The conducted research is part of a project supported by the U.S. National Science Foundation (NSF) and the EPSCoR program to advance fundamental science for converting resources like waste and natural gas into carbon-free or carbon-negative hydrogen and valuable carbon materials, such as nanotubes, without significant CO₂ emissions. Previous studies on CNT synthesis have led to advanced catalytic growth (3), reduced structural damage (4), and nano tube length reduction methods (5). TEA and LCA have been conducted for various CNT production methods like pyrolysis and chemical vapor deposition and feedstocks such as plastic waste (6–8), However, using wastewater as a feedstock highlights a key novelty of this study.
The process yields more than 21,000 tonnes/year of CNTs and 8,400 tonnes/year of hydrogen. By selling hydrogen at $1 per kilogram, the minimum selling price of CNTs drops by $0.40/kg to $2.496/kg, allowing it to compete in the market. The TEA indicates a high Fixed Capital Investment, with the anaerobic digester accounting for the highest purchasing cost of $25M among the units. The LCA, conducted using openLCA, calculates a Global Warming Potential of 8.98 kg CO₂ eq/kg CNT, showing lower emissions than conventional CNT production methods. Normalized impacts also show negative values for wastewater sludge across categories like climate change, resource use, and human toxicity, indicating an overall environmental benefit. These findings suggest that the proposed bioprocess offers a pathway for sustainable CNT production, balancing economic feasibility with environmental benefits such as pollution reduction, resource recovery, and lower carbon emissions.
Future work will concentrate on sensitivity analysis to identify key variables, and refining CNT production techniques. These steps aim to strengthen the process’s practicality and scalability.
Acknowledgements:
The authors gratefully acknowledge the funding for the project from the National Science Foundation (NSF) with the NSF Award number 2218070.
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