Understanding the impacts of operation mode sequences on the biological aniline degradation system: Startup phase, pollutants removal rules and microbial response

Harnessing diurnal dynamics: Understanding the influence of light-dark cycle on algal-bacterial symbiotic system under aniline stress

To assess the inherent effects of light-dark cycle on the aniline degradation and nitrogen removal in algal-bacterial symbiotic system, three groups with different photoperiods (0L:12D;6L:6D;12L:0D) were set up. The results revealed that the aniline degradation rate of the three systems all surpassed 99 %, the total nitrogen removal rate of Z2-6L:6D was approximately 36 % higher than Z1-0L:12D eventually, the Z1-0L:12D was restrained by NH4+-N assimilation and nitrification while anoxic denitrification in Z3-12L:0D. The disappearance of microalgae biomass was accompanied by the sharp decreased of polysaccharide in Z1 and longer illumination suppressed the secretion of extracellular polymeric substances, the Z3 yielded slightly superior biomass production despite the double illumination compared with Z2. Moreover, high throughput sequencing analysis illustrated that the microbial community structure in Z2 was more abundant and even than Z3, the TM7a, norank_f__norank_o__Saccharimonadales, Ellin6067 and Scenedesmus proliferated wildly and the photoinhibition to functional genus was effectively alleviated in Z2.

Redundancy and resilience of microbial community under aniline stress during wastewater treatment

Aniline is one of the most toxic and widespread organic pollutants. Although biological treatment is cost-effective and generates minimal secondary pollution, microbial communities are significantly affected by high aniline concentrations, which result in low degradation efficiency. However, a comprehensive understanding of the microbial community response to aniline stress is lacking. Here, we performed a cyclic experiment with aniline concentrations (200, 600, 1200, 600, and 200 mg/L) to investigate the ability of microbial communities to recover their performance after exposure to high aniline concentrations. At aniline concentrations up to 600 mg/L, the bioreactor exhibited high aniline removal efficiency (almost 100 %). Comamonas, Zoogloea, and Delftia played crucial roles in removing aniline and microbial beta diversity changed. Additionally, alpha diversity and network complexity decreased with increasing aniline concentration, but these metrics recovered to their original levels when the aniline concentration was returned to 200 mg/L. Homogeneous and heterogeneous selection dominated microbial community assembly. Therefore, according to the observed variations in community structure and the recovery of keystones after aniline stress, microbial community redundancy and resilience are pivotal for ensuring system stability. Overall, this study provides valuable insights into the redundancy and resilience of microbial communities under aniline stress and establishes a scientific basis for managing and evaluating wastewater treatment plants.

Deciphering the influence of salinity stress on the biological aniline degradation system: Pollutants degradation performance and microbial response

In order to evaluate the impact of salinity gradients on the aniline biodegradation system, six reactors at salinity concentrations (0%-5%) were established. The results presented the salinity except for 5% imposed negligible effects on aniline degradation performance. Nitrification had prominent resistance to salinity (0%-1.5%) while were significantly restrained when salinity increased. The total nitrogen (TN) removal efficiency of Z4 (1.5%) was 20.5% higher than Z1 (0%) during the stable operation phase. Moreover, high throughput sequencing analysis showed that halophilic bacterium, such as Halomonas, Rhodococcus, remained greater survival advantages in high salinity system. The substantial enrichment of Flavobacterium, Dokdonella, Paracoccus observed in Z4 ensured its excellent nitrogen removal performance. The close cooperation among dominant functional bacteria was strengthened when salt content was below 1.5% while exceeding 1.5% led to the collapse of metabolic capacity through integrating the toxicity of aniline and high osmotic pressure.

