Permeability is the Critical Factor Governing the Life Cycle Environmental Performance of Drinking Water Treatment Using Living Filtration Membranes.

Living Filtration Membranes (LFMs) are a water filtration technology that was recently developed in the lab (Technology Readiness Level 4). LFMs have shown filtration performance comparable with that of ultrafiltration, far better fouling resistance than conventional polymer membranes, and good healing capabilities. These properties give LFMs promise to address two significant issues in conventional membrane filtration: fouling and membrane damage. To integrate environmental considerations into future technology development (i.e., Ecodesign), this study assesses the life cycle environmental performance of drinking water treatment using LFMs under likely design and operation conditions. It also quantitatively ranks the engineering design and operation factors governing the further optimization of LFM environmental performance using a global sensitivity analysis. The results suggest that LFMs' superior fouling resistance will reduce the life cycle environmental impacts of ultrafiltration by 25% compared to those of a conventional polymer membrane in most impact categories (e.g., acidification, global warming potential, and carcinogenics). The only exception is the eutrophication impact, where the need for growth medium and membrane regeneration offsets the benefits of LFMs' fouling resistance. Permeability is the most important factor that should be prioritized in future R&D to further improve the life cycle environmental performance of LFMs. A 1% improvement in the permeability will lead to a ∼0.7% improvement in LFMs' environmental performance in all the impact categories, whereas the same change in the other parameters investigated (e.g., LFM lifespan and regeneration frequency) typically only leads to a <0.2% improvement.

Hydrophobic Gas Transfer Membranes for Wastewater Treatment and Resource Recovery.

Gaseous compounds, such as CH4, H2, and O2, are commonly produced or consumed during wastewater treatment. Traditionally, these gases need to be removed or delivered using gas sparging or liquid heating, which can be energy intensive with low efficiency. Hydrophobic membranes are being increasingly investigated in wastewater treatment and resource recovery. This is because these semipermeable barriers repel water and create a three-phase interface that enhances mass transfer and chemical conversions. This Critical Review provides a first comprehensive analysis of different hydrophobic membranes and processes, and identifies the challenges and potential for future system development. The discussions and analyses were grouped based on mechanisms and applications, including membrane gas extraction, membrane gas delivery, and hybrid processes. Major challenges, such as membrane fouling, wetting, and limited selectivity and functionality, are identified, and potential solutions articulated. New opportunities, such as electrochemical coating, integrated membrane electrodes, and membrane functionalization, are also discussed to provide insights for further development of more efficient and low-cost membranes and processes.

Hydrophobic nanostructured wood membrane for thermally efficient distillation.

Current membrane distillation (MD) is challenged by the inefficiency of water thermal separation from dissolved solutes, controlled by membrane porosity and thermal conductivity. Existing petroleum-derived polymeric membranes face major development barriers. Here, we demonstrate a first robust MD membrane directly fabricated from sustainable wood material. The hydrophobic nanowood membrane had high porosity (89 ± 3%) and hierarchical pore structure with a wide pore size distribution of crystalline cellulose nanofibrils and xylem vessels and lumina (channels) that facilitate water vapor transportation. The thermal conductivity was extremely low in the transverse direction, which reduces conductive heat transport. However, high thermal conductivity along the fiber enables efficient thermal dissipation along the axial direction. As a result, the membrane demonstrated excellent intrinsic vapor permeability (1.44 ± 0.09 kg m-1 K-1 s-1 Pa-1) and thermal efficiency (~70% at 60°C). The properties of thermal efficiency, water flux, scalability, and sustainability make nanowood highly desirable for MD applications.

Hierarchical porous carbon prepared from biomass through a facile method for supercapacitor applications.

The porous carbon with angstrom-sized pores is important in supercapacitor applications, because of its high pack density and high specific capacitance. In this paper, a facile method is proposed for the preparation of hierarchical porous carbon with high-volume angstrom-sized pores. Onion, as the typical biomass in this research, is used as carbon precursor. First, onion was etched by KOH to obtain a water-soluble lignin-potassium-salt/cellulose composite. This composite was further pyrolyzed under N2 atmosphere to obtain onion derived porous carbon (OPC). The morphology and porous structure of OPC were characterized by scanning electron microscope and N2 adsorption/desorption. The supercapacitive performances of OPC were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge. OPC shows high specific surface area with high-volume angstrom-sized pores in carbon matrix. When used as supercapacitor electrode materials, OPC shows high specific capacitance and good cycling stability. This paper opens a general way to prepare porous carbon from biomasses, which will promote the development of biomass utilization, preparation of porous carbon and supercapacitors.

Nickel-Based Membrane Electrodes Enable High-Rate Electrochemical Ammonia Recovery.

