Marisol D. Labas

Scaling up of a photoreactor for formic acid degradation employing hydrogen peroxide and UV radiation

A model for scaling up a homogeneous photoreactor was developed and experimentally verified in a pilot-plant-size apparatus. The procedure is exemplified by the oxidation of dilute aqueous HCOOH solutions with UV radiation (254 nm) and H2O2. First, the kinetic model and the kinetic parameters of the HCOOH degradation were obtained in a well-stirred, small, batch flat-plate photoreactor (volume=70 ml). The method employed in the analysis of the experimental results yielded reaction-rate expressions for HCOOH and H2O2 that were independent of the reactor configuration. These kinetic equations and the corresponding kinetic constants were then used in a mathematical, fully deterministic model of a continuous-flow, 2-m-long, annular reactor (0.0065 m2 of cross section for flow) operating in a laminar-flow regime to predict exit concentrations of HCOOH. Irradiation was provided in both cases by two different types of germicidal lamps. No additional experiments were made to adjust the reactor-model parameters. Theoretical predictions from the representation of the reactor performance obtained were compared with experimental data furnished by experiments in the much-larger-size, cylindrical-flow reactor. Results showed good agreement for the range of variables explored; they corresponded to expected operating conditions in water streams polluted with low concentrations of organic compounds.

Water disinfection with UVC radiation and H2O2. A comparative study

A generalized kinetic model resulting from several modifications of the one originally known as the Series Event Model has been applied to describe three different disinfection processes and compare their efficiencies. The work was performed in a well-defined, versatile batch reactor employing Escherichia coli as a subrogate bacteria. The following systems were studied: (i) UVC radiation alone, (ii) hydrogen peroxide alone and (iii) UVC radiation combined with hydrogen peroxide. The kinetic parameters of the three models were determined. Within the range of studied operating conditions, the use of UVC alone has shown to produce the best results.

A novel approach to explain the inactivation mechanism of Escherichia coli employing a commercially available peracetic acid

The chemical inactivation of Escherichia coli employing a commercial mixture of peracetic acid (PAA) was studied. For this purpose, experiments were carried out using dilutions of the unmodified mixture, and also the same mixture but altered with hydrogen peroxide (HP) previously inhibited. Also, these results were compared to those obtained before employing HP alone. It was found that the mixture is much more efficient than HP and PAA acting separately. Furthermore, it was found that PAA without HP is much more efficient than HP alone. A plausible explanation is presented. The homolysis of PAA would give rise to a chain reaction that generates a significant number of highly oxidizing radicals. An attacking scheme to bacteria in two stages is proposed, where the initial step, mainly caused by PAA, is very fast and eliminates some specific components of the bacteria that would otherwise inhibit the parallel action of HP. Thereafter, the emergence of a potentiating synergetic action of the second oxidant seems to be immediately unveiled.

Degradation of a mixture of pollutants in water using the UV/H2O2 process.

The degradation reaction of a simple mixture of pollutants (dichloroacetic acid + formic acid) employing H2O2 and UVC radiation (253.7 nm) has been studied in a well-mixed reactor which operates inside a recycling system. The aim of this work is to develop a systematic methodology for treating degradation of mixtures of pollutants, starting from a rather manageable system to more complex aggregates. In this contribution, the effects of different variables such as hydrogen peroxide/pollutant mixture initial concentration ratio, pH and incident radiation at the reactor wall were studied. The results show that the best degrading conditions are: pH = 3.5 and hydrogen peroxide concentrations from 3.9 to 11.8 mM (134-400 mg/L), for initial concentrations of 1.10 and 0.39 mM for formic acid and dichoroacetic acid respectively (50 mg/L for both pollutants). The influence of the incident radiation at the reactor wall on the degradation rates of the mixture is significant. In addition to this, it has been shown that in the employed aqueous solution no stable reaction intermediates are formed. On this basis, a complete reaction scheme for the mixture is proposed that is suitable for a reaction kinetics mathematical modeling of the mixture and further studies of increasing complexity.

Kinetic model of water disinfection using peracetic acid including synergistic effects

The disinfection efficiencies of a commercial mixture of peracetic acid against Escherichia coli were studied in laboratory scale experiments. The joint and separate action of two disinfectant agents, hydrogen peroxide and peracetic acid, were evaluated in order to observe synergistic effects. A kinetic model for each component of the mixture and for the commercial mixture was proposed. Through simple mathematical equations, the model describes different stages of attack by disinfectants during the inactivation process. Based on the experiments and the kinetic parameters obtained, it could be established that the efficiency of hydrogen peroxide was much lower than that of peracetic acid alone. However, the contribution of hydrogen peroxide was very important in the commercial mixture. It should be noted that this improvement occurred only after peracetic acid had initiated the attack on the cell. This synergistic effect was successfully explained by the proposed scheme and was verified by experimental results. Besides providing a clearer mechanistic understanding of water disinfection, such models may improve our ability to design reactors.

Dose Estimation Methodology for the UV Inactivation of Bioaerosols in a Continuous-Flow Reactor

Abstract Indoor air microbial pollution may be responsible for various human allergies and diseases. To reduce exposure, airborne bacteria can be directly controlled through devices that employ ultraviolet-C (UV-C) radiation. In this study, a continuous annular photo-reactor was used to evaluate the inactivation dose for two species: Gram-negative Escherichia coli and Pseudomonas aeruginosa. In order to provide meaningful results, a comprehensive kinetic modeling was performed, which included the evaluation of optical properties of the microorganisms and the calculation of radiation field inside the reactor. In this way, intrinsic inactivation rates could be obtained. From the reactor modeling and the experimental data sets, the first order inactivation rate or UV susceptibility for E. coli was 0.1055 m2 J−1, while for P. aeruginosa the obtained value was 0.2579 m2 J−1. The approach used allows a straightforward scaling-up of the process for real applications and microorganism species involved. Copyright