Submerged membrane adsorption hybrid system using four adsorbents to remove nitrate from water

Extracellular electron transfer for aerobic denitrification mediated by the bioelectric catalytic system with zero-carbon source

The slow rate of electron transfer and the large consumption of carbon sources are technical bottlenecks in the biological treatment of wastewater. Here, we first proposed to domesticate aerobic denitrifying bacteria (ADB) from heterotrophic to autotrophic by electricity (0.6 V) under zero organic carbon source conditions, to accelerate electron transfer and shorten hydraulic retention time (HRT) while increasing the biodegradation rate. Then we investigated the extracellular electron transfer (EET) mechanism mediated by this process, and additionally examined the integrated nitrogen removal efficiency of this system with composite pollution. It was demonstrated that compared with the traditional membrane bioreactor (MBR), the BEC displayed higher nitrogen removal efficiency. Especially at C/N = 0, the BEC exhibited a NO3--N removal rate of 95.42 ± 2.71 % for 4 h, which was about 6.5 times higher than that of the MBR. Under the compound pollution condition, the BEC still maintained high NO3--N and tetracycline removal (94.52 ± 2.01 % and 91.50 ± 0.001 %), greatly superior to the MBR (10.64 ± 2.01 % and 12.00 ± 0.019 %). In addition, in-situ electrochemical tests showed that the nitrate in the BEC could be directly converted to N2 by reduction using electrons from the cathode, which was successfully demonstrated as a terminal electron acceptor.

Adsorption of arsenic in aqueous solution onto iron impregnated bagasse fly ash

The present study examined the adsorption of As(III) and As(V) (arsenics) from aqueous solutions using FeCl3 impregnated bagasse fly ash (BFA-Fe). Batch adsorption studies were carried out to evaluate the effect of various parameters like initial pH (pH 0 ), adsorbent dose (m), contact time (t), initial concentration (C 0 ) and temperature (T) on the removal of As(III) and As(V) from aqueous solutions. The maximum removal of As(III) and As(V) was found ~ 95% and ~ 97% at lower concentration (< 20 μg/dm3) and ~ 86% and ~ 87% at higher concentration (500 μg/dm3), respectively, using 3 g/dm3 of BFA dosage at 303 K. The adsorption of arsenics on BFA-Fe was very rapid. Pseudo-second-order kinetic model well represented the adsorption kinetics of both As(III) and As(V). Error analyses functions for adsorption of As(III) and As(V) onto BFA-Fe. Based on these error analyses, R-P isotherm was found to be fitted. Thermodynamic parameters, i.e., ΔG°, ΔH°, and ΔS°, were also calculated. At 25.0 to 45.0 °C, the values of ΔG° lie in the range of -43.85, -45.34, -48.82, -51.31, -53.8, and -44.75, -48.3, -51.84, -55.39, -58.93, -55.57 for As (III), and As (V) respectively, indicating that adsorption is spontaneous and exothermic in nature. Regeneration study was carried out by different solvent and thermal methods. Our results revealed that BFA-Fe can be reused directly for making fire-briquettes to explore its energy value. From this study, As containment is most effective removal from aqueous solution and mimic to any contaminated water resources.

Review of adsorption-membrane hybrid systems for water and wastewater treatment

Adsorption is an effective method for the removal of inorganic and organic contaminants and has been commonly used as a pretreatment method to improve contaminant removal and control flux during membrane filtration. Over the last two decades, many researchers have reported the use of hybrid systems comprising various adsorbents and different types of membranes, such as nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) membranes, to remove contaminants from water. However, a comprehensive evaluation of the removal mechanisms and effects of the operating conditions on the transport of contaminants through hybrid systems comprising various adsorbents and NF, UF, or MF membranes has not been performed to date. Therefore, a systematic review of contaminant removal using adsorption-membrane hybrid systems is critical, because the transport of inorganic and organic contaminants via the hybrid systems is considerably affected by the contaminant properties, water quality parameters, and adsorbent/membrane physicochemical properties. Herein, we provide a comprehensive summary of the most recent studies on adsorption-NF/UF/MF membrane systems using various adsorbents and membranes for contaminant removal from water and wastewater and highlight the future research directions to address the current knowledge gap.

