Mixed dye wastewater treatment in a bioelectrochemical system-centered process

Advances from conventional to biochar enhanced biotreatment of dyeing wastewater: A critical review

DW (Dyeing wastewater) contains a large amount of dye organic compounds. A considerable proportion of dye itself or its intermediate products generated during wastewater treatment process exhibits CMR (Carcinogenic/Mutagenic/Toxic to Reproduction) toxicity. Compared with physicochemical methods, biological treatment is advantageous in terms of operating costs and greenhouse gas emissions, and has become the indispensable mainstream technology for DW treatment. This article reviews the adsorption and degradation mechanisms of dye organic compounds in wastewater and analyzed different biological processes, ranging from traditional methods to processes enhanced by biochar (BC). For traditional biological processes, microbial characteristics and communities were discussed, as well as the removal efficiency of different bioreactors. BC has adsorption and redox electron mediated effects, and coupling with biological treatment can further enhance the process of biosorption and degradation. Although BC coupled biological treatment shows promising dye removal, further research is still needed to optimize the treatment process, especially in terms of technical and economic competitiveness.

Anaerobic-aerobic treatment of high-strength and recalcitrant textile dyeing effluents

Eco-friendly treatment of complex textile and dyeing wastewaters poses a pressing environmental concern. An approach adopting different treatment paths and integrated anaerobic-aerobic processes for high-strength and recalcitrant textile dyeing wastewater was examined. The study demonstrated that over 97% of suspended solids (SS) and more than 70% of chemical oxygen demand (COD) were removed by polyaluminum chloride pre-coagulation of suede fabric dyeing stream. Up to 58% of COD and 83% of SS were removed through hydrolysis pretreatment of other low-strength streams. Notable COD removal of up to 99% from a feed of 20,862 mg COD/L was achieved by integrated anaerobic-aerobic treatment of high strength stream. Besides achieving high COD removal of 97%, the anaerobic granular sludge process demonstrated multi-faceted attributes, including high feed loading, smaller footprint, little sludge production, and good stability. The integrated anaerobic-aerobic treatment offers a robust and viable option for highly contaminated and recalcitrant textile dyeing wastewater.

Electrochemical degradation of acrylic acid using Ti/Ta2O5-IrO2 electrode

Acrylic acid (AA) is widely used as a raw material in the industrial production of various chemicals. Its extensive use has produced environmental problems that need to be solved. The Ti/Ta₂O₅-IrO₂ electrode, a type of dimensionally stable anode, was used to investigate the electrochemical deterioration of AA. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis showed that IrO₂ existed as an active rutile crystal and as a TiO₂-IrO₂ solid solution in Ti/Ta₂O₅-IrO₂ electrode with a corrosion potential of 0.212 V and chlorine evolution potential of 1.30 V. The effects of current density, plate spacing, electrolyte concentration, and initial concentration on the electrochemical degradation of AA were investigated. Response surface methodology (RSM) was used to determine the ideal degradation conditions: current density 22.58 mA cm^-2, plate spacing 2.11 cm, and electrolyte concentration 0.07 mol L^-1, and the highest degradation rate reached was 95.6%. Free radical trapping experiment verified that reactive chlorine played a dominant role in the degradation of AA. The degradation intermediates were analyzed by GC-MS.

Evaluation of the Respective Contribution of Anode and Cathode for Triclosan Degradation in a Bioelectrochemical System

In this work, the bioelectrochemical system (BES) is a feasible alternative for successfully degrading typical refractory emerging contaminant triclosan (TCS). A single-chamber BES reactor with an initial TCS concentration of 1 mg/L, an applied voltage of 0.8 V, and a solution buffered with 50 mM PBS degraded 81.4±0.2% of TCS, exhibiting TCS degradation efficiency improvement to 90.6±0.2% with a biocathode formed from a reversed bioanode. Both bioanode and biocathode were able to degrade TCS with comparable efficiencies of 80.8±4.9% and 87.3±0.4%, respectively. Dechlorination and hydrolysis were proposed as the TCS degradation pathway in the cathode chamber, and another hydroxylation pathway was exclusive in the anode chamber. Microbial community structure analysis indicated Propionibacteriaceae was the predominant member in all electrode biofilms, and the exoelectrogen Geobacter was enriched in anode biofilms. This study comprehensively revealed the feasibility of operating BES technology for TCS degradation.

