Natividad Miguel

Evaluation of trihalomethane formation potential in function of oxidation processes used during the drinking water production process.

The presence of natural organic matter (NOM) in both surface and groundwater supplies produces toxic by-products, mainly trihalomethanes (THMs), during oxidation steps in drinking water production. This research work shows the efficiency of different advanced oxidation processes (AOPs) based on ozone for the degradation of precursors of trihalomethanes in aqueous solutions. Completed treatments comprised different preoxidation processes (chlorination and AOP: O(3), O(3)/H(2)O(2), O(3)/TiO(2) and O(3)/H(2)O(2)/TiO(2)), adsorption with PAC (optional operation), coagulation-flocculation and final postchlorination applied to synthetic samples which were prepared by dilution of the soluble fraction of a humic solution. A direct chlorination of synthetic humic samples which display dissolved organic carbon close to 3 mg l(-1) produced a THM concentration of around 1600 microg CCl(3)l(-1) (measured as THMFP). Comparisons between the trihalomethane formation potential of initial synthetic samples and samples treated by prechlorination and coagulation-flocculation-decantation show that the main factor responsible for THM reduction is the coagulation-flocculation process since a decrease of 90% is achieved. Considering the various completed treatments studied, the most recommendable include preoxidation by ozonation, adsorption by PAC, coagulation-flocculation using aluminium sulphate followed by decantation and final postchlorination.

Bactericidal Effectiveness of O3, O3/H2O2 and O3/TiO2 on Clostridium perfringens

The purpose of this research is to evaluate the bactericidal capacity of different Advanced Oxidation Treatments (AOTs) based on ozone: ozone, ozone/hydrogen peroxide and ozone/titanium dioxide on a wild strain of Clostridium perfringens, a fecal bacterial indicator in drinking water. The dose of ozone consumed ranges from 0.6 mg L−1 min−1 to 5.13 mg L−1 min−1 depending on the process and on the sample. In the treatments combined with O3, H2O2 dose utilized is 0.04 mM and TiO2 dose, 1 g L−1. In order to evaluate the influence of natural organic matter and suspension solids over the disinfection rate, treatments are performed with two types of water – natural water from Ebro River (Zaragoza, Spain) and NaCl solution 0.9%. To achieve 4 log units of inactivation, 3.6 mg O3 L−1 is necessary in O3 treatment, 4.25 mg O3 L−1 in O3/TiO2 system and 2.7 mg O3 L−1 in O3/H2O2 after processing the natural water. In NaCl solution, to get the same inactivation, 0.42 mg O3 L−1 is necessary in O3 treatment, 1.15 mg O3 L−1 in O3/TiO2 system and 0.06 mg O3 L−1 in O3/H2O2 process. Even though the three treatments studied have a high bactericidal activity due to the number of surviving bacteria decreases to non-detectable levels, O3/H2O2 is the most effective system for eliminating C. perfringens cells in a lower contact time, followed by O3 and finally O3/TiO2 system.

Photocatalytic Degradation of Pesticides in Natural Water: Effect of Hydrogen Peroxide

The aim of this paper is to evaluate the effectiveness of photocatalytic treatment with titanium dioxide in the degradation of 44 organic pesticides analyzed systematically in the Ebro river basin (Spain). The effect of the addition of hydrogen peroxide in this treatment is studied, and a monitoring of effectiveness of photocatalytic processes is carried out by measurements of physical-chemical parameters of water. The application of photocatalytic treatment with 1 g L−1 of TiO2 during 30 minutes achieves an average degradation of the studied pesticides of 48%. Chlorine demand, toxicity, and dissolved organic carbon (DOC) concentration of water are reduced. If hydrogen peroxide is added with a concentration of 10 mM, the average degradation of pesticides increases up to 57%, although chlorine demand and toxicity of water increase while DOC concentration remains unchanged with this treatment. The application of either photocatalytic treatments does not produce variations in the physical-chemical parameters of water, such as pH, conductivity, colour, dissolved oxygen, and hardness. The pesticides which are best degraded by photocatalytic treatments are parathion methyl, chlorpyrifos, α-endosulphan, 3,4-dichloroaniline, 4-isopropylaniline, and dicofol while the worst degraded are HCHs, endosulphan-sulphate, heptachlors epoxide, and 4,4′-dichlorobenzophenone.

