Use of Gel Permeation Chromatography To Study Water Treatment

18 Use of Gel Permeation Chromatography To Study Water Treatment Processes Downloaded by UNIV OF ARIZONA on February 1, 2016 | http://pubs.acs.org Publication Date: December 15, 1986 | doi: 10.1021/ba-1987-0214.ch018

A. Bruchet, Y. Tsutsumi, J. P. Duguet, and J. Mallevialle Lyonnaise des Eaux Central Laboratory, 38 rue du President Wilson 78230 Le Pecq, France The efficiency of a water treatment process is often evaluated by using nonspecific and specific parameters. Most of the time, specific determinations involve extraction techniques followed by gas chromatography (GC) or high-performance liquid chromatography. Consequently, determinations are limited to the study of volatile and semivolatile organics. This chapter presents a gel permeation technique used to study higher molecular weight or more polar compounds. The gel permeation chromatography and pyrolysis GC-mass spectrometry were used in a pilot study at Vigneux, south of Paris, to determine the efficiency of the combination of ozone and granular activated carbon unit processes.

tj

V A L U A T I O N O F A W A T E R T R E A T M E N T PROCESS usually involves the

measurement of nonspecific parameters (e.g., dissolved organic carbon [DOC], total organic halogens [TOX], U V absorbance, fluorescence). In addition, the development of chromatographic methods (gas and liquid phase) and extraction techniques (e.g., resin adsorption, continuous liquid-liquid extraction) has expanded analysis to many volatile and semivolatile nonpolar compounds. However, the majority of the organic carbon is generally found in the form of humic and fulvic acids (J) together with other biological macromolecules. These compounds are not well-characterized and are not amenable to analysis with current organic analytical techniques. These humic and fulvic acids contribute substantially to the carbon balance in a unit process. They can also modify the way micropollutants 0065-2393/87/0214/0381$06.00/0 © 1987 American Chemical Society

In Organic Pollutants in Water; Suffet, I. H. (Mel), et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

Downloaded by UNIV OF ARIZONA on February 1, 2016 | http://pubs.acs.org Publication Date: December 15, 1986 | doi: 10.1021/ba-1987-0214.ch018

382

ORGANIC POLLUTANTS IN WATER

act in a process b y association (2), and they may be precursors for volatile halogenated compounds (3, 4). Several attempts to characterize these dissolved organic compounds have resulted in general models for humic acid (5, 6). T w o techniques are generally used to separate organic compounds b y molecular weight: ultrafiltration on membranes and gel permeation chromatography ( G P C ) . Use of ultrafiltration to separate humic acids from natural surface water and to study the effects of ozonation on these humic acids has been previously reported (7). The method was shown to be quite useful but very time-consuming. Recently, G P C using Sephadex gels has been applied in the field of sewage treatment (8) and in the natural environment on lake or ground waters (9, 10). Also, new silica gels for high-pressure liquid chromatography ( H P L C ) have been developed, and their ability to separate natural organic compounds in water has been demonstrated (II, 12). This study reports two gel permeation techniques used to evaluate water at various stages of (potable water) treatment. The water samples were taken f r o m a surface-water pilot treatment plant that employed several levels of ozone treatment. Selected fractions of the permeate were subsequently analyzed b y pyrolysis gas chromatography-mass spectrometry ( G C - M S ) .

