Enhanced azo dye Reactive Red 2 degradation in anaerobic reactors by dosing conductive material of ferroferric oxide

Carbon dots coupled bioelectrocatalysis for enhanced methane productivity in anaerobic co-digestion of sewage sludge and food waste: Focusing on enhancement mechanisms and microbial community succession

The limited electron transfer efficiency and poor stability of microorganisms are challenges in traditional bioelectrocatalytic food waste treatment. Herein, carbon dots (CDs) possess excellent biocompatibility and electrochemical properties. When combined with bioelectrocatalysis, CDs can regulate microbial community structure and enhance electron exchange capacity. The results demonstrated that compared with the control group (28.1 mL/g-VS/d), the CDs at a dosage of 0.50 g/g VS could increase CH4 production by a factor of 7.8. CDs not only increase CH4 production but also improve the digestate's stability, making it suitable for use as bio-fertilizer. Moreover, a significantly high Methanobacterium richness (11.6 %) signified an intensified utilization of hydrogen and formic acid pathways in CH4 production. Particularly, the biocompatible CDs could be absorbed by microorganisms, forming an environmental network that was more conducive to electron transfer with unabsorbed CDs and accelerating interspecies electron transfer. This work provides mechanistic insights into boosting CH4 production in AD.

Synchronous reinforcement azo dyes decolorization and anaerobic granular sludge stability by Fe, N co-modified biochar: Enhancement based on extracellular electron transfer

Anaerobic digestion (AD) treatment of azo dyes wastewater often suffers from low decolorization efficiency and poor stability of anaerobic granular sludge (AnGS). In this study, iron and nitrogen co-modified biochar (FNC) was synthesized based on the secondary calcination method, and the feasibility of this material for enhanced AD treatment of azo dye wastewater and its mechanism were investigated. FNC not only formed richer conducting functional groups, but also generated Fe2+/Fe3+ redox pairs. The decolorization efficiency of Congo red and AD properties (e.g., methane production) were enhanced by FNC. After adding FNC, the content of extracellular polymeric substances (EPS) and the ratio of proteins remained stable under the impact of Congo red, which greatly protected the internal microbial community. This was mainly contributed to the excellent electrochemical properties of FNC, which strengthened the microbial extracellular electron transfer and realized the coupled mechanism of action: On the one hand, an electron transfer bridge between decolorizing bacteria and dyes was constructed to achieve rapid decolorization of azo dyes and mitigate the impact on methanogenic bacteria; On the other hand, the stability of AnGS was enhanced based on enhanced extracellular polymeric substances secretion, microbial community and direct interspecies electron transfer (DIET) process. This study provides a new idea for enhanced AD treatment of azo dyes wastewater.

Influence of perfluorooctanoic acid on alkaline anaerobic fermentation of waste activated sludge: Perspective from volatile fatty acids production and sludge reduction

Alkaline anaerobic fermentation is an effective approach for resource utilization and reduction of waste activated sludge (WAS). Perfluorooctanoic acid (PFOA) is widespread in WAS, however, its potential impact on alkaline anaerobic fermentation of WAS remains largely unknown. Hence, this study focused on investigating the influence of PFOA on volatile fatty acids (VFAs) production and sludge reduction during alkaline anaerobic fermentation (pH = 10 ± 0.1), as well as the critical mechanisms. Results demonstrated that low PFOA concentration (5 mg/kg-TS) raised VFAs yield to 109.37%, while high levels of PFOA (25 and 50 mg/kg-TS) remarkably decreased VFAs production to 89.55% and 80.44% of the control. Mechanism exploration revealed that PFOA facilitated the solubilization process, and low PFOA level enhanced the accumulation of VFAs via increased bioavailable substrates and the activities of enzymes and microorganisms. On the contrary, high levels of PFOA were substantial biotoxicity, inducing excessive ROS production, causing oxidative damage, and reducing enzyme activity and functional microbial abundance, thereby decreasing VFAs production. Additionally, further analysis of sludge physicochemical properties confirmed that the effect of PFOA on WAS reduction exhibited the same trend as VFAs production. This work provides a basis for PFOA environmental risk assessment and WAS resource utilization.

The enhancement effect of n-Fe3O4 on methyl orange reduction by nitrogen-fixing bacteria consortium

Although the anaerobic reduction of azo dyes is ecofriendly, high ammonia consumption remains a significant challenge. This work enriched a mixed nitrogen-fixing bacteria consortium (NFBC) using n-Fe3O4 to promote the anaerobic reduction of methyl orange (MO) without exogenous nitrogen. The enriched NFBC was dominated by Klebsiella (80.77 %) and Clostridium (17.16 %), and achieved a 92.7 % reduction of MO with an initial concentration of 25 mg·L-1. Compared with the control, the consortium increased the reduction efficiency of MO, cytochrome c content, and electron transport system (ETS) activity by 11.86 %, 89.86 %, and 58.49 %, respectively. When using 2.5 g·L-1 n-Fe3O4, the extracellular polymeric substances (EPS) of NFBC were present in a concentration of 85.35 mg·g-1. The specific reduction rates of MO by NFBC were 2.26 and 3.30 times faster than those of Fe(II) and Fe(III), respectively, while the enrichment factor of the ribosome pathway in NFBC exceeded 0.75. Transcriptome, carbon consumption, and EPS analyses suggested that n-Fe3O4 stimulated carbon metabolism and secreted protein synthesized by the mixed culture. The latter occurred due to the increased activity of consortium and the content of redox substances. These findings demonstrate that n-Fe3O4 promoted the efficiency of mixed nitrogen-fixing bacteria for removing azo dyes from wastewater. This innovative approach highlights the potential of integrating nanomaterials with biological systems to effectively address complex pollution challenges.

Azo dye anaerobic treatment in anaerobic reactors coupled with PVA/Fe/Starch gel bead

A novel bio-carrier, PVA/Fe/starch gel bead, was fabricated and developed to enhance the anaerobic treatment performance of synthetic azo dye-containing wastewater. PVA-gel beads with 5 % magnetite and 0.5 % starch were optimal for physical strength and treatment performance. A pair of 2 L-up-flow anaerobic sludge blankets (UASB), one with the bead (UB) and another without (U) as a controller, operated continuously at 30 °C and an HRT of 11-24 h for 302 days. UB showed better performance than U in most phases, especially with influent dye of 200 mg·L-1, suggesting a greater tolerance to dye toxicity of UB than U. Microbial analysis revealed that the PVA/Fe/starch gel beads successfully captured the dye degrader Clostridium. Diversity indices indicated that PVA/Fe/Starch gel beads effectively support microbial diversity and resilience under varying dye concentrations. Overall, these findings demonstrate the potential of PVA/Fe/Starch gel beads to improve the stability and efficiency of the dye treatment system.

