Friends of the Earth: Briefing: THE ENVIRONMENTAL CONSEQUENCES OF PULP AND PAPER MANUFACTURE

THE ENVIRONMENTAL CONSEQUENCES OF PULP AND PAPER MANUFACTURE

INTRODUCTION

The UK is currently the 14th largest per capita consumer of paper and board products in the world, up from 16th position in 1993. In 1995, each person in the UK used 193.6kg of paper and board in comparison with 3.7kg per person in India. Worldwide, the consumption of paper products is set to rise substantially over the next few decades, especially in the developing world.

The aim of this briefing is to provide a general understanding of the processes and issues associated with the paper manufacturing process and provide answers to the following basic questions.

How is paper produced?
What are the environmental impacts ?
What possible alternatives and solutions exist?
Which products/processes are the most environmentally acceptable?

Worldwide, the pulp and paper industry is huge and technically diverse operating a wide variety of manufacture processes on a range of fibre types from tropical hardwoods to straw. This complexity means that this briefing can only be fairly general and provide a simplified overview. The briefing is divided into three sections, based around different fibre sources: wood, recycled fibre, and non wood fibres.

1. WOOD BASED PULP AND PAPER MANUFACTURE

1.1 Pulp

As the vast majority of virgin pulp originates from wood sources, pulping processes will be considered in that context. Pulping of non wood fibres is discussed in the non wood fibres chapter.

For the most part, pulp and paper mills are integrated with all production stages taking place on the same site. However, most mills in the UK produce paper only, relying on imported pulp.

The primary raw material in paper manufacture is cellulose fibre. Wood consists of approximately 50 per cent cellulose, 30 per cent lignin (a resinous adhesive which holds the fibres together), and 20 per cent aromatic hydrocarbons and hemicellulose carbohydrates. In order to obtain cellulose in usable form for paper manufacture the wood or plant material must be pulped to separate the fibres and remove impurities. The higher the cellulose content of the pulp, and the longer the fibres, the better quality the paper. Hardwoods generally contain a higher proportion of cellulose but of shorter fibre length than softwoods, which are more resinous.

Outlined below are the principal pulping processes.

1.1a Chemical Pulping

i. Sulphate (Kraft)

Kraft or sulphate pulping is the dominant method of pulp production in the world by virtue of its versatility and the high strength, long fibre, very low lignin content pulp it produces. There are no Kraft mills in the UK and so all Kraft pulp used by UK paper and board manufacturers (1,399,000 tons in 1995)1 is imported. In fact, the Kraft process was prohibited in several densely populated areas due to the sulphurous smell associated with the mills2. Softwood chips are the principal wood source, although the process can be adapted to any tree species.

The process involves boiling wood chips in a sodium hydroxide (caustic soda) and sodium liquor. This separates the lignin and wood resins from the cellulose fibre pulp, which is then washed and, if necessary, bleached. The majority of Kraft mills operate a closed loop system whereby 95 per cent - 98 per cent of the chemicals used in the process are recovered and reused. This means that, in comparison with other processes, small amounts of chemicals are needed to produce large amounts of pulp: about 20kg of sodium sulphate and 75kg of calcium carbonate are required per ton of pulp3.

The waste products from the process are generally burned to provide energy.

Each ton of wood chips used yields about 0.5 tons of pulp (compared to 0.9 - 0.95 tons for mechanical pulp). Another major disadvantage of Kraft pulp is that, due to its dark colour, it requires strong bleaching agents if it is destined to become white paper.

ii. Sulphite

Sulphite pulping uses similar equipment to Kraft but involves a different chemical process. The resulting pulp is characteristically strong, soft and lighter in colour than Kraft pulp, thus requiring less bleaching. Again there are no sulphite mills in the UK, so all sulphite pulp has to be imported (108,000 tons in 1995)4, its major end use being tissue products.

Sulphuric acid or hydrogen sulphite is used to 'cook' the raw material in a liquor with a reactive metal base (usually calcium, magnesium or sodium) or ammonium to produce an acid sulphite or bisulphite pulp. Whilst closed loop systems can be applied to sulphite processes, they are dependant on the base metal used. In general terms chemical recovery rates for sulphite pulping are not as high as for Kraft although in terms of energy use sulphite has the slight edge (see section 1.6a) with roughly equivalent pulp yields. Water consumption for both chemical pulping methods is high (see section 1.6b).

1.1b Mechanical Pulping

i. Groundwood Pulping

This is the most basic form of pulping and simply involves the grinding of debarked logs or chips to separate the fibres. There are currently two mechanical pulp mills operating in the UK, producing 548,000 tons of pulp in 19955. The quality of the pulp is low as the fibres produced are broken by the grinding and still surrounded by lignin. This means the paper products produced are weak and turn yellow more quickly. As a consequence, mechanical pulp is largely used for newsprint and paper products which require little tear strength. Whilst the pulp yield per ton of wood is much higher than chemical pulping (around 0.95 tons)6 the amount of imported energy required is approximately double that required by the chemical process (see section 1.6a). Water consumption, however, is roughly one third of the amount required by chemical pulp mills (see section 1.6b).

ii. Thermomechanical pulping (TMP)/Chemo- Thermomechanical Pulping (CTMP)

Two variations of the mechanical process are widely used in the pulp industry with the aim of reducing energy consumption by pre-softening the wood chips. In thermomechanical pulping, which is used on softwoods only, the chips are steamed prior to grinding. In the chemo- thermomechanical process the wood chips are first impregnated with sulphur-based chemicals which extract some resin and lignin from the fibre prior to steam softening. Both these modifications results in a stronger pulp which can be applied to higher quality end uses.

