dyna DYNA Dyna rev.fac.nac.minas 0012-7353 Universidad Nacional de Colombia 10.15446/dyna.v85n205.68503 Artículos Application of double filtration with granular activated carbon for Atrazine reduction on water treatment processes Aplicación de la doble filtración con carbón activado granular para la reducción de Atrazina en procesos de tratamiento de agua potable Fuentes-López Lina a Amézquita-Marroquín Claudia a Torres-Lozada Patricia a Study and Control of Environmental Pollution Research Group - ECCA, Faculty of Engineering, Universidad del Valle, Cali, Colombia. lina.fuentes@correounivalle.edu.co, claudia.amezquita@correounivalle.edu.co, patricia.torres@correounivalle.edu.co Universidad del Valle Study and Control of Environmental Pollution Research Group Faculty of Engineering Universidad del Valle Cali Colombia lina.fuentes@correounivalle.edu.co claudia.amezquita@correounivalle.edu.co patricia.torres@correounivalle.edu.co Apr-Jun 2018 85 205 184 190 25 10 2017 21 03 2018 04 05 2018 This is an open-access article distributed under the terms of the Creative Commons Attribution License Abstract

Atrazine is one of the most often used herbicides in the world. It reaches the surface water body by runoff, direct application or airborne dispersal. Conventional water treatment methods do not efficiently remove these types of pollutants, whereas granular activated carbon (GAC) adsorption is an adequate technique for the removal of organic compounds from water. In this work, the Atrazine reduction of water doped with two concentrations of Atrazine, was evaluated during the conventional treatment process (coagulation, flocculation, sedimentation and sand and anthracite filtration), followed by double filtration with two adsorbent granular media (vegetal and mineral GAC), which resulted in an efficient reduction of UV254 (86%) and Atrazine (99%).

 Resumen

La Atrazina es uno de los herbicidas de mayor aplicación en el mundo, ingresa a los cuerpos de agua superficial por escorrentía, aplicación directa o dispersión aérea. Los métodos de tratamiento convencional de agua no remueven eficientemente este tipo de contaminantes, mientras que la adsorción con Carbón Activado Granular (CAG), es una técnica apropiada para la remoción de compuestos orgánicos del agua. En este trabajo, se evaluó la reducción de Atrazina de un agua dopada con dos concentraciones Atrazina, durante el proceso de tratamiento convencional (coagulación, floculación, sedimentación y filtración con arena y antracita) seguido de una doble filtración con dos medios adsorbentes granulares (CAG de origen Vegetal y Mineral), la cual permitió obtener una eficiente reducción de UV254 (86%) y Atrazina (99%).

 Keywords: adsorption drinking water Atrazine granular activated carbon Palabras clave: adsorción agua potable Atrazina carbón activado granular 1. Introduction

Atrazine is an organochlorine herbicide from the triazine family and is used as a selective pre- and post-emergent herbicide to control weeds and as a non-selective herbicide in non-cultivated regions [1]. Being one of the most widely used herbicides in the world, particularly for energetic biomass crops such as maize and sugar cane [2], its annual global production is between 70,000 and 90,000 tons [3-5].

Due to its high water solubility, extensive use and persistence in soil, atrazine presents a high risk of leaching, resulting in the pollution of soils and underground and surface water sources [6], which presents a potential threat to human health due to its association with endocrine disruption and possible teratogenic and carcinogenic effects [4, 7, 8]. Authors such as Graymore 2001 [9] indicate that atrazine has been found in concentrations of up to 1000 μg/L in waters adjacent to treated fields and up to 80 μg/L in drinking water (DW).

In the production of DW, the conventional or complete treatment technology (coagulation, flocculation, sedimentation and conventional filtration), is most often used; however, most of these processes were not designed to remove organic compounds such as pesticides, which due to their heterogeneity are difficult to reduce [10,11]. In contrast, one of the most used and efficient techniques for the removal of organic compounds in water is adsorption [12]. Given that production and regeneration costs are its main limitation, different adsorbent media have been implemented, derived from low-cost materials such as tires, wood, bone, fruit peels and agricultural waste, with low inorganic content and high carbon content [12,13].

In this sense, the effectiveness of the conventional treatment comprised of clarification (coagulation, flocculation and sedimentation) and conventional filtration, followed by a second stage of filtration with two adsorbent media of mineral granular activated carbon (MAC) from bituminous coal, as well as vegetal granular activated carbon (VAC) made from coconut shell, was evaluated. Raw water from the Cauca River, doped with atrazine to reach concentrations close to 0.50 and 1.00 mg/L, was used.

 2. Methodology 2.1. Preparation and characterization of atrazine-doped water

Raw Cauca River Water, coming from the intake of the Puerto Mallarino drinking water treatment plant (DWTP), was doped with 0.44 and 0.86 mg/L atrazine. Turbidity (NTU), UV254 (cm-1: due to its use for the qualitative estimation of the presence of organic substances [14]) and atrazine (mg/L) were measured.

 2.2. Clarification

The clarification tests (coagulation - flocculation - sedimentation) were performed in jar test devices according to the recommendations of [15] and [16] (Table 1); the experimental unit corresponded to a two-liter acrylic jar. Ferric chloride (FeCl3) was used as coagulant due to its high use in DWTPs [17,18]; a constant coagulant dose (22 mg/L) was determined from previous jar tests.

