Study on denitrification of hydroponic wastewater reverse osmosis concentrate using sulfur-autotrophic denitrification

Hydroponic agriculture is one of the sectors that generate the highest amounts of nitrogen-containing wastewater. Sulfur-autotrophic denitrification is considered a promising technology due to its stable and excellent denitrification performance, cost-effectiveness, and operational advantages. In order to investigate the denitrification performance and the contribution of the filter layer under high NO3--N concentration (600 mg·L-1), this experiment designed a denitrification system using Na2S2O3 as an electron donor. The results showed that the reactor achieved the highest denitrification efficiency with a hydraulic retention time of 12 hours, pH of 7, and sulfur to nitrogen ratio of 2, maintaining a stable NO3--N removal efficiency of 99%. The majority of NO3--N was removed by the bottom filter layer (0-300 mm), accounting for 86% of the total denitrification. The microbial community in the lower part of the filter column was dominated by Proteobacteria, with relatively high abundances of the genera Chryseobacterium, Thiobacillus, and Sulfurimonas. Similarly, the microbial community structure in the upper filter layer was dominated by Proteobacteria, with an increased abundance of the genus Chryseobacterium and a significant reduction in the abundance of Sulfurimonas. The study indicates that SAD can achieve stable and efficient denitrification of wastewater from hydroponic reverse osmosis concentrate. Moreover, higher NO3--N concentrations can influence the bacterial community structure within the reactor.