Biomedical subjects

F Javier Rivas

Publications and source records attributed to F Javier Rivas.

7 recordsLinked to original sources

PubMed2006

Polycyclic aromatic hydrocarbons sorbed on soils: a short review of chemical oxidation based treatments.

A brief review is completed on the chemical oxidation of PAHs contaminated soils. Previously, the adsorption and extraction processes are also documented and discussed. The tree main technologies reported in the specialised literature include the use of ozone, hydrogen peroxide (with or without ferrous iron addition) and high temperature pressurized water (both in sub- and super-critical conditions) in the presence of an added oxidant like hydrogen peroxide, oxygen, persulfate, etc. Each process is detailed by the influence of the main operating variables reported in the literature (i.e. presence of organic matter, soil type, reagents dosage, etc.), the kinetics and the description of integrated treatments (i.e. chemical oxidation + biodegradation).

Environmental Pollutants↗

PubMed2005

Phenol and substituted phenols AOPs remediation.

The oxidation of phenol and two substituted species (4-nitrophenol and 4-chlorophenol) has been carried out by means of the O3, UV-vis, O3+UV-vis, TiO2+UV-vis, O(3)+UV-vis+TiO2 and O3+TiO2 systems. From UV-vis experiments, the quantum yield of these organics has been calculated (0.018, 0.005 and 0.017 mol per Einstein for phenol, 4-nitrophenol and 4-chlorophenol, respectively). Broadly speaking, the addition of titania powder results in a slight inhibition of the parent compound degradation rate, although a positive effect is experienced when measuring the chemical oxygen demand (COD) and total organic carbon (TOC) removals. Amongst the technologies investigated, those combining ozone and radiation show the best efficiency in terms of phenols elimination and also COD and TOC decay rates. A simple economy analysis of the processes illustrates how the combinations O3+UV-vis and O3+UV-vis+TiO2 are the most attractive technologies, although some additional considerations have to be taken into account.

Chlorophenols↗

PubMed2004

Stabilized leachates: sequential coagulation-flocculation + chemical oxidation process.

The combined sedimentation-chemical oxidation treatment of medium-stabilized landfill leachates has been investigated. The sequence of stages implemented was: (a) coagulation-flocculation by pH decrease (pH 2) to acidic conditions (COD removal approximately 25% related to COD0 approximately 7500 ppm); (b) coagulation-flocculation by Fe(III) addition (0.01 M) at pH 3.5 (COD removal approximately 40% related to COD of supernatant after step (a); (c) Fenton (Fe(III) = 0.01 M; H2O2 = 1.0 M) oxidation (COD removal approximately 80% related to COD of supernatant after step (a); and (d) coagulation-flocculation of Fenton's effluent at pH 3.5 (COD removal approximately 90% related to COD of supernatant after step (a). The use of Kynch theory allows for the design of clarifiers based on the amount of solids fed. For a general example of 1000 m3 day(-1) of a feeding stream, clarifier area values of 286,111 and 231 m2 were calculated for compacting indices of 3.7, 2.67 and 2.83 corresponding to the first, second and third consecutive sedimentation processes, respectively, (steps (a), (b) and (d)).

Environmental Pollution↗

PubMed2004

Wet peroxide degradation of atrazine.

The high temperature (150-200 degrees C), high pressure (3.0-6.0 MPa) degradation of atrazine in aqueous solution has been studied. Under these extreme conditions atrazine steadily hydrolyses in the absence of oxidising agents. Additionally, oxygen partial pressure has been shown not to affect atrazine degradation rates. In no case mineralisation of the parent compound was observed. The addition of the free radical generator hydrogen peroxide to the reaction media significantly enhanced the depletion rate of atrazine. Moreover, partial mineralisation of the organics was observed when hydrogen peroxide was used. Again, oxygen presence did not influence the efficiency of the promoted reaction. Consecutive injections of hydrogen peroxide throughout the reaction period brought the total carbon content conversion to a maximum of 65-70% after 40 min of treatment (suggesting the total conversion of atrazine to cyanuric acid). Toxicity of the effluent measured in a luminometer decreased from 93% up to 23% of inhibition percentage. The process has been simulated by means of a semi-empirical model.

Atrazine↗

PubMed2004

Aqueous ozone decomposition onto a Co2O3-alumina supported catalyst.

The aqueous ozone decomposition in the presence of a Co2O3-Alumina catalyst was investigated. Activity and estability assays were conducted by reusing the same catalyst in consecutive runs. The catalyst was shown to significantly increase the ozone abatement rate without loss in activity after five consecutive experiments. The process can be acceptably simulated by a double homogeneous-heterogeneous decomposition mechanism. An increase in the working temperature resulted in an opposite effect by increasing the extension of the homogeneous decomposition and lowering the extension of the heterogeneous decomposition. Similarly, different trends were observed by adding two distinct free radical scavengers (terc-butyl alcohol and carbonates).

Aluminum Oxide↗

PubMed2003

Stabilized leachates: ozone-activated carbon treatment and kinetics.

Ozone has been used as a pre-oxidation step for the treatment of stabilized leachates. Given the refractory nature of this type of effluents, the conversion of some wastewater quality parameters has been moderate after 1 h of ozonation (i.e. 30% chemical oxygen demand (COD) depletion). Ozone uptake was calculated in the interval 1.3-1.5 g of ozone per gram of COD degraded. An optimum dose of ozone has been experienced in terms of biodegradability of the processed effluent (60 min of treatment, 1 x 10(-3) mol L(-1) ozone inlet feeding concentration and 50 L h(-1) gas flow-rate). pH and other typical hydroxyl radical generator systems exerted no influence on the efficiency of the process, suggesting the negligible role played by the indirect route of oxidation (generation of hydroxyl radicals). The ozonated effluent was thereafter treated in a second adsorption stage by using a commercial activated carbon. Removal levels up to 90% of COD in approximately 120 h were experienced for adsorbent dosages of 30 g L(-1). Both steps, the single ozonation and the adsorption stage have been modelled by using different pseudoempirical models.

Carbon↗

PubMed2003

Fenton-like oxidation of landfill leachate.

The treatment of stabilized leachates by means of Fenton's like reagent [Fe(III)-H2O2] has been studied. It has been demonstrated that the oxidation state of the catalyst does not influence the efficacy of the process in terms of chemical oxygen demand depletion profiles. The abrupt increase in temperature experienced in oxidation experiments involves a wastage of hydrogen peroxide diminishing the fraction of this reagent addressed at removing COD. If temperature is kept constant, the hydrogen peroxide uptake is 10 mg of H2O2 consumed per mg of COD abated (from 15 to 30 degrees C). Working temperatures above 30 degrees C does not lead to additional COD conversion, contrarily, the percentage of wasted H2O2 is increased. A rough economic analysis of the process indicates that this treatment can be a suitable alternative to deal with this type of effluents.

Hydrogen Peroxide↗