Harnessing iron materials for enhanced decolorization of azo dye wastewater: A comprehensive review

Highly colored azo dye-contaminated wastewater poses significant environmental threats and requires effective treatment before discharge. The anaerobic azo dye treatment method is a cost-effective and environmentally friendly solution, while its time-consuming and inefficient processes present substantial challenges for industrial scaling. Thus, the use of iron materials presents a promising alternative. Laboratory studies have demonstrated that systems coupled with iron materials enhance the decolorization efficiency and reduce the processing time. To fully realize the potential of iron materials for anaerobic azo dye treatment, a comprehensive synthesis and evaluation based on individual-related research studies, which have not been conducted to date, are necessary. This review provides, for the first time, an extensive and detailed overview of the utilization of iron materials for azo dye treatment, with a focus on decolorization. It assesses the treatment potential, analyzes the influencing factors and their impacts, and proposes metabolic pathways to enhance anaerobic dye treatment using iron materials. The physicochemical characteristics of iron materials are also discussed to elucidate the mechanisms behind the enhanced bioreduction of azo dyes. This study further addresses the current obstacles and outlines future prospects for industrial-scale application of iron-coupled treatment systems.

Promotion of anaerobic biodegradation of azo dye RR2 by different biowaste-derived biochars: Characteristics and mechanism study by machine learning

The addition of biochar resulted in a 31.5 % to 44.6 % increase in decolorization efficiency and favorable decolorization stability. Biochar promoted extracellular polymeric substances (EPS) secretion, especially humic-like and fulvic-like substances. Additionally, biochar enhanced the electron transfer capacity of anaerobic sludge and facilitated surface attachment of microbial cells. 16S rRNA gene sequencing analysis indicated that biochar reduced microbial species diversity, enriching fermentative bacteria such as Trichococcus. Finally, a machine learning model was employed to establish a predictive model for biochar characteristics and decolorization efficiency. Biochar electrical conductivity, H/C ratio, and O/C ratio had the most significant impact on RR2 anaerobic decolorization efficiency. According to the results, the possible mechanism of RR2 anaerobic decolorization enhanced by different types of biochar was proposed.

When aerobic granular sludge faces emerging contaminants: A review

The evolution of emerging contaminants (ECs) has caused greater requirements and challenges to the current biological wastewater treatment technology. As one of the most promising biological treatment technologies, the aerobic granular sludge (AGS) process also faces the challenge of ECs. This study summarizes the recent progress and characteristics of several representative ECs (persistent organic pollutants, endocrine disrupting chemicals, antibiotics, and microplastics) in AGS systems that have garnered widespread attention. Additionally, the biodegradation and adsorption mechanisms of ECs were discussed, and the interactions between various ECs and AGS was elucidated. The importance of extracellular polymeric substances for the stabilization of AGS and the removal of ECs is also discussed. Knowledge gaps and future research directions that may enable the practical application of AGS are highlighted. Overall, AGS processes show great application potential and this review provides guidance for the future implementation of AGS technology as well as elucidating the mechanism of its interaction with ECs.

Mathematical modeling for operative improvement of the decoloration of Acid Red 27 by a novel microbial consortium of Trametes versicolor and Pseudomonas putida: A multivariate sensitivity analysis

In this work, it is presented a first approach of a mathematical and kinetic analysis for improving the decoloration and further degradation process of an azo dye named acid red 27 (AR27), by means of a novel microbial consortium formed by the fungus Trametes versicolor and the bacterium Pseudomonas putida. A multivariate analysis was carried out by simulating scenarios with different operating conditions and developing a specific mathematical model based on kinetic equations describing all stages of the biological process, from microbial growth and substrate consuming to decoloration and degradation of intermediate compounds. Additionally, a sensitivity analysis was performed by using a factorial design and the Response Surface Method (RSM), for determining individual and interactive effects of variables like, initial glucose concentration, initial dye concentration and the moment in time for bacterial inoculation, on response variables assessed in terms of the minimum time for: full decoloration of AR27 (R1 = 2.375 days); maximum production of aromatic metabolites (R2 = 1.575 days); and full depletion of aromatic metabolites (R3 = 12.9 days). Using RSM the following conditions improved the biological process, being: an initial glucose concentration of 20 g l-1, an initial AR27 concentration of 0.2 g l-1 and an inoculation moment in time of P. putida at day 1. The mathematical model is a feasible tool for describing AR27 decoloration and its further degradation by the microbial consortium of T. versicolor and P. putida, this model will also work as a mathematical basis for designing novel bio-reaction systems than can operate with the same principle of the described consortium.

Impact of salinity on anaerobic ceramic membrane bioreactor for textile wastewater treatment: Process performance, membrane fouling and machine learning models

Anaerobic membrane bioreactor (AnMBR) shows great potential for textile wastewater treatment, but high salinity in the influent may undermine its performance. This study evaluated the impact of salinity on the treatment performance of an upflow anaerobic sludge blanket (UASB) configured AnMBR using a flat sheet ceramic membrane. The salinity was stepwise increased (0, 5, 10 and 20 g/L) in four phases of the AnMBR operation. Results indicated that increased salinity jeopardized the COD removal efficiency of AnMBR from 92% to 73%, but had a marginal effect on dye removal efficacy (90-96%). Low salinity (5 g/L) boosted the biogas production whilst high salinity (>10 g/L) had a negative impact. Additionally, the increase of salinity resulted in the soluble microbial production (SMP) concentration soar and membrane fouling rate increase, peaking at a salinity of 10 g/L (Phase III) and recovering back to a lower level at a salinity of 20 g/L (Phase IV). This indicated a transition occurrence at a salinity of 10 g/L (Phase III). The microbial diversity analyses further suggested a transition from salinity-sensitive microbes (Aminiphilus, Caldatribacterium, Mesotoga, Methanobrevibacter, Methanobacterium, Methanosaeta) to salinity-tolerant microbes (Longilinea, Ignavibacterium, Rhodovarius, Bosea and Flexilinea). This transition can be associated with the increase SMP concentration and more severe membrane fouling in Phase III, which were mitigated after a new equilibrium was reached when the microbial consortium acclimatized to the high salinity. Finally, a machine learning model of the Adaboost algorithm was established to predict COD removal under different salinities. Importantly, this study revealed that AnMBR process performance and membrane operation can be maintained for high salinity textile wastewater treatment with a halophilic microbial community growth under high-salinity selection pressure.

Stimulating anaerobic digestion to degrade recalcitrant organic pollutants: Potential role of conductive materials-led direct interspecies electron transfer

This review aims to provide a comprehensive understanding of the potential of CMs-dominated DIET in the degradation of recalcitrant organic pollutants in AD. The review covers the mechanisms and efficiencies of recalcitrant organic pollutant degradation by CMs-dominated DIET, the comparison of degradation pathways between DIET and chemical treatment, recent insights on DIET-enhanced degradation, and the evaluation of the potential and future development of CMs-dominated DIET. The review emphasizes the importance of coupled syntrophic microorganisms, electron flux, and physicochemical properties of CMs in enhancing the degradation performance of AD. Additionally, it highlights the advantages of DIET-led syntrophic metabolism over traditional oxidation technologies in terms of environmental friendliness and efficiency. Finally, the review acknowledges the potential risks associated with introducing CMs into AD systems and provides guidance for waste treatment and energy recovery.

