Effects of the presence of nanoscale zero-valent iron on the degradation of polychlorinated biphenyls and total organic carbon by sediment microbial fuel cell

Green low-cost synthesis of zero-valent iron nanoparticles from Palm Petiole Extract for Cr(VI) removal from water

One of the hottest research topics over the last decades was the valorization or/and recycling of agro-industrial wastes into different valuable liquid or solid products, which is considered a sustainable and low-cost approach. In this study, we developed zero-valent iron nanoparticles from Palm Petiole Extract (P-NZVI) using a green and straightforward approach. The as-synthesized P-NZVI was used to adsorb Cr(VI) in water. The physico-chemical characterizations of P-NZVI, including the particle size, crystalline structure, surface area, morphology, and functional groups, were investigated via several techniques such as UV-vis spectroscopy, SEM, TEM, XRD, FTIR, AFM, DLS, pHZPC measurement, and BET analysis. The adsorption performance of P-NZVI was studied under different operational parameters, including pollutant concentration, pH, temperature, and adsorbent mass. The adsorption rate was found to be 89.3% within 40 min, corresponding to the adsorption capacity of 44.47 mg/g under the following conditions: initial Cr(VI) concentration of 40 mg/L, pH 5, and a P-NZVI dosage of 1 g/L. It was found that the adsorption pattern follows the Langmuir and the pseudo-second-order kinetic models, indicating a combination of monolayer adsorption and chemisorption mechanisms. The thermodynamic study shows that the adsorption process is endothermic and spontaneous. The reusability of P-NZVI was carried out four times, showing a slight decrease from 89.3 to 87%. These findings highlight that P-NZVI's could be an effective green adsorbent for removing Cr(VI) or other types of toxic pollutants from water.

Environmental remediation approaches by nanoscale zero valent iron (nZVI) based on its reductivity: a review

The fast rise of organic and metallic pollution has brought significant risks to human health and the ecological environment. Consequently, the remediation of wastewater is in extremely urgent demand and has received increasing attention. Nanoscale zero valent iron (nZVI) possesses a high specific surface area and distinctive reactive interfaces, which offer plentiful active sites for the reduction, oxidation, and adsorption of contaminants. Given these abundant functionalities of nZVI, it has undergone significant and extensive studies on environmental remediation, linking to various mechanisms, such as reduction, oxidation, surface complexation, and coprecipitation, which have shown great promise for application in wastewater treatment. Among these functionalities of nZVI, reductivity is particularly important and widely adopted in dehalogenation, and reduction of nitrate, nitro compounds, and metal ions. The following review comprises a short survey of the most recent reports on the applications of nZVI based on its reductivity. It contains five sections, an introduction to the theme, chemical reduction applications, electrolysis-assisted reduction applications, bacterium-assisted reduction applications, and conclusions about the reported research with perspectives for future developments. Review and elaboration of the recent reductivity-dependent applications of nZVI may not only facilitate the development of more effective and sustainable nZVI materials and the protocols for comprehensive utilization of nZVI, but may also promote the exploration of innovative remediation approaches based on its reductivity.

Sustainable and Green Synthesis of Iron Nanoparticles Supported on Natural Clays via Palm Waste Extract for Catalytic Oxidation of Crocein Orange G Mono Azoic Dye

In this study, the removal of Crocein Orange G dye (COG) from aqueous solution was investigated using an innovative green catalyst to overcome problems with chemical techniques. Clay bentonite El Hamma (HB)-supported nanoscale zero-valent iron (NZVI) was used as a heterogeneous Fenton-like catalyst for the oxidation of harmful COG. Palm waste extract was herein used as a reducing and capping agent to synthesize NZVI, and HB clay was employed, which was obtained from the El Hamma bentonite deposit in the Gabes province of Tunisia. HB and HB-NZVI were characterized by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), X-ray diffraction (XRD), and zeta potential. Under optimal conditions, total degradation of COG was attained within 180 min. Kinetic studies showed that the dye degradation rate followed well the pseudo-second-order model. The apparent activation energy was 33.11 kJ/mol, which is typical of a physically controlled reaction. The degradation pathways and mineralization study revealed that the adsorption-Fenton-like reaction was the principal mechanism that demonstrated 100% degradation efficiency of COG even after three successive runs. Obtained results suggest that HB-NZVI is an affective heterogeneous catalyst for the degradation of COG by H2O2 and may constitute a sustainable green catalyst for azoic dye removal from industrial wastewaters.

