Introduction<\/h3>\n\n\n\n
The extraction, use, and disposal of materials have become significant global challenges for both resource security and environmental sustainability. Municipal solid waste generation is projected to increase from approximately 2.1 billion tonnes in 2023 to nearly 3.8 billion tonnes by 2050, with more than one-third of this waste expected to be openly dumped or burned1<\/a>,2<\/a><\/sup>. Such disposal practices release greenhouse gases and fine particulate matter (PM2.5<\/sub>), degrade soil and water quality, and contribute to climate change and adverse public-health impacts worldwide3<\/a>,4<\/a><\/sup>.<\/p>\n\n\n\n Southeast Asia (SEA) is among the regions most severely affected by these waste and pollution burdens. Agricultural and industrial residues are frequently disposed of through open burning, contributing substantially to poor regional air quality5<\/a>,6<\/a><\/sup>. In Vietnam, approximately 50 million tonnes of crop residues are generated annually, and poorly managed burning of these crop residues has been linked to economic losses of up to \u20ac14.3 billion annually, driven by raw material losses and adverse health impacts7<\/a><\/sup>. Indonesia, Thailand, and Cambodia report similar burning patterns, where open combustion remains the lowest-cost disposal method8<\/a><\/sup>. Biomass burning in the region can increase PM2.5<\/sub>concentrations by tens of \u00b5gm-3<\/sup> during the dry season and has been linked to hundreds to thousands of premature deaths annually9<\/a><\/sup>.<\/p>\n\n\n\n Valorizing agricultural residues by converting them into value-added materials offers a promising strategy for reducing open burning while strengthening regional circular economies. Such approaches can reduce the environmental burdens associated with current disposal practices while creating new opportunities for sustainable construction and furniture materials.<\/p>\n\n\n\n Fungal mycelium provides a natural and biological route to transform regionally abundant agricultural residues into engineered, fully bio-based composites. Mycelium, the filamentous vegetative network of fungi, forms a natural binding matrix that colonizes and consolidates plant-based substrates. Through extracellular enzyme secretion, including oxidoreductases such as laccase, lignin peroxidase, and manganese peroxidase, the mycelium primarily modifies lignin, while hemicellulose is degraded mainly by hydrolases such as glycoside hydrolases and esterases. Together, these enzymatic processes enable progressive colonization of the lignocellulosic substrate and the formation of a cohesive mycelium-bound composite without the use of synthetic binders10<\/a>,11<\/a><\/sup>. This biologically driven process produces lightweight and biodegradable composites with tunable density and mechanical properties. The tropical climate in SEA matches the temperature and humidity conditions required for fungi growth, requiring only limited external energy input for cultivation. As a result, mycelium-based materials have been explored for applications such as packaging, insulation, acoustic panels, and lightweight structural components, demonstrating their potential as sustainable alternatives that contribute to a circular bioeconomy and a low-carbon construction sector12<\/a>,13<\/a>,14<\/a><\/sup>.<\/p>\n\n\n\n Despite significant progress in laboratory-scale demonstrations, industrial adoption of mycelium-based composites remains limited, primarily due to challenges in process control and material consistency. The growth rate and final mechanical properties of fungal composites are influenced by environmental and processing parameters such as temperature, humidity, aeration, particle size, nutrient composition, and compaction pressure11<\/a>,15<\/a>,16<\/a>,17<\/a>,18<\/a><\/sup>. The substrate\u2019s physical and chemical characteristics govern both colonization kinetics and the resulting density of the mycelial network, which in turn affects the composite\u2019s stiffness and strength18<\/a>,19<\/a><\/sup>. Substrate selection is therefore a critical design parameter for achieving reliable and scalable material properties tailored for specific applications.<\/p>\n\n\n\n Traditionally, substrates such as hemp hurds, flax shives, and cereal straw have been widely used for mycelium composites because of their porous structure and balanced nutrient content20<\/a>,21<\/a>,22<\/a><\/sup>. However, these substrates are not readily available in regions around the world, and reliance on non-local feedstocks increases both material costs and the associated environmental footprint. The utilization of locally available agricultural and industrial by-products offers a more sustainable approach by minimizing transportation-related impacts, valorizing regional waste streams23<\/a><\/sup>, and creating opportunities for substantial economic benefits through value-added product development24<\/a><\/sup>.