Annex 47 Complementary information to source category 7a Pulp and Paper Production
Overview of recent revisions
Emission factors for have been revised for power boilers in the pulp and paper industry as explained in the following section.
Derivation of emission factors
Release to Air
For pulp and paper mills, the major sources of PCDD/PCDF release to air are power boilers used to generate heat/power, rather than the pulp and paper production processes. Fuels burned in power boilers commonly include clean hog fuel (waste wood), salt-laden hog fuel (primarily at coastal and near-coastal mills), black liquor, wastewater treatment sludge, and de-inking sludge. However, clean hog fuel may also include other materials – wood product residues, plywood, agricultural wastes, paper, plastics, lubricating oils, municipal and industrial waste, rail ties, tires, etc. – that may impact PCDD/PCDF releases from power boilers (Uloth and van Heek 2002, Sinkkonen et al. 1997, Duo 2008).
Using data from Canadian pulp and paper mills, Uloth and van Heek (2002) derived the air emission factors shown in Table III.47.1:
Table III.47.1 PCDD/PCDF Air Emission Factors for Power Boilers
Type of boiler Fuel EFAir (μg TEQ/t dry fuel) Power boilers Clean hog fuel (with or without wastewater treatment sludge) 0.04 Power boilers Clean hog fuel and de-inking sludge (with or without wastewater treatment sludge) 0.750 Power boilers Black liquor 0.015 Kraft mill smelt dissolving tanks 0.00055 Sulfite process power boilers 0.0005
Based on Environment Canada (2002), the median and mean emissions from eleven U.S. kraft recovery furnaces were of 0.013 and 0.018 ng TEQ/kg black liquor solids (range: 6.6 x 10-5 to 0.0724), respectively, translating to an emission factor of 0.021 and 0.029 g/ADt pulp, respectively. Further, the median and mean emissions of PCDD/PCDFs from 15 pulp mill boilers from the US and Canada, firing 100% inland wood residues, were of 38.5 and 451.6 ng TEQ/bone dry ton hog fuel, respectively (range 3.3 to 2,799). This translates to a median and mean emission rate of 0.04 and 0.45 g TEQ/dry ton of wood combusted, respectively.
Other scientists, national agencies and trade associations have also derived air emission factors for power boilers burning black liquor, based on measurements at mills in their respective countries, as shown in Table III.47.2:
Table III.47.2 PCDD/PCDF air emission factors for power boilers burning black liquor
Agency/Association EFAir (μg I-TEQ/t black liquor solids) New Zealand Ministry of Environment (2011) 0.026, 0.036 and 0.014 Statistics Norway (2011) 1 NCASI (USEPA 2000; used by USEPA 2006a) 0.07 Iwata et al. (2008) (Japan) 0.006/t pulp
In Japan, power boilers burning black liquor have an EFAir of 0.006 μg/t of pulp for PCDD/PCDF and dioxin-like PCBs, an EFAir of 2.4 μg/t for HCB and an EFAir 19.4 μg/t for PCBs (Ota et al. 2005).
Release to Water
The pulp and paper industry is one of the largest industrial water users. If cooling water and other clean water are discharged separately, a bleached Kraft mill discharges water at a rate of 30-50 m³/ADt pulp and an unbleached Kraft mill has a water discharge rate of 15-25 m³/ADt pulp. For sulfite mills, water usage is about 70 m³/ADt pulp (EC 2001).
Concentrations in effluents ranged from 3 pg TEQ/L to 210 pg TEQ/L with a median of 73 pg TEQ/L (USEPA 1998a). The default emission factor for Kraft bleached pulp using old bleaching sequences is 4.5 μg TEQ/t of pulp. Alternatively, the concentration in the effluent can be used and multiplied with the total mass of water discharged per year to calculate the annual release.
