Effects of gibberellin on the activity of anammox bacteria

Rapid enrichment of AnAOB with a novel vermiculite/tourmaline modification technology for enhanced DEAMOX process

The DEnitrifying AMmonium OXidation (DEAMOX) has been proven to be a promising process treating contaminated surface water containing ammonia and nitrate, while the enrichment of the slow-growing anammox bacteria (AnAOB) remains a challenge. In this study, a novel polyurethane-adhesion vermiculite/tourmaline (VTP) modified carrier was developed to achieve effective enrichment of AnAOB. The results demonstrated that the VTP-1 (vermiculite: tourmaline = 1:1) system exhibited the greatest performance with the total nitrogen removal efficiency reaching 87.6% and anammox contributing 63% to nitrogen removal. Scanning electron microscope analysis revealed the superior biofilm structure of the VTP-1 carrier, providing attachment for AnAOB. The addition of VTP-1 promoted the secretion of EPS (extracellular polymeric substances) by microorganisms, which increased to 85.34 mg/g VSS, contributing to the aggregation of anammox cells. The favorable substrate microenvironment created by NH4+ adsorption and NO2- supply via partial denitrification process facilitated the growth of AnAOB. The relative abundance of Candidatus Brocadia and Thauera increased from 0.04% to 0.3%-1.03% and 2.06% in the VTP-1 system, respectively. This study sheds new light on the anammox biofilm formation and provides a valid approach to initiate the DEAMOX process for low nitrogen polluted water treatment.

Potential mechanism of biochar enhanced degradation of oxytetracycline by Pseudomonas aeruginosa OTC-T

Extensive use of oxytetracycline (OTC) and the generation of its corresponding resistance genes have resulted in serious environmental problems. Physical-biological combined remediation is an attractive method for OTC degradation because of its high remediation efficiency, stability, and environmental friendliness. In this study, an effective OTC-degrading strain identified as Pseudomonas aeruginosa OTC-T, was isolated from chicken manure. In the degradation experiment, the degradation rates of OTC in the degradation systems with and without the biochar addition were 92.71-100 % and 69.11-99.59 %, respectively. Biochar improved the tolerance of the strain to extreme environments, and the OTC degradation rate increased by 20.25 %, 18.61 %, and 13.13 % under extreme pH, temperature, and substrate concentration conditions, respectively. Additionally, the degradation kinetics showed that biochar increased the reaction rate constant in the degradation system and shortened the degradation period. In the biological toxicity assessment, biochar increased the proportion of live cells by 17.63 % and decreased the proportion of apoptotic cells by 58.87 %. Metabolomics revealed that biochar had a significant effect on the metabolism of the strains and promoted cell growth and reproduction, effectively reducing oxidative stress induced by OTC. This study elucidates how biochar affects OTC biodegradation and provides insights into the future application of biochar-assisted microbial technology in environmental remediation.

Efficient nitrogen removal from mature landfill leachate by single-stage partial-nitritation anammox using expanded granular sludge bed

The effective retention of anaerobic ammonia oxidizing (anammox) bacteria and its high sensitivity to toxic substances and oxygen posed a major challenge to the application of partial nitrification combined with anammox (PN/A) in mature landfill leachate treatment, although it is a promising and efficient nitrogen removal process. In this study, a single-stage PN/A process based on expanded granular sludge bed was proposed to treat the mature landfill leachate. During the last phase, when the NH+ 4-N concentration of mature landfill leachate in influent was 1150.0 mg/L, the nitrogen removal efficiency (NRE) was 83.64% with 1.07 kg N/(m3·d) nitrogen removal rate (NRR). The activity of anammox bacteria (AnAOB) and ammonia oxidizing bacteria (AOB) was 9.21 ± 0.22 mg N/(gVSS·h) and 14.34 ± 0.65 mg N/(gVSS·h), respectively. The bacteria produced a high amount of tightly bound extracellular polymeric substance (TB-EPS) i.e., 4071.79 mg/(g·VSS). This helped to create granular sludge and provided favorable spatial conditions for the distribution of functional bacteria that were adapted to different environments. Due to the efficient retention of functional bacteria by the granular sludge, the relative abundance of Ca.Brocadia and Ca.Kuneneia was 1.71% and 0.31%, respectively. Redundancy analysis (RDA) and microbial correlation network diagram showed that the relative abundance of Ca. Kuenenia, Nitrosomonas and Truepera had a stronger positive correlation with the increase of the proportion of mature landfill leachate added to the influent. Overall, the PN/A process based on granular sludge provides an effective method for autotrophic biological nitrogen removal from mature landfill leachate.

