Effects of dissolved oxygen concentrations on a bioaugmented sequencing batch rector treating aniline-laden wastewater: Reactor performance, microbial dynamics and functional genes

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.

Dissolved oxygen drives heterotrophic microorganism succession to regulate low carbon source wastewater treatment enhanced by slurry

The limited availability of carbon sources in low carbon source wastewater has always hindered nitrogen removal efficiency. The residual slurry liquid after anaerobic digestion has the potential to be used as a carbon source. This study investigated the optimal parameters of dissolved oxygen (DO) for enhancing the treatment of low carbon source wastewater using slurry, and revealed the characteristics of carbon metabolism gene enrichment and carbon fixation potential driven by DO. The results indicated that treating wastewater under high DO concentrations (3-4 mg/L) conditions could meet the emission standards set by wastewater treatment plants in China. However, the lower-cost DO concentration of 3 mg/L is considered a more cost-effective parameter, effectively removing 85.68% of chemical oxygen demand and 91.56% of total nitrogen. Mechanistic analysis suggested that reducing DO concentration increased the diversity of microbial communities. Regulating DO concentration reshaped the co-metabolic network of microorganisms with different DO sensitivities by influencing Hydrogenophaga and Chlorobium. This ultimately led to the reconstruction of heterotrophic microbial communities dominated by Sphaerotilus and Acidovorax under high DO conditions, and heterotrophic-autotrophic co-enriched microbial communities dominated by Chlorobium under low DO conditions (1-2 mg/L). Additionally, under high DO conditions, high microbial mass transfer efficiency and the enrichment of functional genes were crucial for achieving high nitrogen removal performance. Further, the microbial carbon fixation potential was relatively high under the DO 3 mg/L condition, helping to reduce the consumption of additional carbon sources. This study provided innovative ideas for the sustainable and low-carbon development of wastewater treatment technology.

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.

Treatment of Aniline Wastewater by Membrane Distillation and Crystallization

Aniline is a highly toxic organic pollutant with "carcinogenic, teratogenic and mutagenesis" characteristics. In the present paper, a membrane distillation and crystallization (MDCr) process was proposed to achieve zero liquid discharge (ZLD) of aniline wastewater. Hydrophobic polyvinylidene fluoride (PVDF) membranes were used in the membrane distillation (MD) process. The effects of the feed solution temperature and flow rate on the MD performance were investigated. The results showed that the flux of the MD process was up to 20 L·m^-2·h^-1 and the salt rejection was above 99% under the feeding condition of 60 °C and 500 mL/min. The effect of Fenton oxidation pretreatment on the removal rate of aniline in aniline wastewater was also investigated, and the possibility of realizing the ZLD of aniline wastewater in the MDCr process was verified.

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.

Micro-aeration assisted with electrogenic respiration enhanced the microbial catabolism and ammonification of aromatic amines in industrial wastewater

Improvement of refractory nitrogen-containing organics biodegradation is crucial to meet discharged nitrogen standards and guarantee aquatic ecology safety. Although electrostimulation accelerates organic nitrogen pollutants amination, it remains uncertain how to strengthen ammonification of the amination products. This study demonstrated that ammonification was remarkably facilitated under micro-aerobic conditions through the degradation of aniline, an amination product of nitrobenzene, using an electrogenic respiration system. The microbial catabolism and ammonification were significantly enhanced by exposing the bioanode to air. Based on 16S rRNA gene sequencing and GeoChip analysis, our results indicated that aerobic aniline degraders and electroactive bacteria were enriched in suspension and inner electrode biofilm, respectively. The suspension community had a significantly higher relative abundance of catechol dioxygenase genes contributing to aerobic aniline biodegradation and reactive oxygen species (ROS) scavenger genes to protect from oxygen toxicity. The inner biofilm community contained obviously higher cytochrome c genes responsible for extracellular electron transfer. Additionally, network analysis indicated the aniline degraders were positively associated with electroactive bacteria and could be the potential hosts for genes encoding for dioxygenase and cytochrome, respectively. This study provides a feasible strategy to enhance nitrogen-containing organics ammonification and offers new insights into the microbial interaction mechanisms of micro-aeration assisted with electrogenic respiration.

