Aerobic granulation of nitrifying activated sludge enhanced removal of 17α-ethinylestradiol

The positive correlation between the nitrification activity of activated sludge and 17α-ethinylestradiol (EE2) removal has been widely reported. However, up to now the effect of the granulation of nitrifying activated sludge (NAS) on EE2 removal has not been determined. In this study, nitrifying granular sludge (NGS) exhibited more effective EE2 removal efficiency with 3.705 μgEE2∙(gMLSS∙h)^-1 in a sequential batch reactor (SBR). Through the artificial neural network (ANN) model and Spearman correlation analysis, nitrite accumulation was demonstrated to be the key factor affecting EE2 removal. Notably, under the same aeration condition (0.15 L/min), nitrite accumulation was more easily achieved in NGS because of its dense structure. Full-length 16S rRNA gene sequencing suggested that EE2 could strongly influence the microbial communities of NAS and NGS. NGS exhibited an increase in community diversity and richness, but NAS exhibited a decrease. In addition, the relative abundance of Nitrosomonas (ammonia-oxidizing bacteria, AOB) decreased considerably in both NAS and NGS, whereas the expression of amoA and nirK genes in Nitrosomonas was upregulated. It was suggested that Nitrosomonas was forced to regulate its gene expression to resist the negative effects of EE2. Denitrifying bacteria, such as Comamonas, were enriched in both NAS and NGS, and there were more species of heterotrophs that can degrade micropollutants in NGS with exposure to EE2. The transformation pathways of EE2 were uniform in NAS and NGS. Ammonia monooxygenase (AMO) in AOB directly biotransformed EE2 while reactive species produced by AOB chemically transformed EE2. Heterotrophs degraded EE2 and its transformation products (TPs) generated by AOB. According to TPs and microbial structure, NGS exhibited better performance than NAS regarding the collaborative removal of EE2 by AOB and heterotrophs. These results provide important information for the development and application of NGS to treat wastewater containing estrogen and high-strength ammonium.

Coupling of nitrifying granular sludge into microbial fuel cell system for wastewater treatment: System performance, electricity production and microbial community shift

A novel electrochemical system coupling of nitrifying granular sludge (NGS) into microbial fuel cell (MFC) system was conducted for simultaneous electricity production and wastewater treatment under sequencing batch mode. After 60 days operation, the contaminants of organic and NH₄⁺-N removal efficiencies of the system were high of 95.43% and 98.55%, respectively. The maximum output voltage and power density of the MFC were average at 170 mV and 33.24 mW/m², respectively. According to EEM-PARAFAC model, the soluble microbial products (SMP) released from anode and cathode chambers could be identified two fluorescence components. Additionally, the fluorescence score of protein-like substances changed more obvious than those of humic-like and fulvic acid-like substances. Geobacter and Nitrospiraceae were the dominant functional populations in the anode and cathode chambers, respectively. The result could provide a potential application technology based on NGS-MFC for simultaneously treatment of organic matter and ammonia.