Inducement mechanism and control of self-acidification in elemental sulfur fluidizing bioreactor

The sulfur fluidizing bioreactor (S⁰FB) has significant superiorities in treating nitrate-rich wastewater. However, substantial self-acidification has been observed in engineering applications, resulting in frequent start-up failures. In this study, self-acidification was reproduced in a lab-scale S⁰FB. It was demonstrated that self-acidification was mainly induced by sulfur disproportionation process, accounting for 93.4 % of proton generation. Supplying sufficient alkalinity to both the influent (3000 mg/L) and the bulk (2000 mg/L) of S⁰FB was essential for achieving a successful start-up. Furthermore, the S⁰FB reached 10.3 kg-N/m³/d of nitrogen removal rate and 0.13 kg-PO₄^3-/m³/d of phosphate removal rate, respectively, surpassing those of the documented sulfur packing bioreactors by 7-129 times and 26-65 times. This study offers a feasible and practical method to avoid self-acidification during restart of S⁰FB and highlights the considerable potential of S⁰FB in the treatment of nitrate-rich wastewater.