Improved electrochemical properties of graphite electrodes incubated with iron powders in rice-paddy fields boost power outputs from microbial fuel cells

Studies have shown that the supplementation of anode-surrounding soil with zero-valent iron (ZVI) boosts power outputs from rice paddy-field microbial fuel cells (RP-MFCs). In order to understand mechanisms by which ZVI boosts outputs from RP-MFCs, the present study operated RP-MFCs with and without ZVI, and compositions of anode-associated bacteria and electrochemical properties of graphite anodes were analyzed after 3-month operation. Metabarcoding using 16S rRNA gene fragments showed that bacterial compositions did not largely differ among these RP-MFCs. Cyclic voltammetry showed improved electrochemical properties of anodes recovered from ZVI-supplemented RP-MFCs, and this was attributed to the adhesion of iron-oxide films onto graphite surfaces. Bioelectrochemical devices equipped with graphite anodes recovered from ZVI-supplemented RP-MFCs generated higher currents than those with fresh graphite anodes. These results suggest that ZVI is oxidized to iron oxides in paddy-field soil and adheres onto graphite anodes, resulting in the boost of power outputs from RP-MFCs.

The race between classical microbial fuel cells, sediment-microbial fuel cells, plant-microbial fuel cells, and constructed wetlands-microbial fuel cells: Applications and technology readiness level

Microbial fuel cell (MFC) is an interesting technology capable of converting the chemical energy stored in organics to electricity. It has raised high hopes among researchers and end users as the world continues to face climate change, water, energy, and land crisis. This review aims to discuss the journey of continuously progressing MFC technology from the lab to the field so far. It evaluates the historical development of MFC, and the emergence of different variants of MFC or MFC-associated other technologies such as sediment-microbial fuel cell (S-MFC), plant-microbial fuel cell (P-MFC), and integrated constructed wetlands-microbial fuel cell (CW-MFC). This review has assessed primary applications and challenges to overcome existing limitations for commercialization of these technologies. In addition, it further illustrates the design and potential applications of S-MFC, P-MFC, and CW-MFC. Lastly, the maturity and readiness of MFC, S-MFC, P-MFC, and CW-MFC for real-world implementation were assessed by multicriteria-based assessment. Wastewater treatment efficiency, bioelectricity generation efficiency, energy demand, cost investment, and scale-up potential were mainly considered as key criteria. Other sustainability criteria, such as life cycle and environmental impact assessments were also evaluated.

Methane emission reduction oriented extracellular electron transfer and bioremediation of sediment microbial fuel cell: A review

Sediment is the internal and external source of water environment pollution, so sediment remediation is the premise of water body purification. Sediment microbial fuel cell (SMFC) can remove the organic pollutants in sediment by electroactive microorganisms, compete with methanogens for electrons, and realize resource recycling, methane emission inhibiting and energy recovering. Due to these characteristics, SMFC have attracted wide attention for sediment remediation. In this paper, we comprehensively summarized the recent advances of SMFC in the following areas: (1) The advantages and disadvantages of current applied sediment remediation technologies; (2) The basic principles and influencing factors of SMFC; (3) The application of SMFC for pollutant removal, phosphorus transformation and remote monitoring and power supply; (4) Enhancement strategies for SMFC in sediments remediation such as SMFC coupled with constructed wetland, aquatic plant and iron-based reaction. Finally, we have summarized the drawback of SMFC and discuss the future development directions of applying SMFC for sediment bioremediation.

Development of overlying water aeration system powered by sediment-microbial-fuel-cell for nutrient suppression

Sediment microbial fuel cells (SMFCs) represent a burgeoning technology that allows the remediation of sediments, such as nutrient suppression, while concurrently generating electricity. However, there is a limitation in that the nutrient suppression effect is restricted to a narrow range near the electrode. To address this issue, we developed an SMFC-aeration system, which intermittently aerates the overlying water with the power of SMFCs, thereby enhancing the nutrient suppression effect of SMFCs. The SMFC-aeration system achieved stable charge/discharge cycles through a capacitor-based circuit and aerated the overlying water. The dissolved NH₄⁺ and NO₂^- concentrations in the overlying water decreased. Suppression in the dissolved NH₄⁺ concentration near the anodes was also noticed compared to a consortium that employed only SMFCs. These findings were brought about by the synergistic effect of the SMFC-aeration system, which enabled the remediation of sediments and overlying water. To our knowledge, this is the first report on the intermittent operation of pumps by SMFCs, the increase of DO, and nutrient suppression. The SMFC-aeration system holds great potential as an environmental remediation method in closed-water areas in the future.

