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Home , Pulp and paper industry

Prevention and Abatement Handbook WORLD GROUP Effective July 1998

Pulp and Mills

Industry Description and Practices ical pulping and chemithermomechanical pulping (CTMP) are similar but use less mechani- and paper are manufactured from raw ma- cal energy, softening the pulp with sodium sulfite, terials containing fibers, generally carbonate, or hydroxide. , recycled paper, and agricultural residues. Chemical pulps are made by cooking (digest- In developing countries, about 60% of cellulose ing) the raw materials, using the kraft (sulfate) fibers originate from nonwood raw materials and sulfite processes. Kraft processes produce a such as (sugar cane fibers), straw, variety of pulps used mainly for packaging and , reeds, esparto grass, jute, flax, and si- high-strength and board. Wood chips are sal. This document addresses environmental is- cooked with caustic soda to produce brownstock, sues in pulp and paper with unit which is then washed with water to remove cook- production capacities greater than 100 metric tons ing (black) for the recovery of chemicals per day (tpd). and energy. Pulp is also manufactured from re- The main steps in pulp and paper manufac- cycled paper. turing are preparation, such as Mechanical pulp can be used without bleach- wood debarking and chip making; pulp manu- ing to make papers for applications in facturing; pulp bleaching; paper manufacturing; which low brightness is acceptable—primarily, and fiber . Pulp mills and paper mills . However, for most printing, for copy- may exist separately or as integrated operations. ing, and for some packaging grades, the pulp has Manufactured pulp is used as a source of cellu- to be bleached. For mechanical pulps, most of the lose for fiber manufacture and for conversion into original in the raw pulp is retained but is paper or . bleached with peroxides and hydrosulfites. In the Pulp manufacturing starts with raw material case of chemical pulps (kraft and sulfite), the preparation, which includes debarking (when objective of bleaching is to remove the small frac- wood is used as raw material), chipping, and tion of the lignin remaining after cooking. Oxy- other processes such as depithing (for example, gen, hydrogen peroxide, ozone, peracetic acid, when bagasse is used as the raw material). Cel- sodium hypochlorite, chlorine dioxide, chlorine, lulosic pulp is manufactured from the raw mate- and other chemicals are used to transform lignin rials, using chemical and mechanical means. into an alkali-soluble form. An alkali, such as The manufacture of pulp for paper and card- sodium hydroxide, is necessary in the bleaching board employs mechanical (including thermo- process to extract the alkali-soluble form of lig- mechanical), chemimechanical, and chemical nin. Pulp is washed with water in the bleaching methods. Mechanical pulping separates fibers by process. such methods as disk abrasion and billeting. In modern mills, oxygen is normally used in Chemimechanical processes involve mechani- the first stage of bleaching. The trend is to avoid cal abrasion and the use of chemicals. Thermo- the use of any kind of chlorine chemicals and mechanical pulps, which are used for making employ “total chlorine-free” (TCF) bleaching. products such as newsprint, are manufactured TCF processes allow the bleaching effluents to from raw materials by the application of heat, in be fed to the for steam genera- addition to mechanical operations. Chemimechan- tion; the steam is then used to generate electric-