Data generated and published by NCASI (1998) in the USA from 20 bleach lines at 14 U.S. Kraft mills that use complete chlorine dioxide substitution for chlorine gave 119 data pairs for 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF in pulp mill effluents. The results showed that 2,3,7,8-Cl4DD was not detected in any sample above the proposed guideline concentration of 10 pg/L. 2,3,7,8-Cl4DF was detected in two samples from the acid stage at concentrations in the range of 15-18 pg/L and in the alkaline stage at concentrations in the range 11-18 pg/L.
The default emission factor for releases from modern wood pulp mills utilizing chlorine dioxide will be set to 60 ng TEQ/t of bleached pulp using a conservative approach. The emission factor will be applied only if there is direct discharge into the environment. If sludge is generated, the dioxin freight will be collected in the sludge and the effluents leaving from the effluent treatment plant will have non-accountable concentrations of PCDD/PCDF
In China, a PCDD/PCDF concentration of 10.11 pg TEQ/L was measured in wastewater from an integrated bleached Kraft mill for cereal and rice straw (Zhang et al. 2000). At another Chinese pulp mill for reeds, a PCDD/PCDF concentration of 316 pg I-TEQ/L was measured in wastewater from bleaching processes (Zheng et al. 2001).
In Taiwan, PCDD/PCDF concentrations in raw wastewater of four pulp and paper mills ranged from 0.13 to 10.1 pg I-TEQ/L, with a mean of 5.1 pg I-TEQ/L, and, in the final treated effluent, PCDD/PCDF concentrations ranged from 0.06 to 0.51 pg I-TEQ/L, with a mean of 0.3 pg I-TEQ/L (Duh et al. 2007).
In mechanical pulp and paper mills (integrated mills, TMP), the water systems are usually quite closed in order to maintain high process temperatures. Consequently, wastewater volumes are small – 5-10 m³/ADt. No emission factors were found.
Pulping of pentachlorophenol treated wood may increase the concentrations in the effluent although no data have been published. Any use of PCP or of PCP-treated wood in the pulp and paper industry should be notified.
Release in Products
Products from the pulp and paper industry can be contaminated with PCDD/PCDF, depending on the bleaching technology. High concentrations of PCDD/PCDF in pulp and paper products have been reported with the use of Cl2 in bleaching processes. Replacing Cl2 with chlorine dioxide (ClO2) – so-called elemental chlorine free (ECF bleaching) – may reduce 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF concentrations to non-detectable levels. However, ClO2 commonly contains small amounts of Cl2 so that PCDD/PCDF formation may still occur during ECF bleaching. The extent of such formation depends on the amount of Cl2 in the ClO2 and on the quantity of lignin remaining in the pulp (commonly expressed in “kappa numbers”). With high kappa numbers and more Cl2 in the ClO2, the probability of forming PCDD/PCDF increases.
U.S. EPA scientists reported an average PCDD/PCDF concentration of 22.3 ng I-TEQ/kg in Kraft bleached pulp from five mills (Amendola et al. 1989). PCDD/PCDF concentrations ranging from 0.4 to 196 ng TEQ/kg, with a median of 8.8 ng TEQ/kg, were determined in pulp bleached using elemental chlorine or chlorine derivatives as reported in 1988 and a similar range, with a median of 7.6 ng WHO-TEQ/kg, as reported in 1996 (USEPA 2006a). The default emission factor is 10 μg TEQ/t of Kraft bleached pulp
Chinese bleached pulps exhibited high concentrations of PCDD/PCDF (Zheng et al. 1997, 2001). Zheng et al. (2001) report 24.7 ng I-TEQ/kg of pulp for a C-E-H bleach sequence with a relatively “typical” chlorine bleach pattern (2,3,7,8-Cl4DF = 13.6 ng/kg and 2,3,7,8-Cl4DD = 2.0 ng/kg but high concentrations of 1,2,3,7,8-Cl5DD = 29.8 ng/kg and Cl6DD = 35.8 ng/kg). Zheng et al. (1997) also found high concentrations in five bleached pulp from non-wood fibers that ranged from 33.5 ng I-TEQ/kg to 43.9 ng I-TEQ/kg. These samples were characterized by very high concentrations of 2,3,7,8-Cl4DD, 1,2,3,7,8-Cl5DD, and 1,2,3,4,7,8-Cl6DD but had no quantifiable 2,3,7,8-substituted Cl4DF and Cl5DF.
