Study on Start-Up Membraneless Anaerobic Baffled Reactor Coupled with Microbial Fuel Cell for Dye Wastewater Treatment

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.

Performance and response of coupled microbial fuel cells for enhanced anaerobic treatment of azo dye wastewater with simultaneous recovery of electrical energy

The anaerobic baffled reactor (ABR) is an anaerobic bioreactor that uses baffles to separate the working area into multiple reaction zones. The ABR-microbial fuel cell (MFC) reactor was constructed by embedding MFC in each reaction zone of the ABR. Its degradation of azo dye type (acid mordant red) wastewater and microbial power generation performance were investigated. For different electrode area ratios, the best enhanced treatment and electrical energy output of the coupled system was achieved with an anode/cathode area ratio of 1:1. Compared with the electrode area ratio of 2:1 and 1:2, the power density increased by 82.5% and 80.6%, and the Coulomb efficiency increased by 133.3% and 64.7%. In addition, the best enhanced treatment of printing and dyeing wastewater was achieved by ABR-MFC at 1:1. At a dye concentration of 200 mg/L and a sucrose concentration of 1000 mg/L, the coupled system obtained a COD removal of 92.85% and a chromaticity removal of 96.2%, which achieved a relative COD and chromaticity removal improvement of 1.82% and 2.64%, respectively, relative to the ABR. Scanning electron microscopy (SEM) observation of the electrodes at 1:1 revealed that more microorganisms were attached to the anode surface of the coupled system, the particle size of the granular sludge within the system was larger, and the UV scanning pattern showed lower dye concentration in the water. In conclusion, the microbial fuel cell enhanced anaerobic treatment of dyeing wastewater was the most effective when the electrode area ratio was 1:1, and the best electrical energy output was obtained at the same time. ABR-MFC provides a new idea for the enhanced treatment of dyeing wastewater and electrical energy production.

Unravelling the biodegradation performance and mechanisms of acid orange 7 by aerobic granular sludge at different salinity levels

Azo dyes wastewater is characterized by high-salinity, however, the biodegradation performance and mechanisms of azo dyes by aerobic granular sludge (AGS) under different salinity levels are still unclear. Herein, the results showed that the reactor performance was almost unaffected at low-salinity levels (0.5%-1.0% salinity), and the removal efficiency of acid orange 7 (AO7) was increased by 2.6%-19.1%, possibly due to the excessive secretion of extracellular polymeric substances (EPS) and the enrichment of functional bacteria. Nevertheless, the microbial cell viability was negatively affected by high-salinity level (2.0% salinity), leading to the deterioration of AO7 and nutrient removal efficiencies. The AO7 removal was achieved by rapid adsorption and slow biodegradation. The biodegradation pathway indicated that AO7 was gradually mineralized in the AGS system through desulfurization, deamination, decarboxylation and hydroxylation. Altogether, this work provides an important reference for the application of AGS technology for treating saline azo dye wastewaters.

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.