Recovering nitrogen from separately collected urine can potentially reduce costs and energy of wastewater nitrogen removal and fertilizer production. Through benchtop experiments, we demonstrate the ...recovery of nitrogen from urine as ammonium sulfate using electrochemical stripping, a combination of electrodialysis and membrane stripping. Nitrogen was selectively recovered with 93% efficiency in batch experiments with real urine and required 30.6 MJ kg N–1 in continuous-flow experiments (slightly less than conventional ammonia stripping). The effects of solution chemistry on nitrogen flux, electrolytic reactions, and reactions with electro-generated oxidants were evaluated using synthetic urine solutions. Fates of urine-relevant trace organic contaminants, including electrochemical oxidation and reaction with electro-generated chlorine, were investigated with a suite of common pharmaceuticals. Trace organics (<0.1 μg L–1) and elements (<30 μg L–1) were not detected at appreciable levels in the ammonium sulfate fertilizer product. This novel approach holds promise for selective recovery of nitrogen from concentrated liquid waste streams such as source-separated urine.
▶ A protocol for the selection of optimal draw solutions for forward osmosis (FO) applications was developed. ▶ Experimental data and model results showed that a small group of seven draw solutions ...appeared to be the most suitable. ▶ It was proven that internal concentration polarization is strongly dependent on the diffusion coefficient of the draw solution ▶ The large draw solution matrix, in terms of both constituents and concentrations, made it possible to quantitatively compare the effect of internal concentration polarization on water flux and reverse salt diffusion. ▶ The protocol developed can be used for draw solution selection as new FO membranes and draw solutions are developed and applied to new FO applications.
In this investigation, a protocol for the selection of optimal draw solutions for forward osmosis (FO) applications was developed and the protocol was used to determine the most appropriate draw solutions for specific FO applications using a currently available FO membrane. The protocol includes a desktop screening process and laboratory and modeling analyses. The desktop screening process resulted in 14 draw solutions suitable for FO applications. The 14 draw solutions were then tested in the laboratory to evaluate water flux and reverse salt diffusion through the FO membrane. Internal concentration polarization was found to lower both water flux and reverse salt diffusion by reducing the draw solution concentration at the interface between the support and dense layers of the membrane. Draw solution reconcentration was evaluated using reverse osmosis (RO) system design software. Analysis of experimental data and model results, combined with consideration of the costs associated with the FO and RO processes showed that a small group of seven draw solutions appeared to be the most suitable. The different characteristics of these draw solutions highlighted the importance of considering the specific FO application and membrane types being used prior to selecting the most appropriate draw solution.
In this study, we develop Janus membranes comprising a hydrophilic zwitterionic polymer layer and an omniphobic (all-liquid-repelling) porous substrate that simultaneously possess fouling and wetting ...resistances. An omniphobic membrane was first fabricated by attaching silica nanoparticles (SiNPs) to the fibers of a quartz fiber mat, creating multilevel re-entrant structures, followed by surface fluorination to reduce the surface energy. The Janus membrane was then fabricated by grafting a zwitterionic polymer brush layer via surface-initiated atom-transfer radical-polymerization (ATRP) on the omniphobic substrate. Membrane characterizations, including Fourier-transform infrared spectroscopy, fluorescence microscopy, and contact angle measurements, confirm that the surface hydrophilicity can be finely tuned by adjusting the duration of the ATRP reaction. Also, the zwitterionic polymer brush layer was confined on the top surface of the Janus membrane, rendering the surface hydrophilic, while the remaining part of the Janus membrane remained omniphobic, resisting the wicking of low-surface-tension liquids including ethanol and hexane. A static oil-fouling test showed that crude oil droplets irreversibly fouled an omniphobic membrane (without a hydrophilic top layer) in water. In contrast, oil droplets placed on the Janus membrane in air were immediately desorbed upon its immersion in water. Finally, we performed direct-contact membrane distillation (MD) experiments using a crude-oil-in-saline (NaCl) water emulsion as a feed solution, simulating highly saline oily wastewater. The Janus membrane exhibited superior wetting and fouling resistances, with a stable water flux and nearly perfect salt rejection, while an omniphobic membrane failed in the desalination process. Our work highlights the great potential of antiwetting and antifouling Janus membranes for water reclamation from challenging industrial wastewaters through MD.