Modified biochar prepared from Retinervus luffae fructus for dyes adsorption and aerobic sludge granulation

Retinervus luffae fructus biochar (RLFB) and ZnCl2 pretreated Retinervus luffae fructus biochar (ZRLFB) were prepared by pyrolysis. The as-prepared biochar was investigated for its applicability as a dye adsorber using sunset yellow (SY) and basic red 46 (BR46) dyes. Additionally, ZRLFB was used for the experimental cultivation of granular sludge. The results indicated that the adsorption effect of ZRLFB on the two dyes was higher than RLFB. The adsorption of RLFB to SY was related to the Langmuir and Freundlich models, whereas the adsorption of RLFB-BR46, ZRLFB-SY, and ZRLFB-BR46 was more in line with the Langmuir model. The adsorption process of dyes on two kinds of biochars can be described using pseudo-second-order mechanisms. The maximum adsorption capacity obtained was 1.9586 (RLFB-SY), 6.1286 (RLFB-BR46), 49.2611 (ZRLFB-SY), and 181.4882 mg g^-1 (RLFB-BR46). The result of the SBR operation showed that ZRLFB can potentially be applied as the core of aerobic granular sludge.

Anaerobic-anoxic-oxic biological treatment of high-strength, highly recalcitrant polyphenylene sulfide wastewater

This paper outlines an integrated anaerobic-anoxic-oxic (A2O) treatment scheme for high-strength, highly recalcitrant wastewater from the production of polyphenylene sulfide (PPS) resins and their composite chemicals. An integrated anaerobic granular sludge blanket (GSB) and anoxic-oxic (AO) reactor indicated that the A2O removed chemical oxygen demand (COD) of up to 7,043 mg/L with no adverse impact from high total dissolved solids (25,000 mg/L) on the GSB COD removal and effluent suspended solids. At a Total Kjeldahl Nitrogen (TKN) nitrification load of 0.11 g TKN/L.d and 400 mg NH₃/L, almost 99 % of the NH₃ was degraded with effluent NH₃ < 5 mg/L, meeting the limit of 35 mg/L. High S^2- levels of up to 1470 mg/L can be transformed through aerobic microbial degradation to meet a limit of 1.0 mg/L. With proper microbial acclimation and process designs, the integrated A2O scheme offers a resilient and robust treatment for high-strength recalcitrant PPS wastewater.

Treatment of wastewater containing methyl orange dye by fluidized three dimensional electrochemical oxidation process integrated with chemical oxidation and adsorption

The integrated high-efficiency treatment technology for dye industry wastewater is one of the current research hot topic in industrial wastewater treatment area. This article reports a new fluidized three-dimensional electrochemical treatment process integrating activated carbon adsorption, direct electro-oxidation and ·OH oxidation. In the process, activated carbon is polarized in a fluidized bed electrochemical reactor to enhance the direct electro-oxidation and ·OH oxidation, and there is a synergistic effect of effective adsorption and electrochemical oxidation to strengthen the treatment efficiency. When 200 mg/L methyl orange is processed, its removal rate reaches 99.9% in 30min, and the synergistic efficiency is 57.3%. After 8 cycles of activated carbon reusage in the process, the removal rate of methyl orange still kept at 89.2%. It is also founded that the activated carbon maintains 64.5% of its original adsorption capacity during the cycle. These results shows its interesting application potential in the fields of high-efficiency, low-cost and green treatment of various industrial organic wastewaters. Further improvements should focus on the development of continuous operation model and the improvement of the activated carbon electro-catalytic performance and the practical regeneration ways of the activated carbon particle electrodes.

Pilot-Scale Anaerobic Treatment of Printing and Dyeing Wastewater and Performance Prediction Based on Support Vector Regression

Printing and dyeing wastewater is characterized with complex water quality and poor biodegradability. In this study, a pilot-scale anaerobic baffled reactor (ABR) with packing was verified to effectively degrade the complex organic pollutants in the wastewater through the hydrolysis and acidification of anaerobic microorganisms. At a hydraulic retention time (HRT) of 12 h and an organic loading rate (OLR) of 2.0–2.5 kg COD/(m3·d), the ABR stabilized the fluctuation range of pH and achieved an average colority removal rate of 10.5%, which provided favorable conditions for subsequent aerobic treatment. During the early operation period, the reactor increased the alkalinity of the wastewater; after 97 days of operation, the volatile fatty acid (VFA) content in the wastewater decreased. To demonstrate the suitability of the support vector regression (SVR) technology in predicting the performance of the reactor, two SVR algorithms with three kernel functions were employed to relate the chemical oxygen demand (COD) removal rate to its influencing factors, and the predictions of both the training and validation groups agreed with the measurements. The results obtained from this study can contribute to the design and optimal operation of the anaerobic treatment project of the industrial wastewater treatment plant.