Bioaccumulation of pathogenic bacteria and amoeba by zebra mussels and their presence in watercourses.

Dreissena polymorpha (the zebra mussel) has been invading freshwater bodies in Europe since the beginning of the nineteenth century. Filter-feeding organisms can accumulate and concentrate both chemical and biological contaminants in their tissues. Therefore, zebra mussels are recognized as indicators of freshwater quality. In this work, the capacity of the zebra mussel to accumulate human pathogenic bacteria and protozoa has been evaluated and the sanitary risk associated with their presence in surface water has also been assessed. The results show a good correlation between the pathogenic bacteria concentration in zebra mussels and in watercourses. Zebra mussels could therefore be used as an indicator of biological contamination. The bacteria (Escherichia coli, Enterococcus spp., Pseudomonas spp., and Salmonella spp.) and parasites (Cryptosporidium oocysts and free-living amoebae) detected in these mussels reflect a potential sanitary risk in water.

Synergistic effect of the presence of suspended and dissolved matter on the removal of cyanide from coking wastewater by TiO2 photocatalysis

ABSTRACT This study assesses the influence of the presence of suspended and dissolved matter on the efficiency of TiO2 photocatalysis for the removal of cyanide from coking wastewater. Photocatalytic processes were carried out at basic pH (pH 9) with titanium dioxide (1 g/L), artificial radiation (290–800 nm) and during different time periods (20–100 min). The first assays applied in aqueous solutions achieved promising results in terms of removing cyanide. The maximum cyanide removal obtained in coking wastewater was 89% after 80 min of irradiation in the presence of suspended and dissolved matter. The presence of suspended matter composed of coal improves the efficiency of the photocatalytic process due to the synergistic effect between carbon and TiO2. The absence of dissolved matter also improves the process due to the minimization of the hydroxyl radical scavenging effect produced by carbonate and bicarbonate ions. On the other hand, the presence of certain species in the real matrix such as silicon increases the activity of the titanium dioxide catalyst. In consequence, the improvement achieved by the photocatalytic process for the removal of cyanide in the absence of dissolved matter is counteracted.

Study of the Presence of Pesticides in Treated Urban Wastewaters

The increase of the industrial activity and the consequent economic and social development have produced, at least until some years ago, a growth of big cities which leads and complicates the supply of one of the most important elements to the life, “water”. Nowadays, faced with the growing water demand and the hydric resources shortage, the reuse of treated water is considered as a possible solution in order to increase existing resources. However, all effluents can`t be reused since environmental minimum flows have to be guaranteed downstream of the dumping (Ormad, 2011). The water reuse is the application, before its return to the public water resources and the terrestrial maritime one to a new exclusive use of waters that, having been used by who derived them, they have been subjected to a process or processes of treatment established in the corresponding authorization of dumping and to the necessary in order to get the quality required in function of uses to which it goes to be destined. As well, reuse waters are treated wastewaters that have been subjected to an additional or complementary process which is capable to adapt its quality to the destined use. All this is carried out in reclamation plants, group of installations where treated wastewaters are subjected to additional treatments which can be needed in order to adapt the water quality to the destined use (Royal Decree 1620/2007). Waters which go to be reclaimed, it is, treated wastewaters, are waters that must obey the specifications of Directive 91/271/EEC (Directive 91/271/EEC). However, in these waters can exist some substances which can be pollutants. In general, the composition of these waters mainly depends on two factors: the industrial contribution to the urban dumping and the type of water treatment in the wastewater treatment plant (WWTP). In spite of this, in general, these waters are characterized by: The presence of a great variety of pathogenic germs The presence of organic matter, with a Biologycal Oxygen Demand 5-day (BOD5) up to 25 mg L-1 and a Chemical Oxygen Demand (COD) up to 125 mg L-1 (according to the current legislation). In this generic group, there are two types of organic matter: • Non Hazardous Organic Matter: This organic matter is mayoritary composed by compunds which haven’t degraded in the WWTP. This is because they are refractary compounds or the achieved yields aren’t of 100%; they are organic substances non toxic like carboxilic acids, esters, proteins, carbon hydrates, aminoacids, polihydroxilated alcohols, etc.

