Insights into the decolorization of mono and diazo dyes in single and binary dyes containing wastewater and electricity generation in up-flow constructed wetland coupled microbial fuel cell

Effect of Typha angustifolia, feeding modes and intermittent aeration on the performance of hybrid constructed wetland systems treating Reactive Black 5 diazo dye wastewater

The current research assessed the effectiveness of four hybrid constructed wetland (HCW) systems for the remediation of synthetic dye wastewater with Reactive Black 5 (RB5) azo dye. All HCW systems had identical configurations, consisting of a horizontal CW followed by a vertical CW, and operated under diverse conditions such as the presence of plants (Typha angustifolia), feeding modes (batch and continuous) and intermittent aeration (4 h day-1). Anaerobic-aerobic conditions simulated within the HCW systems were crucial in removing the pollutants from synthetic dye wastewater. The planted HCW system operating in continuous-continuous feeding mode exhibited better colour reduction (91%). The planted HCW system with continuous-continuous feeding mode and intermittent aeration achieved better COD (90%) and BOD5 (99%) removals, and a significant reduction in dye degradation intermediates generated from RB5 reduction. Typha angustifolia had a beneficial effect on pollutant removals, attributed to the enhanced microbial density and biomass activity in the plant rhizosphere. The microbial density and biomass activity in the rhizosphere region of the planted system were (116 ± 28) × 104 CFU mL-1 and 1074 mg COD g VSS-1 day-1, respectively, notably higher than those in the non-rhizosphere region of the planted system ((186 ± 97) × 102 CFU mL-1 and 794 mg COD g VSS-1 day-1) and the unplanted system ((91 ± 35) × 102 CFU mL-1 and 772 mg COD g VSS-1 day-1). The introduction of continuous feeding mode and intermittent aeration in vertical units further improved pollutant removals in the HCW system. This improvement could be attributed to the steady feeding approach inherent in continuous mode operation, which may result in less toxicity to the system and the degradation of organic compounds under more favourable aerobic conditions.

Kinetic study on the degradation of Acid Red 88 azo dye in a constructed wetland-microbial fuel cell inoculated with Shewanella oneidensis MR-1

Removal of Acid Red 88 (AR88) as an azo dye from the synthetic type of wastewater was studied in a laboratory-made constructed wetland microbial fuel cell (CW-MFC) inoculated with Shewanella oneidensis MR-1 (SOMR-1). Plant cultivation was implemented using a typical CW plant known as Cyperus alternifolius. The complexity of the SOMR-1 cell membrane having different carriers of electrons and H+ ions gives the microbe special enzymatic ability to participate in the AR88 oxidation link to the O2 reduction. Nernst equation developed based on analyzing the involved redox potential values in these electron exchanges is describable quantitatively in terms of the spontaneity of the catalyzed reaction. Power density (PD) at 100 mg/L of the AR88 under closed-circuit conditions in the presence of the plant was 11.83 mW/m2. Reduction of internal resistance positively affected the PD value. In determining degradation kinetics, two approaches were undertaken: chemically in terms of first- and second-order reactions and biochemically in terms of the mathematical equations for rate determination developed on the basis of substrate inhibitory concept. The first-order rate constant was 0.263 h-1 without plant cultivation and 0.324 h-1 with plant cultivation. The Haldane kinetic model revealed low ks and ki values indicating effective degradation of the AR88. Moreover, the importance of acclimatization in terms of the crucial role of lactate was discussed. These findings suggest that integrating the SOMR-1 electrochemical role with CW-MFC could be a promising approach for the efficient degradation of azo dyes in wastewater treatment.

Enhancement of energy recovery from caffeine wastewater in constructed wetland-microbial fuel cell through operating conditions

The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12% as the HRT extended from 1 to 5 d. The increment in contact time between the microbes and organic substrates promoted the degradation and contributed to higher power output (3.4-fold), CE (eightfold), and NER (14-16-fold). The MA and MC connections facilitated the electron transfer rate and the degradation rate of organic substrates in the multiple anodic zones, which enhanced the removal efficiency in the anaerobic compartment (Caffeine: 4.2%; COD: 7.4%) and led to higher electricity generation (Power: 4.7-fold) and energy recovery (CE: 1.4-fold; NER: 2.3-2.5-fold) compared to SA. The lower external resistance favored the growth of electrogens and induced higher electron flux, where the best treatment performance and electricity production was obtained when the external resistance approached the internal resistance. Overall, it was noteworthy that the optimum operating conditions were achieved with 5 d HRT, MA, and MC connection along with external resistance of 200 Ω, which significantly outperformed the initial conditions (1 d HRT, SA connection, and 1000 Ω) by 43.7 and 29.8% of caffeine and COD removal in the anaerobic compartment, respectively as well as 14-fold of power generation.

Transformation from biofiltration unit to hybrid constructed wetland-microbial fuel cell: Improvement of wastewater treatment performance and energy recovery

This study aimed to compare the performance of biofiltration, constructed wetland, and constructed wetland microbial fuel cell (CW-MFC). The transformation from a biofiltration unit to a hybrid CW-MFC was demonstrated with the advantages of improvement of wastewater treatment while generating electricity simultaneously. The introduction of plants to the upper region of the bioreactor enhanced the DO level by 0.8 mg/L, ammonium removal by 5 %, and COD removal by 1 %. The integration of electrodes and external circuits stimulated the degradation rate of organic matter in the anodic region (1 % without aeration and 3 % with aeration) and produced 5.13 mW/m³ of maximum power density. Artificial aeration improved the nitrification efficiency by 38 % and further removed the residual COD to an efficiency of 99 %. The maximum power density was also increased by 3.2 times (16.71 mW/m³) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m³ (4.6-fold) and the COD removal efficiency was 98 %. The ohmic overpotential dominated the proportion of total loss (67-91 %), which could be ascribed to the low ionic conductivity. The reduction in activation and concentration loss contributed to the lower internal resistance with the additional aeration and higher organic loading. Overall, the transformation from biofiltration to a hybrid CW-MFC system is worthwhile since the systems quite resemble while CW-MFC could improve the wastewater treatment as well as recover energy from the treated wastewater.