Phosphorus recovery from wastewater using pyridine-based ion-exchange resins: Role of impregnated iron oxide nanoparticles and preloaded Lewis acid (Cu2+ ).

Inputs of P into receiving water bodies are attracting increasing attention due to the negative effects of eutrophication. Presently available P treatment technologies are unable to achieve strict P discharge limits from wastewater treatment plants (WWTPs) that may be as low as 10 µg/L as P. Moreover, P is a nonrenewable resource and needs to be recycled in a closed-loop process for environmental sustainability. This article provides details of a process where a pyridine-based polymeric ion exchanger is modified with a combination of impregnated hydrated ferric oxide (HFO) nanoparticles and a preloaded Lewis acid (Cu2+ ) to effectuate selective P removal from wastewater and its recovery as a solid-phase fertilizer. Three such ion exchangers were studied: DOW-HFO, DOW-Cu, and DOW-HFO-Cu. Each of these materials displays selective phosphate affinity over competing anions chloride and sulfate, and also has the ability to be regenerated upon exhaustion to strip off the P in a concentrated solution. The P in concentrated regenerant can be recovered as struvite, MgNH4 PO4 , a slow-release fertilizer, after addition of MgCl2 and NH4 Cl. Results of equilibrium and kinetic studies and column experiments with synthetic solutions and a real WWTP effluent are discussed. PRACTITIONER POINTS: Fixed-bed columns with DOW-HFO, DOW-Cu, or DOW-HFO-Cu-can selectively remove phosphorus over competing anions. Fixed-bed columns of above-listed ion exchangers can produce an effluent P < 6 µg/L. DOW-Cu fixed-bed column ran for ≈500 Bed Volumes before breakthrough when fed Dartmouth WWTP secondary effluent. Regeneration of the exhausted DOW-Cu column resulted in ≈90% recovery of the phosphorus. Regenerant solution was used to generate high-purity crystals of magnesium ammonium phosphate, MgNH4 PO4 (struvite), a slow-release fertilizer.

Silver recovery as Ag0 nanoparticles from ion-exchange regenerant solution using electrolysis.

Many silver (Ag) containing consumer-products (e.g. textiles) release Ag into the environment, posing ecotoxicological risks. Ag recovery mitigates environmental hazards, recycles Ag, and leads to sustainability. In the present work, Ag has been recovered as Ag0 nanoparticles from the spent solution (thiourea (TU) ~0.5 mol/L pH ~1.1-1.2, and Ag ~550 mg/L) obtained from the regeneration of an Ag-loaded resin using a simple undivided electrolytic cell. The reclaimed regenerant solution has been recycled and reused in a closed-loop scheme over multiple cycles. The process parameters, i.e., current (0.05 A) and stirring speed (600 r/min), have been optimized for Ag recovery of ~94% and TU loss of ~2%. The reclaimed regenerant solution has been shown to regenerate Ag-loaded resin samples with >90% regeneration efficiency over 4 cycles of consecutive extraction and regeneration. The recovered Ag0 nanoparticles are monodisperse, consistently spherical in shape, and have a mean diameter of ~6 nm with standard deviation of the Gaussian fit as ~2.66 nm.

pH-responsive drug release from functionalized electrospun poly(caprolactone) scaffolds under simulated in vivo environment.

The difference in the tumor environment from the normal healthy tissue can be therapeutically exploited to develop new strategies for controlled and site-specific drug delivery. In the present study, a continuous flow system is designed to represent the in vivo environment of a tumor tissue and drug release is studied at different pH that represents normal tissue pH, tumor tissue pH, and stomach pH. The results obtained from these experiments were translated to a human embryonic kidney cell culture system and the effect of drug released from these functionalized PCL scaffolds on cell viability was studied. A significant decrease in cell viability was observed with the doxorubicin hydrochloride concentration that would be released at acidic pH, either present as a result of tumor extracellular environment or could be achieved via fabrication of a composite scaffold with a polyvinyl alcohol hydrogel containing acid. In the end, a study using zebrafish as an animal model is also undertaken in order to study the drug release from the scaffolds in vivo.

Functionalization of electrospun poly(caprolactone) fibers for pH-controlled delivery of doxorubicin hydrochloride.

Functionalized electrospun polymer fibers are a promising candidate for controlled delivery of chemotherapeutic drugs to improve the therapeutic efficacy and to reduce the potential toxic effects by delivering the drug at a rate governed by the physiological need of the site of action. In this study, poly(caprolactone) (PCL) fibers were fabricated by electrospinning, followed by hydrolyzation to introduce functional groups on the fiber surface. Characterization studies were performed on these functionalized fibers using X-ray photoelectron spectroscopy, scanning electron microscopy, and Toluidine Blue O dye assay. The pH-sensitivity of the functional groups on the fiber surface and doxorubicin hydrochloride was utilized to bind the drug electrostatically to these functionalized PCL fibers. The effect of pH on drug loading and release kinetics was investigated. Results indicate successful electrostatic binding of the drug to functionalized electrospun fibers and a high drug payload. The drug delivery response can be modulated by introduction of suitable stimuli (pH).

Hydrolyzed Poly(acrylonitrile) Electrospun Ion-Exchange Fibers.