The feasibility and mechanism of redox-active biochar for promoting anammox performance

Redox-active biochar has been regarded as an effective additive to promote heterotrophic denitrification, yet little is known about the feasibility of adding biochar for promoting anammox performance. In this study, we investigated the effects of different biochar doses (3-14 g/L; 1.5-7.1 g/g VSS) on anammox performance. Results showed that, in a short term (40 days), biochar could enhance anammox nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) by 0-18.0% and 0.2%-11.6%, respectively; this enhancement effect increased at 3-10 g biochar/L assays and reached a plateau at 10-14 g biochar/L assays. The optimal biochar dosage was identified to be 10 g/L (5.1 g/g VSS), with the NRR and NRE being 5.6%-18.0% and 4.0%-11.6% higher than those of the control, respectively. The highest specific anammox activity was simultaneously obtained at 10 g biochar/L assay, being 51% higher than that of the control. It revealed that biochar promoted the secretion of extracellular polymeric substances (increased by 30%-40% compared with that of the control) and increased the ratio of extracellular proteins to polysaccharides as well, directly enhancing the extracellular electron transfer capacity (ETC) of anammox biomass. The increased ETC of anammox biomass would further accelerate the metabolic activities of anammox bacteria, and promote the relative abundance of anammox bacteria, i.e., Ca. Brocadia was enriched by 5.8-12.6 folds than that of the control. These results demonstrate that biochar is feasible to enhance anammox activity and nitrogen removal performance, facilitating to a fast startup and enhanced nitrogen removal of anammox system.

Effects of sludge morphology on the anammox process: Analysis from the perspectives of performance, structure, and microbial community

The nitrogen removal characteristics, physicochemical properties, and microbial community composition of four different anaerobic ammonium oxidation (anammox) sludge morphologies were investigated. The morphologies considered in this study, namely suspended sludge (Rs), biofilm (Rm), granular sludge (Rg), and encapsulated biomass (Re), were prepared from floc sludge. The results show that Re exhibited the maximum anammox activity, followed by Rg, Rm, and Rs. Additionally, the anammox contribution rate was higher in Rg and Re. The higher extracellular polymer content in Rg promoted sludge accumulation, and tryptophan was observed in Rm and Rg, which was replaced by humic acids in Rs. Re showed the largest specific surface area, hydrophobicity and strength, and its good structure ensured enrichment of anammox bacteria (AnAOB). In terms of the microbial community, the functional bacterium Candidatus Kuenenia accounted for the highest proportion in Rm (39.27%), but the presence of both anaerobic and aerobic regions led to increased community complexity with more nitrifying bacteria. In contrast, Rg and Re had a more specific microbial community. In addition, denitrifying bacteria tended to grow in Rs, while nitrifying bacteria were retained in Rm. The AnAOB were more likely to be enriched in sludge aggregates (both Rm and Rg) and carriers (Re). Through correlation analysis, the potential relationship involving bacterial flora evolution of each sample was clarified. Finally, the structural models of different morphologies of sludge were proposed. This study deepens the understanding of various anammox sludge morphologies as well as provides useful information for the cultivation of AnAOB and further application of anammox.

