Tissue paper products are valuable commodities that ameliorate livelihoods by improving sanitation and hygiene needs. Products generally fall under four categories; toilet paper, paper towels, facial tissue, and napkins, they are diverse, widespread, and an essential part of modern life. Though the industry has taken stride in improving its own sustainability, progress has been slow and somewhat sparse. Widespread environmental concerns among governments regarding unsustainable production, high level of consumption patterns in industrialized countries, coupled with water shortages, increased costs of energy, and uneven distribution of natural resources throughout the world are some of the drivers of change in the centuries-old industry. On the surface, the onus of sustainable behavior has been directed to the consumer through behavioral change whether through curbing consumption, changing products preferences, or recycling. Whereas much of the impact of the industry is in fact concentrated within the compounds of factories. Larger companies are seeing the benefit of new tools like Life Cycle Assessments and Environmental Assessment technologies. Such assessments monitor the overall environmental performance in order to improve the manufacturing process through informed decisions while more importantly driving down the overall costs of production in an increasingly competitive market.  

 

The following review is the first article in a two-part series which examines the role of circular economy in mitigating environmental challenges facing the tissue paper industry. 

 

This paper is divided into three main sections; the first section is a brief overview of the key processes involved in the manufacture of tissue paper and provides a glimpse into the type of resources needed in each stage. The second section outlines the environmental impacts that results from traditional manufacturing practices of tissue paper. The final section introduces the rationale behind integrating circular economy in this resource-intensive sector as the consensus of the scientific community provides further evidence to the direct implication of human-related industrial activities in climate change. 

 

Moving over to our next article; we will introduce an overview of the best available environmental techniques in the market that mitigate the impacts of traditional manufacturing and present examples of sustainable approaches from key players in the sector. We will also provide recommendation of a better implementation of the circular economy approach in the industry.

 

BACKGROUND | TISSUE MANUFACTURE 

 

Tissue paper is made from either virgin pulp (fiber coming from the cooked wood chips), or from recycled paper products. To make pulp using wood based raw materials, a pulp mill first has to turn tree logs into wood chips. Which are in turn cooked by an energy and water-intensive harsh chemical process in order to separate wood fibers into cellulose fibers free from natural adhesives such as lignin and sugars. Once the cellulose is separated from unwanted debris, the pulp goes through a series of rollers where water is extracted resulting in a naturally brown colored product. Hence, in the following stage, the pulp is sent through a chemical bleaching process to whiten the product and increasing fiber strength.

 

On the other hand, if raw material is based on recycled paper products, then the latter is mixed in with water and chemicals in a pulper and then screened in order to separate cellulose based fibers from impurities and dirt. 

 

In both processes, the furnish (pulp mixed with chemicals and water) is sent to the tissue machine, on which the sheet of tissue paper is formed.

 

Water is drained and evaporated during its passage in the press section and then on the steam dryer and the air-drying hood. 

 

The dryer is a large cylinder where high steam temperature is used to dry the sheet by rolling it over the dryer surface and allowing the steam to heat up the sheet.

 

The air-drying hood is a cap of hot air blowing on the sheet surface and at the same time used as an exhaust fan to discharge the evaporated water out from the sheet, giving the newly formed sheet main characteristics of thickness, softness and dryness. After that stage the tissue paper is creped or crinkled and rolled on the reel to form the jumbo tissue roll. 

 

Finally, the jumbo tissue paper rolls are sent to a converting machine that generate multiple ply tissues, fold napkins and tissue, and other tissue products that consumers can recognize.

 

ENVIRONMENTAL IMPACT OF THE TISSUE SECTOR 

 

ENERGY CONSUMPTION 

 

As the fourth largest Greenhouse Gases (GHG)  emitter among global manufacturing industries, the Pulp and Paper (P&P) manufacturing industry accounts for 6% of total global industrial energy consumption  while being responsible for around 9% of the total overall CO2 emissions from manufacturing industries (see Figure 2). In effect, the International Energy Agency ranks the sector alongside other energy intensive sectors such as cement, iron and steel. Specifically speaking, in tissue paper production, electricity consumption used to power different motor drivers can accounts for 25 % of the total GHG emissions especially in countries where the national grid is dependent on fossil fuels.  In fact, the Total Life Cycle Energy Requirements of any tissue manufacturer can vary slightly according to the origin of electrical power used to run the facility (solar power vs wind power vs fossil fuel), nevertheless it is common practice for other operations to dependent entirely on fossil fuel. 

