Fs in Chinese Non-Wood Pulp and

Article pubs.acs.org/est

Formation and Emission of PCDD/Fs in Chinese Non-Wood Pulp and Paper Mills Xueli Wang, Yuwen Ni, Haijun Zhang, Xueping Zhang, and Jiping Chen* Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, People's Republic of China S Supporting Information *

ABSTRACT: Chlorine bleaching is still practiced by non-wood pulp and paper mills in China, resulting in considerable formation and emission of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). We investigate the distribution of PCDD/Fs in different papermaking processes and dioxin emissions at six typical Chinese non-wood pulp and paper mills. Raw materials for papermaking included reed, wheat straw, bamboo, and sugar cane bagasse. The formation and emission of PCDD/Fs varied strikingly according to bleaching processes and raw materials. Elemental chlorine bleaching promoted the formation of tetra- to octa-CDDs and 2,3,7,8TCDF, while hypochlorite bleaching only gave rise to a significant increase of 2,3,7,8-TCDF. Bleaching with elemental chlorine and hypochlorite increased 2,3,7,8-TCDF 0.9−42.5 and 0.3−4.1 times, respectively. Most of the 2,3,7,8TCDF formed at hypochlorite bleaching stage was partitioned into the effluent, which indicated that hypochlorite bleaching was also an important emission source of dioxins. The removal of PCDD/Fs occurred visibly during alkaline digestion, alkaline extraction, and hydrogen peroxide bleaching. Furthermore, the annual emission of PCDD/Fs from Chinese non-wood pulp and paper mills was evaluated.

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INTRODUCTION The chlorine bleaching process in pulp and paper industry can produce a lot of adsorbable organic halides (AOX).1 As one group of AOX, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) have been receiving great concern. In the 1980s and 1990s, comprehensive investigations into the formation and emission of PCDD/Fs from wood pulp bleaching with chlorine were conducted in North America and Europe.2−9 The isomer patterns of PCDD/ Fs emitted from pulp bleaching are generally characterized by 2,3,7,8-TCDF, 2,3,7,8-TCDD, and OCDD, and they are obviously distinguishable from those found frequently from incineration sources and organochlorine industries. In 2004, pulp and paper mills have been listed in the Annex C Part of the Stockholm Convention on Persistent Organic Pollutants (POPs Convention) as a relevant emission source of PCDD/ Fs.10 Modern papermaking evolved from ancient China, ca. 105 A.D, with China still having the largest paper making industry in the world. It has been estimated that China produces approximately 80% of the world’s non-wood pulp.11 The main sources of non-wood raw materials are agricultural residues such as cereal straws and sugar cane bagasse (a fibrous residue from processing sugar cane). Bamboo, reeds, and some grass plants are also grown or collected for the pulp industry. The non-woody plants usually contain less lignin, more silica, and more coloring matters than the woody plants.12 These differences result in a reduced requirement for cooking time and increased consumption of water and bleaching agents for © 2012 American Chemical Society

production of the non-wood pulp. Therefore, the formation and emission of PCDD/Fs from non-wood pulp production may be somewhat different from wood pulp production. Nowadays, PCDD/Fs emission levels from pulp production have been reduced greatly in developed countries by eliminating the use of chlorine bleaching and improving chlorination procedures.13−15 However, most non-wood pulp and paper mills in P.R. China still adopt the conventional chlorine bleaching technology. A traditional pulp bleaching sequence includes bleaching with chlorine gas (C stage), alkaline extraction (E stage), and bleaching with hypochlorite (H stage). PCDD/Fs are formed mainly at the C stage.3,5,16,17 The main formation mechanism of PCDD/Fs is considered to be the chlorination of dibenzo-p-dioxin and dibenzofuran (DBD/F) and nonextractable precursors in the pulp.5,7,16 In addition, some studies indicate that the chlorinated phenols are also important precursors of PCDDs.17,18 These chlorinated phenols mainly arise from the degradation of lignin and the contamination of chlorinated phenols.17 Some researchers have also investigated the distribution of PCDD/Fs at the E and H stages.2,19 However, the variation in PCDD/Fs during these two stages cannot be verified due to the lack of data regarding the pulp and effluent mass balance. Received: Revised: Accepted: Published: 12234

August 19, 2012 October 10, 2012 October 15, 2012 October 15, 2012 dx.doi.org/10.1021/es303373b | Environ. Sci. Technol. 2012, 46, 12234−12240

Environmental Science & Technology

Article

Figure 1. The schematic diagram of pulping and papermaking process.

storage tank and finally fed into a paper briquetting machine to make paper. Effluents from the different stages were incorporated (mixed effluent) and transported to a wastewater treatment device. Basic information on the six non-wood pulp and paper mills is given in Table 1.

