Continuous flow operation with appropriately adjusting composites in influent for recovery of Cr(VI), Cu(II) and Cd(II) in self-driven MFC-MEC system

Bioelectrochemical systems-based metal removal and recovery from wastewater and polluted soil: Key factors, development, and perspective

Bioelectrochemical systems (BES) are considered efficient and sustainable technologies for bioenergy generation and simultaneously removal/recovery metal (loid)s from soil and wastewater. However, several current challenges of BES-based metal removal and recovery, especially concentrating target metals from complex contaminated wastewater or soil and their economic feasibility of engineering applications. This review summarized the applications of BES-based metal removal and recovery systems from wastewater and contaminated soil and evaluated their performances on electricity generation and metal removal/recovery efficiency. In addition, an in depth review of several key parameters (BES configurations, electrodes, catalysts, metal concentration, pH value, substrate categories, etc.) of BES-based metal removal and recovery was carried out to facilitate a deep understanding of their development and to suggest strategies for scaling up their specific application fields. Finally, the future intervention on multifunctional BES to improve their performances of mental removal and recovery were revealed.

Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment

Microbial fuel cells (MFC_S) is a promising and expanding technology able to eliminate various pollutants of wastewater while converting its chemical energy into power energy using biocatalysts. The potential application of double-chamber microbial fuel cell (DC-MFC) for chemical oxygen demand (COD) removal and generated power from wastewater in the different conditions is investigated. DC-MFC is operated with anaerobic sludge as an active biocatalyst in an anode section, an aerobic cathode section and a Nafion117 membrane as a separator. The performance of the bioreactor is determined with different concentrations of chemical oxygen demand (COD) loadings in the MFC process, in terms of COD removal, power generation and columbic efficiencies. The results illustrated that COD removal efficiency increased at the high concentrations of organic matter. So that at COD concentration of 2000.0 mg/L the highest COD removal efficiency (84%) was obtained. But with increasing substrate initial concentration to 10000.0 mg/L the efficiency decreased to 79%. The important outputs of the system like the highest voltage, maximum generated power, current density, and energy efficiency with the 100,000 mg/L COD are 447 mV, 50.7 mW/m², 570.0 mA/m², and 18.6%, respectively. The optical density levels increased due to bacterial growth while pH severely decreased in the anode chamber when using high-concentration substrates in the MFC.

Process performance and microbial community functional structure in a thermophilic anaerobic baffled reactor coupled with biocatalysed electrolysis

In this study, the performances of a conventional anaerobic baffled reactor (ABR) and an ABR combined with microbial electrolysis cells (MECs) for enhancing degradation of volatile fatty acids (VFAs) were evaluated in 55°C. The ABR-MECs system achieved a total chemical oxygen demand (COD) removal rate of 97.2% and a methane yield of 236 ± 5 mL g^-1 COD_removed at organic loading rate (OLR) of 6.9 kg COD m^-3 d^-1, which were higher than those of the ABR with 77.6% and 207 ± 5 mL g^-1 COD_removed, respectively, at OLR of 5.1 kg COD m^-3 d^-1. The pyrosequencing analysis confirmed that the introduction of MECs into ABR was conducive to establishing stable functional communities of syntrophic fatty acids oxidizing bacteria (SFOB), exoelectrogens and hydrogenotrophic methanogens, such as Syntrophobacter (5.4%), Thermodesulfovibrio (2.0%), Methanobacterium (43.8%), Methanolinea (20.4%). The content of unclassified bacteria increased from 12.4% in the ABR system to 52.3% in the ABR-MECs system. In contrast, the proportion of aceticlastic methanogens decreased from 50.1% in the ABR to 24.5% in the ABR-MECs system. The improved performance of the thermophilic ABR-MECs system resulted from phase separation, wide ecological niche and intensification of methanogenesis process via functional microbes, which significantly enhanced the degradation of propionic acid and acetic acid.

Process optimization for simultaneous antibiotic removal and precious metal recovery in an energy neutral process

Conventional chemical and physical methods to remove antibiotics from wastewater consume large amount of energy and chemicals, and the efficiency of biological process in converting antibiotics is relatively low. Microbial electrolysis cell (MEC) has been employed to degrade recalcitrant organic compounds recently. Given it is an energy consuming device, it would be more sustainable if driven by renewable energy, e.g. power from microbial fuel cell (MFC). Here, chloramphenicol (CAP) was chosen as a representative antibiotic that is abundant in the environment, and Ag ion contained wastewater as electron acceptor in MFC, to demonstrate the feasibility of a self-driven system for recalcitrant removal and resource recovery. It was found that CAP removal in MEC can be successfully driven by Ag(I) reduced MFC without external energy consumption. Method of one-factor-at-a-time (OFAT) and response surface methodology (RSM) with central composite design were used to evaluate the system performance. Under the optimum condition, 99.8% of Ag(I) in MFC and 98.8% of CAP in MEC can be converted. EDX and XPS revealed that pure silver was obtained on the surface of electrode in MFC, reflecting Ag(I) was reduced to valuable product. The concept and methods developed in this study can be also applied to design other types of self-driven BES systems for simultaneous pollutants removal and resources recovery.

Deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production in stacked bioelectrochemical systems (BESs): Impact of heavy metals W(VI)/Mo(VI) molar ratio, initial pH and electrode material

The deposition and separation of W and Mo from aqueous solutions with simultaneous hydrogen production was investigated in stacked bioelectrochemical systems (BESs) composed of microbial electrolysis cell (1#) serially connected with parallel connected microbial fuel cell (2#). The impact of W/Mo molar ratio (in the range 0.01 mM : 1 mM and vice-versa), initial pH (1.5 to 4.0) and cathode material (stainless steel mesh (SSM), carbon rod (CR) and titanium sheet (TS)) on the BES performance was systematically investigated. The concentration of Mo(VI) was more influential than W(VI) in determining the rate of deposition of both metals and the rate of hydrogen production. Complete metal recovery was achieved at equimolar W/Mo ratio of 0.05 mM : 0.05 mM. The rates of metal deposition and hydrogen production increased at acidic pH, with the fastest rates at pH 1.5. The morphology of the metal deposits and the valence of the Mo were correlated with W/Mo ratio and pH. CR cathodes (2#) coupled with SSM cathodes (1#) achieved a significant rate of hydrogen production (0.82 ± 0.04 m³/m³/d) with W and Mo deposition (0.049 ± 0.003 mmol/L/h and 0.140 ± 0.004 mmol/L/h (1#); 0.025 ± 0.001 mmol/L/h and 0.090 ± 0.006 mmol/L/h (2#)).