Molecular insight into the allocation of organic carbon to heterotrophic bacteria: Carbon metabolism and the involvement in nitrogen and phosphorus removal.

Abstract

Carbon metabolism and nutrient removal are crucial for biological wastewater treatment. This study focuses on analyzing carbon allocation and utilization by heterotrophic bacteria in response to increasing COD concentration in the influent. The study also assesses the effect of denitrification and biological phosphorus removal, particularly in combination with anaerobic ammonia oxidation (anammox). The experiment was conducted in a SBR operating under anaerobic/anoxic/oxic conditions. As COD concentration in the influent increased from 100 to 275 mg/L, intracellular COD accounted for 95.72 % of the COD removed. By regulating the NO₃^- concentration in the anoxic stage from 10 to 30 mg/L, the nitrite accumulation rate reached 69.46 %, which could serve as an electron acceptor for anammox. Most genes related to the tricarboxylic acid (TCA) cycle declined, while the genes involved in the glyoxylate cycle, gluconeogenesis, PHA synthesis increased. This suggests that glycogen accumulation and carbon storage, rather than direct carbon oxidation, was the dominant pathway for carbon metabolism. However, the genes responsible for the reduction of NO₂^--N (nirK) and NO (nosB) decreased, contributing to NO₂^- accumulation. The study also employed metagenomic analysis to reveal microbial interactions. The enrichment of specific bacterial species, including Dechloromonas sp. (D2.bin.10), Ca. Competibacteraceae bacterium (D9.bin.8), Ca. Desulfobacillus denitrificans (D6.bin.17), and Ignavibacteriae bacterium (D3.bin.9), played a collaborative role in facilitating nutrient removal and promoting the combination with anammox.