Assessing the enhanced reduction effect with the addition of sulfate based P inactivating material during algal bloom sedimentation

The typical harm effect of algal bloom sedimentation is to increase sulfides level in surroundings, threatening aquatic organisms and human health; whereas, P inactivating materials containing sulfate are commonly attempted to be used to immobilize reactive P or to flocculate excessive algae in water columns for eutrophication control. In this study, variations in sulfate reduction during algal bloom sedimentation with the addition of sulfate based inactivating materials was comprehensively assessed based on using Al₂(SO₄)₃ with comparison to AlCl₃. The results showed that addition of Al₂(SO₄)₃ had more substantial effect on overlying water and sediment properties compared to those of ACl₃. Al₂(SO₄)₃ can enhance sulfate reduction, resulting in temporary increase of sulfides (p < 0.01) and quick decrease of various Fe (p < 0.01) in overlying water and then promoting the formation of FeS and FeS₂ (determined by EXAFS analysis) in sediments. Most importantly, the increased sulfides, as well as the physical barrier on sediment formed due to Al₂(SO₄)₃ addition, enhanced the transformation of sulfides to odorous contaminants, increasing odorous contaminants (especially methyl thiols) production by approximately one order of magnitude in overlying water. Furthermore, the increased sulfides facilitated to the enrichment of microorganisms related to S cycles (Thiobacillu with relative abundance of 23.8%) and even promoted to enrich bacterial genus potentially with pathogenicity (Treponema) in sediments. The impacts of sulfate tended to be regulated by algae concentration; however, careful management was recommended for sulfate based inactivating materials application to control eutrophication with algal blooms.

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.

Removal of petroleum hydrocarbon-contaminated soil using a solid-phase microbial fuel cell with a 3D corn stem carbon electrode modified with carbon nanotubes

Solid-phase microbial fuel cell (SMFC) can accelerate the removal of organic pollutants through the electrons transfer between microorganisms and anodes in the process of generating electricity. Thus, the characteristics of the anode material will affect the performance of SMFCs. In this study, corn stem (CS) is first calcined into a 3D macroporous electrode, and then modified with carbon nanotubes (CNTs) through electrochemical deposition method. Scanning electron microscope analysis showed the CS/CNT anode could increase the contact area on the surface. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry analysis indicated the electrochemical double-layer capacitance of the CS/CNT anode increased while its internal resistance decreased significantly. These characteristics are crucial for increasing bacterial adhesion capability and electron transfer rate. The maximum output voltage of the SMFC with CS/CNT anode was 158.42 mV, and the removal rate of petroleum hydrocarbon (PH) reached 42.17%, 2.72 times that of unmodified CS. In conclusion, CNT-modified CS is conducive to improve electron transfer rate and microbial attachment, enhancing the removal efficiency of PH in soil.

Recent advances in PCB removal from historically contaminated environmental matrices

Despite being drastically restricted in the 1970s, polychlorinated biphenyls (PCBs) still belong among the most hazardous contaminants. The chemical stability and dielectric properties of PCBs made them suitable for a number of applications, which then lead to their ubiquitous presence in the environment. PCBs are highly bioaccumulative and persistent, and their teratogenic, carcinogenic, and endocrine-disrupting features have been widely reported in the literature. This review discusses recent advances in different techniques and approaches to remediate historically contaminated matrices, which are one of the most problematic in regard to decontamination feasibility and efficiency. The current knowledge published in the literature shows that PCBs are not sufficiently removed from the environment by natural processes, and thus, the suitability of some approaches (e.g., natural attenuation) is limited. Physicochemical processes are still the most effective; however, their extensive use is constrained by their high cost and often their destructiveness toward the matrices. Despite their limited reliability, biological methods and their application in combinations with other techniques could be promising. The literature reviewed in this paper documents that a combination of techniques differing in their principles should be a future research direction. Other aspects discussed in this work include the incompleteness of some studies. More attention should be given to the evaluation of toxicity during these processes, particularly in terms of monitoring different modes of toxic action. In addition, decomposition mechanisms and products need to be sufficiently clarified before combined, tailor-made approaches can be employed.