The production of pulp and paper from non-wood plants is a complex field that deals with different raw materials and consists of different bleaching stages. However, data on the emission of PCDD/Fs from non-wood pulp and paper mills are relatively scarce.20−23 In 2007, P.R. China developed its National Implementation Plan (NIP) for the POPs Convention, in which the pulp and paper industry with chlorine bleaching was assigned as an important emission source of dioxins to be controlled.24 In this study, we conducted a comprehensive investigation on the levels and profiles of PCDD/Fs in raw materials, solid pulps, effluents, products, and sludge from six typical Chinese non-wood pulp and paper mills. On the basis of the surveying data, the dioxin mass distributions at different papermaking stages were calculated. Moreover, the emission factors and emission amounts of PCDD/Fs from nonwood pulp and paper mills in China were evaluated. The obtained data could provide important information for developing the best available technology/best environmental practice (BAT/BEP) to non-wood pulp and paper mill and also provide some data support for the dioxin release inventory.

Table 1. Basic Information of Test Pulp and Paper Mills mill PM1 PM2 PM3 PM4 PM5 PM6

raw material reed reed bamboo wheat straw sugar cane bagasse wheat straw

bleaching process a

b

c

C + Ep + H C + Ep + H C + Ed + H + P e C+E+H C+E+H H

pulp yield (t year−1) 1.0 1.0 1.0 1.0 1.0 4.3

× × × × × ×

105 105 105 105 105 104

a Elemental chlorine bleaching. bAlkaline extraction aiding with hydrogen peroxide. cHypochlorite bleaching. dAlkaline extraction. e Hydrogen peroxide bleaching.

Sampling Methods. A total of 76 samples, including raw materials, solid pulps, effluents, paper products, and sewage sludge were collected and analyzed. Detailed information on the sampling distribution for different mills can be found in Table S1 and Figures S1−S6 (see Supporting Information, SI). Raw materials and sludge were sampled using a multipoint sampling mode. Effluents, solid pulps, and paper products were sampled using a multitime interval sampling mode. Effluent samples were collected and concentrated using XAD-2 resin and five surrogate compounds of the isotopically labeled PCDD/Fs (100 ng mL−1, sampling standards) (Cambridge Isotope Laboratory, SI Table S2) were spiked into XAD-2 resin prior to sampling. All samples were stored in brown glass bottles below 4 °C until further analysis. Information on the solid pulp masses, water addition, and the ratio of solid pulp to effluent at different manufacturing stages was collected (SI Figures S1−S6), to enable calculation of the PCDD/Fs mass balance during papermaking. PCDD/Fs Analysis. PCDD/Fs analysis was performed according to the U.S. EPA Method 1613b.25 Prior to analysis, all samples were freeze-dried and then spiked with a known amount of 13C12-labeled PCDD/Fs (100 ng mL−1) (Cambridge Isotope Laboratory, Table S2 of the SI). Soxhlet extraction was conducted using 250 mL of toluene for approximately 24 h and the extracts were concentrated with a rotary evaporator. The

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EXPERIMENTAL SECTION Pulp and Paper Manufacturing Process. Six typical Chinese non-wood pulp and paper mills (PM1−6) were selected. Their yield was in the range of 4.3−10 thousand tons of air-dry pulp per year. Reed, bamboo, wheat straw, and sugar cane bagasse were used as raw materials. The papermaking processes are shown in Figure 1. An integrated process for the production of pulp and paper is as follows: (1) raw material preparation, (2) mechanical and or chemical separation of fibers to dissolve lignin and extractives, (3) removal of coloring matter by bleaching, and (4) paper product making. The raw materials were first chipped into small pieces and then fed into a large digester, into which the appropriate white liquor was added (mixture of NaOH and Na2S). The raw material chips were digested with steam at specific temperatures to separate the fibers and partially dissolve the lignin and other extractives. After alkaline digestion, the cooked pulp was discharged into a capsule where the steam and volatile materials were siphoned off and then transferred to sequential pulp washers in which the pulp was washed by water and the black liquor separated from the raw pulp. After washing, the raw pulp was submitted to the bleaching sequence. The bleached pulp was discharged into a 12235

dx.doi.org/10.1021/es303373b | Environ. Sci. Technol. 2012, 46, 12234−12240


Article

Figure 2. The I-TEQ mass distribution of PCDD/Fs in solid pulps and effluents at different pulp bleaching stages when one tone of raw material was processed. C: elemental chlorine bleaching, E: alkaline extraction with sodium hydroxide, Ep: alkaline extraction aiding with hydrogen peroxide, H: hypochlorite bleaching, and P: hydrogen peroxide bleaching.

