Integrating forward osmosis into microbial fuel cells for wastewater treatment, water extraction and bioelectricity generation

A novel osmotic microbial fuel cell (OsMFC) was developed by using a forward osmosis (FO) membrane as a separator. The performance of the OsMFC was examined with either NaCl solution or artificial seawater as a catholyte (draw solution). A conventional MFC with a cation exchange membrane was also operated in parallel for comparison. It was found that the OsMFC produced more electricity than the MFC in both batch operation (NaCl solution) and continuous operation (seawater), likely due to better proton transport with water flux through the FO membrane. Water flux from the anode into the cathode was clearly observed with the OsMFC but not in the MFC. The solute concentration of the catholyte affected both electricity generation and water flux. These results provide a proof of concept that an OsMFC can simultaneously accomplish wastewater treatment, water extraction (from the wastewater), and electricity generation. The potential applications of the OsMFC are proposed for either water reuse (linking to reverse osmosis for reconcentration of draw solution) or seawater desalination (connecting with microbial desalination cells for further wastewater treatment and desalination).     

Boric acid permeation in forward osmosis membrane processes: modeling, experiments, and implications

Forward osmosis (FO) is attracting increasing interest for its potential applications in desalination. In FO, permeation of contaminants from feed solution into draw solution through the semipermeable membrane can take place simultaneously with water diffusion. Understanding the contaminants transport through and rejection by FO membrane has significant technical implications in the way to separate clean water from the diluted draw solution. In this study, a model was developed to predict boron flux in FO operation. A strong agreement between modeling results and experimental data indicates that the model developed in this study can accurately predict the boron transport through FO membranes. Furthermore, the model can guide the fabrication of improved FO membranes with decreased boron permeability and structural parameter to minimize boron flux. Both theoretical model and experimental results demonstrated that when membrane active layer was facing draw solution, boron flux was substantially greater compared to the other membrane orientation due to more severe internal concentration polarization. In this investigation, for the first time, rejection of contaminants was defined in FO processes. This is critical to compare the membrane performance between different membranes and experimental conditions.     

Removal of natural steroid hormones from wastewater using membrane contactor processes

Growing demands for potable water have strained water resources and increased interest in wastewater reclamation for potable reuse. This interest has brought increased attention to endocrine-disrupting chemicals (EDCs) as emerging water contaminants. The effect of EDCs, and in particular natural steroid hormones, on humans is of heightened interest in the study of wastewater reuse in advanced life support systems (e.g., space missions) because they are excreted in urine and have high endocrine-disrupting potencies. Direct contact membrane distillation (DCMD) and forward osmosis (FO) are being investigated for wastewater treatment in space. Retention of two natural steroid hormones, estrone and 17beta-estradiol, by these two processes was evaluated in the current investigation. DCMD provided greater than 99.5% hormone rejection; DCMD also provided constant flux, greater than 99.9% urea and ammonia rejection, and high water recovery. FO provided from 77 to 99% hormone rejection depending on experiment duration and feed solution chemistry.     

正渗透膜污染的影响因素及清洗效果研究

为研究正渗透(FO)浓缩过程中的膜通量衰减规律,本文以牛血清白蛋白(BSA)为特征污染物,研究了正渗透过程中原料液的离子强度及BSA浓度、膜方位等参数不同时FO膜的污染规律,以提高膜通量和截留率为目标,对驱动液的种类、浓度,料液流速进行了优化,并优化了适宜的膜清洗方案.结果表明:原料液中离子强度越大,FO膜的初始通量越...     