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.

Microorganisms in sediment microbial fuel cells: Ecological niche, microbial response, and environmental function

A sediment microbial fuel cell (SMFC) is a device that harvests electrical energy from sediments rich in organic matter. 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. The microorganisms inhabiting sediments and the overlying water play a pivotal role in SMFCs. Since the SMFC is applied in an open environment rather than in an enclosed chamber, the effects of the environment on the microbes should be intense and the microbial community succession should be extremely complex. Thus, this review aims to provide an overview of the microorganisms in SMFCs, which few previous review papers have reported. In this study, the anodic and cathodic niches for the microorganisms in SMFCs are summarized, how the microbial population and community interact with the SMFC environment is discussed, a new microbial succession strategy called the electrode stimulation succession is proposed, and recent developments in the environmental functions of SMFCs are discussed from the perspective of microorganisms. Future studies are needed to investigate the electrode stimulation succession, the environmental function and the electron transfer mechanism in order to boost the application of SMFCs for power generation and environmental remediation.

Organic matter stabilized Fe in drinking water treatment residue with implications for environmental remediation

Fe-based materials used to adsorb P are commonly considered to be limited by the increased Fe lability, while Fe in drinking water treatment residue (DWTR) shows stable P adsorption abilities. Accordingly, this study aimed to gain insight into Fe lability in DWTR as compared to FeCl₃ and Fe₂(SO₄)₃ using Fe fractionation, EXAFS, and high-throughput sequencing technologies. The results showed that compared to Fe₂(SO₄)₃ and FeCl₃, Fe was relatively stable in the DWTR under the effects of organic matter, sulfides, and anaerobic conditions. Typically, the addition of FeCl₃ and Fe₂(SO₄)₃ enhanced Fe mobility in sediment and overlying water, promoting the formation of Fe-humin acid and ferrous sulfides (FeS and FeS₂). However, the addition of DWTR, even at relatively high doses of Fe, has limited impact on Fe mobility. The addition remarkably increased oxidizable Fe in sediment (by approximately 63%), causing Fe to be dominated by oxidizable and residual fractions (like those in raw DWTR); EXAFS analysis also suggested that Fe-humin acid increased substantially with the addition of DWTR, becoming the main Fe species in sediment (with a relative abundance of 50.1%). Importantly, the Fe distributions were stable in sediment with DWTR added, which demonstrated that organic matter stabilized the Fe in the DWTR. Further analysis indicated that all materials promoted the enrichment of bacterial genera potentially related to Fe metabolism (e.g., Bacteroides, Dok59, and Methanosarcina). Fe₂O₃ in the FeCl₃ and Fe₂(SO₄)₃ groups and Fe-HA in the DWTR group were the key species affecting the microbial communities. Overall, the stabilizing effect of organic matter on Fe in DWTR could be used to develop Fe-based materials to enhance Fe stability for environmental remediation.

Contaminated aquatic sediments

The remediation of contaminated aquatic sediments requires a range of expertise from assessment (investigation, risk evaluations, modeling, and remedy selection) to design and construction. Research in 2019 has added to knowledge on optimizing the use of passive samplers for assessing chemical concentrations in sediment porewater. The porewater and black carbon appear to be better predictors of contaminant bioaccumulation than total organic carbon alone. This has led to better characterization of potential risk at sediment sites. Tools to identify and model sources of chemicals have been developed and used particularly for some metals, polynuclear aromatic hydrocarbons and polychlorinated biphenyls. There is great emphasis on beneficially using dredged sediment, treating it as a resource rather than a waste. Amendments used in sediment caps continue to be refined including the use of activated carbon within the caps and by itself. A technique involving 16S rRNA has been established as a means of identifying microbiological composition that naturally degrade contaminants. © 2020 Water Environment Federation PRACTITIONER POINTS: Sediment capping technology continues to advance Sampling and testing methods continue to be refined Natural processes such as biodegradation are being better understood Beneficial use of dredged sediment continue to be emphasized.