Unraveling the mechanisms and responses of aniline-degrading biosystem to salinity stress in high temperature condition: Pollutants removal performance and microbial community

To explore the intrinsic influence of different salinity content on aniline biodegradation system in high temperature condition of 35 ± 1 °C, six groups at various salinity concentration (0.0%-5.0%) were applied. The results showed that the salinity exerted insignificant impact on aniline removal performance. The low-level salinity (0.5%-1.5%) stimulated the nitrogen metabolism performance. The G5-2.5% had excellent adaptability to salinity while the nitrogen removal capacity of G6-5.0% was almost lost. Moreover, high throughput sequencing analysis revealed that the g__norank_f__NS9_marine_group, g__Thauera and g__unclassified_f__Rhodobacteraceae proliferated wildly and established positive correlation each other in low salinity systems. The g__SM1A02 occupying the dominant position in G5 ensured the nitrification performance. In contrast, the Rhodococcus possessing great survival advantage in tremendous osmotic pressure competed with most functional genus, triggering the collapse of nitrogen metabolism capacity in G6. This work provided valuable guidance for the aniline wastewater treatment under salinity stress in high temperature condition.

Electrocatalysts for Inorganic and Organic Waste Nitrogen Conversion

Anthropogenic activities have disrupted the natural nitrogen cycle, increasing the level of nitrogen contaminants in water. Nitrogen contaminants are harmful to humans and the environment. This motivates research on advanced and decarbonized treatment technologies that are capable of removing or valorizing nitrogen waste found in water. In this context, the electrocatalytic conversion of inorganic- and organic-based nitrogen compounds has emerged as an important approach that is capable of upconverting waste nitrogen into valuable compounds. This approach differs from state-of-the-art wastewater treatment, which primarily converts inorganic nitrogen to dinitrogen, and organic nitrogen is sent to landfills. Here, we review recent efforts related to electrocatalytic conversion of inorganic- and organic-based nitrogen waste. Specifically, we detail the role that electrocatalyst design (alloys, defects, morphology, and faceting) plays in the promotion of high-activity and high-selectivity electrocatalysts. We also discuss the impact of wastewater constituents. Finally, we discuss the critical product analyses required to ensure that the reported performance is accurate.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m-2 s-1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Evolution of aniline degradation and nitrogen removal performance in electro-enhanced sequence batch reactor under salinity stress: Sludge characteristics and microbial diversity

To explore the influence mechanism of different concentrations of salinity on the electro-enhanced aniline biodegradation system, a control group and experimental groups (0%-NaCl, 0.5%-NaCl, 1.5%-NaCl, 2.5%-NaCl, 3.5%-NaCl) were established. The experimental results showed that the electric field strengthened the denitrification performance, while salinity had little effect on the degradation efficiency of aniline and chemical oxygen demand (COD). The removal rate of TN reached 79.6% and 74.9% in 0.5%-NaCl and 1.5%-NaCl, respectively, which were superior than 0%-NaCl. As salinity increased, the nitrogen removal effect was negatively affected. Microbial diversity analysis indicated that the microbial community structure was uniform in the control group, 0%-NaCl, and 0.5%-NaCl, with the dominant genus OLB8 ensuring the nitrogen removal performance. In contrast, in the 2.5%-NaCl and 3.5%-NaCl experimental groups, the organic degrading bacteria were still active, while nitrifiers and denitrifiers were severely damaged. In conclusion, this study suggested that low concentrations of salinity can improve the decontamination performance of the electro-enhanced aniline biodegradation system, while high concentrations of salinity could lead to the collapse of the decontamination mechanism.

Integrated fixed-film activated sludge systems in continuous-flow and batch mode acclimated from low to high aniline concentrations: Performance, mechanism and metabolic pathways

Integrated fixed-film activated sludge (IFAS) system has considerable advantages in treating aniline wastewater economically and efficiently. However, the response mechanism of IFAS to aniline needs further study. Herein, IFAS in continuous-flow (CF-IFAS) and batch mode (B-IFAS) were set up to investigate it. The removal efficiency of aniline exceeded 99% under different stress intensities. At low stress intensity (aniline ≈ 200 mg/L), the total nitrogen removal efficiency of B-IFAS was approximately 37.76% higher than CF-IFAS. When the stress intensity increased (aniline ≥ 400 mg/L), both were over 82%. CF-IFAS was restrained by denitrification while nitrification in B-IFAS. The legacy effect of perturbation of B-IFAS made microflora quickly reach new stability. The closer interspecific relationship in B-IFAS and more key species: Leucobacter, Rhodococcus, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Ellin6067 and norank_f_NS9_marine_group. Metabolic and Cell growth and death were the most abundant metabolic pathways, resulting both systems the excellent pollutant removal and stability under high stress intensity.