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.

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.

Temperature mediated the balance between stochastic and deterministic processes and reoccurrence of microbial community during treating aniline wastewater

Seasonal temperature changes significantly affect microbial community diversity, composition, and performance in wastewater treatment plants. However, the community assembly mechanisms under seasonal temperature variations remain unclear. Here, we carried out temperature cycling experiments (30 °C, 35 °C, 37 °C, 40 °C, 42 °C, 45 °C, 40 °C, and 30 °C) to investigate how temperature impacts microbial performance and co-occurrence network and how assembly processes determine the structure and function of microbial communities during treating aniline wastewater. During the 195-day operation, the system achieved an efficient and stable aniline removal of 99%. Interestingly, α-diversity and network complexity were negatively correlated with temperature but could be recovered when the temperature was returned to 30 °C. The results showed that functional redundancy was probably responsible for the excellent microbial performance during the whole process. Null model analyses presented that deterministic process dominated the community when the temperature was 30 °C, and stochasticity dominated the assembly process when the temperature was over 30 °C. Overall, the balance between stochastic and deterministic processes in the treatment of aniline wastewater mediated the reoccurrence of microbial community and co-occurrence network at different temperatures. This study provides new insights into microbial community reoccurrence under seasonal temperature changes and a theoretical basis for regulating microbial communities in wastewater treatment plants.

Lysozyme regulates the extracellular polymer of activated sludge and promotes the formation of electroactive biofilm

The formation of electroactive biofilm from activated sludge on electrode surface is a key step to construct a bio-electrochemical system, yet it is greatly limited by the poor affinity between the bacteria and the electrode interface. Herein, we report a new method to promote the formation of electroactive biofilm by regulating the extracellular polymeric substance (EPS) content in activated sludge with lysozyme. The investigation of the effect of lysozyme treatment on the content of extracellular polymers and the biofilm formation of electroactive bacteria suggests that lysozyme can improve the permeability of the positive bacterial cell membrane and thus increase the EPS content in the activated sludge. The characterizations of electrochemical activity, surface morphology and community structure of the anode biofilm indicate that increasing EPS content promotes the adhesion of the mixed bacteria in the activated sludge on the electrode and results in denser biofilms with better conductivities. The microbial fuel cell (MFC) inoculated with the sludge of high EPS content exhibits the power density up to 2.195 W/m², much higher than that inoculated with the untreated sludge (1.545 W/m²). The strategy of adjusting EPS content in activated sludge with a biological enzyme can effectively enhance the ability of the bacterial community to form biofilms and exhibits great application potentials in the construction of high efficiency bio-electrochemical systems.

Effect of aniline and antimony on anaerobic-anoxic-oxic system with novel amidoxime-modified polyacrylonitrile adsorbent for wastewater treatment

There has been increasing concern over the mixed discharge of municipal-textile composite wastewater, which remains challenging for typical wastewater treatment plant (WWTP) using anaerobic-anoxic-oxic process (AAO). Highly-toxic aniline and antimony, typical co-contaminants in textile wastewater, usually lead to increased chemical oxygen demand (COD) in influent and deteriorated effluent quality. Amidoxime-modified polyacrylonitrile (amPAN) adsorbent was prepared and added to adsorb antimony and facilitate substrate removal. With amPAN dosage at 6.0 g L^-1 in oxic bioreactor, 64.2 ± 5.6% of antimony was removed from influent. Extracellular polymeric substance release was simultaneously changed with residual antimony concentration. Meanwhile, amPAN promoted the proliferation of Proteobacteria, Bacteroidetes and Epsilonbacteraeota serving as microorganism carrier. As a result, removal efficiencies of COD (94.4 ± 0.6%), ammonium (NH₄⁺-N, 92.6 ± 3.3%), total nitrogen (TN, 76.4 ± 6.3%) and total phosphorus (TP, 93.4 ± 2.1%) were enhanced to meet Class 1A discharge standard in China. These results indicate that AAO with amPAN is promising for municipal-textile composite wastewater treatment.