The remediation of urban freshwater sediment by humic-reducing activated sludge

Organic pollution of urban rivers caused by stormwater discharge is a global problem. Traditional bioremediation of organic matters (OM) by aerobes could be restrained in anaerobic environments, which usually occurr in polluted river sediments. In this study, an anaerobic remediation technology has been developed to enhance the in-situ removal of organic matters in river sediments, humic-reducing sludge (HRS) was adapted from traditional activated sludge; it exhibited a strong humic-reducing ability. Nitrate and biostimulants were used to stimulate HRS. The change of microbial community between AQDS-adapted and non-AQDS-adapted was analyzed, and the effect of HRS augmentation and Nitrate/biostimulant addition on TOM removal were discussed from the perspective of light and heavy fraction organic matters (LFOM and HFOM). The results have indicated that, after adaptation, HRS had increased the bacterial population of Anaerolineales and Desulfuromonadales, which was related to the carbon metabolism and electron-transfer ability. On the other hand, the adaptation decreased the population of bacteria related to the sulfur/sulfate circulation. This characteristic of the HRS was potentially benificial to reducing the occurrence of black-odor phenomenon. Also, the removal efficiency of TOM in sediment was significantly improved by using HRS because HRS could facilitate the removal of HFOM. Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the advantage of decomposing HFOM using HRS resulted from the fact that the HFOM contained redox mediators to facilitate humic-reducing respiration. In addition, nitrate appeared to be crucial for the enhancement of HRS in sediments. These findings have allowed for the development of a technology for in-situ anaerobic remediation of urban river sediments. They could also help to understand humic-reducing mechanism in the sediment during anaerobic bioremediation.

Insights into Advancements and Electrons Transfer Mechanisms of Electrogens in Benthic Microbial Fuel Cells

Benthic microbial fuel cells (BMFCs) are a kind of microbial fuel cell (MFC), distinguished by the absence of a membrane. BMFCs are an ecofriendly technology with a prominent role in renewable energy harvesting and the bioremediation of organic pollutants through electrogens. Electrogens act as catalysts to increase the rate of reaction in the anodic chamber, acting in electrons transfer to the cathode. This electron transfer towards the anode can either be direct or indirect using exoelectrogens by oxidizing organic matter. The performance of a BMFC also varies with the types of substrates used, which may be sugar molasses, sucrose, rice paddy, etc. This review presents insights into the use of BMFCs for the bioremediation of pollutants and for renewable energy production via different electron pathways.

Chlorella vulgaris on the cathode promoted the performance of sediment microbial fuel cells for electrogenesis and pollutant removal

The lack of electron acceptors in cathode has limited the widespread application of sediment microbial fuel cells (SMFCs). In this study, Chlorella vulgaris (C. vulgaris) was added to the cathode to produce oxygen as an electron acceptor. The synergistic effects between C. vulgaris and electrogenic microorganisms in SMFCs were investigated, and were shown to enhance biodegradation of organic matter in sediments and convert chemical energy into electrical energy. Results showed that the addition of C. vulgaris on the cathode of SMFCs significantly reduced their internal resistance. The low algae concentration SMFC group reduced the initial internal resistance by 67.4% under illumination and produced a maximum power density of 5.17 W/m³, which was 6 times higher than that of SMFCs without addition of C. vulgaris. We also obtained organic matter removal efficiencies 37.2% higher after 16 days, which accelerated the startup time for three times. It was demonstrated that IEF-N and OP, respectively, were forms of nitrogen and phosphorus removed by SMFCs. Additionally, high-throughput sequencing of microbial communities indicated that C. vulgaris increased the abundance of electrogenic bacteria (Geobacter and Desulfobulbaceae) in the anode and types of photosynthetic bacteria that support oxygen production in the cathode. The combined application of microalgae- and SMFC-based technologies offer a promising remediation approach for organically-contaminated sediments.

