Montserrat Tobajas

Enhancement of cometabolic biodegradation of 4-chlorophenol induced with phenol and glucose as carbon sources by Comamonas testosteroni

The biological degradation of phenol and 4-chlorophenol (4-CP) by Comamonas testosteroni CECT 326T has been studied. Phenol and 4-CP were treated alone as a sole carbon and energy source, but only phenol was completely degraded by C. testosteroni. Since the presence of cosubstrates can enhance the toxic compounds removal by pure cultures, phenol and glucose were added as growth substrates for cometabolic transformation of 4-CP. High efficiencies were obtained in all the experiments carried out in presence of both cosubstrates. In spite of the fact that the addition of glucose reduced the lag phase of 4-CP removal, lower phenol concentrations were required to obtain the same degradation efficiencies. The cometabolic transformation of 4-CP was closely related with the extent of phenol removal. The values of the 4-CP/biomass concentration ratio (S/X) obtained for discriminating between complete (S/X ≤ 0.11) and partial 4-CP (S/X ≥ 0.31) transformation showed a narrower range than that reported in the literature. The extent of the cometabolic 4-CP transformation in the presence of phenol could be further enhanced by using glucose as an additional carbon and energy source. However, no significant influence of glucose concentration on 4-CP removal was observed over the concentration range studied.

Degradation of chlorophenoxy herbicides by coupled Fenton and biological oxidation

A combined treatment for the degradation of the chlorophenoxy herbicides 2,4-D and MCPA in water by means of Fenton and biological oxidation has been studied. The chemical oxidation step was necessary to achieve an efficient removal of these pollutants due to their toxicity and low biodegradability. Aqueous herbicide solutions (180mgL(-1)) were subjected to Fenton oxidation upon different H2O2 doses (from the theoretical stoichiometric amount referred to initial COD to 20% of this value). The toxicity and biodegradability tests of the Fenton effluents suggested that the ones resulting upon treatment with 80% and 60% of stoichiometric H2O2 were the optimal for subsequent biological treatment dealing with 2,4-D and MCPA, respectively. These effluents were treated in a sequencing batch reactor achieving nearly 90% conversion of organic matter measured as COD.

Coupling Fenton and biological oxidation for the removal of nitrochlorinated herbicides from water.

The combination of Fenton and biological oxidation for the removal of the nitrochlorinated herbicides alachlor, atrazine and diuron in aqueous solution has been studied. The H2O2 dose was varied from 20 to 100% of the stoichiometric amount related to the initial chemical oxygen demand (COD). The effluents from Fenton oxidation were analyzed for ecotoxicity, biodegradability, total organic carbon (TOC), COD and intermediate byproducts. The chemical step resulted in a significant improvement of the biodegradability in spite of its negligible or even slightly negative effect on the ecotoxicity. Working at 60% of the stoichiometric H2O2 dose allowed obtaining highly biodegradable effluents in the cases of alachlor and atrazine. That dose was even lower (40% of the stoichiometric) for diuron. The subsequent biological treatment was carried out in a sequencing batch reactor (SBR) and the combined Fenton-biological treatment allowed up to around 80% of COD reduction.

Assessment of toxicity and biodegradability on activated sludge of priority and emerging pollutants

ABSTRACT Several methods for evaluating the toxicity and biodegradability of hazardous pollutants (chlorinated compounds, chemical additives and pharmaceuticals) have been studied in this work. Different bioassays using representative bacteria of marine and terrestrial ecosystems such as Vibrio fischeri and Pseudomonas putida have been used to assess the ecotoxicity. Activated sludge was used to analyse the effect of those pollutants in a biological reactor of a sewage treatment plant (STP). The results demonstrate that none of the compounds is toxic to activated sludge, except ofloxacin to P. putida. The additives tested can be considered moderately toxic according to the more sensitive V. fischeri assays, whereas the EC50 values of the pharmaceuticals depend on the specific microorganism used in each test. Regarding the biodegradability, respirometric measurements were carried out for fast biodegradability assessment and the Zahn–Wellens test for inherent biodegradability. The evolution of the specific oxygen uptake rate (SOUR) showed that only diethyl phthalate was easily biodegradable and acetylsalicylic acid was partially biodegradable (98% and 65% degradation, respectively). The persistence of dichloromethane, ofloxacin and hidrochlorothiazide was confirmed along the 28 days of the Zahn-Wellens test whereas 1,1,1-trichloroethane showed inherent biodegradability (74% removal). Most of the chlorinated compounds, pharmaceuticals, bisphenol A and ethylenediaminetetraacetic acid were partially degraded in 28 d with total organic carbon (TOC) reduction ranging from 21% to 51%. Sulphamethoxazole showed certain biodegradation (50% removal) with TOC decrease around 31%, which indicates the formation of non-biodegradable by-products.

Ag-Coated Heterostructures of ZnO-TiO2/Delaminated Montmorillonite as Solar Photocatalysts

Heterostructures based on ZnO-TiO2/delaminated montmorillonite coated with Ag have been prepared by sol–gel and photoreduction procedures, varying the Ag and ZnO contents. They have been thoroughly characterized by XRD, WDXRF, UV–Vis, and XPS spectroscopies, and N2 adsorption, SEM, and TEM. In all cases, the montmorillonite was effectively delaminated with the formation of TiO2 anatase particles anchored on the clay layer’s surface, yielding porous materials with high surface areas. The structural and textural properties of the heterostructures synthesized were unaffected by the ZnO incorporated. The photoreduction led to solids with Ag nanoparticles decorating the surface. These materials were tested as photocatalysts for the degradation of several emerging contaminants with different nitrogen-bearing chemical structures under solar light. The catalysts yielded high rates of disappearance of the starting pollutants and showed quite stable performance upon successive applications.

A simple mathematical model of the process of Candida utilis growth in a bioreactor

A methodology is suggested in this paper for the description of microbial processes following a pattern similar to that used for the description of chemical processes in which physical and chemical phenomena occurring in reactors are considered. The description is based on stoichiometric relations, kinetics and mass transfer characteristics. For process simulation, only the kinetic parameters are necessary as experimental data. The stoichiometry of the conversion reactions is calculated by using the black box model which is based on elemental balances and from the yield of biomass from the C-source. The volumetric mass transfer coefficient is estimated by using a theoretical model based on a mechanical energy balance, Higbies penetration theory and Kolmogoroffs theory of isotrophic turbulence. It is shown that the method can be used to simulate the curves of biomass production, substrate consumption, variation of dissolved oxygen concentration and carbon dioxide production for batch cultures of Candida utilis conducted in an airlift reactor over a wide range of growth conditions.