Effect of Ozone Treatment upon Biodegradability of Water-Soluble Polymers Junzo Suzuki', Keiko Hukushima, and Shizuo Suzuki Faculty of Pharmaceutical Science, Science University of Tokyo, lchigaya Funagawara-machi, Shinjuku-ku, Tokyo, Japan
molecular weight of the biodegradable fragments produced by ozonization.
The biodegradability of water-soluble polymers, i.e., polyethylene glycol, poly(viny1 alcohol), poly(vinylpyrro1idone), polyacrylamide, and sodium polyacrylate, and the effect of ozonization upon the biodegradability were studied by using river bed mud as inoculum. Biodegradability was estimated from the drop of total organic carbon (TOC) in culture solution and the variation of molecular weight distribution. Although poly(viny1 alcohol) was biodegraded slowly, the other original polymers were scarcely biodegraded. Ozonization contributed to improving the biodegradability of the four kinds of polymers except in the case of polyacrylamide. Little improvement was noted in the biodegradability of polyacrylamide in spite of the marked lowering of the molecular weight by ozonization.
Biodegradability and toxicity of organic substances are significant factors for determining their behavior in a natural environment and in the biological treatment of wastewater. With respect to surfactants and other general organic substances that are relatively readily biodegraded, their degrees of biodegradability have been studied by many researchers (1-3). However, studies on substances that are very hard to biodegrade, especially synthetic polymers, have been few in number because determination of their biodegradability is difficult. Furthermore, most reports have concerned plastics ( 4 , 5 )and not water-soluble polymers. Water-soluble synthetic polymers, for example, polyacrylamide (PAA) and poly(viny1 alcohol) (PVA), are' widely used as water-treatment agents or food additives, and appear to be expelled in large volume into river water. Therefore, determining the biodegradability of these polymers is very important in evaluating their effect on the environment. The biodegradation of PVA among such water-soluble polymers has been reported by Suzuki et al. They isolated PVA-metabolizing bacteria and elucidated the mode of degradation of PVA by the bacteria (6). On the other hand, Fincher and Payne reported on the bacterial utilization of polyethylene glycol (PEG) with low molecular weight (approximately less than 400) ( 7 ) .Recently, Haines and Alexander (8),and Ogata et al. (9) reported that higher molecular weight PEG can also be utilized by bacteria. Those reports, however, are in any case merely information relating to isolants and do not necessarily show the biodegradability of the polymers in the natural environment. For the purpose of determining their behavior in the natural environment, it is necessary to determine the biodegradability under experimental conditions as close to natural conditions as possible. In this study, therefore, river bed mud was used as the inoculum for estimating the biodegradability. On the other hand, the biodegradability of polymers is thought to be affected by the high molecular weight. Accordingly, lowering the molecular weight has a beneficial effect in improving the biodegradability. For example, Guillet et al. reported that photodegraded polymers were biologically oxidized both in natural soils and in a sewage environment (10, 11).
The object of this report is to explore t o what extent the biodegradability of five kinds of water-soluble polymers may be affected by lowering the molecular weight by ozonization. In particular, the variation of molecular weight was examined thoroughly by gel filtration chromatography to determine the 1180
Environmental Science & Technology
Experimental Materials. Water-Soluble Polymers. The polymer samples used in this biodegradability examination consisted of five kinds of water-soluble polymers, that is, polyethylene glycol (PEG), poly(viny1 alcohol) (PVA), poly(viny1 pyrrolidone) (PVP), sodium polyacrylate (PANa), and polyacrylamide (PAA) and those ozonized. The original PAA was prepared by radical polymerization in water a t 80 "C using potassium persulfate as the initiator, and the polymerized product was purified twice by precipitating with acetone. The other clriginal polymers were obtained from Wako Pure Chemical Industries Ltd. I t was confirmed by gel filtration chromatography that no such low molecular weight components as polymerization catalyst or oligomer were contained in these original polymer samples. The approximate average molecular weight of these samples was estimated by viscometry (for original polymers) or by gel filtration chromatography (for ozonized polymers) and is