Unraveling the nexus of Cr (Ⅵ), Aniline, and Microbial Ecology on aniline-degrading biosystem: Removal efficiency, sludge type, microbial ecology

In order to explore the stress principle of Cr (Ⅵ) on aniline biodegradation system, a control group and experimental groups with the concentration of Cr (Ⅵ) at 2, 5, 8 mg/L were set up. The results demonstrated that Cr (Ⅵ) had minimal effects on the degradation efficiency of aniline but significantly inhibited nitrogen removal function. When Cr (Ⅵ) concentration was below 5 mg/L, the nitrification performance recovered spontaneously, while denitrification performance was severely impaired. Furthermore, the secretion of extracellular polymeric substances (EPS) and its fluorescence substance concentration were strongly inhibited with increasing Cr (Ⅵ) concentration. High-throughput sequencing revealed that the experimental groups were enriched with Leucobacter and Cr (Ⅵ)-reducing bacteria, but the abundance of nitrifiers and denitrifiers was significantly decreased compared to the control group. Overall, the effects of Cr (Ⅵ) stress at different concentrations on nitrogen removal performance were more significant than those on aniline degradation.

Understanding the impacts of intermittent electro field on the bioelectrochemical aniline degradation system: Performance, microbial community and functional enzyme

On account of the lack of a sustainable electron donor source and the inhibitory effect of aniline on denitrogenation make it tough to achieve simultaneous removal of aniline and nitrogen. Herein, the strategy of adjusting electric field mode was applied to the electro-enhanced sequential batch reactors (E-SBRs: R1 (continuous ON), R2 (2 h-ON/2 h-OFF), R3 (12 h-ON/12 h-OFF), R4 (in the aerobic phase ON), R5 (in the anoxic phase ON)) to treat aniline wastewater. Aniline removal rate reached approximately 99% in the five systems. Decreasing electrical stimulation interval from 12 to 2 h significantly improved the electron utilization efficiency for aniline degradation and nitrogen metabolism. The total nitrogen removal was achieved from 70.31% to 75.63%. Meanwhile, the hydrogenotrophic denitrifiers of Hydrogenophaga, Thauera, and Rhodospirillales, enriched in reactors of minor electrical stimulation interval. Accordingly, the expression of functional enzyme related to electron transport was incremental with the proper electrical stimulation frequency.

Retrospect and prospect of aerobic biodegradation of aniline: Overcome existing bottlenecks and follow future trends

Aniline is a highly bio-toxic industrial product, even at low concentrations, whose related wastewater has been flowing out worldwide on a large scale along with human production. As a green technology, aerobic biological treatment has been widely applied in industrial wastewater and exhibited various characteristics in the field of aniline wastewater. Meanwhile, this technology has shown its potential of synchronous nitrogen removal, but it still consumes energy badly. In the face of resource scarcity, this review comprehensively discusses the existing research in aerobic biodegradation of aniline wastewater to find out the developmental dawn of aerobic biological treatment. Primarily, it put forward the evolution history details of aniline biodegradation from pure culture to mixed culture and then to simultaneous nitrogen removal. On this basis, it presented the existing challenges to further expand the application of aerobic biotechnology, including the confusions of aniline metabolic mechanism, the development of co-degradation of multiple pollutants and the lack of practical experience of bioreactor operation for aniline and nitrogen removal. Additionally, the prospects of the technological shift to meet the needs of an energy-conserving society was described according to existing experiences and feasibility. Including but not limiting to the development of multifunctional bacteria, the reduction of greenhouse gases and the combination of green technologies.