Direct interspecies electron transfer enables anaerobic oxidation of sulfide to elemental sulfur coupled with CO2-reducing methanogenesis

Electric syntrophy between fatty acid oxidizers and methanogens through direct interspecies electron transfer (DIET) is essential for balancing acidogenesis and methanogenesis in anaerobic digestion. Promoting DIET using electrically conductive additives proved effective in enhancing methanogenesis; however, its possibility to affect other microbial redox reactions in methanogenic systems has been little studied. This study provides the first confirmation of the electro-syntrophic coupling of sulfide oxidation to S0 with CO2-reducing methanogenesis in sulfur-rich methanogenic cultures supplemented with conductive magnetite (100-700-nm particle size). The H2S content in biogas, initially exceeding 5000 ppmv, decreased to below 1 ppmv along with an accumulation of extracellular S0 (60-70 mg/L; initially <1 mg/L) at a magnetite dose of 20 mM Fe, while there were no significant changes in methane yield. A comprehensive polyphasic approach demonstrated that the S0 formation occurs through electro-syntrophic oxidation of sulfide coupled with CO2-reducing methanogenesis, involving Methanothrix as the dominant methanogen.

Simultaneous removal of refractory organic pollutants and nitrogen using electron shuttle suspended biofilm carriers in an integrated hydrolysis/acidification-anoxic/aerobic process

Azo dyes wastewater contains refractory pollutant and nitrogen, which threatens human health and ecological environment when discharged into environment directly. Electron shuttle (ES) is able to participate in the extracellular electron transfer, and thus enhances the removal efficiency of refractory pollutant. However, the continuous dosing of soluble ES would rise operation cost and cause contamination inevitably. In this study, a type of insoluble ES (carbonylated graphene oxide (C-GO)) was developed and melt blended into polyethylene (PE) to prepare novel C-GO-modified suspended carriers. Compared to those of conventional carrier (31.60%), the surface active sites of novel C-GO-modified carrier increased to 52.95%. An integrated hydrolysis/acidification (HA, filled with C-GO-modified carrier) - anoxic/aerobic (AO, filled with clinoptilolite-modified carrier) process was applied to remove azo dye acid red B (ARB) and nitrogen simultaneously. ARB removal efficiency was significantly improved in the reactor filled with C-GO-modified carriers (HA2) compared to the reactor filled with conventional PE carriers (HA1) or activated sludge (HA0). Total nitrogen (TN) removal efficiency of the proposed process increased by 25.95-32.64% compared to the reactor filled with activated sludge. Moreover, the intermediates of ARB were identified by liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway of ARB through ES was proposed. C-GO-modified carriers induced ARB-removal-related bacterial enrichment (such as Chloroflexi, Lactivibrio, Longilinea, Bacteroidales and Anaerolineaceae). Besides, the relative abundance of denitrifiers and nitrifiers in the AO reactor filled with clinoptilolite-modified carrier was increased by 11.60% compared with activated sludge. Copy numbers of genes related to membrane transport, carbon/energy metabolism and nitrogen metabolism increased significantly on the surface-modified carriers. This study proposed an efficient approach for simultaneous azo dyes and nitrogen removal, showing potential in actual application.

Evaluation of dye decolorization using anaerobic granular sludge from an expanded granular sludge bed based on spectrometric and microbiome analyses

The decolorization of 11 dyes by granular sludge from an anaerobic expanded granular sludge bed (EGSB) reactor was evaluated. Biological decolorization of Reactive Red 21, 23, and 180, and Reactive Yellow 15, 17, and 23 in model textile wastewater was observed for the first time after a 7-day incubation (over 94% decolorization). According to the sequencing analysis of 16S rRNA gene amplicons from EGSB granular sludge, the operational taxonomic unit related to Paludibacter propionicigenes showed the highest increase in relative abundance ratios in the presence of dyes (7.12 times on average over 11 dyes) compared to those without dyes.

Sludge decay kinetics and metagenomic analysis uncover discrepant metabolic mechanisms in two different sludge in situ reduction systems

A comparative study was conducted between an anaerobic side-stream reactor (ASSR) process and a sludge process reduction (SPR) activated sludge (SPRAS) process for uncovering crucial metabolic mechanisms governing sludge reduction. Both of two processes were efficient in removing pollutants, while the SPRAS (62.3 %) obtained much higher sludge reduction than the ASSR (27.9 %). The highest rate coefficients of sludge decay, heterotroph lysis and particles hydrolysis were 0.106, 0.219 and 0.054 d^-1 in the SPR module, followed by ASSR with coefficients of 0.060, 0.135 and 0.047 d^-1. The SPR module achieved an 81.9 % higher sludge decay mass with a 32.8 % smaller volume than the ASSR module. The SPR module preferentially enriched hydrolytic/fermentative and slow-growing bacteria. Metagenomic analysis revealed that SPR strengthened the key hydrolases and L-lactate dehydrogenase in the glycolysis pathways and weakened the citrate cycle, inducing metabolic uncoupling due to the reduced biosynthesis of ATP. Inserting ASSR only altered the ATP biosynthesis pathway, but maintenance metabolism was dominant for sludge reduction, with a long sludge retention time prolonging the food chain for predation.

Landfill leachate treatment by graphite engineered anaerobic membrane bioreactor: Performance enhancement and membrane fouling mitigation

Low efficiency of anaerobic digestion and membrane fouling, treating landfill leachate, are big barriers in the application of anaerobic membrane bioreactor (AnMBR). Anaerobic digestion enhancement and membrane fouling mitigation of AnMBR with graphite addition, treating landfill leachate, were investigated in this study. The effect of graphite on organics removal, biogas production, methane content in biogas, membrane fouling, microbial responses and foulant compositions were analyzed. With the graphite addition, chemical oxygen demand (COD) removal of 78% was achieved for influent COD concentration of 3000 mg/l, which was significantly higher than the stage without graphite addition (65%) for influent COD concentration of 2000 mg/l. Similarly, methane content in biogas with graphite addition was 56%, while without graphite addition it was 46%. These digestion improvements were due to the promotion of organics degradation, facilitated by direct interspecies electron transfer (DIET) mechanism via graphite addition in AnMBR. The graphite addition prolonged membrane cleaning cycle from 13 days to 30 days. Protein content in loosely bound extracellular polymeric substance (LB-EPS) was the main fouling agent, which decreased with the graphite addition. The main mechanism behind membrane fouling mitigation was the protein content reduction in LB-EPS, which was biodegraded by Trichococcus being increased in relative abundance with the graphite addition. Furthermore, abundance of Denitratisoma decreased in anaerobic sludge and its accumulation reduced on membrane surface, subsequently membrane fouling was mitigated. Overall, graphite addition in AnMBR is a potential eco-innovative approach that efficiently removes pollutants from landfill leachate, enhances biogas quality and mitigates membrane fouling.

