Constructed Wetland-microbial Fuel Cell Research Articles

Applying multiple bio-cathodes in constructed wetland-microbial fuel cell for promoting energy production and bioelectrical derived nitrification-denitrification process

A multiple bio-cathodes constructed wetland-microbial fuel cell (CW-MFC) system, aiming for higher power production and therefore the improved N removal, was investigated in this study. As the bio-cathode number increased from 1 to 3, the energy losses on both anode and cathode showed a significant decrement (from 97.85 mV to 46.09 mV for anode and from 221.5 mV to 45.89 mV for cathode, respectively). Accordingly, the maximum power density of the system showed a notable increase from 12.56 to 26.16 mW/m2. In addition to the improved electrical performance, enhanced simultaneous nitrification & denitrification process was triggered due to the influence of the bioelectrical derived interaction between power production and systematic nitrification rate (rNi) and denitrification rate (rDe). Insight into the nitrification & denitrification process has been given that rNi increased from 98.59 ± 4.53 mg/(m2·d) of the control system to 179.11 ± 7.65 mg/(m2·d) of three bio-cathodes system while rDe increased from 89.64 ± 4.57 mg/(m2·d) to 163.55 ± 11.88 mg/(m2·d). Correction analysis showed that the amount of electrical related nitrogen removal is almost linearly correlated to the produced electricity. Overall, this study presented a promising strategy and provided insight for higher energy production and the enhanced nitrogen removal from the newly established CW-MFC system.

Maximizing the energy harvest from a microbial fuel cell embedded in a constructed wetland

Direct energy harvesting from the newly established constructed wetland-microbial fuel cell (CW-MFC) offers it a competitive position compared with traditional constructed wetlands (CWs) to allow the CWs for wastewater treatment and concomitantly achieve power generation. However, the integration of MFC into CWs always faces a large portion of energy losses due to the existence of higher internal resistance. This paper reports tests of a novel strategy, namely a capacitator engaged duty cycling (CDC) strategy, to harvest energy from an open air bio-cathode CW-MFC. Results show that with duty cycle value of 31.6% (D = 31.6%), the effective charge obtained from CDC strategy is 19.81% higher than the conventional continuous loading (CL) mode within the same discharging time. With a lower D value of 20% (D = 20%), the total charge harvested increased about 25.0%. The CDC operation mode shows advantages over the higher internal resistance system and contributes to a higher normalized COD removal rate. This operation strategy can minimize the energy losses with a suitable D value. It is a simple but effective way to maximize the energy harvesting from the CW-MFC system.

Biorefractory wastewater degradation in the cathode of constructed wetland-microbial fuel cell and the study of the electrode performance

In this study, azo dye decolorization and degradation were realized in the air cathode of constructed wetland-microbial fuel cells (CW-MFCs). Additionally, the relationship between cathode and anode was studied. The cathode diameter was varied from 20 to 30 cm to study the cathode degradation and electricity generation performances, the effects of the cathode on the anode, and the influence of plants in the cathode layer. Different external resistances were applied to study the effects of current intensity on degradation and electricity generation performances. Cathode decolorization performance increased with increasing cathode diameter. Electricity generation performance first increased and then decreased with increasing cathode diameter. The highest decolorization volume (397.64 mg/L) was observed in the CW-MFC with a cathode 25 cm in diameter when the external resistance was 620 Ω. Meanwhile, it had a chemical oxygen demand removal volume of 317.65 mg/L. The highest cathode exchange current density (0.539 A/m2) was observed in the CW-MFC with a cathode 27.5 cm in diameter when the external resistance was 200 Ω. There were more electricity generation generas in the anode layer and there were more anaerobes and amphimicrobes in the larger cathode layer.

Relationship between electrogenic performance and physiological change of four wetland plants in constructed wetland-microbial fuel cells during non-growing seasons

To find suitable wetland plants for constructed wetland-microbial fuel cells (CW-MFCs), four commonly used wetland plants, including Canna indica, Cyperus alternifolius L., Acorus calamus, and Arundo donax, were investigated for their electrogenic performance and physiological changes during non-growing seasons. The maximum power output of 12.82mW/m2 was achieved in the A. donax CW-MFC only when root exudates were being released. The results also showed that use of an additional carbon source could remarkably improve the performance of electricity generation in the C. indica and A. donax CW-MFCs at relatively low temperatures (2–15°C). However, A. calamus withered before the end of the experiment, whereas the other three plants survived the winter safely, although their relative growth rate values and the maximum quantum yield of PSII (Fv/Fm) significantly declined, and free proline and malondialdehyde significantly accumulated in their leaves. On the basis of correlation analysis, temperature had a greater effect on plant physiology than voltage. The results offer a valuable reference for plant selection for CW-MFCs.

Influence of glass wool as separator on bioelectricity generation in a constructed wetland-microbial fuel cell

To figure out the impact of the separator on the electrical performance of the newly established constructed wetland-microbial fuel cell (CW-MFC), two parallel upflow CW-MFC systems, with and without glass wool (GW), were set up in this study. System performances in terms of bioelectricity production were monitored for more than 4 months. Results showed that the highest voltage was achieved in non-separator (NS) system (465.7 ± 4.2 mV with electrode spacing of 5 cm), which is 48.9% higher than the highest value generated in GW system (312 ± 7.0 mV with electrode spacing of 2 cm). The highest power density was produced in NS system (66.22 mW/m2), which is 3.9 times higher than the value in GW system (17.14 mW/m2). The diffusion of oxygen from the open air was greatly hindered by the biofilm formed under the cathode. This kind of biofilm can be severed as the “microbial separator”, playing the same role in a real separator.