Table 2. I-TEQ Concentration of PCDD/Fs in the Solid Samples (ng I-TEQ kg−1) air-dry pulp

a

mills

raw material

raw pulp

after C

PM1 PM2 PM3 PM4 PM5 PM6

4.05 2.20 1.35 1.57 1.49 2.80

1.69 1.68 1.05 1.12 1.10 1.32

4.23 2.86 2.77 31.47 3.21

a

after E/Epb

after Hc

4.11 1.81 1.33 2.83 1.14

2.46 1.99 2.57 2.96 1.56 0.80

after Pd

1.25

paper

sludge

3.14 1.98 1.31 2.62 1.32 1.34

12.66

2.46

Elemental chlorine bleaching. bAlkaline extraction (E) or alkaline extraction aiding with hydrogen peroxide (Ep). cHypochlorite bleaching. Hydrogen peroxide bleaching.

d

Table 3. I-TEQ Concentration of PCDD/Fs in the Liquid Samples (pg I-TEQ L−1) effluent

a

mills

black liquor

after Ca

after E/Epb

after Hc


3.55 1.84 0.91 1.45 2.52 1.45

18.39 7.27 7.46 41.79 19.71

4.17 3.04 15.08 7.87 3.98

55.52 261.17 12.12 6.51 38.80 125.14

after Pd

1.46

mixed effluent

wastewater

5.35 1.87 5.57 7.33 5.95 2.32

1.22

2.23

Elemental chlorine bleaching. bAlkaline extraction (E) or alkaline extraction aiding with hydrogen peroxide (Ep). cHypochlorite bleaching. Hydrogen peroxide bleaching.

d

All data were obtained in the selected-ion monitoring (SIM) mode at 10 000 resolving power. Toxic equivalents (TEQ as 2,3,7,8-TCDD) values were calculated using the internationaltoxicity equivalency factor (I-TEF). Quality Assurance and Quality Control. The method detection limit (MDL) was determined according to the Chinese national standard method HJ 77.3−2008 (MEP of P.R. China, 2009).26 MDL values were obtained by analyzing the spike prepared at an appropriately low concentration (generally 3−10 times the expected MDL) and processed through the entire analytical method. Three times of the standard deviation was taken as the MDL value. The determined MDL of the 2,3,7,8-substituted PCDD/Fs ranged from 0.001 to 0.018 pg g−1 for the solid samples and from 0.008 to 0.126 pg L−1 for the effluent (SI Table S3). Recoveries of the sampling standards and internal standards met the demand of U.S. EPA 1613b.25 At the same time, eight laboratory quality control samples were also analyzed by three other dioxin laboratories in P.R. China to ensure the accuracy of the analytical results.

concentrated extracts were then subjected to a series of cleanup steps with a multilayer silica gel column and a basic alumina column. Finally, the clean extracts were reduced to approximately 1 mL by rotary evaporator and evaporated to dryness with a gentle stream of nitrogen. Ten microliters of 13C121,2,3,4-TCDD (100 ng mL−1) (Cambridge Isotope Laboratory, SI Table S2 ) were added to the sample prior to injection. The purified extract was analyzed using an Autospec Ultima high resolution mass spectrometer (Micromass, U.K.) interfaced with a Hewlett−Packard (Palo Alto, CA, U.S.) 6890 Plus gas chromatograph (HRGC/HRMS). An Rtx-5 MS capillary column (60 m × 0.25 mm i.d. × 0.25 μm df) was employed. Samples were injected in a splitless mode with an initial column temperature of 120 °C. After 1 min, the column temperature was programmed at 43 °C min−1 to 220 °C (held 15 min), 2.3 °C min−1 to 250 °C, 0.9 °C min−1 to 260 °C, and finally 20 °C min−1 to 310 °C (held 20 min). The injection port and transfer line temperatures were 280 and 260 °C, respectively. The ion source was operated at 260 °C with ionization energy of 37 eV. 12236



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Figure 3. The mass distribution of 2,3,7,8-TCDF in solid pulps and effluents at different pulp bleaching stages when one ton of raw materials was processed. C: elemental chlorine bleaching, E: alkaline extraction with sodium hydroxide, Ep: alkaline extraction aiding with hydrogen peroxide, H: hypochlorite bleaching, and P: hydrogen peroxide bleaching.