Wastewater contains significant amounts of nitrogen that can be recovered and valorized as fertilizers and chemicals. This study presents a new membrane electrode coupled with microbial electrolysis that demonstrates very efficient ammonia recovery from synthetic centrate. The process utilizes the electrical potential across electrodes to drive NH4+ ions toward the hydrophilic nickel top layer on a gas-stripping membrane cathode, which takes advantage of surface pH increase to realize spontaneous NH3 production and separation. Compared with a control configuration with conventionally separated electrode and hydrophobic membrane, the integrated membrane electrode showed 40% higher NH3-N recovery rate (36.2 ± 1.2 gNH3-N/m2/d) and 11% higher current density. The energy consumption was 1.61 ± 0.03 kWh/kgNH3-N, which was 20% lower than the control and 70-90% more efficient than competing electrochemical nitrogen recovery processes (5-12 kWh/kgNH3-N). Besides, the negative potential on membrane electrode repelled negatively charged organics and microbes thus reduced fouling. In addition to describing the system's performance, we explored the underlying mechanisms governing the reactions, which confirmed the viability of this process for efficient wastewater-ammonia recovery. Furthermore, the nickel-based membrane electrode showed excellent water entry pressure (∼41 kPa) without leakage, which was much higher than that of PTFE/PDMS-based cathodes (∼1.8 kPa). The membrane electrode also showed superb flexibility (180° bend) and can be easily fabricated at low cost (<20 $/m2).

Microbial electrochemical nutrient recovery in anaerobic osmotic membrane bioreactors.

This study demonstrates that by incorporating a microbial electrochemical unit into an anaerobic osmotic membrane bioreactor (AnOMBR), the system addressed several challenges faced by traditional anaerobic membrane bioreactors and recovered biogas, nitrogen, and phosphorus while maintaining high effluent quality with low dissolved methane. The microbial recovery cell (MRC)-AnOMBR system showed excellent organic (>93%) and phosphorus removal (>99%) and maintained effluent COD below 20 mg/L. Furthermore, the reactor effectively recovered up to 65% PO43- and 45% NH4+ from the influent, which can be further improved if membranes with higher selectivity are used. Nutrients removal from bulk solution mitigated NH4+ penetration to the draw solution and reduced scaling potential caused by PO43-. The maximum methane yield was 0.19 L CH4/g COD, and low methane (<2.5 mL CH4/L) was detected in the effluent. Further improvement can be made by increasing charge efficiency for better nutrient and energy recovery.

Microbial fuel cells and osmotic membrane bioreactors have mutual benefits for wastewater treatment and energy production.

This study demonstrates that microbial fuel cells (MFCs) and osmotic membrane bioreactors (OMBRs) can be mutually beneficial when integrated together for wastewater treatment. When connecting MFCs with OMBRs, the solute buildup increased conductivity and buffer capacity, which greatly increased MFC power density from 3 W/m(3) up to 11.5 W/m(3). In turn, the MFCs conditioned and reduced sludge production and therefore reduced forward osmosis (FO) membrane fouling. The MFC-OMBR equipped with new thin-film composite (TFC) membrane showed excellent organic (>95%) and phosphorus removal (>99%) and therefore maintained effluent sCOD below 20 mg/L. However, the nitrogen removal was limited due to the negative surface charge of the thin-film composite membrane and solution chemistry, which led to higher flux of ammonium toward the OMBR draw solution. Further studies are needed to improve nitrogen removal, reduce fouling, and optimize system integration.

Simultaneous removal of multi-pollutants in an intimate integrated flocculation-adsorption fluidized bed.

A novel intimate integrated flocculation-adsorption fluidized bed (IFAFB) was designed based on the hydraulic classification theory, and the operation, performance, characterization, and mechanisms of the novel process were developed. In this system, 150 mg · L(-1) kaolin clay and 100 mg · L(-1) phenol were used to simulate multi-pollutants in synthetic influent; resin beads and silica beads were the solid phases for the fluidized flocculator, and polymer aluminum chloride (PAC) and granular activated carbon were the flocculant and the adsorbent, respectively. The results showed that the Euler numeral was the most suitable dynamic parameter for flocculation in the fluidized bed when compared with the velocity gradient (G), Reynolds number (Re), and GRe (-1/2) . Additionally, the adsorption capacities of the fluidized regime were 8.77 and 24.70 mg · g(-1) greater than those of the fixed regime at superficial velocities of 6 and 8 mm · s(-1), respectively. In the IFAFB, the removal efficiencies of kaolin clay and phenol in the IFAFB reached 95 and 80 % simultaneously at total initial bed height of 35 mm. Flocs size, fractal dimension, and scanning electron microscopy (SEM) confirmed that the relationship of flocculation and adsorption in the IFAFB was mutually beneficial. Adsorption favored continuous growth of flocs and protected flocs from breakage, while flocculation removed fine particles as the first stage to prevent the adsorption of kaolin clay.

