Microbial reduction of nitrate and perchlorate through electron storage capacity of wood-derived biochar

Abstract

Perchlorate and nitrate contamination pose significant environmental and health concerns globally. Human activities, including agriculture, livestock farming, and the production of munitions for military purposes, have significantly contributed to the elevated levels of nitrate and perchlorate pollution in the environment. Current physical and chemical remediation methods for these contaminants often have limitations and can generate additional environmental impacts. Microbial reduction has emerged as a promising approach, but traditional microbial substrates can produce toxic byproducts. In this study, we investigated the efficacy of wood-derived biochar as an exclusive electron donor for the microbial reductive transformation of nitrate and perchlorate into non-toxic products such as nitrogen gas and chloride. Our results demonstrated that biochar effectively facilitated the degradation of nitrate and perchlorate, even in small quantities. In just 4 days, 1 g of reduced biochar successfully facilitated the reductive transformation of 1.55 mM perchlorate into chloride. Similarly, within a span of 13 days, 0.5 g of biochar mediated the conversion of 3.8 mM nitrate into harmless N2. These transformation rates far exceed the established Maximum Contamination Level for perchlorate (300 times higher) and nitrate (30 times higher). Notably, these rates were reached much more rapidly compared to conventional microbiological methods, underscoring the exceptional efficacy of biochar as a remediation agent. Importantly, biochar did not generate any toxic byproducts, distinguishing it from previous methodologies. We also observed a proportionality between the mass of biochar and the rate and extent of reduction, providing valuable insights for system design. Biochar's affordability, environmental friendliness, and absence of toxic byproducts make it a promising tool for controlling nitrate and perchlorate fate and transport. Further research may be needed to assess its feasibility and scalability in real-world scenarios. Nevertheless, this study lays a solid foundation for advancing environmental engineering practices and mitigating pollution impacts associated with these contaminants.