Polyelectrolyte-promoted forward osmosis-membrane distillation (FO-MD) hybrid process for dye wastewater treatment

Polyelectrolytes have proven their advantages as draw solutes in forward osmosis process in terms of high water flux, minimum reverse flux, and ease of recovery. In this work, the concept of a polyelectrolyte-promoted forward osmosis-membrane distillation (FO-MD) hybrid system was demonstrated and applied to recycle the wastewater containing an acid dye. A poly(acrylic acid) sodium (PAA-Na) salt was used as the draw solute of the FO to dehydrate the wastewater, while the MD was employed to reconcentrate the PAA-Na draw solution. With the integration of these two processes, a continuous wastewater treatment process was established. To optimize the FO-MD hybrid process, the effects of PAA-Na concentration, experimental duration, and temperature were investigated. Almost a complete rejection of PAA-Na solute was observed by both FO and MD membranes. Under the conditions of 0.48 g mL(-1) PAA-Na and 66 °C, the wastewater was most efficiently dehydrated yet with a stabilized PAA-Na concentration around 0.48 g mL(-1). The practicality of PAA-Na-promoted FO-MD hybrid technology demonstrates not only its suitability in wastewater reclamation, but also its potential in other membrane-based separations, such as protein or pharmaceutical product enrichment. This study may provide the insights of exploring novel draw solutes and their applications in FO related processes.     

Performance of forward (direct) osmosis process: membrane structure and transport phenomenon

The performance of a forward (direct) osmosis (FO) process was investigated using a laboratory-scale unit to elucidate the effect of membrane structure and orientation on waterflux. Two types of RO membrane and a FO membrane were tested using ammonium bicarbonate, glucose, and fructose as the draw solution to extract water from a saline feed solution. The FO membrane was able to achieve higher water flux than the RO membranes under the same experimental conditions while maintaining high salt rejection of greater than 97%. Increasing operating temperature increased the water flux in FO process. To investigate the effect of membrane orientation on water flux, the FO membrane was tested normally (dense selective layer facing draw solution) and reversely (dense selective layer facing feed solution). Explanations on transport phenomenon in FO process were proposed which explain the observation that the FO membrane, when used in the normal orientation, performed better due to lesser internal concentration polarization. This study suggests that an ideal FO membrane should consist of a thin dense selective layer without any loose fabric support layer.     

Emerging forward osmosis and membrane distillation for liquid food concentration: A review

As emerging membrane technologies, forward osmosis (FO) and membrane distillation (MD), which work with novel driving forces, show great potential for liquid food concentration, owing to their low fouling propensity and great driving force. In the last decades, they have attracted the attention of food industry scientists in global scope. However, discussions of the FO and MD in liquid food concentration advancement, membrane fouling, and economic assessment have been scant. This review aims to provide an up-to-date knowledge about liquid food concentration by FO and MD. First, we introduce the principle and applications of FO and MD in liquid food concentration, and highlight the effect of process on liquid food composition, membrane fouling mechanism, and strategies for fouling mitigation. Besides, economic assessment of FO and MD processes is reviewed. Moreover, the challenges as well as future prospects of FO and MD applied in liquid food concentration are proposed and discussed. Comparing with conventional membrane-based or thermal-based technologies, FO and MD show outstanding advantages in high concentration rate, good concentrate quality, low fouling propensity, and low cost. Future efforts for liquid food concentration by FO and MD include (1) development of novel FO draw solution (DS); (2) understanding the effects of liquid food complex compositions on membrane fouling in FO and MD concentration process; and (3) fabrication of novel membranes and innovation of membrane module and process configuration for liquid food processing.     

High performance thin-film composite forward osmosis hollow fiber membranes with macrovoid-free and highly porous structure for sustainable water production

The development of high-performance and well-constructed thin-film composite (TFC) hollow fiber membranes for forward osmosis (FO) applications is presented in this study. The newly developed membranes consist of a functional selective polyamide layer formed by highly reproducible interfacial polymerization on a polyethersulfone (PES) hollow fiber support. Using dual-layer coextrusion technology to design and effectively control the phase inversion during membrane formation, the support was designed to possess desirable macrovoid-free and fully sponge-like morphology. Such morphology not only provides excellent membrane strength, but it has been proven to minimize internal concentration polarization in a FO process, thus leading to the water flux enhancement. The fabricated membranes exhibited relatively high water fluxes of 32-34 LMH and up to 57-65 LMH against a pure water feed using 2 M NaCl as the draw solution tested under the FO and pressure retarded osmosis (PRO) modes, respectively, while consistently maintaining relatively low salt leakages below 13 gMH for all cases. With model seawater solution as the feed, the membranes could display a high water flux up to 15-18 LMH, which is comparable to the best value reported for seawater desalination applications.     