Clarification test conditions

Source: The authors

 2.2. Conventional filtration

As the experimental unit for the conventional filtration and GAC filtration, transparent glass filters of 19 mm in inner diameter, 25 mm in nominal diameter and 40 cm in length were used; the filter bed thickness was 15 cm, with a metal mesh as support to avoid plugging the filter outlet with the filter medium [19-21]. The outlet consisted of a silicone hose with one end attached to the bottom part of the filter and the other end placed above the upper part of the filter bed to promote an available hydraulic load so that the bed would not run out of water (Figure 1). The experiments were performed in triplicate with a total of six experimental units.

Filtration experimental unit scheme. Source: The authors

For the conventional filtration, sand and anthracite were used with the configuration defined by [22]: sand (30%) with an effective size (d10) of 0.61 mm and anthracite (70%) with an effective size (d10) of 1.16 mm, with a flow rate of 12 ml/min. The filtration was performed for seven hours; the effluent water was subjected to the next phase of the treatment. Turbidity (NTU) (2130B) and UV254 (cm-1) (2510B) were measured every 15 minutes, and the atrazine (mg/L) (EPA 523) was measured at the beginning and end of the experiment [23].

2.3. GAC filtration

The water obtained from the conventional filtration was stored for the second filtration stage, which lasted four hours. The filtration columns consisted entirely of the selected adsorbent media: mineral granular activated carbon (MAC) and vegetal granular activated carbon (VAC) [24-26]. According to authors such as Mukherjee et al., 2007; Giraldo & Moreno 2008; Giraldo & Moreno 2012; and Vukčević et al., 2015 [27-30], the GAC adsorbent media must be washed several times to remove impurities and residual chemical substances from the GAC activation process; in this case, the media were washed seven times with distilled water. The same was performed for sand and anthracite.

The experiments were performed in triplicate using three experimental units for each adsorbent medium (MAC and VAC) and atrazine concentration, resulting in a total of 12 experimental units. A flow distribution system and a constant load tank were used for the dosing of the conventional filtered water. Figure 2 shows the experimental configuration for one concentration.

Flow distribution system and filter configurations for each evaluated atrazine concentration. Source: The authors

The filtration was performed for four hours, and the samples collected during the filtration test for the two concentrations were measured for turbidity (NTU) and UV254 (cm-1) every 15 minutes during filtration; the atrazine (mg/L) was measured at the beginning and end of the process.

 2.4. Statistical analysis

An analysis of variance (ANOVA), using the statistical program Minitab 17 [31], was performed to determine if there were statistically significant differences between the evaluated filter media configurations.

 3. Results and discussion 3.1. Clarification

Table 2 presents the turbidity, UV254 and atrazine concentration of raw water, atrazine-doped water and clarified water.

Characterization of raw, doped and clarified water.

Source: The authors

Table 2 shows that the addition of atrazine to the doped water did not alter the turbidity level because it is primarily related to colloidal and suspended matter [32]. In contrast, the UV254 absorbance increased with the addition of atrazine due to its relationship with the dissolved material and the organic matter content [33,34].

After the clarification process (coagulation, flocculation and sedimentation), the turbidity decreased by 98 and 99% for concentrations 1 and 2, respectively. In contrast, the low performance was confirmed based on organic compound reduction in terms of UV254 and the atrazine concentration; the UV254 efficiency reductions were 38 and 39% for concentrations 1 and 2, respectively.

Regarding atrazine reduction, a reduction efficiency of 20% was obtained for concentration 2. Notably, atrazine is characterized by its high solubility (28 mg/L) and partition coefficient (2.30) [35]. According to [36], compounds with partition coefficients above 3.20 are more easily reduced by this type of process; therefore, it is likely that conventional processes are not very effective for the reduction of atrazine.

3.2. Evaluation of conventional filtration and GAC filtration 3.2.1. Characteristics of filter media and adsorbents

Table 3 shows the characteristics of the filter media and absorbents used.

Characteristics of the filter media and adsorbents

Source: Supplier information

Sand and anthracite, which have a smaller effective particle size and uniformity coefficient than GAC, which in turn favors the entrapment of particles that cause turbidity, were used for the conventional filtration. Thus, the conventional media are expected to have a higher turbidity reduction efficiency than that of GAC [37,38].

The GAC media used differ in the precursor and the effective particle size. In this study, MAC presented lower values; in its manufacture, there is a tendency to form a wide range of pores, and therefore, it is more often used for applications in which the compounds to be retained are of different molecular sizes, such as the substances in water, whereas the VAC manufactured from coconut shell tends to present small pores [12]. According to these characteristics, it could be expected that MAC would present a greater decrease in organic compounds.

 3.2.2. Turbidity

Figure 3 shows a box-plot of the turbidity results of the conventional and GAC filtrations for the two concentrations used.