Development of biogenic bimetallic Pd/Fe nanoparticle-impregnated aerobic microbial granules with potential for dye removal

The objective of this study was to develop bimetallic core-shell Pd/Fe nanoparticles on the surface of aerobic microbial granules (Bio-Pd/Fe) and to evaluate their dye removal potential using a representative dye, methyl orange (MO). The aerobic microbial granules (1.5 ± 0.32 mm) were grown for 70 days in a 3-L glass sequencing batch reactor (SBR) with a 12-h cycle time. The Bio-Pd/Fe formation was catalyzed by the Bio-H₂ gas produced by the granules. The developed Bio-Pd/Fe was further used for MO removal from aqueous solutions, and the reaction parameters were optimized by response surface methodology (RSM). The XRD, SEM, EDAX, elemental mapping, and XPS studies confirmed the formation of Bio-Pd/Fe. Under the optimized removal conditions, 99.33% MO could be removed by Bio-Pd/Fe, whereas removal by Bio-Pd, Bio-Fe, aerobic microbial granules, and heat-killed granules were found to be quite low (68.91 ± 0.2%, 76.8 ± 0.3%, 19.8 ± 0.6%, and 6.59 ± 0.2%, respectively). The mechanism of removal was investigated by UV-visible spectroscopy, redox potential analysis, HR-LCMS analyses of the solution phase, and XRD and XPS analyses of the solid sorbent. The degradation products of MO exhibited m/z values corresponding to 292, 212, and 160 m/z. The remnant toxicity of the intermediate degradation products was analysed using freshwater algae, Scenedesmus sp. And Allium cepa, as indicator organisms. These assays suggested that after the treatment with Bio-Pd/Fe, MO was transformed to a lesser toxic form.

Responses of microbial communities and their interactions to ibuprofen in a bio-electrochemical system

Ibuprofen has caused great concerns due to their potential environmental risks. However, their removal efficiency and their effects on microbial interactions in bio-electrochemical system remain unclear. To address these issues, a lab-scale bio-electrochemical reactor integrated with sulfur/iron-mediated autotrophic denitrification (BER-S/IAD) system exposing to 1000 μg L^-1 ibuprofen was operated for about two months. Results revealed that the BER-S/IAD system obtained efficient simultaneous denitrification (98.93%) and phosphorus (82.67%) removal, as well as an excellent ibuprofen removal performance (96.98%). Ibuprofen had no significant impacts on the nitrate (NO₃^--N) removal and the ammonia (NH₄⁺-N) accumulation, but decreased the total nitrogen (TN) and total phosphorus (TP) removal efficiencies. MiSeq sequencing analysis revealed that ibuprofen significantly (P < 0.05) decreased the microbial community diversity and changed their overall structure. Some bacteria related to denitrification and phosphorus removal, such as Pseudomonas and Thiobacillus, decreased significantly (P < 0.05). Moreover, molecular ecological network (MEN) analysis revealed that ibuprofen decreased the network's size and complexity, and enhanced the negative correlations of Proteobacteria and Firmicutes. Besides, ibuprofen decreased the links of some keystone bacteria related to denitrification and phosphorus removal. This research could provide a new dimension for our comprehending of the responses of microbial communities and their interactions to ibuprofen in bio-electrochemical system.

Pulsed Discharge Plasma in High-Pressure Environment for Water Pollutant Degradation and Nanoparticle Synthesis

The application of high-voltage discharge plasma for water pollutant decomposition and the synthesis of nanoparticles under a high-pressure argon gas environment (~4 MPa) was demonstrated. The experiments were carried out in a batch-type system at room temperature with a pulsed DC power supply (15.4 to 18.6 kV) as a discharge plasma source. The results showed that the electrode materials, the pulsed repetition rates, the applied number of pulses, and the applied voltages had a significant effect on the degradation reactions of organic compounds. Furthermore, carbon solid materials from glycine decomposition were generated during the high-voltage discharge plasma treatment under high-pressure conditions, while Raman spectra and the HRTEM images indicated that titanium dioxide with a brookite structure and titanium carbide nanoparticles were also formed under these conditions. It was concluded that this process is applicable in practice and may lead to advanced organic compound decomposition and metal-based nanoparticle synthesis technologies.

