Efficient sulfur cycling improved the performance of flowback water treatment in a microbial fuel cell

Unlocking the applicability of Ni-based self-supported anodes in microbial fuel cells for the shale gas flowback wastewater treatment

The NiCo2O4 (NCOC) and Ni-P (NPC) self-supported anodes were successfully fabricated and utilized in microbial fuel cells (MFCs) for the treatment of actual shale gas flowback wastewater in this study. As a result, the NCOC and NPC displayed outstanding output voltages at 579.1 mV and 537.1 mV, as well as significantly decreased apparent internal resistances to 228.3 Ω and 396.7 Ω compared to the blank carbon cloth (CC, 206.7 mV and 1850.0 Ω). The electrochemical properties, rough surfaces and biocompatibility of NCOC (649.8 mW/m2) and NPC (436.1 mW/m2) endowed MFCs with superior power generation that was 11.7 and 7.8 times that of CC (55.7 mW/m2). Additionally, the removal ratios of the chemical oxygen demand based on NCOC and NPC achieved 61.5 % (1040.4 ± 34.1 mg/L) and 67.2 % (1136.7 ± 34.1 mg/L) with the increased energy conversion ratios from 8.4 % to 11.2 % and 9.7 %. Ultimately, the successful formation of the biofilms and the enrichment of the functional microorganisms such as Marinobacterium, Halomonas and Desulfuromonas on the prepared anodes further verified that NCOC and NPC could be potential research candidates in MFCs for decontaminating high-salty industrial wastewater.

Impact of sediment microbial fuel cells on the distribution of different forms of phosphorus in lake sediment and water

The continuous release of phosphorus from sediments by geochemical processes can cause endogenous eutrophication. This study examined the effect of carbon felt-sediment microbial fuel cells (CF-SMFCs) on the release of deposited phosphorus into the overlying water. In the CF-MFC system, the voltage ranged from 27 to 584 mV and the anode electrode potential increased from -130 mV to 202 mV. The Standard Measurements and Testing (SMT) method was employed to sequentially extract the sediment phosphorus in the sediments. A notable vertical increase in NaOH-P and HCl-P concentrations was observed downward in the sediment. The DGT phosphorus, visualized by Zr-Oxide DGT with submillimeter resolution, was removed by 52.04% in CF-SMFC. CF-SMFC notably facilitated the stabilization of phosphorus, promoting its conversion from pore water to sediment. The underlying mechanism suggests that the dissolution of solid-phase phosphorus into the overlying water was mitigated by the competition for organic substrates between Fe(III) reduction and the solid electrode. CF-SMFC can be used to increase the redox potential of the sediment and in-situ stabilize phosphorus in the sediment.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor

The high-concentration sulfate (SO42-) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42- removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42- removal rate (SRR) of 113.2 ± 5.7 mg SO42--S L-1 d-1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L-1 d-1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42--S L-1 d-1; SPR = 25.5 ± 9.7 mg S0-S L-1 d-1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g-1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42- reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Chemical-physical parameters and microbial community changes induced by electrodes polarization inhibit PCB dechlorination in a marine sediment

Microbial reductive dechlorination of organohalogenated pollutants is often limited by the scarcity of electron donors, that can be overcome with microbial electrochemical technologies (METs). In this study, polarized electrodes buried in marine sediment microcosms were investigated to stimulate PCB reductive dechlorination under potentiostatic (-0.7 V vs Ag/AgCl) and galvanostatic conditions (0.025 mA·cm-2-0.05 mA·cm-2), using graphite rod as cathode and iron plate as sacrificial anode. A single circuit and a novel two antiparallel circuits configuration (2AP) were investigated. Single circuit polarization impacted the sediment pH and redox potential (ORP) proportionally to the intensity of the electrical input and inhibited PCB reductive dechlorination. The effects on the sediment's pH and ORP, along with the inhibition of PCB reductive dechlorination, were mitigated in the 2AP system. Electrodes polarization stimulated sulfate-reduction and promoted the enrichment of bacterial clades potentially involved in sulfate-reduction as well as in sulfur oxidation. This suggested the electrons provided were consumed by competitors of organohalide respiring bacteria and specifically sequestered by sulfur cycling, which may represent the main factor limiting the applicability of METs for stimulating PCB reductive dechlorination in marine sediments.