Search

Bioelectrochemical systems such as microbial fuel cells (MFCs) have gained extensive attention due to their abilities to simultaneously treat wastewater and generate renewable energy resources. Recently, to boost the system performance, the photoelectrode has been incorporated into MFCs for effectively exploiting the synergistic interaction between light and microorganisms, and the resultant device is known as photo-assisted microbial fuel cells (photo-MFCs). Combined with the metabolic reaction of organic compounds by microorganisms, photo-MFCs are capable of simultaneously converting both chemical energy and light energy into electricity. This article aims to systematically review the recent advances in photo-MFCs, including the introduction of specific photosynthetic microorganisms used in photo-MFCs followed by the discussion of the fundamentals and configurations of photo-MFCs. Moreover, the materials used for photoelectrodes and their fabrication approaches are also explored. This review has shown that the innovative strategy of utilizing photoelectrodes in photo-MFCs is promising and further studies are warranted to strengthen the system stability under long-term operation for advancing practical application.

The discharged saline wastewater has severely influenced the aquatic environment as the treatment performance of many wastewater treatment techniques is limited. In addition, the sources of saline wastewater are also plentiful from agricultural and various industrial fields such as food processing, tannery, pharmaceutical, etc. Although high salinity levels negatively impact the performance of both physicochemical and biological processes, membrane bioreactor (MBR) processes are considered as a potential technology to treat saline wastewater under different salinity levels depending on the adaption of the microbial community. Therefore, this study aims to systematically review the application of MBR widely used in the saline wastewater treatment from the perspectives of microbial structure and treatment efficiencies. At last, the concept of carbon dioxide capture and storage will be proposed for the MBR-treating saline wastewater technologies and considered toward the circular economy with the target of zero emission.

In the present study, water recovery from wastewater was accomplished simultaneously with the electrical energy production from biofuel as a source of organic matter, by the novel integration of distillation membrane and microbial fuel cell to create a system called the membrane distillation microbial fuel cell (MDMFC). A hydrophobic 0.45 μm membrane made of polytetrafluoroethylene (PTFE) was employed as a separator between the cathodic and anodic compartments to investigate multiple benefits of MDMFC for electricity generation, wastewater treatment and water reclamation at different temperature conditions. A high open-circuit voltage of 0.724 ± 0.07 V and a short circuit current of 64.55 ± 2.56 μA were achieved at 45 °C with an initial flux of 3.5 LMH. In the anodic chamber, Firmicutes, Proteobacteria, and Bacteroidetes were detected as dominant species at 45 °C, among which the Proteobacteria and Firmicutes were the most abundant sequences when an artificial substrate was used for feeding. The results indicate that 45 °C is the temperature that most significantly influences the electrochemical performance of MDMFC because of the dominance of bacterial community. Moreover, the power density increased by 99.9% when the temperature increased from 35 °C (0.99 μW m−3) to 45 °C (1552 μW m−3) and decreased by 97% when the temperature was further increased to 55 °C (43.91 μW m−3). Consequently, this study confirms that MD and MFC can be combined for the sustainable development of a water-energy nexus.

Progressive freezing is a solvent purification technology with low energy requirements and high concentration efficiency. Although these advantages make it a promising technology, the technique has never been explored for draw solution recovery for forward osmosis (FO). Hence, in this study, the progressive freezing process was used to concentrate three common diluted draw solutions: NaCl, MgCl2, and EDTA-2Na with different ice front speeds, stirring rates, and initial draw solution concentrations. Effective partition and intrinsic partition constants were also evaluated. The results reveal that the freezing process can achieve a draw solution recovery rate of 99.73%, 99.06%, and 98.65% with NaCl, MgCl2, and EDTA-2Na, respectively, using an ice front speed of 0.5 cm/h, a stirring rate of 2.62 m/s, and 30% of percentage of ice phase. Higher concentration efficiency for NaCl and MgCl2 was achieved due to the high solubility of NaCl and MgCl2 increased solute diffusion into the liquid phase solutions. The concentration factors for all three draw solutions exceeded 1.9, indicating that the draw solutes could be reused for the FO process. In addition, the two mass transfer coefficients depended on the ice front speed and the stirring rates were also obtained for scaling up the experiment in the future.