Performance assessment of aeration and radial oxygen loss assisted cathode based integrated constructed wetland-microbial fuel cell systems

The present study explores low-cost cathode development possibility using radial oxygen loss (ROL) of Canna indica plants and intermittent aeration (IA) for wastewater treatment and electricity generation in constructed wetland-microbial fuel cell (CW-MFC) system. Two CW-MFC microcosms were developed. Amongst them, one microcosm was planted with Canna indica plants for evaluating the ROL dependent cathode reaction (CW-MFC dependent on ROL) and another microcosm was equipped with intermittent aeration for evaluating the intermittent aeration dependent cathode reaction (CW-MFC with additional IA). The CW-MFC with additional IA has achieved 78.71% and 53.23%, and CW-MFC dependent on ROL has achieved 72.17% and 46.77% COD removal from synthetic wastewater containing glucose loads of 0.7gL−1and 2.0gL−1, respectively. The maximum power density of 31.04mWm−3 and 19.60mWm−3 was achieved in CW-MFC with additional IA and CW-MFC dependent on ROL, respectively.

The salinity effects on the performance of a constructed wetland-microbial fuel cell

The objective of the present work is to study the influence of the wastewater salinity concentration on the performance of a Constructed Wetland-Microbial Fuel Cell (CW-MFC) for simultaneous water pollution control and electricity generation. The work has been carried out under the hypothesis that increasing the salinity may improve the electricity production because of a lower internal ohmic resistance, although it could damage the microbiological processes or the plants. A pilot-scale horizontal subsurface flow CW, modified to function as an MFC, was operated under a continuous operation mode over five consecutive experimental periods of approximately 2 months each. The wastewater salinity was increased in each new period by steeply increasing the NaCl concentration in the synthetic wastewater from 0.51 to 9.51gL−1. The CW-MFC performance was monitored during every stationary period. The increasing salinity first improved the cell voltage, and the resultant maximum voltage (130mV) under continuous operation corresponded to a salinity concentration between 4 and 5gL−1. However, subsequently higher salinity levels caused the opposite effect. The maximum voltage was obtained in an unstable condition, as microbiological inhibition in the anode zone appeared early, at approximate salinity levels of only 3gL−1. Batch experiments confirmed the results, and higher cell voltage values up to 600mV were obtained if longer retention times were allowed. The wetland plants (Phragmites australis) were only damaged at a salinity concentration of 9.51gL−1.

Effects of influent organic loading rates and electrode locations on the electrogenesis capacity of constructed wetland‐microbial fuel cell systems

Three novel constructed wetland‐microbial fuel cells (CW‐MFCs), based on electrode location, were developed for wastewater treatment and sustainable electricity production by embedding a MFC into a CW system. In the three CW‐MFCs, electrodes were placed in different locations, including bottom anode‐rhizosphere cathode CW‐MFC (BA‐RC‐CW‐MFC), rhizosphere anode‐air cathode CW‐MFC (RA‐AC‐CW‐MFC), and bottom anode‐air cathode CW‐MFC (BA‐AC‐CW‐MFC), to investigate the combined effects of organic loading rates (OLRs) and reactor configurations on the electrogenesis capacity of the hybrid system. All the systems operated continuously to treat five types of synthetic wastewater with increasing OLRs: 9.2, 18.4, 27.6, 55.2, and 92.0 g chemical oxygen demand (COD) m−2 d−1. The BA‐RC‐CW‐MFC failed to produce electricity at any OLR, whereas the maximum power densities of 0.79 ± 0.01 and 10.77 ± 0.52 mW m−2 were achieved in the RA‐AC‐CW‐MFC with 18.4 g COD m−2 d−1 influent OLR and in the BA‐AC‐CW‐MFC with 27.6 g COD m−2 d−1 influent OLR, respectively. The coulombic efficiencies of the RA‐AC‐CW‐MFC and BA‐AC‐CW‐MFC decreased gradually with the increase in influent OLRs. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 435–441, 2017

Performance assessment of innovative constructed wetland-microbial fuel cell for electricity production and dye removal

This research work deals with performance assessment of constructed wetlands-microbial fuel cell (CW-MFC) for electricity production and wastewater treatment. Microbial fuel cell consists of two chambers i.e. anaerobic and aerobic, where oxidation and reduction reactions take place. Constructed wetland also consists of aerobic and anaerobic zones where oxidation and reduction processes take place. These similarities in both technologies motivated us to design and develop a new type constructed wetland-microbial fuel cell. In this CW-MFC, the removal of dye and COD were investigated along with electricity generation. Experiments were performed in batch mode using different dye (methylene blue dye) concentration containing synthetic wastewater. Our results show that 76.2, 80.87, 69.29 and 93.15 percentage dye removal could be achieved after 96h of treatment of wastewater containing 2000, 1500, 1000 and 500mgl−1 initial concentration respectively. Also, the CW-MFC is able to remove 75% of COD form wastewater with 1500mgl−1 initial concentration of dye. The maximum power density of 15.73mWm−2 and maximum current density of 69.75mAm−2 could be achieved during treatment of 1000mgl−1 initial dye concentration containing wastewater.