Turbidity box-plot for: (a) Conventional filtration and (b) GAC filtration for the two evaluated concentrations. Source: The authors

In Colombia, the maximum permissible level of turbidity in drinking water is 2 NTU [39], whereas the Pan American Health Organization (PAHO) [40] recommends a turbidity below 1.00 NTU for achieving an effective disinfection, and the World Health Organization (WHO) [14] recommends that the turbidity median must be lower than 0.10 NTU. The Environmental Protection Agency (EPA) [41] establishes 1.00 NTU as the maximum limit for treated water and a 95th percentile of 0.15 NTU and a maximum of 0.30 NTU for the control of the microbiological risk due to cryptosporidium.

With the conventional sand and anthracite filtration, minimum values between 0.05 and 0.09 NTU were achieved for concentrations 1 and 2, respectively; in the second filtration with GAC, the minimum values obtained were higher (between 0.15 and 0.21 NTU); in this sense, authors such as Feng et al., 2012 [42], indicate that filters that use GAC are more susceptible to turbidity infiltration. Another important aspect that could affect the turbidity of the GAC filtration effluent is the washing of the adsorbent medium [27-30].

The statistical analysis by the ANOVA test shows that for the conventional filtration, there are no significant differences between the two evaluated pesticide concentrations. Likewise, no significant differences were found between the two adsorbent media used (MAC and VAC) with each evaluated pesticide concentration; notably, in all cases, the data were below 2.00 NTU, the upper limit of the Colombian standard for drinking water [39].

 <bold>3.2.3. UV</bold> <sub>254</sub> <bold>absorbance</bold>

Figure 4 shows a box-plot of the UV254 results of the conventional filtration and GAC filtration for the two concentrations used.

UV<sub>254</sub> box-plot for: (a) Conventional filtration and (b) GAC filtration, for the two evaluated concentrations. Source: The authors

The conventional filtration effluent varied between 0.065 and 0.092 cm-1 for concentration 1 and between 0.075 and 0.098 cm-1 for concentration 2. The ANOVA tests indicate that there are statistically significant differences between the two pesticide concentrations, being lower under the lowest concentration condition (CF1). According to [43], when using a conventional treatment with sand filters, the UV254 values of the filtered water decrease slightly.

Regarding the second filtration with GAC, lower values were obtained compared to conventional filtration (between 0.049 and 0.079 cm-1), which confirms the higher organic compounds removal capacity (represented in terms of UV254) of the GAC filter media. The application of the ANOVA tests showed that there are significant differences between the media used only for concentration 2, because this concentration corresponds to the highest doped concentration (0.86 mg/L). Previous studies have shown that GAC filters are more efficient than sand filters and dual media composed of sand and GAC or other media in the removal of organic matter (UV254) [44, 45, 42, 21], which is in accordance with this study.

 3.2.4. Atrazine

To determine the reduction of atrazine, its concentration was measured in raw water (1.92 × 10-3 mg/L), in water doped with the two pesticide concentrations, and at the end of each of the following processes: clarification (coagulation - flocculation - sedimentation), conventional filtration and GAC filtration (MAC and VAC). Table 4 presents the concentrations and the reduction percentages in the different processes.

Atrazine concentrations and reduction percentages throughout the treatment process

Source: The authors

Although the pesticide concentration was reduced in each stage of the treatment, the GAC filtration (MAC and CAV) stage is what obtained a sufficient reduction (99.73 and 99.80% for MAC with concentrations 1 and 2, respectively, and 99.74 and 93.26% for VAC with concentrations 1 and 2, respectively), with MAC being more efficient.

Factors such as the contact time and the presence of dissolved organic matter (DOM) in water influenced the absorption efficiency of the media used [46, 47], perhaps because the contact time may have been insufficient for adsorption of the pesticide, and the presence of DOM reduces the GAC effectiveness; these conditions can be explained because most of the results are within the limit established by the WHO [48] (0.002 mg/L), and the efficiencies with concentration 2 are lower.

Adsorption with different materials has been demonstrated to effectively reduce pesticides, such as in [49], where GAC filters were used for the removal of chlorpyrifos, diazinon and carbofuran, attaining removal efficiencies on the order of 80%, subsequent to the conventional treatment, which had a maximum removal efficiency of approximately 20%. For atrazine, wood charcoal has been used with a maximum efficiency of 95.50% [50], coconut charcoal with reduction efficiencies between 85.90 and 86.30% [3], and sawdust with efficiencies of approximately 74.70 - 80.50% [3]; notably, these studies were performed with distilled water or drinking water doped with the pesticide.

Regarding the regulation for drinking water, the EPA [41] establishes a concentration of 0.003 mg/L as the permissible limit of atrazine; the WHO [48] establishes a limit of 0.002 mg/L; and in Colombia, according to [39], the sum of the pesticide concentrations cannot exceed 0.010 mg/L. The concentrations evaluated in this study (0.44 and 0.86 mg/L) are concentrations that are found in surface water in the local and international context [51]. The atrazine concentrations at the end of the treatment process varied between 1.16 × 10-3 and 1.75 × 10-3 mg/L. Thus, they complied with the regulation in all cases other than concentration 2 filtered with VAC, which presented a concentration of 0.06 mg/L.

 4. Conclusions

The clarification processes, in addition to conventional sand and anthracite filtration, reduced turbidity by 97%, with turbidity values below 0.80 NTU; however, these treatments are inefficient in the reduction of organic compounds, represented in this study in terms of UV254 absorbance and atrazine.

