Microbial Desalination Cell for Sustainable Water Treatment: A Critical Review.

In view of increasing threats arising from the shortage of fresh water, there is an urgent need to propose sustainable technologies for the exploitation of unconventional water sources. As a derivative of microbial fuel cells (MFCs), microbial desalination cell (MDC) has the potential of desalinating saline/brackish water while simultaneously generating electricity, as well as treating wastewater. Therefore, it is worth investigating its practicability as a potential sustainable desalination technology. This review article first introduces the fundamentals and annual trends of MDCs. The desalination of diverse types of solutions using MDCs along with their life cycle impact assessment (LCIA)  and economic analysis is studied later. Finally, limitations and areas for improvement, prospects, and potential applications of this technology are discussed. Due to the great advantages of MDCs, improving their design, building materials, efficiency, and throughput will offer them as a significant alternative to the current desalination technologies.

Synthesis and study of CuNiTiO3 as an ORR electrocatalyst to enhance microbial fuel cell efficiency.

Microbial fuel cells (MFCs) have the capability of simultaneous sewage treatment and electricity generation. Modifying the cathode electrode enhances their efficiency. In this study, NiTiO3 and CuNiTiO3 were synthesized for practical application as cathode catalysts in a dual-chamber MFC and the performance of the modified cathodes was evaluated against a bare graphite electrode. SEM images showed that the particle sizes were mostly in the range of 40-120 and 20-80 nm for NiTiO3 and CuNiTiO3, respectively. According to AFM results, CuNiTiO3 presented a higher surface roughness than NiTiO3. MFC using CuNiTiO3/G electrode with a reduction potential value of -0.27 V (vs. SCE) and a power density of 62.18 mW m-2 showed better oxygen reduction reaction (ORR) activity compared with NiTiO3/G and the bare graphite. MFC using CuNiTiO3 cathode also showed the highest values in terms of chemical oxygen demand (COD) removal (75%) and the calculated coulombic efficiency (CE, 10%). The results obtained in this study, introduce CuNiTiO3 as a promising electrocatalyst for further improvement of the cathodic reactions in MFC applications.

Visible-light enhanced azo dye degradation and power generation in a microbial photoelectrochemical cell using AgBr/ZnO composite photocathode.

In this study, a dual-chamber microbial photoelectrochemical cell (MPEC) composed of a bio anode and a photoresponse AgBr/ZnO-modified graphite as a photocathode was investigated. The cell efficacy in degrading reactive black 5 (RB5), a diazo dye, in the cathodic chamber and simultaneously, electricity generation was analyzed. The synthesized AgBr/ZnO photocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectra (UV-vis DRS), photoluminescence (PL), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). Under light irradiation, the MPEC equipped with AgBr/ZnO-modified photocathode yielded 61% RB5 dye degradation over 72 h which indicated a highly enhanced performance compared with the irradiated bare graphite (11.74%). Besides, the maximum power density produced was 53.8 mW m-2 under visible light illumination and 32.5 mW m-2 in dark conditions. The MPEC reported in this research seems to be a promising system for bioelectricity generation, wastewater treatment in the anodic chamber, and also, dye pollutant degradation in the cathodic chamber.

Treatment of mixed dairy and dye wastewater in anode of microbial fuel cell with simultaneous electricity generation.

Microbial fuel cell (MFC) is a green technology that converts the stored chemical energy of organic matter to electricity; therefore, it can be used for wastewater purification and energy production simultaneously. In this study, three kinds of dairy products, including milk, cheese water, and yogurt water, were mixed with Acid orange 7 (AO7) as the model wastewater and used as the anolyte of an MFC. The capability of the system in energy production and dye removal was also investigated. The FESEM images were used to investigate the biofilms attachment to the anodes. Moreover, the polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry (CV), voltage-time profiles, and coulombic efficiency were used to evaluate the electrochemical activity of the MFCs. Based on the CV results, the biofilm formation significantly improved the electrochemical activity of the electrodes. Maximum power density, voltage, and coulombic efficiency were obtained as 44.05 mW.m-2, 332.4 mV, and 1.76%, respectively, for cheese water + AO7 anolyte, but the milk + AO7 MFC produced a stable voltage for a long time and its performance was similar to the cheese water + AO7 anolyte. Maximum COD removal and decolorization efficiencies were obtained equal to 84.57 and 92.18% for yogurt water + AO7 and cheese water + AO7 anolytes, respectively.

Application of immobilized ZnO nanoparticles for the photocatalytic regeneration of ultrasound pretreated-granular activated carbon.

In this study, the photocatalytic regeneration by ZnO was employed for the regeneration of the granular activated carbon (GAC) which was saturated with the reactive red 43. The ultrasound was applied as a pretreatment step due to the cleanup of the adsorbent surface and providing a higher surface area and adsorption capacity. According to the nitrogen gas adsorption-desorption results, the ultrasound pretreated-GAC had the highest surface area and the total pore volume. The SEM and XRD analyses confirmed the immobilization of ZnO nanoparticles on the GAC. Response surface methodology (RSM) was used to model and optimize the preparation of the granular activated carbon/ZnO nanocomposite. The sonication time, pH, GAC/ZnO ratio, and calcination temperature were used as four effective parameters on nanocomposite preparation. Optimum amounts of pH, GAC/ZnO ratio, calcination temperature, and sonication time were found to be equal to 4, 5, 300 °C, 210 min, respectively; in these conditions, 83.98% of the capacity of the exhausted granular activated carbon was regenerated. ANOVA results, high R2, R2-adj values, and also normal and random distribution of residuals showed that application of RSM for the modeling and optimizing the preparation step of GAC/ZnO nanocomposite was successful.

