M.M. Ballesteros Martín

Degradation of a four-pesticide mixture by combined photo-Fenton and biological oxidation.

Complete degradation of a pesticide mixture by a combination of a photo-Fenton pretreatment and an activated-sludge batch reactor is demonstrated. Four commercial pesticides, Laition, Metasystox, Sevnol and Ultracid were chosen for this experiment. The active ingredients are, respectively, dimethoate, oxydemeton-methyl, carbaryl and methidathion. The original pesticide concentration was 200 mg L(-1). Biotreatment began after 31% photocatalytic mineralization, which after 5 h in a 6-L stirred batch-mode tank reactor with non-acclimated activated sludge, leaves the photo-Fenton effluent completely degraded. This biotreatment time is shorter than commonly found in municipal wastewater treatment plants (approximately 8-10 h). Therefore, the combined process is effective for rapid pesticide degradation in wastewater with complete removal of parent compounds and the associated DOC concentration. Nonetheless, assessment of this technology should take into account higher pesticide concentrations and how this factor affects both the photocatalytic and the biological oxidation.

Economic evaluation of the photo-Fenton process. Mineralization level and reaction time: The keys for increasing plant efficiency

The use of the solar photo-Fenton process is proposed to degrade Paracetamol in water in order to form biodegradable reaction intermediates which can be finally removed with a downstream biological treatment. Firstly, biodegradability enhancement with photo-Fenton treatment time has been evaluated; the minimum mineralization level should be at least 18.6% where Paracetamol has been degraded and biodegradability efficiency is higher than 40%. 20 mg L(-1) of Fe(2+) and 200 mg L(-1) of H(2)O(2) were selected in a lab-scale study looking at Paracetamols degradation rate and organic carbon mineralization rate. As a result of scaling up the process at a pilot plant, 157.5 mg L(-1) of Paracetamol (∼1 mM) was treated in 25 min of photo-Fenton treatment achieving the desired biodegradability. A further economic evaluation shows how the proposed treatment strategy markedly increases plant efficiency, resulting in an 83.33% reduction in reagent cost and a 79.11% reduction in costs associated with reaction time. Total cost is reduced from 3.4502 €/m(3) to 0.7392 €/m(3).

A comparative study of different tests for biodegradability enhancement determination during AOP treatment of recalcitrant toxic aqueous solutions

Four biodegradability tests (Pseudomonas putida bioassay, Zahn-Wellens test, BOD5/COD ratio and respirometry assay) have been used to determine the biodegradability enhancement during the treatment of wastewater containing 200 mg L(-1) of dissolved organic carbon (DOC) of a five commercial pesticides mixture (Vydate, Metomur, Couraze, Ditumur and Scala) by an advanced oxidation process (AOP). A comparative study was carried out taking into account repeatability and precision of each biodegradability test. Solar photo-Fenton was the AOP selected for pesticide degradation up to three levels of mineralization: 20%, 40% and 60% of initial DOC. Intra- and interday precisions were evaluated conducting each biodegradability test by triplicate and they were applied three times on different dates over a period of three months. Fishers least significant difference method was applied to the means, P. putida and Zahn-Wellens tests giving higher repeatability and precision. The P. putida test requires a shorter time to obtain reliable results using a standardized inoculum and constitutes a worthwhile alternative to estimate biodegradability in contrast to other less accurate or more time consuming methods.

Effect of pesticide concentration on the degradation process by combined solar photo-Fenton and biological treatment

The influence of pesticide concentration, expressed as dissolved organic carbon (DOC), on combined solar photo-Fenton and biological oxidation treatment was studied using wastewater containing a mixture of five commercial pesticides, Vydate, Metomur, Couraze, Ditumur and Scala. Two initial DOC concentrations, 200 mg L(-1) and 500 mg L(-1) were assayed. Variation in biodegradability with photocatalytic treatment intensity was tested using Pseudomonas putida. Thus the mineralisation required for combining with biodegradation of intermediates by activated sludge was 33% and 55% at 200 mg L(-1) and 500 mg L(-1), respectively. Biotreatment was carried out in a stirred tank in sequencing batch reactor (SBR) mode. As revealed by the biodegradation kinetics, intermediates generated at the higher pesticide concentration caused lower carbon removal rates in spite of the longer photo-Fenton treatment time applied. One strategy for treating water with high concentrations of pesticides and overcoming the low biodegradability of photo-Fenton intermediates is to mix it with a biodegradable carbon source before biological oxidation. This combination of photo-Fenton and acclimatized activated sludge in several SBR cycles led to complete biodegradation of a concentrated pesticide solution of 500 mg L(-1) DOC in approximately 5h with a carbon removal efficiency of 90%.

Confirming Pseudomonas putida as a reliable bioassay for demonstrating biocompatibility enhancement by solar photo-oxidative processes of a biorecalcitrant effluent.

Experiments based on Vibrio fischeri, activated sludge and Pseudomonas putida have been employed to check variation in the biocompatibility of an aqueous solution of a commercial pesticide, along solar photo-oxidative process (TiO(2) and Fenton reagent). Activated sludge-based experiments have demonstrated a complete detoxification of the solution, although important toxicity is still detected according to the more sensitive V. fischeri assays. In parallel, the biodegradability of organic matter is strongly enhanced, with BOD(5)/COD ratio above 0.8. Bioassays run with P. putida have given similar trends, remarking the convenience of using P. putida culture as a reliable and reproducible method for assessing both toxicity and biodegradability, as a substitute to other more time consuming methods.

Integration of Solar Photocatalysis and Membrane Bioreactor for Pesticides Degradation

Wastewater containing recalcitrant contaminants as pesticides can be treated by a coupled system which consists of a solar photo-Fenton pretreatment followed by a biological oxidation process. Membrane bioreactor technology (MBR) is particularly suitable for advanced biological treatment of wastewater containing biorecalcitrant compounds and shows a variety of advantages that make it a good alternative to be coupled with photo-Fenton, especially for water reclamation. In this sense, there is a lack of research about the integration of the photo-Fenton oxidation process with biodegradation in MBR. The aim of this work is to demonstrate the viability of the coupled system to treat toxic wastewater containing pesticides. The effluent obtained in the coupled system was high quality water ready to reuse, with low residual DOC concentration, absence of pesticides, absence of solids, and low turbidity values. The present study confirms that the combination of solar photo-Fenton and membrane bioreactors is an effective approach for the treatment of wastewaters polluted with pesticides, achieving carbon removal percentages higher than 95%.