Table 1: Summary of Pulping Characteristics

	Yield	Water Use7	Pulp Quality
Kraft	50 per cent	160-205 tonnes/tonne pulp	High
Sulphite	50 per cent	160-205 tonnes/tonne pulp	High
Mechanical	90-95 per cent	45-68 tonnes/tonne pulp	Low
(C)TMP	-	-	Medium
Non Wood Fibre	-	-	All grades
Recycled	60-90 per cent	1-100 tonnes/tonne paper	All grades

Note: Figures are approximate; where necessary they have been converted from different units. Figures are unavailable for non wood fibres and (C)TMP due to the wide diversity of different processes in use. Figures apply only to the pulping process unless otherwise stated.

1.2 Bleaching

The bleaching part of the pulp and paper manufacture process has so far proved to be the most controversial in environmental terms. The process is dependent on the type of pulp involved and the destined end use.

1.2a Hydrogen peroxide brightening

Mechanical pulp, being high in lignin content, is usually 'brightened' using hydrogen peroxide. This alters the chemical structure of the lignin, lightening its colour but leaving it present in the pulp. Lignin removing chemicals such as chlorine are not used because this would result in a large reduction in yield8. Hydrogen peroxide is environmentally benign but the process does require quite high levels of energy and is relatively expensive. Other chemicals used to produce brighter mechanical pulps include hypochlorites and sodium bisulphite9. It should be noted that approximately half the mechanical pulp produced is used for products which do not require brightening 10.

1.2b Chlorine bleaching

Chemical pulp is routinely delignified to remove the 5 per cent - 10 per cent of lignin remaining after the pulping process. Traditionally chlorine gas has been used for this, followed by several stages of treatment with chlorine dioxide or hyperchlorite to further whiten the pulp.50 to 80 kilograms of elemental chlorine are required to bleach one tonne of pulp (see glossary). Approximately 10 per cent of this chlorine will combine with organic molecules to form a range of organochlorines in the process effluent11. Most notorious amongst these are dioxins and furans.

The dioxin scares of the mid-1980s drove forward bleaching technology towards Totally Chlorine Free (TCF), and Elemental Chlorine Free (ECF) processes.

1.2c TCF bleaching

TCF bleaching combines oxygen delignification with peroxide brightening in a series of treatment stages. Enzymes may be used to enhance the bleaching process and a 'chelating' agent (EDTA) is added to bind the metal ions contained in the pulp and prevent them decomposing the hydrogen peroxide. TCF technology is improving, but as yet paper whiteness achieved by this method is only ISO 70- 86 per cent ('full brightness' is ISO 90 per cent+). The addition of an ozone bleaching stage to the sequence can improve this to ISO 85-90 per cent. However the use of ozone is problematic as it readily attacks cellulose and the level of process control required contributes significantly to the cost.

1.2d ECF bleaching

ECF bleaching technology also uses oxygen delignification, but later stages use chlorine dioxide, in combination with other chemical agents, in a sequence of treatments to achieve 'full brightness'. A typical sequence would include chlorine dioxide, caustic soda, oxygen and hydrogen peroxide12.

Both ECF and TCF processes are likely to yield less pulp per tonne of wood fibre than conventionally bleached pulp, because the increased number of bleach/wash stages results in greater fibre loss. TCF, which has the most protracted bleaching cycle, has the lowest yield.

Industry opinion is divided as to the relative merits of ECF and TCF processes. Market demand for TCF pulp is almost exclusively European (primarily German) and it is produced predominantly by the Nordic pulp and paper industry to give them a market advantage in Europe over North American pulp. The North American industry elected to install ECF technology, arguing that not only was it cheaper but that the environmental benefits of TCF over ECF were questionable13.

1.3 Paper production

The huge diversity of paper and packaging products and the processes necessary for their manufacture make any in-depth description unrealistic in this context. This section will therefore concentrate on general product types and environmental issues raised by their production.

1.3a Paper types (see Table 2 on page 4)

i. Newsprint

Newsprint is cheap, often contains a high proportion of recycled fibre with little or no additives and is of low strength and quality. Brightness requirements for newsprint are low and can therefore be easily and cheaply achieved without chlorine. Recent development of colour printing technology has led to demand for a slightly higher quality product, but of all paper product categories newsprint is still potentially the most benign in environmental terms.

ii. Printing and Writing

A broad range of products come under this heading which includes fine and coated papers. Typically, they would require an opaque paper with an even water repellent surface. A number of additives are used to achieve these specifications.