Arsenate removal from drinking water using by-products from conventional iron oxyhydroxides production as adsorbents coupled with submerged microfiltration unit

Arsenic is among the major drinking water contaminants affecting populations in many countries because it causes serious health problems on long-term exposure. Two low-cost micro-sized iron oxyhydroxide-based adsorbents (which are by-products of the industrial production process of granular adsorbents), namely, micro granular ferric hydroxide (μGFH) and micro tetravalent manganese feroxyhyte (μTMF), were applied in batch adsorption kinetic tests and submerged microfiltration membrane adsorption hybrid system (SMAHS) to remove pentavalent arsenic (As(V)) from modeled drinking water. The adsorbents media were characterized in terms of iron content, BET surface area, pore volume, and particle size. The results of adsorption kinetics show that initial adsorption rate of As(V) by μTMF is faster than μGFH. The SMAHS results revealed that hydraulic residence time of As(V) in the slurry reactor plays a critical role. At longer residence time, the achieved adsorption capacities at As(V) permeate concentration of 10 μg/L (WHO guideline value) are 0.95 and 1.04 μg/mg for μGFH and μTMF, respectively. At shorter residence time of ~ 3 h, μTMF was able to treat 1.4 times more volumes of arsenic-polluted water than μGFH under the optimized experimental conditions due to its fast kinetic behavior. The outcomes of this study confirm that micro-sized iron oyxhydroxides, by-products of conventional adsorbent production processes, can successfully be employed in the proposed hybrid water treatment system to achieve drinking water guideline value for arsenic, without considerable fouling of the porous membrane. Graphical abstract.

Effect of Nanoparticle Size in Pt/SiO2 Catalyzed Nitrate Reduction in Liquid Phase

Effect of platinum nanoparticle size on catalytic reduction of nitrate in liquid phase was examined under ambient conditions by using hydrogen as a reducing agent. For the size effect study, Pt nanoparticles with sizes of 2, 4 and 8 nm were loaded silica support. TEM images of Pt nanoparticles showed that homogeneous morphologies as well as narrow size distributions were achieved during the preparation. All three catalysts showed high activity and were able to reduce nitrate below the recommended limit of 50 mg/L in drinking water. The highest catalytic activity was seen with 8 nm platinum; however, the product selectivity for N₂ was highest with 4 nm platinum. In addition, the possibility of PVP capping agent acting as a promoter in the reaction is highlighted.

Mathematical modeling of arsenic(V) adsorption onto iron oxyhydroxides in an adsorption-submerged membrane hybrid system

The adsorption of arsenic (V), As(V), on two porous iron oxyhydroxide-based adsorbents, namely, micro-sized tetravalent manganese feroxyhyte (μTMF) and granular ferric hydroxide (μGFH), applied in a submerged microfiltration membrane hybrid system has been investigated and modeled. Batch adsorption tests were carried out to determine adsorption equilibrium and kinetics parameters of As(V) in a bench-scale slurry reactor setup. A mathematical model has been developed to describe the kinetic data as well as to predict the As(V) breakthrough curves in the hybrid system based on the homogeneous surface diffusion model (HSDM) and the corresponding solute mass balance equation. The kinetic parameters describing the mass transfer resistance due to intraparticle surface diffusion (D_s) involved in the HSDM was determined. The fitted D_s values for the smaller (1-63 μm) and larger (1-250 μm) diameter particles of μGFH and μTMF were estimated to be 1.09 × 10^-18 m²/s and 1.53 × 10^-16 m²/s, and 2.26 × 10^-18 m²/s and 1.01 × 10^-16 m²/s, respectively. The estimated values of mass transfer coefficient/ kinetic parameters are then applied in the developed model to predict the As(V) concentration profiles in the effluent of the hybrid membrane system. The predicted results were compared with experimental data for As(V) removal and showed an excellent agreement. After validation at varying adsorbent doses and membrane fluxes, the developed mathematical model was used to predict the influence of different operation conditions on As(V) effluent concentration profile. The model simulations also exhibit that the hybrid system benefits from increasing the amount of adsorbent initially dosed and from decreasing the membrane flux (increasing the contact time).

Removal of silica from brackish water by integrated adsorption/ultrafiltration process

A lab-scale unit of the hybrid continuous stirred tank reactor (CSTR) adsorption/ultrafiltration (UF) system was used to evaluate the removal efficiency of silica from brackish water. The semi-batch adsorption process was carried out using iron oxy/hydroxide agglomerates (IOAs) as adsorbent and hollow fiber ultrafiltration membrane as a barrier to the adsorbent passage to the product water. The effect of residence time, concentration of silica, and adsorbent dosage on the silica removal and UF membrane blockage was examined. It was found that a short residence time of 15 min was sufficient to achieve the maximum adsorption capacity similar to that obtained in batch isotherm experiments. The adsorption capacity increased with the augmentation of the silica concentration and decreased with the increase in the adsorbent dosage. The UF was effectively employed to separate the loaded adsorbent without fouling the membrane until breakthrough. A simple model was applied to accurately predict the adsorption breakthrough curves.