Synthesis and characterization of a nanoparticle-enhanced filter medium for decentralized water purification systems

Date
2011
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University of Delaware
Abstract
A synthesis procedure was developed to generate a tailored point of use (POU) filter medium that incorporates nanoscale zero-valent iron (nZVI) and granular activated carbon (GAC) for the enhanced treatment of drinking water. Several characterization techniques were employed to evaluate the efficiency of the synthesis procedure and the generated product itself. First, iron quantification via nitric acid extraction illustrated that at low iron loadings transfer of iron onto GAC was efficient and complete, and that negligible iron loss occurred post calcination during either sieving or reduction. Second, Brunauer, Emmett, and Teller (BET) specific surface area measurements for the virgin-GAC and nZVI-GAC were determined to be 798 m²-g.¹ and 792 m²-g.¹ respectively, indicating a negligible decrease in GAC surface area post synthesis. Third, scanning electron microscopy (SEM) imagery and energy-dispersive X-ray spectroscopy (EDS) measurements confirmed the presence and general surface distribution of iron nanoparticles on GAC. Finally, X-ray diffraction (XRD) intensity patterns confirmed the presence of ZVI on the surface of GAC and that the synthesis procedure successfully reduced ferric iron to its zero-valent state. To simulate drinking water contaminated with enteric microorganisms, two bacteriophages MS2 and φX174 were used as surrogates. A series of batch tests were performed to measure removal efficiencies for each bacteriophage over different time intervals. Varying degrees of removal were observed for each bacteriophage. Experimental results showed that the nZVI-GAC filter medium demonstrated greater removal efficiency for MS2 compared to virgin-GAC. The first-order rate coefficients for MS2 removal by virgin-GAC and nZVI-GAC were determined to be 0.037 and 0.0961 PFU-min.¹, respectively. However, performance for φX174 removal appeared to be similar between both the control and nZVI filter medium. The first-order rate coefficients for φX174 removal by virgin-GAC and nZVI-GAC were 0.0298 and 0.0413 PFU-min.¹, respectively. The varying effect on MS2 removal was also observed by adjusting the percent weight of iron coated on the GAC surface. The experimental results from the varied percent iron loading tests identified a rate-limited removal capacity for nZVI. Removal mechanisms were then suggested to explain the observed experimental data. Finally, drawing on conclusions from the observed experimental data, the potential application for such a nanoparticle-enhanced POU filter medium was explored. Ultimately, the engineered application of nZVI-GAC was suggested as a substitute for the conventional in-the-field POU technologies.
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