Electro-Fenton assisted sonication for removal of ammoniacal nitrogen and organic matter from dye intermediate industrial wastewater

The intricacy in the treatment of effluents from the textile sector attracts the researchers since 20th century. Dye intermediate manufacturing industries are responsible for producing the toxic pollutants such as nitro-aromatics, benzene, toluene, phenol, heavy metals etc. with intense colour. The present study focuses on the performance of combined Electro-Fenton (EF) and sonication for the removal of ammoniacal nitrogen and COD from dye intermediate manufacturing wastewater. Batch experiments of EF were performed using graphite electrodes and sonication was applied to the EF treated wastewater to enhance the treatment performance. A number of experiments were executed to discover the influence of pH, applied voltage, Fenton catalyst dosage and time of electrolysis on the removal efficiency of EF batch process was scrutinized. The pH was varied between 2 and 4, applied voltage from 1 to 4V, Fenton catalyst dosage between 50 and 200 mg L^-1 and time between 15 and 180 min. At optimum condition i.e. pH 3, applied voltage 3V, Fenton catalyst dosage of 100 mg L^-1and 120 min electrolysis time, the percentage removal obtained for ammoniacal nitrogen and COD were 59.4% and 79.2% respectively. The removal efficiency was increased to 65.5% for ammoniacal nitrogen and 85.4% for COD after applying sonication to the EF treated wastewater. The removal of ammoniacal nitrogen and COD can be achieved in a scientific and feasible way by combining EF process with sonication.

Startup and performance of full-scale anaerobic granular sludge blanket reactor treating high strength inhibitory acrylic acid wastewater

High strength inhibitory wastewaters from chemical industries are commonly treated by energy-intensive physicochemical methods. The present work examines the startup and performance of a full-scale anaerobic granular sludge blanket (GSB) plant for treatment of an inhibitory acrylic acid wastewater. From a performance test on chemical oxygen demand (COD) loading up to 9800 mg/L and 3074 kg/d, the GSB plant removed 95% of COD. Coupled with a two-stage aerobic effluent polishing unit, the integrated anaerobic-aerobic plant achieved a remarkable total COD removal of 98-99% at full design load. Final effluent ranging from 173 to 278 mg COD/L conformed to the public sewer limits of 500 mg/L. Acclimated microbes and granulation resulted in efficient degradation of the inhibitory wastewater. Adequate reactor and process designs are crucial for granulation and robust treatment. The anaerobic and aerobic processes complement each other as anaerobic prime degrader and aerobic polisher in the integrated processes.

Laboratory trial and full-scale implementation of integrated anaerobic-aerobic treatment for high strength acrylic acid wastewater

Sustainable treatment of highly polluting industrial wastewaters poses a challenge to many municipalities. This study presented treatment of a high strength inhibitory acrylic acid wastewater by integrated anaerobic-aerobic processes. A novel scheme integrating anaerobic granular sludge blanket (GSB) reactor, aerobic carrier biofilm (CBR) reactor and activated sludge reactor (ASR) was tested. The laboratory trial showed that the GSB was able to degrade exceptionally high chemical oxygen demand (COD up to 32,420 mg/L) acrylic acid wastewater laden with 5% waste oil. Operated under a high volumetric loading (VLR) rate of 21.6 g/L·d, the integrated GSB-CBR-ASB achieved 99% of COD removal, of which 90% were removed by the anaerobic process and 9% by the aerobic processes. Full-scale implementation indicated comparable performance with overall removal up to 99%, thus meeting the discharge limits of 500 mg COD/L of public sewer. The integrated scheme was effective in which the anaerobic GSB functioning as a prime degrader that degraded most of the pollutants, while the aerobic CBR-ASB serving as a polisher that removed the remaining COD. With adequate microbial acclimation and granulation, the novel integrated scheme offers a resilient and robust treatment system for high strength inhibitory acrylic acid wastewater.

