Hemp hurds (HHs), a lignocellulosic agricultural waste, have the potential for bioconversion into bio-based products. However, the matrix structure of biomass comprising cellulose, hemicellulose, and lignin makes cellulose inaccessible. Pre-treatment is essential for accessing cellulose by removing lignin, hemicellulose, and extractives. This study compares lignocellulose structure modification of HH using low-concentration chemical pretreatment methods, including organosolvent, 60% ethanol (EtOH), 3% hydrogen peroxide with 3% ammonia (H₂O₂/NH₃), and 2% sodium hydroxide (NaOH) with sonication. X-ray diffractor (XRD) analysis, using Segal method as a guide, showed that post treatments, the crystallinity index increased from 39.26% in untreated HH to 65.80% for NaOH-treated hurds. Polysaccharide content decreased compared to HH, attributed to the combination of solubilisation of hemicellulose, degradation of amorphous carbohydrates, and loss of sample during treatment wash. Although there was a reduction in polysaccharide content compared to HH, NaOH treated HH showed the highest total carbohydrate content of 48.6% and the most disrupted surface structure, based on scanning electron microscope (SEM) images at 2000× magnification. Fourier-transform infrared spectrophotometer (FTIR) analysis indicated a reduction in lignin and hemicellulose peaks for NaOH and H₂O₂/NH₃ treatments, while thermogravimetric analyser (TGA) and derivative thermogravimetric analysis (DTG) results showed improved thermal stability for NaOH-treated samples. The ultrasound-assisted NaOH-treated sample had the most structural disruption in recovered solid fraction, based on comparative compositional and structural analyses. This gives a guide on the selection of pretreatment to pursue for HH processing.

Lignocellulose biomass (LB) has gained interest as a second-generation renewable feedstock for producing bio-based products within a circular economy framework. Hemp hurds, a byproduct of industrial hemp processing, are one of the LB feedstocks that have gained attraction. This study examines the physicochemical properties of hemp hurds to evaluate their suitability as substrates for bioproduct synthesis. The chemical analysis of hemp hurds showed that the polysaccharide content is 53.4%, lignin is 20.8%, extractives are 15%, and ash is 4.35%. The moisture content is 6.34%, and the density is 1.0016 g/mL, indicating low porosity and a small surface area, which limits enzyme access to cellulose. Structural analysis using X-ray diffraction (XRD) indicated a crystallinity index of 40.20%, and the Fourier Transform Infrared Spectrophotometer (FTIR) confirmed the characteristic peaks representing cellulose, hemicellulose, and lignin at 3332 cm⁻¹, 1734 cm⁻¹, and 1510 cm⁻¹, respectively. The Scanning Electron Microscope (SEM) revealed a tightly packed surface with smooth, low porosity, whereas the Thermogravimetric Analyser (TGA) indicated decomposition in phases for hemicellulose, cellulose, and lignin. The structural and chemical findings of hemp hurds characterisation suggest that they are a suitable raw material for producing various bio-based materials.

The enzymatic conversion of lignocellulosic biomass (LB) into fermentable sugars is important for the development of sustainable biorefineries. This study investigated the immobilisation of Trichoderma reesei (T. reesei) cellulase on amine-functionalised magnetic nanoparticles (MNPs) and evaluated the resulting biocatalyst for the hydrolysis of pretreated hemp hurd (HH) biomass. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) provided evidence consistent with cellulase association with the nanoparticles, with the estimated dry-state particle diameter increasing from 22.4 ± 0.4 to 27.8 ± 0.3 nm after immobilisation. The selected immobilised catalyst loading produced approximately 89% of the total filter-paper assay response obtained with the selected free-enzyme loading, although this comparison was not normalised to protein content. During 7 h hydrolysis experiments, glucose production increased progressively for both enzyme forms. Across the tested enzyme dilutions, immobilised cellulase generated approximately 88–91% of the glucose produced by free cellulase. The immobilised enzyme also retained approximately 64% of its initial hydrolysis performance after five reuse cycles. These findings demonstrate the potential of magnetic cellulase nanobiocatalysts for recoverable and reusable hydrolysis of lignocellulosic biomass. However, further studies are required to determine protein-normalised activity, immobilisation efficiency, longer-term stability, process economics and industrial scalability.

Hemp hurds (HHs), an underutilised lignocellulosic biomass (LB) from agricultural waste, offer potential for bioconversion into high-value bioproducts within a circular bioeconomy. Building on prior work involving magnetic nanoparticle-immobilised cellulase hydrolysis of pretreated HH, this study computationally designed candidate phaCAB expression constructs for cellulolytic hosts toward future polyhdroxybutyrate (PHB) production. The objective was to evaluate, in silico, the feasibility of introducing the phaC1, phaA and phaB1 genes from Cupriavidus necator H16 (C. necator) (assembly GCA_000009285.2; loci H16_A1437–H16_A1439) into the cellulolytic hosts Clostridium thermocellum DSM 1313 (C. thermocellum) and Trichoderma reesei RUT C-30 (T. reesei). Coding sequences were retrieved and translated individually and host-specific expression compatibility was assessed via codon adaptation index, effective number of codons, GC content and rare-codon frequency/clustering. Host-specific architectures were designed: three independent tef1-promoter cassettes with fungal Kozak contexts and cbh1 terminators for T. reesei (TrePHB3 integration construct), and a single groEL-promoter operon with graded ribosome-binding sites for the pIKM1-based C. thermocellum construct (pCtPHB1); Escherichia coli BL21 (DE3) (E. coli)/pET-24a(+) served only as an intermediate assembly platform. Clustal Omega alignment, virtual plasmid assembly and simulated restriction digestion (SnapGene) confirmed preservation of the open reading frames and expected fragment sizes. ProtParam analysis indicated instability indices below 40 and negative GRAVY values for PhaC, PhaA and PhaB, indicating overall hydrophilic character. This computational framework links HH valorisation, cellulolytic Consolidated Bioprocessing (CBP) hosts and PHB pathway design within a conceptual biorefinery, supporting future integrated biomass-valorisation platforms; it is computational only and does not demonstrate transformation, expression, PHB accumulation or biomass conversion, which require experimental validation.

Agriculture generates vast quantities of crop residues, animal manure, and agro-processing waste, much of which is still treated as a disposal burden rather than a productive resource. This contributes to nutrient loss, air pollution, and missed economic opportunities. As sustainability and resilience become increasingly important, the circular economy (CE) offers a framework for transforming agricultural waste into compost, bioenergy, soil amendments, and biobased materials. However, implementation remains complex. This chapter examines how CE principles can be applied to agricultural waste systems and why technically viable approaches often struggle under economic, social, and institutional constraints. Drawing on examples from Africa, Latin America, and Asia, it highlights the importance of local knowledge, existing value chains, infrastructure, finance, and governance. It also explores key challenges, including subsidy dependence, additional labour demands on rural households, and the tendency of advanced technologies to benefit larger, better-resourced actors over smallholders. Emerging opportunities such as decentralized biorefineries, improved quality standards, digital advisory tools, and targeted climate finance are also considered. The chapter argues that successful circular agricultural systems require context-specific approaches that balance technological feasibility with social, economic, and institutional realities.