Materials and Methods The source of water samples was a 4-m /h pilot plant on the Seine River located upstream f r o m Paris, France. The background organic concentration ranged f r o m 2 to 3 m g / L . The process, shown in Figure 1, included an u p f l o w solids contact clarifier (Pulsator, Degremont, Rueil Malmaison, France) f o l l o w e d b y rapid sand filtration (RSF). The effluent of the R S F was then split into four lines, which received various levels of ozonation followed b y granular activated carbon ( G A C ) adsorption. Postchlorination (0.2 mg/L residual after 1 h) was used for bacterial control. 3

G e l Permeation Chromatography. The molecular weight distributions were determined b y gel permeation chromatography ( G P C ) on Sephadex G25 (Sephadex Pharmacia, Uppsala, Sweden). Conditions were as follows: column size, 0.25 X 90 c m ; eluant, water; f l o w rate, 100 m L / h . Water samples were first concentrated b y rotary evaporation to obtain a total organic carbon ( T O C ) concentration between 100 and 200 mg/L. T e n milliliters of these concentrates was then injected into the Sephadex column. Fractions were collected following chromatographic separation for analysis. U V absorbance at various wavelengths, T O C (Dohrman D C 8 0 , Envirotech C o r p . ) , and fluorescence (excitation wavelength = 320 n m , emission wavelength = 405 nm) were measured on the fractions collected. In Organic Pollutants in Water; Suffet, I. H. (Mel), et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.


18.

B R U C H E T E T AL.

383

Gel Permeation Chromatography

QAC

Filtr.

Figure 1. Diagram of Vigneux pilot plant. High-pressure G P C was performed on a D u Pont 8800 ehromatograph equipped with two T S K G 2000 S W columns (7.5 X 300 m m each column) in series. The chromatograph was operated at 1 m L / m i n , and 5 m M phosphate buffer was used as the eluent. Detection was b y U V at 254 n m . Pyrolysis G C - M S Analysis. Flash pyrolysis was performed b y using a pyroprobe 100 (Chemical Data Systems) temperature-control system. Samples were p y r o l y z e d f r o m 150 to 750 °C with a temperature program of 20 °C/ms and a final hold for 20 s. After pyrolysis, the fragments were separated on a 25-m C P W A X 57 fused silica capillary column (temperature program: 25-220 ° C at 3 °C/min), followed b y M S on a R 10-10 C (Ribermag, Rueil-Malmaison, France) operated at 70 e V and scanned f r o m 20 to 400 m/z.

Remits and Discussion Size Exclusion Chromatography. Examples of H P L C chromatograms obtained f o r line I b y using T S K G 2000 S W are shown i n Figure 2. The chromatograms came from rapid sand-filtered water (RSW), ozonated water, and G A C - f i l t e r e d water. In each chromatogram, three peaks were observed i n less than 15 m i n . Because no exclusion peak o c c u r r e d , apparently no U V - a b s o r b i n g c o m p o u n d s h a v i n g molecular weights ( M W ) >10,000 were present. In Organic Pollutants in Water; Suffet, I. H. (Mel), et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986.

384

O R G A N I C P O L L U T A N T S IN W A T E R


τ

1

1—ι

1

1

1—ι

1

1

r

Figure 2. HPLC chromât ο grams obtained for Une I by using TSK G 2000 SW.

The predominant effect of ozone and subsequent G A C contact is seen in the first two peaks. These peaks represent intermediate molecular weights and undergo a dramatic reduction in concentration. T h e third peak is only slightly diminished b y the treatment process. The use of U V excitation at 254 n m (UV254) introduces potential interfer ences f r o m inorganic materials. Several solutes (nitrate, chloride, phos phate, sulfate) were analyzed to determine their contribution to the UV254 response. Only nitrate was found in sufficient quantity to substan tially contribute to the peaks observed. This situation is shown graph ically in Figure 2 in the ozone + G A C chromatogram. Nitrate, at a concentration of 20 m g / L , accounted for 30% of the third peak. This method p r o v e d to be both easy to operate and rapid. However, some drawbacks may limit its applicability. Silanol groups on the gel may adsorb materials irreversibly and can bleed organic carbon into the system. Because of the l o w volumes of sample injected, T O C balances using this type of technique are not possible. Size-exclusion chromatography with Sephadex gel was used to study changes in the organic matrix as it passed through the treatment process at Vigneux. The results obtained are presented in Figures 3-7. Points where significant differences were observed are indicated b y arrows.



