Bioresource Technology 94 (2004) 267–274

Dechlorination and decolorization of chloro-organics in pulpbleach plant E-1 effluents by advanced oxidation processes

Rui Wang a,b, Chen-Loung Chen a,*, Josef S. Gratzl a

a Department of Wood and Paper Science, North Carolina State University, Raleigh, NC 27695-8005, USAb Mead-Westvaco Corp., Covington mill, Covington, VA 24426, USA

Received 28 April 2003; received in revised form 12 January 2004; accepted 12 January 2004

Available online 27 February 2004

Abstract

Studies were conducted on the composition of chloro-organics in kraft-pulp bleach plant E-1 effluents and their response toward

advanced oxidation processes, such as UV-, O2/UV-, O3/UV- and O3–H2O2/UV-photolysis processes with irradiation of 254 nm

photons. The studies were extended to ozonation and O3–H2O2 oxidation systems in alkaline aqueous solution. The effects of

process variables included initial pH, addition of oxidant to the UV-photolysis system on the decolorization and dechlorination of

the chloro-organics the E-1 bleaching effluents were also studied. The decolorization and dechlorination rate constants are increased

in the presence of molecular oxygen in the UV-photolysis systems, but are decreased on addition of hydrogen peroxide. The

dechlorination rate constants are increased appreciably on oxidation with ozone alone and a combination of ozone and hydrogen

peroxide as compared to those of the corresponding UV-photolysis systems under aerial atmosphere.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Pulp plant bleaching effluent; Chloro-organics; Color carriers; Advanced oxidation processes; Decolorization; Dechlorination; UV-

irradiation; 254 nm photons; Oxygen; Ozone; Hydrogen peroxide

1. Introduction

A pulp from a normal kraft pulping usually contains

approximately 3% of residual lignin (Marton, 1971).

Bleaching of the pulp is required to remove the residual

lignin in order to enhance brightness. In conventional

bleaching process, removal of the bulk of residual lignin

can be achieved by treatment of pulp with elemental

chlorine under acidic condition (C-stage) and alkaline

extraction (E-1 stage) (Dence and Annergren, 1979).These treatments account for the major portion of the

chloro-organics generated in the conventional bleaching

processes (Hardell and de Sousa, 1977; Lindstr€om et al.,

1984; Kringstad and Lindstr€om, 1984). A typical kraft

mill producing 1000 metric ton/day of bleached pulp

employing conventional bleaching technology annually

generates approximately 24,000 ton of chloro-organics

that contains more than 2000 ton of organically boundchlorine (OCl). In 1984, the annual worldwide discharge

*Corresponding author. Tel.: +1-919-515-5749; fax: +1-919-515-

6302.

E-mail address: chen-looung_chen@ncsu.edu (C.-L. Chen).

0960-8524/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biortech.2004.01.005

of OCl along with the bleaching effluents into receiving

water was estimated to be approximately 250,000 ton inthe pulp and paper industry (Kringstad and Lindstr€om,

1984).

Increasing public concern about the disposal of po-

tential toxicants, and anticipated future stringent regu-

latorymeasures to control the discharge of suchmaterials

led to the development of several abatement processes.

Unfortunately, none of the existing waste treatment

processes offer a perfect solution. Progress has been madein the past two decades in adopting environmentally

benign bleaching processes using partial substitution of

chlorine with chlorine dioxide (Marwah et al., 1991;

Rajan et al., 1994) and totally chlorine free oxidants such

as oxygen and hydrogen peroxide (Gierer, 2000; Geller-

stedt and Zhang, 2001; Kadla and Chang, 2001). How-

ever, the appreciable reduction in the discharge of

potentially toxic chloro-organics is expected to be a long-term mission. Thus, it is of primary importance to de-

velop industrially viable processes to decompose the

potentially hazardous chloro-organics before the

bleaching effluents are discharged into the receiving

water, i.e., the environment. The limited ability of the

268 R. Wang et al. / Bioresource Technology 94 (2004) 267–274

conventional biological treatment systems to effectively

decolorize and degrade the organic color carriers has

directed our attention to look for alternative treatments

with advanced oxidation processes. Consequently, this

study was undertaken to explore the response of chloro-

organics in the kraft-pulp bleaching effluents towards

advanced oxidation processes as well as effectiveness of

these processes in decoloration of the effluents.

