Effects of electrochemical processes application on the modification of mixed liquor characteristics of an electro-membrane bioreactor (e-MBR)

Treatment of azo dye-containing wastewater in a combined UASB-EMBR system: Performance evaluation and membrane fouling study

This work investigated the treatment of azo dye-containing wastewater in an upflow anaerobic sludge blanket (UASB) reactor combined with an electro-membrane bioreactor (EMBR). Current densities of 20 A m-2 and electric current exposure mode of 6'ON/30'OFF were applied to compare the performance of the EMBR to a conventional membrane bioreactor (MBR). The results showed that dye (Drimaren Red CL-7B) removal occurred predominantly in the UASB reactor, which accounted for 57% of the total dye removal achieved by the combined system. When the MBR was assisted by electrocoagulation, the overall azo dye removal efficiency increased from 60.5 to 67.1%. Electrocoagulation batch tests revealed that higher decolorization rates could be obtained with a current density of 50 A m-2. Over the entire experimental period, the combined UASB-EMBR system exhibited excellent performance in terms of chemical oxygen demand (COD) and NH4+-N removal, with average efficiencies above 97%, while PO43--P was only consistently removed when the electrocoagulation was used. Likewise, a consistent reduction in the absorption spectrum of aromatic amines was observed when the MBR was electrochemically assisted. In addition to improving the pollutants removal, the use of electrocoagulation reduced the membrane fouling rate by 68% (0.25-0.08 kPa d-1), while requiring additional energy consumption and operational costs of 1.12 kWh m-3 and 0.32 USD m-3, respectively. Based on the results, it can be concluded that the combined UASB-EMBR system emerges as a promising technological approach for textile wastewater treatment.

Evaluating the performance and membrane fouling of a submerged membrane bioreactor (MBR) treating plywood industry wastewater

This study evaluates the performance of a membrane bioreactor (MBR) for treating wastewater from the laminated plywood industry. To this end, a pilot-scale MBR was operated for 60 days with a hydraulic retention time of 20 h and a solid retention time of 20 days. The reactor's performance was assessed based on the removal of chemical oxygen demand (COD), phenol, turbidity, and apparent color. Furthermore, we monitored the solids content, dissolved oxygen concentration, and pH of the mixed liquor, as well as the progression of the transmembrane pressure (TMP). The wastewater exhibited a COD/biochemical oxygen demand (BOD) ratio of 5.5, suggesting low biodegradability, usually when this ratio is higher than 4.0. Nevertheless, it was observed that the MBR's performance was stable and satisfactory, with average removal efficiencies of 98% for COD, 70% for phenol, 99% for turbidity, and 93% for true color. The evolution of TMP indicated gradual membrane fouling; however, the operational limit of 0.6 bar was not reached during the study period. In conclusion, the utilization of MBR presents a promising approach to mitigate the environmental impacts associated with wastewater from the laminated plywood industry.

Effects of solid retention time and exposure mode to electric current on Remazol Brilliant Violet removal in an electro-membrane bioreactor

The performance of an electrochemically assisted anoxic-oxic membrane bioreactor (A/O-eMBR) was assessed as an alternative for azo dye (Remazol Brilhant Violet (RBV)) removal from simulated textile wastewater. The A/O-eMBR was operated under three experimental conditions (runs I, II, and III), in which different solids retention time (SRT) (45 and 20 d) and exposure mode to electric current (6'ON/30'OFF and 6'ON/12'OFF) were assessed. The reactor exhibited excellent decolorization performance for all runs, with average dye removal efficiency ranging from 94.3 to 98.2%. Activity batch assays showed that the dye removal rate (DRR) decreased from 16.8 to 10.2 mg RBV L^-1 h^-1 when the SRT was reduced from 45 to 20 d, likely attributed to the lower biomass content under lower sludge age. At the electric current exposure mode of 6' ON/12'OFF, a more substantial decrease of DRR to 1.5 mg RBV L^-1 h^-1 was noticed, suggesting a possible inhibitory effect on dye removal via biodegradation. By reducing the SRT to 20 d, a worse mixed liquor filterability condition was observed, with a membrane fouling rate (MFR) of 0.979 kPa d^-1. In contrast, using the electric current exposure mode of 6'ON/12'OFF resulted in lower membrane fouling propensity, with an MFR of 0.333 kPa d^-1. A more attractive cost-benefit ratio for dye removal was obtained using the exposure mode of 6'ON/30'OFF, for which the energy demand was estimated at 21.9-22.6 kWh kg dye^-1 removed, almost two times lower than that observed for the mode of 6'ON/12'OFF.