Evaluation of hybrid pressure-driven and osmotically-driven membrane process for non-thermal production of apple juice concentrate

This study investigates the potential of hybrid membrane processes including microfiltration (MF), ultrafiltration (UF) and forward osmosis (FO) for non-thermal concentration of apple juice. The process performance and characteristics (physicochemical properties, nutritional and aroma components and microbiological quality) of apple juice were studied. The clarity of apple juice was significantly promoted as pore size of membrane reduced. MF and UF can also ensure microbiological safety in pre-treated apple juice. According to its efficiency of filtration as well as performance of simultaneous clarification and cold-sterilization, 0.22 μm MF membrane was identified as the optimal membrane for the pre-treatment. The pre-treated apple juice can be concentrated up to 65°Brix by subsequent single stage FO. FO retained nutritional and volatile compounds of apple juice while significant reductions were found in the juice concentrated by vacuum evaporation. Hybrid MF-FO can be a promising non-thermal technology to produce apple juice concentrate with high quality.     

Impact of seawater-quality and water treatment procedures on the active bacterial assemblages at two desalination sites

Inorganic and organic compounds, particles and microorganisms in intake waters are mainly responsible for fouling of reverse osmosis membranes, which reduces the efficiency of the desalination process. The characterization of seawater quality to better predict its fouling potential remains a challenge for the desalination field and little is known about the seasonal variability of water quality parameters in the coastal waters used to supply desalination plants. In this study, standard water quality methods were combined with flow cytometry and molecular methods (16S rRNA sequencing and fingerprinting) to assess in parallel, the physicochemical properties, the microbial abundance and the active microbial community composition of the intake waters and their associated pretreated waters at two desalination sites from July 2007 to July 2008. The overall assessment of quality parameters revealed that microfiltration followed by slow sand filtration were the most efficient in removing microorganisms than the conventional dual media filtration routinely used in full-scale desalination plants, and that all treatments were inefficient for organic matter reduction. Temporal variation of the environmental parameters such as temperature, turbidity and silt density index only moderately affected the bacterial community structure in raw waters, but that interestingly, water treatment compartments changed the composition and diversity of the metabolically active bacterial populations and thus create distinct ecological post-treatment niches.     

Synthesis and characterization of novel forward osmosis membranes based on layer-by-layer assembly

Forward osmosis (FO) has received considerable interest for water- and energy-related applications in recent years. FO does not require an applied pressure and is believed to have a low fouling tendency. However, a major challenge in FO is the lack of high performance FO membranes. In the current work, novel nanofiltration (NF)-like FO membranes with good magnesium chloride retention were synthesized using layer-by-layer (LbL) assembly. The membrane substrate was tailored (high porosity, finger-like pores, thin cross-section, and high hydrophilicity) to achieve a small structural parameter of 0.5 mm. Increasing the number of polyelectrolyte layers improved the selectivity of the LbL membranes while reducing their water permeability. The more selective membrane 6#LbL (with 6 polyelectrolyte layers) had much lower reverse solute transport compared to 3#LbL and 1#LbL. Meanwhile, the FO water flux was found to be strongly affected by both membrane water permeability and solute reverse transport. Severe solute reverse transport was observed for the active-layer-facing-draw-solution membrane orientation, likely due to the suppression of Donnan exclusion as a result of the high ionic strength of the draw solution. In contrast, the active-layer-facing-feed-solution orientation showed remarkable FO performance (15, 20, and 28 L/m2.h at 0.1, 0.5, and 1.0 M MgCl?, respectively, for membrane 3#LbL using distilled water as feed solution), superior to other NF-like FO membranes reported in the literature. To the best of the knowledge of the authors, this is the first work on the synthesis and characterization of LbL based FO membranes.     