395 396 PROJECT GUIDELINES: SECTOR GUIDELINES ity, thereby reducing the amount of pollutants dried pulp is defined as 90% bone-dry fiber and discharged. Elemental chlorine-free (ECF) pro- 10% water.) Other typical generation rates are: cesses, which use chlorine dioxide, are required particulate matter, 75–150 kg/t; oxides, for bleaching certain grades of pulp. 0.5–30 kg/t; nitrogen oxides, 1–3 kg/t; and vola- The use of elemental chlorine for bleaching is not organic compounds (VOCs), 15 kg/t from recommended. Only ECF processes are acceptable, black liquor oxidation. In the sulfite pulping pro- and, from an environmental perspective, TCF cess, sulfur oxides are emitted at rates ranging processes are preferred. from 15 kg/t to over 30 kg/t. Other pulping pro- The soluble organic substances removed from cesses, such as the mechanical and thermo- the pulp in bleaching stages that use chlorine or mechanical methods, generate significantly chlorine compounds, as well as the substances lower quantities of air emissions. removed in the subsequent alkaline stages, are Steam- and electricity-generating units using chlorinated. Some of these chlorinated organic or emit fly ash, sulfur oxides, and ni- substances are toxic; they include dioxins, chlo- trogen oxides. Coal burning can emit fly ash at rinated phenols, and many other chemicals. It is the rate of 100 kg/t of ADP. generally not practical to recover chlorinated or- ganics in effluents, since the chloride content Liquid Effluents causes excessive corrosion. The finished pulp may be dried for shipment Wastewaters are discharged at a rate of 20–250 (market pulp) or may be used to manufacture cubic meters per metric ton (m3/t) of ADP. They paper on site (in an “integrated” mill). are high in biochemical oxygen demand (BOD), Paper and cardboard are made from pulp by at 10–40 kg/t of ADP; total suspended solids, 10– deposition of fibers and fillers from a fluid sus- 50 kg/t of ADP; chemical oxygen demand (COD), pension onto a moving device that also 20–200 kg/t of ADP; and chlorinated organic removes water from the pulp. The water remain- compounds, which may include dioxins, furans, ing in the wet web is removed by pressing and and other adsorbable organic halides, AOX, at then by drying, on a series of hollow-heated cyl- 0–4 kg/t of ADP. inders (for example, rolls). Chemical Wastewater from chemical pulping contains additives are added to impart specific proper- 12–20 kg of BOD/t of ADP, with values of up ties to paper, and may be added for to 350 kg/t. The corresponding values for color. mechanical pulping wastewater are 15–25 kg BOD/t of ADP. For chemimechanical pulping, Characteristics BOD discharges are 3 to 10 times higher than those for mechanical pulping. Pollution loads The significant environmental impacts of the for some processes, such as those using non- manufacture of pulp and paper result from the wood raw materials, could be significantly dif- pulping and bleaching processes. In some pro- ferent. cesses, sulfur compounds and nitrogen oxides are and nitrogen are also released into emitted to the air, and chlorinated and organic wastewaters. The main source of nutrients, ni- compounds, nutrients, and metals are discharged trogen, and phosphorus compounds is raw ma- to the wastewaters. terial such as wood. The use of peroxide, ozone, and other chemicals in bleaching makes it neces- Air Emissions sary to use a complexing agent for heavy metals such as manganese. In the kraft pulping process, highly malodorous emissions of reduced sulfur compounds, mea- Solid sured as total reduced sulfur (TRS) and includ- ing hydrogen sulfide, methyl mercaptan, The principal solid wastes of concern include dimethyl sulfide, and dimethyl disulfide, are wastewater treatment sludges (50–150 kg/t of emitted, typically at a rate of 0.3–3 kilograms per ADP). Solid materials that can be reused include metric ton (kg/t) of air-dried pulp (ADP). (Air- waste paper, which can be recycled, and bark, Pulp and Paper Mills 397 which can be used as fuel. Lime sludge and ash ( of 10) for hardwood by ex- may need to be disposed of in an appropriate tended cooking and by oxygen delignification . under elevated pressure; optimize pulp wash- ing prior to bleaching; use TCF or at a mini- Pollution Prevention and Control mum, ECF bleaching systems; use oxygen, ozone, peroxides (hydrogen peroxide), perace- The most significant environmental issues are the tic acid, or enzymes (cellulose-free xylanase) discharge of chlorine-based organic compounds as substitutes for chlorine-based bleaching (from bleaching) and of other toxic organics. The chemicals; recover and incinerate maximum unchlorinated material is essentially black liquor material removed from pulp bleaching; where that has escaped the mill recovery process. Some chlorine bleaching is used, reduce the chlorine mills are approaching 100% recovery. Industry charge on the lignin by controlling pH and by developments demonstrate that total chlorine- splitting the addition of chlorine. free bleaching is feasible for many pulp and pa- • Minimize sulfur emissions to the atmosphere per products but cannot produce certain grades by using a low-odor black liquor re- of paper. The adoption of these modern process covery furnace. developments, wherever feasible, is encouraged. • Use energy-efficient processes for black liquor Pollution prevention programs should focus chemical recovery, preferably aiming for a high on reducing wastewater discharges and on mini- solid content (say, 70%). mizing air emissions. Process recommendations may include the following: Target Pollution Loads

• Use energy-efficient pulping processes wher- Implementation of cleaner production processes ever feasible. Acceptability of less bright prod- and pollution prevention measures can yield both ucts should be promoted. For less bright economic and environmental benefits. The fol- products such as newsprint, thermomechan- lowing production-related targets can be ical processes and recycled fiber may be achieved by measures such as those described considered. above. The values relate to the production pro- • Minimize the generation of effluents through cesses before the addition of pollution control process modifications and recycle wastewa- measures.