Table 1

Characteristics of the E-1 effluent

pH 11.35± 0.06

Color (Co–Pt unit) 13,000± 260

Total solid (g/l) 5.6 ± 0.2

Organic solid (g/l) 3.5 ± 0.1

Inorganic solid (g/l) 2.1 ± 0.06

Total chlorine (mg/l) 957± 19

Cl� (mg/l) 689± 14

OCl (mg/l) 268± 5

OCl in ether extractive (mg/l) 12.8± 0.3 (4.8% of OCl)

Ether extractive at pH 14 1.2± 0.1

Ether extractive at pH 9 3.0± 0.1

Ether extractive at pH 3 8.6± 0.2

Relative molecular mass (Mr) 5000± 150

2. Methods

2.1. E-1 effluent

E-1 effluent was obtained from bleaching of Loblolly

pine kraft pulps successively with Cl2 (C stage), extracted

with a NaOH solution (E stage), H2O2 (P stage), thentwice with ClO2 (DD stage), i.e., bleaching sequence

CEPDD. The bleached board division of Mead-Westv-

aco Corporation, Covington VA donated the effluent.

2.2. Chlorophenols

2,4,6-Trichlorphenol (mp 69–80 �C) and 2,3,4,5-tetrachlorophenol (mp 116–117 �C) were purchased

from Aldrich Chemical Inc., Milwaukee, WI, USA and

4,5-dichloroguaiacol (mp 68–70 �C) from Helix Biotech.

Corp., Toronto, Ontario, Canada. These phenols were

recrystallized from CHCl3–petroleum ether to constant

melting point.

2.3. Ozone

Ozone was prepared by passing oxygen through an

ozone generator (Model T-816, Polymetric, Inc. San

Jose, CA, USA) at a constant power. The concentration

of ozone produced was controlled at the range of either

2.0–2.5% or 4.0–4.5% depending on the requirement ofparticular studies. The concentration of the ozone

stream was constantly monitored with an ozone monitor

(Model HC, PCI Ozone and Control System, Inc. West

Caldwell, NJ, USA) before sending to the reactor.

2.4. Characterization of E-1 Effluent

Total solid content of the E-1 effluent was determined

by modified Tappi Method T 650 om-89 (Tappi, 1996),

while organic solid content was determined by weight

loss of the evaporated and oven-dried solid from the E-1

effluent on combustion in a muffle furnace. Experi-

mental errors were ±2%. Monomeric chlorophenols

were identified and quantitatively determined from the

Et2O extractive of the E-1 effluent by GC and GCMSanalyzes according to the procedure of Rajan et al.

(1994). Experimental errors were ±2%. Total organically

bound chlorine (TOCl) was determined by the Sch€oniger

method in combination with ion chromatograph,

Dionex 2010I (Dionex Corp. Sunnyvale, CA, USA),

equipped with an anion separator column AS-4 to

analyze and quantify the chloride anion formed during

dechlorination. Experimental error was ±2%. Relative

molecular mass distribution was determined by size

exclusion chromatography using FPCL system (Phar-

macia LKB Biotech, Piscataway, NJ, USA) with aSuperdex G-75 column according to the procedure of

Chen et al. (2003). Experimental error was ±3%. The

results are listed in Tables 1 and 2.

2.5. Chlorinated phenols identified in the E-1 effluent by

GCMS

4-Chlorophenol (1): MSEI (70 eV), m/z (rel. int.) 130

(Mþ +2, 73.4), 128 (Mþ 100), 92 (20.8), 64 (24.8).

2,4-Dichlorophenol (2): MSEI (70 eV), m/z (rel. int.)

166 (Mþ +4, 9.8), 164 (Mþ +2, 64.5), 162 (Mþ 100), 128

(6.8), 126 (9.1), 100 (20.8), 98 (28.8), 63 (24.8).2,4,6-Trichlorophenol (3): MSEI (70 eV), m/z (rel.

int.) 202 (Mþ +6, 2.8), 200 (Mþ +4, 28.8), 198 (Mþ +2,

93.4), 196 (Mþ 100), 162 (10.2), 160 (17.8), 134 (32.4),

133 (10.2), 132 (49.8), 99 (25.4), 98 (14.2), 97 (54.2), 83

(3.6), 73 (9.8), 72 (6.0), 71 (10.2), 65 (13.8), 62 (15.2), 61

(10.2), 48 (13.8).