Odorous compounds in municipal wastewater effluent and potable water reuse systems

The presence of effluent-derived compounds with low odor thresholds can compromise the aesthetics of drinking water. The potent odorants 2,4,6-trichloroanisole and geosmin dominated the profile of odorous compounds in wastewater effluent with concentrations up to 2 orders of magnitude above their threshold values. Additional odorous compounds (e.g., vanillin, methylnaphthalenes, 2-pyrrolidone) also were identified in wastewater effluent by gas chromatography coupled with mass-spectrometry and olfactometry detection. Full-scale advanced treatment plants equipped with reverse osmosis membranes decreased odorant concentrations considerably, but several compounds were still present at concentrations above their odor thresholds after treatment. Other advanced treatment processes, including ozonation followed by biological activated carbon and UV/H(2)O(2) also removed effluent-derived odorants. However, no single treatment technology alone was able to reduce all odorant concentrations below their odor threshold values. To avoid the presence of odorous compounds in drinking water derived from wastewater effluent, it is necessary to apply multiple barriers during advanced treatment or to dilute wastewater effluent with water from other sources.     

Use of a liter-scale microbial desalination cell as a platform to study bioelectrochemical desalination with salt solution or artificial seawater

Bioelectrochemical desalination is potentially advantageous because of bioenergy production and integrated wastewater treatment and desalination. In this work, the performance and energy benefits of a liter-scale upflow microbial desalination cell (UMDC) were evaluated. The UMDC desalinated both salt solution (NaCl) and artificial seawater, and the removal rate of total dissolved solid (TDS) increased with an increased hydraulic retention time, although TDS reduction in artificial seawater was lower than that in salt solution. Our analysis suggested that electricity generation was a predominant factor in removing TDS (more than 70%), and that other factors, like water osmosis and unknown processes, also contributed to TDS reduction. It was more favorable given the high energy efficiency, when treating salt solution, to operate the UMDC under the condition of high power output compared with that of high current generation because of the amount of energy production; while high current generation was more desired with seawater desalination because of lower salinity in the effluent. Under the condition of the high power output and the assumption of the UMDC as a predesalination in connection with a reversal osmosis (RO) system, the UMDC could produce electrical energy that might potentially account for 58.1% (salt solution) and 16.5% (artificial seawater) of the energy required by the downstream RO system. Our results demonstrated the great potential of bioelectrochemical desalination.     

Evaluation of membrane fouling for in-line filtration of oil sands process-affected water: the effects of pretreatment conditions

Membrane filtration is an effective reclamation option for oil sands process-affected water (OSPW). However, fresh OSPWs contain suspended solids and inorganic constituents in suspended and dissolved forms that can severely foul membranes. Pretreatment of OSPW with coagulation-flocculation (CF) was investigated to determine the effects of different coagulant aids (anionic, cationic, and nonionic polymers) on membrane surface properties and fouling. Our results showed that CF pretreatment effectively enhanced nanofiltration (NF) and reverse osmosis (RO) membrane permeate flux and salt rejection ratio through reducing membrane fouling. It was shown that coagulants and coagulant aids applied to OSPW feedwater can affect membrane physicochemical properties (surface hydrophilicity, zeta potential, and morphology), membrane performance, and the fouling indexes. Membrane rejection of ionic species increased significantly with the inclusion of an anionic coagulant aid and slightly with a cationic coagulant aid. Among three coagulant aids tested, anionic coagulant aids led to the most enhanced membrane performance through increasing membrane surface negativity and decreasing the formation of a fouling layer. Conversely, although cationic coagulant aids were the most effective in reducing OSPW turbidity, the application of cationic coagulant aids promoted the adsorption of foulants on membrane surfaces.     

蒸馏/反渗透海水淡化及其耦合工艺研究

海水淡化是解决淡水危机的重要途径,新工艺、新型膜材料及新能源的利用,有望进一步降低海水淡化成本.介绍了多效蒸发、多级闪蒸、压气蒸馏、反渗透等海水淡化工艺以及基于膜技术的海水淡化集成工艺的最新进展,分析了利用风能、太阳能、核能和化学热能等可替代能源进行海水淡化的可能性,在此基础上,提出了海水淡化未来的发展方向.     

