Removal of the waterborne parasite Cryptosporidium parvum from drinking water using granular activated carbon

Journal of Environmental Chemical Engineering 11 (2023) 111185 Available online 4 October 2023 2213-3437/© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Removal of the waterborne parasite Cryptosporidium parvum from drinking water using granular activated carbon Seila Couso-P´ erez a , 1 , María Jesús Abeledo-Lameiro a , 2 , Ana Isabel Vidal-Varela a , Hip´ olito G´ omez-Couso a , b , * a Laboratory of Parasitology, Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, A Coru˜ na, Spain b Institute of Research on Chemical and Biological Analysis (IAQBUS), University of Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, A Coru˜ na, Spain ARTICLE INFO Editor: Luigi Rizzo Keywords: Activated granular carbon Cryptosporidium Drinking water Household water treatment ABSTRACT Cryptosporidium is a genus of apicomplexan parasites that infect the gastrointestinal tract of a wide range of vertebrate hosts, including humans. These enteropathogens are commonly detected in surface waters and Cryptosporidium is responsible of numerous waterborne outbreaks in industrialised countries. Filters of granular activated carbon (GAC) are mainly used to eliminate emerging micropollutants or control unpleasant odour and taste in drinking water. Recently, GAC has been also employed for removal of microorganisms from different types of water. This work evaluates the capability of GAC in the elimination of the infective forms of Cryptosporidium parvum (oocysts) from drinking water. For this, well water was spiked with oocysts of C. parvum and passed through a chromatographic column filled with fresh GAC at different bed heights (5–50 cm) and a filtration rate of 100 mL/min, approximately. By immunofluorescence microscopy, the number of oocysts in the water samples was determined. The logarithmic reduction (LR) was calculated by comparing the number of oocysts quantified in the filtered samples and the corresponding influent samples. High efficiencies of GAC in removing C. parvum oocysts from water were obtained. Thus, with a bed height of 35 cm, removal efficiencies > 2 LR were achieved. The highest LR (3.47 ±0.31) was observed when a GAC bed height of 50 cm was used. Taking into account the results obtained, C. parvum oocysts were eliminated remarkably and, therefore, GAC adsorption filters may be considered additional barriers against this waterborne enteropathogen in drinking water at the household level in developing countries. 1. Introduction Cryptosporidium is a genus of apicomplexan parasites that infect the gastrointestinal tract of a wide range of vertebrate hosts, including humans [1]. Cryptosporidiosis is transmitted by the faecal-oral route and can be acquired both directly, through contact with infected hosts, and indirectly, by ingestion of food and water contaminated with oocysts (the robust infective form), being the latter the most common source of infection [1,2]. The ubiquitous occurrence of Cryptosporidium in the environment, its persistence, and resistance to conventional disinfection treatments based on physical, chemical and biological methods have made this waterborne parasite one of the critical pathogens for the drinking water industry [3]. Thus, Cryptosporidium was involved in 76.5% of waterborne outbreaks reported in industrialised countries during the period 2017–2020 [4]. In middle and low-income countries, Cryptosporidium, along with Rotavirus and Shigella, are the three pathogens that most commonly cause diarrhoeal disease in children under 2 years old, with Cryptosporidium being responsible for 30–50% of childhood mortality in these countries [5,6]. Unsafe drinking water is still responsible for more than half of the * Corresponding author at: Laboratory of Parasitology, Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, A Coru˜ na, Spain. E-mail address: [email protected] (H. G´ omez-Couso). 1 Current address: Nanotechnology and Integrated BioEngineering Centre (NIBEC), School of Engineering, Ulster University, Belfast Campus, 2–24 York Street, Belfast BT15 1AP, United Kingdom 2 Current address: Plataforma Solar de Almería–CIEMAT, Carretera Sen´ es, Km 4.5, 04200, Tabernas, Almería, Spain Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece https://doi.org/10.1016/j.jece.2023.111185 Received 26 May 2023; Received in revised form 1 September 2023; Accepted 4 October 2023 Journal of Environmental Chemical Engineering 11 (2023) 111185 2 diarrhoeal diseases in the world [7]. The World Health Organization (WHO) estimates that around 2 billion people are currently using contaminated water sources [8]. For this reason, the United Nations approved “The 2030 Agenda for Sustainable Development”, which includes 17 Sustainable