Recent advancements in data-driven process control and performance analysis could provide the wastewater treatment industry with an opportunity to reduce costs and improve operations. However, big ...data in wastewater treatment plants (WWTP) is widely underutilized, due in part to a workforce that lacks background knowledge of data science required to fully analyze the unique characteristics of WWTP. Wastewater treatment processes exhibit nonlinear, nonstationary, autocorrelated, and co-correlated behavior that (i) is very difficult to model using first principals and (ii) must be considered when implementing data-driven methods. This review provides an overview of data-driven methods of achieving fault detection, variable prediction, and advanced control of WWTP. We present how big data has been used in the context of WWTP, and much of the discussion can also be applied to water treatment. Due to the assumptions inherent in different data-driven modeling approaches (e.g., control charts, statistical process control, model predictive control, neural networks, transfer functions, fuzzy logic), not all methods are appropriate for every goal or every dataset. Practical guidance is given for matching a desired goal with a particular methodology along with considerations regarding the assumed data structure. References for further reading are provided, and an overall analysis framework is presented.
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•Wastewater treatment produces nonstationary, autocorrelated, & co-correlated data.•A fundamental understanding of statistical process control is needed for facilities.•Method modifications are needed to account for the unique features of wastewater.•Neural networks can be limited by the quality of data produced by facilities.•Statistical process control is also not a silver bullet for wastewater treatment.
Water treatment technologies that employ sustainable driving forces for treatment of high ionic strength, complex feed streams and have the capacity to separate a broad range of contaminants are ...needed for economical treatment of flowback and produced waters in the oil and gas industry. This is especially true given the surging interest in treatment of oil and gas wastewaters for reuse in hydraulic fracturing or discharge to the environment in lieu of deep well injection. Forward osmosis is a robust membrane separation technology that can provide superior rejection of a broad range of feed stream contaminants and dissolved ions, thus providing a brine stream suitable for reuse in hydraulic fracturing or excellent pretreatment for downstream desalination processes. In this work, the impacts of membrane selection (asymmetric cellulose triacetate versus polyamide thin-film composite) and system operating conditions on the performance of FO membranes for desalination of produced water for the Niobrara shale formation are investigated. Specifically, water flux, contaminant rejection, membrane fouling, and chemical cleaning were evaluated using a combination of standard methodology and operating conditions analogous to those employed when operating industrial spiral wound FO membrane modules. Membrane autopsy was conducted to determine what effect(s) membrane physiochemical properties might have on system performance and to interpret the potential molecular level interactions occurring near the membrane-feed stream interface. Results from this study indicate that FO can achieve high rejection of organic and inorganic contaminants, membrane fouling can be mitigated with chemical cleaning, and long-term FO system performance might be better controlled with optimized hydrodynamic conditions near the membrane surface (i.e., feed flow velocity, module design, membrane packing) and not by membrane selection.
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•Produced water from the Niobrara shale play was treated with FO at the bench-scale.•Performance of CTA and next generation polyamide TFC membranes was investigated.•Operating conditions analogous to industrial spiral wound FO modules were employed.•Membrane fouling is dominated by initial water flux and permeation drag.•High rejection of feed stream contaminants from produced water was achieved.
Membrane distillation (MD) is an emerging desalination technology that has the ability to desalinate hypersaline brines, including those used in mineral production. MD can potentially replace ...evaporation ponds in conventional mineral production processes because of its small footprint and ability to utilize industrial low-grade heat. In the current study MD was investigated for sustained water recovery and concentration of hypersaline brines. Direct contact MD (DCMD) experiments were performed with water from the Great Salt Lake (>150,000 mg/L total dissolved solids) as the feed stream and deionized water as the distillate stream. DCMD was able to concentrate the feed solution to twice its original concentration, achieving close to complete inorganic salt rejection. During experiments water flux declined to 80% of its initial value (from 11 to 2 L m-2 h-1). Real-time microscopy revealed that precipitation of salts on the membrane surface was the main contributor to the decline in water flux. The application of novel scale-mitigation techniques was highly effective in preventing scale formation on membrane surfaces, sustaining high water flux and salt rejection, and eliminating chemical consumption used for membrane cleaning. MD was compared to natural evaporation and was found to potentially replace 4047 m2 (1 acre) of evaporation ponds with approximately 24 m2 (259 ft2) of membrane area and to be nearly 170 times faster in concentrating hypersaline brines.
Pressure retarded osmosis (PRO) was investigated as a viable source of renewable energy. In PRO, water from a low salinity feed solution permeates through a membrane into a pressurized, high salinity ...draw solution; power is obtained by depressurizing the permeate through a hydroturbine. A PRO model was developed to predict water flux and power density under specific experimental conditions. The model relies on experimental determination of the membrane water permeability coefficient (
A), the membrane salt permeability coefficient (
B), and the solute resistivity (
K).