Effects of granular activated carbon and Fe-modified granular activated carbon on anammox process start-up

In this study, granular activated carbon (GAC) and Fe-modified granular activated carbon (FeGAC) prepared by ultrasonic impregnation method were added into respective up-flow anaerobic sludge blanket (UASB) reactors to explore their effects on the anammox process start-up. The results showed that the time of anammox system start-up could be reduced from 108 d in R1 (control group) to 94 d in R2 (GAC reactor) and to 83 d in R3 (FeGAC reactor). After 120 days of operation, the nitrogen removal rates (NRR) of all reactors could reach more than 0.8 kg-N m⁻³ d⁻¹. Extracellular polymeric substance (EPS) amount, heme c content and the anammox bacterial functional gene copy numbers gradually increased in all reactors with the passage of culture time, and manifested the superiority in R3 especially. High throughput sequencing revealed that Candidatus Kuenenia was the dominant species in all reactors in the end. It was also demonstrated that FeGAC markedly strengthened the growth and aggregation of anammox bacteria, which is promising for the practical application of the anammox process.

In this study, granular activated carbon (GAC) and Fe-modified granular activated carbon (FeGAC) prepared by ultrasonic impregnation method were added into respective up-flow anaerobic sludge blanket (UASB) reactors to explore their effects on the anammox process start-up.

Effects of biotin on promoting anammox bacterial activity

Anaerobic ammonium oxidation (anammox) bacteria significantly improve the efficiency and reduce cost of nitrogen removal in wastewater treatment plants. However, their slow growth and vulnerable activity limit the application of anammox technology. In this paper, the enhancement of biotin on the nitrogen removal activity of anammox bacteria in short-term batch experiments was studied. We found that biotin played a significant role in promoting anammox activity within a biotin concentration range of 0.1-1.5 mg/L. At a biotin concentration of 1.0 mg/L, the total nitrogen removal rate (NRR) increased by 112%, extracellular polymeric substance (EPS) secretion and heme production significantly improved, and anammox bacterial biomass increased to maximum levels. Moreover, the predominant genus of anammox bacteria was Candidatus Brocadia.

Insight into the benefits of anammox bacteria living as aggregates

This work tried understanding aggregation preference of anammox bacteria from benefit-driven perspective. Aggregated anammox sludge (AGS) gained benefits in specific anammox activity (SAA) (increased by 40.47 ± 12.64%) and in toxicity resistance (enhanced by 65.41%) than scattered anammox sludge (SCS), which were verified by kinetics. The increased heme c content by 35.67 ± 5.77% and enhanced relative abundance of anammox bacteria by 9.29% supported the benefits in biological activity and improved EPS content by 1097.59 ± 43.06% (622.16 ± 61.73% for protein (PN), 2403.47 ± 162.75% for humic acid (HA) and 1145.34 ± 97.33% for polysaccharide (PS)) justified the benefits in toxicity resistance. The diverse microbial communities and organized spatial structures owned by AGS promoted interactions between species, as the intrinsic justification for obtaining the benefits. We expect our findings to provide theoretical guidance for promotions and applications of the anammox process with excellent nitrogen removal capacity and stability.

Insight into the short-term effect of fulvic acid on nitrogen removal performance and N-acylated-L-homoserine lactones (AHLs) release in the anammox system

Fulvic acid (FA) can serve as electron shuttles between bacteria and electron acceptors. It explored the short-term effect of FA dose on nitrogen removal performance and N-acylated-_L-homoserine lactones (AHLs) release change in the anaerobic ammonium oxidation (anammox) system. The results demonstrated that the total inorganic nitrogen removal efficiency increased with the FA dosages from 0.5 mM to 1 mM. FA addition improved anammox bacteria activity, together with extracellular polymeric substances production. FA addition from 0.5 mM to 1 mM stimulated AHLs release in both water and biomass phases, which indicated that the quorum sensing could be improved. These findings revealed that the addition of FA could improve quorum sensing and then enhance nitrogen removal performance.