Exploitation of Spirogyra sp. as an Alternative Raw Material for Sustainable Paper Production

Abstract

The global paper industry relies predominantly on wood-based cellulose, resulting in substantial environmental burdens associated with deforestation, chemical-intensive pulping, and the discharge of polluted effluents. This study evaluates Spirogyra sp., a rapidly growing filamentous green alga, as a lignin-free alternative raw material for sustainable paper production within a green chemistry framework. The objectives were to culture and optimize the growth of Spirogyra sp., minimize the use of toxic chemicals in processing, produce algal paper sheets, and evaluate their physicochemical and mechanical properties. Spirogyra sp. cultures were optimized using three growth media, CHU 10, BBM, and 3N BBM over a 6-day period (initial inoculum ~10 mg). Growth in 3N BBM produced the highest biomass increase (10.2±0.1 mg to 12.7±1.2 mg), whereas CHU 10 supported minimal growth, declining to 3.1±1.0 mg by day 6. ANOVA indicated significant differences among treatments (p<0.05). Further optimization using a 100 mg inoculum (n=16) showed maximal biomass accumulation at 72-96 h (137.9±4.9 mg), defining the optimal harvest window. Scaling cultures to 500 mL was successful, with dissolved oxygen identified as a limiting factor. Pigment removal using hot saturated salicylic acid solution and fibre softening with dilute fabric softener solution enabled lignin-free paper sheet formation using a deckle and mould process. The resulting sheets exhibited a grammage of 182.4±1.6 g/m², thickness of 0.32±0.01 mm, moisture content of 11.48±0.47%, density of 0.563 g/cm³, and bulk of 1.776 cm³/g. Long filament lengths (up to 5 cm) contributed to high grammage, although tensile strength remained low (0.4416 N; 29.44 N/m). Blending Spirogyra sp. fibres with softwood pulp improved mechanical properties, demonstrating the potential of algal biomass as a supplementary resource for sustainable paper manufacturing.

Keywords: Spirogyra sp., Algal cellulose, Sustainable paper production, Alternative fibre, Environmental impact