. Description .
Inspiration
As Mr. Gorky said, “Books are the ladder of human progress.” Books not only record and spread knowledge but also provide readers with the opportunity to gain insights and experiences from scholars, thereby extending intellectual ideologies. As one of the Four Great Inventions of ancient China, paper has served as a vital carrier of knowledge, spreading across the world via the Silk Road, fostering economic and cultural exchanges among nations, and promoting human progress. With the advancement of civilization and technology, paper’s applications have expanded to packaging, cleaning, decorating, and writing. Unfortunately, the rapid population growth has driven heavy demands for paper, leading to extensive deforestation and disturbing the ecological balance, thereby exacerbating the climate crisis. Enhancing the recycling of waste paper can mitigate deforestation, offering a significant contribution to addressing the climate crisis. Inspired by this, our project aims to investigate the current state and challenges of waste paper recycling, provide innovative solutions to the recycling bottleneck, and raise public awareness about resource recycling and the climate crisis.
Background
The ongoing climate crisis driven by high levels of greenhouse gas (GHG) emissions has led to numerous disasters and heavy losses worldwide. Climate-related disasters, such as hurricanes, droughts, floods and wildfires, have become increasingly frequent and severe over the years. These result in significant economic losses and substantial human casualties, reaching nearly $143 billion annually and approximately 60,951 deaths in the last 20 years (1). The root cause of these crises is the increase GHG like carbon dioxide, methane, and nitrous oxide, which contribute to global warming.
Forests act as carbon sinks, absorbing GHG and mitigate climate change. However, with the rapid development of human society and the explosive growth of the population, the rate of deforestation far exceeds the rate at which forests can grow. Each year, approximately 4.7 million hectares of forest are lost globally (2).
Paper promotes the development of human civilization, but the manufacturing process of paper causes significant pollution. Featuring the extensive use of virgin wood, the pulp and paper industry not only causes deforestation but also generate huge amount of GHG in material processing. From 1961 to 2019, the pulp and paper industry generated 43.5 billion tons of carbon dioxide, accounting for 4.2% of global anthropogenic GHG emissions (3). If much of the paper can be recycled, it can greatly reduce the cutting down of trees and alleviate the climate crisis.
According to U.S. Environmental Protection Agency, Recycling one ton of paper can save approximately 17 trees, 7,000 gallons of water, and 4,000 kilowatt-hours of electricity (4). Therefore, paper recycling not only conserves natural resources but also reduces the environmental footprint. Despite the importance of paper recycling, traditional methods pose severe environmental challenges. The deinking process consumes large amount of water and chemicals such as sodium hydroxide, hydrogen peroxide and chlorine-based bleach. Moreover, the sludge from deinking contains heavy metals and toxic chemicals. It releases carbon dioxide and various toxic gases when incinerated and contaminates soil and water if landfilled. This underscores the necessity for innovative methods that enhance recycling efficiency and minimize pollution.
The Problem
As one of the large-scale manufacturing industries in the world, the pulp and paper industry not only contributes to the rapid development of modern technology and society's progress but also exerts a significant adverse impact on forests, the water environment, and, ultimately, the climate. Around 405 million tons of paper and paperboard are produced annually, accounting for 13-15% of total wood consumption. With the demand for paper products increasing, global production could double by 2050 (5). If waste paper is not recycled, 240 million tons of paper will end up becoming landfill waste or being incinerated, equivalent to a loss of 408 thousand hectares of forests (6).
Unfortunately, the current situation of waste paper recycling is not optimistic. China has one of the largest paper production industries worldwide; only about half of the waste paper produced is recycled, and the utilization rate for waste paper has been declining over the years, dropping from 72.2% in 2013 to 53.5% in 2022 (Figure 1). Such figures indicate that a significant portion of waste paper resources is underutilized in China.