2,3,4,5-Tetrachlorophenol (4): MSEI (70 eV), m/z

(rel. int.) 238 (Mþ +8, 1.6), 236 (Mþ +6, 12.8), 234(Mþ +4, 78.8), 232 (Mþ +2, 132.4), 230 (Mþ 100), 198

(6.1), 196 (18.8), 194 (19.8), 170 (16.2), 168 (50.8), 166

(52.6), 133 (34.22), 131 (56.4), 96 (16.8), 95 (11.2), 65

(13.8), 61 (10.2).

4-Chloroguaiacol (5): MSEI (70 eV), m/z (rel. int.)

160 (Mþ +2, 12.8), 158 (Mþ 41.5), 123. 4,5-Dichloro-

guaiacol (6): MSEI (70 eV), m/z (rel. int.) 196 (Mþ +4,

6.2), 194 (Mþ +2, 43.8), 192 (Mþ 59.2), 179 (63.6) 177(100), 151 (30.2), 149 (48.2), 113 (31.6), 85 (20.8), 50

(11.5).

3,4,5-Trichloroguaiacol (7): MSEI (70 eV), m/z (rel.

int.) 230 (Mþ +4, 20.2), 228 (Mþ +2, 62.8), 226 (Mþ

64.6), 215 (30.4), 213 (97.2) 211 (100), 201 (10.8), 199

Table 2

Quantity of chlorophenols identified in E-1 effluent

Compounds Original E-1 effluent

(mg/1000 l)

O3-oxid.a;b

(mg/1000 l)

O3/UV-photo.a;b

(mg/1000 l)

O3–H2O2/UV-photo.a;b;c

(mg/1000 l)

4-Chlorophenol (1) + 13± 0.3 NDd 1250± 25

2,4-Dichlorophenol (2) 94± 1.9 430± 8.6 100± 2 940± 18.8

2,4,6-Trichlorophenol (3) 16± 0.3 65± 1.3 NDd 50± 1

2,3,4,5-Tetrachlorophenol (4) 467± 9.3 NDd 106± 2.1 NDd

4-Chloroguaiacol (5) + 160± 3.2 NDd 360± 7.2

4,5-Dichloroguaiacol (6) 682± 13.6 NDd 64± 1.3 NDd

3,4,5-Trichloroguaiacol (7) 141± 2.8 NDd NDd NDd

4,5,6-Trichloroguaiacol (8) 47± 0.9 NDd NDd NDd

3,4,5,6-Tetrachloroguaiacol (9) 136± 2.7 NDd NDd NDd

aReaction time: 60 min.bOzone charge 0.6 g per 10 min.cHydrogen peroxide charge: 2 ml of 30% H2O2.dND denotes not detected.

R. Wang et al. / Bioresource Technology 94 (2004) 267–274 269

(34.8), 197 (36.2), 187 (12.4), 185 (41.8), 183 (43.7), 149

(33.5), 147 (52.4), 121 (13.4), 119 (24.2), 110 (20.2), 84(24.5).

4,5,6-Trichloroguaiacol (8): MSEI (70 eV), m/z (rel.

int.) 230 (Mþ +4, 22.6), 228 (Mþ +2, 69.6), 226 (Mþ

70.6), 215 (31.2), 213 (96.8) 211 (100), 201 (8.2), 199

(28.2), 197 (29.5), 187 (10.8), 185 (35.4), 183 (37.2), 149

(30.8), 147 (47.9), 121 (11.2), 119 (19.6), 84 (22.4), 43

(10.5).

3,4,5,6-Tetrachloroguaiacol (9): m/z (rel. int.) 266(Mþ +6, 8.8), 264 (Mþ +4, 48.8), 262 (Mþ +2, 82.2), 260

(Mþ 64.8), 251 (8.6), 249 (60.4), 247 (100) 245 (75.8), 231

(32.4), 217 (40.4), 187 (6.4), 185 (40.2), 183 (58.4), 181

(50.8), 157 (6.2), 155 (18.8), 153 (20.2), 120 (14.8), 118

(23.6), 83 (6.7).

