorption was treated with 5% sodium hydroxide following saturation at a flow rate of 6.6 BVIh to study protein desorption. The concentration of caustic was half that used in batch BSA recovery studies where a 92% recovery was achieved. The desorption of protein from the resin volume resulted in a recovery of 98% with nearly 95% of the protein desorbed in the four BV following the initial displacement BV. The data showed that sorption of BSA may be readily reversed by caustic. Cyclic operation would be required to determine if resin treatment of protein or virus containing solutions results in any loss of resin capacity with continued operation, but the experiences of others would suggest that loss of capacity with weak base anion exchange resins with continued operations is unlikely ( 4 ) .
Summary and Conclusions The sorption of amphoteric macromolecules onto weak base resins is complex, and generally sorption behavior may be attributed to a combination of several mechanisms. The sorption of proteins will be influenced by the configuration of the molecules, the nature of the sidechains, and the amount of water bound to both resin and protein present, in addition to strictly electrostatic factors ( 2 5 ) .In this study the sorption of albumin on a weak base resin involved sorption onto the resin matrix in addition to interactions with the resin functional groups. At extreme solution pH values, electrostatic repulsion between the resin functional groups and BSA occurred, while in the pH region above pH 5 and below pH 8 the major means of protein uptake appeared to be by an ion exchange mechanism involving the protein carboxyl groups. Sorption was accompanied by a decrease in solution pH and was decreased with increasing ionic strength. It would appear that weak base resins have a good deal of potential for removal of proteinaceous and other organic materials from secondary effluents. However, the nature of competitive effects and the operational variables associated with continuous flow processes need to be more fully investigated. While the sorption capacity of A-7 resin for virus in wastewater was satisfactory, a strong interference by competing organics with sorption was observed which considerably reduced the acceptable length of operation compared to a
similar system where only virus and buffer were present. Caustic regeneration resulted in a nearly complete recovery of applied protein within the first few bed volumes, indicating that resin fouling difficulties often encountered with strong base resins should not be a problem with weak base resin systems. L i t e r a t u r e Cited (1) Bunch, R. L., Barth, E., Ettinger, M. B., J . Water Pollut. Control Fed., 33, 122 (1961). ( 2 ) Painter, H. A., Viney, M., Bywaters, A., J . Znst. Sewage Purif., Part 4, 302 (1961). ( 3 ) Courchaine. R. J.. Proc. 18th Indust. Waste Conf., D 38, Purdue University, Lafayette, Ind., 1963. (4) Abrams, I. M., Chem. Eng. Prog., S y m p . Ser., 65,106 (1969). (5) Lowry, 0. H., Rosenbrough, N. J., Farr, A. L., Randall, R. J., J . Biol Chem., 193, 265 (1951). 161 Overbv. L. R.. Barlow. G. H.. Doi, R. H., Jacob.. M.. SDiegleman, S., J . Bac’teriol.’, 91,442 (1966). (7) Burao, N., Water Res., 8,19 (1974). (8) Jain, J. S., “Competitive Adsorption of Organic Compounds from Aqueous Systems Using Active Carbon”, P h D thesis, University of Illinois, Urbana, Ill., 1972. (9) Abrams, I. M., Ind. Eng. Chem. Prod. Res. Deuelop., 14, 108 (1975). (10) Cookson, J. T., Jr., Enuiron. Sei. Technol., 1,157 (1967). (11) Sproul, 0. J.,Warner, M., LaRochelle, L. R., Brunner, D. R., in Proc. Fourth International Conference on Water Pollution Research, Prague, Pergamon Press, London, England, 1969.