ters, aiming for total recycling. For air emissions, the target is 1.5 kg NOx per • Reduce effluent volume and treatment require- ton for both kraft and sulfite processes; for me- ments by using dry instead of wet debarking; chanical and chemimechanical processes used in recovering pulping chemicals by concentrat- newsprint manufacture, 260 nanograms per joule

ing black liquor and burning the concentrate (ng/J) of NOx for coal; 130 ng/J for oil; and 86 in a recovery furnace; recovering cooking ng/J for gas used as fuel. chemicals by recausticizing the smelt from the Wastewater generation rates should not exceed recovery furnace; and using high-efficiency 50 m3/t of ADP, and levels of 20 m3/t of ADP (or washing and bleaching equipment. product) should be targeted. For paper mills, ef- • Minimize unplanned or nonroutine discharges fluent discharges should be less than 5 m3/t of of wastewater and black liquor, caused by ADP. Wherever feasible, use a total wastewater equipment failures, human error, and faulty recycling system, along with a TCF pulp-bleach- maintenance procedures, by training opera- ing system, and incinerate bleaching effluents in tors, establishing good operating practices, the recovery boiler. As a minimum, use chlorine and providing sumps and other facilities to dioxide as a substitute for elemental chlorine in recover liquor losses from the process. pulp bleaching. • Reduce bleaching requirements by process de- sign and operation. Use the following mea- Treatment sures to reduce emissions of chlorinated compounds to the environment: before bleach- Sulfur oxide emissions are scrubbed with slightly ing, reduce the lignin content in the pulp alkaline solutions. The reduced sulfur-com- 398 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES pounds gases are collected using headers, hoods, The following guidelines present emissions and venting equipment. Condensates from the levels normally acceptable to the World Bank digester relief condenser and evaporation of Group in making decisions regarding provision black liquor are stripped of reduced sulfur com- of World Bank Group assistance. Any deviations pounds. The stripper overhead and nonconden- from these levels must be described in the World sable are incinerated in a lime kiln or a dedicated Bank Group project documentation. The emis- combustion unit. Approximately, 0.5 kg sulfur sions levels given here can be consistently per ton of pulp for the and 1.5 kg achieved by well-designed, well-operated, and sulfur per ton for the are consid- well-maintained pollution control systems. ered acceptable emissions levels. Electrostatic The guidelines are expressed as concentrations precipitators are used to control the release of to facilitate monitoring. Dilution of air emissions particulate matter into the atmosphere. or effluents to achieve these guidelines is un- Wastewater treatment typically includes (a) acceptable. neutralization, screening, sedimentation, and All of the maximum levels should be achieved floatation/hydrocycloning to remove suspended for at least 95% of the time that the plant or unit solids and (b) biological/secondary treatment to is operating, to be calculated as a proportion of reduce the organic content in wastewater and annual operating hours. destroy toxic organics. Chemical precipitation is also used to remove certain cations. Fibers col- Air Emissions lected in primary treatment should be recovered and recycled. A mechanical clarifier or a settling Air emissions from pulp and paper manufac- pond is used in primary treatment. Flocculation turing should achieve the levels presented in to assist in the removal of suspended solids is also Table 1. sometimes necessary. Biological treatment sys- tems, such as activated sludge, aerated lagoons, Liquid Effluents and anaerobic fermentation, can reduce BOD by over 99% and achieve a COD reduction of 50% to Liquid effluents from pulp and paper manufac- 90%. Tertiary treatment may be performed to re- turing should achieve the levels presented in duce toxicity, suspended solids, and color. Table 2. Solid waste treatment steps include dewater- ing of sludge and combustion in an incinerator, Solid Wastes bark boiler, or fossil-fuel-fired boiler. Sludges from a clarifier are dewatered and may be incin- Solid wastes should be sent to combustion de- erated; otherwise, they are landfilled. vices or disposed of in a manner that avoids odor The following levels can be achieved by adopt- generation and the release of toxic organics to the ing good industrial practices: COD, 35 kg/t (aim environment. for 15 kg/t); AOX, 2 kg/t of ADP (aim for 0.2 kg/t); total phosphorus, 0.02 kg/t; total nitrogen, 0.15 kg/t; and solid waste generation, 150 kg/t Table 1. Air Emissions from Pulp and Paper Manufacturing of ADP. (milligrams per normal cubic meter) Emissions Guidelines Parameter Maximum value

a Emissions levels for the design and operation of PM 100 for recovery furnace Hydrogen sulfide 15 (for lime kilns) each project must be established through the en- Total sulfur emitted vironmental assessment (EA) process on the ba- Sulfite mills 1.5 kg/t ADP sis of country legislation and the Pollution Prevention Kraft and other 1.0 kg/t ADP and Abatement Handbook, as applied to local con- Nitrogen oxides 2 kg/t ADP ditions. The emissions levels selected must be a. Where achieving 100 mg/Nm3 is not cost-effective, an emis- justified in the EA and acceptable to the World sions level up to 150 mg/Nm3 is acceptable. Air emissions re- Bank Group. quirements are for dry gas, at 0°C and 1 atmosphere. Pulp and Paper Mills 399