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.

Metagenomic insights into the effects of various biocarriers on moving bed biofilm reactors for municipal wastewater treatment

Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH₄⁺-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to stronger simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.

Application oriented bioaugmentation processes: Mechanism, performance improvement and scale-up

Bioaugmentation is an optimization method with great potential to improve the treatment effect by introducing specific strains into the biological treatment system. In this study, a comprehensive review of the mechanism of bioaugmentation from the aspect of microbial community structure, the optimization methods facilitating application as well as feasible approaches of scale-up application has been provided. The different contribution of indigenous and exogenous strains was critically analyzed, the relationship between microbial community variation and system performance was clarified. Operation regulation and immobilization technologies are effective methods to deal with the possible failure of bioaugmentation. The gradual expansion from lab-scale, pilot scale to full-scale, the transformation and upgrading of wastewater treatment plants through the combination of direct dosing and biofilm, and the application of side-stream reactors are feasible ways to realize the full-scale application. The future challenges and prospects in this field were also proposed.

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.

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

Comparative evaluation of SBRs under different modes (AX/O, AN/AX/O, AN/O/AX, O/AX) with same aniline wastewater arrangements, presenting the startup and performance differences of reactors. The results revealed that the four systems realized the efficient aniline and NH₄⁺-N removal on the basis of sufficient aerobic time. Anaerobic aniline degradation was also achieved in the first three reactors after acclimation. The denitrification efficiency was the highest in O/AX reactor and the lowest in AN/O/AX due to mode sequence setup. Pollutants variations in the typical cycles experimental data combined with microbial diversity analysis were highlighted that aerobic denitrification contributed the most under O/AX mode, while the other three modes relied on anoxic denitrification. Meanwhile, low nitrifiers and aerobic denitrifiers abundance might be another reason for the poor denitrification of AN/O/AX mode. It was inferred that denitrification was most susceptible to operation mode sequences.

Response of wastewater treatment performance, microbial composition and functional genes to different C/N ratios and carrier types in MBBR inoculated with heterotrophic nitrification-aerobic denitrification bacteria

To operate the moving bed biofilm reactor inoculated with HN-AD bacteria (B-MBBR) instead of activated sludge for livestock and poultry breeding wastewater (LPBW) disposal in most efficient manner, nitrogen removal (NR) efficiency and microbial composition of two MBBRs with different carrier types under various C/N ratios were explored. Results indicated that the performance on NR greatly various in different carrier types under various C/N ratios. Attributing to the bacterial protection provided by the porous structure of polyvinyl alcohol (PVA) gel, MBBR using PVA gel as the carrier exhibited a more stable NR performance (range from 78.05% to 83.76%) versus that using Kaldnes (K1) as the carrier (range from 78.05% to 83.76%). Besides, microbial analysis indicated that MBBR with PVA gel as the carrier is conducive to the growth of oligotrophic and HN-AD bacteria (Paracoccus and Acinetobacter), and the highest relative abundance was 16.37% at C/N ratio of 6.

A metagenomic view of how different carbon sources enhance the aniline and simultaneous nitrogen removal capacities in the aniline degradation system

To cross nitrogen removal barrier, carbon sources (sodium succinate (Z1), sodium acetate (Z2) and glucose (Z3)) were applied in aniline degradation reactor to enrich heterotrophic nitrifiers and denitrifiers. The aniline was degraded almost completely and the nitrogen removal performance was improved in three systems. The total nitrogen (TN) removal efficiency of Z2 was the highest. The dominant bacteria were phylum Proteobacteria, class BetaProteobacteria, and genus Thauera (Z1, Z3), Leptothrix (Z2). Different aniline degrading bacteria, heterotrophic nitrifiers and denitrifiers were enriched, and Z2 had more high-abundance communities. Three systems followed the meta-cleavage pathway for the aniline degradation according to the genes annotation. Particularly, the contribution of each genus to nitrogen metabolism and aromatic compounds degradation in the Z2 was more evenly distributed, rather than relying mainly on the contribution of Thauera in Z1 and Z3 so that more functional genes related nitrogen metabolism and aniline degradation were more abundant in Z2.