Enhanced aerobic granulation, stabilization, and nitrification in a continuous-flow bioreactor by inoculating biofilms.

In this study, the possibility of using backwashed biofilm as seed in an aerobic granular sludge continuous-flow airlift fluidized bed (CAFB) reactor was investigated. After the addition of the inoculated backwashed biofilm, the start-up period of this reactor fed with municipal wastewater was reduced to 25 days, and aerobic granulation and stabilization were enhanced. At steady state, the chemical oxygen demand (COD) removal efficiency and nitrification efficiency were as high as 80-90 and 60 %, respectively. The CAFB was operated continuously and totally for 90 days, and its performance was much more stable when compared with system inoculated with activated sludge. Microbial distribution analyzed by fluorescence in situ hybridization (FISH) showed that the nitrite-oxidizing bacteria (NOB) and ammonium-oxidizing bacteria (AOB) were compatible with heterotrophic bacteria and distributed evenly throughout the granules. Such unique population distribution might be attributed to the low COD level and abundant dissolved oxygen in the entire granule as simulated by the mathematic models. Moreover, scanning electron microscopy revealed broad holes in the granules, which might promote the mass transfer of the nutrients from the surface to the center and enable simultaneous COD removal and nitrification. In conclusion, backwashed biofilm is an alternative seed of the conventional flocculent activated sludge in the aerobic granular sludge system to enhance carbonaceous oxidization and nitrification.

Gypsum scaling in pressure retarded osmosis: experiments, mechanisms and implications.

Pressure retarded osmosis (PRO) is an osmotically-driven membrane process that can be used to harvest salinity-gradient power. The PRO performance (both water flux and power density) can be severely limited by membrane fouling. The current study, for the first time, investigates PRO scaling in a bench-scale pressurized system using calcium sulfate dihydrate (gypsum) as a model scalant. In addition to the bulk feed solution (FS) saturation index (SI bulk), gypsum scaling was found to be strongly affected by the draw solution (DS) type and concentration, the applied hydraulic pressure, and the membrane orientation. The commonly recommended active layer facing draw solution (AL-DS) orientation was highly prone to internal scaling. In this orientation, severe internal concentration polarization (ICP) of scaling precursors induced gypsum clogging in membrane support layer even when the FS was undersaturated (e.g., SI bulk = 0.8). At higher SI bulk values, external gypsum crystal deposition occurred in addition to internal scaling. More severe scaling was observed when the DS contained scaling precursors such as Ca(2+) or SO4(2-), suggesting that the reverse diffusion of these precursors into the FS can significantly enhanced gypsum scaling. Increasing applied hydraulic pressure could enhance reverse solute diffusion and thus result in more severe gypsum scaling when the DS contained scaling precursors. A conceptual model, capturing the two important PRO scaling mechanisms (ICP of scaling precursors from FS and reverse diffusion of scaling precursors from the DS), is presented to rationalize the experimental results. Our results provide significant implications for PRO scaling control.

Preparation, characterization and performance of a novel visible light responsive spherical activated carbon-supported and Er3+:YFeO3-doped TiO2 photocatalyst.

A novel spherical activated carbon (SAC) supported and Er(3+):YFeO(3)-doped TiO(2) visible-light responsive photocatalyst (Er(3+):YFeO(3)/TiO(2)-SAC) was synthesized by a modified sol-gel method with ultrasonic dispersion. It was characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), powder X-ray diffractometer (XRD) and UV-vis diffuse reflectance spectrophotometer (DRS). The photocatalytic activity of Er(3+):YFeO(3)/TiO(2)-SAC was evaluated for degradation of methyl orange (MO) under visible light irradiation. The effects of calcination temperature and irradiation time on its photocatalytic activity were examined. The experimental results indicated that Er(3+):YFeO(3) could function as an upconversion luminescence agent, enabling photocatalytic degradation of MO by TiO(2) under visible light. The Er(3+):YFeO(3)/TiO(2) calcinated at 700°C showed the highest photocatalytic capability compared to those calcinated at other temperatures. The photocatalytic degradation of MO followed the Langmuir-Hinshelwood kinetic model. Although the photocatalyst showed a good physical stability and could tolerate a shear force up to 25 × 10(-3)N/g, its photocatalytic activity decreased over a four-cycle of reuse in concentrated MO solution, indicating that the decreased activity was ascribed to the fouling of catalyst surface by MO during the degradation process. However, the fouled Er(3+):YFeO(3)/TiO(2)-SAC could be regenerated through water rinsing-calcination or acid rinsing-calcination treatment.