Sulfur–boron mud autotrophic denitrification for simultaneous nitrate and phosphate removal from wastewater: batch, column, and pilot-scale experiments

Abstract

Boron mud is a nearly zero-cost, abundant industrial waste characterized with multiple active components, strong alkalinity, and a large specific surface area. However, its application in sulfur-based autotrophic denitrification (SAD) processes to the simultaneous removal of NO₃⁻–N and PO₄³⁻–P has remained unexplored until now. In this study, a sulfur–boron mud autotrophic denitrification (SBMAD) system was constructed. Batch experiments demonstrated that the SBMAD system could achieve simultaneous NO₃⁻–N and PO₄³⁻–P removal, with significantly superior denitrification performance compared to the conventional sulfur–limestone (SLAD) system. The optimal parameters (HRT 2 h, temperature 22–26 °C) of the NO₃⁻–N and PO₄³⁻–P removal of the SBMAD system were determined by column experiments with high removal efficiencies of NO₃⁻–N (>99.45%) and PO₄³⁻–P (up to 96.27%). Pilot-scale experiment further validated the system's effectiveness, showing average removal efficiencies of 91.07% for NO₃⁻–N and 81.24% for PO₄³⁻–P at an HRT of 1 h, with effluent concentrations (1.31 mg L⁻¹ NO₃⁻–N and 0.17 mg L⁻¹ PO₄³⁻–P) consistently meeting the national discharge standard. Notably, incorporating boron mud significantly enhanced the NO₃⁻–N and PO₄³⁻–P removal effect of the SAD process, with Fe²⁺ from the boron mud contributing 6.90% to the NO₃⁻–N removal efficiency. These findings demonstrate that the SBMAD system is a promising technology for efficient simultaneous NO₃⁻–N and PO₄³⁻–P removal in low C/N ratio wastewater treatment.