Insight into nitrogen recovery from municipal wastewater to harness energy: state of the art, challenges, and way forward

The rational response to issues like greenhouse gas emissions and energy crises is found in the advancement of clean, sustainable, and eco-friendly technology. A transitional shift towards carbon-neutral chemical fuels can reduce carbon emissions in the energy sector. One potential synthetic fuel technique involves nitrogen-based fuels which carry hydrogen alternative to carbon. Hydrogen contains almost three times the calorific value of gasoline when compared on a weight basis making it a viable fuel. On the other hand, it is necessary to remove nitrogen compounds from wastewater because of environmental and ecological concerns. Most of the wastewater treatment plants across the world encounter problems associated with the treatment of wastewater with high levels of urea, ammonia-nitrogen and other nitrogen-based compounds. The current article emphasizes the recovery of nitrogen-based compounds like urea, ammonia-nitrogen, aqueous ammonium hydroxide & urea, aqueous ammonia & ammonium nitrate, aqueous urea & ammonium nitrate, hydrazine, etc., from wastewater using different techniques and their possible application as fuel. Even though there are a number of nitrogen recovery techniques, such as air stripping, bio-electrochemical systems, membrane separation processes, and electro-dialysis, many still have issues like low selectivity or inefficient energy use. With an emphasis on their viability, environmental advantages, and scalability, this article objectively assesses the existing approaches.