Bio-Based Guadua angustifolia Biochar/TiO₂ Composite and Biochar: Applications in Environmental and Agricultural Fields

Guadua angustifolia Kunth, a towering bamboo species native to Colombia, stands as a cornerstone of the nation's agricultural and industrial landscape. Revered for its structural strength, it dominates construction, furniture making, and handicraft industries, with 90% of harvested culms used in civil works alone. Yet, this productivity comes with a hidden cost: up to 80% of each processed culm becomes waste—culms, bark, chips, and sawdust—traditionally discarded in landfills or incinerated. This waste, rich in lignocellulosic biomass, was long viewed as a liability, but emerging research reveals it as a goldmine of sustainable potential.

Guadua sawdust, in particular, carries unique properties that make it ideal for transformation. Its composition—high in cellulose, hemicellulose, and lignin—coupled with naturally occurring silicon and potassium, provides a robust foundation for creating value-added biomaterials. Unlike many agricultural wastes, Guadua sawdust retains these compounds even after processing, making it a versatile feedstock for innovations in environmental remediation and agriculture.

Pyrolysis: The Alchemical Process Turning Sawdust into Biochar

At the heart of this transformation lies pyrolysis—a controlled thermal decomposition process that converts organic matter into biochar under low-oxygen conditions. In laboratory trials, researchers subjected Guadua angustifolia sawdust (GAKS) to pyrolysis at 300°C for 1 hour, yielding a stable, porous biochar named BGAK. This process achieved a 33% conversion rate, meaning 160 kg of sawdust (20% of the waste from 1 ton of culms) produces 52.8 kg of biochar—a significant yield for large-scale applications.

The physical and chemical shifts between raw sawdust and BGAK are striking. Raw GAKS exhibits an acidic pH (5.03 ± 0.31), low water retention (40 ± 3%), and a porous structure (54.6 ± 3.6%). Post-pyrolysis, BGAK transforms into a neutral material (pH 7.61 ± 0.26) with enhanced water retention (55 ± 2%) and porosity (59 ± 3%). Its carbon content jumps from 57.83% to 66.92%, while the oxygen-to-carbon ratio drops from 0.710 to 0.399—indicators of increased aromaticity and stability. This stability ensures BGAK resists decomposition, making it an effective long-term carbon sink in soil.

The Biochar-TiO₂ Composite: A Powerful Tool for Water Purification

While biochar alone offers value, combining BGAK with titanium dioxide (TiO₂) creates a composite with extraordinary photocatalytic properties. The production process involves mixing BGAK and TiO₂ in an acidified aqueous solution (pH 2.0), followed by sonication, drying, and calcination at 450°C for 1 hour. This bonds TiO₂ nanoparticles to the biochar's surface, forming a material that excels at neutralizing harmful pathogens.

In testing, the BGAK/TiO₂ composite demonstrated remarkable efficacy against Escherichia coli (E. coli), a common indicator of fecal contamination. With an initial bacterial concentration of 6.5 ± 0.3 log₁₀ CFU/mL, the composite reduced levels to 1.97 ± 0.2 log₁₀ CFU/mL within 60 minutes under UV light (253 nm). This 85% reduction stems from the composite's ability to generate reactive oxygen species (ROS) like hydroxyl radicals, which destroy bacterial cell walls and disrupt DNA.

Notably, the composite maintains functionality across multiple uses. It retains over 70% efficiency for up to 5 cycles, with gradual degradation thereafter—still achieving 41.4% efficiency by the 10th cycle. This reusability makes it cost-effective for rural wastewater treatment, where access to advanced infrastructure is limited.

BGAK as a Soil Conditioner: Boosting Medicinal Plant Productivity

Beyond water purification, BGAK shines as a soil amendment, particularly for medicinal plants. Trials using 2% BGAK in nursery soils yielded significant increases in bioactive compounds in two key species: Bidens pilosa L. and Guadua angustifolia itself.

Bidens pilosa, a herb used in traditional medicine, showed a near 100% increase in total phenols (from 0.61 to 1.14 mg GAE/g dry matter) and a 10.5% rise in flavonoids (from 0.19 to 0.21 mg RE/g dry matter). For Guadua angustifolia, total phenols per plant increased by 62% (from 0.08 to 0.13 mg GAE). These compounds—known for antioxidant, anti-inflammatory, and anticancer properties—enhance the plants' medicinal value.

The mechanism behind these improvements lies in BGAK's ability to modify soil properties. It increases water retention, balances pH, and releases nutrients like potassium (from 61.2 to 304 mg kg^-1 in B. pilosa soils) and silicon, which stimulate secondary metabolite production. While BGAK slightly reduced plant biomass in trials, the trade-off for higher bioactive compound concentrations is invaluable for pharmaceutical crop cultivation.

Environmental and Economic Impacts: Closing the Sustainability Loop

The conversion of Guadua sawdust into biochar and composites delivers multifaceted benefits. Environmentally, it addresses waste management issues, reducing methane emissions from landfills and CO₂ from open burning. BGAK's carbon sequestration potential—when added to soil—complements Guadua plantations' natural capacity to store 149.9–328.4 tCO₂/ha, contributing to Colombia's climate goals.

Economically, the technology strengthens the bamboo value chain. By replacing imported peat (costing $60 ± 10 per 50 kg) with locally produced BGAK ($30–40 per 50 kg), nursery costs drop by 50%. For the composite, substituting pharmaceutical-grade TiO₂ with industry-grade alternatives (used in paints or glass) further reduces production expenses, making it accessible to small-scale farmers and communities.

Future Directions: Expanding the Reach of Guadua Innovations

Research continues to unlock new applications for Guadua-derived materials. Modifying the BGAK/TiO₂ composite with metallic elements could extend its photocatalytic activity to visible light, eliminating the need for UV lamps. Combining BGAK with beneficial microbes may create "bioinoculants" that enhance soil fertility and disease resistance. Additionally, scaling pyrolysis through automated reactors—powered by solar or biomass energy—could enable on-site waste conversion, minimizing transportation costs.

These advancements position Guadua bamboo as more than a crop: it is a catalyst for sustainable development, aligning with UN Sustainable Development Goals (SDGs) such as zero poverty (SDG 1), clean water and sanitation (SDG 6), and climate action (SDG 13).

Conclusion

Guadua angustifolia sawdust, once a discarded byproduct, has emerged as a versatile resource driving innovations in environmental protection and agriculture. Through pyrolysis and composite synthesis, this waste is transformed into biochar that sequesters carbon, purifies water, and boosts medicinal plant productivity. As Colombia and other nations seek sustainable solutions, Guadua bamboo stands as a model of circular economy thinking—proving that with ingenuity, waste can indeed become wonder.

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This article is for research use only and cannot be used for any clinical purposes.