Combined Pretreatment of Sugarcane Leaves with Potassium Hydroxide and Urea for Enhancing Composting Efficiency

The complex lignocellulosic structure of sugarcane leaves poses a major challenge for direct composting, leading to slow degradation and long processing cycles. To address this, efficient pretreatment is crucial for enhancing resource recovery. In this study, a combined potassium hydroxide (KOH) and urea pretreatment was applied to sugarcane leaves, and its effects on feedstock composition, structural properties, biodegradability, and cocomposting performance were systematically investigated. Under the selected pretreatment conditions (2.5% KOH, 1.5% urea, 80 °C, 2 h), the lignin content decreased markedly from 17.09 to 4.67%, while cellulose was largely preserved. This led to a substantial reduction in the lignin-to-cellulose ratio. Structural analyses revealed increased surface roughness and porosity, attenuation of characteristic lignin peaks, and enhanced crystallinity after pretreatment. Prior to composting, the pretreated material was subjected to a 15-day solid-state biodegradation test to evaluate its degradability. The results showed that the degradation rate was 165.5% higher than that of the untreated control. Subsequently, the pretreated sugarcane leaves were co-composted with cattle manure. Compared to conventional composting of untreated leaves under identical conditions, the pretreatment shortened the maturation time by about 50% and increased the total potassium content in the final compost by 63.6%. Furthermore, the pretreatment promoted the conversion of organic matter into humic substances, thereby improving compost stability and maturity. This process ultimately enhanced the nutrient content and agronomic safety of the final product. This study demonstrates that the combined KOH-urea pretreatment is an effective strategy for substantially enhancing the biodegradability of sugarcane leaves, accelerating the composting process, and producing high-quality organic fertilizer. It thus provides a viable pathway for the efficient resource utilization of this agricultural waste.