2.6. UV-photolysis

Thin film reactor (Ace Glass Laboratories, Vineland,

NJ, USA) used in this study was made of borosilicateglass and equipped with a weir arrangement to provide a

flow of reactant solution over a knife edge and down the

inner wall of the reactor. An impeller type fluid pump

with adjustable pumping capacity is provided to circu-

late the effluent through the reactor. A low pressure Hg

lamp, 12 W with energy profile of approximately 3.4 W

at 254 nm was held vertically and surrounded by a

water-cooled jacket. In this study, the volume of the E-1effluent was 400 ml with circulation rate of 250 ml/min.

The flow rate of both O2 and O3 streams were either 50

or 100 ml/min when applied to the system. Introduction

of 4.5% O3 stream with flow rate of 50 ml/min for 2 min

corresponds to approximately 0.2 mmol of O3. The 3.5%

O3 stream with flow rate of 400 ml/min for 1 min cor-

responds to O3 charge of 30 mg/min. In the case of

studies under N2 atmosphere, N2 was introduced intothe reactor at 1 l/min for at least 1 h to assure comple-

tion of air displacement. The pH of the solution was

monitored through the entire reaction period. Samples

were withdraw at certain intervals from the sample port

and injected into ion chromatography, Dionex 2010i(Dionex Corp. Sunnyvale, CA, USA), equipped with an

anion separator column AS-4 to analyze and quantify

the chloride anion formed during dechlorination.

Experimental error was ±2%. Color of the samples from

the E-1 effluent was measured by the spectrophotometric

method as described in NCASI technical bulletin no.

253 (NCASI, 1971). The method consists of diluting the

effluent samples until the color value falls between 150–500, adjusting the pH of the diluted solution to about

7.6 and filtering the samples through a 0.8 lm filter to

remove any suspended solids or precipitates. The pH of

the samples solutions were finally readjusted to 7.6 and

UV absorption of the resulting solutions at 465 nm was

measured with a Perkin–Elmer Lambda 3B UV–VIS

spectrophotometer (Perkin–Elmer Instruments, Shelton,

CT, USA). Experimental error was ±2%.

2.7. Experimental errors

All experiment was conducted at least in triplicate.The experimental errors were then determined in term of

accuracy, i.e., the average deviation (a.d.) of a mean

value. It was calculated from the average deviation of a

single determination (a.d.) divided by the square root of

the number (n) of determination made: a:d: ¼ a:d:=n1=2.

3. Results and discussion

3.1. Characteristics of E-1 effluent

The effluent contains considerable color carriers

contribute to its color, 13,000 Co–Pt units (Table 1). The

total solid of the effluent is 5.6 g/l, of which 3.5 and2.1 g/l are organic and inorganic materials, respectively.

The total chlorine content of the effluent is 957 mg/l,

of which 689 and 268 mg/l are chloride (Cl�) and

270 R. Wang et al. / Bioresource Technology 94 (2004) 267–274

organically bound chlorine (OCl), respectively. Ap-

proximately 5% of the OCl are ether extractable (Table

1). Thus, it is evident that the major part of the OCl is

present in the high relative molecular mass fractions that

are not extractable by ether.

The chlorophenols identified in the E-1 effluent in-

clude 4-chlorophenols (1), 2,4-dichlorophenol (2), 2,4,

6-trichlorophenol (3), 2,3,4,5-tetrachlorophenol (4), 4-chloroguaiacol (5), 4,5-dichloroguaiacol (6), 3,4,5-tri-

chloroguaiacol (7), 4,5,6-trichloroguaiacol (8) and 3,4,5,

6-tetrachloroguaiacol (9) (see Fig. 1 for structure).

