Efficient nitrite accumulation and elemental sulfur recovery in partial sulfide autotrophic denitrification system: Insights of seeding sludge, S/N ratio and flocculation strategy

Partial sulfide autotrophic denitrification (PSAD) has been proposed as a promising process to achieve elemental sulfur recovery and nitrite accumulation, which is required for anaerobic ammonium oxidation reaction. This study investigated the effect of seeding sludge on the start-up performance of PSAD process, with different sludge taken from the oxidation zone (S-o) of wastewater treatment plants, partial denitrification reactor (S-PD), and anoxic/oxic reactor (S-A/O). The results showed that the PSAD process could be achieved rapidly in three systems on day 22, 29 and 26, respectively. In particular, the S–O system completed the start-up in the shortest time of 22 d, with NO3−-N and S2− removal efficiency of 85.3% and 99.3%, respectively. Selected the S–O system to operate long term, the nitrite (NO2−-N) and biological elemental sulfur (S0) accumulation efficiencies were systematically investigated under different S/N ratios (in a range of 0.71–1.2). The maximum NO2−-N and S0 accumulation efficiencies were 85.2% and 73.5%, respectively, at the S/N ratio of 1.1. In addition, the separation and recovery of S0 in effluent was achieved by employing polyaluminum chloride (PAC) as a flocculant. Using 2D Gaussian function as quadratic model for the maximizing of S0 flocculant efficiency (SFR), an optimal condition of PAC dosage 7.92 mL/L and pH 5.14 was obtained, and the SFR reached 94.1%, under such conditions. The findings offered useful information to facilitate the application of the PSAD process. [Display omitted] •Efficient nitrite accumulation and elemental sulfur recovery were achieved via PSAD process.•Effects of seeding sludges on the start-up of PSAD were compared.•At S/N ratio of 1.1, NO2−-N and S0 accumulation rates were 85.2% and 73.5%, respectively.•SFE reached 94.1%, as PAC dosage and pH were 7.92 mL/L and 5.14.