Dual-Granule Biotechnology Mediated by S0 and Anammox toward Sustainable Wastewater Treatment Even at Winter Low Temperatures

Abstract Wastewater treatment safeguards natural water health and secures urban water supplies; however, the global drive toward the Sustainable Development Goals has highlighted the sustainability shortcomings of the traditional energy- and resource-intensive paradigms. Here, we propose a dual-granule biotechnology comprising elemental sulfur (S0)-siderite composite granules and anaerobic ammonium oxidation (anammox) granules for low-carbon and high-efficiency wastewater treatment. This novel paradigm inherits the superiorities of two advanced nitrogen removal biotechnologies (S0-driven denitrification and anammox), acquires highly synergistic nutrient metabolism pathways, and, more importantly, does not require any aeration, organic carbon, or additional chemical inputs. During a long-term operation, the biosystem demonstrated remarkable feasibility and reliability against challenging conditions such as seasonal cooling and fluctuating nitrogen loading. Even at winter low temperatures of 7.4 ± 0.7 °C, NO3– and NH4+ removal efficiencies reached 96.1 ± 2.6% and 92.1 ± 3.1%, respectively, with a total inorganic nitrogen removal rate as high as 0.28 ± 0.03 kg N/(m3·d). Beyond energy and resource savings, the bonus PO43– removal, suppressed N2O emissions, and limited free sulfide generations bring further sustainability benefits. As a fresh technical concept, the dual-granule biotechnology takes a step forward toward the low-carbon and high-efficiency goals of the wastewater sector.