s N. Costa

Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems

Changes in disinfectant type could trigger a cascade of reactions releasing pipe-anchored metals/metalloids into finished water. However, the effect of pre-formed disinfection by-products on the release of sorbed contaminants (arsenic-As in particular) from drinking water distribution system pipe scales remains unexplored. A bench-scale study using a factorial experimental design was performed to evaluate the independent and interaction effects of trihalomethanes (TTHM) and haloacetic acids (HAA) on arsenic (As) release from either scales-only or scale-biofilm conglomerates (SBC) both anchored on asbestos/cement pipe coupons. A model biofilm (Pseudomonas aeruginosa) was allowed to grow on select pipe coupons prior experimentation. Either TTHM or HAA individual dosing did not promote As release from either scales only or SBC, detecting <6 μg AsL(-1) in finished water. In the case of scales-only coupons, the combination of the highest spike level of TTHM and HAA significantly (p<0.001) increased dissolved and total As concentrations to levels up to 16 and 95 μg L(-1), respectively. Similar treatments in the presence of biofilm (SBC) resulted in significant (p<0.001) increase in dissolved and total recoverable As up to 20 and 47 μg L(-1), respectively, exceeding the regulatory As limit. Whether or not, our laboratory-based results truly represent mechanisms operating in disinfected finished water in pipe networks remains to be investigated in the field.

Novel catalytic and mechanistic studies on wastewater denitrification with hydrogen

The present work reports up-to-date information regarding the reaction mechanism of the catalytic hydrogenation of nitrates in water media. In the present mechanistic study, an attempt is made, for the first time, to elucidate the crucial role of several catalysts and reaction parameters in the mechanism of the NO(3)(-)/H(2) reaction. Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed on supported Pd-Cu catalysts for the NO(3)(-)/H(2) and NO(3)(-)/H(2)/O(2) reactions. The latter experiments revealed that the formation and surface coverage of various adsorbed active intermediate N-species on the support or Pd/Cu metal surface is significantly favored in the presence of TiO(2) in the support mixture and in the presence of oxygen in the reactions gaseous feed stream. The differences in the reactivity of these adsorbed N-species, found in the present work, adequately explain the large effect of the chemical composition of the support and the gas feed composition on catalyst behaviour (activity and selectivity). The present study leads to solid mechanistic evidence concerning the presence of a hydrogen spillover process from the metal to the support. Moreover, this study shows that Cu clusters are active sites for the reduction of nitrates to nitrites.

The effect of several parameters on catalytic denitrification of water by the use of H2 in the presence of O2 over metal supported catalysts.

The present paper involves a detailed study of the selective catalytic reduction of nitrates in aqueous mediums by the use of H2 in the presence of O2 over monometallic and bimetallic supported catalysts. In this study, an attempt has been made to improve the denitrification efficiency (XNO3(-), SN2) of several catalysts by regulating some experimental parameters that are involved in the process. Therefore, the effects of the type of reactor (semi-batch reactor vs continuous flow reactor), the nature of the active phase (Pd, Cu, and Pd-Cu) and the particle size of γ-Al2O3 spheres (particle diameter = 1.8 mm and 3 mm) on catalytic activity and reaction selectivity, as well as the adsorption capacity of γ-Al2O3 spheres for nitrates, were examined. As the review indicates, most of the research has so far been conducted on batch or semi-batch reactors. This study successfully demonstrates the benefits of using a continuous flow reactor in terms of catalytic activity (XNO3(-), %) and reaction selectivity (SN2, %). Another important aspect of this study is the crucial role of bimetallic Pd-Cu clusters for the prevention of NH4(+) formation. Moreover, the use of 1.8 mm diameter γ-Al2O3 spheres as a support was proved to significantly enhance the catalytic performance of bimetallic Pd-Cu catalysts towards nitrate reduction compared to 3 mm diameter γ-Al2O3 spheres. This difference may be attributed to mass (NO3(-), OH(-)) transfer effects (external mass transfer phenomena).

Computer simulation of a submerged membrane bioreactor treating high COD industrial wastewater

A dynamic model was developed to simulate the behavior of the biological processes taking place in a membrane bioreactor (MBR) pilot plant treating industrial wastewater at the Heraklion Industrial Park including the cake development on the membrane surface. The modified extended CES-ASM3 model has been used. Hydrolysis rates of the soluble microbial products have been added. Membrane fouling was taken into account and trans membrane pressure (TMP) was modeled and compared to experimental data. Simulation results are presented for the operation period between February 2012 and May 2013 and the prediction ability of the model is shown through the computation of the mean relative error of each measured state variable. Overall, the model estimates match the experimental data satisfactorily, as they follow similar trends while for all input variables their mean value was used as a constant input in the simulations. The operation of the MBR was conducted at three different sludge retention times.

