Modeling and application of direct contact membrane distillation for fluoride removal from aqueous solutions

© 2017 Desalination Publications. All rights reserved. The practicability of direct contact membrane distillation (DCMD) process for the removal of fluoride was investigated under different feed water, operational and membrane characteristics. Commercially available hydrophobic 0.22 mm porous polytetrafluoroethylene (PTFE) and polyvinylidenefluoride (PVDF) membrane applied on fluoridated ultrapure water exhibit over 99% rejection of fluoride, yielding fluxes of up to 39.3 and 26.4 kg/m2 h at 60°C, respectively. The dusty gas mathematical model and energy balance equations were employed to study the mass and heat transfer mechanisms. In addition to the good agreement between the theoretical and experimental comparison, the overall mass transfer analysis revealed that Knudsen–molecular–Poiseuille transition diffusion and Knudsen–Poiseuille diffusion are the dominant mass transfer mechanisms across the 0.22 mm flat sheet PVDF and PTFE membranes, respectively. The effects of different parameters, such as temperature, initial fluoride concentration, feed flow rate, and membrane properties, on the flux and removal efficiencies were also evaluated, and feed temperature was found to be the most important operating parameter since higher temperatures induce the lowest temperature polarization coefficient (TPC) and a higher thermal efficiency (TE). Moreover, a wetting rate analysis in actual industrial wastewater sample indicated that a solution with higher organic matter, an membrane distillation (MD) system with PTFE membrane, and a sample with bigger initial fluoride concentration induce bigger wetting rate. Therefore, the DCMD process can be applied on fluoride affected water sources toward producing high-quality water suitable for a potable water supply. Exploiting renewable source potentials or industrial waste (free) energy will bring better economic advantage on the application

Membrane distillation for industrial wastewater treatment: Studying the effects of membrane parameters on the wetting performance

© 2018 Elsevier Ltd Substantial amounts of trace hazardous elements have been detected in industrial wastewater (e.g fluoride > 900 mg/L). Feed water characteristics, operational parameters, and membrane properties are major factors affecting flux and rejection of the MD process. Membrane parameters such as membrane material type and pore size have been investigated. Fluoride ion rejection was selected to setup a methodology to remove trace elements from wastewater by adjusting the membrane parameters in DCMD. Study of the fouling thickness of the MD membrane using pH and feed water composition revealed that a PVDF membrane with a smooth surface holds a thicker fouling layer, which enhances fluoride rejection while reducing the permeate flux. On the other hand, PTFE and PP membranes showed higher mass transfer and higher wetting performance, respectively. Therefore,a PVDF membrane with low organic feed water at higher alkaline pH can be utilized to obtain high-quality permeate, while PTFE can provide the highest flux with acceptable permeate water quality. Therefore, this methodology can be applied toidentify the optimum membrane to fit the required permeate flux, rejection requirements,and operating pH to treat any kind of non-volatileinorganic pollutants from industrial wastewater

Analysis of mass transfer behavior in membrane distillation: Mathematical modeling under various conditions

© 2019 Four commercially available hydrophobic membranes with different pore sizes were separately used in a direct contact membrane distillation (DCMD) apparatus to investigate the effect of fouling on the mass transfer coefficient, and the dominant mass transport mode under different conditions defined by the temperature, membrane material, flow regime, and membrane pore size. Both ultrapure deionized water and simulated industrial wastewater were considered as the feed water. The results of the investigation confirmed that the fouling layer impacted the mass transport directly by resisting it, and indirectly by altering the heat transfer mechanism. In addition to the surface fouling layer, a significant number of particles were also observed to accumulate in the membrane pores. It was further determined that the contribution of Poiseuille flow to the entire mass transport was significant at higher temperatures when using a membrane with large pores. This highlighted the need for careful consideration of Poiseuille flow in the modeling and simulation of a membrane distillation (MD) mass transport process. It was also observed that the flow rate did not affect the Poiseuille flow and therefore did not directly impact the entire mass transfer. The study findings provide systematic insight for the development of a strategy for selecting an appropriate operating feed for DCMD and adjusting the permeate temperature to fit the prevailing water demand and environmental conditions

Removal of fluoride in membrane-based water and wastewater treatment technologies: Performance review

© 2019 The presence of excess fluoride in aqueous media above local environmental standards (e.g., the U.S. Environmental Protection Agency (EPA) standard of 4 mg/L) affects the health of aquatic life. Excess fluoride in drinking water above the maximum contaminant level (e.g., the World Health Organization (WHO) standard of 1.5 mg/L) also affects the skeletal and nervous systems of humans. Fluoride removal from aqueous solutions is difficult using conventional electrochemical, precipitation, and adsorption methods owing to its ionic size and reactivity. Thus, new technologies have been introduced to reduce the fluoride concentration in industrial wastewater effluents and various drinking water sources. Membrane technology is one of the newer technologies found to be very effective in significantly reducing fluoride to desired standards levels; however, it has received less attention than other technologies because it is perceived as a costly process. This study critically reviewed the performance of various membrane process and compared it with effluent and zero liquid discharge (ZLD) standards. The performance review has been conducted with the consideration of the theoretical background, rejection mechanisms, technical viability, and parameters affecting flux and rejection performance. This review includes membrane systems investigated for the defluoridation process but operated under pressure (i.e., reverse osmosis [RO] and nanofiltration [NF]), temperature gradients (i.e., membrane distillation [MD]), electrical potential gradients (i.e., electrodialysis [ED] and Donnan dialysis [DD]), and concentration differences (i.e., forward osmosis [FO]). Moreover, the study also addressed the advantages, limitations, & applicable conditions of each membrane based defluoridation process