<\/p>\n\n\n\n Three lignocellulosic residues were selected as substrates for fungal growth: Albizia chinensis<\/em> woodchips (AWC), sugarcane bagasse (SC), and cassava pulp. These materials were chosen because they represent abundant agricultural and industrial by-products in Southeast Asia that remain underutilized or disposed of through open burning, contributing to regional air pollution and greenhouse gas emissions25<\/a>,26<\/a>,27<\/a>,28<\/a><\/sup>.<\/p>\n\n\n\n The first residue stream, SC, is a by-product of the sugar production process. It accounts for approximately 30% of the mass of harvested raw sugarcane processed. Indonesia\u2019s annual sugarcane production of approximately 33 million tonnes, therefore, generates approximately 10 million tonnes of bagasse. Comparable volumes are produced in Thailand and the Philippines, where large, centralized sugar mills operate year-round29<\/a>,30<\/a><\/sup>. SC contains approximately 40\u201345% cellulose, 25\u201330% hemicellulose, and 20\u201325% lignin on a structural dry-weight basis31<\/a><\/sup>, which white rot fungi can enzymatically degrade to sustain growth. In addition, studies have reported the release of up to 0.4 g\/g of soluble sugars (including sucrose, glucose and fructose), which may also promote initial mycelial colonization.<\/p>\n\n\n\n The second residue stream, cassava pulp, is generated as a by-product of starch extraction from fresh cassava roots. Thailand processes approximately 33 million tonnes of cassava annually, while Lampung province in Indonesia hosts a concentrated cluster of cassava processing factories and is among the country\u2019s leading cassava-producing regions32<\/a>,33<\/a><\/sup>. Together, these regions generate substantial quantities of cassava pulp, providing an abundant feedstock for mycelium-based composite production. Despite being considered a low-value by-product, cassava pulp contains 30\u201380% residual starch, which serves as a readily available nutrient source for fungal metabolism, and promotes rapid mycelial colonization34<\/a>,35<\/a><\/sup>.<\/p>\n\n\n\n Wood processing contributes a third major residue stream, with sawmills and panel mills typically generating around 40\u201350% residues relative to input wood volume28<\/a>,36<\/a><\/sup>. Fast-growing plantation species commonly cultivated for plywood and other wood-based panel production include Albizia chinensis<\/em> and Paraserianthes falcataria<\/em>. Processing these species for furniture, plywood, and particleboard applications generates residual chips and fines37<\/a>,38<\/a><\/sup>. Albizia chinensis<\/em> woodchips from sawmills and plywood industries contain 40\u201350% cellulose, 15\u201325% hemicellulose and 20\u201330% lignin, providing structurally rigid fibers that support fungal adhesion and the formation of an interconnected mycelial network39<\/a>,40<\/a>,41<\/a><\/sup>.<\/p>\n\n\n\n Together, these three industries generate a large, regionally concentrated reservoir of lignocellulosic biomass across Indonesia, Thailand, and the Philippines. Repurposing even a small portion of this underutilized feedstock into engineered bio-based composites offers environmental and economic benefits. The benefits of valorizing agricultural residues include reducing open-burning emissions and waste accumulation, lowering dependence on imported wood and fossil-derived materials, and establishing region-specific circular value chains. These value chains support the development of sustainable materials for construction, furniture, and interior applications within the SEA region.<\/p>\n\n\n\n Building on these material characteristics, this study investigates the feasibility of utilizing these locally abundant by-products, either individually or in combination, as substrates for the white-rot fungus Ganoderma lucidum<\/em>. By systematically linking substrate composition, fungal growth behaviour, and resulting mechanical properties, this work advances our understanding of their relationship. This study demonstrates a pathway for the conversion of regional waste streams into functional bio-based materials suited for construction and furniture applications in tropical contexts.<\/p>\n\n\n\n Many fungal species have been studied for mycelium-based composites, each exhibiting different metabolic pathways and hyphal architectures. White-rot fungi, such as Pleurotus<\/em>, Trametes<\/em>, and Ganoderma<\/em> are particularly suitable, as they degrade lignin while modifying cellulose and hemicellulose with their diverse set of lignin-modifying enzymes, including laccases, lignin peroxidases, and manganese peroxidases, enabling efficient colonization of lignocellulosic materials10<\/a>,11<\/a>,42<\/a><\/sup>. G. lucidum<\/em>, particularly, produces dense and well-bonded mycelial networks, and is widely employed for composite fabrication due to its enzymatic versatility and strong fiber-binding capability7<\/a>,8<\/a><\/sup>. The broad enzymatic capacity to modify the major cell wall polymers is associated with more uniform bonding between substrate particles, which may contribute to improved structural integrity in the resulting composites.