Bioelectricity generation by wetland plant-sediment microbial fuel cells (P-SMFC) and effects on the transformation and mobility of arsenic and heavy metals in sediment

Interactions between arsenic migration and CH4 emission in a soil bioelectrochemical system under the effect of zero-valent iron

Dissimilatory soil arsenic (As) reduction and release are driven by microbial extracellular electron transfer (EET), while reverse EET mediates soil methane (CH₄) emission. Nevertheless, the detailed biogeochemical mechanisms underlying the tight links between soil As migration and methanogenesis are unclear. This study used a bioelectrochemical-based system (BES) to explore the potential effects of zero-valent iron (ZVI) addition on "As migration-CH₄ emission" interactions from chemical and microbiological perspectives. Voltage and ZVI amendment experiments showed that dissolved As was efficiently immobilized with increased CH₄ production in the soil BES, As release and CH₄ production exhibited a high negative exponential correlation, and reductive As dissolution could be entirely inhibited in the methanogenic stage. Gene quantification and bacterial community analysis showed that in contrast to applied voltage, ZVI changed the spatial heterogeneity of the distribution of electroactive microorganisms in the BES, significantly decreasing the relative abundance of arrA and dissimilatory As/Fe-reducing bacteria (e.g., Geobacter) while increasing the abundance of aceticlastic methanogens (Methanosaeta), which then dominated CH₄ production and As immobilization after ZVI incorporation. In addition to biogeochemical activities, coprecipitation with ferric (iron) contributed 77-93% dissolved As removal under ZVI addition. This study will enhance our knowledge of the processes and microorganisms controlling soil As migration and CH₄ emission.

Comparison of pennywort and hyacinth in the development of membraned sediment plant microbial fuel cell for waste treatment

Membraned Sediment Plant Microbial Fuel cells (SPMFCs) are appealing bioelectrochemical systems that generate power from organic compounds in sediment through exoelectrogen decomposition and are used to treat wastewater. This research was designed to develop a single-chambered sediment plant microbial fuel cell using two membrane electrodes; one carbon plate cathode and one anode. Wastewater and sediment mixture was sampled from Rawalpindi, Pakistan, and bacterial isolation was performed by serial dilution. Five strains were selected on the basis of morphology and growth-promoting characteristics. The selected strains were identified by 16s rRNA sequencing and designated as A (Geobacter sulfurreducens OP527025), B (Shawanella putrefaciens OP522353), C (Bacillus subtilus OP522349), D (Azospirillum humicireducens OP527050) and E (Pseudomonas putida OP526951). Consortium of five strains was developed. Two aquatic plants pennyworts (Hydrocotyle umbellate), and Hyacinth (Eichhornia crassipes) were used in the SPMFCs along with consortium. A maximum voltage of 1120mv was observed in SPMFCs treated with the consortium and water hyacinth, which was followed by 543.3 mv of SPMFCs treated with water pennyworts. Physicochemical analysis of wastewater showed a remarkable reduction of 74.5%, 71%, and 76% in nitrate, phosphate, and sulphate content of wastewater treated with microbes and water hyacinth. The heavy metal analysis showed a reduction of Zn (99.8%), Mg (99.9%), and Ni (98.4%) in SPMFCs treated with the consortium and water hyacinth. Mebraned SPMFCs showed an increase of 30% and 20% in shoot and root length of water hyacinth. A remarkable increase of 25%, 18%, and 12% were recorded in chlorophyll content, membrane stability index and relative water content of water hyacinth in SPMFCs treated with consortium compared to untreated cells. Osmolyte content had shown significant increase of 25% with consortium treated water hyacinth plant as compared to untreated one. An increase of 15%, 20% and 12% was noted in superoxide dismutase (SOD), peroxidase dismutase (POD) and catalase content of consortium treated water hyacinth as compared to control one. The present research gave insight into the potential of sediment plant microbial fuel cells along with aquatic plants for treatment of wastewater. This could be a effective method for removal of hazrdaous substances from wastewater and alternative approach for voltage production.

Electrical generation and methane emission from an anoxic riverine sediment slurry treated by a two-chamber microbial fuel cell

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K₃[Fe(CN)₆]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K₃[Fe(CN)₆] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW·m^-2, respectively. With increasing K₃[Fe(CN)₆] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m³·h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m³·h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m³·h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m³·h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m³·h). Our results demonstrate that adding an electron acceptor (K₃[Fe(CN)₆]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.

