Highland Barley Paper, a specialty paper product made from agricultural waste such as wheat straw, faces significant environmental concerns regarding its bleaching process. While traditional chlorine-based bleaching techniques achieve high whiteness, the resulting organochlorides (such as AOX) pose carcinogenic, teratogenic, and mutagenic risks, causing long-term pollution to water and soil. To reduce environmental impact, optimizing the bleaching process for Highland Barley Paper requires a comprehensive approach encompassing alternative chemicals, process innovation, resource recycling, and process control.
Elemental chlorine-free bleaching (ECF) is currently the mainstream environmentally friendly bleaching technology. This technology replaces traditional chlorine or hypochlorite with chlorine dioxide (ClO₂), significantly reducing AOX formation. The strong oxidizing properties of ClO₂ efficiently decompose lignin, while its reaction products, chlorides, are present in extremely low amounts, resulting in a substantial reduction in the toxicity of bleaching wastewater. Studies have shown that after ECF bleaching, AOX levels in wheat straw pulp bleaching wastewater decrease by 93%, and toxicity is almost eliminated. Furthermore, ECF bleached pulp exhibits a viscosity increase of over 30% and a whiteness of up to 80% ISO, meeting the demands of high-quality paper products. By optimizing parameters such as ClO₂ dosage, reaction temperature, and time, the bleaching effect and environmental benefits can be further balanced.
Total Chlorine-Free Bleaching (TCF) represents an upgrade from ECF technology. Its core principle is the use of oxygen-containing bleaching agents such as oxygen (O₂), hydrogen peroxide (H₂O₂), and ozone (O₃) to completely eliminate the generation of organochlorides. For example, in the oxygen bleaching stage, controlling oxygen pressure, temperature, and alkali dosage can achieve deep lignin removal; adding stabilizers (such as sodium silicate) in the hydrogen peroxide bleaching stage can improve bleaching efficiency. TCF bleaching wastewater is biodegradable and, after simple treatment, can be used for pulp washing or chemical preparation, achieving water resource recycling. Although TCF technology is more expensive, its environmental advantages are significant, making it particularly suitable for the production of Highland Barley paper, which has stringent ecological requirements.
Biological bleaching technology provides a new approach to environmentally friendly bleaching. This technology utilizes lignin-degrading enzymes (such as laccase and manganese peroxidase) or microorganisms (such as white-rot fungi) to decompose lignin, reducing the amount of chemical bleaching agents used. For example, treating wood chips with fungi before mechanical pulping can save 25%-50% of electrical energy; pre-treating wheat straw with enzymes before chemical cooking can reduce kappa number and alkali consumption. Combining biological and chemical bleaching (such as biological-ECF or biological-TCF) can further reduce environmental impact while improving pulp strength and brightness stability.
Medium-high consistency bleaching technology reduces water consumption and wastewater discharge by increasing pulp consistency (10%-15%). Under high consistency conditions, the bleaching agent contacts the pulp more evenly, improving reaction efficiency and reducing energy consumption. For example, high-consistency hydrogen peroxide bleaching and high-consistency ozone bleaching have been implemented in engineering applications, reducing wastewater discharge by 60% and COD emissions significantly compared to traditional low-consistency bleaching. Furthermore, medium-high consistency technology can reduce fiber loss and improve raw material utilization, aligning with the concept of sustainable development.
Bleaching wastewater treatment and resource recovery is the last line of defense in reducing environmental impact. A combination of physicochemical methods (such as sedimentation and filtration) and biological methods (such as activated sludge and anaerobic digestion) can effectively remove suspended solids, organic matter, and nutrients from wastewater. Furthermore, membrane separation technologies (such as ultrafiltration and reverse osmosis) can recover alkalis and organic matter from wastewater for use in cooking or bleaching processes, achieving "zero discharge." For example, three-dimensional deformable tube MVR evaporator technology can reduce wastewater treatment energy consumption to 70% of traditional equipment while saving 29% of heat exchange area, significantly improving resource utilization efficiency.
Optimizing the bleaching process for Highland Barley paper requires balancing environmental benefits with economic feasibility. By promoting ECF/TCF bleaching technology, exploring the potential of biological bleaching, applying high-concentration processes, and strengthening wastewater resource recovery, a clean production system can be built, reducing the emission of toxic substances and improving resource recycling rates. In the future, with increasingly stringent environmental regulations and growing demand for green consumption, Highland Barley Paper manufacturers need to continue to innovate and promote the evolution of bleaching technology towards low-carbon, high-efficiency, and sustainable directions, providing a model for the industry's green transformation.
