Commercial powdered activated carbon achieves high-efficiency nitrogen removal in sulfur-driven autotrophic denitrification at low temperatures

Sulfur-driven autotrophic denitrification (SAD), a nitrate removal process, is characterized by low carbon emissions and high sustainability. However, its efficiency is notably affected by low temperatures. This study confirmed that the addition of powdered activated carbon (PAC) could enhance denitrification capacity at low temperatures in the SAD process. At 15-10 °C, the nitrogen removal efficiency was 80.38 %, 1.38 times higher than that of the blank reactor. At low temperatures, PAC enhanced the activities of nitrate reductase and nitrite reductase. Meanwhile, PAC stimulated extracellular polymeric substances secretion and improved bio-electrochemical properties. Concurrently, both extracellular and intracellular electron transfer were enhanced by the addition of PAC. Microbial analysis indicated that the microbial network with PAC addition exhibited greater stability and robustness. Furthermore, PAC increased the relative abundances of denitrifying bacteria at low temperatures, particularly those of Ferruginibacter and Dokdonella. Metagenomic sequencing indicated that PAC enhanced pathways related to nucleotide sugar metabolism and synthesis, tRNA charging, and coenzyme A biosynthesis. At the genes level, the functional genes narIL, nirS, nasE, norCE, nosZ, soxA, soxZ, and dsrA were enriched with PAC addition. This study proposed and validated the feasibility of using PAC to enhance nitrogen removal efficiency in the wastewater treatment process at low temperatures, and further elucidated the underlying mechanisms.