Optimized dilute acid pretreatment of agro-industrial and urban wastes for maximum fermentable sugars production

Abstract Agro-industrial and urban residues are promising feedstocks for the production of fermentable sugars, which serve as precursors for second-generation (2G) ethanol. This study evaluated banana pseudostem (BPS), guava seed cake (GSC), and urban tree pruning (UTP) residues to determine the optimal conditions for maximizing xylose and glucose yields. Both monosaccharides can be fermented by microorganisms to produce 2G ethanol, contributing to an increased supply of this biofuel. A 2³ factorial experimental design was employed to assess xylose and glucose solubilization, performed via acid pretreatment with sulfuric acid (H₂SO₄), followed by enzymatic hydrolysis of the pretreated biomass. During pretreatment, xylose solubilization reached 5.66 g.L⁻¹ in BPS, 9.24 g.L⁻¹ in GSC, and 8.13 g.L⁻¹ in UTP residues. Statistical analysis identified the optimal pretreatment conditions for BPS and GSC as moderate temperature, reaction time, and acid concentration (140 °C, 40 min, and 3.5% (w/v) H₂SO₄). In the subsequent enzymatic hydrolysis step (Cellic Ctec 2, 12 FPU.g − 1 , 50 °C/24 h, 140 rpm), maximum glucose solubilization was 8.6 g.L⁻¹ for BPS, 2.33 g.L⁻¹ for GSC, and 1.06 g.L⁻¹ for UTP residues. According to the data, BPS is the most promising material for the highest yield of total fermentable sugars, excelling primarily in hexoses. However, UTP also stands out for its production of pentoses (xylose and others). These findings demonstrate efficient xylose and glucose solubilization, optimizing process conditions and underscoring the potential of the selected residues and applied pretreatment techniques.