Fillers and coatings: Used to increase opacity (as a cheaper alternative to using more pulp). China clay is the most common (used in about 90 per cent of all applications), calcium carbonate (chalk) or titanium oxide are also used. World consumption of fillers and coatings in 1988 was 20 million tons14.
Size: Used to coat pulp fibre to increase water repellence, prevent ink blotting and reduce fibre dust, which can clog printing machinery. Usually starch, rosin and alum, gelatine or latex. A number of synthetic sizing agents are also now available.
Others: A number of other chemicals and additives are used for specific purposes. These include salt (used as an anti-static agent in copying paper) and silicon powder (used for coating ink jet printing paper).

iii. Household and sanitary (tissues)

All tissue products need to be absorbent. Resin acids and other wood products which coat the cellulose fibres reduce their absorbency and therefore need to be removed by strong bleaching agents - traditionally chlorine. However, chlorine-free tissue products are now available which use a combination of hydrogen peroxide bleaching and specialised drying processes to achieve high absorbency levels.

Many household and sanitary products also require wet strength. To achieve this synthetic resins (some of which may be organochlorine based), Urea or melamine formaldehyde are added to the pulp.

iv. Packaging

Many packaging products are coated with a variety of coverings, depending on end use. Polyvinyl Chloride (PVC) and Polyvinylidene Chloride (PVDC) plastics are commonly used, which emit furans and dioxins when incinerated and are not degradable if committed to landfill. Packaging products are often bleached unnecessarily.

1.4 Pollution From Pulp and Paper Mills

1.4a Liquid effluent discharges

Table 2: Paper Production by Product Category

Product Type	World production in Tonnes15	UK paper consumption16 ( per cent of UK total)	Pulp / fibre type	Additives
Newsprint	32,404,000 (14 per cent)	19.5 per cent	mostly mechanical and/or recycled with some Kraft or sulphite	-
Printing and Writing	70,039,000 (31 per cent)	32.4 per cent	bleached wood free chemical, some unbleached (C)TMP	china clay (gloss), chalk (matt), titanium dioxide, size
Household and Sanitary	13,125,000 (6 per cent)	5.4 per cent (Tissues)	softwood sulphite, some Kraft and recycled	synthetic resins, Urea, melamine formaldehyde
Packaging	98,983,000 (43 per cent)	39.5 per cent	Kraft	wax, plastic, metal foil
Other	13,858,000 (6 per cent)	3.2 per cent	-	-

Whilst a great deal of technical literature exists on the effects of pulp/paper effluents on their receiving watercourses, several factors make it difficult to produce a conclusive picture:

The majority of research has been carried out on Northern species of wood, predominantly softwood. Little is therefore known about specific effluent problems which may arise from Southern wood species, or the effects of effluents in tropical, subtropical and warmer temperate climates.
Technology in the pulp and paper industry is so diverse and dynamic in its advances that effluent characteristics are by no means uniform.
The level of wastewater treatment varies widely throughout the world dependent upon individual mill policy, company policy and state legislation.
Advances in monitoring technology have meant that 'new' environmental effects are constantly being discovered.

However, general areas of concern can be identified and these are outlined below.

General organic pollution and suspended solids
The most common organic pollutants in effluents are lost cellulose fibre, carbohydrate, starch and hemi-cellulose (or the organic acids resulting from their breakdown). The levels of these pollutants are measured by the Biological Oxygen Demand (BOD) or Chemical Oxygen Demand (COD) (see Glossary). COD discharge can range from 25- 125 kg per tonne of pulp17. This demand for oxygen depletes that available to fauna and flora, thus damaging wildlife near to, and downstream from, effluent discharges.
High levels of suspended solids can also cause problems of both water opacity and blanketing of river or lake beds. Severe blanketing may also result in anaerobic decomposition under the blanket releasing hydrogen sulphide into the aquatic ecosystem.

These problems are reasonably localised. However, organic solids can also absorb many of the toxins present in mill

effluents, such as resin and fatty acids and heavy metals. This can have long-term effects over a wider area as a result of bioaccumulation and transportation through the food chain.
Acidic Compounds
Predominantly natural resin acids, which occur in high concentrations in softwood pulp, and are most concentrated in mechanical and (C)TMP pulp effluents (96-98mg/l18). They can be chlorinated in bleached Kraft pulp effluent. Although, both resin acids and chlorinated resin acids are moderately toxic and persistent, generally acidic compounds are of relatively minor concern in these concentrations as they are readily biodegradable and do not bioaccumulate. Also known as abietic and dehydroabietic acids.
General organochlorine products
As mentioned earlier, 5-8kgs of elemental chlorine per tonne of bleached chemical pulp combine with wood products to form organochlorines. About 300 such organochlorine compounds have been identified, although the effects of all of them are not known. It is likely that several hundred more remain unidentified19.
The collective quantity of organochlorines present can however be measured and three techniques are commonly used for this: AOX (which is most commonly used), EOX and TOCl (see Glossary). Whilst these measurements are useful up to a point, there is no direct correlation between the observed toxicity of mill effluents and the quantity of organochlorines present.

Chlorophenolics
Formed in chlorine-bleached chemical pulping processes (up to 70g/tonne - highest in softwood pulp effluents20). Not only are they themselves toxic, persistent and bioaccumulative, but they can transform into other compounds which are even more so.