Among the chlorophenols identified, 4 and 6 are the

major components, while 1 and 5 are detected in trace

amount (Table 2). In addition, the total yield of 1–9 is

1.583 mg/l (Table 2). This follows that the chlorophenols

identified is less than 13% of the total ether extractableOCl carrier, which contains 12.8 mg/l of OCl. When the

E-1 effluent was oxidized with ozone alone without the

UV-photolysis, the compounds 1–3 and 5 in the resulting

reaction mixture were increased; 1 from trace amount to

136 mg/1000 l, 2 from 94 to 430 mg/1000 l, 3 from 16 to

65 mg/l, and 5 from trace amount to 160 mg/1000 l,

whereas the compounds 4 and 6–9 were not detected

(Table 2). In contrast, when the E-1 effluent was treatedwith O3/UV-photolysis, the compounds 4 and 6 in the

resulting reaction mixture were decreased; 4 from 469 to

106 mg/1000 l and 6 from 682 to 64 mg/1000 l, while 1, 3,

5 and 7–9 were not detected. Only the compound 2 was

increased, from 94 to 100 mg/1000 l (Table 2). However,

when the E-1 effluent was treated with O3–H2O2/UV-

photolysis, compounds 1–3 and 5 in the resulting reac-

tion mixture were increased; 1 from trace amount to 1250mg/1000 l, 2 from 94 to 940 mg/1000 l, 3 from 16 to 50

mg/l, and 5 from trace amount to 360 mg/1000 l, whereas

the compounds 4 and 6–9 were not detected (Table 2).

The increased in the monomeric chlorophenols must be

released by oxidation of high molecular mass chloro-

organics, such as polychlorinated oxylignins (Xie, 1994).

The high molecular mass materials are the major

products formed in the conventional bleaching. They

OH

Cl

OH

Cl

Cl Cl

OH

Cl

OH

Cl

OH

Cl

OCH3 OOCH3

Cl ClCl

1 2

5 6 7

Fig. 1. Structure of chlorophenols

consist of polychlorinated oxylignins (PCOLs) and

contain not only large portion of OCl, but also the bulk

of chromophoric structures that contribute appreciably

to the color of the effluent. Furthermore, these materials

consist mostly of non-aromatic moieties (Xie, 1994). On

Ar–F� excimer laser photolyis, PCOLs are readily de-

chlorinated (Xie, 1994; Thomas et al., 1995a,b).

3.2. Decolorization and dechlorination of E-1 effluent

Alkaline extraction effluent from bleaching of Lob-

lolly pine kraft pulp with a CEPDD sequences was

subjected to UV-photolysis under similar reaction con-ditions as described in the model compound study

on dechlorination. Since the effluent contains not only

substances with OCl but also color carriers with chro-

mophoric structures, changes in both the OCl content

and color unit of the effluent were determined by the

UV-photolysis as well as the ozone treatment of effluent.

The UV-photolysis investigated included O3/UV-, H2O2/

UV- and O3–H2O2/UV-photolysis systems with 254 nmphotons using the UV-photolysis under nitrogen atmo-

sphere as reference. The kinetics of decolorization and

dechlorination were monitored by change in the UV

absorbance at 465 nm and chloride content with certain

intervals through the entire reaction period, respectively.

3.2.1. Decolorization

With a 12 W low pressure Hg lamp as the UV light

source (254 nm), the irradiation of effluent with 254 nm

photons under nitrogen atmosphere is not effective in

decolorizing the effluent. Less than 6% of color carriers

were removed for reaction time of 60 min with first or-der decoloration rate constant of 1.1 · 10�4 s�1 with re-

spect to the Co–Pt unit. Addition of hydrogen peroxide

(H2O2 charge: 10% on the solid) to the UV-photolysis

system appreciably increased the decolorization rate;

approximately 66% of color carrier (chromophores)

were destroyed within 5 min with first order decolor-

ation rate constant of 2.26 · 10�3 s�1 for initial phase.

OH

Cl

Cl

OH

Cl

Cl

ClCl

CH3

OH

Cl

OCH3

Cl

OH

Cl

OCH3

ClCl

Cl

3 4

8 9

Cl

identified in the E-1 effluents.

0

2000

4000

6000

8000

10000

12000

14000

0 10 20 30 40 50 60 70

UV-Irradiation Time (min)

Col

or (

Co-

Pt C

olor

Uni

t)

Fig. 2. Decolorization of E-1 effluent. UV-photolysis with 254 photons under N2 atmosphere: (-r-); O3 alone: (-N-); O3/UV-photolysis with 254

photons under aerial atmosphere: (-j-); H2O2/UV-photolysis with 254 photons under aerial atmosphere: (-�-); O3-H2O2/UV-photolysis with 254 nm

photons under aerial atmosphere: ( ). Initial pH: 10.34; temperature: ambient; O3 charge: 0.86 mmol/min; H2O2 charge: 10% on sold by weight; UV

source: 12 W low pressure Hg lamp (254 nm photons). Experimental error: ±2%.