Laminar-flow microfluidic microbial fuel cell (LMMFC) has attracted attention due to the advantage of the liquid-liquid interface between anolyte and catholyte without the use of membrane as a separator resulting in less fabrication cost. Unlike previous studies of LMMFC using syringe pumps, this study proposes the use of osmotic pumps to feed anolyte and catholyte in the microchannel without any additional power supply. The osmotic pump was constructed with two cylindrical chambers separated by a forward osmosis membrane, with the initial draw solution concentration of 90 g l

The development of cost-effective and energy-efficient technologies to recover nutrients from digestate is important. Anaerobic digestate can be concentrated into bio-nutrient products through an electrodialysis (ED) process in an energy-efficient manner. Despite recent advances, the operation modes of ED for nutrient recovery from swine digestate are yet to be systematically evaluated from the perspective of energy-water efficiencies, and the determination of optimal operations in ED units is still ambiguous. In this study, two different operating modes of electrodialysis, i.e., constant voltage and constant current, are designed to evaluate the energy efficiency and effectiveness of nutrient recovery from anaerobic swine digestate. The ion removal ratio and current efficiency of the different modes and their associated electromigration performance (e.g., rate constants) are evaluated. The results indicate that the maximum removal efficiency (in terms of electrical conductivity) is 92.8% at a cell voltage of 2.4 V/cell using the constant voltage operation. The current efficiencies of NH

This study is aimed to comprehend the treatment of non-submerged attached growth systems using bio-sponge, bio-cord, and bio-cloth media. Three reactors were set up with internal recirculation ratio of 1 (IR = 1) and similar media surface area. Bio-sponge and bio-cloth reactors showed removal of COD (79 vs. 76%) and NH4+–N (78 vs. 73%). While bio-cord treatment was deteriorated due to time-dependent process. Multiple linear regression revealed that alkalinity governed the formation degree of the anaerobic zone in bio-sponges, partially affecting nitrification. Increasing IR from 1 to 3 caused sloughing of the attached biomass and was positively correlated with effluent nitrite nitrogen concentration, indicating the sensitivity of nitrification to spatial distribution effects. In addition, bio-sponge system obtained superior performance at IR of 2 while bio-cloth one might be also an effective media for wastewater treatment if having good durability.

Understanding the environmental niche segregation of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and its impact on their relative contributions to nitrification and nitrous oxide (N

Nitrification inhibitors (NIs) such as dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and allylthiourea (AT) are commonly used to suppress ammonia oxidization at different time scales varying from a few hours to several months. Although the responses of NIs to edaphic and temperature conditions have been studied, the influence of the aforementioned factors on their inhibitory effect remains unknown. In this study, laboratory-scale experiments were conducted to assess the short-term (24 h) influence of eight abiotic and biotic factors on the inhibitory effects of DCD, DMPP, and AT across six cropped and non-cropped soils at two temperature conditions with three covariates of soil texture. Simultaneously, the dominant contributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to potential ammonia oxidization (PAO) were distinguished using the specific inhibitor 2 phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Our results revealed that AT demonstrated a considerably greater inhibitory effect (up to 94.9% for an application rate of 75 mg of NI/kg of dry soil) than DCD and DMPP. The inhibitory effect of AT was considerably affected by the relative proportions of silt, sand, and clay in the soil and total PAO. In contrast to previous studies, the inhibitory effects of all three NIs remained largely unaffected by the landcover type and temperature conditions for the incubation period of 24 h. Furthermore, the efficacy of all three tested NIs was not affected by the differential contributions of AOA and AOB to PAO. Collectively, our results suggested a limited influence of temperature on the inhibitory effects of all three NIs but a moderate dependence of AT on the soil texture and PAO. Our findings can enhance the estimation of the inhibitory effect in soil, and pure cultures targeting the AOA and AOB supported ammonia oxidization and, hence, nitrogen dynamics under NI applications.

Understanding the environmental niche segregation of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and its impact on their relative contributions to nitrification and nitrous oxide (N2O) production is essential for predicting N2O dynamics within an ecosystem. Here, we used ammonia oxidizer-specific inhibitors to measure the differential contributions of AOA and AOB to potential ammonia oxidization (PAO) and N2O fluxes over pH (4.0-9.0) and temperature (10-45 °C) gradients in five soils and three wetland sediments. AOA and AOB activities were differentiated using PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), 1-octyne, and acetylene. We used square root growth (SQRT) and macromolecular rate theory (MMRT) models to estimate cardinal temperatures and thermodynamic characteristics for AOA- and AOB-dominated PAO and N2O fluxes. We found that AOA and AOB occupied different niches for PAO, and soil temperature was the major determinant of niche specialization. SQRT and MMRT models predicted a higher optimum temperature for AOA-dominated PAO and N2O fluxes compared with those of AOB. Additionally, PAO was dominated by AOA in acidic conditions, whereas both AOA- and AOB-dominated N2O fluxes decreased with increasing pH. Consequently, net N2O fluxes (AOA and AOB) under acidic conditions were approximately one to three-fold higher than those observed in alkaline conditions. Moreover, structural equation and linear regression modeling confirmed a significant positive correlation (R2 = 0.45, p