Table 2. Liquid Effluents from New Pulp and Monitoring of air emissions for opacity (maxi- Paper Manufacturing mum level of 10%) should be continuous; daily Parameter Maximum value monitoring should be conducted for hydrogen sulfide and annual monitoring for other pollut- pH 6–9 ants. Liquid effluents should be monitored for COD 300 mg/l and 15 kg/t for kraft and the listed parameters at least daily, or more often CTMP pulp mills; 700 mg/l and 40 kg/t when there are significant process changes. for sulfite pulp mills; 10 mg/l and 5 kg/t Monitoring data should be analyzed and re- for mechanical and recycled fiber pulp; 250 mg/l for paper mills viewed at regular intervals and compared with AOX 40 mg/l and 2 kg/t (aim for 8 mg/l and the operating standards so that any necessary 0.4 kg/t for retrofits and for 4 mg/l and corrective actions can be taken. Records of moni- 0.2 kg/t for new mills) and 4 mg/l for toring results should be kept in an acceptable paper mills format. The results should be reported to the re- Total phosphorus 0.05 kg/t sponsible authorities and relevant parties, as re- Total nitrogen 0.4 kg/t quired. Temperature < 3°Ca

Note: Molecular chlorine should not be used in the process. Key Issues Effluent requirements are for direct discharge to surface wa- ters. a. The effluent should not result in a temperature increase of The key production and control practices that will more than 3° C at the edge of the zone where initial mixing and lead to compliance with emissions guidelines can dilution take place. Where the zone is not defined, use 100 be summarized as follows: meters from the point of discharge. • Prefer dry debarking processes. • Prevent and control spills of black liquor. Ambient Noise • Prefer total chlorine-free processes, but at a minimum, use elemental chlorine-free bleach- Noise abatement measures should achieve either ing systems. the levels given below or a maximum increase in • Reduce the use of hazardous bleaching chemi- background levels of 3 decibels (measured on the cals by extended cooking and oxygen A scale) [dB(A)]. Measurements are to be taken delignification. at noise receptors located outside the project • Aim for zero-effluent discharge where feasible. property boundary. Reduce wastewater discharges to the extent feasible. Incinerate liquid effluents from the Maximum allowable log pulping and bleaching processes. equivalent (hourly • Reduce the odor from reduced sulfur emis- measurements), in dB(A) sions by collection and incineration and by Day Night using modern, low-odor recovery boilers fired Receptor (07:00–22:00) (22:00–07:00) at over 75% concentration of black liquor. • Dewater and properly manage sludges. Residential, institutional, • Where wood is used as a raw material to the educational 55 45 process, encourage of to en- Industrial, sure sustainability of . commercial 70 70 Sources Monitoring and Reporting Kirkpatrick, N. 1991. Environmental Issues in the Pulp Frequent sampling may be required during start- and Paper Industries. Surrey, U.K.: Pira International. up and upset conditions. Once a record of con- Nordic Council of Ministers. 1993. “Study of Nordic sistent performance has been established, and the Environment.” sampling for the parameters listed in this docu- Nordiske Seminar-g Arbejds-rapporter 1993:638. ment should be as described below. Copenhagen. 400 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES

UNEP (United Nations Environment Programme). Background Information for Proposed Air Emission 1987. “Pollution Abatement and Control Technol- Standards, Manufacturing Processes at Kraft, Sulfite, ogy (PACT), Publication for the Pulp and Paper In- Soda, and Semi-Chemical Mills. EPA-453 R-93-050a. dustry.” UNEP Industry and Environment Office of Air Quality Planning and Standards. Re- Information Transfer Series. Paris. search Triangle Park, N.C. UNIDO (United Nations Industrial Development Or- ————. 1993. Development Document for Proposed Ef- ganization). 1992. “Draft Pulp and Paper Industrial fluent Limitations Guidelines and Standards for the Pollution Guidelines.” Vienna. Pulp, Paper and Point Source Category. EPA-821-R-93-019. Office of Water, Code ————. 1991. “Case Study No. 1, Pulp and Paper.” 4303, Washington, D.C. Conference on Ecologically Sustainable Industrial Development, Copenhagen, October 1991. Vienna. World Bank. 1996. “Pollution Prevention and Abate- ment: Pulp and Paper Mills.” Draft Technical Back- USEPA ( Environmental Protection ground Document. Environment Department, Agency). 1993. Pulp, Paper, and Paperboard Industry Washington, D.C.