Phosphomolybdic acid immobilized on graphite as an environmental photoelectrocatalyst.

A new phosphomolybdic acid (PMA)/Graphite surface was prepared based on electrostatic interactions between phosphomolybdic acid and graphite surface. The PMA/Graphite was characterized by cyclic voltammetry (CV) analysis and scanning electron microscope (SEM). SEM images showed that the phosphomolybdic acid particles were well stabilized on the graphite surface and they were evidenced the size of particles (approximately 10 nm). The CV results not only showed that the modified surface has good electrochemical activity toward the removal of the dyestuff, but also exhibits long term stability. The PMA/Graphite was used as a photoanode for decolorization of Reactive Yellow 39 by photoelectrocatalytic system under UV irradiation. The effects of parameters such as the amount of phosphomolybdic acid used in preparation of PMA/Graphite surface, applied potential on anode electrode and solution pH were studied by response surface methodology. The optimum conditions were obtained as follows: dye solution pH 3, 1.5 g of immobilized PMA on graphite surface and applied potential on anode electrode 1 V. Under optimum conditions after 90 min of reaction time, the decolorization efficiency was 95%.

Monitoring simultaneous photocatalytic-ozonation of mixture of pharmaceuticals in the presence of immobilized TiO2 nanoparticles using MCR-ALS: Identification of intermediates and multi-response optimization approach.

The present study has focused on the degradation of a mixture of three pharmaceuticals, i.e. methyldopa (MDP), nalidixic acid (NAD) and famotidine (FAM) which were quantified simultaneously during photocatalytic-ozonation process. The experiments were conducted in a semi-batch reactor where TiO2 nanoparticles (crystallites mean size 8nm) were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology and roughness of the bare and TiO2-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An analytical methodology was successfully developed based on both recording ultraviolet-visible (UV-Vis) spectra during the degradation process and a data analysis using multivariate curve resolution with alternating least squares (MCR-ALS). This methodology enabled the researchers to obtain the concentration and spectral profiles of the chemical compounds which were involved in the process. A central composite design was used to study the effect of several factors on multiple responses namely MDP removal (Y1), NAD removal (Y2) and FAM removal (Y3) in the simultaneous photocatalytic-ozonation of these pharmaceuticals. A multi-response optimization procedure based on global desirability of the factors was used to simultaneously maximize Y1, Y2 and Y3. The results of the global desirability revealed that 8mg/L MAD, 8mg/L NAD, 8mg/L FAM, 6L/h ozone flow rate and a 30min-reaction time were the best conditions under which the optimized values of various responses were Y1=95.03%, Y2=84.93% and Y3=99.15%. Also, the intermediate products of pharmaceuticals generated in the photocatalytic-ozonation process were identified by gas chromatography coupled to mass spectrometry.

Electrosorption and photocatalytic one-stage combined process using a new type of nanosized TiO2/activated charcoal plate electrode.

In the present study, an activated charcoal (AC) plate was prepared by physical activation method. Its surface was coated with TiO2 nanoparticles by electrophoretic deposition (EPD) method. The average crystallite size of TiO2 nanoparticles was determined approximately 28 nm. The nature of prepared electrode was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area measurement before and after immobilization. The electrosorption and photocatalytic one-stage combined process was investigated in degradation of Lanasol Red 5B (LR5B), and the effect of dye concentration, electrolyte concentration, pH, voltage, and contact time was optimized and modeled using response surface methodology (RSM) approach. The dye concentration of 30 mg L(-1), Na2SO4 concentration of 4.38 g L(-1), pH of 4, voltage of 250 mV, and contact time of 120 min were determined as optimum conditions. Decolorization efficiency increased in combined process to 85.65% at optimum conditions compared to 66.03% in TiO2/AC photocatalytic, 20.09% in TiO2/AC electrosorption, and 1.91% in AC photocatalytic processes.

Optimization of activated carbon fiber preparation from Kenaf using K2HPO4 as chemical activator for adsorption of phenolic compounds.

The present work reports the preparation of activated carbon fiber (ACF) from Kenaf natural fibers. Taguchi experimental design method was used to optimize the preparation of ACF using K(2)HPO(4). Optimized conditions were: carbonization at 300 degrees C, impregnation with 30%w/v K(2)HPO(4) solution and activation at 700 degrees C for 2h with the rate of achieving the activation temperature equal to 2 degrees C min(-1). The surface characteristics of the ACF prepared at optimized conditions were also studied using pore structure analysis, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Pore structure analysis shows that micropores constitute the most of the porosity of the prepared ACF. The ability of the ACF prepared at optimized conditions to adsorb phenol and p-nitrophenol from aqueous solution was also investigated. The equilibrium data of phenol and p-nitrophenol adsorption on the prepared ACF were well fitted to the Langmuir isotherm. The maximum adsorption capacities of phenol and p-nitrophenol on the prepared ACF are 140.84 and 136.99 mg g(-1), respectively. The adsorption process follows the pseudo-first-order kinetic model.