Development Goals (SDGs). The SDG 6 pursues “ensuring water availability and sustainable water management and sanitation for all” [9,10]. To protect public health, the WHO established the concept of reference pathogen, which includes the pathogens within a group that are most difficult to remove or control and have the largest associated health burden, both on a population and individual basis [3]. Regarding the protozoan parasites group that may be transmitted to humans through the drinking water route (Cryptosporidium, Giardia, Entamoeba, Toxoplasma, Balantidium and Cyclospora), Cryptosporidium parvum was chosen by the WHO as the reference pathogen because its oocysts are the most persistent in the environment, the most resistant to chemical disinfection, and the smallest in size. Therefore, this protozoan species is the most difficult to remove by filtration processes [3]. The WHO estimates that around 2 billion people live in areas without access to safe drinking water and two-thirds of the world’s population live in areas of high water stress [8]. Currently, many households in middle and low-income countries use surface water, which may be contaminated with pathogens of different origins, for cooking, drinking, bathing and recreational activities [4,11]. Contamination of water with the enteropathogen Cryptosporidium is a universal challenge because it compromises the protection of water supplies [12]. Major waterborne outbreaks of cryptosporidiosis associated with contaminated drinking water have been attributed to treatment deficiencies and therefore, C. parvum infectious oocysts shall represent a challenge in the evaluation of water treatment systems in terms of protozoa reduction or inactivation performance [4,13]. Activated carbon (AC) is the name given to a group of porous carbons manufactured by carbonising carbonaceous materials impregnated with dehydrating chemicals or by treating charcoal (carbonized wood) with oxidising gases. The main feature of ACs is their porous structure, as these carbons exhibit a high porosity degree and a large internal surface area, which makes these materials an excellent adsorbent. Molecules from the gas or liquid phase can be attached to the surface of the AC by van der Waals-type forces, although chemisorption is also possible by stronger valence forces on the so-called active sites of the carbon surface [14,15]. Although the use of charcoal was described in Egypt around 1550 BC, its commercial production began in the early 20th century, extending its uses to the purification of chemical, pharmaceutical, water and food trades. Today, AC is used in a wide range of industrial applications, including gas and air cleaning. However, its main application is in the water industry, to eliminate emerging micropollutants or control unpleasant odour and taste in drinking water [14]. Moreover, AC is also employed in groundwater, service water and wastewater treatments due to its capability to adsorb dissolved organic impurities and to eliminate substances affecting odour, taste, and colour and also several pollutants such as aromatic compounds, hydrocarbons, detergents, soluble dyes, etc. [14,15]. Thus, AC can be used in drinking water treatment plants in two forms: powdered activated carbon (PAC) or granular activated carbon (GAC). PAC (particles size typically between 10 and 100 µm in diameter) is normally applied as needed to deal, for example, with a rapid influx of taste and odour compounds or toxins from cyanobacteria [16]. The incorporation of PAC occurs during the coagulant dosing before coagulation/flocculation or during sedimentation prior to sand filtration [17]. By contrast, GAC (particles in the range of 0.2–5 mm in size) is placed in filters for continuous application as a final barrier to anthropogenic micropollutants before water disinfection [17,18]. The use of GAC has been also employed for removal of microorganisms from different types of water during the last 20 years [19]. Nevertheless, the studies that evaluate at laboratory and pilot scales the capability of GAC filters (columns or cartridges), to remove Cryptosporidium oocysts are scarce [19–21]. The aim of this study was to evaluate the capability of GAC to remove Cryptosporidium oocysts from drinking water as a method for household water treatment in middle and low-income countries or poor resource environments. 