Metagenomic and extracellular polymeric substances analysis reveals the mechanism of exogenous N-hexanoyl-L-homoserine lactone in alleviating the inhibition of perfluorooctanoic acid on anammox process.

To alleviate the negative effects of perfluorooctanoic acid (PFOA) on nitrogen removal via anaerobic ammonia oxidation (anammox), an exogenous signaling factor (N-hexanoyl-L-homoserine lactone, C6-HSL) was introduced into an anammox reactor. Results showed that 2 µmol/L C6-HSL promoted the nitrogen removal efficiency of the anammox reactor under PFOA stress, with the removal efficiencies of ammonia and nitrite increasing from 79.7 ± 4.8 % and 80.8 ± 3.8 %, to 94.4 ± 4.3 % and 97.1 ± 3.8 %. Exogenous C6-HSL enhanced the compactness of the extracellular proteins, and improved the sludge hydrophobicity. Meanwhile, C6-HSL resulted in a microbial shift, with the relative abundance of Planctomycetes increasing from 30.2 % to 49.5 %. Candidatus Kuenenia stuttgartiensis replaced Candidatus Brocadia sp. BL1 as the dominant species, while the available space for other nitrogen-removing bacteria was reduced. Exogenous C6-HSL promoted the expression of anammox-related genes, such as hzsB and hdh, while denitrifying genes were down-regulated. In addition, the relative abundance of HdtS, which synthesizes AHLs, increased by 0.02446%.

Use of iron-loaded biochar to alleviate anammox performance inhibition under PFOA stress conditions: Integrated analysis of sludge characteristics and metagenomics.

The negative effects of perfluorooctanoic acid (PFOA) on biological nitrogen removal performance in wastewater treatment plants, are receiving increasing attention due to the widespread reporting of this issue. In this study, pomelo peel iron-loaded biochar (Fe-PBC) was added to an anammox bioreactor to alleviate the negative effects of PFOA. Results showed that the addition of Fe-PBC increased the ammonia and nitrite removal efficiencies from 77.7 ± 9.6 % and 79.5 ± 5.6 % to 94.45 ± 5.1 % and 95.9 ± 5.0 %, respectively. In addition, Fe-PBC promoted the removal of PFOA from wastewater, increasing the PFOA removal efficiency from 5.2 % to 29.2 ± 4.3 % from 100 to 200 days. The introduction of iron-loaded biochar into the anammox bioreactor increased the CO ratio by 13.64 % by 150 days. In addition, a CO fitting peak was detected in the Fe-PBC, indicating that the Fe-PBC was loaded with microorganisms. Microbial community analysis showed a decrease in the relative abundances of Proteobacteria and Nitrospirae from 31 % and 3.4 % to 16.8 % and 0.9 %, respectively, while the relative abundance of Planctomycetes increased from 26.8 % to 44.1 %. Metagenomic analysis found that the functional genes hzsB and hdh increased from 98,666 ± 11,400 and 3190 ± 460 to 119,333 ± 15,534 and 138,650 ± 11,233 copy numbers/MLSS. The increase in anammox biomass may be attributed to the presence of iron, an essential element for the synthesis of key anammox enzyme. Furthermore, iron was also associated with the enhanced extracellular electron transfer in the anammox system induced by Fe-PBC.

Effects of PFOA on the physicochemical properties of anaerobic granular sludge: Performance evaluation, microbial community and metagenomic analysis.

The impact of perfluorooctanoic acid (PFOA) on the anaerobic granular sludge was evaluated through a sequential batch experiment. Results showed that PFOA inhibited the chemical oxygen demand (COD) removal rate of the sludge and the dosage of 100 mg/L PFOA was more obvious. However, this negative effect would gradually weaken with the adaptation of microorganisms. For the 50 mg/L PFOA experimental group, the proteins content in the extracellular polymeric substances (EPS) of the anaerobic granular sludge increased from 1.53 mg/g to 3.65 mg/g. Meanwhile, PFOA inhibited the 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) activity of the anaerobic granular sludge. Furthermore, 100 mg/L PFOA reduced the relative abundance of Proteobacteria by 5.99% and Longilinea by 1.11%. 100 mg/L PFOA mainly restricted COD removal by affecting the glycolysis process, with the abundances of glucokinase and pyruvate kinase reduced by 8% and 28.1%, respectively. Compared with the control group, the relative abundance of the methyl-coenzyme M reductase alpha subunit increased by 84%, respectively, under 100 mg/L PFOA.

Long-term effect of perfluorooctanoic acid on the anammox system based on metagenomics: Performance, sludge characteristic and microbial community dynamic.

The effects of PFOA on the nitrogen removal performance, microbial community and functional genes of anaerobic ammonium oxidation (anammox) sludge in an anaerobic baffled reactor (ABR) were investigated. The removal efficiencies of ammonia nitrogen (NH4+-N) and nitrite (NO2--N) decreased from 93.90 ± 3.64% and 98.6 ± 1.84% to 77.81 ± 6.86% and 77.96 ± 1.88% when PFOA increased from 5 mg/L to 50 mg/L, respectively. X-ray photoelectron spectra analysis of the anammox sludge showed the presence of both C-F and CaF2 forms of F. Metagenomics analysis of the anammox sludge in the first compartment illustrated that the relative abundance of Ca.Brocadia and Ca.Kuenenia decreased from 22.21% and 5.61% to 2.11% and 2.84% at 50 mg/L PFOA compared with that without PFOA. In addition, the nitrogen metabolism pathway showed that adding 50 mg/L PFOA decreased the expression of HzsB, HzsC, and Hdh (anammox genes) by 0.096%, 0.05% and 0.062%, respectively.