For the waste paper entered into the recycling process, the removal of ink in the waste paper is the main intractable problem in the recycling industry. The issue includes but is not limited to the following points:
(1) High cost: Plenty of water and chemical reagents were used to deal with the ink in waste
paper, and the effluent treatment also cost many processing fees.
(2) Environmental pollution: The improper process mode (incinerate or landfill solid sludge) may
result in severe pollution.
(3) Health risk: The use of a large number of chemical reagents, such as hydrogen peroxide and
sodium hydroxide, poses significant health risks to workers in paper factories.
Current Solution
The first step of the waste paper recycling process was pulping, in which the sorted paper was mixed with water and chemicals and subsequently stirred into fibers. Then, the pulp undergoes alkaline deinking (8), flotation and washing process to remove the ink. Because the alkaline treatment diminishes the brightness and whiteness of the pulp (9), the deinked pulp is typically subjected to bleaching. Traditional bleaching methods often use chlorine-based chemicals, such as chlorine and hypochlorite, which will produce harmful chlorinated organic compounds. At last, in terms of heavy metals present in post-deinking wastewater, these substances tend to settle into the sludge after wastewater treatments. The sludge is then incinerated or landfilled, which poses significant risks to the air and soil (10).
In conclusion, this conventional approach demands a substantial amount of toxic chemicals. It further results in the release of poisonous organic agents and heavy metals that may cause environmental contamination. What's more, those substances involved in the deinking process complicate wastewater and sludge treatment, necessitating additional procedures prior to disposal.
Project
To ameliorate the climate crisis, our project has focus on:
(1) investigating the current situation and problems of waste paper recycling.
(2) providing an unprecedented answer to the bottleneck of recycle utilization.
(3) arousing broad public concern on the resources recycling and climate crisis.
1. Investigating the current situation and problems
We conducted a series of investigations, visiting waste collectors, sorting stations, recycling industry associations, and paper mills to research the issues of waste paper recycling. Our findings revealed several significant challenges. The high cost associated with the recycling process is a major concern, as a substantial amount of water and chemical reagents, such as hydrogen peroxide and sodium hydroxide, are required to remove ink from waste paper. The post-deinking effluent containing these chemicals necessitates further treatment, adding to the overall expenses. Additionally, the use of chemical deinking agents and bleach poses significant health risks to workers in the factory.
Environmental pollution is another critical issue. The sludge generated during the recycling process is usually incinerated or landfilled. These practices release harmful substances into the air and soil, leading to severe environmental contamination.
2. Providing an unprecedented answer
Based on the main results from our investigation and analysis, our project focuses on tackling the challenges of high cost, environmental pollution and health risks. We also proposed a standard operating procedure (SOP) for the technological process of signal peptide-mediated enzyme catalytic deinking.
Toward the problems of high cost, we replace the alkaline deinking by signal peptide-mediated enzyme catalytic deinking, which bypass the expensive protein purification step but also avoided the use of great number of alkaline reagent. Furthermore, we construct a rapid screening system, which successfully screen some enzymes with higher performance in deinking efficiency, providing reassurance about the effectiveness of our process (see Design for details) .
Toward the problems of environmental pollution, we constructed a metallothioneins-based biosorption system to adsorb heavy metals in post-deinking water, which minimizes the content of heavy metals in the waste.
Toward the problems of health risk, our highly efficient enzymes greatly reduce the demand for hazardous chemical reagents such as hydrogen peroxide and sodium hypochlorite, protecting workers in the factories.
3. Arousing broad public concern
To raise public awareness about paper recycling, we organized a series of educational and promotional activities. We held informative lectures at the elementary school, where our team members shared the importance of recycling paper and its environmental benefits to the students. We also held interactive sessions at the Xiamen Science and Technology Museum, including educational presentations and fun activities, spreading the concept of recycling to both young and old. To gather public opinions and attitudes towards paper recycling, we launched a comprehensive survey and it provided valuable insights into current recycling habits and areas needing improvement. Lastly, we published informative articles on social media, reaching a wide audience and encouraging greater participation in recycling efforts (see Human Practices for details).