 

Figure 1: largest energy end-uses by sector

 

The transportation of virgin wood from forests to pulp making mills and then to the paper manufacturing site is an energy extensive activity. In reality, each starch of the operation could be occurring in a different country from a different continent. According to Gemechu et al. (2013), tissue paper manufactured in Catalonia can procure 75% of its wood pulp from Europe by lorry and import about 25% from South America by ship, in contrast, waste paper can be sourced from a 250 km radius from around the Catalonia area thus significantly cutting down on the Total Life Cycle Energy Requirements. 

 

According to the same study, the extensive use of steam and hot air in the tissue paper production is also a major contributor of GHG emission, where it can be responsible for up to 23% of the overall tally (which followed a cradle–to-grave approach whereby logging, chemicals, and transportation were included in the calculations). In fact, most of the steam is needed in the drying stage of the paper making process. The process uses large quantities of steam in order to evaporate residual water left from the previous pressing stage. Steam heat generation in the mill is indeed entirely dependent on the use of fossil fuel.

 

In reality, newer technologies are presenting the industry with many opportunities for saving of electrical and thermal energies including the introduction of Combined Heat and Power co-generation which allows energy self-sufficiency in the process. Noting that any saving of electricity (high grade energy) translates into 3 to 4 times saving of primary thermal energy. 

 

I.1. RESOURCE CONSUMPTION

 

The primary input material in tissue manufacture is pulp sourced from either Virgin Wood (VW), annual plants, or other sources of fibers such as RWP. High value logs are generally directed to the construction and furniture sectors, whereas lower value logs and wood waste from sawmills are preferably directed to P&P processes leaving little to be wasted from the forest industry. Wood can be considered a sustainable resource should the forestry practices adopted by the sector promote sustainable forest management. The P&P sector as a whole uses about 42% of all wood harvested globally for industrial use, this figure is critical to deforestation and other severe environmental outcomes like drought and desertification.  Deforestation alone contributes 25% of the annual carbon emissions caused by human activities. 

 

Tissue paper products are derived from two types of virgin pulp: softwood and hardwood. Despite tropical rainforest never being harvested for this use due to environmental, economic, and most importantly, technical considerations, virgin fiber remains by far the most destructive and common source of pulp. You see, hardwood originates from deciduous trees whereas softwood is obtained from coniferous trees from areas such the Canadian boreal forests which is a zone of closed-crown conifer forests with some deciduous species. In fact, Northern Bleached Softwood kraft (NBSK), a type of softwood pulp for which Canada is known, is the most desired grade of softwood pulp for tissue products in the United States constituting between 20-40% of toilet paper and facial tissue products, and 25 to 75% of paper towels. 

 

Forests are essential for carbon sequestration by capturing carbon dioxide from the atmosphere and transforming it into biomass through photosynthesis. By considering emission release due to loss of woodland through decomposition of fiber tissue, carbon release from soil, and eventual loss of carbon storage, one can conclude that the manufacture of tissue products from virgin fiber has a substantially higher carbon footprint than those made from other biomass. Truly, the manufacture of products purely from virgin fiber generates 3 times as much carbon as those made from other sources.  Additionally, the use of RWP in tissue products reduces the use of excessively harsh chemicals and eliminates the use of bleach compared to the use of VW (even though the overall quantities of chemicals used are slightly higher, see Figure 2). However, it is not possible to recycle paper ad infinitum as fiber cannot be recycled more than seven times, thus not all recycled content is created equal. Accordingly, from a comprehensive perspective, emphasis should be directed to not only substitute VW with RWP, but to also optimize the process and reduce the amount of raw material (and consequently energy and water) needed in the first place. This becomes more feasible as technological advances allow RWP to be used to obtain products with the same quality and functionality as that produced from VW.

 

Figure 2: comparison of GHG between virgin wood and recycled waste paper

 

SOLID WASTE GENERATION 

 

Solid waste generated from pulping processes consists of bark and wood residues from the debarking which are usually burned in boilers; washing and screening of chips, fiber rejects (primary sludge); ash from energy production which is usually disposed of in landfills or more creatively used in building material; and excess sludge from external biological wastewater treatment.   The biggest waste fraction consists of different types of sludge, mainly fiber-containing primary sludge. A more detailed list of types of residues encountered in the P&P manufacture is presented in the table below. 