Thermo-mechanical pulp (TMP) pulp in Sweden had concentrations of around 1 μg TEQ/t pulp and between 0.17 ng I-TEQ/kg and 1.65 ng I-TEQ/kg in Germany (Santl et al. 1994). The emission factor for TMP is 1 μg TEQ/t pulp.
Recycled papers from waste papers with low PCDD/PCDF content has an emission factor of 3 μg TEQ/t based on information provided by CORMA (2004) and recycled pulp/paper from impacted sources, e.g., waste papers with high PCDD/PCDF content has an emission factor of 10 μg TEQ/t based on data by Santl et al. (1994).
Replacement of Cl2 in the first bleaching stage by ClO2 will dramatically reduce the formation of 2,3,7,8-Cl4DD and 2,3,7,8-Cl4DF and to 0.1-0.3 pg/g bleached pulp corresponding to 0.1-0.3 μg/t of bleached pulp.
Concentrations of PCDD/PCDF in Kraft bleached papers using free chlorine (Cl2 gas) and the respective default emission factors are 5 μg TEQ/t for cosmetic tissues, shopping bags and other consumer papers and 2 μg TEQ/t for filter papers and newspapers from primary fibers. If chlorine dioxide or total chlorine-free bleaching is utilized, the emission factor will be 0.5 μg TEQ/t.
Sulfite papers using old technologies have an EFProduct of 1 μg TEQ/t paper. Applying new technology will lower the emission factor to 0.1 μg TEQ/t.
Unbleached papers have an emission factor of 0.5 μg TEQ/t.
Recycling papers will have an emission factor of either 10 μg TEQ/t for recycling papers originating from pulp made by the old Kraft process or 3 μg TEQ/t for recycling papers made of primary papers made with modern bleaching technology.
Release in Residues
A survey of pulp and paper mills in Canada found that total residues were generated at a rate greater than 80 kg/t of product and consisted of the following three types of residue (Elliott and Mahmood 2005):
- Wastewater treatment residues (sludges resulting from primary clarification, secondary treatment and deinking operations) with a generation rate of 50 kg/t;
- Fly ash and bottom ash from power and auxiliary boilers; and
- "Other inorganics" - electrostatic precipitator dust from boilers and recausticizing residues (lime mud), and grits and dregs.
Among mills of all types, newsprint mills with de-inking processes had the highest rate of residue generation, 148 kg/ADt, while newsprint mills with no de-inking had the lowest rate, 65 kg/ADt (Elliott and Mahmood 2005).
European companies report total waste generation rates from their pulp and paper mills that range from 23 to 163 kg/t of product, with a mean of 125 kg/t product (Monte et al. 2009). Of this total waste, the most significant waste streams include wastewater treatment sludges, lime mud, lime slaker grits, green liquor dregs, boiler and furnace ash, scrubber sludges and wood processing residuals. In general, wastewater treatment sludge constitutes the largest residual waste stream in terms of volume (Monte et al. 2009).
In 1989, a Canadian study reported concentrations of 2,3,7,8-TCDD ranging from 170 to 370 ng/kg in sludge from 10 pulp and paper mills (8 bleached Kraft mills and 2 sulfite mills (Clement et al. 1989).
At a recovered paper mill, Santl et al. (1994) found 24.9 and 44.37 ng TEQ/kg in two samples of the de-inking sludge and, in the wastewater treatment sludge, 11.01 ng I-TEQ/kg. In this Toolkit, an emission factor of 30 μg TEQ/t sludge will be applied for the combined deinking and fiber sludges.