Distinguishing responses of acetoclastic and hydrogenotrophic methanogens to ammonia stress in mesophilic mixed cultures

A shift from the acetoclastic to the hydrogenotrophic pathway in methanogenesis under ammonia inhibition is a common observation in anaerobic digestion. However, there are still considerable knowledge gaps concerning the differential ammonia tolerance of acetoclastic and hydrogenotrophic methanogens (AMs and HMs), their responses to different ammonia species (NH₄⁺, NH₃), and their recoverability after ammonia inhibition. With the successful enrichment of mesophilic AMs and HMs cultures, this study aimed at addressing the above knowledge gaps through batch inhibition/recovery tests and kinetic modeling under varying total ammonia (TAN, 0.2-10 g N/L) and pH (7.0-8.5) conditions. The results showed that the tolerance level of HMs to free ammonia (FAN, IC₅₀=1345 mg N/L) and NH₄⁺ (IC₅₀=6050 mg N/L) was nearly 11 times and 3 times those of AMs (NH₃, IC₅₀=123 mg N/L; NH₄⁺, IC₅₀=2133 mg N/L), respectively. Consistent with general belief, the AMs were more impacted by FAN. However, the HMs were more adversely affected by NH₄⁺ when the pH was ≤8.0. A low TAN (1.0-4.0 g N/L) could cause irreversible inhibition of the AMs due to significant cell death, whereas the activity of HMs could be fully or even over recovered from severe ammonia stress (FAN≤ 0.9 g N/L or TAN≤10 g N/L; pH ≤8.0). The different tolerance responses of AMs and HMs might be associated with the cell morphology, multiple energy-converting systems, and Gibbs free energy from substrate-level phosphorylation.

Bioregeneration of sulfate-laden anion exchange resin

Ion exchange technology removes ionic compounds from waters effectively but treatment of the spent regenerant is expensive. The bioregeneration of sulfate-laden strong base anion exchange resin was successfully tested using both pure and mixed sulfate-reducing bacterial cultures. The resin was first used for removal of sulfate from neutral (pH 6.7 ± 0.5) synthetic sodium sulfate solutions, after which the spent resin was regenerated by incubating with a viable sulfate-reducing bacterial culture in batch and column modes. In the batch bioregeneration tests, the achieved bioregeneration was 36-95% of the original capacity of the fresh resin (112 mg SO₄^2-/g) and it increased with regeneration time (1-14 days). The capacity achieved in the column tests during 24 hours of bioregeneration was 107 mg SO₄^2-/g after the first regeneration cycle. During the bioregeneration, sulfate was mainly reduced by the sulfate-reducing bacteria (approx. 60%), but part of it was only detached from the resins (approx. 30%). The resin-attached sulfate was most likely replaced with ions present in the liquid sulfate-reducing bacterial culture (e.g., HCO₃^-, HS^-, and Cl^-). During the subsequent exhaustion cycles with the bioregenerated resin, the pH of the treated sodium sulfate solution increased from the original 6.7 ± 0.5 to around 9. The study showed that biological sulfate reduction could be used for sulfate removal in combination with ion exchange, and that the exhausted ion exchange resins could be regenerated using a liquid sulfate-reducing bacterial culture without producing any brine.

Molecular response of Anoxybacillus sp. PDR2 under azo dye stress: An integrated analysis of proteomics and metabolomics

Treating azo dye wastewater using thermophilic bacteria is considered a more efficient bioremediation strategy. In this study, a thermophilic bacterial strain, Anoxybacillus sp. PDR2, was regarded as the research target. This strain was characterized at different stages of azo dye degradation by using TMT quantitative proteomic and non-targeted metabolome technology. A total of 165 differentially expressed proteins (DEPs) and 439 differentially metabolites (DMs) were detected in comparisons between bacteria with and without azo dye. It was found that Anoxybacillus sp. PDR2 can degrade azo dye Direct Black G (DBG) through extracellular electron transfer with glucose serving as electron donors. Most proteins related to carbohydrate metabolism, including acetoacetate synthase, and malate synthase G, were overexpressed to provide energy. The bacterium can also self-synthesize riboflavin as a redox mediator of in vitro electron transport. These results lay a theoretical basis for industrial bioremediation of azo dye wastewater.

Towards passive bioremediation of dye-bearing effluents using hydrous ferric oxide wastes: Mechanisms, products and microbiology

A novel, circular economy-inspired approach for the "passive" (non-powered and reagent-free) treatment of dye-bearing effluent is presented. The treatment utilises the biogeochemical interaction of dye-bearing wastewater with hydrous ferric oxide (HFO) bearing sludges. The work presented demonstrates for the first time the reuse of HFO-rich waste sludges from potable water and mine water treatment. The waste was used directly without modification or reagent addition, as media/substrate in simple flow-through reactors for the decolourisation and biodegradation of methyl orange (MO) and mixed dyes textile effluent. Three phases of exploratory proof of concept work were undertaken. Columns containing HFO sludges were challenged with solution of MO, and MO amended with glycerol (Phase I), MO in a synthetic textile effluent recipe (Phase II), and real mixed textile effluent containing a mixture of dyes (Phase III). After an initial lag period extensive decolourisation of dye was observed in all cases at rates comparable with pure strains and engineered bioreactor processes, with evidence of biodegradation beyond simple cleavage of the mono azo chromophore and mineralisation. The microbiology of the initial sludge samples in both cases exhibited a diverse range of iron oxidising and reducing bacteria. However, post experiment the microbiology of sludge evolved from being dominated by Proteobacteria to being dominated by Firmicutes. Distinct changes in the microbial community structure were observed in post-treatment MWTS and WTWS where genera capable of iron and sulphate reduction and/or aromatic amine degradation were identified. Average nitrogen removal rates for the columns ranged from 27.8 to 194 g/m³/day which is higher than engineered sequential anaerobic-aerobic bioreactor. Postulated mechanisms for the fast anaerobic decolourisation, biodegradation, and mineralisation of the dyes (as well nitrogen transformations) include various direct and indirect enzymatic and metabolic reactions, as well as reductive attack by continuously regenerated reductants such as Fe(II), HFO bound Fe(II), FeS, and HS^-. The ability of iron reducers to degrade aromatic rings is also considered important in the further biodegradation and complete mineralisation of organic carbon. The study reveals that abundant and ubiquitous HFO-rich waste sludges, can be used without amendment, as a substrate in simple flow-through bioremediation system for the decolourisation and partial biodegradation of dyes in textile effluent.

