Polypyrrole/sewage sludge carbon as low-cost and high-effective catalyst for enhancing hexavalent chromium reduction and bio-power generation in dual chamber microbial fuel cells

Hexavalent chromium waste removal via bioelectrochemical systems - a life cycle assessment perspective

Bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs) present numerous benefits for the removal and recovery of heavy metals from industrial and municipal wastewater. This study evaluated the life cycle environmental impact of simultaneous hexavalent chromium (Cr(vi)) removal and bioelectricity generation in a dual chamber MFC. Results indicate a global warming potential (GWP) of -0.44 kg carbon dioxide (CO2)-eq. per kg of chromium recovered, representing a total saving of up to 97% in comparison with existing technologies for the treatment of Cr(vi) laden wastewater. The observed savings in GWP (kg CO2-eq.) reduced to 61.8% with the removal of the allocated credits from the MFC system's life cycle. Of all the various sub-systems considered within the chromium waste treatment plant, the MFC unit and the chromium metal recovery unit had the largest impact in terms of GWP (kg CO2-eq.), non-renewable energy use (NREU) (MJ primary), and mineral extraction (MJ surplus). A statistical analysis of the results showed that an increase in chemical oxygen demand (COD) was associated with a reduction in GWP (kg CO2-eq.), NREU (MJ primary), and terrestrial ecotoxicity (kg triethylene glycol equivalents into soil (TEG soil)-eq.). The life cycle assessment (LCA) output showed a high sensitivity to changes in the materials and construction processes of MFC reactors, indicating the need for further research into sustainable materials for MFC reactor construction. The observed interaction effects of process variables also suggest the need for combined optimization of these variables. Analysis with other types of metals is also important to further demonstrate the practical viability of metal removal through MFCs.

Tubular Sediment-Water Electrolytic Fuel Cell for Dual-Phase Hexavalent Chromium Reduction

A novel tubular sediment-water electrolytic fuel cell (SWEFC) was fabricated for the reduction of Cr(VI) in a dual-phase system. The approach simulates a standing water body with Cr(VI)-contaminated overlying water (electrolyte) and bottom sediment phase with electrodes placed in both the phases, supplemented with urea as a potential electron donor. Cr(VI) reduction efficiency of 93.2 ± 1.3% from electrolyte (in 1.5 h) and 81.2 ± 1.3% from the sediment phase (in 8 h) with an initial Cr(VI) concentration of 1,000 mg/L was observed in a single-cell configuration. The effect of initial Cr(VI) concentration, variation in sediment salinity and pH, and different electron donors on the SWEFC performance were systematically investigated. SWEFC showed enhanced performance with 2.4-fold higher current (193.9 mA) at 400 mg/L Cr(VI) concentration when cow dung was used as a low-cost alternative to urea as an electron donor. Furthermore, reactor scalability studies were carried out with nine-anode and nine-cathode configuration (3 L electrolyte and 2 kg sediment), and reduction efficiencies of 98.9 ± 0.9% (in 1 h) and 97.6 ± 2.2% (in 8 h) were observed from the electrolyte and sediment phases, respectively. The proposed sediment-water electrolytic fuel cell can be an advanced and environmentally benign strategy for Cr(VI) remediation from contaminated sediment-water interfaces along with electricity generation.

Synchronous Cr(VI) Remediation and Energy Production Using Microbial Fuel Cell from a Subsurface Environment: A Review

Applying microbial fuel cell (MFC) technology for eco-remediation of Cr(VI) pollution from a subsurface environment has great scientific value and practical significance due to its promising advantages of pollutant remediation and renewable energy generation. The aim of the current review is to summarize the migration characteristics of Cr(VI) in a subsurface soil/water environment and investigate the factors affecting the MFC performance for synchronous Cr(VI) remediation and power generation, and sequentially highlight diverse challenges of MFC technology for in situ remediation of subsurface groundwater and soils. The critical review put forward that Cr(VI) removal efficiency and energy production of MFC can be improved by enhancing the adjustability of cathode pH, setting potential, modifying electrode, and incorporating other technologies into MFC. It was recommended that designing typical large-scale, long-term continuous flow MFC systems, adding electron shuttle media or constructing artificial electron according to actual groundwater/soil and Cr(VI) pollution characteristics, site geology, and the hydrogeology condition (hydrochemical conditions, colloid type, and medium) are essential to overcome the limitations of the small size of the laboratory experiments and improve the application of technology to in situ Cr(VI) remediation. This review provided reference and ideas for future research of MFC-mediated onsite Cr(VI) remediation.

Polypyrrole-Bentonite composite as a highly efficient and low cost anionic adsorbent for removing hexavalent molybdenum from wastewater

The aim of current study was to develop a new material for the fast and efficient removal of hexavalent molybdenum (Mo(VI)) from contaminated water. In this work, a novel adsorbent was synthesized through the polypyrrole intercalation modification of bentonite (PPy-BT) via in-situ chemical polymerization method for effectively removal of Mo(VI) from aqueous solution. The surface morphology and chemical composition of PPy-BT composites were investigated by X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, scanning electron microscopy techniques and X-ray photoelectron spectroscopy. PPy and BT could well resist the aggregation of each other, and therefore resulted in a loose-packed structure and good exposure of active sites. Using materials for the adsorption of Mo(VI) revealed has a maximum adsorption capacity of 100.17 mg/g at 25 °C and pH 4.0 by the Langmuir model. The adsorption kinetics and isotherm data are found to be well elucidated through pseudo-second-order and Langmuir models. Moreover, high regeneration ability (>89.3%) of PPy-BT was noted for five consecutive adsorption-desorption cycles. These findings highlight the potential of PPy-BT for practical water treatment applications. The intercalation material of PPy-BT could provide a new strategy to develop cost-effective clay-based nanomaterials for wastewater treatment.

Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Influence of Cr (VI) concentration on Cr (VI) reduction and electricity production in microbial fuel cell

Microbial fuel cell is an efficient technology to reduce pollutants of the heavy metal ions. Herein, a dual-chamber microbial fuel cell (MFC) coupled with abio-cathode and electrochemically active bacteria is fabricated to treat Cr (VI) containing wastewater and harvest bioelectricity simultaneously. To investigate the wide application of MFC for various industries, four different concentrations of Cr (VI) (6 mg/L, 15 mg/L, 40 mg/L, 100 mg/L) are used to explore the removal efficiency of Cr (VI) and the corresponding power performance. We find that the power performance gradually increases with the increment of the initial Cr (VI) concentration. Significantly, a maximum power density of 35.3 mW/m² can be achieved with the initial concentration of 100mg/L Cr (VI), while MFC only generate negligible power density (2.6 mW/m²) without the presence of Cr (VI). Meanwhile, MFC combined with the initial Cr (VI) concentration of 15 mg/L shows the highest Cr (VI) removal of 66.5%. Moreover, partial precipitates are found on the cathode surface and X-ray photoelectron spectroscopy (XPS) analysis has demonstrated that the Cr (VI) is successfully reduced into Cr (III). This study offers an alternative technology to remove Cr (VI) and synchronous electricity generation.