<\/p>\n\n\n\n G. lucidum<\/em> is a trimitic fungus, meaning its hyphal system consists of three types of hyphae: generative, skeletal, and binding hyphae. Skeletal and binding hyphae are typically thick-walled and contribute to the rigidity and mechanical strength of the mycelial network43<\/a><\/sup>. Compared with commonly used monomitic fungi such as Pleurotus<\/em>, which possess only generative hyphae, the trimitic hyphal system of G. lucidum<\/em> is therefore expected to provide a mechanically robust mycelial network. In addition, G. lucidum<\/em> tolerates a wide range of humidity and temperature conditions, and has been successfully used in prior studies on mycelium-based composites for its consistent morphology, predictable growth kinetics, and reliable mechanical performance19<\/a>,44<\/a><\/sup>. Together, these characteristics make G. lucidum<\/em> a suitable fungal species for developing bio-based composites from agricultural and industrial residues as sustainable raw materials available in tropical regions.<\/p>\n\n\n\n While mycelium composites are typically cultivated as a lightweight, foam-like material, they can exhibit sufficient rigidity for self-supporting and non-load-bearing applications 45<\/a><\/sup>. Camilleri et al. highlighted that improving the mechanical performance of mycelium-based composites is a key step toward expanding their applications across a broad range of industries. The processing strategy investigated in this study contributes to this objective by examining how substrate selection and nutrient supplementation influence the composite microstructure and mechanical performance46<\/a><\/sup>. Previous studies have explored post-growth densification techniques, such as hot and cold pressing after mycelium deactivation to improve the mechanical properties, but these approaches present several limitations19<\/a>,47<\/a><\/sup>. While hot pressing can enhance strength through thermally induced lignin bonding, it is energy-intensive23<\/a><\/sup>. Cold pressing, in contrast, generally leads to limited improvement in material strength due to disruption of the existing mycelial network without the presence of heat-induced re-bonding. Here, we therefore propose an alternative approach in which the substrate is compressed during active mycelial growth. This mid-growth compression approach allows the compressed material to undergo further fungal growth and consolidation while avoiding the high energy requirements of hot pressing and using regionally available agricultural by-products.<\/p>\n\n\n\n In this study, three locally available residues were selected to evaluate their suitability as substrates for G. lucidum.<\/em>Both AWC and SC successfully served as base substrates for growing mycelium-based composites. The addition of cassava pulp to the base substrates produced contrasting effects depending on the base substrate, substantially increasing the compressive strength and modulus of AWC-based composites while reducing both properties in SC-based composites. The results indicate that substrate composition is a key factor influencing the development of mycelium-based composites, as it influences substrate-hypha interactions and, consequently, the mechanical performance of the resulting material.<\/p>\n\n\n\n Mycelium growth was achieved on both AWC and SC-based substrates, both with and without cassava pulp. Using the three-stage growth and mid-growth compression approach, all formulations produced dense mycelium composites. Across all formulations, the dried composites had an average density of 365\u2009\u00b1\u200984 kg\/m3<\/sup>, approximately twice that of naturally packed mycelium foams prepared with similar substrates48<\/a>,49<\/a><\/sup>.<\/p>\n\n\n\n Mycelial growth initiated uniformly from the inoculation points and spread through the substrate matrix during the first incubation phase. Both AWC and SC substrates supported continuous mycelial colonization, with the three-stage growth process completed within 10\u201320 days, depending on the substrate formulation. Visual observations showed that hyphal strands initially filled the pore spaces between substrate particles and subsequently formed a cohesive, continuous network, consistent with the established colonization pattern of G. lucidum<\/em>.<\/p>\n\n\n\n At the end of the growth process, all samples developed a white, continuous mycelial skin approximately 1\u20132 mm thick, indicating complete surface colonization (Fig. 1<\/a>a).<\/p>\n\n\n This outer surface consisted of a dense, highly interconnected network of aerial mycelial hyphae, giving the composite its characteristic white appearance (Fig. 1<\/a>b). In contrast, the core remained dominated by the lignocellulosic substrate and exhibited a less densely interconnected mycelial network. Although mycelium was present throughout the core and contributed to binding the substrate particles, its lower density allowed the underlying brown lignocellulosic substrate to remain visible.<\/p>\n\n\n\n The consistent formation of a uniform outer skin and successful internal colonization across all samples demonstrates the suitability of these tropical residues for producing mycelium-based composites.<\/p>\n\n\n\n …<\/p>\n\n\n\nResults<\/h2>\n\n\n\n
Suitability of substrates for mycelium growth<\/h3>\n\n\n\n
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