Sixto Malato

Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination—A review

Nowadays there is a continuously increasing worldwide concern for development of alternative water reuse technologies, mainly focused on agriculture and industry. In this context, Advanced Oxidation Processes (AOPs) are considered a highly competitive water treatment technology for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. Although chemical oxidation for complete mineralization is usually expensive, its combination with a biological treatment is widely reported to reduce operating costs. This paper reviews recent research combining AOPs (as a pre-treatment or post-treatment stage) and bioremediation technologies for the decontamination of a wide range of synthetic and real industrial wastewater. Special emphasis is also placed on recent studies and large-scale combination schemes developed in Mediterranean countries for non-biodegradable wastewater treatment and reuse. The main conclusions arrived at from the overall assessment of the literature are that more work needs to be done on degradation kinetics and reactor modeling of the combined process, and also dynamics of the initial attack on primary contaminants and intermediate species generation. Furthermore, better economic models must be developed to estimate how the cost of this combined process varies with specific industrial wastewater characteristics, the overall decontamination efficiency and the relative cost of the AOP versus biological treatment.

Photocatalysis with solar energy at a pilot-plant scale: an overview

Abstract Advanced oxidation processes (AOPs) are characterized by a common chemical feature: the capability of exploiting the high reactivity of OH radicals in driving oxidation processes which are suitable for achieving the complete abatement and through mineralization of even less reactive pollutants. This paper reviews the use of sunlight to produce OH radicals. The experimental systems necessary for performing pilot-plant scale solar photocatalytic experiments are described. It outlines the basic components of these pilot plants and the fundamental parameters related to solar photocatalysis reactions. This paper summarizes also most of the research carried out at Plataforma Solar de Almeria (PSA) related with solar photocatalytic degradation of water contaminants. A description is given of how solar photocatalysis could become a significant segment of the wastewater treatment technologies related with the degradation of very persistent toxic compounds. It outlines also the decomposition of organic and inorganic contaminants and different examples are also shown for better comprehension of the ability of solar energy for carrying out oxidation and reduction processes. These examples include chlorophenols, chlorinated solvents, pesticides and cyanide. Besides, the possibility of using the photo-Fenton reaction illuminated with solar light opens the boundary where solar photocatalysis could be applied.

The photo-fenton reaction and the TiO2/UV process for waste water treatment − novel developments

Abstract Solar applications of photochemical waste water oxidation methods driven by UV and/or visible light, especially TiO2/UV and the Photo-Fenton reaction (Fe2+/H2O2/UV-VIS), have been investigated. Degradation results of 4-Chlorophenol and some other model compounds at laboratory scale are discussed. A photoreactor with immobilized TiO2 has led to a higher quantum efficiency than the suspension treatment. Electron densities were calculated to predict the oxidizing properties of UV irradiated TiO2. Al doped TiO2 powders showed better performance than undoped samples in laboratory scale degradation experiments. Experiments with different waste waters (e.g. landfill leachates, plastics industry, etc.) using the Fe2+/H2O2/UV-VIS system in a photoreactor prototype are reported. Solar treatment of a model waste water in a glass basin has been investigated. Furthermore, experiments performed at the Plataforma Solar de Almeria (Spain) with different methods, reactor types and waste waters are compared. According to a comparison of costing the solar driven Fenton reaction is a cheap method for water treatment, also for highly contaminated effluents.

Solar photocatalysis: a clean process for water detoxification

The photocatalytic degradation of various toxic organic compounds has been proposed as a viable process to detoxify drinking water. Irradiating pulverulent semi-conductors like TiO2 in suspension or fixed to various supports in aqueous solutions containing organic pollutants, creates a redox environment able to destroy these pollutants. Solar photocatalytic mineralization of organic water pollutants has a strong potential in the industrial destruction of toxic organics in water as this has been widely demonstrated in recent years, and the applications and target compounds are numerous. The aim of this paper is to present the basic principle of the photocatalysis and especially to show the various applications of the solar photocatalysis in the field of the decontamination of wastewater.

Degradation of fifteen emerging contaminants at μg L−1 initial concentrations by mild solar photo-Fenton in MWTP effluents

The degradation of 15 emerging contaminants (ECs) at low concentrations in simulated and real effluent of municipal wastewater treatment plant with photo-Fenton at unchanged pH and Fe=5 mg L(-1) in a pilot-scale solar CPC reactor was studied. The degradation of those 15 compounds (Acetaminophen, Antipyrine, Atrazine, Caffeine, Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole and Triclosan), each with an initial concentration of 100 microg L(-1), was found to depend on the presence of CO(3)(2-) and HCO(3)(-) (hydroxyl radicals scavengers) and on the type of water (simulated water, simulated effluent wastewater and real effluent wastewater), but is relatively independent of pH, the type of acid used for release of hydroxyl radicals scavengers and the initial H(2)O(2) concentration used. Toxicity tests with Vibrio fisheri showed that degradation of the compounds in real effluent wastewater led to toxicity increase.

Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation.

In this work, the photocatalytic degradation of the antibiotic sulfamethoxazole (SMX) by solar photo-Fenton at pilot plant scale was evaluated in distilled water (DW) and in seawater (SW). Degradation and mineralization of SMX were strongly hindered in SW compared to DW. The influence of H(2)O(2) and iron concentration on the efficiency of the photocatalytic process was evaluated. An increase in iron concentration from 2.6 to 10.4 mg L(-1) showed only a slight improvement in SMX degradation and mineralization. However, an increase in H(2)O(2) concentration up to 120 mg L(-1) during photo-Fenton in DW decreased SMX solution toxicity from 85% to 20%, according to results of Daphnia magna bioassays. The same behaviour was not observed after photo-Fenton treatment in SW. Despite 45% mineralization in SW, toxicity increased from 16% to 86% as shown by Vibrio fischeri bioassays, which suggests that the intermediates generated in SW are different from those in DW. A SMX degradation pathway during the photo-Fenton treatment in DW is proposed.

Photo-Fenton treatment of water containing natural phenolic pollutants

Phenolic compounds are known to be present in high concentrations in various types of agro-industrial wastes. As they are highly biorecalcitrant, the possibility of treatment by advanced oxidation processes should be investigated. In this work, six model phenolic compounds (vanillin, protocatechuic acid, syringic acid, p-coumaric acid, gallic acid and L-tyrosine) were chosen for a demonstration of degradation by photo-Fenton reaction, under artificial light in laboratory experiments in Vienna and under sunlight in pilot-plant experiments at the Plataforma Solar de Almería in Spain. All compounds were completely mineralised. No non-degradable intermediates were produced, either in experiments with single substances or in a more complex matrix of a mixture of phenolic compounds. The expected selectivity of the photo-Fenton reaction for aromatic compounds was proven by comparison of the decrease in total organic carbon with the removal of total phenolic content.

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor--IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H2O2 (kinetic study) and another with controlled H2O2 dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H2O2, nalidixic acid degradation was complete at 66 mM of H2O2 consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H2O2 dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO3- generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.

Applicability of the Photo-Fenton method for treating water containing pesticides

Abstract The Photo-Fenton process, i.e., the system Fe2+/H2O2/UV-Vis, was successfully applied to a mixture of ten commercially available pesticides that served as a model for a proposed recycling plant for pesticide bottles. Experiments with single pesticides revealed that although all of them were degradable, there were remarkable differences concerning the reaction rate. Sunlight driven pilot scale experiments with the complete mixture were conducted. For the pesticide mixture the initial pollutant concentration and the amount of iron was varied. The addition of oxalate and different modes of oxidant addition were tested in order to improve the process. Thereby, the reaction rate was increased, while the final degree of TOC reduction was affected only slightly. All the experiments carried out were considerably faster than the previously published results of degradation tests that applied solar driven TiO2/UV and TiO2/Na2S2O8/UV photocatalysis.

Degradation of the antibiotic amoxicillin by photo-Fenton process - Chemical and toxicological assessment

The influence of iron species on amoxicillin (AMX) degradation, intermediate products generated and toxicity during the photo-Fenton process using a solar simulator were evaluated in this work. The AMX degradation was favored in the presence of the potassium ferrioxalate complex (FeOx) when compared to FeSO(4). Total oxidation of AMX in the presence of FeOx was obtained after 5 min, while 15 min were necessary using FeSO(4). The results obtained with Daphnia magna biossays showed that the toxicity decreased from 65 to 5% after 90 min of irradiation in the presence of FeSO(4). However, it increased again to a maximum of 100% after 150 min, what indicates the generation of more toxic intermediates than AMX, reaching 45% after 240 min. However, using FeOx, the inhibition of mobility varied between 100 and 70% during treatment, probably due to the presence of oxalate, which is toxic to the neonates. After 240 min, between 73 and 81% TOC removal was observed. Different pathways of AMX degradation were suggested including the opening of the four-membered β-lactamic ring and further oxidations of the methyl group to aldehyde and/or hydroxylation of the benzoic ring, generating other intermediates after bound cleavage between different atoms and further oxidation to carboxylates such acetate, oxalate and propionate, besides the generation of nitrate and ammonium.