Search

Carbon-based materials that serve as microbial carriers, and the role of surface-formed biofilms in anaerobic digestion, merit further investigation. This study explored the role and mechanism behind the biodegradation enhancement of biofilms formed onto anthraquinone-loaded biochar (AQS-BC) surfaces through the anaerobic decolorization process of azo dye Reactive Red 2, and optimized the conditions for AQS-BC biofilm formation. The results indicated that the AQS-BC biofilm system exhibited high treatment efficiency and stability in RR2 anaerobic decolorization. RR2 led to the accumulation of volatile fatty acids (VFAs) and inhibition of methane production, while the presence of AQS increased methane production. The effects of sludge concentration, contact time, carbon source concentration, and RR2 concentration on biofilm maturity were also analyzed. Combining biochemical characteristics, electrochemical properties, surface structure, and microbial community analysis, a mechanism for the anaerobic decolorization of RR2 via AQS-BC as a microbial carrier was proposed. This study provides insights into the roles of biofilms in the anaerobic wastewater treatment processes. Article Highlights: AQS-BC biofilm system exhibited superiority and stability in long-term anaerobic biodecolorization of RR2. AQS-BC biofilm effectively promoted the production of VFAs and alleviated the inhibitory of RR2 on methanogenesis. AQS-BC biofilm had a higher EPS content, denser structure, and higher microbial diversity compared to BC biofilm. Four inoculation conditions affecting biofilm formation were elucidated. [ABSTRACT FROM AUTHOR]

Abstract Carbon-based materials that serve as microbial carriers, and the role of surface-formed biofilms in anaerobic digestion, merit further investigation. This study explored the role and mechanism behind the biodegradation enhancement of biofilms formed onto anthraquinone-loaded biochar (AQS-BC) surfaces through the anaerobic decolorization process of azo dye Reactive Red 2, and optimized the conditions for AQS-BC biofilm formation. The results indicated that the AQS-BC biofilm system exhibited high treatment efficiency and stability in RR2 anaerobic decolorization. RR2 led to the accumulation of volatile fatty acids (VFAs) and inhibition of methane production, while the presence of AQS increased methane production. The effects of sludge concentration, contact time, carbon source concentration, and RR2 concentration on biofilm maturity were also analyzed. Combining biochemical characteristics, electrochemical properties, surface structure, and microbial community analysis, a mechanism for the anaerobic decolorization of RR2 via AQS-BC as a microbial carrier was proposed. This study provides insights into the roles of biofilms in the anaerobic wastewater treatment processes. Graphical Abstract

Textile wastewater (TWW) represents a major source of pollution worldwide, carrying high organic loads, recalcitrant azo dyes and engineered nanoparticles (ENP), namely silver nanoparticles (AgNP). The development of cost-efficient, environmentally-friendly TWW treatment solutions is critical. Despite the successful biodecolorization of azo dyes under anaerobic conditions, clear evidence for subsequent aerobic biodegradation of the often toxic breakdown sulfonated aromatic amines is scarce. Moreover, the debatable AgNP toxicity mechanisms, and apparent AgNP retention in activated sludge have raised concerns regarding eventual negative impacts on wastewater treatment efficiency. The aerobic granular sludge (AGS) technology, which has recently been scaled-up and implemented for the treatment of domestic wastewater and some industrial wastewaters, seems highly promising for TWW treatment, due to the high biomass retention capacity, anaerobic/anoxic/aerobic microenvironments within granules and enhanced tolerance towards high organic loads and toxic compounds. A review of the existing literature on AGS application to TWW treatment is presented, with a focus on the removal of azo dyes and their metabolites and ENP. The applicability of AGS to dye-containing synthetic and real TWW has been tested in different SBR systems. Their hydrodynamic regimens and operational conditions have been optimized, namely regarding granulation, long-term stability, azo dye decolorization and biodegradation of aromatic amines. Although promising results have been published regarding AGS resistance towards ENP (particularly AgNP), their long-term effects on the physical stability, biochemical properties and microbial community of AGS deserve more investigation. Overall, this review provides relevant support for the application of AGS SBRs in TWW treatment as a potential sustainable alternative to avoid the pollution of natural water bodies with synthetic dyes and ENP. [ABSTRACT FROM AUTHOR]

