Nanomaterial-enhanced anaerobic digestion for sustainable bioenergy production : opportunities, challenges and territorial issues. A systematic bibliometric review

Anaerobic digestion (AD) is a promising biotechnology for organic waste management, simultaneously contributing to sustainable bioenergy generation. Despite its potential, enhancing methane production and achieving process optimization remain significant challenges. The integration of nanomaterials (NMs) into AD systems has shown promise in enhancing biogas quality and yield, as well as stabilizing the process. Nevertheless, the diversity of NMs (including metallic and carbon-based) applied to various types of organic wastes leads to inconsistent results, highlighting the need for a more comprehensive understanding of the underling biochemical mechanisms when NMs are incorporated. This review examines current research challenges and opportunities related to the application of NMs in the AD processes. Through a systematic literature review, following a protocol for the selection of scientific articles and patents, 46 articles and 36 patents are identified. The majority of relevant studies are concentrated in developed countries, and patent analysis suggests the technology is evolving from the emerging stage to the growth phase, with maturity anticipated by 2037. Metadata analysis reveals that the application of NMs can enhance biogas production by up to 25 % compared to conventional AD processes, with iron-based metallic NMs demonstrating superior methane yield in the treatment of manure, sewage sludge, and lignocellulosic waste. In contrast, carbon-based NMs, while less effective in enhancing biogas yield, also face cost-related barriers that may hinder industrial scalability. This article identified seven key research challenges and opportunities to guide the application of NMs in AD processes and promote their large-scale implementation in waste-to-energy conversion.