Effects of anode/cathode electroactive microorganisms on arsenic removal with organic/inorganic carbon supplied

This study reports the effects of an external voltage (0 V, 0.4 V and 0.9 V) on soil arsenic (As) release and sequestration when amended with organic carbon (NaAc) and inorganic carbon (NaHCO₃), respectively, in a soil bioelectrochemistry system (BES). The results demonstrated that although an external voltage had no effect on the As removal capacity in an oligotrophic environment fueled with NaHCO_3, 93.6% of As(III) in the supernatant was removed at 0.9 V with an NaAc amendment. Interestingly, the content of As detected on the electrodes was higher than that removed from the supernatant, implying a continuous release of soil As under external voltages and rapid adsorption onto the electrodes, especially the cathode. In addition, the species of As on the cathode were similar to those in the supernatant (the As(III)/As(V) ratio was approximately 3:1), indicating that the removal capacity was independent of preoxidation. From the viewpoint of electroactive microorganisms (EABs), the relative abundances of the arrA gene and Geobacter genus were specifically enriched at the anode, thus signifying stimulation of the reduction and release of soil As in the anode region. By comparison, Bacillus was particularly abundant at the cathode, which could contribute to the oxidation and sequestration of As in the cathode region. Additionally, specific extracellular polymeric substances (EPSs) secreted by EABs could combine with As, which was followed by electrostatic attraction to the cathode under the effect of an electric field. Furthermore, the formation of secondary minerals and coprecipitation in the presence of iron (Fe) may have also contributed to As removal from solution. The insights from this study will enable us to further understand the biogeochemical cycle of soil As and to explore the feasibility of in situ As bioremediation techniques, combining the aspects of microbial and physicochemical processes in soil bioelectrochemical systems.

A taxonomy of design factors in constructed wetland-microbial fuel cell performance: A review

The past decade has seen the rapid development of constructed wetland-microbial fuel cell (CW-MFC) technology in many aspects. The first publication on the combination of constructed wetland (CW) and microbial fuel cell (MFC) appeared in 2012, subsequently, research on the subject has grown exponentially to improve the performance of CW-MFCs in their dual roles of wastewater treatment and power generation. Although significant research has been conducted on this technology worldwide, a comprehensive and critical review of effective controlling parameters is lacking. More broadly, research is needed to draw up-to-date conclusions on recent developments and to identify knowledge gaps for further studies. This review paper systematically enumerates and reviews research studies published in this area to determine the key design factors and their role in CW-MFC performance. Moreover, a taxonomy of all CW-MFC design parameters has been synthesised from the literature. Importantly, this original work provides a comprehensive conceptual framework for future researchers, designers, builders, and users to understand CW-MFC technology. Within the taxonomy, parameters are placed in three main categories (physical/environmental, chemical, and biological/electrochemical) and comprehensive details are given for each parameter. Finally, a comprehensive summary of the parameters has been tabulated showing their impact on CW-MFC operation, design recommendations from literature, and the significant research gaps that this review has identified within the existing literature. It is hoped that this paper will provide a clear and rich picture of this technology at its current stage of development and furthermore, will facilitate a deeper understanding of CW-MFC performance for long-term and large-scale development.

Recent advances in soil microbial fuel cells for soil contaminants remediation

The cost-effective and eco-friendly approaches are needed for decontamination of polluted soils. The bio-electrochemical system, especially microbial fuel cells (MFCs) offer great promise as a technology for remediation of soil, sediment, sludge and wastewater. Recently, soil MFCs (SMFCs) have been attracting increasing amounts of interest in environmental remediation, since they are capable of providing a clean and inexhaustible source of electron donors or acceptors and can be easily controlled by adjusting the electrochemical parameters. In this review, we comprehensively covered the principle of SMFCs including the mechanisms of electron releasing and electron transportation, summarized the applications for soil contaminants remediation by SMFCs with highlights on organic contaminants degradation and heavy metal ions removal. In addition, the main factors that affected the performance of SMFCs were discussed in details which would be helpful for performance optimization of SMFCs as well as the efficiency improvement for soil remediation. Moreover, the key issues need to be addressed and future perspectives are presented.

Positive matrix factorization on source apportionment for typical pollutants in different environmental media: a review

A bibliometric analysis of published papers with the key words "positive matrix factorization" and "source apportionment" in 'Web of Science', reveals that more than 1000 papers are associated with this research and that approximately 50% of these were produced in Asia. As a receptor-based model, positive matrix factorization (PMF) has been widely used for source apportionment of various environmental pollutants, such as persistent organic pollutants (POPs), heavy metals, volatile organic compounds (VOCs) as well as inorganic cations and anions in the last decade. In this review, based on the papers mainly from 2008 to 2018 that focused on source apportionment of pollutants in different environmental media, we provide a comparison and summary of the source categories of typical environmental pollutants, with a special focus on polycyclic aromatic hydrocarbons (PAHs), apportioned using PMF. Based on the statistical average, coal combustion and vehicular emission, are shown to be the two most common sources of PAHs, and contribute much more to emissions than other sources, such as biomass burning, biogenic sources and waste incineration. Heavy metals were mainly from agricultural activities, industrial and vehicular emissions and mining activities. Quantitative source apportionment on pollutants such as VOCs and particulate matter were also apportioned, showing a prominent contribution from fossil-fuel combustion. We conclude that, aside from natural sources, abatement strategies should be focused on changes in energy structure and industrial activities, especially in China. Source apportionment of typical POPs including polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), halogenated flame retardants (HFRs) and perfluorinated compounds (PFCs) is less comprehensive and further study is required.