R. Wang et al. / Bioresource Technology 94 (2004) 267–274 271

The decolorization then leveled off (Fig. 2). Conceiv-

ably, the structures of residual color carriers are likely to

remain unchanged in the second phase of the H2O2/UV-

photolysis. Ozone is also an effective oxidant for

removing the color carriers. The treatment of the efflu-

ent with an ozone stream with ozone charge of 30 mg/

min resulted in decolorization of approximately 76%within 15 min with first order decoloration rate constant

of 1.56 · 10�3 s�1 for the initial phase. The O3/UV-

photolysis is less effective than the treatment with ozone.

It decolorized the effluent approximately 72% with UV

(254 nm photons) irradiation time of 15 min with first

order decoloration rate constant of 1.32 · 10�3 s�1 for

the initial phase. When the ozone stream was introduced

into the H2O2/UV-photolysis system with ozone chargeof 30 mg/min, color reduction of approximately 85%

was achieved within 15 min of irradiating 254 nm pho-

tons with first order decoloration rate constant of

3.25 · 10�3 s�1. The color reduction then slowed down.

The effect of the initial pH of the effluent on the O3/

UV-photolysis system has been investigated. The oxi-

dation carried out with initial pH of 7 was found less

effective on reducing color (Fig. 3). At an initial pH of11.35, approximately 10–15% more color reduction was

observed at an UV irradiation time of 60 min.

3.2.2. Dechlorination

The dechlorination rate of the E-1 effluent by UV-

photolysis under nitrogen atmosphere and O3–H2O2/

UV-photolysis proceeds with two phases, a very fast

initial phase, up to first 5 min of the reaction then level

off at second phase (Fig. 4). By contrast, the dechlori-

nations of the E-1 effluent by O3 alone and by the O3/

UV-photolysis proceeded with three phases: a very fast

initial phase up to first 5 min of the reaction, followed by

a very slow second phase from reaction time of 5–50

min, and finally a moderately fast third phase fromreaction time of 50–60 min.

Similar to the color reduction, the irradiation of

effluent with 254 nm photons under nitrogen atmo-

sphere is not effective in dechlorinating the effluent; for

the initial phase, the first order dechlorination rate

constant is only 9.83 · 10�5 s�1 with respect to organi-

cally bound chlorine (OCl) (Fig 4). It is evident that over

40% of the OCl in the E-1 effluent are ozone sensitive.They readily undergo dechlorination to give chloride

anion on treatment with the ozone stream correspond-

ing to ozone charge of 30 mg/min with first order

dechlorination rate constant of 1.83 · 10�3 s�1 for the

initial phase. Nevertheless, the dechlorination of the

effluent by the O3/UV-photolysis is less effective than

that by the treatment with ozone; first order dechlori-

nation rate constant for the initial phase, 1.83 · 10�3

versus 1.51 · 10�3 s�1. In addition, the dechlorination of

the effluent proceeds better in alkaline condition. The

dechlorination efficiency was appreciably lower, only

approximately 20% of OCl can be removed as chloride

anion with first order dechlorination rate constant of

8.07 · 10�4 s�1 for initial phase, when the O3/UV-

photolysis of the effluent was carried out under neutral

0

2000

4000

6000

8000

10000

12000

14000

0 10 20 30 40 50 60 70

UV-Irradiation Time (min)

Col

or (

Co-

Pt C

olor

Uni

t)

Fig. 3. Effect of the initial pH on decolorization of the E-1 effluent with ozone/UV-photolysis with 254 nm photons under aerial atmosphere. pH 7:

(-r-); pH 11.35: (-j-). Temperature: ambient; O3 charge: 0.86 mmol/min; UV source: 12 W low pressure Hg lamp (254 nm photons). Experimental

error: ±2%.

40

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70

UV-Irradiation Time (min)

Org

anic

ally

Bou

nd C

hlor

ine

(Mol

% p

er O

rigi

nal)

Fig. 4. Dechlorination of chloro-organics in the E-1 effluent. UV-photolysis under N2 atmosphere: ( ); O3 /UV-photolysis with 254 photons under

aerial atmosphere: ( ); O3 alone: ( ); O3–H2O2/UV-photolysis with 254 nm photons under aerial atmosphere: ( ). Initial pH: 10.34; temperature:

ambient; O3 charge: 0.86 mmol/min; H2O2 charge: 10% on sold by weight; UV source: 12 W low pressure Hg lamp (254 nm photons). Experimental

error: ±2%.

