Dry non-thermal plasma pre-treatment for biomass valorization: A sustainable approach for spent coffee grounds and banana peels

The development of sustainable and efficient biomass pre-treatment technologies is crucial for advancing biorefinery applications. In this study, a dry non-thermal plasma (NTP) pre-treatment was investigated as a novel approach for processing spent coffee grounds (SCG) and banana peels (BP). The process was performed at 45 °C for 3–5 min without the addition of chemical reagents, ensuring minimal environmental impact. The effects of key operating parameters—including applied voltage (7.5–16 kV), air flow rate (0.5–2 NL/min), and treatment time (1–5 min)—on biomass composition and enzymatic hydrolysis efficiency were evaluated. Under optimal conditions (12 kV, 1 NL/min, 5 min), SCG showed a 2.46 % increase in cellulose availability and a 2.77 % reduction in insoluble lignin, resulting in a glucose yield of 7.24 mg/g biomass. For BP, NTP treatment led to a 3.15 % decrease in insoluble lignin while maintaining stable cellulose content, achieving a glucose release of 19.96 mg/g biomass. Although the absolute improvements are modest, they were achieved under very mild operating conditions without chemical additives, confirming the potential of dry NTP as a low-energy, environmentally friendly alternative. In contrast, conventional pre-treatments often require harsh conditions (e.g., >120 °C, hours of processing, and strong acids/alkalis) to achieve higher sugar yields, making the dry NTP approach a sustainable proof-of-concept with lower environmental and energy costs. Structural and chemical characterizations (SEM, TGA, FTIR) confirmed the effectiveness of NTP in modifying lignocellulosic structures. Compared to conventional pre-treatments, dry NTP demonstrated significant advantages in terms of energy efficiency, process simplicity, and environmental sustainability, making it a promising proof-of-concept for industrial-scale biomass processing.