As a group, chlorophenolics and their transformation products are probably the most hazardous chemical group in pulp and paper mill effluents, being present in higher concentrations than more toxic compounds such as dioxins. Substituting chlorine dioxide for elemental chlorine in some bleaching process stages significantly increases chlorophenolic production21.

The chlorophenolic group contains phenols, guaiocols and catecholes. Biotransformation products include anisoles and verathroles. The most common chlorophenolics are the extremely toxic and persistent trichlorophenol and pentachlorophenol.

Dioxins (PCDD) and Furans (PCDF)
Dioxins are extremely toxic, persistent and carcinogenic. Furans are chemically similar but an order of magnitude less toxic and less persistent than dioxins. Raw material type does not seem to significantly influence the amounts formed. Dioxins and furans tend to accumulate more in the pulp itself than in the effluent. This has led to concern about dioxin levels in finished paper products and wastewater treatment sludge disposed of via landfill or incineration, as well as in liquid mill effluents. Dioxins are also known to be present in mill flue gases.

The known effects of PCDD and PCDF on fish and mammals are wide-ranging but any link to effects on humans is proving hard to establish. They are, however, suspected of causing miscarriages, birth defects, liver damage, skin complaints and behavioural and neurological problems. Bioconcentration through the food chain, via fish, is a major concern.

Chloroform and other neutral chlorinated compounds
This group includes chloroform, chloro-acetones, - aldehydes and -acetic acids which are formed during the bleaching process but in lower concentrations than chlorophenolics. Whilst generally compounds in this group are non-persistent and non-bioaccumulative, some are moderately toxic, mutagenic and/or suspected carcinogens. The major concern is the likely effect of human exposure to chloroform via drinking water and air. The United States Environmental Protection Agency (US-EPA) has identified pulp bleaching as the single largest source of atmospheric chloroform22.
Other environmental issues relating to effluent discharge
Technological advances in paper making processes, waste treatment and environmental monitoring have led to several 'new' environmental problems associated with the manufacturing process becoming apparent. For example, physiological changes in fish reproductive organs and hormone production consistent with oestrogenic pollutants have been observed. These effects do not appear to be related to the pollutants mentioned above. As yet the cause remains largely unidentified, but it is thought compounds present in the wood itself, which may be chemically modified by the Kraft process, are responsible23.
Use of chlorine dioxide, the basis of ECF bleaching, has led to problems of chlorate production. Chlorate is a powerful herbicide which can severely affect waterborne algae.

Chelating agents used in TCF technology bind trace metal ions in the pulp to prevent them degrading the peroxide. This increases the metal load in effluents and is an issue of concern; however, the environmental impact of the process is so far largely unknown24.

1.4b Air emissions

Air emissions from chemical pulp mills are primarily made up of particulates, hydrogen sulphide, oxides of sulphur and oxides of nitrogen. Micro-pollutants include chloroform, dioxins and furans, other organochlorines and other volatile organics. As with liquid effluent discharges the levels of emissions are highly dependent upon the type of process technology employed and individual mill practice. Another important factor is the fuel type and quality. Whilst older mills caused severe air pollution, mitigating technology now exists to eliminate most harmful gas and particulate emissions. Whether this technology is utilised depends on local factors such as legislation, company and mill policy and proximity to populated areas. The major pollutants and their effects are summarised in Table 3 on page 6.

The contribution of the paper industry to global warming has been an ongoing debate for several years, with some suggesting that the absorption of carbon dioxide by plantation forestry more than offsets the emissions of greenhouse gases caused during the production, transportation and disposal of pulp and paper products. A recent study by the International Institute for Environment and Development (IIED) dismisses this argument, concluding that the paper cycle results in the net addition of some 450 million C02 equivalent units per year25.

1.4c Solid Waste

Solid waste from paper manufacture ranges from 10- 250kg/t (dry equivalent)26. Disposal is usually to landfill, although incineration is becoming increasingly widespread. Other experimental disposal techniques include using the waste as a soil improver but, as with all disposal options, there is some concern about possible dioxin and heavy metal contamination.

1.5 Effluent Treatment in Pulp and Paper Mills

Table 3: Air Emissions from the Pulp and Paper Industry

Pollutant	Effects	Source	Comments
Carbon dioxide	greenhouse gas	fuel combustion	see section 1.4b
Hydrogen sulphide	rotten egg smell	Kraft process	very low odour threshold (5 to 10 ppb) makes it very difficult to remove smell completely. Kraft process is banned in Germany because of this.
Sulphur dioxide	acid rain	fuel combustion and pulping process. (Kraft 1-3 kg SO2/tonne)27 , sulphite 5kg SO2/tonne )	contribution to acid rain problem could be significantly reduced by switching from fossil to wood waste fuels.
Volatile organics	some toxic effects and precursors to the formation of ozone	various
Chloroform	toxic, possible carcinogen	chlorine bleaching	see liquid effluent discharges
Other organo- chlorines	some highly toxic	chlorine bleaching	see liquid effluent discharges

ppb=parts per billion

1.5a Primary treatment

Primary treatment involves the mechanical removal of suspended solids from effluents by settlement or other means. It may be the only wastewater treatment employed in many mills worldwide; however, more often emission standards require secondary and possibly tertiary treatment. The effectiveness of these subsequent treatments depends upon efficient primary treatment, which itself reduces BOD and AOX.