In general, the second filtration with both types of evaluated GAC (MAC and VAC) showed a favorable effect on the reduction of UV254 and atrazine, obtaining atrazine values within the international and national standards for drinking water.

 Acknowledgments

The authors thank the Universidad del Valle and Pontificia Universidad Javieriana - Cali, for the financing of research project CI 2869, and the Universidad del Valle and COLCIENCIAS for the financing of research project CI 2937; the authors are also thankful for the financing of student Claudia Patricia Amézquita Marroquín - fellow of the National Doctorate support program [programa de apoyo a Doctorados Nacionales] - Call 567-2012 of COLCIENCIAS.

 References [1] Mendas, G., Vuletic, M., Galic, N. and Drevenkar, V., Urinary metabolites as biomarkers of human exposure to atrazine: Atrazine mercapturate in agricultural workers. Toxicol Letters, 210(2), pp. 174-181, 2012. DOI: 10.1016/j.toxlet.2011.11.023 Mendas G. Vuletic M. Galic N. Drevenkar V. Urinary metabolites as biomarkers of human exposure to atrazine: Atrazine mercapturate in agricultural workers Toxicol Letters 210 2 174 181 2012 10.1016/j.toxlet.2011.11.023 [2] Jablonowski, N., Hamacher, G., Martinazzo, R., Langen, U., Köppchen, S., Hofmann, D. and Burauel, P., Metabolism and persistence of atrazine in several field soils with different atrazine application histories. Journal of Agricultural and Food Chemistry, 58(24), pp. 12869-12877, 2010. DOI: 10.1021/jf103577j Jablonowski N. Hamacher G. Martinazzo R. Langen U. Köppchen S. Hofmann D. Burauel P. Metabolism and persistence of atrazine in several field soils with different atrazine application histories Journal of Agricultural and Food Chemistry 58 24 12869 12877 2010 10.1021/jf103577j [3] Sharma, R., Kumar, A. and Joseph, P., Removal of atrazine from water by low cost adsorbents derived from agricultural and industrial wastes. Bulletin of Environmental Contamination and Toxicology, 80(5), pp. 461-464, 2008.DOI: 10.1007/s00128-008-9389-6 Sharma R. Kumar A. Joseph P. Removal of atrazine from water by low cost adsorbents derived from agricultural and industrial wastes Bulletin of Environmental Contamination and Toxicology 80 5 461 464 2008 10.1007/s00128-008-9389-6 [4] Udikoviç, N., Scott, C. and Martin, F., Evolution of atrazine-degrading capabilities in the environment. Applied Microbiology and Biotechnology, 96(5), pp 1175-1189, 2012. DOI: 10.1007/s00253-012-4495-0 Udikoviç N. Scott C. Martin F. Evolution of atrazine-degrading capabilities in the environment Applied Microbiology and Biotechnology 96 5 1175 1189 2012 10.1007/s00253-012-4495-0 [5] Hou, X., Huang, X., Ai, Z., Zhao, J. and Zhang, L., Ascorbic acid induced atrazine degradation. Journal of Hazardous Materials, 327, pp. 71-78, 2017.DOI: 10.1016/j.jhazmat.2016.12.048 Hou X. Huang X. Ai Z. Zhao J. Zhang L. Ascorbic acid induced atrazine degradation Journal of Hazardous Materials 327 71 78 2017 10.1016/j.jhazmat.2016.12.048 [6] Papadakis, E., Tsaboula, A., Kotopoulou, A., Kintzikoglou, K., Vryzas, Z. and Papadopoulou, E., Pesticides in the surface waters of Lake Vistonis Basin, Greece: Occurrence and environmental risk assessment. The Science of the Total Environment, 536, pp. 793-802, 2015.DOI: 10.1016/j.scitotenv.2015.07.099. Papadakis E. Tsaboula A. Kotopoulou A. Kintzikoglou K. Vryzas Z. Papadopoulou E. Pesticides in the surface waters of Lake Vistonis Basin, Greece: Occurrence and environmental risk assessment The Science of the Total Environment 536 793 802 2015 10.1016/j.scitotenv.2015.07.099 [7] Copeland, C., Pesticide use and water quality: are the laws complementary or in conflict. Congressional Research Service [online]. 2012 [Reference date 15 June of 2017]. Available at: Available at: https://www.fas.org/sgp/crs/misc/RL32884.pdf Copeland C. Pesticide use and water quality: are the laws complementary or in conflict Congressional Research Service 2012 15 June of 2017 Available at: https://www.fas.org/sgp/crs/misc/RL32884.pdf [8] Lesmes, C. and Binder, C., Pesticide flow analysis to assess human exposure in greenhouse flower production in Colombia. International Journal of Environmental Research and Public Health, 10(4), pp. 1168-1185, 2013. DOI: 10.3390/ijerph10041168 Lesmes C. Binder C. Pesticide flow analysis to assess human exposure in greenhouse flower production in Colombia International Journal of Environmental Research and Public Health 10 4 1168 1185 2013 10.3390/ijerph10041168 [9] Graymore, M, Stagnitti, F. and Allinson, G., Impacts of atrazine in aquatic ecosystems. Environment International, 26(7-8), pp. 483-495, 2001. DOI: 