Enhanced deep denitrification for high-salinity wastewater treatment by constructing biofilm-based technology

Biofilm-based technologies, particularly the sequencing biofilm batch reactor (SBBR), have emerged as a robust solution for high-salinity wastewater treatment. However, there were contradiction in the performance on high-salinity wastewater treatment of suspended carrier and fibrous carrier in SBBR. Additionally, it was seldom that biofilm formation, recovery capability, and pollutant removal for different carriers were systematically studied during the gradually increasing salinity condition. Therefore, two SBBR reactors were operated with two different shapes of carriers (suspended carrier and fibrous carrier) in treating high-salinity wastewater with gradually increasing salinity from 0.5 % to 2 % in this study. The results showed that under increasing salinity, the removal capacity of fibrous carrier group (R2) and suspended carrier group (R1) for COD and TIN far surpasses that of the conventional activated sludge group (R3). Under 2 % salinity, the removal rates of COD in R1 and R2 achieved 83.9 % and 84.8 %, and those of TIN in R1 and R2 reached 81.7 % and 81.0 %, respectively. Meanwhile, under increasing salinity conditions, the R2 group demonstrated a significantly higher COD and NH₄⁺-N removal speed per single operational cycle compared to R1 group. The primary reason was that the excessive secretion of EPS and increased protein-like components in the R2 group enhanced its biofilm adaptability under high-salinity conditions, thereby facilitating the enrichment of salt-tolerant functional microbial communities (e.g., Pseudofulvimonas). Finally, when applied to actual high-salinity pickle wastewater, the fibrous carrier demonstrated superior performance (e.g., COD removal efficiency of 93 %, TIN removal efficiency of 95 %) due to its efficient partial nitrification and denitrification, and lower energy consumption costs. Overall, these findings highlight the potential of new biofilm-based technology as a promising solution for high-salinity wastewater treatment.