Understanding the effect of residual aluminum salt coagulant on activated sludge in sequencing batch reactor: Performance response, activity restoration and microbial community evolution

To investigate the effect of residual coagulant after coagulation pretreatment on activated sludge system of wastewater treatment plants (WWTPs), comparative evaluation of lab-scale sequencing batch reactors under different poly-aluminum chloride (PAC) concentrations (20 and 55 mg/L), presenting the performance differences of reactors. Results showed that the PAC concentration of 20 mg/L slightly enhanced the average removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN), up to 93.43% and 72.52%. Whereas, an inhibition effect was exerted at the PAC concentration of 55 mg/L, the average removal efficiencies decreased to 88.56% and 57.80% respectively. Similarly, the residual aluminum salts showed a concentration effect of low promotion and high inhibition on sludge activity index. The content of specific oxygen utilization rate (SOUR) and dehydrogenase (DHA) sharply decreased by 30.17% and 53.56% under the high PAC concentration of 55 mg/L. Activity recovery phase showed that the suppression of aluminum salt coagulant on biological system was reversible. High-throughput sequencing presented that the relative abundance of microbes showed obvious variations at different PAC concentrations, and certain bacteria in Chloroflexi and Bacteroidota exhibited better adaptability to the high PAC concentration environment. Nevertheless, the antagonism action between denitrifying genera and other genera as well as the downregulation of functional enzymes regarding nitrogen metabolism gave rise to the deterioration of denitrification under the high PAC concentration of 55 mg/L. This study revealed the influence mechanism of residual aluminum salt coagulant on activated sludge system, providing strategies for efficient decontamination and long-term stable operation of biological system in wastewater treatment plant under the condition of adding PAC.

Exploring the impact of intensity and duration of Cu (II) depression on aniline-degrading biosystem: Performance, sludge activity and microbial diversity

To evaluate the ecological risk of aniline wastewater biodegradation, the aniline wastewater (200 mg/L) was treated in this work under the stress of Cu (II) at 3, 6 and 10 mg/L, respectively. The slight fluctuation of aniline-degrading performance and the significant inhibition of nitrogen removal was caused by the Cu (II) stress at below 6 mg/L. Meanwhile, the tolerance of nitrifying performance to Cu (II) was higher than denitrifying. The collapse of biosystem was caused by the Cu (II) stress at 10 mg/L and the decontamination function was disabled within 8 days. The activity and stability of sludge declined under the increase of Cu (II) content. Microbial diversity results demonstrated that the genera with heavy-metal tolerance represented by Zoogloea and Azospira significantly dominated under the continuously Cu (II) stress. Whereas, the biosystem with these dominant genera did not achieve the comparable aniline and nitrogen removal performance as the control group.

Simultaneous removal of aromatic pollutants and nitrate at high concentrations by hypersaline denitrification:Long-term continuous experiments investigation

If we can use toxic aromatic compounds as supplementary carbon source, the simultaneous removal of nitrate (NO₃^-) and aromatic compounds may be achieved at much lower chemical costs. This study uses the expanded granular sludge bed (EGSB) reactors to investigate the hypersaline (> 3%) denitrification performance, the removal of aromatic compounds, i.e., aniline, phenol, and their mixture, and the mechanisms involved in. The four reactors exhibit high removal efficiency of NO₃^- (> 92.8%) and aromatic compounds (> 73.9%) at 0-1200 mg/L of aromatic compounds. The formation of toxic intermediates such as catechol and azo dyes is revealed by gas chromatography mass spectrometry (GC-MS) with and without N,O-Bis(trimethylsilyl) trifluoroacetamide (BSTFA) derivation, and their toxic effects lead to the lower cell survival ratios after exposing to phenol (64.2% ∼ 68.9%) than to aniline and mixture (72.7% ∼ 78.0%). The stable performance is associated with the more secretion of extracellular polymeric substances (EPS) and the adsorption of pollutants on EPS, and this was indicated from the higher fluorescence intensity in three-dimensional excitation-emission matrix (3D-EEM). Moreover, the Halomonas and Azoarcus show high abundance and play important roles in the removal of both NO₃^- and aromatic compounds. Besides, quantitative real time PCR (RT-qPCR) results demonstrate the key role of highly abundant nosZ and nirS genes in denitrification. The toxic organics in industrial wastewaters are potentially feasible carbon sources for denitrification even under high-salinity stress.