10.1016/S0160-4120(01)00031-9 Graymore M Stagnitti F. Allinson G. Impacts of atrazine in aquatic ecosystems Environment International 26 7-8 483 495 2001 10.1016/S0160-4120(01)00031-9 [10] Sarkar, B., Venkateswralu, N., Rao, R., Bhattacharjee, C. and Kale, V., Treatment of pesticide contaminated surface water for production of potable water by a coagulation-adsorption-nanofiltration approach. Desalination, 212(1-3), pp. 129-140, 2007. DOI: 10.1016/j.desal.2006.09.021 Sarkar B. Venkateswralu N. Rao R. Bhattacharjee C. Kale V. Treatment of pesticide contaminated surface water for production of potable water by a coagulation-adsorption-nanofiltration approach Desalination 212 1-3 129 140 2007 10.1016/j.desal.2006.09.021 [11] Jardim, W., Montagner, C., Pescara, I., Umbuzeiro, G., Di Dea Bergamasco, A., Eldridge, M. and Sodré, F., An integrated approach to evaluate emerging contaminants in drinking water. Separation and Purification Technology, 84, pp. 3-8, 2012. DOI: 10.1016/j.seppur.2011.06.020 Jardim W. Montagner C. Pescara I. Umbuzeiro G. Di Dea Bergamasco A. Eldridge M. Sodré F. An integrated approach to evaluate emerging contaminants in drinking water Separation and Purification Technology 84 3 8 2012 10.1016/j.seppur.2011.06.020 [12] Gupta, V. and Ali, I., Environmental water: water treatment for inorganic pollutants by adsorption technology, Elsevier, 2013 Gupta V. Ali I. Environmental water: water treatment for inorganic pollutants by adsorption technology Elsevier 2013 [13] Peláez, A. and Teutli, M., Lignocellulosic precursors used in the synthesis of activated carbon - characterization techniques and applications in the wastewater treatment: lignocellulosic precursors used in the elaboration of activated carbon, México, InTech, 2012. Peláez A. Teutli M. Lignocellulosic precursors used in the synthesis of activated carbon - characterization techniques and applications in the wastewater treatment: lignocellulosic precursors used in the elaboration of activated carbon México InTech 2012 [14] World Health Organization (WHO). Drinking water guidelines, Volumen 1, 3ra. Edición 2006 World Health Organization Drinking water guidelines 1 3ra 2006 [15] Di Bernardo, L. and Di Bernardo, A., Métodos e técnicas de tratamento de água. Brasil, Rima, Editor. 2005. Di Bernardo L. Di Bernardo A. Métodos e técnicas de tratamento de água Brasil Rima 2005 [16] Di Bernardo, L. and Sabogal, L., Seleção de tecnologias de tratamento de água, Brasil, LDiBe, editor, 2008. Di Bernardo L. Sabogal L. Seleção de tecnologias de tratamento de água Brasil LDiBe 2008 [17] Arboleda, J., Teoría y práctica de la purificación del agua, Colombia, McGraw-Hill, editor. 2000. Arboleda J. Teoría y práctica de la purificación del agua Colombia McGraw-Hill 2000 [18] Freese, S., Nozaic, D., Pryor, M., Rajogopaul, R., Trollip, D. and Smith, R., Enhanced coagulation: a viable option to advance treatment technologies in the South African context. Water Science and Technology [online], 1(1), pp. 33-41, 2001. [Reference date 17 July of 2017]. Available at: Available at: http://elaguapotable.com/Mejora de la coagulacion.pdf . Freese S. Nozaic D. Pryor M. Rajogopaul R. Trollip D. Smith R. Enhanced coagulation: a viable option to advance treatment technologies in the South African context Water Science and Technology 1 1 33 41 2001 17 July of 2017 Available at: http://elaguapotable.com/Mejora de la coagulacion.pdf [19] Ho, L. and Newcombe, G., Granular activated carbon adsorption of 2-methylisoborneol (MIB): pilot- and laboratory-scale evaluations. Journal of Environmental Engineering, 136(9), pp. 965-974, 2010. DOI: 10.1061/(ASCE)EE.1943-7870.0000231. Ho L. Newcombe G. Granular activated carbon adsorption of 2-methylisoborneol (MIB): pilot- and laboratory-scale evaluations Journal of Environmental Engineering 136 9 965 974 2010 10.1061/(ASCE)EE.1943-7870.0000231 [20] Di Bernardo, L., Di Bernardo, A. y Nogueira, P., Tratabilidad del agua y residuos generados en estaciones de tratamiento de agua: procedimientos para realización de ensayos de tratabilidad de agua, Brasil, LDiBe , 2011. Di Bernardo L. Di Bernardo A. Nogueira P. Tratabilidad del agua y residuos generados en estaciones de tratamiento de agua: procedimientos para realización de ensayos de tratabilidad de agua Brasil LDiBe 2011 [21] Rigobello, E., Di Bernardo, A., Di Bernardo, L. and Vieira, E., Removal of diclofenac by conventional drinking water treatment processes and granular activated carbon filtration. Chemosphere, 92(2), pp. 184-191, 2013. DOI: 10.1016/j.chemosphere.2013.03.010. Rigobello E. Di Bernardo A. Di Bernardo L. Vieira E. Removal of diclofenac by conventional