蒸馏／反渗透海水淡化及其耦合工艺研究

海水淡化是解决淡水危机的重要途径，新工艺、新型膜材料及新能源的利用，有望进一步降低海水淡化成本。介绍了多效蒸发、多级闪蒸、压气蒸馏、反渗透等海水淡化工艺以及基于膜技术的海水淡化集成工艺的最新进展，分析了利用风能、太阳能、核能和化学热能等可替代能源进行海水淡化的可能性，在此基础上，提出了海水淡化未来的发展方向。     

正渗透技术浓缩苹果汁过程中反向溶质扩散的研究

反向渗透扩散（RSF）是正渗透技术中的一大挑战,本实验立足于研究正渗透技术浓缩苹果汁性能以及功能性汲取液（乙酸钠、碳酸氢钠、柠檬酸钠溶液）的溶质扩散规律。首先,利用NaCl溶液为汲取液研究正渗透膜的基础特性,通过改变NaCl溶液浓度、进水流速以及膜操作模式,探究正渗透体系的水通量、反向溶质扩散及截留率,分析对去离子水和苹果汁的浓缩能力及溶质扩散规律;其次,对比不同功能性汲取液对苹果汁浓缩的效果和对RSF的影响,以期达到将RSF化弊为利的目的。结果表明,汲取液浓度和膜操作模式影响浓缩效率和RSF;采用压力延迟渗透（PRO）模式,苹果汁浓缩倍数和RSF均比正渗透（FO）模式高,PRO模式下,5 mol·L?1 NaCl汲取液RSF达87.34±6.32 g·m?2·h?1;不同种类功能性汲取液浓缩苹果汁的能力不同,汲水能力:碳酸氢钠>氯化钠>乙酸钠>柠檬酸钠。RSF:乙酸钠>碳酸氢钠>氯化钠>柠檬酸钠。2 mol·L?1柠檬酸钠汲取液的RSF为29.61±2.19 g·m?2·h?1,仅为同浓度NaCl汲取液的一半,与传统的NaCl汲取液相比,柠檬酸钠汲取液可有效控制RSF。     

无机陶瓷膜在海水预处理中的应用

简要介绍了无机陶瓷膜作为一种新型的膜材料在海水预处理中的应用,反渗透法海水淡化预处理工艺流程及无机陶瓷膜的污染和防治措施,最后指出无机陶瓷膜在海水预处理中的发展方向和应用前景.     

Role of soluble microbial products (SMP) in membrane fouling and flux decline

Soluble microbial products (SMP), a significant component of effluent organic matter (EfOM), play an important role in membrane fouling and flux decline in wastewater reclamation/reuse applications. The SMP compounds of a microbial origin are derived during biological processes of wastewater treatment. They exhibit the characteristics of hydrophilic organic colloids and macromolecules. These high molecular weight compounds play an important role in creating high resistance of the membrane, leading to a reduction of permeate flux. The SMP fouling of RO, NF, and tight UF membranes is associated with formation of a cake/gel layer due to size (steric) exclusion. FTIR spectra of SMP- and EfOM-fouled membranes exhibited foulants' composition, consisting of polysaccharides, proteins, and/or aminosugar-like compounds. This finding reveals the important role of the SMP components as factors in membrane fouling and flux decline associated with EfOM source waters. Solids retention time (SRT) affects the characteristics and amounts of SMP, however, SRT did not affect flux decline trends of RO and NF membranes.     

草鱼咸干的脱盐与卤鱼加工风味的研究

研究了草鱼咸干的脱盐工艺和加工工艺,比较了静水脱盐和真空渗透脱盐过程中电导率、可溶蛋白质的变化。结果表明,水料体积质量比10∶1、水温30℃,脱盐180min后草鱼干可满足生产需要。正交优化卤鱼最佳工艺为预干时间1.5h、卤制时间2.5h、干燥时间1.5h、酱制时间1h。采用顶空固相微萃取气相色谱一质谱法(HS-SPME-GC-MS)法,分析检测了卤鱼的挥发性风味成分,共鉴定出48种风味化合物。