Step feed mode synergistic mixed carbon source to improve sequencing batch reactor simultaneous nitrification and denitrification efficiency of domestic wastewater treatment

The limited efficiency of nitrogen removal has traditionally hindered wide application of simultaneous nitrification and denitrification (SND) technology. Here, the nitrogen removal characteristics of a sequencing batch reactor were studied by adopting a strategy of a step-feeding mode, synergistic regional oxygen limitation, and a mixed carbon source. The changes of the microbial population succession and nitrogen metabolism functional genes were analyzed. This strategy provided a favorable level of dissolved oxygen and continuous carbon sources for driving the denitrification process. The total nitrogen removal efficiency and SND rate reached 92.60% and 96.49%, respectively, by regulating the ratio of sodium acetate to starch in the step feed to 5:1. This procedure increased the relative abundance of denitrifying functional genes and induced the growth of a variety of traditional denitrifying bacteria and aerobic denitrifying bacteria participating in the process of nitrogen removal. Overall, this work offers a new strategy for achieving efficient SND.

Intermittent Microaeration Technology to Enhance the Carbon Source Release of Particulate Organic Matter in Domestic Sewage

Domestic sewage treatment plants often have insufficient carbon sources in the influent water. To solve this problem, the commonly used technical means include an additional carbon source, primary sludge fermentation, and excess sludge fermentation, but these methods are uneconomical, unsustainable, and not applicable to small-scale wastewater treatment plants. Intermittent microaeration technology has the advantages of low energy-consumption, ease of application, and low cost, and can effectively promote anaerobic digestion of municipal sludge; however little research has been reported on its use to enhance the carbon sources release of particulate organic matter (POM) from domestic wastewater. Therefore, the effect of intermittent microaeration on the carbon source release of POM was evaluated in this study, with POM as the control test. The results showed that the release concentration of soluble chemical oxygen demand (SCOD) was the highest on day 4 under microaerobic conditions, and the concentrations of SCOD, NH4+-N, and PO43−-P in the liquid phase were 1153, 137.1, and 13 mg/L, respectively. Compared with the control group, the SCOD concentration increased by 34.2%, and the NH4+-N and PO43−-P concentrations decreased by 18.65% and 17.09%, respectively. Intermittent microaeration can effectively promote the growth of Paludibacter, Actinomyces, and Trichococcus hydrolytic fermentation functional bacteria. Their relative abundances increased by 282.83%, 21.77%, and 23.47%, respectively, compared with the control group. It can simultaneously inhibit the growth of acetate-type methanogenic archaea, Methanosaeta and Methanosarcina, with a decrease in relative abundances of 16.81% and 6.63%, respectively. The aforementioned data show that intermittent microaeration can not only promote the hydrolysis of POM, but can also reduce the loss of acetic acid carbon source, which is a cost-effective technical way to enhance the release of a carbon source of particulate organic matter in domestic sewage.

Synthesis of magnetic hydrochar from Fenton sludge and sewage sludge for enhanced anaerobic decolorization of azo dye AO7

A novel magnetic hydrochar synthesized from Fenton sludge (FS) and sewage sludge (SS) was employed in the anaerobic decolorization of acid orange 7 (AO7). The stable presence of Fe₃O₄ in magnetic hydrochar was confirmed by physicochemical characterization. The degradation efficiency of AO7 in the anaerobic system with the addition of hydrochar prepared in an optimal proportion (SS:FS=1:3, named as HC-1:3) could reach 98.55%, which was 1.91 times higher than the control system. Particularly, superior electrical conductivity, electron transport system activity and azo reductase activity of the sludge in anaerobic system with HC-1:3 were achieved. The redox of Fe(Ⅲ)/Fe(Ⅱ) in anaerobic system was realized by dissimilatory iron-reducing bacteria enriched with HC-1:3. According to the six-cycle batch experiments and 120-day continuous-flow UASB experiments, the addition of HC-1:3 into the anaerobic system facilitated the diversity of microbiological community and increased the ecological stability of anaerobic system. The possible electron transfer mechanism involving in the magnetic hydrochar-based anaerobic system for AO7 removal was speculated preliminarily. The as-prepared magnetic hydrochar not only showed a promising future in anaerobic system for recalcitrant contaminants degradation, but also provided a new approach for the resource utilization of FS and SS.

Degradation of Azo Dyes: Bacterial Potential for Bioremediation

The use of dyes dates to ancient times and has increased due to population and industrial growth, leading to the rise of synthetic dyes. These pollutants are of great environmental impact and azo dyes deserve special attention due their widespread use and challenging degradation. Among the biological solutions developed to mitigate this issue, bacteria are highlighted for being versatile organisms, which can be applied as single organism cultures, microbial consortia, in bioreactors, acting in the detoxification of azo dyes breakage by-products and have the potential to combine biodegradation with the production of products of economic interest. These characteristics go hand in hand with the ability of various strains to act under various chemical and physical parameters, such as a wide range of pH, salinity, and temperature, with good performance under industry, and environmental, relevant conditions. This review encompasses studies with promising results related to the use of bacteria in the bioremediation of environments contaminated with azo dyes in the most diverse techniques and parameters, both in environmental and laboratory samples, also addressing their mechanisms and the legislation involving these dyes around the world, showcasing the importance of bacterial bioremediation, specialty in a scenario in an ever-increasing pursuit for sustainable production.

Effects of ferroferric oxide on azo dye degradation in a sulfate-containing anaerobic reactor: From electron transfer capacity and microbial community

Anaerobic decolorization of azo dye in sulfate-containing wastewater has been regarded as an economical and effective method, but it is generally limited by the high concentration of azo dye and accumulation of toxic intermediates. To address this problem, Fe₃O₄ was added to one of the anaerobic reactors to investigate the effects on system performances. Results showed that AO7 removal rate, COD removal rate, and sulfate reduction were enhanced with the addition of Fe₃O₄ under various influent AO7 concentrations (153 mgCOD/L - 1787 mgCOD/L). According to the proposed pathway for the degradation of AO7, more intermediates (2-hydroxy-1,4-naphthoquinone, phthalide, 4-methylphenol) were produced in the presence of Fe₃O₄. The electron transfer capacity of sludge was also increased since Fe₃O₄ could stimulate to secrete humic acid-like organics in EPS. Microbial analysis showed that iron-reducing bacteria like Clostridium and Geobacter were also enriched, which were capable of azo dye and aromatic compounds degradation.

Decolorization mechanism, identification of an FMN-dependent NADH-azoreductase from a moderately halotolerant Staphylococcus sp. MEH038S, and toxicity assessment of biotransformed metabolites

The application of halotolerant microorganisms capable of decolorizing is attractive. Decolorization mechanism, the effect of different parameters on the decolorization percentage, and toxicity analysis of Reactive Black 5 before and after decolorization were investigated in the present study. The decolorization percentage for live cells of Staphylococcus sp. strain MEH038S was more than dead cells, which demonstrated that Reactive Black 5 was decolorized through the degradation process. The results confirmed that an FMN-dependent NADH-azoreductase gene was responsible for the decolorization and then was identified as Staphylococcus sp. EFS01 azoreductase from a moderately halotolerant Staphylococcus strain for the first time. The maximal decolorization of 98.15% was observed at pH 6.5 and 35 ^° C for 50 mg/L of Reactive Black 5. In addition, more than 90% decolorization was achieved with 5-40 g/L of NaCl. The results of Gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy showed that Reactive Black 5 was broken to the lower molecular weight compounds without any chromophoric azo groups. Phytotoxicity and fish toxicity proved that the biotransformed metabolites of Reactive Black 5 degradation were more toxic than the original dye. The moderate halotolerant strain exhibited a remarkable decolorization capability and can be applied for textile wastewater treatment. PRACTITIONER POINTS: An azoreductase gene from a moderately halotolerant Staphylococcus was identified. More than 90% decolorization efficiency was observed under high-salt conditions. Biotransformed metabolites of RB5 degradation were identified. Toxicity analysis of biotransformed metabolites was investigated.