drinking water treatment processes and granular activated carbon filtration Chemosphere 92 2 184 191 2013 10.1016/j.chemosphere.2013.03.010 [22] Perea, L., Torres, P., Cruz, C. y Escobar, J., Influencia de la configuración del medio filtrante sobre el proceso de filtración a tasa constante del agua clarificada del río Cauca. Revista de Ingeniería [en línea], (38), pp. 38-44, 2013 [Referencia: Mayo 12 de 2017]. Disponible en: Disponible en: http://www.redalyc.org/articulo.oa?id=121028408006 . Perea L. Torres P. Cruz C. Escobar J. Influencia de la configuración del medio filtrante sobre el proceso de filtración a tasa constante del agua clarificada del río Cauca Revista de Ingeniería 38 38 44 2013 Mayo 12 de 2017 Disponible en: http://www.redalyc.org/articulo.oa?id=121028408006 [23] Environmental Protection Agency (EPA). Method 523: Determination of triazine pesticides and their degradates in drinking water by Gas Chromatography/Mass Spectrometry (GC/MS) Version 1.0. 2012. Environmental Protection Agency Method 523: Determination of triazine pesticides and their degradates in drinking water by Gas Chromatography/Mass Spectrometry (GC/MS) Version 1.0 2012 [24] Huang, J., Wang, X., Jina, Q., Liua, Y. and Wang, Y., Removal of phenol from aqueous solution by adsorption onto OTMAC-modified attapulgite. Journal of Environmental Management, 84, pp. 229-236, 2007. DOI: 10.1016/j.jenvman.2006.05.007. Huang J. Wang X. Jina Q. Liua Y. Wang Y. Removal of phenol from aqueous solution by adsorption onto OTMAC-modified attapulgite Journal of Environmental Management 84 229 236 2007 10.1016/j.jenvman.2006.05.007 [25] Kim, J. and Kang, B., DBPs removal in GAC filter-adsorber. Water Research, 42(1-2), pp. 145-152, 2008. DOI: 10.1016/j.watres.2007.07.040 Kim J. Kang B. DBPs removal in GAC filter-adsorber Water Research 42 1-2 145 152 2008 10.1016/j.watres.2007.07.040 [26] Gibert, O., Lefèvre, B., Fernández, M., Bernat, X., Paraira, M. and Pons, M., Fractionation and removal of dissolved organic carbon in a full-scale granular activated carbon filter used for drinking water production. Water Research , 47(8), pp. 2821-2829, 2013. DOI: 10.1016/j.watres.2013.02.028 Gibert O. Lefèvre B. Fernández M. Bernat X. Paraira M. Pons M. Fractionation and removal of dissolved organic carbon in a full-scale granular activated carbon filter used for drinking water production Water Research 47 8 2821 2829 2013 10.1016/j.watres.2013.02.028 [27] Mukherjee, S., Kumar, S., Misra, A. and Fan, M., Removal of phenols from water environment by activated carbon, bagasse ash and wood charcoal. Chemical Engineering Journal, 129(1), pp. 133-42, 2007. DOI: 10.1016/j.cej.2006.10.030 Mukherjee S. Kumar S. Misra A. Fan M. Removal of phenols from water environment by activated carbon, bagasse ash and wood charcoal Chemical Engineering Journal 129 1 133 142 2007 10.1016/j.cej.2006.10.030 [28] Giraldo, L. and Moreno, J., Pb2+ adsorption from aqueous solutions on activated carbons obtained from lignocellulosic residues. Brazilian Journal of Chemical Engineering, 25(1), pp. 143-151. 2008. DOI: 10.1590/S0104-66322008000100015 Giraldo L. Moreno J. Pb2+ adsorption from aqueous solutions on activated carbons obtained from lignocellulosic residues Brazilian Journal of Chemical Engineering 25 1 143 151 2008 10.1590/S0104-66322008000100015 [29] Giraldo, L. and Moreno, J., Synthesis of activated carbon mesoporous from coffee waste and its application in adsorption zinc and mercury ions from aqueous solution. E-Journal of Chemistry, 9(2), pp. 938-948, 2012. DOI: 10.1155/2012/120763 Giraldo L. Moreno J. Synthesis of activated carbon mesoporous from coffee waste and its application in adsorption zinc and mercury ions from aqueous solution E-Journal of Chemistry 9 2 938 948 2012 10.1155/2012/120763 [30] Vukčević, M., Kalijadis, A., Vasiljević, T., Babić, B., Laušević, Z. and Laušević, M., Production of activated carbon derived from waste hemp (Cannabis sativa) fibers and its performance in pesticide adsorption. Microporous Mesoporous Mater, 214, pp. 156-165, 2015. DOI: 10.1016/j.micromeso.2015.05.012 Vukčević M. Kalijadis A. Vasiljević T. Babić B. Laušević Z. Laušević M. Production of activated carbon derived from waste hemp (Cannabis sativa) fibers and its performance in pesticide adsorption Microporous Mesoporous Mater 214 156 165 2015 10.1016/j.micromeso.2015.05.012 [31] Montgomery, D. y Runger, G., Probabilidad y estadística aplicadas a la ingeniería, McGraw-Hill, 2012. Montgomery D. Runger G. Probabilidad y estadística aplicadas a la ingeniería McGraw-Hill 2012 [32] Marcó, L., Azario, R., Metzler, C. y Garcia, M., La turbidez como indicador básico