Enrichment of Sulfur-Based Autotrophic Denitrifying Microbiota and Characteristics of Nitrate Removal

Mariculture wastewater is characterized by low organic carbon to nitrogen ratio (C/N) but high nitrate concentration, which makes it difficult to remove nitrate by the completely heterotrophic denitrification. However, high nitrate discharge poses a threat to the natural environment and human health. Thus, we enriched sulfur-based autotrophic denitrifying (SAD) microbiota and optimized the nitrate removal under different environmental factors and electron donor conditions. The results showed that the dominant genera in the enriched microbiota were previously confirmed autotrophic denitrifiers, Sulfurovum , Thioalkalispira-Sulfurivermis , and Sedimenticola , with a high relative abundance of 41.14%, 21.01%, and 6.17%. Among the environmental factors, pH was the key factor affecting SAD microbiota, and pH 7-9 favored nitrate removal. However, high pH led to nitrite accumulation (e.g. 10 mg/L at pH=9), which should be strictly avoided. With regard to electron donors, the initial concentration of thiosulfate was proportional to the nitrate removal rate, while higher concentrations of organic carbon stimulated the heterotrophic denitrification potential of microbiota and thus benefited to dentrification. This study showed that the enriched SAD microbiota was able to achieve efficient nitrate removal under suitable environmental conditions and mixed electron donors, and thus presented the potential for application in the treatment of mariculture wastewater.