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RESULTS AND DISCUSSION Dioxin Concentration Levels and I-TEQ Mass Distributions. The concentrations of seventeen 2,3,7,8-substitued PCDD/F congeners in the solid and liquid samples collected from different pulp and paper mills, together with their detection limits, are listed in SI Tables S3−S9. A value of MDL/2 was assigned to congeners with concentrations below the MDL for calculating the I-TEQ value. Meanwhile, the ITEQ mass distributions of PCDD/Fs in different papermaking stages were estimated with results shown in Figure 2 and SI Table S10. The I-TEQ concentrations of PCDD/Fs in the six types of chipped raw materials varied from 1.35 to 4.05 ng TEQ kg−1 (Table 2). Two types of reeds had the largest I-TEQ concentrations, followed by two types of wheat straws. After alkaline digestion, the black liquors and raw pulps were sampled. The PCDD/Fs in the raw pulps and black liquors were determined to be in the ranges of 1.05−1.69 ng TEQ kg−1 and 0.91−3.55 pg TEQ L−1, respectively (Table 2 and 3). The dioxin mass balance calculation indicated that alkaline digestion decreased the I-TEQ value of the PCDD/Fs (Figure 2). The total I-TEQ masses of PCDD/Fs in black liquors and raw pulps were 17.2−54.0% lower than those in the raw materials. This implies that the alkaline cooking process gave rise to the removal of dioxin congeners in the raw materials. Raw pulps in PM 1−5 were submitted first to elemental chlorine bleaching (C stage). The concentrations of PCDD/Fs in these five types of bleached pulps ranged from 2.77 to 31.47 ng I-TEQ kg−1, which were 0.7−27.2 times higher than those in the raw pulps (Table 2). Meanwhile, the higher contents of PCDD/Fs were also identified in the effluents after C stage. These results verified the significant dioxin formation during the bleaching of pulp with elemental chlorine. The largest dioxin formation was found in PM4 which uses wheat straw as raw material. The total I-TEQ mass of PCDD/Fs in the solid pulp and effluent after C stage of PM4 was 27.9 times higher than that in the raw pulp. The pulps bleached with chlorine subsequently enter the alkaline extraction stage (E stage), in which lignin was dissolved from the fiber surface. The extracting agent was sodium hydroxide in PM3−5, while it was a mixture of sodium hydroxide and hydrogen peroxide in PM1 and PM2. Being similar to the alkaline digestion process, alkaline extraction also gave rise to a decrease in dioxins. In PM2−5, the I-TEQ concentrations of PCDD/Fs in the solid pulps after E stage

decreased by 36.8−91.0%, and the total I-TEQ masses of PCDD/Fs in solid pulp and effluent after the E stage was lower 38.2−91.1%, compared with the solid pulps after C stage. PM6 only adopted a one-stage bleaching with hypochlorite for the raw pulp, and the solid pulps after E stage of PM1−5 were also submitted to hypochlorite bleaching (H stage). As shown in Figure 2, after H stage the I-TEQ contents of PCDD/ Fs in the solid pulps of PM2−5 increased, whereas decreased in the solid pulps of PM1 and PM6. Moreover, the higher I-TEQ concentrations were found in the effluents after H stage, especially for PM2 and PM6. This implied that hypochlorite bleaching was also an important emission source of dioxins during the papermaking process. The dioxin mass balance indicated that dioxin was obviously formed during H stage of PM2, PM3, PM5, and PM6. For these four types of pulp and paper mills, the total I-TEQ masses of PCDD/Fs in the solid pulp and effluent after H stage were 0.4−1.5 times higher than those in the solid pulps after E stage. The solid pulp after H stage of PM3 was further submitted to hydrogen peroxide bleaching (P stage). Being different from chlorine and hypochlorite bleaching, the hydrogen peroxide bleaching process favored the removal of PCDD/Fs. The ITEQ concentration of PCDD/Fs in solid pulp was decreased from 2.57 to 1.25 ng I-TEQ kg−1. The total I-TEQ mass of PCDD/Fs in solid pulp and effluent after P stage was 51.0% lower than that in the solid pulp after H stage. The partitioning of PCDD/Fs between the solid pulp and effluent was found to be highly variable among the different bleach stages and different mills. The ratios of I-TEQ mass of PCDD/Fs in the solid pulps to that in effluents ranged from 0.32 from 93.25 (SI Table S10). The concentrations of PCDD/ Fs in the mixed effluents were in the range of 1.87−7.33 pg TEQ L−1. The discharged wastewater and sludge in the sewage treatment plant were sampled from PM1 and PM4. After sewage treatment, the I-TEQ concentrations of PCDD/Fs in the wastewater from PM1 and PM4 were decreased to 1.22 and 2.23 pg TEQ L−1, respectively. These two values were far lower than the emission limit for dioxins (30 pg TEQ L−1) via wastewater discharge from the pulp and paper industry in P.R. China.27 Higher dioxin contents were found in the sludge of sewage treatment plants, especially in PM1 (12.66 ng I-TEQ kg−1). The I-TEQ concentrations of PCDD/Fs in the paper ranged from 1.31 to 3.14 ng TEQ kg−1, which are lower than the reported values (8.24 ng TEQ kg−1) in the U.S. EPA database.28 12237