shown in Table I together with the ozonization condition. Inoculum. The river bed mud collected from the Yamato River, an urban river polluted by various organic matters, was used as the inoculum for the biodegradability examination. This is because multifarious microorganisms inhabit such river mud. Methods. Ozonization Procedure. All ozone treatment of the water-soluble polymers was carried out in 0.4% aqueous solution (pH 12) at room temperature. The ozonization techniques have been reported in detail in another paper (12). The other ozonization conditions and the molecular weight of each polymer are summarized in Table I. Estimation of Biodegradability. Ten grams (dry weight) of fresh river mud as an inoculum, and 250 mL of a solution (pH 7.4) containing KzHP04 (9.28 g), KHzPO4 (1.81 g), ( N H 4 ) ~ S 0(0.5 4 g), Na2S04 (0.5 g), and MgS04.7H20 (0.1 g) per liter of distilled water and polymer samples of 0.1% (original polymer) or 0.2% (ozonized polymer) as substrate, were placed in a shaker flask (500 mL) and cultured a t 37 "C
Table 1. Ozonization of Water-Soluble Polymers and Their Molecular Weight polymers
polyethylene glycol
ozonization time
ozone consumed (mg/g of
(h)
polymer)
0 2
poly(viny1alcohol)
0
poly(vinylpyrro1idone)
0.5 4 0 2 4
sodium polyacrylate
0 2 4
polyacrylamide
0 2 4
0 836 0 85 468 0 655 1273 0 384 860 0 345 910
mol wt
8000 250 28000
... 460 27000
... 560 4 10000
... 250 280000
... 340
0013-936X/78/0912-1180$01.00/0 @ 1978 American Chemical Society
I
t . original
(A)
0-0
4.985, was consequently obtained in the range of molecular weight 4000 to 100, where M is the molecular weight, and V is the effluent volume (mL). Strictly speaking, the above equation should be applied only to PEG, since the dimension of molecule is varied by not only the molecular weight but also the molecular structure. However, standard samples for other polymers were not available, and an accurate molecular weight was not necessarily required in this investigation. Therefore, all of the molecular weights hereinafter described were estimated on the basis of the above equation and the individual gel filtration pattern,, according to Cazes' method (13).
' I
PEG PEG ozonized for 2 hrs
600
b-o-c_oh.o, 15
OO
5
IO
Incubation
0-0
25
30
R e s u l t s a n d Discussion
time (dpy)
...... e--.
20
original PEG initial culture filtrate culture filtrate incubated for 5 days
0
100-
Figure 1. t3iodegradation rate of PEG (A) and gel filtration chromatogram with Sephadex G-25 of culture filtrate containing PEG ozonized for 2 h (B) Arrow shows that TOC value in elution pattern of original polymer (broken line) follows right ordinate
with shaking. As the water of the culture solution was evaporated during incubation, distilled water corresponding to the amount of the evaporated water (calculated from the weight loss) was added to the culture solution. The solution of about 10 mL w#iiscollected at appropriate time intervals, centrifuged a t 6000 rpm for 60 min, and then the supernatant was filtered with a 0 . 4 5 - ~ mmembrane filter. The total organic carbon (TOC) ofthe filtrate was determined with a Toshiba Beckman TOC analyzer. The TOC of the filtrate reflects the concentration of the substrate, that is, polymer compound contained within the filtrate, since the organic components eluted from the river mud itself constituted a few ppm in TOC. A conixol experiment was carried out using starch (0.1%) as a substrate, and the TOC of the filtrate fell to one-tenth through incubation for two days. On the other hand, no TOC drop was confirmed in the control experiments sterilized by an autoclave and by addition of mercuric chloride (50 ppm). Consequently, it is reasonable to consider that the TOC drop in the filtrate is due to the degradation of the substrate by the microorganisms in the river mud and that the rate of TOC drop reflects the biodegradability of the substrate, that is, polymer compound. Gel F i l t r a t i o n C h r o m a t o g r a p h y . The molecular weight distribution of all polymer samples and its variation as a result of biodegradation were measured by gel filtration chromatography with Sephadex G-25 gel (column size 2.6 cm4 X 100 cm). Thle cultured solution samples were filtered with a 0.45-pm membrane filter after being centrifuged at 6000 rpm. The sample volume in the chromatography was 5 mL, and the effluent was fractionated into 5-mL portions. A sodium chloride solution of 1 M was used as a solvent to prevent the adsorption of solute in the swollen gel. The concentration of the solute in each fraction was measured with a TOC analyzer. The relationship between elution volume and molecular weight was calibrated by using monodispersed PEG of known molecular weight. The linear equation, log M = -0.008V