For the first time, an osmotic microbial fuel cell (OsMFC) was employed for simultaneous hexavalent chromium [Cr(VI)] removal, organic contaminant removal, energy production, and water reclamation. In this system, draw solutions were prepared from 0 to 1 M NaCl mixed with 12 mg/L Cr(VI). Cr(VI) reduction and power generation at different pH were studied. In terms of power generation, the results revealed that the highest power density of 6.6 mW/m2 (170 mW/m3) was obtained using the 1 M NaCl catholyte at pH 7. However, the greater Cr(VI) reduction of 44.5% and 97.6% was achieved using the 0.2 M NaCl/Cr(VI) based catholyte at pH 7 and 2, respectively. This can be attributed to the competition between Cr(VI) and oxygen reduction due to the high rate of dilution at higher concentrations of NaCl. Additionally, the highest open-circuit voltage of 0.752–0.845 V was recorded at 0.2 M NaCl/Cr(VI) as a proof to support that 0.2 M NaCl was a favorite condition for reducing Cr(VI). Moreover, through cyclic voltammetry, the signals of oxidation-reduction peaks were observed in the case of 0.2 M NaCl/Cr(VI), while, reduction peaks mostly disappeared in other cases. Additionally, more precipitate [Cr(OH)3(s)] was observed to be deposited on the surface of the cathode electrode when 0.2 M NaCl was used as the draw solution. Hence, 0.2 M NaCl was the optimal catholyte concentration for Cr(VI) reduction. The Cr(VI) removal efficiency was 97.6% for an initial pH of 2 with the 0.2 M NaCl catholyte because low pH is thermodynamically favored for Cr(VI) reduction.

Herein, poly(sodium 4-styrenesulfonate) (PSS) with molecular weight of 70,000 (PSS-70,000) coupled with non-ionic surfactant Triton X-114 (TX-114) was exerted as draw solution (DS) in forward osmosis (FO) process for the first time to reduce salt reversal flux and enhance water recovery. In order to evaluate performances of this new type of draw solution, different concentrations of PSS-70,000 and TX-114 were prepared and implemented in FO process accordingly. When pure PSS-70,000 was used, high viscosity of 100% PS-70,000 inhibited the water flux as comparing with 50% PSS-70,000 since water passage was prevented from transferring through increasing thickness of draw solution. Interestingly, adding 1 mM TX-114 in 50% PSS-70,000 just slightly influenced on water flux but salt reversal flux was significantly reduced by 70% from 2.71 gMH to 0.92 gMH and reverse sodium was also reduced by 35.9%. Specifically, large molecular size of PSS-70,000 polyelectrolyte combining with a nucleophile ethylene oxide of TX-114 could effectively perform as a barrier to restrain electrophile sodium of PSS-70,000 reversing to the feed side. Moreover, the hydrophobic hydrocarbon tails of TX-114 retained on the hydrophobic surface of FO membrane was caused by the nonpolar–nonpolar interaction resulting in less reverse sodium. It can be concluded that the utilization of TX-114 with PSS-70,000 produced beneficial achievements since it did not only improve the performance of FO through reducing salt reversal flux but also effectively enhance the regeneration of diluted DS operated by membrane distillation (MD) process. Expressly, the repeatability of FO performance was revamped depending on the nonpolar interaction between the hydrophobic natures of 50% PSS-70,000/1 mM TX-114 based DS and hydrophobic surface of MD membrane.

The overpopulation in the future will result in burning issues of our environment and the negative effects of global warming, environmental pollution, and habitat loss in the worldwide human community. Moreover, the nonrenewable natural resources such as fossil fuels and clear water are consumed at the speed faster than their rate of regeneration. Worldwide demand has increased year by year, which is required to exceed production from known and anticipated resources. Last but not least, the demands of water used in agriculture, industries, and supporting population growth have increased and become of the most challenges in later centuries. Under those circumstances, there are prerequisites for finding alternative renewable energy resources and cost-effective wastewater treatment technologies with less energy expenditure. Among various technologies that have been well investigated, microbial fuel cell might be the potential candidate to administer with the recent situation of wastewater–energy nexus. In general, the microbial fuel cell is a cross-disciplinary technology so that survey area has extended to energy, material sciences, biology, and environment. In this chapter, we aim to present the possibility of generating electricity in MFC from a wide range of organic waste and hazardous wastes. In addition, the integrations between microbial fuel cells and other technologies are also introduced which have supposedly made great opportunities to concurrently reach sustainable energy production, efficient wastewater treatment, and reuse.