Enhanced electricity generation in rice paddy-field microbial fuel cells supplemented with iron powders

Microbial fuel cells installed in rice paddy fields (RP-MFCs) are able to serve as on-site batteries for operating low-power environmental sensors. In order to increase the utility and reliability of RP-MFCs, however, further research is necessary for boosting the power output. Here we examined several powdered iron species, including zero valent iron (ZVI), goethite, and magnetite, for their application to increasing power outputs from RP-MFCs. Soil around anodes was supplemented with either of these iron species, and RP-MFCs were operated for several months during the transplanting and harvesting. It was found that power outputs from RP-MFCs supplemented with ZVI were more than double the outputs from control (not supplemented with iron species) and other RP-MFCs, even after iron corrosion was ceased, and the maximum power density reached 130 mW/m² (per projected area of the anode). Metabarcoding of 16S rRNA gene amplicons suggested that several taxa represented by fermentative and exoelectrogenic bacteria were substantially increased in MFCs supplemented with ZVI. Results suggest that ZVI lowers oxidation/reduction potential around anodes, activates anaerobic microbes involved in the conversion of organic matter into electricity and increases power output from RP-MFCs.

Simultaneous wastewater treatment and energy harvesting in microbial fuel cells: an update on the biocatalysts

The development of microbial fuel cell (MFC) makes it possible to generate clean electricity as well as remove pollutants from wastewater. Extensive studies on MFC have focused on structural design and performance optimization, and tremendous advances have been made in these fields. However, there is still a lack of systematic analysis on biocatalysts used in MFCs, especially when it comes to pollutant removal and simultaneous energy recovery. In this review, we aim to provide an update on MFC-based wastewater treatment and energy harvesting research, and analyze various biocatalysts used in MFCs and their underlying mechanisms in pollutant removal as well as energy recovery from wastewater. Lastly, we highlight key future research areas that will further our understanding in improving MFC performance for simultaneous wastewater treatment and sustainable energy harvesting.

Pd/Fe nanoparticle integrated PMAA-PVDF membranes for chloro-organic remediation from synthetic and site groundwater

The poly(methacrylic acid) (PMAA) was synthesized in the pores of commercial microfiltration PVDF membranes to allow incorporation of catalytic palladium/iron (Pd/Fe) nanoparticles for groundwater remediation. Particles of 17.1 ± 4.9 nm size were observed throughout the pores of membranes using a focused ion beam. To understand the role of Pd fractions and particle compositions, 2-chlorobiphenyl was used as a model compound in solution phase studies. Results show H2 production (Fe0 corrosion in water) is a function of Pd coverage on the Fe. Insufficient H2 production caused by higher coverage (> 10.4% for 5.5 wt%) hindered dechlorination rate. With 0.5 wt% Pd, palladized-Fe reaction rate (surface area normalized reaction rate, ksa = 0.12 L/(m2-h) was considerably higher than isolated Pd and Fe particles. For groundwater, in a single pass of Pd/Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics, such as trichloroethylene (177 ppb) and carbon tetrachloride (35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The degradation rate (observed ksa) followed the order of carbon tetrachloride > trichloroethylene > tetrachloroethylene > chloroform. A 36 h continuous flow study with organic mixture and the regeneration process show the potential for on-site remediation.

Enhancing the power performance of sediment microbial fuel cells by novel strategies: Overlying water flow and hydraulic-driven cathode rotating

Sediment microbial fuel cells (SMFCs) are promising power sources for environmental monitoring in remote areas and environment-friendly solutions to river sediment contamination. However, cathodic limitations will significantly decrease power performance and limit its practical application. In this work, the control SMFC (SMFC-C) with cathode horizontally and fully submerged below the overlying water, and the hydraulic-driven rotating cathode SMFC (SMFC-R) was constructed. Overlying water flow and hydraulic-driven cathode rotating as novel strategies for SMFCs towards field applications were proposed. Results demonstrated that better power performance under static condition was obtained in SMFC-R than in SMFC-C, that the overlying water flow could significantly increase the maximum power density (MPD) in SMFC-C over the static condition, and that the cathode rotating further improved MPD in SMFC-R. The MPD obtained under static condition were 26.5 mW/m² and 45.1 mW/m² in SMFC-C and SMFC-R, which increased to 38.8 mW/m² and 47.3 mW/m² under water flow and cathode rotating condition, respectively. Analyses on cathode potential, overlying water pH and dissolved oxygen suggested severe cathodic limitations in SMFC-C under static condition which could be diminished by overlying water flow. However, almost no such limitations were observed in SMFC-R even under static condition, which is probably due to the fact that the cathodic oxygen reaction in SMFC-R mainly occurred on the cathode exposed to the air rather than on that submerged below the water. Identical anode performance was obtained in both SMFCs under different conditions, which were not an influencing factor leading to different power performance.