A novel inhibition mechanism of aniline on nitrification: Aniline degradation competes dissolved oxygen with nitrification

Aniline is a toxic aromatic amine and an inhibitor of nitrification. This study explored the inhibition effect and underlying mechanism. After sludge acclimation, 540 mg/L aniline was removed in 24 h and almost all ammonia released from aniline was oxidized to nitrate. However, nitrification never started until no aniline left. The cellular adenosine triphosphate (cATP) concentration of acclimated sludge reduced only by 2% after aniline exposure. Neither transmembrane transport of ammonia nor ammonia monooxygenase (AMO) activity was affected by aniline. Growing initial aniline concentration did not deteriorate the specific nitrification rate (NR). These all revealed that the toxicity of aniline only play a minor role in inhibition. Competition for dissolved oxygen (DO) was proposed to be another possible inhibition mechanism. The oxygen affinity constant (Ks) of aniline degraders and ammonia-oxidizing bacteria (AOB) was calculated to be 0.894 mg/L and 1.274 mg/L respectively, suggesting the former possessed much stronger oxygen affinity (P < 0.01). With aniline and ammonium as initial substrates, increasing aeration intensity advanced nitrification and increased the NR. Max NR of 0.63 mgN/(gMLSS·h) was achieved at the highest aeration intensity of 1000 mL/min. This study brings one step closer to better removal of aniline and derived nitrogen pollutants.

Microbial community and function evaluation in the start-up period of bioaugmented SBR fed with aniline wastewater

An enhanced sequencing batch reactor (SBR) system was developed to treat synthetic wastewater rich in 600 mg/L aniline. The aniline degradation efficiency was almost 100%, and the total nitrogen (TN) removal rate was more than 50%. Metagenomics technology revealed the community structure, functional genes and metabolic mechanism during the start-up of the enhanced reactor. Sequencing results showed that Proteobacteria, Bacteroidetes, Chloroflexi and Actinobacteria were dominant phylum. The proportion of degradation of aromatic compounds function increased gradually, but the proportion of nitrogen metabolism function changed little. Functional genes involved in aniline degradation including benA-xylX and dmpB/xylE were detected. The functional genes of nitrogen metabolism were involved in complete nitrification, traditional denitrification, assimilation nitrate reduction and dissimilation nitrate reduction. The functional contribution analysis and network analysis showed that the cooperation and competition of Thauera, Delftia, Diaphorobacter, Micavibrio and Azoarcus ensured the effective removal of aniline and nitrogen.

Preparation of PP-g-(AA-MAH) Fibers Using Suspension Grafting and Melt-Blown Spinning and its Adsorption for Aniline

This paper uses polypropylene (PP) as the matrix and acrylic acid (AA) and maleic anhydride (MAH) as functional monomers to prepare PP-g-(AA-MAH) fibers by suspension grafting and melt-blown spinning technology that are easy to industrially scale-up. The fibers can be used to adsorb aniline. Results showed that the grafting ratio reached the maximum of 12.47%. The corresponding optimal conditions were grafting time of 3 h, AA: MAH = 0.75, total monomer content of 55%, benzoyl peroxide 1.4%, xylene concentration of 6 mL/g PP, and deionized water content of 8 mL/g PP. Owing to its good fluidity and thermal stability, the product of suspension grafting can be used for melt-blown spinning. Infrared spectroscopic and nuclear magnetic resonance spectroscopic analyses indicated that AA and MAH were successfully grafted onto PP fibers. After grafting, the hydrophilicity of PP-g-(AA-MAH) fiber increased. Therefore, it had higher absorptivity for aniline and the adsorption capacity could reach 42.2 mg/g at 45 min and pH = 7. Moreover, the PP-g-(AA-MAH) fibers showed good regeneration performance.