The concentrations in pulp sludge using old bleaching sequences is in the range from 2 ng TEQ/kg d.m. to 370 ng TEQ/kg d.m. with a median of 93 ng TEQ/kg sludge. The emission factor for bleached Kraft sludge is 4.5 μg TEQ/t of bleached Kraft pulp. Alternatively, the concentration in the sludge of 100 ng I-TEQ/kg sludge can be used and multiplied with the total mass of sludge disposed of per year to calculate the annual release.
Almost no difference in the concentrations of the sludge from wastewater treatment systems was found between mills using conventional delignification and those mills using oxygen delignification. The sludges have been analyzed for 2,3,7,8-substituted Cl4DD and Cl4DF as well as for all 17 2,3,7,8-substituted PCDD and PCDF congeners. The concentrations ranged from 3.8 ng TEQ/kg d.m. to 5.2 ng TEQ/kg d.m. for conventional delignification and from 1.8 ng TEQ/kg d.m. to 4.5 ng TEQ/kg d.m. for ED or ED/OD delignification.
With an estimated average of 4 ng TEQ/kg d.m., the default emission factor for pulp sludge using modern technology will be 0.2 μg TEQ/t of pulp.
Release vectors into the environment will be determined by the way the sludge is handled. Common disposal practices include landfill and surface impoundment, land application, recycling (compost, animal bedding) or incineration.
Ash residuals generated from power boilers combusting wood residues, sludges, or auxiliary fuels constitute a major fraction of the solid residues produced by pulp and paper mills (Elliott and Mahood 2006). In some countries, such as Canada and the U.S., landfilling is the primary method of ash disposal (Elliott and Mahood 2006). Land application of ashes produced from salt-laden hog fuels at coastal pulp and paper mills is regulated for PCDD/PCDF.
USEPA (2006a) derived an EFResidue for boiler ash of 13.2 μg I-TEQ/t of fuel, based on five NCASI studies in which wood, bark and sawdust were burned in boilers equipped with multicyclones or ESPs.
Based on data from Uloth and van Heek (2002) that describe the ash generation rates for power boilers burning clean hog fuel and the PCDD/PCDF concentrations of the ashes, an estimated average EFResidue of 15.6 μgTEQ/t of fuel can be calculated, as shown in Table III.47.3:
Table III.47.3 Ash generation rates and PCDD/PCDF concentrations for power boilers at pulp and paper mills (Uloth and van Heek 2002)
Power boilers burning clean hog fuel (with or without wastewater treatment plant sludge) Grate or bottom ash Multicyclone ash for ESP, scrubber or combined flyash PCDD/PCDF, μgTEQ/t ash 0.02 0.10 0.46 Ash generation rate, kg/t hog fuel 10-20 12-16 18-41 PCDD/PCDF release to residue, μgTEQ/t hog fuel (mean) 0.2-0.4
Mean total PCDD/PCDF release to residue, μg TEQ/t hog fuel 15.6
In a Canadian study of boilers fired with salt-laden hog fuel, PCDD/PCDF concentrations in ashes were 3.80 μg TEQ/kg ash and, with the addition of 2-5% tire-derived fuel, 2.63 μg TEQ/kg (Duo et al. 2002). Using the first value and estimating a total ash generation rate of 60 kg/t, based on mean of the values given in Table III.47.3, an EFResidue of 228 μg TEQ/ADt can be derived for ash when salt-laden hog fuel is burned.
The median and mean concentrations of PCDD/PCDFs in 43 fly ashes (ESP/wet scrubber or combined multiclone/ESP/scrubber ashes) from 24 boilers (16 U.S. and 8 Canadian) firing 100% inland wood residues in pulp mills and panel plants were of 0.46 and 5.35 ppt TEQ (where ppt TEQ corresponds to 10-12 g TEQ/g ash), respectively (range: 0.0 to 29.4) (Environment Canada 2002).
The disposal of ash should be described and PCDD/PCDF releases estimated to the greatest extent possible, e.g., fractions sent to landfills, applied to land, etc.