Insight into enhanced enrichment and nitrogen removal performance of Anammox bacteria with novel biochar/tourmaline polyurethane sponge modified biocarrier

A novel biochar/tourmaline polyurethane sponge modified biocarrier (BTP) could enhance Anammox bacteria (AnAOB) enrichment and nitrogen removal performance. With higher hydrophilicity and specific surface area, BTP significantly improved total inorganic nitrogen (TIN) removal efficiency to 80 ± 2 %, compared to unmodified biocarrier of 67 ± 3 % when influent TIN reached 633.9 ± 22.0 mg/L. BTP stimulated the upregulation of amino acid synthases genes abundance and improved protein secretion in extracellular polymer substances (EPS). Moreover, significant increases were found in heme concentration, specific anammox activity and hydrazine dehydrogenase of AnAOB with BTP compared to unmodified biocarrier. Extracellular electron transfer pathway of AnAOB was improved by BTP via upregulating cytochrome C and ferredoxin synthesis. Candidatus Brocadia was the main genus in Anammox biofilm, with relative abundance of 20.1 % and 27.6 % in the control and BTP, respectively, which explained the improvement of nitrogen removal performance.