+
Polyethylene Glycol. Figure I A shows the drop in TOC of the culture solution which was incubated a t 37 "C using PEG or ozonized PEG as the sole carbon source. In the case of the ozonized PEG, the TOC (800 ppm) of the culture solution dropped to 200 ppm after 5 days incubation (TOC loss 75%) and to 40 ppm after 20 days incubation (TOC loss 95%). However, no remarkable drop of TOC was observed in the case of the original PEG. These results indicate that the biodegradability of PEG is markedly improved by ozonization. On the other hand, the PEG of molecular weight 8000 was deteriorated to average molecular weight 250 by ozonization for 2 h as can be seen in Table I. Figure 1B shows the gel filtration pattern of the initial culture filtrate (incubated for 3 h) and that of the culture filtrate incubated for 5 days. The TOC peak, which appears in effluent volume 400 mL, is due to the elution of the fragments of molecular weight less than 100, which is the separation lower limit of the gel. The broken line is the elution pattern of original PEG of molecular weight 8000, and it appears in effluent volume 200 mL, which is the void volume of the gel. It can be seen from the elution pattern of the initial culture filtrate that the ozonized PEG is broadly distributed over a molecular weight region of 2000 to less than 100. The elution pattern of the fifth day has two peaks in effluent volume 220 and 400 mL, which correspond to molecular weight 800 and less than 100, respectively. On the other hand, we reported in another paper that oligoethylene glycol and aldehyde compounds such as formaldehyde and formic ester were formed chiefly in the ozonization of PEG (121, and that formaldehyde inhibited the utilization of oligoethylene glycol by Pseudomonas aeruginosa ( 1 4 ) .The molecular weights of the fragments which were biodegraded during the initial incubation period (5 days) are less than 800 being predominantly 200-300 as can be seen in Figure 1B. Accordingly, these fragments are probably oligoethylene glycol. On the other hand, the two peaks remaining in the elution pattern of the fifth day appear to be fragments that correspond to the high molecular weight PEG and the aldehyde compound, which are difficult to biodegrade compared with the oligoethylene glycol. However, the TOC fell further to 40 ppm during subsequent incubation for 15 days. This fact indicates that even the PEG of average molecular weight 800 (1000 to 600) and the aldehyde compounds of low molecular weight were slowly biodegraded in river mud. Poly(viny1 alcohol). The biodegradation rate of original PVA and ozonized PVA is shown in Figure 2A. The original PVA was readily degraded by ozone, and the molecular weight of 28000 was lowered to 460 as a result of ozonization for 4 h as shown in Table I. In spite of such a remarkable lowering of the molecular weight, no marked improvement in biodegradation rate was observed, except that the rate of TOC drop in the initial intubation accelerated somewhat. On the other hand, Figure 2B shows the gel filtration patterns of the culture solution incubated for 0,11, and 35 days using PVA ozonized for 4 h as substrate (the TOC of each culture filtrate was 810,490, and 280 ppm, respectively). From Volume
12, Number 10, October 1978
1181
this period were within the whole range of the distribution pattern as shown in Figure 2B. Furthermore, the rate of TOC drop in the period was about the same as that of original PVA, in spite of the remarkable difference in the molecular weight. These results show that the biodegradability of PVA is not so dependent on molecular weight, and that it is improved ultimately by thoroughly ozonizing to form compounds of molecular weight less than 100 which are probably not PVA. Poly(vinylpyrro1idone). Figure 3A shows the biodeg-
the variation of the pattern, it is determined that the fragments, which were biodegraded in the initial incubation period and corresponded to 320 ppm for TOC, are compounds of molecular weight 100 or so. As a result of this initial biodegradation of the low molecular weight fragments, the average molecular weight of the substrate in the 11th day became about 800. The TOC of the culture filtrate dropped further to 280 ppm (TOC loss 26%) during subsequent incubation for 24 days. However, the fragments which were biodegraded in
origind PVA w PVA ozonized f w 30 mln w FVA ozonized f w 2 hrs 0-0
- 600
-"
-
400
0
:
-
7
/
0
4
i
Horiginal,
-
-a--
t-
1
2oot 5
IO 15 Incubation
fi I\
20 time (day)
...... original
(B)
25
PVA
w PAA ozonized for 2 h n PAA ozonized for 4 hrs
200
OO
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IO
15 20 Incubation t h e ( d a y )
-
ArlL
C.