Biosafety
The heavy metal adsorbing bacteria may escape through the wastewater pipelines and cause genetic contamination in the natural environment. So, we designed a blue light-induced kill switch in E. coli to ensure biosafety (Figure 2). LexRO is a light-sensitive protein that forms a homodimer and binds to pColE408 to repress gene expression in darkness. When exposed to blue light, LexRO dissociates, leading to the activation of gene expression. The circuit functions by the LexRO-regulated expression of cytotoxic protein CcdB and anti-CcdB protein CcdA.
Future Prospect
We've noticed that there is another factor barricading the sustainable development of paper resources: the waste of paper products. In daily life, writing remains indispensable, yet it inevitably involves error and leaves non-erasable marks. Our team has frequently noticed paper wastage due to these unavoidable mistakes, which adversely affect the utilization rate of paper and burden the process of recycling.
Stationery manufacturers have taken note of the need for pen mark erasure in daily use, leading to the development of various erasure products like correction tapes, erasable pens, and correction fluids. However, these products have their flaws considering effectiveness, safety, and environmental impact. However, some obvious modification traces (abrasion or cover) are inaesthetic and even unwarrantable for some important documents.
We tested several compounds and found their potential in pen mark removal. Rhamnolipids are highly efficient biosurfactants that can form micelles in water, thereby enhancing the solubility of ink. Limonene, a natural terpene compound, can also promote the solubility of ink. Together, they facilitate the detachment and dissolution of ink particles.
Chitosan is a natural biopolymer derived from chitin. Cross-linking agent glutaraldehyde can react with the amino groups on chitosan to form porous cross-linked chitosan with huge adsorption capacity.
Our proposed solution for pen mark erasure in daily use leads to a user-friendly “eraser pen”. This pen uses rhamnolipid and limonene as its “bio-ink” to dissolve pen marks and has a chitosan bio-absorbent on its tail to absorb ink particles, has the potential to revolutionize the way we use paper, sparking excitement and optimism about the future.
Conclusion
As climate change continues to accelerate, the need to preserve our forests has never been more critical. Deforestation, driven by commercial purposes such as paper production, exacerbates this issue by the destruction of vital carbon sinks. Paper recycling is an effective way to protect the forests. However, separating ink and paper once they are combined is a significant challenge. The difficulty in eliminating ink from paper hampers industrial waste paper recycling. Moreover, the wastewater resulting from the deinking process contains high-level heavy metals and various pollutants. These issues have guided our focus toward bio-deinking and the detoxification of post-deinking wastewater this year.
References
- R. Newman, I. Noy, The global costs of extreme weather that are attributable to climate change. Nature Communications 14, 6103 (2023).
- FAO, "Global Forest Resources Assessment 2020," (2020).
- M. Dai et al., Country-specific net-zero strategies of the pulp and paper industry. Nature 626, 327-334 (2024).
- https://archive.epa.gov/wastes/conserve/materials/paper/web/html/index-2.html
- https://wwf.panda.org/discover/our_focus/forests_practice/forestry/pulp_and_paper/
- B. o. I. Recycling, "Paper and board recycling in 2020: Overview of world statistics," (2022).
- 中国造纸协会, "中国造纸工业2022年度报告(2022 Annual Report of China's Paper Industry)," (2023).
- H. Grossmann, T. Handke, T. Brenner. (2014).
- H. Zhang, S. Fu, Y. Chen, Basic understanding of the color distinction of lignin and the proper selection of lignin in color-depended utilizations. International Journal of Biological Macromolecules 147, 607-615 (2020).
- P. Bajpai, in Biotechnology for Pulp and Paper Processing, P. Bajpai, Ed. (Springer Singapore, Singapore, 2018), chap. Chapter 22, pp. 481-510.
