Anaerobic digestion (AD) is an eco-friendly process to treat organic waste and generate renewable energy like methane. However, AD faces challenges such as low substrate conversion efficiency and process instability. Adding biochar (BC), a carbon-rich material derived from organic waste pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, has shown potential to enhance methane production. Recent studies have focused on nitrogen-doped biochar (NBC) to further improve AD efficiency.

This review explores how NBC improves AD. Nitrogen doping enhances the physical and chemical properties of biochar, such as electrical conductivity, pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More buffering, and electron transfer capability. These features optimize microbial community structures, accelerate organic matter conversion, and promote electron transfer processes critical for methanogenesis. Key nitrogen forms in NBC—pyrrolic, pyridinic, graphitic, amino, and oxidized nitrogen—contribute uniquely to these improvements.

NBC also supports direct interspecies electron transfer (DIET), a pathway that facilitates faster methane production compared to traditional interspecies hydrogen transfer. NBC’s large surface area aids in enriching electroactive microorganisms, making it an effective DIET facilitator.

While NBC shows promise, challenges remain. Efficient preparation methods, economic assessments, and environmental impact evaluations are necessary for its industrial application. Additionally, further research is needed to quantify how different nitrogen forms affect microbial interactions and AD performance.

By summarizing the current progress, this review highlights NBC as a promising tool for improving AD, offering insights into its preparation, roles, and future research directions.