Treatment of the highly polluting and variable textile industry wastewater using aerobic granular sludge (AGS) sequencing batch reactors (SBRs) has been recently suggested. Aiming to develop this technology application, two feeding strategies were compared regarding the capacity of anaerobic-aerobic SBRs to deal with disturbances in the composition of the simulated textile wastewater feed. Both a statically fed, anaerobic-aerobic SBR and an anaerobic plug-flow fed, anaerobic-aerobic SBR could cope with shocks of high azo dye concentration and organic load, the overall chemical oxygen demand and color removal yields being rapidly restored to 80%. Yet, subsequent azo dye metabolite bioconversion was not observed, along the 315-day run. Moreover, switching from a starch-based substrate to acetate in the feed composition deteriorated AGS stability. Overall, the plug-flow fed SBR recovered more rapidly from the imposed disturbances. Further research is needed towards guaranteeing long-term AGS stability during the treatment of textile wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • AGS characteristics and nutrient removal were unaffected by 5–10 mg/L AO7. • 1.0% salinity level facilitated AGS structural stability and enhanced AO7 removal. • AO7 degradation bacteria and functional enzyme were enriched at 1.0% salinity level. • 1.0% salinity level up-regulated the genes involved with key metabolic functions. • Enhancement mechanism of AO7 degradation under low salinity conditions was revealed. The biodegradation performance of azo dyes can be enhanced under low salinity conditions, but the internal biodegradation mechanism is still unclear. Aerobic granular sludge (AGS), a salt-tolerant biological wastewater treatment technology, was used in this study to explore the enhancement mechanism of acid orange 7 (AO7) degradation at low salinity level (1.0 %). Results indicated that the AGS structure and reactor performance were almost unaffected by different AO7 concentrations (5–10 mg/L). Compared with salt-free conditions, the AO7 removal efficiency was elevated by 9.9 %–19.0 % at 1.0 % salinity level, owing to the enrichment of AO7 decolorizing bacteria (e.g. Acinetobacter) and functional enzymes (e.g. FMN-dependent azoreductase). The up-regulated genes involving in the key metabolic functions (e.g. carbon metabolism and oxidative phosphorylation) promoted the electron and energy production, thereby facilitating the AO7 decolorization and degradation. These results aid understanding of the enhancement mechanism of AO7 biodegradation under low salinity conditions from macroscopic and microscopic perspectives. [ABSTRACT FROM AUTHOR]

• Fe@C composites enhanced the anaerobic degradation of azo dye. • The duration of bioaugmentation of Fe@C was greater than that of NZVI. • Synergistic interactions between the carbon layer and EPS improved electron utilization. • Intermittent dosage of Fe@C maintained the high expression of genes related to dye degradation. Nano zero-valent iron (NZVI) has been widely used to improve refractory wastewater treatment. However, the rapid dissolution of NZVI causes a waste of resources and an unstable bioaugmentation. Herein, to verify the essential role of slow release of NZVI on biological systems, a core-shell structured Fe@C composite was developed to demonstrate the long-term feasibility of Fe@C for enhancing azo dye biodegradation in comparison to a mixture of NZVI and carbon powder (Fe+C). The 150 days of long-term reactor operation showed that, although both Fe@C and Fe+C enhanced azo dye degradation, the former achieved a better performance than the latter. The strengthening effect of Fe@C was also more durable and stable than Fe+C. It may be due to the fact that the carbon layer of Fe@C could interact with extracellular polymeric substances (EPS) through physical adsorption and chemical bonding to form a stable buffer to regulate NZVI dissolution. The buffer layer could not only regulate the attack of H+ on NZVI to reduce its dissolution rate but also complex released Fe2+ and neutralize OH− to alleviate the passivation layer formed on the NZVI surface. Moreover, microbial community analysis indicated that both Fe@C and Fe+C increased the abundance of fermentative bacteria (e.g., Bacteroidetes_vadinHA17, Propionicicella) and methanogens (e.g., Methanobacterium), but only Fe@C promoted the growth of azo dye degraders (e.g., Clostridium, Geobacter). Metatranscriptomic analysis further revealed that only Fe@C could substantially stimulate the expression of azoreductase and redox mediator (e.g., riboflavin, ubiquinone) biosynthesis involved in the extracellular degradation of azo dye. This work provides novel insights into the bioaugmentation of Fe@C for refractory wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

