In Situ Bioremediation Using Sediment Microbial Fuel Cell

Stimulating bioelectric generation and recovery of toxic metals through benthic microbial fuel cell driven by local sago (Cycas revoluta) waste

Benthic microbial fuel cell (BMFC) is the most promising type of bioelectrochemical approach for producing electrons and protons from natural organic waste. In the present work, a single-chamber BMFC was used, containing sago (Cycas revoluta) waste as the organic feed for microorganisms. The local wastewater was supplemented with heavy metal ions (Pb2+, Cd2+, Cr3+, Ni2+, Co2+, Ag+, and Cu2+) and used as an inoculation source to evaluate the performance of BMFC against the toxic metal remediations. According to the experimental results, the maximum power density obtained was 42.55 mW/m2 within 25 days of the BMFC operation. The maximum remediation efficiency of the metal ion removal from the wastewater was found to be 99.30% (Ag+). The conductive pili-type bacteria species (Acinetobacter species, Leucobacter species, Bacillus species, Proteus species. and Klebsiella pneumoniae) were found in the present study during isolation and identification processes. This study's multiple parameter optimization revealed that pH 7 and room temperature is the best condition for optimal performance. Finally, this study included the mechanism, future recommendations, and concluding remarks.

Strategies for Restoring and Managing Ecological Corridors of Freshwater Ecosystem

Along with accelerating urbanization and associated anthropogenic disturbance, the structure and function of freshwater ecosystems worldwide are substantially damaged. To improve ecosystem health, and thus enhance the ecosystem security of the urban ecosystem, numbers of management approaches and engineering projects have been applied to mitigate the degradation of freshwaters. Nevertheless, there is still a lack of comprehensive and systematic research on the ecological corridor restoration of freshwater ecosystems; especially for Suzhou Grand Canal, one section of the world's longest and ancient Grand Canal which is inclined to severe ecosystem degradation. Through investigating the adjacent land use characteristics, habitat quality, vegetation cover, instream water quality, and habitat composition, we aimed to: (i) assess the water quality of the Suzhou Grand Canal; (ii) evaluate the ecological characteristics of the canal ecosystem; (iii) develop strategic countermeasures to restore the ecological corridors for the mitigation of ecological problems. The results demonstrated: a large built area, a smaller ecological zone, a low habitat quality and habitat connectivity, and a high degree of habitat fragmentation within the canal corridor, also a simplified instream habitat composition, and greater nutrient and COD concentrations in the surface water-especially in the upstream and midstream canal. All urbanization-induced multiple stressors, such as land use changes, altered hydrology, and the simplified riparian zone et al., contributed synergistically to the degradation of the canal ecosystem. To alleviate the ecosystem deterioration, three aspects of recommendations were proposed: water pollution control, watershed ecosystem restoration, and ecological network construction. Basically, building a comprehensive watershed ecological network-on the basis of associated ecosystem restoration, and the connection of multi-dimensional ecological corridors-would dramatically increase the maintenance of aquatic-terrestrial system biodiversity, and improve the regional ecological security pattern and watershed resilience toward stochastic future disturbances. This study contributes to the understanding of the ecological challenges and related causes of the canal ecosystem. The integrated strategy introduced in this study provides policymakers, water resource managers, and planners with comprehensive guidelines to restore and manage the ecological corridor of the canal ecosystem. This can be used as a reference in freshwater ecosystems elsewhere, to improve ecosystem stability for supporting the sustainable development of urban ecosystems.

Suppression of phosphorus release from eutrophic lake sediments by sediment microbial fuel cells

Sediment microbial fuel cells (SMFCs) have served as an alternative technique to suppress phosphorus release from lake sediments to water bodies and thus mitigate eutrophication. However, the phosphorus regulation mechanism remains unclear. The purpose of this research was to understand the electrochemical influence of an SMFC on the phosphorus concentration in interstitial water. In this study, a lab-scale SMFC was applied to acetate-spiked sediments (ace+) and unspiked sediments (sed) with closed-circuit (CC)/open-circuit (OC) columns, and the circuitry was switched to investigate the relationship between electron transfer and phosphorus concentration. The dissolved total phosphorus (DTP) concentration in the sediment interstitial water in CC columns significantly decreased to below 0.1 mg/L, whereas the DTP in OC columns remained high for nine weeks. After switching the circuit, the DTP in OC→CC columns dropped but that in CC→OC columns increased within one week. At the end of the experimental period, the DTP concentrations in CC/sed, CC/ace+, OC/sed, and OC/ace+ columns were 0.10 ± 0.02, 0.03 ± 0.00, 0.82 ± 0.01, and 1.66 ± 0.12 mg/L, respectively. The respective estimated anode capacitances of those columns were 2.05 ± 0.49, 5.15 ± 0.14, 0.72 ± 0.19, and 0.71 ± 0.12 nF. We concluded that the phosphorus may have been electrochemically attracted and retained on the anode in the sediment because the adsorbed DTP contents and the increased anode capacitances were strongly correlated. Thus, SMFCs can be used for suppressing phosphorus release from eutrophic lake sediments.

Microbial Electrochemical Technologies for Sustainable Nitrogen Removal in Marine and Coastal Environments

For many years, the world's coastal marine ecosystems have received industrial waste with high nitrogen concentrations, generating the eutrophication of these ecosystems. Different physicochemical-biological technologies have been developed to remove the nitrogen present in wastewater. However, conventional technologies have high operating costs and excessive production of brines or sludge which compromise the sustainability of the treatment. Microbial electrochemical technologies (METs) have begun to gain attention due to their cost-efficiency in removing nitrogen and organic matter using the metabolic capacity of microorganisms. This article combines a critical review of the environmental problems associated with the discharge of the excess nitrogen and the biological processes involved in its biogeochemical cycle; with a comparative analysis of conventional treatment technologies and METs especially designed for nitrogen removal. Finally, current METs limitations and perspectives as a sustainable nitrogen treatment alternative and efficient microbial enrichment techniques are included.

