Jordi Bacardit

Simple Models for the Control of Photo-Fenton by Monitoring H2O2

Abstract It has been demonstrated that Photo-Fenton process is feasible for the remediation of wastewater containing multiple organic pollutants. In order to promote its industrialization, control strategies have to be defined and tested. The objective of the present work is to describe a mathematical equation that fits the amount of COD abated regarding the dose of H2O2. UVA Laboratory-scaled and solar up-scaled experiments are compared. Also two H2O2 supply strategies are compared; one in which H2O2 is added at the beginning of an experiment; the second, H2O2 is added in doses through an experiment. According to the results, simple equations have been found to fit experimental COD degraded depending on the amount of H2O2 supplied. There is also a ratio of COD degraded per amount of H2O2 consumed that fits a wide range of operating conditions. The ratio is estimated to be 0.51 (mg O2/mg H2O2) which can be considered as a stoichiometry of Photo-Fenton process in the current conditions.

Comparison between Ozonation and Photo-Fenton Processes for Pesticide Methomyl Removal in Advanced Greenhouses

So-called “Advanced Greenhouses” are a new approach to the concept of protected agriculture. Among other technological and structural improvements, these facilities give the possibility of recycling the irrigation surplus water, rich in lixiviates, salts, pesticides and its metabolites. After many cycles, the current is so concentrated on those substances that it becomes necessary for the presence of a membrane separation stage which brine, highly concentrated on those named pollutants, has to be treated before being sent to the public sewage system. Advanced Oxidation Processes, among other chemical treatments, can be considered an alternative to process this current effluent. In this work, concentrated aqueous solutions of methomyl as model pesticide (200 mg·L−1) have been subjected to two of those processes: ozonation and photo-Fenton reaction. Analysis of the elimination of the pesticide itself and the grade of mineralization achieved have shown how, while the ozonation is the most effective process decomposing the pesticide (eliminating the total concentration in 60 minutes), the photo-Fenton reaction mineralizes successfully the 40% of the total organic load (the ozonation only can cope with 20%) but only decompose a 40% of the pesticide. Evolution of biodegradability and toxicity of the effluent along both processes was also analyzed. Intermediates generated both by ozonation and photo-Fenton did not increase the biodegradability of the treated effluents. Nevertheless, while acute toxicity just after 15 minutes of treatment with ozone is notably higher than for raw solution, and it is maintained till the end of the experiment (120 min), though, toxicity along photo-Fenton reaction has two growing and decreasing regions, always shows lower values than the provoked during ozonation. None of the two assayed processes has been proved to increase biocompatibility of highly concentrated methomyl solutions.

Experimental design applied to photo-Fenton treatment of highly methomyl-concentrated water

This work is focused on the study of the suitability of the photo-Fenton process as a pretreatment for water highly contaminated with a methomyl commercial formulation in Advanced Greenhouses devices. Initial concentrations of reagents and pesticide were evaluated according to a central composite experimental design, with methomyl depletion and biocompatibility of the final effluent as response functions. A triad of optimal operation conditions could be determined, [Met.](0)=50 mg L(-1), [H(2)O(2)](0)=254 mg L(-1) and [Fe(2+)](0)=77 mg L(-1) for the best elimination yield and an acceptable BOD(5)/COD value, and initial concentration of methomyl can be established as the most important parameter for the performance of the treatment due to the limitations that impose on the hydrogen peroxide doses in the presence of the excipients of the commercial formulation.

Reverse osmosis membranes oxidation by hypochlorite and chlorine dioxide: spectroscopic techniques vs. Fujiwara test

Abstract The aim of this work was the study of degradation of a commercial polyamide membrane by two commonly employed oxidants for disinfection in seawater desalination, hypochlorite, and chlorine dioxide. A conventional reverse osmosis (RO) membrane is a thin film composite membrane composed of three different layers, a polyester support web, a microporous polysulfone interlayer, and a thin cross-linked polyamide barrier layer on the top surface, which is the active layer of the RO membrane. The degree of membrane degradation in seawater was evaluated in terms of decline in membrane performance calculated from permeability and salt rejection. In order to establish a relationship between the hydraulic properties and spectroscopic data, infrared and X-ray photoemission techniques (ATR-FTIR and XPS) were employed. The obtained results were compared with the Fujiwara test which is usually performed in membrane autopsies to check the degradation of polyamides with halogens. The chemical degradation of the su...

Fosetyl-Al photo-Fenton degradation and its endogenous catalyst inhibition

Interferences from many sources can affect photo-Fenton reaction performance. Among them, catalyst inhibition can be caused by the complexation and/or precipitation of iron species by the organic matter and salts present in the reaction media. This is the case of the oxidation of effluents containing organophosphorous fosetyl-Al. The degradation of this fungicide generates phosphate anions that scavenge iron and hinder Fe(II) availability. Experimental design was applied to artificially enlighten photo-Fenton reaction, in order to evaluate fosetyl-Al degradation. The performed experiments suggested how iron inhibition takes place. The monitoring of photo-Fenton reaction over a mixture of fosetyl-Al with other two pesticides also showed the interferences caused by the presence of the fungicide on other species degradation. Solar empowered photo-Fenton was also essayed for comparison purposes. Artificial and solar light photo-Fenton reactions were revealed as effective treatments for the elimination of tested fungicide. However, the phosphate ions generated during fosetyl oxidation decreased iron availability, what hampered organic matter degradation.

High salinity effect on bioremediation of pretreated pesticide lixiviates from greenhouses

Hydroponics culture greenhouses usually work in closed and semi-closed irrigation systems for nutrients and water-saving purposes. Photo-Fenton reaction has been revealed as an efficient way to depollute that kind of recycled effluents containing pesticides, even for high salinity concentrations. However, the inefficacy of organic matter chemical depletion imposes the use of a subsequent treatment. This work proposes the suitability of an integration of advanced oxidation process with a subsequent bioreactor to treat greenhouse lixiviates effluents at high or extremely high conductivity (salts concentration: up to 42 g L−1). As a first step in this study, the performance of a series of sequencing batch reactors was monitored in order to check the biocompatibility of photo-Fenton pretreated effluents depending on their salinity content. In the second step, those same pretreated effluents were loaded to a biofiltration column filled with expanded clay. Finally, bacterial 16S rRNA gene sequencing was carried out to analyse microbial diversity of the biomass developed in the column. Results stated that the chemical–biological coupled system is effective for the treatment of water effluents containing pesticides. The integrated system is able to deplete more than 80% of the organic load, even under extremely high salinity.