Co-occurrence profiles of trace elements in potable water systems: a case study

Potable water samples (Nu2009=u200974) from 19 zip code locations in a region of Greece were profiled for 13 trace elements composition using inductively coupled plasma mass spectrometry. The primary objective was to monitor the drinking water quality, while the primary focus was to find novel associations in trace elements occurrence that may further shed light on common links in their occurrence and fate in the pipe scales and corrosion products observed in urban drinking water distribution systems. Except for arsenic at two locations and in six samples, rest of the analyzed elements was below maximum contaminant levels, for which regulatory values are available. Further, we attempted to hierarchically cluster trace elements based on their covariances resulting in two groups; one with arsenic, antimony, zinc, cadmium, and copper and the second with the rest of the elements. The grouping trends were partially explained by elements’ similar chemical activities in water, underscoring their potential for co-accumulation and co-mobilization phenomena from pipe scales into finished water. Profiling patterns of trace elements in finished water could be indicative of their load on pipe scales and corrosion products, with a corresponding risk of episodic contaminant release. Speculation was made on the role of disinfectants and disinfection byproducts in mobilizing chemically similar trace elements of human health interest from pipe scales to tap water. It is warranted that further studies may eventually prove useful to water regulators from incorporating the acquired knowledge in the drinking water safety plans.

Catalytic removal of pharmaceutical compounds in water medium under an H2 stream over various metal-supported catalysts: A promising process

To date, very few prescriptive studies have been reported in the literature concerning the catalytic removal of pharmaceutical substances in wastewater using H2 in the presence of O2 for the in situ formation of H2O2, while the mechanism of the reaction has not been studied in detail yet. Hydrogen peroxide is a potent oxidizing agent used extensively in catalytic wet air oxidation (CWAO) applications and can be used for the elimination of pharmaceuticals from waste water. In the present work, an attempt has been made to elucidate the actual effects of the in situ production of hydrogen peroxide on the CWAO of pharmaceuticals. Therefore, the effects of the nature of the active phase (Pd, Pt, and Rh), as well as the feed gas composition have been examined toward the reaction at hand. The results showed that 1% Pd/Al2O3 and 1% Rh/Al2O3 are the most effective catalysts for the elimination of paracetamol from the reaction medium using hydrogen-rich streams, having a conversion of up to 70% in 2 h. A maximum conversion of paracetamol of 90% was obtained in just 30 min of reaction over 1 wt.% Rh/Al2O3, when using pure hydrogen in the feed. Total organic carbon measurements performed over the latter catalyst showed that practically no organic carbon is removed from the liquid phase, indicating the conversion of paracetamol to a different organic (probably aromatic) compound, through hydrogenation. Toxicity tests that followed showed a dramatic decrease in the toxicity of the products solution, indicating that paracetamol hydrogenation might be a promising method for the elimination of its toxicity.

Multi-level Risk Analysis and Sensitivity Mapping for the Mediterranean Sea Basin—RAOP-MED Project

The present work was conducted within the framework of RAOP-MED project which was funded by the ENPI CBC MED programme.

Preventing maritime transport of pathogens: the remarkable antimicrobial properties of Ag supported catalysts for ships ballast water disinfection

Ship ballast water (SBW) antimicrobial treatment is considered as a priority issue for the shipping industry. The present work investigates the possibility of utilizing antimicrobial catalysis as an effective method for the treatment of SBW. Taking into account the well-known antimicrobial properties of ionic silver (Ag+), five silver-supported catalysts (Ag/γ-Al2O3) with various loadings (0.05, 0.1, 0.2, 0.5, and 1 wt%) were prepared and examined for the antimicrobial treatment of SBW. The bactericidal activity of the aforementioned catalysts was investigated towards the inhibition of Escherichia coli (Gram-negative) and Escherichia faecalis (Gram-positive) bacteria. Catalytic experiments were conducted in a three-phase continuous flow stirred tank reactor, used in a semi-batch mode. It was found that using the catalyst with the lowest metal loading, the inhibition of E. coli reached 95.8% after 30 minutes of treatment of an E. coli bacterial solution, while the inhibition obtained for E. faecalis was 76.2% after 60 minutes of treatment of an E. faecalis bacterial solution. Even better results (100% inhibition after 5 min of reaction) were obtained using the catalysts with higher Ag loadings. The results of the present work indicate that the prepared monometallic catalysts exert their antimicrobial activity within a short period of time, revealing, for the first time ever, that the field of antimicrobial heterogeneous catalysis using deposited ionic silver on a solid support may prove decisive for the disinfection of SBW.

The new concept of antimicrobial catalysis: disinfection of ships ballast water

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