Towards the practical application of bioelectrochemical anaerobic digestion (BEAD): Insights into electrode materials, reactor configurations, and process designs

Anaerobic digestion (AD) is one of the most widely adopted bioenergy recovery technologies globally. Despite the wide adoption, AD has been challenged by the unstable performances caused by imbalanced substrate and/or electron availability among different reaction steps. Bioelectrochemical anaerobic digestion (BEAD) is a promising concept that has demonstrated potential for balancing the electron transfer rates and enhancing the methane yield in AD during shocks. While great progress has been made, a wide range of, and sometimes inconsistent engineering and technical strategies were attempted to improve BEAD. To consolidate past efforts and guide future development, a comprehensive review of the fundamental bioprocesses in BEAD is provided herein, followed by a critical evaluation of the engineering and technical optimizations attempted thus far. Further, a few novel directions and strategies that can enhance the performance and practicality of BEAD are proposed for future research to consider. This review and outlook aim to provide a fundamental understanding of BEAD and inspire new research ideas in AD and BEAD in a mechanism-informed fashion.

Construction of a new lipase- and xylanase-producing oleaginous yeast consortium capable of reactive azo dye degradation and detoxification

A new oleaginous yeast consortium Y-BC-SH which stands for molecularly identified species Yarrowia sp., Barnettozyma californica and Sterigmatomyces halophilus was successfully constructed in this study. This multipurpose oleaginous yeast consortium was developed based on its higher ability to accumulate large amounts of lipids in the form of triacylglycerol, grow on xylose, produce lipase and xylanase and it could rapidly decolorize and degrade commonly-used textile reactive azo dyes. The specific enzyme activities of lipase, xylanase, xylan esterase, β-xylosidase, CMCase, β-glucosidase and cellobiohydrolase produced by Y-BC-SH were significantly higher than that of individual strains. As chemical oxygen demand reduction had occurred in the dye mixture solutions, it was evidence of their color removal and mineralization by Y-BC-SH. The significant induction of oxidoreductive enzymes by Y-BC-SH was probably due to the coordinated metabolic interactions of the individual strains. Phytotoxicity assay confirmed that metabolites generated after dye degradation by Y-BC-SH are non-toxic.

Laboratory and full-scale performances of integrated anaerobic granule-aerobic biofilm-activated sludge processes for high strength recalcitrant paint wastewater

Sustainable treatment of wastewaters generated from paint production is increasingly posing an environmental concern. Recalcitrant paint wastewaters are mostly treated by energy and cost intensive physicochemical methods like incineration, distillation or advanced oxidation. This paper reported for the first time a case study applying biological treatment processes to properly handle a high-strength recalcitrant paint wastewater with 5-day biochemical oxygen demand (BOD₅)/chemical oxygen demand (COD) less than 0.02. A biological treatment scheme integrating anaerobic granular sludge blanket reactor, aerobic carrier biofilm reactor and aerobic activated sludge bioreactor was proposed and examined. Laboratory and full-scale trials demonstrated satisfactory operation with overall COD removal up to 99%. Besides yielding consistent effluent quality conforming to the discharge limits, the full-scale plant gained considerable savings in operating cost over a 5-year operation. With proper microbial adaptation and cultivation, as well as adequate reactor and process designs, the scheme offers a good feasibility for efficient and cost-effective treatment of the high strength and recalcitrant paint wastewater.

Fabrication and Characterization of a Novel Composite Magnetic Photocatalyst β-Bi2O3/BiVO4/MnxZn1-xFe2O4 for Rhodamine B Degradation under Visible Light

β-Bi₂O₃/BiVO₄/Mn_xZn_1−xFe₂O₄ (BV/MZF) composite magnetic photocatalyst was first synthesized using the hydrothermal and calcination method. BV/MZF was a mesoporous material with most probable pore size and specific surface area of 18 nm and 17.84 m²/g, respectively. Due to its high saturation magnetization (2.67 emu/g), the BV/MZF composite can be easily separated and recovered from solution under an external magnetic field. The results of photo-decomposition experiments show that the decomposition rate of Rhodamine B (RhB) by BV/MZF can reach 92.6% in 3 h under visible light. After three cycles, BV/MZF can still maintain structural stability and excellent pollutant degradation effect. In addition, analysis of the photocatalytic mechanism of BV/MZF for RhB shows that the p-n heterojunction formed in BV/MZF plays a vital role in its photocatalytic performance. This work has potential application in the future for solving environmental pollution.