A novel dynamic membrane-equipped element sulfur-based denitrification reactor for efficient and easily maintainable treatment of high-nitrate wastewater

Using powdered sulfur (S⁰) with high specific surface area enables high efficiency in an elemental sulfur-based denitrification (ESDeN) reactor but faces challenges with S⁰ retention. While integrating the ESDeN process with microfiltration membranes (MM) has been shown to effectively reject S⁰ powder, severe membrane fouling and high membrane costs restrict its practical application. This study, for the first time, reports a dynamic membrane-equipped ESDeN (ESDeN-DM) reactor. The DM was formed by in-situ pre-coating a solid mixture (particle size: 0.4 μm to 110 μm) of S⁰ powder and denitrifying sludge onto inexpensive nylon fabrics. Initially, we optimized the DM formation conditions, determining that a nylon fabric pore size of 25 μm and a pre-coating flux of 300 L m^-² h^-1 resulted in permeate turbidity lower than 5 NTU within 60 mins. Subsequently, we identified the duration (12.5 days) of a transmembrane pressure (TMP)-dependent run (≤30 KPa) for the reactor and found that the TMP increase was related to the thickening and densification of the cake layer. Finally, we conducted a comparative examination of the ESDeN-DM reactor and the conventional ESDeN-MM reactor during long-term operation. The results demonstrated that the ESDeN-DM reactor achieved a comparable denitrification rate to the ESDeN-MM reactor (both with the maximum value more than 3 kg N m⁻³ d⁻¹) but exhibited significantly better membrane fouling tolerance (56 % longer TMP-dependent run time), easier regeneration of specific flux (online backwash versus offline chemical cleaning), and exceptional cost-effectiveness (over 90 % total cost reduction). This study presents a highly efficient and easily maintained membrane-equipped ESDeN process with great potential for treating high-nitrate industrial wastewater.