High concentration powder carrier bio-fluidized bed process: A new perspective for domestic wastewater treatment

The nitrogen removal mechanism of the high concentration powder carrier bio-fluidized bed (HPB) process was investigated with actual domestic wastewater. The micron-size (10-70 μm) powder carriers were diatomite and Fe-C. Results showed diatomite enriched the relative abundances of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, accordingly increasing the rate of nitrification. Even a 100% increase of genes associated with the ammonia oxidation was achieved. Fe-C enhanced the rate of substrate utilization mainly by increasing the activity of the electron transfer system. Hydrocyclone separator, as a key device of HPB, was able to recover the carriers with high efficiency (recovery efficiency of 72.66 ─ 82.50% after 75 days), thus, indirectly improving the functionality of the carriers. Furthermore, it could renew the surface of microbial aggregations, consequently improving the adsorption capacity to substrates. HPB could provide the feasibility of shortening the hydraulic retention time and expanding the capacity of wastewater treatment plants.

Transfer of functional microorganism: Regulation of N-acyl-homoserine lactones on the microbial community in aniline-degrading sequencing batch biofilm reactor

Due to the inhibition of nitrification from aniline toxicity, exogenous N-acyl-homoserine lactones (AHLs) addition was attempted to enhance nitrogen removal in this work. Two sequencing batch biofilm reactors (SBBRs): S1 (the control) and S2 (C6-HSL and 3-oxo-C8-HSL dosing) were used to treat aniline wastewater. The NH₄⁺-N and TN removal rates of S2 were 42.50% and 26.99% higher than S1 in the aerobic phase, respectively. It revealed the nitrogen removal performance of S2 much better than S1. High-throughput sequencing results indicated that many nitrifiers and denitrifiers of S2, such as Nitrosomonas and Thauera, transferred from sludge to biofilm significantly and built closer relationships each other. Overall, main nitrogen removal was contributed by biofilm rather than sludge with the regulation of AHLs. A mild and collaborative environment of biofilms for microorganisms enhanced nitrogen removal. The work provided a new idea for reconciling the contradiction between nitrification and denitrification in aniline wastewater treatment.

An attempt to stimulate aniline degrading bioreactor by exogenous auto-inducer: Decontamination performance, sludge characteristics, and microbial community structure response

To break the contradiction between aniline and nitrogen metabolism in activated sludge reactor by influencing microbial interspecific communication, Auto-inducer C6-HSL and 3-oxo-C8-HSL were selected in this study to interfere with aniline degradation system. The two Auto-inducers enhanced the aniline degradation rate and ammonia removal efficiency of the systems, especially C6-HSL. Meanwhile, the main ammonia removal way was assimilation. Exogenous Auto-inducer effectively stabilized the sludge structure and activity from the destruction of aniline, and promoted EPS secretion. Microbial diversity analysis showed that most of functional microflora of seed sludge gradually deactivated with the operation of the reactor, while Rhodococcus, Leucobacter, g_norank_f_Saprospiraceae proliferated wildly under the action of Auto-inducer. Additionally, the interspecific relationship also demonstrated a different trend. Exogenous Auto-inducer was proved to exert positive effects on aniline degradation system to a certain extent, providing new insights in the field of aniline wastewater bio-degradation.

Control of aeration time in the aniline degrading-bioreactor with the analysis of metagenomic: Aniline degradation and nitrogen metabolism

The strategy of adjusting aeration time (5 h/6 h/7 h) was applied to the sequential batch reactors to optimize the treatment of aniline wastewater (600 mg/L) conveniently and economically. Three reactors degraded aniline effectively. The nitrogen removal ability of system with 6 h aeration time was better, performing the similar denitrification property as 5 h and nitrification performance as 7 h. Meanwhile, longer aeration time potentially damaged the sludge structure. The metagenomic analysis explained the micro-mechanism for the better performance of the system with 6 h aeration time. Appropriate aeration time was conducive to the enrichment of synergistic microflora, including aniline degrading-bacteria, heterotrophic nitrifiers and denitrifiers. Then, the tilt of environmental resources to these floras in the system was beneficial to the maximum value utilization of living substrates. Accordingly, these bacteria were more closely related to genes, resulting in higher expression of functional genes in the system.