Ranking nano-enabled hybrid media for simultaneous removal of contaminants with different chemistries: Pseudo-equilibrium sorption tests versus column tests.

The underlying hypothesis of this study was that pseudo-equilibrium and column testing conditions would provide the same sorbent ranking trends although the values of sorbents' performance descriptors (e.g. sorption capacity) may vary because of different kinetics and competition effects induced by the two testing approaches. To address this hypothesis, nano-enabled hybrid media were fabricated and its removal performances were assessed for two model contaminants under multi-point batch pseudo-equilibrium and continuous-flow conditions. Calculation of simultaneous removal capacity indices (SRC) demonstrated that the more resource demanding continuous-flow tests are able to generate the same performance rankings as the ones obtained by conducing the simpler pseudo-equilibrium tests. Furthermore, continuous overlap between the 98% confidence boundaries for each SRC index trend, not only validated the hypothesis that both testing conditions provide the same ranking trends, but also pointed that SRC indices are statistically the same for each media, regardless of employed method. In scenarios where rapid screening of new media is required to obtain the best performing synthesis formulation, use of pseudo-equilibrium tests proved to be reliable. Considering that kinetics induced effects on sorption capacity must not be neglected, more resource demanding column test could be conducted only with the top performing media that exhibit the highest sorption capacity.

Potential health implications of water resources depletion and sewage discharges in the Republic of Macedonia.

Potential health implications of deficient sanitation infrastructure and reduced surface water flows due to climate change are examined in the case study of the Republic of Macedonia. Changes in surface water flows and wastewater discharges over the period 1955-2013 were analyzed to assess potential future surface water contamination trends. Simple model predictions indicated a decline in surface water hydrology over the last half century, which caused the surface waters in Macedonia to be frequently dominated by >50% of untreated sewage discharges. The surface water quality deterioration is further supported by an increasing trend in modeled biochemical oxygen demand trends, which correspond well with the scarce and intermittent water quality data that are available. Facilitated by the climate change trends, the increasing number of severe weather events is already triggering flooding of the sewage-dominated rivers into urban and non-urban areas. If efforts to develop a comprehensive sewage collection and treatment infrastructure are not implemented, such events have the potential to increase public health risks and cause epidemics, as in the 2015 case of a tularemia outbreak.

Arsenate removal by nanostructured ZrO2 spheres.

A new zirconium oxide-based media for arsenate removal from water was fabricated and evaluated in batch and continuous flow experiments. Highly porous (epsilonp approximately 0.9) nanostructured zirconium oxide spheres were fabricated by the impregnation of macroporous ion-exchange media (CalRes 2103, Calgon) with zirconium salt; the media was then ashed at T > 750 +/- 50 degrees C to remove the organic polymer resin and obtain ZrO2 spheres. The spheres generally ranged from 200 to 800 microm in diameter, and consisted of ZrO2 nanoastructures generally ranging between 20 and 100 nm. They also exhibited monoclinic and tetragonal crystalline structures, and had an isoelectric point of 5.6. Equilibrium batch experiments were conducted in 10 mM NaHCO3 buffered nanopure water at three pH values (6.4,7.3, and 8.3) with 120 microg/L As(V). Data were fit with the Freundlich isotherm equation (q(e) = Kx CE(1/n)), resulting in an intensity parameter (1/n) of approximately 0.33 and capacity parameters (K) ranging from 115 to 400 (microg As(V) g(-1) dry media)(L microg(-1))1/n. The pore diffusion coefficient and toruosity were estimated to be 6.4 x 10(-6) cm2 s(-1) and 1.3, respectively. For a packed bed adsorbent operating at a loading rate of 11.5 m3 m(-2) hr(-1) in a realistic continuous flow experiment, the external mass transport coefficient was estimated to be kf approximately 6.3 x 10(-3) cm s(-1). The pore diffusion coefficient and the external mass transport coefficient were used with the pore surface diffusion model (PSDM) to predict the arsenate breakthrough curve. A short bed adsorbent (SBA) test was conducted under the same conditions to validate the model. In this study, surface diffusion was ignored because the particles have a very high porosity. The validated model was used to predict arsenate breakthrough in a simulated full-scale system. The overall combined use of modeling, material characterization, equilibria, and kinetics tests determined the suitability of the media for arsenate treatment cheaper, easier, faster, and with less media than a long duration pilot test would have. Although the fabricated zirconium oxide spheres exhibited adsorption capacity comparable to some commercially available media such as iron based (hydr)oxides, the high cost of fabrication may render the media not feasible for wide use in commercial applications. However, the very high porosity of this media provides for improved pore diffusion and faster overall mass transport, which may be critical for applications where mass transport is the limiting factor.