1.5b Secondary treatment

Secondary treatment uses micro-organisms to accelerate the natural decomposition of organic waste. The two main methods used are aerated stabilisation and activated sludge treatment - both are known as aerobic treatments.

The efficiency of these two systems varies widely, depending on climate, influent quality, pulp type, fibre source and mill practice. In ideal conditions, activated sludge performs better at reducing BOD and removing suspended solids28. Disadvantages of both methods of aerobic treatment include high energy consumption and production of sludge waste.

Newer anaerobic treatments are now coming into use, particularly with effluents from the (C)TMP process.

1.5c Tertiary treatment

Tertiary or non-biological chemical treatments are expensive and only applied in a few mills. Aluminium oxide, ferric oxide and polyelectrolytes assist coagulation of waste in the effluents, which are then sand filtered.

1.6 Other Resource Use

1.6a Energy

The pulp and paper industry is a major energy consumer, using 2,000-6,500 kWh to produce one tonne of dried pulp. Whilst chemical pulping actually requires more energy than mechanical(6,350 kWh/tonne Kraft; 5,400 kWh/tonne sulphite) the processes are largely energy self-sufficient through the burning of waste products to generate steam. Mechanical pulping requires imported electrical energy (2,000 kWh/tonne)29. Different bleaching processes require varying amounts of energy, with ECF requiring most at 4.0 kWh/kg and TCF requiring least at 1.0 -2.0 kWh/kg30.

1.6b Water

Abstraction of water for the industry is significant both in terms of quantities used and the possible damage caused to the adjacent environment. Problems associated with water use include increased sedimentation and turbidity, increased water temperature, loss of habitat diversity, possible concentration of toxic material and lowering of water tables. Chemical pulping uses 159,000-204,000 litres / tonne, whereas mechanical pulping uses less, at 45,000- 68,000 litres / tonne31.

2. RECYCLED FIBRE

The term 'recycled' can be broadly interpreted to include three types of waste fibre:

Mill broke: waste from the manufacture process itself. Mill broke has always been reused and is not considered as true recycled fibre.
Pre-consumer waste: industrial by-products such as off cuts and trimmings from printers, rejects etc.
Post-consumer waste: paper which has been used then collected and recycled.

Different recycled paper products may contain any or all of these types of waste; most are now classified so that it is possible to determine the fibre source. Most often 'recycled' includes both pre-consumer and post-consumer waste.

Worldwide use of recycled fibre in paper production was approximately 114 million tons in 199532, which is 39 per cent of total fibre used. This figure is projected to rise to 190 million tons by 2005 (49 per cent). In the UK 55 per cent of fibre used by UK manufacturers is recycled33, although this varies with product type, with a high proportion being used in packaging but very little in office paper. Only 33.9 per cent34 of the paper we consume is recovered. The packaging industry is committed to increasing waste paper recovery, in line with EU requirements, to 50 per cent by the year 2000 and the newspaper industry has undertaken a voluntary commitment to increase recycled content to 40 per cent by 200035.

2.1 Production

Waste paper and board is categorized into 11 grades ranging from high-quality printing and writing (grade 1) to low-quality unsorted (grade 11). See Table 4 on page 8.

2.1a Mechanical pulping

Bulk grades are usually mechanically re-pulped, often with the addition of caustic soda and aluminium sulphate. Large contaminants such as wrapping and baling wire are removed before the pulp is washed and sorted to remove smaller impurities and short fibres which would weaken the new product. Dispersion agents are often used at this stage, and the pulp will be washed and milled at least twice, the water used is then treated to concentrate the contaminants.

The resulting mechanical pulps are prone to darkening, which is prevented by the use of hydrogen peroxide or sodium hypochlorite. Additional bleaching as described for virgin pulp may also be used. Sulphuric acid is sometimes added to the pulp to stabilise it and maintain brightness.

2.1b De-inking

For higher quality products, de-inking or a chemi- mechanical pulping process which includes de-inking is necessary. After the re-pulped fibre has been washed and sorted to remove solid impurities it is heavily diluted. Chemicals such as detergents, dispersants and foaming agents are added which separate the ink from the fibre and the pulp is aerated so that the ink forms a foam on the surface. This is then separated off and concentrated into a sludge for disposal.

The fibre yield from re-pulping and de-inking is dependent on the filler content and quality of the input fibre, the process technology and final product, but ranges from 60- 92 per cent36. Recycling low quality and heavily printed fibres and tissue products produces the lowest yields.

2.2 Environmental Impacts of the Recycling Process

Studies on emissions from recycling plants are much more limited than those for virgin pulp and paper mills and the data available is not conclusive by any means. However, the indications from two fairly comprehensive and independent studies is that effluents from recycling plants have less environmental impact than virgin pulp effluents37.