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Dioxin Congener Profiles. The profiles of 2,3,7,8substitued PCDD/F congeners in the six types of raw materials were all predominated by OCDD, 2,3,7,8-TCDF, 1,2,3,4,6,7,8HpCDD or OCDF (SI Tables S4−S9) . In the raw materials of PM1, PM2, and PM6, the contents of OCDD were higher than the sum of the other 2,3,7,8-substitued PCDD/F congeners. After alkaline digestion, the relative contents of OCDD in the raw pulps of these three pulp and paper mills decreased to 25%, 14%, and 19%, respectively. However, for the raw materials with lower OCDD content, alkaline digestion seemed not to change the dioxin congener profiles significantly, although this process gave rise to an obvious reduction in I-TEQ mass. Moreover, the congener profiles of PCDD/Fs in solid pulps and effluents varied significantly according to the bleaching stages. The elemental chlorine bleaching process accelerated the formation of tetra- to octa-CDDs and tetra-CDFs, especially the 2,3,7,8-TCDF (SI Figures S7−S16). Among seventeen 2,3,7,8-substituted PCDD/Fs, congener 2,3,7,8-TCDF was found to be the highest content in all the solid pulps and effluents after C stage, except for PM5. The mass balance calculation indicated that elemental chlorine bleaching increased the total masses of 2,3,7,8-TCDF by 0.9−42.5 times (Figure 3). The corresponding values for 2,3,7,8-TCDD were 0.4−7.5 times. The congener profiles of PCDD/Fs in the solid pulps and effluents after C stage were similar to those in the other non-wood pulp and paper mills,20−23 and also consistent with those in the wood pulp and paper mills.2,29 The strong resemblance of dioxin profiles suggested the same formation mechanism of PCDD/Fs at the elemental chlorine bleaching stage. The formation of 2,3,7,8-TCDF and 2,3,7,8TCDD should mainly originate from the chlorination of DBD/ F and residual lignin (nonextractable precursors), as described by LaFleur et al and Hrutfiord et al.5,16 Some penta- to octaCDDs maybe also originate from the condensation of chlorinated phenols or chlorinated benzoquinones.30,31 These chlorinated compounds mainly come from the degradation of lignin and the contamination of chlorinated phenols.17,31 On the contrary, the alkaline extraction process promoted the removal of tetra- to hexa-CDDs and tetra-CDFs (SI Figures S7−S16). The more PCDD/Fs that were formed at C stage, the more PCDD/Fs were reduced at E stage. The total mass of 2,3,7,8-substituted tetra- to hexa-CDDs in the solid pulps and effluents after E stage was lower 28.8−96.4% than those in the solid pulps after C stage, and the masses of 2,3,7,8-TCDF decreased by 29.1−94.0% (Figure 3). These results imply that the tetra- to hexa-CDD/Fs formed at C stage can be more easily removed under strong alkali condition. However, the removal mechanism is not clear. It is known that PCDDs can be preferably formed from chlorophenols by base mediated process at low temperature.32 The dioxin removal during alkaline extraction process might resulted from the hydroxylation.31 The increased formation of 2,3,7,8-TCDF occurred again at H stage (Figure 3). In PM1−6, hypochlorite bleaching increased the mass of 2,3,7,8-TCDF 0.3−4.1 times. However, being different from elemental chlorine bleaching, hypochlorite bleaching did not affect the profiles of the PCDD congeners considerably. We also noted that the 2,3,7,8-TCDF contents in the effluents after H stage were very high. This suggests that the dioxin formation at H stage occurred mainly in the effluents and most of the dioxins formed were adsorbed on the suspended substance in the effluents. The mechanisms of

