Denitrifying Bacteria and Iron Amended Eastern Redcedar Biochar for Enhanced Aqueous Nutrient Removal

Abstract

Eastern redcedar (Juniperus virginiana), an invasive-like woody species in central U.S. grasslands, presents both ecological challenges and an abundant biomass resource. This research evaluated whether eastern redcedar can be converted into biochar and used to mitigate nitrate (NO3-N) and phosphate (PO4-P) pollution in freshwater systems. Eastern redcedar feedstock was pyrolyzed at 650 °C to produce biochar, which was characterized for proximate properties (moisture, volatile matter, and ash content), nutrient and trace metal composition, and structural properties using scanning electron microscopy (SEM). Pyrolysis decreased moisture and volatile matter while increasing organic carbon and ash content. The resulting biochar was alkaline and stable, with a low H:C molar ratio. Trace metal concentrations were within acceptable ranges defined by the International Biochar Initiative (IBI) standards. Laboratory experiments used cycled batch reactors with alternating 12-hour wetting and drying periods, and samples were collected at 6 and 12-hours over 26-days. Results showed that biochar produced greater and more rapid decreases in nitrate and phosphate concentrations compared to eastern redcedar feedstock. Additional experiments examined biochar amended with denitrifying microbes, iron, or both. Microbial amendments showed the greatest observed decreases in nitrate concentrations, although differences among treatments were not statistically significant. In contrast, phosphate responses were strongly influenced by iron amendments, with iron containing treatments exhibiting greater decreases compared to non-iron treatments, while no difference was observed between the iron only and combined microbe + iron treatments. Physicochemical properties remained stable across treatments. Overall, these results indicate that eastern redcedar biochar is a stable, high-quality material capable of influencing nitrate and phosphate dynamics in water, highlighting its potential as a sustainable biochar and nature-based approach for improving water quality.