Alkaline pretreatment wastewater from lignocellulosic biomass: challenges and emerging management strategies

Alkaline pretreatment is the most widely employed chemical process for lignocellulosic biomass, particularly at an industrial scale. However, this method generates a significant volume of complex wastewater, which contains recalcitrant organic molecules, high concentrations of biopolymers, and hazardous chemicals. These waste streams have been largely overlooked, with conventional disposal methods, such as incineration in recovery boilers, posing serious environmental and resource inefficiency concerns. This review offers a comprehensive assessment of alkaline wastewater management, with a focus on the hierarchical structure of treatment strategies and the recovery of valuable resources. The paper highlights various advanced treatment techniques, including membrane filtration, advanced oxidation processes (AOPs), biological treatment, and hybrid methods, emphasizing the importance of wastewater recycling through minimal liquid discharge (MLD) technologies. A techno-economic analysis is also provided to evaluate the feasibility of these approaches within a biorefinery framework. By addressing the environmental hazards associated with alkaline pretreatment and promoting sustainable resource recovery, this study aims to establish a more efficient and eco-friendly strategy for managing complex wastewater in the pulp and paper industry.