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i ia
0-0
filtrate incubated for i i days culture filtrate incubated f w 35 days
-30
E30
-
i i
I
PAA inifiai culture filtrate cuture filtrate incubated for 8 days-I50 days
I
, I
i
i
150
200
300 350 400 Effluent volume ( m l )
250
450
Figure 2. Biodegradation rate of W A (A) and gel filtration chromatogram with Sephadex G-25 of culture filtrate containing PVA ozonized for 4. h (B)
200
ii -1lo 00 o::
z -
r
3
P
i
20
I50
30
\
,
1 ,
25
..... original
(B)
.-
w initial culture fiitrate
PAA
250
350
500
4 5 6 -0
400
0
Ef f bent volume ( m I )
Figure 4. Biodegradation rate of PAA (A) and gel filtration chromatogram with Sephadex G-25 of culture filtrate containing PAA ozonized for 4 h (B)
--
d,
H
1 : Ij/ 0 0 4j : original PVP c-a PVP ozonized for 2 hn o--o PVP, ozmized , for 4 hn,
original PAN0 PANa ozonized for 2 hs PANa ozonized for 4 h s
co
,
,
c200~
5
00
IO
15 20 Incubation time ( d a y )
25
5
30
I " "- " (B1
H
IO
-
n
:
n
?
150
initial culture filtrate culture filtrate incubated for 13 days
n
300 350 400 Effluent volume ( m l )
I
i i
PANa 80
u culture filtrate incubated 34 days
for
Environmental Science & Technology
!
,
0
450
Figure 3. Biodegradationrate of PVP (A) and gel filtration chromatogram with Sephadex G-25 of culture filtrate containing PVP ozonized for 4 h (B) 1182
30
230-
I
250
25
1
40-
-
;o
200
20 time (day)
..... original
?
230-
I5 Incubation
r
..... original PVP
40
200
Figure 5. Biodegradation rate of PANa (A) and gel filtration chromatogram with Sephadex G 2 5 of culture filtrate containing PANa ozonized for 4 h (B)
radation rate of original PVP and ozonized PVP. In the case of the ozonized PVP, a steep drop of TOC was observed in the first two days of incubation. However, the subsequent rate of TOC drop was the same as that of original PVP. The initial TOC drop in PVP ozonized for 4 h was larger than that ozonized for 2 h, and the former was 200 ppm and the latter about 100 ppm. The fragments biodegraded in such initial incubation are found to be mainly ozonization products of molecular weight less than 100 from the variation of gel filtration pattern shown in Figure 3B. The biodegradability of ozonization products of molecular weight larger than 100 was the same as that of the original, even when the molecular weight was only a few hundred. On the other hand, the effluent peak corresponding to the molecular weight less than 100 still remained in the pattern of the 13th day. This phenomenon indicates that it is difficult to biodegrade some of the ozonization products of low molecular weight. The ozonization mechanism of PVP cannot be elucidated a t present. Accordingly, the nature of the low molecular weight compound produced by ozonization is still obscure. Polyacrylamide. The biodegradation rate and the variation of the gel filtration pattern relating to PAA are shown in Figure 4. The PAA was undoubtedly deteriorated by ozone, and the molecular weight of 280000 was lowered to average 340 a s t h e result of 4 h ozonization as can be seen in Table I and Figure 4B. However, the biodegradation rate of the ozonized PAA was about the same as that of original PAA, and the biodegradability of PAA was hardly affected by ozonization. Also, as can be seen from the gel filtration pattern, even the ozonization products of molecular weight less than 100 were scarcely biodegraded during 8 days incubation. These results suggest that PAA's resistance to biodegradation results from not only the high molecular weight but also the molecular structure containing amide group.