A and
B were determined under reverse osmosis conditions, while
K was determined under forward osmosis (FO) conditions. The model was tested using experimental results from a bench-scale PRO system. Previous investigations of PRO were unable to verify model predictions due to the lack of suitable membranes and membrane modules. In this investigation, the use of a custom-made laboratory-scale membrane module enabled the collection of experimental PRO data. Results obtained with a flat-sheet cellulose triacetate (CTA) FO membrane and NaCl feed and draw solutions closely matched model predictions. Maximum power densities of 2.7 and 5.1
W/m
2 were observed for 35 and 60
g/L NaCl draw solutions, respectively, at 970
kPa of hydraulic pressure. Power density was substantially reduced due to internal concentration polarization in the asymmetric CTA membranes and, to a lesser degree, to salt passage. External concentration polarization was found to exhibit a relatively small effect on reducing the osmotic pressure driving force. Using the predictive PRO model, optimal membrane characteristics and module configuration can be determined in order to design a system specifically tailored for PRO processes.
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•SPAC had up to s480 times higher adsorption mass loading of PFAAs than GAC.•SPAC and GAC adsorption efficiency depends on PFAS chain length.•The ceramic MF membrane had minimal ...fouling during long-term filtration.•PFASs were effectively removed by the combined SPAC/MF system.
Contamination of drinking water sources with per- and polyfluoroalkyl substances (PFASs) is a major challenge for environmental engineers. While granular activated carbon (GAC) is an effective adsorbent-based treatment technology for long-chained PFASs, GAC is less effective for removal of short-chained compounds, necessitating a more complete treatment strategy. Super-fine powder activated carbon (SPAC; particle diameter <1 um) is potentially a superior adsorbent to GAC due to high specific surface area and faster adsorption kinetics. This study served to evaluate SPAC coupled with ceramic microfiltration (CMF) for PFAS removal in a continuous flow system. Comparison of PFAS mass loading rates onto SPAC and GAC to 10% breakthrough of PFASs using contaminated groundwater indicates that SPAC has nearly double the adsorption potential of GAC. Limitations reaching breakthrough for the SPAC system led to additional higher mass loading experiments where PFAS adsorption onto SPAC reached 2990 μg/g (for quantifiable PFASs), 480x greater than GAC and is thought to be a function of adsorbent size, pore content and PFAS chain length. Additional analysis of system performance through the application of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) revealed the presence of additional PFASs in influent samples that were removed by the SPAC/CMF system.
•Direct contact membrane distillation was used to desalinate hypersaline brines.•Crystallization of supersaturated NaCl on the membrane was reversible.•Crystallization of supersaturated Great Salt ...Lake brine was irreversible.•Membrane pores were impacted by mineral crystallization during DCMD desalination.
Membrane distillation (MD) is a thermally-driven separation process that utilizes a difference in vapor pressure across a porous, hydrophobic membrane as the driving force. MD may be applied to aqueous systems at concentrations up to and exceeding saturation of both sparingly soluble salts and soluble salts such as sodium chloride (NaCl), leading to potential application in high-recovery desalination processes that approach Zero Liquid Discharge (ZLD) operation, or as a concentration strategy for mineral recovery. Scaling and fouling is a significant risk for such processes, and knowledge of the effects of these phenomena on performance is essential to the evaluation of MD as a viable technology for these applications. The present study investigated the scaling and fouling behavior of a hypersaline brine collected from the North Arm of the Great Salt Lake (GSL), which was nearly saturated with respect to NaCl, and also contained high concentrations of dissolved minerals and organic carbon. Effects on water flux, thermal efficiency, and salt rejection were measured, and membranes used were analyzed before and after testing to evaluate potential causes of these effects. Scaling by NaCl crystallization on the membrane surface limited water recovery to approximately 10%, and also caused damage to the internal pore structure of the membrane when the temperature difference (ΔT) between the feed and distillate was higher than 20°C. Analysis of the solution chemistry of the GSL water was effective in predicting the scaling tendency of NaCl, but inadequate in predicting the scaling tendency of other salts. Amorphous scaling structures on the membrane surfaces containing magnesium and oxygen were implied as the dominant factors contributing to performance decline at concentrations below NaCl saturation, and the result of fouling due to interactions between organic matter and magnesium. Operation at a maximum water recovery of 8% combined with intermittent reversal of the temperature gradient were effective strategies to prevent both scaling and fouling and maintain long-term performance.
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