272 R. Wang et al. / Bioresource Technology 94 (2004) 267–274

condition (Fig. 5). In contrast, at the initial pH of 11.35,

approximately 36% of OCl are converted into chloride

anion with first order dechlorination rate constant of1.51 · 10�3 s�1 for the initial phase within 5 min of

irradiation in the O3/UV-photolysis. The residual OCl is

difficult to undergo dechlorination by O3/UV- and O3–

H2O2/UV-photolyses, even by oxidation with ozone in

alkaline solution (Fig. 4). Conceivably, energy output ofthe UV source used in this study is not high enough to

meet the need for the oxidative decomposition of the O3/

40

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70

UV-Irradiation Time (min)

Org

anic

ally

Bou

nd C

hlor

ine

Con

tent

(Mol

% p

er O

rigi

nal)

Fig. 5. Effect of the initial pH on dechlorination of the E-1 effluent with ozone/UV-photolysis with 254 nm photons. pH 7: ( ); pH 11.35: ( ).

Temperature: ambient; O3 charge: 0.86 mmol/min; UV source: 12 W low pressure Hg lamp (254 nm photons). Experimental error: ±2%.

R. Wang et al. / Bioresource Technology 94 (2004) 267–274 273

UV-photolysis-stable organically bound chlorines in

substrates, presumably aliphatic chlorides, in the E-1

effluent. Only approximately 5% of the OCl were de-

chlorinated by the irradiation of 254 nm photons alone

under nitrogen atmosphere. This portion could be cor-

responding to the extractable chlorophenols. Most ofthe major chlorophenols identified in the E-1 effluents

were not detected in all the reaction mixtures obtained

from treatment with UV-photolysis systems involving

ozone. However, some minor chlorophenols were pro-

duced in the treatment. For example, approximately 1.2

mg/l of 4-chlorophenol (1) and 1 mg/l of 2,4-dichloro-

phenol (2) were detected in the reaction mixture of E-1

effluent treated with the O3–H2O2/UV-photolysis for60 min. It is conceivable that these chlorophenols are

originated from degradation of high molecular mass

polychlorinated oxylignins (PCOLs) in the second phase

and undergo dechlorination in the third phase of the

photolysis. Only 0.1 mg/l of 2 but not 1 was detected in

the reaction mixture of E-1 effluent treated with O3/UV-

photolysis. This implies that the addition of hydrogen

peroxide in the O3/UV-photolysis system promotes thedechlorination of chlorophenols produced by degrada-

tion of PCOLs.

4. Conclusions

With a major energy source at 254 nm, the UV-

photolysis alone did not show appreciable effectiveness

color reduction and removal of organically bound

chlorine (OCl) in E-1 effluent. Addition of hydrogen

peroxide promotes the reduction of color carriers and

degradation of polychlorinated oxylignins (PCOLs),

but does not improve appreciably in the dechlorina-

tion.

Introduction of ozone stream into the UV-photolysissystem result in appreciable improvement in both

decolorization and dechlorination of E-1 effluent. Up to

approximately 40% of total organically bound chlorine

in these chloro-organics was converted into chloride ion

within reaction time of 5 min. Degradation of high

molecular mass polychlorinated oxylignins might be the

orignin of monomeric chlorophenols generated when

hydrogen peroxide was added into the UV-photolysis ofE-1 effluent.

Ozonation of E-1 effluent under alkaline pH is an

effective method for degradation of high molecular mass

polychlorinated oxylignins without irradiation of 254

nm photons. The ozonation is pH dependent. When pH

of the effluent was adjusted to neutral, less effectiveness

on both dechlorination and decolorization were ob-

served.

Acknowledgements

This project is supported by the USDA competitive

research grant under cooperative agreement no. 88-33521-4084, for which the authors are thankful. The

authors are also grateful to Westvaco Corporation for

supplying the E-1 effluent for this study.

274 R. Wang et al. / Bioresource Technology 94 (2004) 267–274

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