Sodium Polyacrylate. As shown in Figure 5A, the biodegradation rate of the ozonized PANa was larger than that of the original, and the biodegradability of PANa was improved by ozonization. On the other hand, from the variation of gel filtration pattern in Figure 5B, it can be seen that the PANa of molecular weight 1000 to 100 produced by ozonization disappeared by biodegradation during 34 days of incubation and that low molecular weight portions predominantly remained without being biodegraded. These results indicate that lowering the molecular weight of PANa by ozonization contributes toward an improvement in biodegradability, but some of the low molecular weight compounds produced at the same time are hard to biodegrade.
Literature Cited (1) Pitter, P., Water Res., 10,231 (1976). (2) Patterson, S. J., Scott, C. C., Tucker, K.B.F., J . A m . Oil Chem. SOC.,47,37 (1970). (3) Rossall, B., Int. Biodeterior. Bull.,, 10,95 (1974). (4) Richard, T., Kaplan, A. M., Appl. Microbiol., 16,900 (1968). (5) Booth, G . H., Cooper, A. W., Robb, J. A., J . Appl. Bacteriol., 31, 305 (1968). (6) Suzuki, T., Ichihara, Y., Yamada, M., Tonomura, K., Agric. Biol. Chem., 37,747 (1973). (7) Fincher, E. L., Payne, W. J., Appl. Microbiol., 10, 542 (1962). (8) Haines, J. R., Alexander, M., ibid., 29,621 (1975). (9) Ogata, K., Kawai, F., Fukaya, M., Tarii, Y., J . Ferment. Technol., 53,757 (1975). (10) . . Jones. P. H.. Prasad. D.. Hesins. M.. Morean. M. H.. Guillet. J. E., Enuiron. Sci. Technol.,' 8,919 (1974). (11) Spencer, L. R., Heskins, M., Guillet, J . E., Proc. of3rd Int. Biodegradation Symp., USA, p 753, 1975. (12) Suzuki, J., J . A p p l . Polym. Sci., 20,93 (1976). (13) Cazes, J., J . Chem. Educ., 43, A567 (1966). (14) Suzuki, J., Nakagawa, H., Ito, H., J . Appl. Polym. Sci., 20,2791 (1976).
Received for review September 6, 1977. Accepted May 15, 1978
Feasibility Study of Condensation Flue Gas Cleaning (CFGC) System John C. Cooper', Richard M. Ostermeier", and Russell J. Donnelly Department of Physics, University of Oregon, Eugene, Ore. 97403 ~
The feasibility of control of large stationary source (nonparticulate) emissions by condensation is studied. Measurements of condensation rates and calculations of the heat load characteristics for a variety of coal-air mixtures are made. Based on these results and certain assumptions concerning particulates, ice removal, and latent heat recovery, a system design and an order of magnitude cost estimate are made for a 700-MWe coal-burning power plant. The technique can control emissions of S02. The relatively higher vapor pressures of NO2, sulfates, and heavy metal vapors suggest that these pollutants may also be contained. It is estimated that the CFGC system will cost between $180 and 275/kWe (1976 dollars) and require 5-8% auxiliary power depending on plant performance and coal composition. These costs may be reduced by optimization or process changes. H
Is the removal of SO2 from coal-fired power plant flue gas by cryogenic condensation economically feasible? This question was answered in the negative in an earlier study (1) in which a final condensation stage at LN2 temperatures was assumed. Our preliminary calculations indicated condensation of SO2 could be accomplished a t considerably higher temperatures and therefore lower cost. In addition, the potential for simultaneous removal of a number of other pollutants warranted a more detailed study of the condensation technique. This report describes a feasibility study of the CFGC system for control of SO2 emissions from a 700-MWe coalburning power plant. The study included an experimental determination of the condensation rates of SO2 and C 0 2 for various simulated flue gas mixtures under a variety of flow conditions; heat load calculations for different coal compositions and excess air ratios; and a preliminary system design and cost estimate based on the condensation data and heat load calculations ( 2 ) . Condensation Experiments
Present address, Manufacturing Processes Laboratory, Ford Motor Co., 24500 Glendale Avenue, Detroit, Mich. 48239. 0013-936X/78/0912-1183$01.00/0
The absence of condensation data in the literature for flue gas mixtures in a flowing nonequilibrium system necessitated
@ 1978 American Chemical Society
Volume 12, Number 10, October 1978
1183
