The Key Role of Carbon Materials in the Biological and Photocatalytic Reduction of Nitrates for a Sustainable Management of Wastewater

This work explores the influence of material properties and experimental conditions on both bi-ological and photocatalytic nitrate reduction processes. For the biological route, results demon-strate that carbon supports, specifically carbon gels, with open porosity, slight acidity, and high purity enhance E. coli adhesion and promote the formation of highly active bacterial colonies. However, carbon supports of bacteria, produced from waste biomass, emerges as a sustainable and cost-effective alternative, improving scalability and environmental value. Complete con-version of nitrates to nitrites, followed by full nitrite reduction, is achieved under optimized conditions. Photocatalytic nitrate reduction under solar radiation is proposed also as a promis-ing and ecofriendly upgrade method to conventional wastewater treatment. Graphene oxide (GO) was used to enhance the photocatalytic activity of TiO2 nanoparticles for the degradation of nitrates. The efficiency of nitrate reduction is found to be highly sensitive to solution pH and the physicochemical nature of the photocatalyst surface, which governs nitrate interactions through electrostatic forces. Screening of hole scavengers revealed that formic acid, in combination with the TiO2–GO composite, delivered exceptional performance, achieving complete nitrate reduc-tion in just 15 minutes under batch conditions at acidic pH.