elemental chlorine bleaching are electrophilic substitution, nucleophilic substitution, and oxidization, but it is only oxidization for hypochlorite bleaching. The difference suggests that the mechanism of dioxin formation at H stage may be somewhat different from that at C stage. The further studies on the mechanism of dioxin formation during hypochlorite bleaching are needed. Being similar to alkaline extraction, hydrogen peroxide bleaching also promoted the removal of tetra- to hexa-CDDs. The total mass of 2,3,7,8-substituted tetra- to hexa-CDDs in the solid pulp and effluent after P stage was lowered by 68.6% than those in the solid pulp after H stage. The removal of dioxins during the hydrogen peroxide bleaching process should be attributed to oxidative degradation. The congener 2,3,7,8-TCDF is an indicator pollutant in the mixed effluents, sludge, and discharged wastewater. Meanwhile, some of the samples have quite high OCDD compared with other 2,3,7,8-substituted PCDDs. These results were consistent with the other findings of wood pulp and paper.6,9,33,34 In addition, it was found that OCDD predominated the congener profile of 2,3,7,8-substituted PCDD/Fs in the papers. This should result from the usage of some papermaking additives with higher OCDD contents, such as pentachloroohenol (PCP) and sodium pentachlorophenate (PCP-Na).35 In P.R. China, PCP and its sodium salt are still frequently added in the paper products as the antibacterial agents. Estimation of Dioxin Emission. The emission factors of PCDD/Fs via the discharge of mixed effluent and paper output from PM1−6 were calculated by multiplying the I-TEQ concentrations and output rates with the results shown in Table 4. The emission factors of PCDD/Fs via the discharge of Table 4. Emissom Factors of PCDD/Fs for the Test Pulp and Paper Mills mill

mixed effluent dischargea(μg I-TEQ ton−1 AD pulp)

paper outputb(μg I-TEQ ton−1 paper)


0.43 0.15 0.41 0.51 0.48 0.19

3.14 1.98 1.31 2.62 1.32 1.34

a

The emission amount of PCDD/Fs via the discharge of mixed effluent when producing 1 ton air-dry (AD) pulp. bThe emission amount of PCDD/Fs via paper out when producing 1 ton paper.

mixed effluent were in the range of 0.15−0.51 μg I-TEQ ton−1 pulp (air-dry weight), with an arithmetical mean of 0.36 μg ITEQ ton−1 pulp. These values were all much lower than the dioxin emission factor reported by UNEP PCDD/PCDF Toolkit 2005, in which the emission factor of PCDD/Fs via effluent discharge from the wood pulp and paper mills with elemental chlorine bleaching was estimated to be 4.5 μg I-TEQ ton−1 pulp.36 Meanwhile, the emission factors of PCDD/Fs via paper output were estimated to be in the range of 1.31−3.14 μg I-TEQ ton−1 paper, with a arithmetical mean of 1.95 μg I-TEQ ton−1 paper. The average dioxin emission factor was also far lower than the value reported by UNEP PCDD/PCDF Toolkit 2005, in which the emission factor of dioxin via pulp and paper output from the non-wood pulp and paper mills with elemental chlorine bleaching was estimated to be 30 μg I-TEQ ton−1 product.36 12238



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In 2010, the activity level of non-wood pulp production was 12.97 million tons in P.R. China.37 Using the average concentration of PCDD/Fs in the mixed effluent, the annual emission of PCDD/Fs via the discharge of mixed effluent from non-wood pulp and paper mills in P.R. China was calculated to be 4.67 g I-TEQ. On the assumption that 1.00 ton of pulp can produce 1.09 ton of paper,35 the annual yield of paper from non-wood pulp was estimated to be 14.14 million tons in P.R. China. Accordingly, the annual emission of PCDD/Fs via paper output from non-wood pulp and paper mills in P.R. China was calculated to be 27.59 g I-TEQ, when the average concentration of PCDD/Fs in paper was used.

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ASSOCIATED CONTENT

S Supporting Information *

Tables on the information of samples number for each mill, isotopically labeled standards of PCDD/Fs, congener concentrations in each pulp mill samples, detection limit, the total TEQ mass distribution of PCDD/Fs in solid pulp and effluent, figures of the papermaking processes and sampling points for each pulp mill. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

* Phone/fax: +86-411-8437-9562; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (Grant No. 21037003).

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REFERENCES

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