18.

BRUCHET ET AL.


385

RAPID SAND FILTRATION. A comparison between raw water and sand-filtered water is shown in Figure 3. Three main fractions are typically recovered with Sephadex G25 f r o m l o w - T O C surface waters. These fractions w i l l be referred to as G l , G3, and G5, which correspond to the fraction numbers b y order of elution. T h e apparent M W s for these fractions are as follows: >5000 daltons for G l , 1000-5000 daltons for G 3 , and 5000 daltons, 17% ( G l ) ; 1000-5000 daltons, 29% (G3); and

H > Ζ H Ζ

G

r r

s

Ο 50 Ο > Ζ


18.

BRUCHET ET AL.

Gel Permeation

Chromatography

387

indicate where changes in any parameter occur across the unit operation of ozonation. U V 2 6 0 and fluorescence are greatly reduced for fraction G5, and the reduction increases with ozone dose and contact time. This finding is interpreted as destruction of aromatic rings and unsaturated bonds. A slight decrease i n T O C is observed i n the high molecular weight ( H M W ) fraction ( G l ) , but increasing the ozone dose and contact time does not bring about complete destruction of this fraction. Thus, a portion of the H M W fraction is apparently composed of organics very resistant to ozonation, such as sugars and proteins (14). The most surprising result was that transformation of compounds does not i n crease the T O C of the lowest M W fraction (G5), which shows a decrease. O n the other hand, the intermediate fraction (G3) shows an increase in T O C . This shift could be partially due to transformation of the H M W to fraction G3. However, the increase in T O C for fraction G 3 seems to be too great to be explained solely b y migration f r o m G l to G 3 . Thus, some of the T O C may have shifted f r o m G 5 to G 3 , either because of the formation of polar oxidation byproducts with elution volumes matching those of G 3 (under the experimental conditions used, certain carboxylic acids such as acetic or citric acid would be eluted in fraction G3) or possibly b y the mechanism of oxidative polymerization (15, 16). G A C A D S O R P T I O N . Figure 5 shows the evolution of parameters for G A C filtration. In this case, significant reductions in the parameters had already occurred for G A C preceded b y ozonation. G A C further reduced the T O C of the l o w (G5) and intermediate (G3) fractions, whereas the H M W fraction remained relatively unchanged. In the case of G A C filtration without preozonation, the UV260 was reduced compared with the R S W , but not to the same degree as was observed for ozonation at 5 mg/L. DISINFECTION. Figure 6 shows the distribution of parameters after disinfection. T h e addition of chlorine or chlorine dioxide after G A C filtration (without preozonation) d i d little to affect the parameters reported here. A slight decrease was observed for fluorescence and UV260 for fractions G 3 and G5, both for chlorine and chlorine dioxide. The effect of the various treatments on the distribution of T O C within the three molecular weight fractions is summarized in Table I. Arrows are used to show whether the T O C increased, decreased, or remained unchanged. The only unexpected result was the increase in the intermediate M W T O C after ozonation.

Pyrolysis G C - M S . Pyrolysis G C - M S was used to obtain general information on the composition of each Sephadex fraction. This tech-



t

t

• 50

ι

\ ! •

FMC.NO

DOC

Fluo.

10

5

0

0.1

0.2

0.3f

ίο μ

5

0

0.1

0.2

0.3f-

? 50

Fr*c. No.

ι

ι

1

>'

•

GAC

• GAC

Frac.No.

0Z0NE(5mg/l 10mm)

30

Figure 5. Evolution of parameters for GAC filtration.

OZONE (1mg/l 10mm) • GAC

30

ι·ι

.ΊU s a

•ι

RAPID SAND FILTRATION - • F r a c . No.

Ε 220 Ε260



Figure 6. Distribution of parameters after disinfection.


