Natural zeolite-enhanced hydrothermal carbonization of wetland biomass: Potential for carbon sequestration and...

Disposal of harvested wetland biomass is a crucial challenge for the efficient and sustainable application of constructed wetlands. Hydrothermal carbonization (HTC) is an emerging low-energy technology for processing wetland biomass, which is a renewable resource, producing hydrochar with potential for long-term carbon sequestration and ammonia nitrogen (NH₄⁺-N) adsorption capacity. However, the carbon sequestration ability and adsorption capacity of hydrochar require enhancements to improve the feasibility of HTC. Here, we developed a natural zeolite-enhanced HTC to convert wetland biomass to hydrochar-zeolite composites (HZCs). Results showed that the carbon sequestration potential of hydrochar significantly increased by 49.7% due to the enhancement of yield, aromaticity, and stability under optimal conditions (180 °C, an NZ-to-biomass ratio of 2, 150 rpm, and 1 h). The resulting HZCs exhibited the most excellent adsorption capacity of 1.46 mg/g and the highest microbial loading of 1309.91 nmol P/g, achieving a 96.94% NH₄⁺-N removal efficiency after 24 h (a 57.50% enhancement through co-culture with Pseudomonas stutzeri). This study demonstrated that integrating natural zeolite into low-temperature HTC of wetland biomass is a promising approach that not only solves the biomass disposal problem but also enhances carbon sequestration and wetland wastewater remediation performance.