2. Material and methods 2.1. Cryptosporidium oocysts Oocysts of Cryptosporidium were obtained from a faecal sample collected from the rectum of a naturally infected neonatal Friesian–Holstein calf. The faecal sample was subjected to a diphasic concentration method and the oocysts were purified, quantified and molecularly characterized according to the protocols previously described [22]. Briefly, faecal material was homogenized in phosphate buffered saline (PBS, 0.04 M, pH 7.2) and filtered through two sieves (mesh sizes 150 and 45 µm). Then, diethyl ether (2:1, v/v) was added and a diphasic concentration method (centrifugation at 2000g, for 15 min, at 4 ◦C) was applied. The supernatant was discarded, and the sediment was washed with PBS (0.04 M, pH 7.2) by centrifugation at 2000g for 15 min at 4 ◦C. The purification of the Cryptosporidium oocysts was performed by discontinuous caesium chloride gradients of 1.05, 1.10 and 1.40 g/mL by centrifugation at 2000g for 30 min at 4 ◦C [23]. The oocysts were quantified using a modified Neubauer haemocytometer chamber under a phase contrast microscope (BH2, Olympus Optical Co. Ltd., Tokyo, Japan). Finally, by amplification and sequencing of fragments of ~587 bp and ~850 bp of the small subunit rDNA (SSU rDNA) and the 60 kDa glycoprotein (GP60) genes, respectively [24,25], the isolate was molecularly identified as C. parvum subtype IIaA15G2R1. 2.2. Water type Well water (WW) collected in a private house was used in this study and was stored at 8 ◦C until its use. The pH was measured using a pH meter (CRISON Instruments, S.A., Barcelona, Spain) [26] and a turbidity meter (TN-100, Eutech Instruments Pte Ltd., Singapore) was used to measure the turbidity of water [27]. Total dissolved solids (TDS) were measured by weighing a filtered sample and drying it until no further mass was lost [28]. Moreover, water samples were sent to the Department of Soil Science and Agricultural Chemistry of the University of Santiago de Compostela to determine the alkalinity and the free chlorine of the water [27]. Table 1 shows the physicochemical and microbiological characteristics of the WW. 2.3. Experimental design A chromatography column (ø =2.5 cm; height 50 cm +reservoir) filled with fresh GAC at different bed heights (5–50 cm) was employed in each assay, which included three contamination steps. The GAC used was a commercial product (Norit® GAC 1240, 12–40 mesh, Acros Organics, Geel, Belgium) obtained from a vegetal source, specifically coconut shell by steam activation, with particle size between 1680–0.425 mm. Thus, the column was loaded with the corresponding GAC bed and washed with bi-distilled water for bed expansion. Then, WW was spiked with 5 ×10 5 C. parvum oocysts per litre (influent) and passed through the chromatography column at a filtration rate of 100 mL/min, approximately (contact time ⁓5 min) (Fig. 1). The filtered samples (effluents) were collected and passed through nitrocellulose membranes (47 mm diameter; 3 µm pore size; Merck Millipore Ltd., Carrigtwohill, Ireland), which were placed in vacuum filtration units connected to a pump (Fisherbrand™ FB 70155, Fisher Scientific S.L., Madrid, Spain). The membranes were inserted in re-sealable polyethylene bags and washed three times with 5 mL of PBS 0.04 M pH 7.2. Then, the samples were centrifuged at 2000g for 15 min. Similarly, 0.5 L of the influent samples were subjected to the same procedure. The supernatant was discarded and the sediments from the influent and effluent samples were S. Couso-P´ erez et al. Journal of Environmental Chemical Engineering 11 (2023) 111185 3 resuspended in 5 and 1.5 mL of PBS 0.04 M pH 7.2, respectively. Each bed GAC assay, carried out in duplicate, involved three contaminations and 10 washes with 0.5 L of clean well water between each contamination (total operating filter time was approximately 165 min). Finally, the GAC was removed, and the column was washed with bi-distilled water and dried in an oven at 65 ◦C before the evaluation of another bed height. 2.4. Quantification of C. parvum oocysts A direct immunofluorescence antibody test (Aqua Glo™ G/C Direct, Waterborne Inc., New Orleans, LA, USA) and subsequent staining with the fluorogenic dye 4 ′ ,6-diamino-2-fenilindol (DAPI; Waterborne Inc.) were applied on all samples to identify and quantify the number of C. parvum oocysts in the water [29]. Briefly, aliquots of 10 μ L of the influent samples (previously diluted 1:10 with bi-distilled water) and aliquots of 100 μ L of the effluent samples were deposited on 3-well slides (Gerhard Menzel B.V & C. KG, Braunschweig, Germany) treated with a 0.1% poly-L-lysine solution (Sigma-Aldrich, Inc., St. Louis, MO, USA). Once the samples were air-drying at room temperature, they were fixed with 50 μ L of absolute methanol (Mallincrof Baker B.V., Deventer, The Netherlands). Then, a total of 40 μ L mix containing 10 μ L of anti-- Cryptosporidium monoclonal antibodies labelled with fluorescein isothiocyanate (FITC) (Aqua-Glo™ G/C Direct, Waterborne Inc.), 5 μ L of Evans blue counterstain (Waterborne Inc.) and 15 μ L of PBS 0.04 M pH 7.2 was added over each sample. The slides with the samples were incubated in humid chambers for 30 min, at 37 ◦C and in darkness and then they were