Influence of the physicochemical properties of inorganic supports on the activity of immobilized bacteria for water denitrification.

The denitrification of polluted water was studied by using supported E-coli bacteria. The physicochemical characteristics of supports and the influence of these properties on the bacteria performance were analyzed. Inorganic supports oxides and zeolites were selected in order to cover a wide range of porosity and surface chemical properties and the denitrification process systematically studied. Consecutive denitrification cycles in batch experiments and the toxicity of supports were also analyzed. The acidity of supports provokes a slower reduction processes, favoring also a high concentration of intermediate nitrites in solution for longer periods. The NO3(-) reduction is faster than the NO2(-) one, being also less influenced by the support characteristics. Anyway, the total denitrification is reached in all cases. The best performance was obtained with bacteria supported on mesoporous and non-acid silica support.

Effectiveness of different oxidizing agents for removing sodium dodecylbenzenesulphonate in aqueous systems.

The present study investigates the efficacy of various oxidizing treatments (ClO(-), ClO(2), KMnO(4), O(3), O(3)/H(2)O(2), O(3)/activated carbon) to remove from waters sodium dodecylbenzenesulphonate (SDBS), considered as model surfactant. Results obtained show that the use of ClO(-) and ClO(2) does not cause appreciable SDBS degradation. Additionally, in the case of ClO(-), trihalomethanes are generated, increasing system toxicity. Because the reaction kinetics between SDBS and KMnO(4) is very slow, a decrease in contaminant concentration is not observed, even at very acid pH values. SDBS reactivity with ozone is very low, with a kinetic constant (k(O)(3)) of 3.68 M(-1)s(-1), but its reactivity with HO() radicals is very high (k(OH)=1.16 x 10(10)M(-1)s(-1)), therefore O(3)/H(2)O(2) and O(3)/activated carbon, which can also generate HO(), appear as promising advanced oxidation processes to remove this contaminant from waters. The method based on ozone and activated carbon was the only process studied that produced both an increase in SDBS removal rate (due to the generation of HO() radicals in the O(3)-PAC or O(3)-GAC interaction) and a considerable reduction in the concentration of dissolved organic carbon in the system due to the PAC adsorbent properties.

Behavior of two different constituents of natural organic matter in the removal of sodium dodecylbenzenesulfonate by O3 and O3-based advanced oxidation processes.

The objective of this study was to analyze the role played by two components of natural organic matter (NOM), gallic acid (GAL) and humic acid (HUM), in the removal of the surfactant sodium dodecylbenzenesulfonate (SDBS) from waters by O(3)-based oxidation processes, i.e., O(3)/H(2)O(2), O(3)/granular activated carbon (GAC), and O(3)/powdered activated carbon (PAC). It was found that the presence of low concentrations of these compounds (1 mg/L) during SDBS ozonation increases both the ozone decomposition rate and the rate of SDBS removal from the medium. Because of the low reactivity of SDBS with ozone, these effects are mainly due to an increase in the transformation rate of ozone into HO(*) radicals. Results obtained demonstrate that the presence of GAL and HUM during SDBS ozonation increases the concentration of O(2)(-*) radicals in the medium, confirming that GAL and HUM act as initiating agents of ozone transformation into HO(*). It was also found that this effect was smaller with a larger molecular size of the acid. Presence of GAL and HUM during SDBS removal by O(3)/H(2)O(2), O(3)/GAC, and O(3)/PAC systems also increases the SDBS degradation rate, confirming the role of these compounds as initiators of ozone transformation into HO(*) radicals.

Adsorption of sodium dodecylbenzenesulfonate on activated carbons: effects of solution chemistry and presence of bacteria.

The objective of the present investigation was to determine the effectiveness of activated carbon in removing sodium dodecylbenzenesulfonate (SDBS) and to analyze the chemical and textural characteristics of the activated carbons that are involved in the adsorption process. Studies were also performed on the influence of operational variables (pH, ionic strength, and presence of microorganisms) and on the kinetics and interactions involved in the adsorption of this pollutant on activated carbon. The kinetics study of SDBS adsorption revealed no problems in its diffusion on any of the activated carbons studied, and Weisz-Prater coefficient (C WP) values were considerably lower than unity for all activated carbons studied. SDBS adsorption isotherms on these activated carbons showed that: (i) adsorption capacity of activated carbons was very high (260-470 mg/g) and increased with larger surface area; and (ii) dispersive interactions between SDBS and carbon surface were largely responsible for the adsorption of this pollutant. SDBS adsorption was not significantly affected by the solution pH, indicating that electrostatic adsorbent-adsorbate interactions do not play an important role in this process. The presence of electrolytes (NaCl) in the medium favors SDBS adsorption, accelerating the process and increasing adsorption capacity. Under the working conditions used, SDBS is not degraded by bacteria; however, the presence of bacteria during the process accelerates and increases SDBS adsorption on the activated carbon. Microorganism adsorption on the activated carbon surface increases its hydrophobicity, explaining the results observed.