A potential ion-exchange material was developed from poly(acrylonitrile) fibers that were prepared by electrospinning followed by alkaline hydrolysis (to convert the nitrile group to the carboxylate functional group). Characterization studies performed on this material using X-ray photoelectron spectroscopy, scanning electron microscopy, Fourier-Transform infra-red spectroscopy, and ion chromatography confirmed the presence of ion-exchange functional group (carboxylate). Optimum hydrolysis conditions resulted in an ion-exchange capacity of 2.39 meq/g. Ion-exchange fibers were used in a packed-bed column to selectively remove heavy-metal cation from the background of a benign, competing cation at a much higher concentration. The material can be efficiently regenerated and used for multiple cycles of exhaustion and regeneration.

Selective removal of phosphorus from wastewater combined with its recovery as a solid-phase fertilizer.

Influx of Phosphorus (P) into freshwater ecosystems is the primary cause of eutrophication which has many undesirable effects. Therefore, P discharge limits for effluents from WWTPs is becoming increasingly common, and may be as low as 10 µg/L as P. While precipitation, filtration, membrane processes, Enhanced Biological Phosphorus Removal (EBPR) and Physico-chemical (adsorption based) methods have been successfully used to effect P removal, only adsorption has the potential to recover the P as a usable fertilizer. This benefit will gain importance with time since P is a non-renewable resource and is mined from P-rich rocks. This article provides details of a process where a polymeric anion exchanger is impregnated with iron oxide nanoparticles to effectuate selective P removal from wastewater and its recovery as a solid-phase fertilizer. Three such hybrid materials were studied: HAIX, DOW-HFO, & DOW-HFO-Cu. Each of these materials combines the durability, robustness, and ease-of-use of a polymeric ion-exchanger resin with the high sorption affinity of Hydrated Ferric Oxide (HFO) toward phosphate. Laboratory experiments demonstrate that each of the three materials studies can selectively remove phosphate from the background of competing anions and phosphorus can be recovered as a solid-phase fertilizer upon efficient regeneration of the exchanger and addition of a calcium or magnesium salt in equimolar (Ca/P or Mg/P) ratio. Also, there is no leaching of Fe or Cu from any of these hybrid exchangers.

Nanostructured surfaces for enhanced protein detection toward clinical diagnostics.

"Label-free" biomolecule sensors for detection of inflammatory cardiovascular biomarker associated with vulnerable coronary vascular plaque rupture were designed and fabricated using micro- and nanotextured polystyrene (PS) polymer structures that functioned as sensing elements coupled with electronic measurement equipment. We demonstrated that scaling down the surface texturing from the micro- to the nanoscale enhances the amplitude of the measured detected signal strength. We believe that the nanoscale fiber morphology provides size-matched spaces for trapping and immobilizing the protein biomolecule, resulting in improved detection signal strength. We selected PS as the model system and demonstrated the detection of human serum C-reactive protein. We employed these findings in designing a platform "lab-on-a-chip" protein sensor. Comparative studies were performed on PS textured surfaces of two different surface features: a PS microsphere mat and an electrospun PS nanofiber matrix. FROM THE CLINICAL EDITOR: In this study, nanotechnology-based biosensors for vulnerable coronary vascular plaque rupture were designed and fabricated using micro- and nanotextured polystyrene polymer structures. The authors demonstrated that scaling down the surface texturing from the micro- to the nanoscale enhances the sensitivity of this detection method.

Onsite wastewater denitrification using a hydrogenotrophic hollow-fiber membrane bioreactor.

Hydrogenotrophic wastewater denitrification was investigated using a bench-scale hollow-fiber membrane bioreactor (HFMB). In the HFMB, hydrogen (H2) was passed through the lumen of hollow-fiber membranes and nitrified wastewater was supplied to the shell of the reactor. A mass transfer model was developed and found to be a good tool to estimate H2 mass transfer coefficients at varying recirculation velocities. Under steady conditions, effluent NO3(-)-N concentrations less than 10 mg/L were achieved at an empty bed contact time of 8.3 hours when pH and membrane fouling were controlled. An average nitrogen flux of 0.88 g NO3(-) -N/m2 x d was observed. Dissolved oxygen in the influent wastewater did not adversely affect overall nitrogen removal. Under transient conditions, similar to those of onsite processes, overall nitrogen removal efficiencies of 74 to 82% were observed. Confocal laser scanning microscopy revealed that the denitrifying biofilm was loosely associated with the membrane surfaces.

Investigation of solid-phase buffers for sulfur-oxidizing autotrophic denitrification.

This paper investigates biological denitrification using autotrophic microorganisms that use elemental sulfur as an electron donor. In this process, for each gram of nitrate-nitrogen removed, approximately 4.5 g of alkalinity (as calcium carbonate) are consumed. Because denitrification is severely inhibited below pH 5.5, and alkalinity present in the influent wastewaters is less than the alkalinity consumed, an external buffer was needed to arrest any drop in pH from alkalinity consumption. A packed-bed bioreactor configuration is ideally suited to handle variations in flow and nitrate loading from decentralized wastewater treatment systems, as it is a passive system and thus requires minimal maintenance; therefore, a solid-phase buffer packed with the elemental sulfur in the bioreactor is most suitable. In this research, marble chips, limestone, and crushed oyster shells were tested as solid-phase buffers. Bench- and field-scale studies indicated that crushed oyster shell was the most suitable buffer based on (1) the rate of dissolution of buffer and the buffering agent released (carbonate, bicarbonate, or hydroxide), (2) the ability of the buffer surface to act as host for microbial attachment, (3) turbidity of the solution upon release of the buffering agent, and (4) economics.