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1-3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

The application status, development and future trend of nano-iron materials in anaerobic digestion system

Growing environment problem and emphasis of environmental protection motivate intense research efforts in exploring technology to improve treatment efficiency on refractory organic pollutants. Hence, finding a method to make up for the deficiency of anaerobic digestion (AD) is very attractive and challenging tasks. The recent spark in the interest for the usage of some nanomaterials as an additive to strengthen AD system. The adoption of iron compounds can influence the performance and stability in AD system. However, different iron species and compounds can influence AD system in significantly different ways, both positive and negative. Therefore, strengthening mechanism, treatment efficiency, microbial community changes in Nanoscale Zero Valent Iron (nZVI) and Fe₃O₄ nanoparticles (Fe₃O₄ NPs) added AD systems were summarized by this review. The strengthening effects of nZVI and Fe₃O₄ NPs in different pollutants treatment system were analyzed. Previous study on the effects of nZVI and Fe₃O₄ NPs addition on AD have reported the concentration of nZVI and Fe₃O₄ NPs, and the types and biodegradability of pollutants might be the key factors that determine the direction and extent of effect in AD system. This review provides a summary on the nZVI and Fe₃O₄ NPs added AD system to establish experiment systems and conduct follow-up experiments in future study.

Novel strategy for enhancing acetic and formic acids generation in acidogenesis of anaerobic digestion via targeted adjusting environmental niches

Optimization of acetic acid and formic acid production efficient methanogenesis is always the research hot spot in anaerobic digestion. It is a promising approach to adjust the operation parameters to influence the functional microorganisms for better acetic acid and formic acid production in acidogenesis. Herein, the effects of pH, oxidation-reduction potential (ORP) and carbon-nitrogen (C/N) ratio were determined in batch experiments to probe acetic and formic acids production, and were further verified in continuous stirred tank reactor (CSTR). The results revealed that the content of volatile fatty acids (VFAs) reached to maximum at pH 6.0 or ORP -350 mV, while the production of acetic and formic acids was the highest at pH 7.0 or ORP -450 mV in 9 h fermentation. Also, fermentation products dominated by acetic and formic acids were adjusted in the CSTR under the operating conditions of pH 7.0 and ORP -450 mV. Microbiological analysis from batch test showed that fermentation at pH value of 7.0 enriched the diversity of microorganism, and provided a niche for microbes (Petrimonas, norank_f__Synergistaceae, vadinBC27_wastewater-sludge_group, and Trichococcus) to produce acetic and formic acids. Correspondingly, 78.70% of the carbon was converted to acetic and formic acids in pH 7.0. This study provides a promising strategy for the targeted regulation of acetic and formic acids production in acidogenesis of anaerobic digestion.

Bacterial and fungal diversity in the lorandite (TlAsS2) mine 'Allchar' in the Republic of North Macedonia

The Allchar mineral mine is one of the oldest arsenic-antimony mines in the Republic of North Macedonia. The mine is a well-known reservoir of the worldwide purest source of the thallium-bearing mineral, lorandite (TlAsS2). The current study evaluated the bacterial and fungal diversity of three As- and Tl-contaminated sites in Allchar mineral mine. We used a combination of high-throughput sequencing and bioinformatic analyses. Trace metal content was detected using inductively coupled plasma optical emission spectrometry. Our analysis showed the presence of 25 elements and confirmed a high concentration of As and Tl. Alpha diversity indices suggested a high diversity and evenness of bacterial and fungal communities. Bacterial phyla that dominated the environment were Bacteroidetes, Acidobacteria, Planctomycetes, Actinobacteria and Verrucomicrobia. Looking at the genus level, we found the following groups of bacteria: Chryseolinea, Opitutus, Flavobacterium, Pseudomonas, Terrimonas, Sphingomonas and Reyranella. For the fungi genera, we report Tetracladium sp., Coprinellus micaceus, Coprinus sp. from Ascomycota and Basidiomycota phyla in all sites. We also observed a high abundance of the fungal species Pilidium sp., Dendroclathra lignicola, Rosellinia desmazieri, Hypomyces rosellus and Coprinellus disseminatus. This study is the first to identify specific As- and Tl-tolerant fungal (Pilidium sp., Cladophialophora sp., Neobulgaria sp. and Mycena acicula) and bacterial (Trichococcus, Devosia, Litorilinea and Gimesia) genera from Allchar mine, suggesting bioremediation and industrial potential.

Deeper insights into effect of activated carbon and nano-zero-valent iron addition on acidogenesis and whole anaerobic digestion

Conductive materials presented promising advantages for enhancing anaerobic digestion (AD) performance. This study evaluated the effects of activated carbon (AC) and nano-zero-valent iron (nZVI) on the acidogenesis and whole AD to explore their potential mechanisms. AC increased the content of lactic and propionic acids in acidogenesis. nZVI increased the production of formic acid, acetic acid and H₂ in acidogenesis, thus significantly promoted the methane yield in the whole AD. Mechanism exploration proved that AC enriched Trichococcus, and norank_f__Bacteroidetes_vadinHA17, and then improved the activity of enzymes involved in the production of lactic and propionic acids. nZVI buffered the pH to increase the activity of pyruvate formate-lyase (PFL) in formic acid production. Furthermore, nZVI enriched the Methanobacterium which use H₂ and formic acid as substrate. The research paves pathway for the efficient enhancement of conductive materials added novel AD process.

Microbes trading electricity in consortia of environmental and biotechnological significance

Favorable interspecies associations prevail in natural microbial assemblages. Some of these favorable associations are co-metabolic dependent partnerships in which extracellular electrons are exchanged between species. For such electron exchange to occur, the cells must exhibit electroactive interfaces and get involved in direct cell-to-cell contact (Direct Interspecies Electron Transfer/DIET) or use available conductive mineral grains from their environment (Conductive-particle-mediated Interspecies Electron Transfer/CIET). This review will highlight recent discoveries and knowledge gaps regarding DIET and CIET interspecies associations in artificial co-cultures and consortia from natural and man-made environments and emphasize approaches to validate DIET and CIET. Additionally, we acknowledge the initiation of a movement towards applying electric syntrophies in biotechnology, bioremediation and geoengineering for natural attenuation of toxic compounds. Next, we have highlighted the urgent research needs that must be met to develop such technologies.