SMFC as a tool for the removal of hydrocarbons and metals in the marine environment: a concise research update

Marine pollution is becoming more and more serious, especially in coastal areas. Because of the sequestration and consequent accumulation of pollutants in sediments (mainly organic compounds and heavy metals), marine environment restoration cannot exempt from effective remediation of sediments themselves. It has been well proven that, after entering into the seawater, these pollutants are biotransformed into their metabolites, which may be more toxic than their parent molecules. Based on their bioavailability and toxic nature, these compounds may accumulate into the living cells of marine organisms. Pollutants bioaccumulation and biomagnification along the marine food chain lead to seafood contamination and human health hazards. Nowadays, different technologies are available for sediment remediation, such as physicochemical, biological, and bioelectrochemical processes. This paper gives an overview of the most recent techniques for marine sediment remediation while presenting sediment-based microbial fuel cells (SMFCs). We discuss the issues, the progress, and future perspectives of SMFC application to the removal of hydrocarbons and metals in the marine environment with concurrent energy production. We give an insight into the possible mechanisms leading to sediment remediation, SMFC energy balance, and future exploitation.

Fuel cells for carbon capture applications

The harmful effect of carbon pollution leads to depletion of the ozone layer, which is one of the main challenges confronting the world. Although progress is made in developing different carbon dioxide (CO₂) capturing methods, these methods are still expensive and face several technical challenges. Fuel cells (FCs) are efficient energy converting devices that produce energy via an electrochemical process. Recently varying kinds of fuel cells are considered as an effective method for CO₂ capturing and/or conversion. Among the different types of fuel cells, solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), and microbial fuel cells (MFCs) demonstrated promising results in this regard. High-temperature fuel cells such as SOFCs and MCFCs are effectively used for CO₂ capturing through their electrolyte and have shown promising results in combination with power plants or industrial effluents. An algae-based microbial fuel cell is an electrochemical device used to capture and convert carbon dioxide through the photosynthesis process using algae strains to organic matters and simultaneously power generation. This review present a brief background about carbon capture and storage techniques and the technological advancement related to carbon dioxide captured by different fuel cells, including molten carbonate fuel cells, solid oxide fuel cells, and algae-based fuel cells.

Electrical current generation from a continuous flow macrophyte biocathode sediment microbial fuel cell (mSMFC) during the degradation of pollutants in urban river sediment

A new type of sediment microbial fuel cell (SMFC) with floating macrophyte Limnobium laevigatum, Pistia stratiotes, or Lemna minor L. biocathode was constructed and assessed in three phases at different hydraulic retention time (HRT) for electrical current generation during the degradation of urban river sediment. The results showed a highest voltage output of 0.88 ± 0.1 V, maximum power density of 80.22 mW m^-3, highest columbic efficiency of 15.3%, normalized energy recovery of 0.030 kWh m^-3, and normalized energy production of 0.005 kWh m^-3 in the Lemna minor L. SMFC during phase 3 at HRT of 48 h, respectively. Highest removal efficiencies of total chemical oxygen demand of 80%, nitrite of 99%, ammonia of 93%, and phosphorus of 94% were achieved in Lemna minor L. system, and 99% of nitrate removal and 99% of sulfate removal were achieved in Pistia stratiotes and Limnobium laevigatum system during the SMFC operation, respectively. Pistia stratiotes exhibited the highest growth in terms of biomass and tap root system of 29.35 g and 12.2 cm to produce the maximum dissolved oxygen of 16.85 ± 0.2 mg L^-1 compared with other macrophytes. The predominant bacterial phylum Proteobacteria of 62.86% and genus Exiguobacterium of 17.48% were identified in Limnobium laevigatum system, while the class Gammaproteobacteria of 28.77% was observed in the control SMFC. The integration of technologies with the continuous flow operation shows promising prospect in the remediation of polluted urban river sediments along with the generation of electrical current.

Effect of aquatic macrophyte growth on landscape water quality improvement

The water of urban landscape park is often confronted with microalgal blooms due to its stagnancy. Bioremediation using the combined emergent and submerged plants to control the microalgae growth was investigated in the present study. Two water bodies (Bei and Xin) of Yuyuantan Park in Beijing were selected for the field experiments, and the other lakes with different vegetation of macrophytes were selected as the comparison. The concentrations of chlorophyll a (chl a), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP), and water temperature and transparency were monitored before and after bioremediation from 2015 to 2017. Results showed that the effects of microalgal inhibition were more significant 2 years after bioremediation. Specifically, the chl a of Dong Lake without any vegetation of macrophytes was up to 65.1 μg/L in summer of 2017, while the Bei and Xin Lakes was only 6.2 and 11.3 μg/L, respectively. In addition, the water quality and transparency also improved, with water bodies being crystal clear. Submerged plants played major roles in microalgal control and water quality improvement, compared to the lakes with only emergent plants. The intensity of humic acid-like substances in three-dimensional fluorescent spectra was stronger for the lakes with submerged plants.

Electrochemistry and microbiology of microbial fuel cells treating marine sediments polluted with heavy metals

Novel laboratory-designed aerated and non-aerated sediment microbial fuel cell (SMFC) models were constructed for power generation and heavy metal bioremediation.