Influence of biodegradable polybutylene succinate and non-biodegradable polyvinyl chloride microplastics on anammox sludge: Performance evaluation, suppression effect and metagenomic analysis.

Microplastics (MPs) has been widely detected in wastewater treatment plants. However, there is a lack of research on its influence on anaerobic ammonia oxidation (anammox) process. Therefore, the effects of polybutylene succinate (PBS) and polyvinyl chloride (PVC) MPs on the nitrogen removal performance, microbial community and metabolites of anammox sludge were investigated. Results showed that PBS and PVC MPs reduced the nitrite removal efficiency of the anammox sludge, and PVC1 (0.1 g/L PVC) group was the most significant at 19.2 %. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra showed that PBS2 (0.5 g/L PBS) group increased the polysaccharide content in the anammox sludge. This may be because of the byproduct, which was produce during the biodegradation of PBS MPs, and decrease the agglomeration capacity of sludge, so as to increase the mass transfer. PBS2 group reduced the relative abundance of Methanosaeta (10.18 %) and the methane modules, and stimulated the anammox bacteria Ca. Brocadia (1.17 %) and the relative nitrogen metabolism modules. PVC2 group reduced the relative abundance of Ca. Brocadia (3.02 %), while was enriched Methanosaeta (2.1 %). Non-biodegradable PVC MPs was more harmful to anammox sludge, which would draw attention to the entry of PVC MPs into the anammox system.

Influence of polyether sulfone microplastics and bisphenol A on anaerobic granular sludge: Performance evaluation and microbial community characterization.

The retention of polyether sulfone (PES) and bisphenol A (BPA) in wastewater has received extensive attention. The effects of PES and BPA on the removal of organic matter by anaerobic granular sludge were investigated. We also analyzed the changes in the electron transport system and the effects on the composition of extracellular polymeric substances (EPS), as well as alternations of the microbial community in the anaerobic granular sludge. In the experimental groups which received BPA, the removal of the chemical oxygen demand (COD) were significantly suppressed, which an average removal efficiency of less than 65%, 30% lower than that of the control group. In the loosely-bound EPS (LB-EPS) excitation-emission matrix (EEM) spectra, the absorption peak of tryptophan disappeared when the BPA pollutants was added, which it was present in the control group without added pollutants. The addition of PES and BPA also affected protease, acetate kinase, and coenzyme F420 activities in the anaerobic granular sludge. Especially, the coenzyme F420 reduced from 0.0045 to 0.0017 µmol/L in the presence of PES and BPA. The relative abundance of Spirochaetes decreased in the presence of PES and BPA, while the relative abundance of Bacteroidetes increased from 12.98% to 22.87%. At the genus level, in the presence of PES and BPA, the relative abundance of Acinetobacter increased from 2.20% to 9.64% and Hydrogenophaga decreased sharply from 15.58% to 0.12%.

Effects of exposure to polyether sulfone microplastic on the nitrifying process and microbial community structure in aerobic granular sludge.

The effects of polyether sulfone (PES) microplastic concentration on the nitrifying process of aerobic granular sludge (AGS) were investigated together with the microbial community structure of AGS. The PES microplastic concentration inhibited the removal of ammonia nitrogen only to a small extent. The average total nitrogen removal rate increased by 5.6% after PES addition. On the 30th day, the addition of 0.5 g/L PES inhibited the specific nitrate reduction rate (SNRR) by 38.84 mg N/(g MLSS·h). Nitrite oxidase (NOR) performance of the AGS were inhibited with addition the PES. According to the high-throughput sequencing results, in the presence of PES, the abundance of Bacillales_Incertae Sedis XII reduced, while the abundance of Anaerolineaceaen increased in the AGS. According to the clusters of orthologous groups (COG) and kyoto encyclopedia of genes and genomes (KEGG), the content of cytochrome c-containing reduced and the Amino Acid Metabolism increased with addition 0.5 g/L PES microplastic.

Exposure to polyamide 66 microplastic leads to effects performance and microbial community structure of aerobic granular sludge.

Microplastic polyamide 66 (PA66) was used to explore its mechanism of influence on the contaminants removal from aerobic granular sludge (AGS) and the corresponding change to the microbial community. Results showed that the removal pollution efficiency of the experimental groups with PA66 were inhibited during the early treatment stage. However, as the experiment progressed, the removal efficiencies of chemical oxygen demand (COD) (92.66%, 93.10%, 93.11%, 93.79%) and ammonia nitrogen (94.25%, 94.58%, 95.61%, 94.73%) were similar in the addition 0 g/L (A), 0.1 g/L (B), 0.2 g/L (C) and 0.5 g/L (D) PA66 beakers at the last 10 days. On the first day, the intensity of fluorescence peaks representing tryptophan protein-like and aromatic protein-like substances of loosely-bound extracellular polymeric substances (LB-EPS) indicated that the PA66 microplastic caused damage to the sludge structure, and the intensity of fluorescence peaks representing fulvic acid-like and humic acid-like substances were stronger than those in the control beaker (A). Microbial community analysis showed that the main phyla were Firmicutes (49.11%, 59.77%, 44.33%, 41.21%), Proteobacteria (26.44%, 11.96%, 31.44%, 19.4%) and Bacteroidetes (9.24%, 13.05%, 11.89%, 14.71%) in the four beakers. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, genes representing [T] Signal transduction mechanisms illustrated that adding PA66 microplastic resulted in more signaling molecules in the AGS.