Catalytic degradation of P-chlorophenol by muscovite-supported nano zero valent iron composite: Synthesis, characterization, and mechanism studies

P-chlorophenol (P–CP) is a recalcitrant toxicant in wastewater. Recently, the use of composite materials and environmentally friendly technology in the degradation of pollutants in wastewater has attracted widespread attention. For the first time, the nano zerovalent iron nano zerovalent iron (NZVI)-loaded muscovite (NZVI@muscovite), a novel composite material, was synthesized by liquid-phase reduction. The different physicochemical properties of NZVI@muscovite indicated that the muscovite could support NZVI of 40–50 nm sizes. The NZVI@muscovite had a low agglomeration degree, good dispersibility, and improved catalytic activity. In addition, the optimization experiments of P–CP degradation demonstrated that NZVI@muscovite actively degraded P–CP at a pollutant:catalyst ratio of 714 mg:1 g. This ratio was higher than that of the other composite materials under optimal operating conditions. Adsorption and degradation by Fenton-like reaction were the main mechanisms underlying P–CP degradation. This study extended the use of NZVI@muscovite as an efficient composite material for the degradation of P–CP in an aqueous environment

Ammonia recovery from human urine as liquid fertilizers in hollow fiber membrane contactor: Effects of permeate chemistry

The production of the existing nitrogen fertilizer is costly and less environmental-friendly. Various green technologies are currently emerging toward providing alternative options. In this study, a liquid/liquid hydrophobic hollow-fiber membrane contactor was employed at ambient temperature and natural urine pH ~ 9.7 to recover ammonium fertilizers from human urine. Results showed that permeate side chemistry was one of the major factors affecting the ammonia mass transfer. The study on the ammonia capturing performance of diluted sulfuric acid, phosphoric acid, nitric acid, and DI water confirmed that acid type, acid concentration, and permeate side operating pH were the most important parameters affecting the ammonia capturing tendency. Sulfuric acid was slightly better in capturing more ammonia than other acid types. The study also identified increasing acid concentration didn’t necessarily increase ammonia mining tendency because there was always one optimum concentration value at which maximum ammonia extraction was possible. The best permeate side operating pH to extract ammonia for fertilizer purposes was selected based on the dissociation equilibrium of different types of acids. Accordingly, the analysis showed that the membrane process has to be operated at pH &gt; 3 for sulfuric acid, between 3.5 to 11.5 for phosphoric acid, and above 0.5 for nitric acid so as to produce their respective high-quality liquid ammonium sulfate, ammonium monophosphate/diphosphate, and ammonium nitrate fertilizer. Therefore, permeate side acid concentration, pH, and acid type has to always be critically optimized before starting the ammonia mining experiment.</jats:p

Green Synthesis of Fe<inf>3</inf>O<inf>4</inf>@Carbon Filter Media for Simultaneous Phosphate Recovery and Nitrogen Removal from Domestic Wastewater in Biological Aerated Filters

Copyright © 2019 American Chemical Society. Domestic wastewater depth processing and reclamation are essential in the alleviation of global water shortage. In this study, an innovative filter media (i.e., Fe3O4@Carbon filter media [FCM]) was synthesized and subsequently used in a biological aerated filter (BAF) for simultaneous phosphate recovery and nitrogen removal (SPN) from domestic wastewater. The performance of FCM was compared with the commercially available ceramsite (CAC). The results showed that the performance of FCMBAF was better than that of CACBAF; as far as SPN is concerned, the magnetic field of FCMBAF could accelerate the growth rate of biofilm. Moreover, the nitrospira and nirK gene copy numbers of FCMBAF were considerably higher than those of CACBAF. Interestingly, the interconnectivity and uniformity of pores were also suitable for the microdistribution of biofilm, where different aerobic and anaerobic zones of the FCM were formed. This facilitates the microinteraction between the key microorganisms and the filter media that successfully enhanced the nitrogen removal. The phosphate recovery was attained via hydroxyapatite (Ca10(PO4)6(OH)2) formation, which resulted from the reaction between phosphate (PO43-) and FCM. The average effluent concentrations of total organic carbon (TOC), total nitrogen (TN), ammonia nitrogen (NH4+-N), and PO43- were 8.12, 6.18, 0.997, and 0.073 mg/L of FCMBAF, respectively, which were lower than those from the national standard (CODcr ≤ 50 mg L-1, NH4+-N ≤ 5.0 mg L-1, TN ≤ 15 mg L-1, TP ≤ 0.5 mg L-1, GB 18918-2002, first standard). Thus, FCM demonstrated a promising potential for SPN and wastewater recycling of BAF in domestic wastewater treatment

