Nanobiotechnology-enabled enhancement of process stability and methane production in anaerobic digestion

Anaerobic digestion (AD) is widely recognised as a sustainable technology for managing organic waste and generating renewable energy. Despite its potential, slow kinetics, instability under varying operational conditions, and inhibition from toxic intermediates often hinder AD processes. Nanobiotechnology has emerged as a mechanistically promising approach to enhance process stability and methane production by strengthening microbial performance, accelerating hydrolysis kinetics, and reinforcing syntrophic electron transfer pathways. The addition of zero-valent iron, carbon nanotubes, and metal oxides enhances hydrolysis rates, stimulates methanogenic pathways, and facilitates direct interspecies electron transfer (DIET). These mechanisms collectively improve methane yield while maintaining redox balance, buffering capacity, and long-term operational stability. Evidence from laboratory- and pilot-scale studies indicates that nanomaterial amendments can enhance methane production, typically by 10%–60% under optimised dosing conditions in most systems, with higher enhancements reported for selected conductive transition metal carbides under controlled experimental regimes. Reductions in lag phase duration of 15%–40% and improved tolerance to ammonia concentrations exceeding 1.5–3.0 g L −1 NH 4 + –N have also been documented, depending on reactor configuration and substrate type. These enhancement ranges are derived from condition-resolved extraction of experimental studies meeting predefined inclusion criteria and were normalised against non-amended controls under identical operational settings rather than selectively cited maximum values. Additionally, integrating nanomaterials with pretreatment techniques, bioaugmentation, and bio-electrochemical systems offers synergistic pathways for optimising biogas production. However, the application of nanomaterials also raises important environmental and biosafety concerns, including their transformation during digestion, partitioning into digestates, potential impacts on soil and aquatic systems following land application, and challenges related to dose optimisation, recovery, and lifecycle risk assessment. This review applies a condition-resolved quantitative synthesis by extracting methane yield and production rate and stability indicators (e.g., lag phase, VFA, alkalinity, TAN/FAN tolerance) and normalising enhancements against non-amended controls within operational clusters (temperature regime, reactor configuration, ISR/SIR, substrate class, and nanomaterial dose).