390

O R G A N I C P O L L U T A N T S IN W A T E R


Table I. Evolution of the Sephadex Fractions (TOC) Fraction (MW)

Sand Filtration

>5000 1000-5000 5000). Most of the pyrolysis fragments found i n this fraction are derived f r o m the three general classes just mentioned. Pyrrole and methylpyrrole originate f r o m proteinaceous material such as polypeptides as well as f r o m single amino acids such as proline and hydroxyproline. A quantitative relationship between amino acid hydrolyzable content and pyrrole abundance was established b y Bracewell (20) for some Scottish b r o w n forest soils, and such a correlation probably could be established for water. The phenols and cresols observed on the pyrochromatogram could arise f r o m tyrosine-containing proteins, which yield phenol and p-cresol (17 21) during pyrolysis. However, because of (1) the similarity i n concentration ofTO-and p-cresol and (2) the l o w p-cresol/phenol ratio found here (—0.1 expressed as the ratio of the peak areas) compared with the higher values observed with natural proteins such as bovine serum albumin (BSA) (21) for which this ratio was close to 1, it is more likely that these phenolic peaks originated f r o m polyhydroxyaromatic compounds. T h e relatively l o w yield of phenol generated (compared with acetamide, for instance) indicates that humic substances are not major constituents of this higher M W fraction. Furfural and methylfurfural are highly characteristic of sugars. 2-Cyclopenten-l-one has been described as a characteristic product of polycarboxylic acids (22). H o w e v e r , it has also been detected during furnace pyrolysis of D-glucose (17) and i n this laboratory during the pyrolysis of Dextran, along with t w o other cyclic ketones tentatively identified as 2- a n d 3-methyl-2-cyclopenten-l-one. Thus, possible polysaccharide origin is suggested. Acetol (l-hydroxy-2-propanone) also arises f r o m sugars and may become the main pyrolysis fragment if salts are present (23). y


BRUCHET ET AL.

18.


sjouaqd |^H1 IN 3


|oua

Hd

ap i i u e u e d o j j

ap i u i n a o y

d υ d ι r ι qd r|s| auazuaqoueXQ |fjnjjnj|4qia w

J J X d ι X t| τ a

ρ ID e D i u o i d o j j

a jo 3N0l ^ u

u a d o

!

02I^^H£

3 X

-

auoia)| \k\[i*w | / j n j g pioe • π a D ^ |e 3N

jnj jnj

Olu*luadop/ 2|Xtoaw2 3

auo-i-uaiuadop^Q-g |0)aoy auipij/d|Xq)a^ auaj^iç 230 auanjoji NOH^ ο ο

ο y. ^


ο ο

In Organic Pollutants in Water; Suffet, I. H. (Mel), et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1986. en Ο

V.

ο ο

0C2

(β* Qo

ro ο ο

-*

0C3 . Àcetol 2__Cyclopenten-1- one 2 Methyl 2Cyclopenten 10 NE

Ο ο

ο ο


CM

ο

Furfural Acetîc acid

(Λ

Pyrrole 3Methyl2Cyclopenten 10NE C-+i· < δ*

ο ο

Propionicacid Methyl pyrrole Methyl furfural

LA Ο ϊ> Ζ en Ο Ο

3

Naphtalene ι

ο ο

Ci Ο

Methylnaphtalene Acetamide

Ci

Propanamide ο ο

Dimethylnaphtalene

CL Phenol 00 ο ο

SX

i

Methylphenols CD

ο ο

C2Phenol C3Phenol

ΗΉΧΥΛΥ NI S X N V X n n O d 3INV0HO

Z6£

B R U C H E T E T AL.

18.

393


ο κ> χ ο • ζ ο χ •

CM Ο Ο


U

• ι 200

•

•

ι 400

ι 600

ι 800

ι 1000

SCAN

Figure 9. Pyrochromatogram of fraction G5 (MW

Use of Gel Permeation Chromatography To Study Water Treatment

Recommend Documents