Enterococcus sp. Inactivation by Ozonation in Natural Water: Influence of H2O2 and TiO2 and Inactivation Kinetics Modeling

ABSTRACT This article presents the results about the disinfectant power of treatments based on the application of ozone (578 mg O3 h−1) and ozone combined with TiO2 (1 g L−1) and H2O2 (0.04 mM) on Enterococcus sp., a bacteria indicator used in the control of water quality. The results show that all the ozone-based treatments under study achieve the inactivation of Enterococcus sp. solution in natural water. Moreover, the combination of ozone with H2O2 or TiO2 lightly improves the inactivation of Enterococcus sp. compared to the ozonation. However, the treatment with O3, H2O2 and TiO2 is less effective than the use of O3, O3/H2O2 or O3/TiO2. Finally, the primary mathematical models are applied (Hom, biphasic and Mafart) and they adequately describe the disinfection kinetics of the ozonation treatments studied for Enterococcus sp.

Limitations of the removal of cyanide from coking wastewater by ozonation and by the hydrogen peroxide-ozone process

The purpose of this study is to compare the efficiency of ozonation and the hydrogen peroxide-ozone process for the removal of cyanide from coking wastewater. The most efficient oxidation process is combined with coagulation-flocculation-decantation and lime-soda ash softening pretreatments. The oxidation in aqueous solution and industrial wastewater (at pH 9.5-12.3) by O3 was carried out using a range of concentration of consumed O3 from 10 to 290 mg/L. A molar ratio of H2O2/O3 from 0.1 to 5.2 with different concentrations of O3 constants was used for the H2O2-O3 process. The maximum cyanide removal obtained in coking wastewater was 90% using a mass ratio of O3/CN(-) of 9.5. Using lower concentrations of O3, cyanide is not removed and can even be generated due to the presence of other cyanide precursor organic micropollutants in the industrial matrix. The concentration of O3 is reduced to half for the same cyanide removal efficiency if the pretreatments are applied to reduce the carbonate and bicarbonate ions. The cyanide removal efficiency in coking wastewater is not improved if the O3 is combined with the H2O2. However, the preliminary cyanide removal treatment in aqueous solution showed an increase in the cyanide removal efficiency for the H2O2-O3 process.

Influence of the Activated Carbon Nature and the Aqueous Matrix on the Pesticides Adsorption

Water flowing through surface and/or subsoil acquires a chemical composition due to its dissolution effect on soluble minerals of rocks and organic compounds deriving from the degradation of organic matter. This natural composition of water is basically altered by four pollution sources: domestic wastewaters, industrial wastewaters, uncontrolled wastewaters and run-off pollution in agricultural areas. The latter can result in the presence of pesticides in natural waters, because these compounds can pass through the soil and subsoil and pollute surface and groundwaters which are supplies sources for water intended for human consumption. Pesticides are a group of artificially synthesized substances used to fight pests and improve agricultural production. However, they are generally toxic for living organisms and are very difficult to degrade, being toxic agents with persistent and bioaccumulative effects. In spite of their benefits in the agriculture, they have undesirable effects due to its toxicity, carcinogenesis and mutagenesis (Becker & Wilson, 1980; Kouras et al., 1998). In Europe, pesticides are considered Hazardous Pollutants in accordance with current legislation relating to water (Directive 2000/60/CE; Directive 2006/11/CE). In the Ebro River Basin (Spain), these substances are controlled via a Pesticides Control Network, which systematically analyzes 44 organic pesticides in surface waters. These pesticides were selected in accordance with their appearance in lists of hazardous substances and/or their high level of use in Spanish agriculture (Claver et al., 2006). Among these substances, there are a big variety of pesticides, such as triazines, urea derivates, drins, etc. Although the concentration of these substances detected in natural waters is generally very low, the maximum permissible concentration in human drinking waters in Spain is often exceeded (ROYAL DECREE 140/2003), which establishes a limit of 0.5 μg L-1 as the total amount of pesticides and 0.1 μg L-1 for any single pesticide. Consequently, the treatment used to produce drinking water must guarantee the removal of these types of substances or at least reduce their concentration below the limits established in current legislation. Systems of drinking water production consist of different stages depending on the initial water quality. Actually, a lot of drinking water plants use an adsorption stage onto activated