Rectorite-supported nano-Fe<inf>3</inf>O<inf>4</inf> composite materials as catalyst for P-chlorophenol degradation: Preparation, characterization, and mechanism

© 2019 Elsevier B.V. Clay minerals, as abundant natural resources, are among the most suitable supporting materials for nano metal. In this manuscript, new Fe3O4 nanoparticle/rectorite (Fe3O4/rectorite) catalysts are developed via in-situ precipitation oxidation reaction. Various physicochemical characterizations of Fe3O4/rectorite show that Fe3O4 nanoparticles (nano-Fe3O4) with an average particle diameter of approximately 10–20 nm are effectively loaded on the surface of acid leached rectorite (Al-rectorite) and have low coaggregation and improved dispersion. Moreover, the catalytic activity of Fe3O4/rectorite on degradation of P-chlorophenol by heterogeneous Fenton method is studied. Results of degradation experiments show that Fe3O4/rectorite has higher degradation efficiency of P-chlorophenol than bare nano-Fe3O4. Regeneration studies also show that Fe3O4/rectorite maintains 100% of its maximum P-chlorophenol degradation capacity after seven consecutive cycles. Fe3O4/rectorite can be easily separated by magnetic separation, and thus has good stability and reusability. The degradation mechanism of Fe3O4/rectorite is adsorption coupled with a Fenton-like reaction, which accounts for P-chlorophenol degradation of up to 625 mg/g. This work demonstrates a new composite material for the effective remediation of refractory organic compounds from wastewater

Simultaneous adsorption and degradation of bisphenol A on magnetic illite clay composite: Eco-friendly preparation, characterizations, and catalytic mechanism

Excess bisphenol A (BPA) is a pollutant of concern in different water sources. In this work, magnetic illite clay-composite material (Fe3O4@illite) was synthesized via the coprecipitation method by loading Fe3O4 nanoparticles (nano-Fe3O4) onto the surfaces of illite clay. Results from different characterizations showed that nano-Fe3O4 was embedded into illite clay nanosheets and existed on the surfaces of illite clay, thereby reducing the degree of agglomeration and improving dispersibility. The catalytic BPA degradation of Fe3O4@illite and nano-Fe3O4 confirmed the superior performance of Fe3O4@illite compared with that of nano-Fe3O4. The optimum operating parameters for degradation were 0.3 mL of H2O2 at pH of 3 in the presence of Fe3O4@illite, which provided a maximum degradation capacity up to 816, 364, 113, and 68 mg/g for epoxy BPA concentration of resin wastewater (266 mg/L), synthetic wastewater (80 mg/L), Hefei City swan lake (25 mg/L), and Hefei University lake wastewater (14.94 mg/L), respectively, in 180 min reaction time. The degradation data conformed to the pseudo-first-order kinetic model. The degradation pathways and mineralization study revealed that the adsorption-Fenton-like reaction was the principal mechanism that demonstrated 100% degradation efficiency of Fe3O4@illite even after nine successive runs. The regeneration and reusability tendency analysis ensured that Fe3O4@illite can be easily separated by using magnets. Therefore, Fe3O4@illite composite with H2O2 Fenton-like technology was a promising method for BPA degradation

Bentonite-supported nano zero-valent iron composite as a green catalyst for bisphenol A degradation: Preparation, performance, and mechanism of action.

Bisphenol A (BPA) is a toxic environmental pollutant commonly found in wastewater. Using non-toxic materials and eco-friendly technology to remove this pollutant from wastewater presents multiple advantages. Treatment of wastewater with clay minerals has received growing interest because of the environment friendliness of these materials. Bentonite is a 2:1 layered phyllosilicate clay mineral that can support nano-metal catalysts. It can prevent the agglomeration of nano-metal catalysts and improve their activity. In this article, a green catalytic nano zero-valent iron/bentonite composite material (NZVI@bentonite) was synthesized via liquid-phase reduction. The average size of NZVI was approximately 40-50 nm. Good dispersion and low aggregation were observed when NZVI was loaded on the surface or embedded into the nanosheets of bentonite. Degradation of BPA, a harmful contaminant widely found in wastewater at relatively high levels, by NZVI@bentonite was then investigated and compared with that by pristine NZVI through batch Fenton-like reaction experiments. Compared with pristine NZVI and bentonite alone, the NZVI@bentonite showed a higher BPA degradation ratio and offered highly effective BPA degradation up to 450 mg/g in wastewater under optimum operating conditions. Adsorption coupled with the Fenton-like reaction was responsible for BPA degradation by NZVI@bentonite. This work extends the application of NZVI@bentonite as an effective green catalyst for BPA degradation in aqueous environments