Animal manures (AMs) are valuable organic fertilizers, but they often contain significant levels of emerging pollutants, including heavy metals, which pose environmental and health risks. Composting is a key strategy for managing AMs and mitigating these risks. A new preprint by Mitra Mohammadi, Ali Almasi, Seyyed Alireza Mousavi, and Mostafa Hadei, posted in Research Square, investigates the impact of 650-million-year-old natural mineral biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More (NMB) on the fate of pollutants during the co-composting of natural mineral biochar and animal manures (cow manure:poultry manure, CWM:PUM) in an intermittent aeration and mixing bioreactor.

The study, which monitored 12 different composting treatments over 60 days, aimed to evaluate the changes in pollutants, nutrients, and associated environmental risks. The researchers found that NMB significantly enhanced the removal efficiencies of heavy metals. For instance, initial zinc (Zn) concentrations in treatments with varying NMB levels ranged from 197.15 g/kg to 336.32 g/kg. By day 60, these concentrations had decreased significantly, with the most notable reduction observed in the treatment with 15% NMB (T10), where Zn levels dropped from 244.16 g/kg to 129.58 g/kg. Similarly, copper (Cu) concentrations in the final compost decreased from initial values ranging from 97.4 g/kg to 240.25 g/kg to final concentrations between 76.11 g/kg and 228.31 g/kg. Chromium (Cr) concentrations, while remaining largely unchanged in the control treatment, saw significant reductions in NMB-containing treatments, decreasing to as low as 6.76 g/kg in the 5% NMB treatment.

The removal efficiency of these heavy metals varied depending on the NMB concentration. In control groups, the order of removal was Zn>Cu>Cr. However, with 5% NMB, the order shifted to Cr>Cu>Zn. For treatments with 10% and 15% NMB, the most effective pollutant immobilization was observed, with the order being Zn>Cr>Cu. The significant reductions in Zn, Cu, and Cr concentrations were attributed to mechanisms such as adsorption, surface complexation, and pH-mediated processes. Notably, the final concentrations of all three heavy metals in the mature compost were below the standards set by the U.S. Environmental Protection Agency (EPA).

Beyond heavy metal removal, the study also highlighted NMB’s positive impact on overall compost quality. The addition of NMB led to a higher heating rate and an extended thermophilic phase during composting, indicating improved mineralization and compost maturity. The thermophilic phase, crucial for eliminating pathogens and parasites, lasted up to 16 days in treatments with higher NMB levels and lower CWM/PUM ratios, ensuring that all treatments met standard hygiene requirements. NMB also facilitated nitrogen fixationNitrogen is a crucial nutrient for plant growth, but plants can’t directly absorb it from the air. Nitrogen fixation is a process where certain bacteria convert atmospheric nitrogen into a form that plants can use. Biochar can provide a home for these nitrogen-fixing bacteria, enhancing More, reducing nitrogen loss due to its high adsorption capacity, large specific surface area, and internal pore volume. The presence of surface acidic functional groups and cation exchange sites further limited ammonia volatilization during composting.

The findings of this study underscore the potential of NMB as a sustainable and eco-friendly solution for managing AMs and mitigating the risks posed by emerging pollutants. Incorporating NMB into composting systems not only improves compost quality by enhancing microbial activity, adsorption, and nutrient stabilization, but also contributes to better resource utilization and promotes circular agricultural practices. This research represents a significant step towards transforming raw manure with associated environmental risks into safer, low-risk compost products.

Source: Mohammadi, M., Almasi, A., Mousavi, S. A., & Hadei, M. (2025). The fate of pollutants in the co-composting of natural mineral biochar and animal manures in an intermittent aeration and mixing bioreactor (IAMB). Research Square.