de calidad de agua potabilizada a partir de fuentes superficiales. Propuesta a propósito del estudio del sistema de potabilización y distribución en la ciudad de Concepción del Uruguay, higiene, sanidad y ambiente [en línea], pp. 72-82, 2004. [Referencia agosto 10 de 2017]. Disponible en: Disponible en: http://salud-publica.es/secciones/revista/revistaspdf/bc 510156890491c_Hig.Sanid.Ambient.4.72-82(2004).pdf Marcó L. Azario R. Metzler C. Garcia M. La turbidez como indicador básico de calidad de agua potabilizada a partir de fuentes superficiales Propuesta a propósito del estudio del sistema de potabilización y distribución en la ciudad de Concepción del Uruguay, higiene, sanidad y ambiente 72 82 2004 agosto 10 de 2017 Disponible en: http://salud-publica.es/secciones/revista/revistaspdf/bc 510156890491c_Hig.Sanid.Ambient.4.72-82(2004).pdf [33] Aráuz, M. y Castillo, V., Determinación de la concentración de trihalometanos producidos por reacción del cloro con la materia orgánica nitrogenada en muestras del río Fonseca, Departamento de Boaco, BSc. Tesis, Facultad de Ciencia, Tecnología y Ambiente, Universidad Centroamericana, Managua, Nicaragua, 2008. Aráuz M. Castillo V. Determinación de la concentración de trihalometanos producidos por reacción del cloro con la materia orgánica nitrogenada en muestras del río Fonseca, Departamento de Boaco BSc. Facultad de Ciencia, Tecnología y Ambiente, Universidad Centroamericana Managua, Nicaragua Managua, Nicaragua 2008 [34] Leiva, A., Caracterización de calidad de agua en el ciclo de consumo del municipio de Guaimaca, Franciso Morazán, Honduras. Escuela Agrícola Panamericana, San Antonio de Oriente, Honduras, 2010. Leiva A. Caracterización de calidad de agua en el ciclo de consumo del municipio de Guaimaca, Franciso Morazán, Honduras Escuela Agrícola Panamericana Honduras 2010 [35] Fray, M., Occurrence of herbicides/pesticides in drinking water, United States, American Water Works Association, editors, 2000. Fray M. Occurrence of herbicides/pesticides in drinking water United States American Water Works Association 2000 [36] Tadkaew, N., Hai, F., McDonald, J., Khan, S. and Nghiem, L., Removal of trace organics by MBR treatment: The role of molecular properties. Water Research , 45(8), pp. 2439-2451, 2011. DOI: 10.1016/j.watres.2011.01.023 Tadkaew N. Hai F. McDonald J. Khan S. Nghiem L. Removal of trace organics by MBR treatment: The role of molecular properties Water Research 45 8 2439 2451 2011 10.1016/j.watres.2011.01.023 [37] Friedler, E. and Alfiya, Y., Physicochemical treatment of office and public buildings greywater. Water Science and Technology , 62(10), pp. 2357-2363, 2010. DOI: 10.2166/wst.2010.499. Friedler E. Alfiya Y. Physicochemical treatment of office and public buildings greywater Water Science and Technology 62 10 2357 2363 2010 10.2166/wst.2010.499 [38] Christopher, D., The effect of granular activated carbon pretreatment and sand pretreatment on microfiltration of greywater, MSc Thesis, Civil Engineering, Clemson University, South Carolina, United States, 2012. Christopher D. The effect of granular activated carbon pretreatment and sand pretreatment on microfiltration of greywater MSc Clemson University South Carolina, United States South Carolina, United States 2012 [39] Ministerio de Ambiente Vivienda y Desarrollo Territorial (MAVDT). Resolución 2115, Colombia, 2007. Ministerio de Ambiente Vivienda y Desarrollo Territorial Resolución 2115 Colombia 2007 [40] Organización Panamericana de Salud (OPS). Guías para la calidad del agua potable, Número 481, Volumen 3, Org PAH, editor. 1987. Organización Panamericana de Salud Guías para la calidad del agua potable 481 3 Org PAH 1987 [41] United States Environmental Protection Agency (USEPA). EPA 816-F-09-004, National Primary Drinking Water Regulations. 2009. United States Environmental Protection Agency EPA 816-F-09-004, National Primary Drinking Water Regulations 2009 [42] Feng, S., Xie, S., Zhang, X., Yang, Z., Ding, W., Liao, X., Liu, Y. and Chen, Ch., Ammonium removal and microbial community in GAC-sand dual media filter in drinking water treatment. Journal of Environmental Sciences, 24(9), pp. 1587-1593, 2012. DOI: 10.1016/S1001-0742(11)60965-0. Feng S. Xie S. Zhang X. Yang Z. Ding W. Liao X. Liu Y. Chen Ch. Ammonium removal and microbial community in GAC-sand dual media filter in drinking water treatment Journal of Environmental Sciences 24 9 1587 1593 2012 10.1016/S1001-0742(11)60965-0 [43] Serrano, M., Montesinos, I., Cardador, M., Silva, M. and Gallego, M., Seasonal evaluation of the presence of 46 disinfection by-products throughout a drinking water treatment plant. The