Towards practical integration of MBR with electrochemical AOP: Improved biodegradability of real pharmaceutical wastewater and fouling mitigation

In the current study, we report enhanced treatment of real pharmaceutical wastewater by integration of Electrooxidation (EO) with Membrane Bio-Reactor (MBR) for the first time. Integrated pre-pilot EO-MBR plant consisted of a 3D printed electrochemical flowcell equipped with graphite electrodes installed in the effluent recirculation line of an MBR equipped with a hollow fiber membrane module. Results demonstrated that 5 V was the optimum voltage level for an isolated EO system. Isolated EO system led to 40% COD removal and 2.5 fold biodegradability index (BOD₅/COD) improvement after 24 hr treatment at the optimum voltage of 5 V and 160 mL.min^-1 flowrate. Almost complete removal of COD and BOD₅ was observed for the EO-MBR system with 160 mL.min^-1 recirculation rate and 24 hr HRT, while respective values were 60 and 87% for the MBR system at same operational conditions. Oxidation of pharmaceutical compounds identified in real wastewater and the fate of main oxidation-recalcitrant by-products were confirmed using liquid chromatography techniques. In addition, the integrated EO-MBR system led to significant membrane fouling mitigation with a 28 day extended operational time before reaching the Trans Membrane Pressure (TMP) limit value of 30 kPa. Measurements revealed reduced Extracellular Polymeric Substances (EPS) Concentration of membrane sludge cake layer of EO-MBR along with significant reduction of proteinaceous compounds in the LB-EPS fraction of cake layer in comparison with isolated MBR system. Fouling behavior improvement of the EO-MBR system was attributed to the electrophilic attack of electrochemically generated hydroxyl radicals to the electron-rich moieties of EPS organic foulants. Reduced proteinaceous/humic-like substances of LB-EPS from the cake layer were further confirmed by Emission Excitation matrix (EEM) and Fourier Transform InfraRed (FTIR) spectroscopic methods. The results of current research provide a helpful basis for future studies by elucidating the complex operating/fouling mechanism of integrated Advanced Oxidation Processes (AOPs) with MBR systems for enhanced treatment of organics polluted wastewaters with low biodegradability.

Effect of cathode material and charge loading on the nitrification performance and bacterial community in leachate treating Electro-MBRs

Electro-MBR technology, which combines an electrocoagulation process inside the mixed liquor of a membrane bioreactor, was studied for the treatment of a high-strength ammonia leachate (124 ± 4 mg NH₄-N L^-1). A lab-scale aerobic Electro-MBR was operated with a solid retention time of 45 days, hydraulic retention times of 24h and 12h, and charge loading ranging from 100 to 400 mAh L^-1. At 400 mAh L^-1, with a combination of a Ti/Pt cathode and a sacrificial iron anode, removal percentages for ammonia nitrogen, total organic carbon, and total phosphorus were 99.8%, 38%, and 99.0%, respectively. At 400 mAh L^-1, the estimated ferric ion dosage was 325 mg Fe³⁺ L^-1. Experiments conducted with different cathode materials showed that previously reported inhibition phenomena may result from a cathodic nitrate reduction into ammonia nitrogen. Conventional cathode materials, such as graphite, have electrochemical nitrate reduction rates of -0.03 mg NO₃-N mAh^-1. By comparison, when using Ti/Pt, the rate was -0.0045 mg NO₃-N mAh^-1(85% lower than graphite due to its low hydrogen overpotential). Charge loading tested in this study had no significant impact on both nitrification performance and microbial population diversity. However, the relative abundance of the mixed liquor's Nitrosomonas increased from 4.8% to 8.2% when the charge loading increased from 0 to 400 mAh L^-1. Results from this study are promising for future applications of the Ti/Pt - Iron Electro-MBR in various high-strength ammonia wastewater treatment applications.