(12) Drewry, W. A., Water Resources Center Report No. 24, Water Resources Research Center, University of Tennessee, Knoxville, Tenn., 1971. (13) Gerba, C. P., Sobsey, M. D., Wallis, C., Melnick, J. L., Enuiron. sci. Technol., 9,727 (1975). (14) Kim, B. R., MS thesis, University of Illinois, Urbana, Ill., 1974. (15) Diamond Shamrock, Duolite Data Sheet No. 4, Diamond Shamrock Chemical Co., Redwood City, Calif., June 1971. (16) Fruton, J. S., Simmonds, S., “General Biochemistry”, Wiley, New York, N.Y., 1958. (17) Hoare, D. G., Koshland, D. E., Jr., J . Biol. Chem., 242, 2447 (1967). (18) Tabachnick, M., Sabotka, A,, ibid., 234,1726 (1959). (19) Tabachnick, M., Sabotka. H.. ibid.. 235.1051 (1960). (20) Feitelson, J.,“Ion Exchange”, J . A. Marinsky, Ed., Dekker, New York, N.Y., 1969. (21) Simha, R., Frisch, M. L., Eirich, F. R., J . Phys. C h e m , 57,584 1195.1) ~. ._ (22) Rebhun, M., Kaufman, W. J., “Removal of Organic Contaminants: Sorption of Organics by Synthetic Resins and Activated Carbon”, SERL REPT No. 67-9, University of California, Berkeley, Calif., 1967. (23) Schnack, G., Kaufman, J., “Removal of Organic Contaminants: Optimizing Resin Column Operations”, SERL R E P T No. 70-11, University of California, Berkeley, Calif., 1967. (24) Kim, B. R., Snoeyink, V. L., Saunder, F. M., presented at 47th Annual Conf., Water Poll. Cont. Fed., Denver, Colo., October 1974.
Receiued for reuieu FebruarJi 2, 1976. Accepted J u l y 20, 1976
Kinetics and Mechanism of Oxidation of Hydrogen Sulfide by Hydrogen Peroxide in Acidic Solution Michael R. Hoffmann‘ Environmental Engineering Science, W. M. Keck Laboratories, California Institute of Technology, Pasadena, Calif. 9 1125
w The kinetics of the oxidation of hydrogen sulfide and hydrosulfide ion to sulfur and sulfate in aqueous solution by hydrogen peroxide is studied potentiometrically. In the pH range 8-3, the rate law for the oxidation of H2S is -d [HzS]/dt = kl[HzS] [H202] + k2Ka1[H2S][H202]/[H+] where K,1 is the first acid dissociation constant of HzS, k2 = 29.0 M-I min-’, and k l = 0.5 M-l min-l. The rate law and other data indicate that the reaction proceeds via a nucleophilic displacement by sulfide on hydrogen peroxide with the formation of polysulfide intermediates. In recent years the potential of hydrogen peroxide for industrial pollution control has been examined and advocated by two commercial producers of Hz02, E. I. du Pont de Nemours & Co. and the FMC Corp. ( I , 2). Both FMC and Du Pont recommend H202 for the treatment of odors due to the generation of H2S in municipal sewage treatment systems, in concrete sewer lines, and in other anaerobic environments where organic matter and sulfates are present. In addition to being a primary contributor to malodorous conditions, H2S is a major cause of corrosion in concrete sewer lines ( 3 ) . Oxidation of H2S by H202 in neutral or acidic solution to elemental sulfur may provide a convenient and economical method for the control of sulfide wastes and their associated odors. With this in mind, the stoichiometry, kinetics, and mechanisms of the oxidation of H2S by H202 have been inPresent address, Department of Civil and Mineral Engineering, University of Minnesota, Minneapolis, Minn. 55455.
vestigated and are reported here. Hopefully, the results of this study will help a potential user of HzOz determine the optimal conditions for control of odor and corrosion due to H2S. The stoichiometry for the reaction of H2S and H202 in a neutral or acidic solution is normally written as
H2S + H202 --* 2H20 + S
(1)
where zero valent sulfur is formed in the colloidal state. Since colloidal sulfur ( 4 , 5 )is a complex mixture of cyclohexasulfur, cyclooctasulfur, polycatenasulfur, and higher-molecularweight sulfanes, Equation 2 would be more appropriate considering the complexity of the reaction. H2S
+
H202
-
l/XS,
+ H20
(2)
Relatively few investigations of this reaction have been published in the open literature. This may reflect the analytical difficulties encountered with a complex mixture of gaseous HzS, aqueous H2S, H202, sulfur, polysulfides, and other higher-order sulfur species. The classically accepted stoichiometry in acidic solution, which is given in Equation 1,is based on the work of Classen and Bauer (6).In basic solution, sulfate was the only product observed. Wasserman (7) determined that in the pH range 2-4, 20-40% of the H2S originally present was oxidized to sulfate depending upon the amount of H202 initially present. However, Satterfield et al. (8)did not observe the formation of sulfate in acidic solution. Feher and Heuer (9) detected transitory polysulfide intermediates during the course of the reaction in acidic solution. Satterfield et al. (8) studied the rate of reaction of acidic Volume 11, Number 1, January 1977 61