2.2a Wastewater emissions

Pre-treatment levels of suspended solids and Biological Oxygen Demand are likely to be higher in de-inked re- cycled effluents than virgin pulp effluents but, more significantly, COD and AOX (see Glossary) are likely to be lower38. Non de-inked recycled fibre effluents show significantly lower TSS, BOD and COD than de-inked, hence BOD and TSS levels will be higher the lower the grade of paper used. As discussed in the previous section, technology is available to remove most of these pollutants from effluent streams.

Heavy metals in recycling mill effluents is also a cause for concern. Metals such as copper, chromium, lead, zinc, nickel and cadmium are commonly used in printing inks and are discharged not only to wastewater but also to waste sludges and some remain in the final paper product.

Dioxins and furans do occur in re-pulped effluents, although little is known about their precise source. Ogilvie (1992)39 maintains that, overall, recycling reduces dioxin emissions by reducing demand for bleached woodpulp.

2.2b Air emissions

Gaseous and particulate emissions to air from the recycled paper making process primarily come from the incineration of de-inking sludges and fuel combustion. Direct emissions from the process itself are minimal and considered to be relatively insignificant, although again little research has been done in this field.

2.2c Solid waste

Relatively large amounts of solid waste result from the production of recycled paper although, obviously, overall recycling reduces waste volume. This waste comes in the form of bale wrappers and wire, sorting rejects and, more significantly, pulping and de-inking sludges, comprising water, cellulose fibre, fillers and ink. The amount of waste is dependent upon paper source and product type but is typically 15-100kg solid waste and 90kg (newsprint) to 520kg (tissues) sludge per tonne of de-inked recycled paper40.

Traditionally this waste has been consigned to landfill. Incineration is becoming more widespread but is an unsatisfactory solution as burning sludge produces a relatively high proportion of ash and gaseous emissions. Other disposal options in the initial stages of development include composting and techniques to remove clay and other fillers for reuse are also being developed.

Table 4: Waste Paper Categories

Grade	Source	End use
Grades 1 to 4	Pulp substitute grades ie. high-quality sorted printing and writing	Printing and Writing Kraft wrappings Tissues
Grade 5	Newsprint	Newsprint
Grades 6 to 11	Bulk grades ie Lower quality unsorted paper	Packaging and Board products

The toxicity of the sludge is a matter of debate within the industry. Heavy metal contamination is of concern with respect to direct landfill, incinerator ash disposal and composting, and incineration produces significant air emissions of CO2, NOx, CO, SO2 and hydrocarbons as well as dioxins.

Overall studies suggest that for all the above gaseous pollutants, the environmental burden is significantly less if paper is recycled41. Sludge derived from de-inked recycled paper manufacture is comparable to, or less harmful than, municipal wastewater treatment sludges42.

2.2d Energy use

The overall energy consumed in the manufacture of recycled paper is low compared to other paper types at 16.3MJ/kg and represents a calculated energy saving of 28- 70 per cent43compared to virgin pulp and paper manufacture processes. The source of this energy, however, is primarily imported electrical and therefore most commonly derived from non-renewable fossil fuels (unlike virgin chemical pulp production which is often largely energy self- sufficient). Increasing use of incineration/energy recovery for process waste may go some way to redressing the balance but would be of questionable environmental benefit.

2.2e Water use

Recycled paper production requires approximately 100,000 litres of water to produce 1 tonne of pulp. However with re- circulation and reuse of water during the process, abstraction can be reduced to between 1,000 and 30,000 litres per tonne of pulp44. This compares favourably to virgin pulp production (see section 1.6b).

2.3 Life Cycle Analyses

Much of the research concerning recycled paper takes the form of life cycle studies comparing the environmental impacts of various wastepaper disposal / use scenarios (Recycling vs. Landfill, Recycling vs. Incineration and Landfill vs. Incineration). These studies show inconsistencies and their use presents the following problems:

Most of the studies ignore forest management issues as their emphasis is centred around exploring the waste paper disposal /use issue. Those which do consider forest management contradict each other.
Large assumptions and simplifications must be made in order to compare such widely differing processes. Most comparisons with incineration, for example, assume that incinerators are modern and operated at best practice. This is often not the case in reality.
None of the studies considered the micro-pollutants dioxins, furans and heavy metals in any detail. This is undoubtedly because not enough is known about the path of these chemicals through the paper life cycle. There is however much concern about emissions from incinerators, fly ash contamination etc.

Despite encountering these problems, in their 'Towards a Sustainable Paper Cycle' study, IIED undertook to try to find general trends in their findings. They concluded as follows:

“Most of the studies support the view that recycling and incineration are environmentally preferable to landfill. There is less agreement on whether recycling is preferable to incineration. Critical factors are the nature of the pulp and paper making process, the level of technology at all stages of the life cycle and the energy structure of the countries under study. Interpretation also plays a role in weighing up of increases in some emmissions against reductions in others.”45

Friends of the Earth opposes incineration on the grounds that it is wasteful of resources and polluting.