Science of the Total Environment , 56(13), pp 246-58, 2015. DOI: 10.1016/j.scitotenv.2015.02.070. Serrano M. Montesinos I. Cardador M. Silva M. Gallego M. Seasonal evaluation of the presence of 46 disinfection by-products throughout a drinking water treatment plant The Science of the Total Environment 56 13 246 258 2015 10.1016/j.scitotenv.2015.02.070 [44] Babi, K., Koumenides, K., Nikolaou, A., Makri, C., Tzoumerkas, F. and Lekkas, T., Pilot stufy of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption. Desalination, 210(1-3), pp. 215-224, 2007. DOI: 10.1016/j.desal.2006.05.046. Babi K. Koumenides K. Nikolaou A. Makri C. Tzoumerkas F. Lekkas T. Pilot stufy of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption Desalination 210 1-3 215 224 2007 10.1016/j.desal.2006.05.046 [45] Lu, Y., Wang, D., Ma, C. and Yang, H., The effect of activated carbon adsorption on the photocatalytic removal of formaldehyde. Building and Environment, 45(3), pp 615-621, 2010. DOI: 10.1016/j.buildenv.2009.07.019. Lu Y. Wang D. Ma C. Yang H. The effect of activated carbon adsorption on the photocatalytic removal of formaldehyde Building and Environment 45 3 615 621 2010 10.1016/j.buildenv.2009.07.019 [46] Zadaka, D., Nir, S., Radian, A. and Mishael, Y., Atrazine removal from water by polycation - clay composites : Effect of dissolved organic matter and comparison to activated carbon. Water Research , 43(3), pp. 677-683, 2009. DOI: 10.1016/j.watres.2008.10.050 Zadaka D. Nir S. Radian A. Mishael Y. Atrazine removal from water by polycation - clay composites : Effect of dissolved organic matter and comparison to activated carbon Water Research 43 3 677 683 2009 10.1016/j.watres.2008.10.050 [47] Tejada, C., Villabona, Á. y Núñez, J., Uso de biomasas para la adsorción de plomo, níquel, mercurio y cromo. Universidad de Cartagena Colombia, Ingenium, 9, pp 41-51, 2015. DOI: 10.21774/ingenium.v9i24.520 Tejada C. Villabona Á. Núñez J. Uso de biomasas para la adsorción de plomo, níquel, mercurio y cromo Universidad de Cartagena Colombia Ingenium 9 41 51 2015 10.21774/ingenium.v9i24.520 [48] World Health Organization (WHO). Atrazine in drinking-water background document for development of WHO guidelines for drinking-water quality, Geneva, 2003. World Health Organization Atrazine in drinking-water background document for development of WHO guidelines for drinking-water quality Geneva 2003 [49] Pham, T., Nguyen, V. and Van der Bruggen, B., Pilot-scale evaluation of GAC adsorption using low-cost, high-performance materials for removal of pesticides and organic matter in drinking water production. Journal of Environmental Engineering , 139(7), pp. 958-965, 2013. DOI: 10.1061/(ASCE)EE.1943-7870.0000704. Pham T. Nguyen V. Van der Bruggen B. Pilot-scale evaluation of GAC adsorption using low-cost, high-performance materials for removal of pesticides and organic matter in drinking water production Journal of Environmental Engineering 139 7 958 965 2013 10.1061/(ASCE)EE.1943-7870.0000704 [50] Alam, J., Dikshit, A. and Bandyopadhyay, M., Efficacy of adsorbents for 2, 4-D and atrazine removal from water environment. Global Nest: The Int. J. [online], 2(2), pp. 139-48, 2000 [Reference date: 6 July of 2017]. Available at: Available at: https://journal.gnest.org/sites/default/files/Journal Papers/02_dikshit.pdf . Alam J. Dikshit A. Bandyopadhyay M. Efficacy of adsorbents for 2, 4-D and atrazine removal from water environment Global Nest: The Int. J. 2 2 139 148 2000 6 July of 2017 Available at: https://journal.gnest.org/sites/default/files/Journal Papers/02_dikshit.pdf [51] Perez-Vidal, A., Torres-Lozada, P. and Escobar-Rivera, J., Hazard identification in watersheds based on water safety plan approach: case study of Cali-Colombia. Environmental Engineering and Management [online]. 15(4), pp. 861-872, 2016. [Reference date: 18 may of 2017]. Available at: Available at: https://www.researchgate.net/publication/312210775_Hazard_identification_in_watersheds_based_on_water_safety_plan_approach_case_study_of_Cali-Colombia . Perez-Vidal A. Torres-Lozada P. Escobar-Rivera J. Hazard identification in watersheds based on water safety plan approach: case study of Cali-Colomb ia. Environmental Engineering and Management 15 4 861 872 2016 18 may of 2017 Available at: https://www.researchgate.net/publication/312210775_Hazard_identification_in_watersheds_based_on_water_safety_plan_approach_case_study_of_Cali-Colombia

Fuentes-López, L., Amézquita-Marroquín, C. and Torres-Lozada, P., Application of double filtration with granular activated carbon for Atrazine reduction on water treatment processes. DYNA, 85(205), pp. 184-190, June, 2018.