Effects of biowaste-derived biochar on the electron transport efficiency during anaerobic acid orange 7 removal

In this study, different biochar (based on different pyrolytic temperatures and iron dosage) were prepared, characterized and used as individual additives for promoting acid orange 7 (AO7) anaerobic digestion. After X-ray diffraction (XRD), fourier transform infrared spectrometer (FTIR) characterization, 600 °C was proved to be the preferred temperature. Subsequently, biochar pyrolyzed at 600 °C with different iron dosage were added into five anaerobic reactors. Results showed that COD removal efficiency reached the maximum value (88.5%) with the presence of 600-1 biochar, which was 19.0% higher than control reactor (without biochar added). Further analysis indicated that more functional groups were found in 600-1 biochar could effectively improve the electron accepting capacities (EAC) and electron donating capacities (EDC). Combined with the enrichment of exoelectrogens related to syntrophic metabolism, it can be concluded that the addition of biochar could effectively improve the electron transfer efficiency which would be beneficial for AO7 removal.

Accelerated anaerobic biodecolorization of sulfonated azo dyes by magnetite nanoparticles as potential electron transfer mediators

Anaerobic decolorization of azo dyes has been evidenced to be an economical and effective pretreatment method, but its generally limited by the low decolorization efficiency, especially for biodecolorization sulfonated azo dyes. In this study, magnetite nanoparticles (MNPs) as a conductive material, was coupled into anaerobic system for enhancing decolorization of sulfonated azo dyes, i.e., methyl orange (MO), with technology feasibility and system stability emphasized. The results showed that the anaerobic decolorization capacity was significantly enhanced with addition of MNPs (at dose of 1 g/L), where the efficiencies of MO decolorization and aromatic amines formation were as high as 97.28 ± 0.78 % and 99.44 ± 0.25%, respectively. In addition, both electron transport system activity and sludge conductivity were also significantly improved, suggesting that a direct extracellular electron transfer had been successfully established via MNPs as RMs. Under continuous-flow experiments, addition of MNPs not only improved anaerobic system resistance environmental stress (e.g., high MO concentration, low hydraulic retention time and low co-substance concentration) but also accelerated sludge granulation. The relative abundance of functional species related to dissimilatory iron reduction and MO biodegradation were also enriched under MNPs stimulation. The observed long-term stable performance suggests the full-scale application potential of this coupled system for treatment of wastewater containing sulfonated azo dyes.

Effects of foam nickel supplementation on anaerobic digestion: Direct interspecies electron transfer

Stimulating direct interspecies electron transfer with conductive materials is a promising strategy to overcome the limitation of electron transfer efficiency in syntrophic methanogenesis of industrial wastewater. This paper assessed the impact of conductive foam nickel (FN) supplementation on syntrophic methanogenesis and found that addition of 2.45 g/L FN in anaerobic digestion increased the maximum methane production rate by 27.4 % (on day 3) while decreasing the peak production time by 33 % as compared to the control with no FN. Cumulative methane production from day 2 to 6 was 14.5 % higher with addition of 2.45 g/L FN than in the control. Levels of FN in excess of 2.45 g/L did not show benefits. Cyclic voltammetry results indicated that the biofilm formed on the FN could generate electrons. The dominant bacterial genera in suspended sludge were Dechlorobacter and Rikenellaceae DMER64, whereas that in the FN biofilm was Clostridium sensu stricto 11. The dominant archaea Methanosaeta in the FN biofilm was enriched by 14.1 % as compared to the control.

A comparison and evaluation of the effects of biochar on the anaerobic digestion of excess and anaerobic sludge

The mechanisms and enhancing effects of different biochar loadings on the digesters receiving low and high excess (or anaerobic) sludge loadings were thoroughly examined in the present study. This was done to explore an efficient method for converting excess sludge to anaerobic sludge. Biochar had an obvious effect on the anaerobic digestion of excess sludge but not on the anaerobic sludge. When the amount of biochar added was equivalent to 100% of the sludge TS, the cumulative methane yields of anaerobic digestion inoculated with small and large amounts of excess sludge were respectively 30.2 and 1.7 times that of those without biochar. The number of methanogens in the digesters that received small and large inoculations of excess sludge with 100% biochar, were respectively 105.4% and 20.6% higher than those without biochar. The biochar enhanced the systems performance because it selectively enriched the Trichococcus and Methanomicrobiales tightly attach to it. This enhanced the synergy and overall activity of the system by promoting biofilm development. Ultimately, the integration of 100% biochar and excess sludge can be used as a substitute for anaerobic sludge as an inoculum by giving similar overall performance.

Resuscitation, isolation and immobilization of bacterial species for efficient textile wastewater treatment: A critical review and update

Given highly complex and recalcitrant nature of synthetic dyes, textile wastewater poses a serious challenge on surrounding environments. Until now, biological treatment of textile wastewater using efficient bacterial species is still considered as an environmentally friendly and cost-effective approach. The advances in resuscitating viable but non-culturable (VBNC) bacteria via signaling compounds such as resuscitation-promoting factors (Rpfs) and quorum sensing (QS) autoinducers, provide a vast majority of potent microbial resources for biological wastewater treatment. So far, textile wastewater treatment from resuscitating and isolating VBNC state bacteria has not been critically reviewed. Thus, this review aims to provide a comprehensive picture of resuscitation, isolation and application of bacterial species with this new strategy, while the recent advances in synthetic dye decolorization were also elaborated together with the mechanisms involved. Discussion was further extended to immobilization methods to tackle its application. We concluded that the resuscitation of VBNC bacteria via signaling compounds, together with biochar-based immobilization technologies, may lead to an appealing biological treatment of textile wastewater. However, further development and optimization of the integrated process are still required for their wide applications.

High-rate anaerobic decolorization of methyl orange from synthetic azo dye wastewater in a methane-based hollow fiber membrane bioreactor

Anaerobic biological techniques are widely used in the reductive decolorization of textile wastewater. However, the decolorization efficiency of textile wastewater by conventional anaerobic biological techniques is generally limited due to the low biomass retention capacity and short hydraulic retention time (HRT). In this study, a methane-based hollow fiber membrane bioreactor (HfMBR) was initially inoculated with an enriched anaerobic methane oxidation (AOM) culture to rapidly form an anaerobic biofilm. Then, synthetic azo dye wastewater containing methyl orange (MO) was fed into the HfMBR. MO decolorization efficiency of ∼ 100 % (HRT = 2 to 1.5 days) and maximum decolorization rate of 883 mg/L/day (HRT = 0.5 day) were obtained by the stepwise increase of the MO loading rate into the methane-based HfMBR. Scanning electron microscopy (SEM) and fluorescence in situ hybridization (FISH) analysis visually revealed that archaea clusters formed synergistic consortia with adjacent bacteria. Quantitative PCR (qPCR), phylogenetic and high-throughput sequencing analysis results further confirmed the biological consortia formation of methane-related archaea and partner bacteria, which played a synergistic role in MO decolorization. The high removal efficiency and stable microbial structure in HfMBR suggest it is a potentially effective technique for high-toxic azo dyes removal from textile wastewater.

