Performance and mechanism of glycerol-driven denitrifying phosphorus removal from low organic matter sewage

Metabolic and ecological responses of denitrifying consortia to different carbon source strategies under fluctuating C/N conditions

Frequent fluctuations in the carbon-to-nitrogen (C/N) ratio of urban wastewater influent can undermine denitrification performance, posing challenges for stable nitrogen removal. Although supplying additional carbon sources is a recognized strategy to mitigate these issues, the underlying microbial interactions and metabolic reconfigurations triggered by changing C/N ratios remain incompletely understood. Here, we employed methanol, glycerol, sodium acetate, and glucose in long-term denitrification reactors and integrated denitrification kinetics, 16S rRNA gene amplicon sequencing, metagenomic binning, and metabolic modeling to elucidate how these systems respond to a declining C/N ratio. Our results show that lower C/N ratios diminished denitrification efficiency in all treatments, with each carbon source eliciting distinct shifts in microbial assemblages. Fluctuations in the C/N ratio determine the extent of directional selection of microbial communities based on carbon source metabolism and induce significant changes in non-dominant microorganisms. Throughout the process, the synthesis potential of PHA is closely linked to the system's ability to withstand fluctuations. Notably, metabolic modeling indicated that heightened tricarboxylic acid (TCA) cycle activity in the methanol- and glucose-fed communities was associated with suboptimal nitrogen removal. These findings offer novel insights into the metabolic and ecological mechanisms governing carbon source-driven denitrification under fluctuating C/N conditions, providing a valuable framework for optimizing nitrogen removal in urban wastewater treatment systems.

Enhancing low-temperature nitrification biofilter with Acinetobacter harbinensis HITLi7T for efficient ammonia nitrogen removal in engineering applications

Low temperature has always been a significant limitation for the biological removal of ammonia nitrogen (NH3-N) from water. Acinetobacter harbinensis HITLi7T (HITLi7T) was used to enhance the low-temperature nitrification biofilter (LTNB) with a treatment capacity of 20,000 m3/d. At 2 °C, with an empty bed contact time of 3 h, the LTNB achieved NH3-N removal levels of 1.2 ∼ 1.5 mg/L. The nitrifying bacteria (Nitrosomonas, Nitrosospira, Nitrospira and Candidatus_Nitrotoga) were significantly enriched. PICRUSt2 and FAPROTAX revealed the nitrification pathway of NH3-N conversion to hydroxylamine, then to nitrite, and finally to nitrate. The high co-occurrence of HITLi7T with the nitrifying bacteria suggested that HITLi7T might also promote the enrichment of nitrifying bacteria. Life cycle assessment showed that LTNB was an economical and environmentally friendly method for NH3-N removal. These results indicated that HITLi7T enhanced the nitrification performance of biofilters, improved the cold tolerance of nitrifying bacteria, and had potential for practical applications.

Start-up of glycerol-driven denitrifying phosphorus removal from wastewater: The effects of the microaerobic environment

Glycerol, an abundant by-product of biodiesel production, represented a promising carbon source for enhancing nutrient removal from low C/N ratio wastewater. This study discovered a novel approach to initiate glycerol-driven denitrifying phosphorus removal (DPR) in situ by creating a short-term microaerobic environment within the aerobic zone. This approach facilitated the in-situ conversion of glycerol, which was subsequently utilized by denitrifying phosphate accumulating organisms (DPAOs) for DPR. The feasibility and stability of glycerol-driven DPR were validated in a continuous-flow pilot-scale reactor. Anaerobic phosphorus release increased from 1.0 mg/L/h to 2.5 mg/L/h, with fermentation bacteria and related functional genes showing significant increases. The stable stage exhibited 92.8% phosphorus removal efficiency and 55.5% DPR percentage. The microaerobic environment enhanced fermentation bacteria enrichment, crucial for glycerol-driven DPR stability. The collaborative interaction between fermentation bacteria and phosphate accumulating organisms (PAOs) played a key role in sustaining glycerol-driven DPR stability. These findings provide a robust theoretical foundation for applying glycerol-driven DPR in established wastewater treatment plants.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.