3. NON-WOOD FIBRE SOURCES

In addition to wood-based fibres, a wide variety of non- wood material is used worldwide in the manufacture of paper. Whilst worldwide production of non-wood pulp is estimated at 5-11 per cent46 of total fibre produced, its use is very regionialised, being concentrated almost exclusively in less developed countries which have few forest resources and whose paper consumption is comparatively low. For example, China produces nearly 90 per cent of its pulp from non- wood sources, India 48 per cent and Thailand 36 per cent47. By contrast, in high consumption developed countries such as the USA and UK, non-wood pulp production is 0.3 per cent48 and 1 per cent49 of total production respectively. However, production in developed nations is estimated to have risen 8.3 per cent annually between 1981 and 1992 whilst falling in less developed countries by 5.3 per cent per annum in the same period50.

The reasons for this large regional difference are complex. Non-wood pulp is generally produced on a small scale, relying on local annual fibre sources, supplying local markets and requiring low capital investment, thus suiting the economic infrastructure of less developed countries. As such, however, they cannot hope to compete with the global operation and huge economies of scale of the large transnational wood pulp producers. Nor can they afford to invest in developing efficient modern production processes and so often rely on outdated machinery designed to pulp wood. Concern about pollution levels has led to the closure of some mills and increasing expansion into new markets by transnational paper producers is taking its toll. China, which produces three-quarters of the world's non-wood fibre, has recently begun shifting towards plantation forestry.

3.1 Non-wood fibre types

Essentially three categories of plants are used in non-wood fibre production, although in theory almost any fibrous plant can be used.

Annual fibre crops: eg hemp, kenaf, flax, jute
Agricultural residue: eg wheat, corn or rice straw, bagasse, sisal
Wild plants: eg grasses, bamboo and seaweed51

Straw is by far the most widely used, accounting for 47 per cent of world production, followed by bagasse at 12 per cent and bamboo at 6 per cent (figures are for 1993)52.

Compared with wood, these plants are generally lower in lignin, higher in silica and ash with equivalent cellulose content53. Different plant species produce different pulp types suitable for a variety of products. For example bagasse and straw are used to produce predominantly low grade pulps, whereas hemp, kenaf and flax are often used in higher quality and speciality papers such as banknotes and cigarette papers54.

3.2 Environmental Impacts of Non-wood Fibre Pulp and Paper

3.2a Crop production

Needless to say, judgement of the environmental impacts of non-wood and wood fibre crop production is entirely dependent upon the specific management regimes employed by the producer and different fibre crops will place greater or lesser demands on the environment.

Yields
International Institute for Environment and Development (IIED) estimate that fibre yields from hemp and kenaf, at around 15 tonnes/annum/ha, are equivalent to the highest yield hardwood (Eucalypt) plantations and higher than other wood fibre species. However, they assert that: “Non- wood and wood fibre crops used for similar paper grades and grown under similar conditions generally yield roughly the same amount of paper-making fibre per hectare”55. In real terms, however, such comparisons are fairly meaningless as the proportion of the crop used for paper-making from both wood and non-wood sources is hugely variable and by-products etc must be taken into account.
Agrochemical Use
Where chemical agents are used to improve crop yields IIED estimate that wood-based fibre production theoretically has the environmental advantage. One crop rotation in a tree plantation (minimum seven years) would use approximately equivalent amounts of pesticides and fertilizers as one annual rotation of non-wood fibre crops56.

It is important to note, however, that using agricultural residue such as straw for paper results in no additional use of agrochemicals. Most crops grown especially for fibre are disease resistant and hardy, and chemical use is low or non-existent. Hemp and kenaf are both considered capable of out-competing most weeds, and hemp produced in the UK (by Hemcore) and in France57 is grown without the use of any insecticides, fungicides or herbicides. Organically grown hemp showed no decrease in yield over a seven-year period and the crop is recommended in rotation with cereal crops to improve soil structure 58. Trials using kenaf in the USA found it less vulnerable to pests and agriclimatic factors than other crops grown in the same area , with lower nutrient and management requirements59.

After harvesting, insecticides and fungicides may be applied to non-wood fibre crops. This is because their annual nature and moisture content means that they may be stored for long periods, during which time they are vulnerable to fungal and microbiological attack.

3.2b The manufacture process

At the current time the majority of paper manufactured from non-wood fibres is produced by old technology designed to process wood. This causes a number of problems because of the different physical characteristics of wood and non-wood fibre species.

Preparation
There are two distinct types of fibres from hemp, flax and kenaf: the bark or 'bast' fibres and the core or 'hurds'. Bast fibres are too long for conventional paper-making machines and cause filters to become blocked. It is therefore necessary to reduce fibre length by precutting the stems (if the whole stem is being pulped) or by extending the pulping of the bast fibre (if it has been separated from the hurds). Both of these processes require additional expenditure and additional machinery.
Pulping
The physical characteristics of non-wood fibres are significant when the conventional chemical pulping process is used, particularly the higher silica and hemicellulose content and thinner fibres.

Lower lignin levels in non-wood fibres are an advantage in mechanical and C(T)MP pulping, as less energy is required to remove it (tyhe FAO estimates a 30 per cent saving). However, with mechanical pulping the lignin is the primary 'fuel' in the black liquor combustion so, as such, less energy will be recovered. Lower lignin levels also have the advantage that correspondingly less bleach and energy will be required if the pulp is brightened, dependent upon the pulping process used.

