Sukalyan Sengupta

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.

Performance of Nitrogen-Removing Bioretention Systems for Control of Agricultural Runoff

This research evaluated nitrogen-removing bioretention systems for control of nutrients, organics, and solids in agricultural runoff. Pilot-scale experiments were conducted with bioretention systems incorporating aerobic nitrification and anoxic denitrification zones with sulfur or wood chips as denitrification substrates. Varying hydraulic loading rates (HLRs), influent concentrations, and wetting and drying periods were applied to the units during laboratory and two seasons of field tests with dairy farm runoff. Total N removal efficiencies greater than 88% were observed in both units with synthetic storm water. In first-season field tests, moderate removal efficiencies were observed for chemical oxygen demand (46%), suspended solids (69%), total phosphorous (TP) (66%), and total N (65%). During the second season, operational changes in the farm resulted in lower organic, solids, and nutrient loadings resulting in improved effluent quality, especially for suspended solids (81% removal) and total N (82% ...

Electro-partitioning with composite ion-exchange material: an innovative in-situ heavy metal decontamination process

Selective in-situ removal of heavy metals from a contaminated soil/sludge combines the benefits of: (a) being a low risk operation since the soil/sludge is not excavated and transported, (b) being economically prudent since only the target contaminant is removed, and (c) providing the possibility of reuse/recycle of the heavy metals since they are selectively removed. However, the main problem faced in such a process is inserting a material into the soil/sludge which can selectively remove heavy metals from the background of other ions which are much higher in concentration than the target heavy metals but are innocuous from a regulatory point-of-view. The affinity of chelating ion-exchange resins toward heavy metal cations is well established but their morphology (spherical beads of diameter <5 mm) is unsuitable for use in an in-situ process. This communication explores the use of a novel material termed composite ion-exchange material (CIM) which allows microspheres of chelating resins to be entrapped in a Teflon® network, thus producing a thin sheet (≈0.5 mm) which can be easily introduced into or withdrawn from a soil/sludge sample. The CIM is used in a physico-chemical process where application of DC potential gradient forces the heavy metal cations to move toward the cathode and consequently contact the CIM sheet wrapped around the cathode. The strong affinity of chelating exchangers inside the CIM forces selective uptake of the heavy metals from the contaminated solid phase. After passage of current for a determined amount of time, the CIM is withdrawn from the soil/sludge and chemically regenerated, thus allowing the heavy metals to be concentrated in an acid solution. This communication presents preliminary results of experiments performed to explore the use of this process and also discusses modifications required to achieve higher suitability.

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).

Heavy-metal separation from sludge using chelating ion exchangers with nontraditional morphology

Abstract Solid-phase wastes or hazardous waste sites containing heavy metals are a major environmental concenr due to the toxicity characteristic of the heavy metal. Generally, in such cases the heavy metals constitute a small fraction (usually

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.

Chelating ion-exchangers embedded in PTFE for decontamination of heavy-metal-laden sludges and soils

Abstract Selective removal of small amounts of heavy metal precipitates from the background of bulk amounts of innocuous sludge or soil is a challenging separation problem. This study identifies and investigates a novel material that has the potential to overcome such a challenge. The material, termed Composite Ion-Exchanger Material (CIM), is made of fine particles of chelating polymers entrapped in thin sheets of porous polytetrafluoroethylene (PTFE). The composite ion-exchange material is not fouled by high concentration of suspended solids but retains the original properties of the chelating exchangers. In this communication, various physico-chemical properties of the new ion-exchange material are discussed as regards their use in the decontamination of heavy-metal-laden soils and sludges.

Quantitative characterization of functionally modified micron–submicron fibers for tissue regeneration: a review

Tissue regeneration relies on building carefully crafted scaffold material in the micron–submicron scale and imparting specific functionality in order to best mimic the in vivo environment in terms of chemical composition, morphology, and surface functional groups. Fibrous meshes with structural features at the micron to submicron level for ideal three-dimensional tissue regeneration scaffolds can be an inexpensive scale-up option. Bio-inert polymers lack the functional motifs for specific bioactivity; however, functionalization of the scaffolds can provide biological functions to actively induce tissue regeneration and promote cell adhesion by targeting specific cell–matrix interactions. It is therefore important to characterize the scaffolds and understand the relationship between the efficacy of the functionalization, the surface properties of the scaffolds, and their biological performance. This paper is a comprehensive review of the current understanding in functionalization and characterization of fibrous scaffolds and their biological efficacy. We begin with a compilation of various functionalization schemes including physical adsorption, co-electrospinning, wet chemical techniques, and surface graft polymerization methods and their application to fibers. After a critical literature review, the state of the art for characterization of these functionalized nano-fibers is then discussed. We emphasize the importance of covalent binding of biomolecules and the subsequent need for characterization of functional group distribution, or local density of functionalization, on the scaffold surface. Current challenges and future directions are outlined so that quantitative characterization of scaffold surfaces can aid in the development of next generation scaffolds.

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

Abstract 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.

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.