The paper evaluates the different bioreactor systems in the treatment of real textile wastewater containing Reactive Red 120 dye concentrated in nanofiltration processes as well as real textile wastewater taken from a working factory. The two-stage sequential semi-fed batch bioreactors and the continuous system with activated carbon used as support material in the anaerobic fixed film bioreactor combined with an aerobic bioreactor, after an acclimatisation period, were very efficient in colour removal, which achieved 95%. The aromatic amine ( orthanilic acid) released as a result of the azo bond cleavage was traced both in anaerobic (accumulation) and aerobic (degradation) conditions. Biogas production in both systems was very low. Nevertheless indirect biogas production assessment showed some biogas production potential in nanofiltration concentrate without an additional carbon source. Furthermore the nanofiltration concentrate did not inhibit biogas production from synthetic wastewater. Scanning electron microscope visualisation allowed for investigation of biofilm on activated carbon which consisted of at least two layers. [ABSTRACT FROM AUTHOR]

An anoxic fixed film bioreactor (FFB) with biomass immobilized on activated carbon and an aerobic continuous stirred tank bioreactor with overflow were applied to degrade concentrate from nanofiltration of real textile effluents containing Reactive Red 120 (RR-120). The efficiency of color removal was 99 % irrespective of the fraction of nanofiltration concentrate in the feed. An approximate dye balance based on the assessed adsorption capacity of RR-120 by activated carbon indicated that the dye was removed by means of adsorption as well as of biological processes. Aromatic amine released from a dye molecule was fully adsorbed by activated carbon. COD level in the outflow of the system was above that imposed by legislation. Despite an adjustment of the feed pH to 7 this was constantly increasing up to the value above 9 in both reactors. Neither the nanofiltration concentrate nor the effluents from the bioreactors affected the growth of Pseudomonas putida used as toxicity indicator. [ABSTRACT FROM AUTHOR]

The complete biodegradation of azo dye, Fast Acid Red GR, was observed under microaerophilic conditions by Shewanella decolorationis S12. Although the highest decolorizing rate was measured under anaerobic condition and the highest biomass was obtained under aerobic condition, a further biodegradation of decolorizing products can only be achieved under microaerophilic conditions. Under microaerophilic conditions, S. decolorationis S12 could use a range of carbon sources for azo dye decolorization, including lactate, formate, glucose and sucrose, with lactate being the optimal carbon source. Sulfonated aromatic amines were not detected during the biotransformation of Fast Acid Red GR, while H2S formed. The decolorizing products, aniline, 1,4-diaminobenzene and 1-amino-2-naphthol, were followed by complete biodegradation through catechol and 4-aminobenzoic acid based on the analysis results of GC-MS and HPLC. [ABSTRACT FROM AUTHOR]

The biodegradation of dyes remains one of the biggest challenges of textile wastewater. Azo dyes are one of the most commonly employed dye classes, and biological treatment processes tend to generate recalcitrant aromatic amines, which are more toxic than the parent dye molecule. This study aimed to isolate bacterial strains with the capacity to degrade both the azo dye and the resulting aromatic amines towards the development of a simple and reliable treatment approach for dye-laden wastewaters. A mixed bacterial enrichment was first developed in an anaerobic-aerobic lab-scale sequencing batch reactor (SBR) fed with a synthetic textile wastewater containing the model textile azo dye Acid Red 14 (AR14). Eighteen bacterial strains were isolated from the SBR, including members of the Acinetobacter , Pseudomonas and Oerskovia genera, Oerskovia paurometabola presenting the highest decolorization capacity (91% after 24 h in static anaerobic culture). Growth assays supported that this is a facultative bacterium, and decolorization batch tests with 20–100 mg AR14 L−1 in a synthetic textile wastewater supplemented with yeast extract indicated that O. paurometabola has a high color removal capacity for a significant range of AR14 concentrations. In addition, a model typically used to describe biodegradation of xenobiotic compounds was adjusted to the results, to predict AR14 biodegradation time profiles at different initial concentrations. HPLC analysis confirmed that decolorization occurred through azo bond reduction under anaerobic conditions, the azo dye being completely reduced after 24 h of anaerobic incubation for the range of concentrations tested. Interestingly, partial (up to 63%) removal of one of the resulting aromatic amines (4-amino-naphthalene-1-sulfonic acid) was observed when subsequently subjected to aerobic conditions. Overall, this work showed the azo dye biodegradation potential of specific bacterial strains isolated from mixed culture bioreactors, reporting for the first time the decolorization capacity of an Oerskovia sp. with further biodegradation of a recalcitrant sulfonated aromatic amine metabolite. Image 1 • High azo dye decolorization capacity in O. paurometabola was newly demonstrated. • Decolorization occurred by anaerobic azo bond reduction, generating aromatic amines. • O. paurometabola aerobically converted one of the azo dye reduction product amines. • A simple model was adjusted to the decolorization in view of further scale-up. [ABSTRACT FROM AUTHOR]