 

 

 

Closing the loop in this section is the use of RWP as a raw material. Though it is considered the more environmentally friendly option considering the lower production process emissions as well as the amount of waste paper sent to landfills and the wood harvesting demands; RWP processing highly depends on the origin of the recycled fiber. Virgin fiber pulping, papermaking, printing, and packaging processes use a variety of chemicals that can have an influence on recyclability of paper (see Section II-2 for limits of paper recyclability). Certainly, due to strict consumer expectations of tissue paper including softness, high absorbency, and high levels of cleanliness, the processing of paper for recycling of tissue can also generate its own slew of residual waste. Pulp fiber have to be free from ash and dirt (see Section I for more on this topic), whereas their content in recycling paper can be up to 35 – 45 %. The process of washing out these components decreases the yield during processing paper for recycling goes down to 53 – 58 % creating along the way a substantial amount of waste that required treatment.  Though, it has been noted that dewatering and incineration with the intention of generating energy seems to be a growing trend in the industry. 

 

WATER CONSUMPTION AND WASTEWATER GENERATION

 

Another essential component of the tissue paper industry is water. Throughout this review, water consumption was tackled in different forms (Section I [need for extensive washing and pulping], Section II-1 [steam], Section II-3 [generation of effluents]). Truly, the pulp and paper industry is ranked as the world’s third largest consumer of water and is consequently producing high amounts of wastewaters;  high consumption of freshwater is one of the most important environmental concerns in the paper industry. In tissue production, water consumption is higher than in many other grades like newsprint or fine paper and usually ranges from 8 to 100 m3/ton. This is because tissue products have very high quality standards in brightness, texture, and odor necessitating more frequent washing. 

 

Water scarcity is an issue that concerns all and that cannot be ignored for long. The reduction of the water use in the process is no longer a matter of simply caring about the environment, but in fact a matter of (1) adhering to governmental regulations and restriction in terms of water consumption and discharge, (2) reducing the consumption of freshwater and the ensuing economic, environmental and sociological costs, and (3) reducing the amount of wastewater that should be treated. 

 

Water plays a diverse role in the process whereby it is needed for cleaning, lubrication, cooling, and in the development of the product’s quality. A common methodology to reduce water consumption is the utilization of a closed loop water system. Unfortunately, the use of high temperature water leads to increased concentration of suspended and dissolved solids. The accumulating solids can severely damage used technologies while also negatively impacting the quality of the product depending on the extent of the closed water system. “Equilibrium between the advantages and the disadvantages relevant to water consumption restrictions should be established.”  Fortunately, the development of new processes and other technical improvements have decreased the fresh- water consumption over the years.

 

Concerns in the P&P industries around water and wastewater revolve around (1) the high level of toxic compounds and chemical oxygen demand (COD) found in the effluents, (2) The pulp and paper industry is the sixth largest polluter discharging a variety of gaseous, liquid and solid wastes into the environment, (3) the typical methodology for treating paper mill wastewater should consist of a combination of biological, physical, and chemical treatment, though most P&P mills resort to only biological treatment leaving much pollutants to be discharged into watercourses.  Untreated industrial wastewater streams pose a serious threat to human life, plants, and animals, and to the ecosystems of the bodies of water they enter, luckily tougher environmental regulation have curbed the release of raw industrial wastewater around the world, though the level of implementation and accountability leaves something to be desired. 

 

INTRODUCING CIRCULAR ECONOMY 

 

Following decades of scrutiny, the tissue industry has made very positive initiatives in improving its environmental sustainability performance. Through the increasing use of sustainable forest products, use of Recycled Waste Paper (RWP), advances in wastewater treatment technologies, optimization of the process and re-use of water, etc. the industry aimed to tackle problems such as deforestation, water pollution, extensive energy use, air pollution emissions; toxic pulping and bleaching process chemicals, and the production of greenhouse gases (CO2, Methane). Nevertheless, many opportunities are still up for grabs including the integration of the circular economy approach in the industry. 

 

By definition, a circular economy is an alternative to a traditional linear economy (make, use, dispose) in which resources are used and re-used for as long as possible to extract the maximum value from them whilst in use, then recover and regenerate products and materials at the end of each service life. A prime example would the use of RWP in the making of new tissue products, the integration of eco-designs in the packaging of products, the use of Combined Heat and Power co-generation, the re-use of water in looped cycles, etc. The key advantages of this circular approach are (1) the reduction of operational costs through energy, water and resource conservation and (2) an improved image opening up doors to new consumers who are looking for more sustainable options.