Chemical and energy recovery are fundamental to modern closed-loop chemical plants. In non-wood fibre pulping, the so-called 'black liquor' comprising pulping chemicals, lignin and other residues becomes contaminated by silica, which significantly reduces efficiency. Without chemical recovery, the organic residues cannot be incinerated to provide energy, more chemicals are needed, and effluent loads are very much higher. Technical solutions could undoubtedly be found to solve these problems but it requires investment.

There are several new experimental chemical pulping methods using, for example, organic solvents (alcohol), potassium hydroxide or new technology which may address these problems. One apparent success is the BIVIS process developed in France that is ideally suited to small- scale processing of long fibres. It uses conventional caustic chemicals but in significantly reduced amounts (75 per cent less60) with big energy, bleach and water savings also. BIVIS systems are in use in the UK, France and Spain pulping cotton, straw, hemp and flax. Other technology is at earlier stages of development.

Another option to tackle the problem caused by silica in non-wood fibres is to develop technology that can remove silica from the black liquor allowing normal chemical and energy recovery. Some research has been done and experimental systems developed; however, as yet the results have been disappointing, although investment in such research has been very small.

Other important characteristics of non-wood fibres include higher hemicellulose content which, combined with longer fibre lengths and the high silica content, causes black liquor to be more viscous, leading to poor drainage of the pulp.

Reported pulp yields of non-wood fibre are highly variable and dependent upon fibre type, process etc. Mechanical yields upwards of 90 per cent compare well to wood pulp, and chemically pulped kenaf yields of 44 per cent -70 per cent61 are similar to the equivalent Eucalyptus yield of 53 per cent.
Paper production
Once the pulp has been produced, the paper-making process is identical to that of wood pulp, although some additional fibre shortening may be necessary for long fibre non-wood species such as hemp and kenaf.

CONCLUSIONS

The complexity of the paper issue means that firm conclusions are hard to draw. All paper manufacture causes harm to the environment and more often than not the determining factors in a paper mill's environmental performance are not the process, paper type or fibre source but the location, mill practice and mill operator. Hence to try to grade paper products or production techniques into some kind of hierarchy of environmental performance, based solely on the manufacture process, is extremely difficult.

Mechanical pulp is arguably the least environmentally damaging virgin wood pulp and it has the advantage of producing a very high pulp yield compared to other processes. Mechanical pulp also causes lower levels of water pollution and uses less water, but has the disadvantages of being a major user of electrical energy and producing generally lower grade pulp. However, newsprint quality, mechanically-pulped paper contains few additives, can be recycled up to 4 times and is adequate for many purposes for which chemically pulped products are currently used.

Chemical pulps can produce very high quality strong products with the potential to be re-used, should this be possible, and recycled many times. They need not be highly polluting but yields, per volume of wood, are low.

Improvements in bleaching technology have had a beneficial effect on effluent quality where they have been introduced. However, a more general approach to improving/reducing effluents, particularly in less developed countries and more comprehensive research is required into the biological impact of pulp mill effluents and closed-loop (effluent-free) technology. The precautionary principle should be applied particularly with regard to organochlorine pollutants.

In environmental terms, whilst recycled fibre pulp does cause some problems, overall the production process is more benign than virgin pulping. The UK as an importer of virgin pulp in large quantities is in a good position in economic terms to expand its recycling industry as an alternative to imported pulp.

Using alternative fibres to reduce pressure on forests, whilst offering the social benefits that a small-scale agricultural-based industry would provide for rural economies, is an attractive idea. Hemp and agricultural residues certainly have great potential as fibre sources in the UK. However, greater investment is needed to develop appropriate technology for their use.

GLOSSARY

AOX: Absorbable Organic Halogens. This is the most common measure of the mass of available organic halogens (in this case organochlorines) in a particular medium. See EOX.
BOD: Biological Oxygen Demand. A measure of the amount of organic matter requiring oxygen for decomposition used in the context of organic pollution of water bodies. See COD.
COD: Chemical Oxygen Demand. A measure of the amount of organic matter requiring oxygen for oxidation similar to BOD. COD is more widely used as it is a simpler procedure and includes the effects of non-biodegradable organic matter which can account for up to half the material discharged.
(C)TMP: (Chemo)Thermomechanical Pulping. A variation on the mechanical pulping process.
ECF: Elemental Chlorine Free. Bleaching process which uses Chlorine dioxide as opposed to elemental chlorine gas.
EOX: Extractable Organic Halogens. That fraction of AOX (1 to 3 per cent typically) which is likely to bioaccumulate. A further fraction of this is Extractable Persistent Organic Halogens (EPOX) which measures bioaccumulative organic halogens which are resistant to sulphuric acid and thus not likely to degrade.
ISO: The percentage of light reflected back by a given surface. Used to measure the 'brightness' of paper products.
TCF: Totally Chlorine Free. Bleaching process which uses no chlorine products.
TOCL: Total Organically-bound Chlorine. A measure of the mass of organically-bound chlorine compounds present in a given medium. It has now been largely superseded by AOX, EOX and EPOX.
Tonne/Ton: Imperial tons and metric tonnes are roughly equivalent and both units are used in this briefing. 1 tonne = 0.9842 tons.
TSS: Total Suspended Solids.