Supported growth of inorganic-organic nanoflowers on 3D hierarchically porous nanofibrous membrane for enhanced enzymatic water treatment

Organic-inorganic nanoflower is a new type of functional material that can effectively immobilize a wide range of enzymes to form flower-like structures for various enzymatic applications with enhanced catalytic performance and stability. In order to avoid the processing inconvenience and flower structure damage caused by the particular form of these hybrid nanoflowers during material fabrication and catalytic application, different substrates have been used to carry out supported growth of hybrid nanoflowers. However, all previously used substrates have only 2-dimensional feature and only incorporate hybrid nanoflowers on surface with limited nanoflower loading. In this study, three-dimensional (3D) hierarchically porous nanofibrous PVA-co-PE membranes (HPNM) are prepared by a simple template method for effectively immobilizing laccase-Cu₂(PO₄)₃•3H₂O hybrid nanoflowers. Compared with dense nanofibre membrane with only small sized pores (<1 micron), the coexistence of both small and large sized (30-80 microns) pores of HPNM could significantly increase the nanoflower density and allow the penetrated growth of hybrid nanoflowers into the inner structure of the membrane. The hybrid nanoflower containing hierarchically porous nanofibrous membranes (HNF-HPNM) show excellent catalytic performance in degrading different types of textile dyes (reactive blue 2, acid blue 25, acid yellow 76 and indigo carmine), with a degradation efficiency of ˜99.5% for indigo carmine. In addition, the HNF-HPNM could be reused at least 14 times for indigo carmine degradation, with a negligible degradation efficiency drop from 99.48% to 98.52%. These results indicate that hierarchically porous nanofibrous membrane can be a promising type of materials for supported hybrid nanoflower growth for practical applications such as waste water treatment, dye degradation and biosensing.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

Highly efficient biodegradation of reactive blue 19 under the activation of tea residue by a newly screened mixed bacterial flora DDMY2

In this study, a newly screened mixed bacterial flora DDMY2 had high decolorization capacity for anthraquinone dye reactive blue 19 (RB19) and the decolorization efficiency of 300 mg L-1 RB19 could reach up to 98% within 48 h in the presence of tea residue. Results indicated that RB19 could be efficiently decolorized by flora DDMY2 in wide ranges of pH values (5.0-9.0), temperatures (30-40 °C) and initial dye concentrations (50-500 mg L-1) under the activation of tea residue. Concentration of tea residue had been proved to significantly impact the decolorization performance. UV-vis spectrophotometry, Fourier transform infrared spectrometry and liquid chromatography/time-of-flight/mass spectrometry analysis showed three identified degradation products and the possible degradation pathway of RB19 was speculated. High-throughput sequencing analysis revealed the community structures of bacterial flora before and after domestication by tea residue. Based on the result, it was inferred that unclassified_o_Pseudomonadales, Brevibacillus, Stenotrophomonas and Bordetella activated by tea residue were responsible for the excellent decolorization performance. Results of this research deepen our understanding of the biodegradation process of anthraquinone dyes by bacterial flora and broaden the knowledge of utilizing tea residue as a bioactivator in biological treatment.

Study on enhancing sludge methanogenesis by adding acetylene black and effect on the characteristics & microbial community of anaerobic granular sludge

The effect of acetylene black (ACET) as additives on methane production, extracellular polymeric substances (EPS), microbial community structure and methanogenesis pathway during sludge anaerobic digestion (AD) was investigated in this study. The results indicated that the addition of 2 g L-1 ACET resulted in a 44.36% increase in methane accumulation. ACET, which resulted in the increase of EPS and VSS/TSS by 4.71-50.64%, effectively improved the physicochemical properties of anaerobic granular sludge (AnGS). During anaerobic digestion, the high throughput sequencing presented direct evidence that the ACET increased microbial diversity and enriched functional microorganisms such as norank_f__Synergistaceae, norank_f__Anaerolineaceae, and unclassified_f__Clostridiaceae_3, which can improve the hydrolysis acidification process and the acetotrophic pathway. These results were reaffirmed by applying metagenome inference and gene content inference (16S function prediction). Microscopically, significant enhancement in the AD efficiency can be due to the methanogenesis promoted by the ACET that can construct direct interspecies electron transfer (DIET) between the unclassified_f__Clostridiaceae_3, norank_f__Anaerolineaceae, and Methanosaeta. These results were expected to provide primary research data for improving the performance of anaerobic reactors and the development of microbial fuel cells.

Goethite Hinders Azo Dye Bioreduction by Blocking Terminal Reductive Sites on the Outer Membrane of Shewanella decolorationis S12

Iron (hydr)oxides are the most ubiquitous Fe(III)-containing minerals in the near-surface environments and can regulate organic pollutant biotransformation by participating in bacterial extracellular electron transfer under anaerobic conditions. Mechanisms described so far are based on their redox properties in bacterial extracellular respiration. Here, we find that goethite, a typical iron (hydr)oxide, inhibits the bioreduction of different polar azo dyes by Shewanella decolorationis S12 not through electron competition, but by the contact of its surface Fe(III) with the bacterial outer surface. Through the combined results of attenuated total reflectance (ATR) Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, and confocal laser scanning microscope, we found that the outer membrane proteins MtrC and OmcA of strain S12 are key binding sites for goethite surface. Meanwhile, they were identified as the important reductive terminals for azo dyes. These results suggest that goethite may block the terminal reductive sites of azo dyes on the bacterial outer membrane to inhibit their bioreduction. This discovered role of goethite in bioreduction provides new insight into the microbial transformation processes of organic pollutants in iron (hydr)oxide-containing environments.

Degradation of organic pollutants by anaerobic methane-oxidizing microorganisms using methyl orange as example

Anaerobic oxidation of methane (AOM) microorganisms widespread in nature and they are able to utilize methane as electron donor to reduce sulfate, nitrate, nitrite, and high valence metals. However, whether persistent organic contaminants can also be degraded remains unknown. In this study, the organic pollutant methyl orange (MO) was used to address this open question. The initial concentration of MO affected its degradation efficiency and higher concentration (>100 mg/L) caused considerable inhibition. A ¹³CH₄ isotope experiment indicated that methane oxidation was involved in MO degradation, which produced N, N-dimethyl-p-phenylenediamine, and 4-aminobenzenesulfonic acid corresponded stoichiometrically. During the long-term experiment, the maximum degradation rate was 47.91 mg/(L·d). The percentage of Candidatus Methanoperedens and Pseudoxanthomonas significantly increased after 30-d of MO degradation under CH₄ conditions; moreover, Candidatus Methanoperedens dominated (46.83%) the microbial community. Candidatus Methanoperedens, either alone or in combination with Pseudoxanthomonas, utilized methane as the sole carbon source to degrade MO via direct interspecies electron transfer or the syntrophy pathway. This study will add to our understanding of the functions and applications of AOM microorganisms.