washed with PBS 0.04 M pH 7.2. Finally, 50 μ L of 1X DAPI solution (1 μ L of 2 mg/mL of DAPI stock solution added to 5 mL of PBS 0.04 M pH 7.2) was added over each sample and the slides were again incubated for 2 min, at room temperature and in darkness. After washing the samples with PBS 0.04 M pH 7.2 to remove excess of DAPI and air-drying, the slides with the samples were mounted using a commercial medium (No-Fade™ Mounting Medium, Waterborne Inc.). The oocysts were identified by examining the samples under an epifluorescence microscope (AX70, Olympus Optical Co., Ltd., Tokyo, Japan) equipped with a FITC filter (excitation at 450–480 nm; barrier at 515 nm) on the basis of their shape, size and the pattern and intensity of immunofluorescence staining following the characteristics established by the United States Environmental Protection Agency (USEPA) [29]. The oocyst identification was confirmed by further examination under UV filter for DAPI staining (excitation at 358–461 nm; barrier at 500 nm), again in accordance with USEPA [29]. For each assay, the quantification of C. parvum oocysts was performed in triplicate, applying the corresponding multiplication factor on the influent and effluent samples (5000 and 15, respectively). An USEPA analytical quality test was applied on the detection method selected to verify the recovery percentages obtained, which acceptance criteria for Cryptosporidium are mean percentage recovery of 38–100% and precision of 46 expressed as maximum relative percentage difference [29]. 2.5. Calculation of the removal capability of GAC The mathematical parameter of logarithmic reduction (LR) was used to evaluate the capability of the GAC to eliminate the infectious forms of C. parvum from water. This parameter is recommended by the WHO to evaluate the effectiveness of a system in the disinfection or microbiological decontamination used as household water treatment methods [30]. Logarithmic reduction is calculated using the geometric mean (GM) of the number of oocysts obtained in water samples according to the following equation [30]: Logaritmic reduction = − log10(GMeff /GMinf )(1) where GM inf is the GM of the C. parvum oocyst number in influent samples and GM eff is the GM of the C. parvum oocyst number in the effluent water samples. Table 1 Physical, chemical, and microbiological parameters of well water (WW) used in the evaluation of the capability of granular activated carbon (GAC) to remove Cryptosporidium parvum oocysts. Parameter Value Units Physical Turbidity 1.0 NTU Total Dissolved Solids (TDS) 90.0 mg/L Conductivity 190.0 μ S/cm Chemical pH 5.6 - Ammonia <0.1 mg/L Sulphates <25.0 mg/L Nitrites 0.2 mg/L Nitrates 23.7 mg/L Phosphates 0.1 mg/L Total phosphorous 0.4 mg/L Combined chlorine <0.1 mg/L Free chlorine <0.1 mg/L Aluminium <0.1 mg/L Iron <0.1 mg/L Potassium 2.2 mg/L Magnesium 10.0 mg/L Calcium 90.0 mg/L Alkalinity 100.0 mg/L CaCO 3 Microbiological Total Coliforms at 37 ◦C 0 CFU/100 mL Escherichia coli 0 CFU/100 mL Enterococcus spp. 0 CFU/100 mL Fig. 1. Materials employed during the experiments. A, 50 cm graduated chromatography column with reservoir; B, fresh granular activated carbon (GAC); C, oocysts of Cryptosporidium parvum. Bar =10 µm. S. Couso-P´ erez et al. Journal of Environmental Chemical Engineering 11 (2023) 111185 4 2.6. Statistical analysis Statistical tests were performed using Statgraphics Centurion 18 v.18.1.12 (©1982–2018 Statgraphics Technologies, Inc., The Plains, VA, USA). The Kolmogorov-Smirnov test was used to test the data fit to a normal distribution. Differences in the GM between the different GAC beds evaluated were compared using ANOVA and Fisher´s least significant difference (LSD) multiple comparison tests. Differences were considered statistically significant at P<0.05. The results presented in the graph are the average of three replicates with the standard deviation as the error bar. 3. Results and discussion The present work evaluates the capability of GAC for removal C. parvum oocysts from water as a simple, sustainable, and effective method for household drinking water treatment. High efficiencies of GAC to remove oocysts of C. parvum from drinking water was obtained, and as expected, the removal capability was increased as the GAC bed height increased. Thus, removal efficiencies >2 LR were reached at ≥30 cm bed heights and >3 LR were determined when bed heights ≥45 cm were used. When the highest established GAC bed height (50 cm) was loaded, oocysts of C. parvum were removed by 3.47 ±0.31 LR (Fig. 2). Significant statistical differences were observed among the GM of the GAC bed heights (F =63.67; P<0.01), detecting significant differences between the results obtained using the GAC height of 30 cm in comparison with ≤25 cm, and 50 cm with respect to ≤40 cm GAC beds (P<0.05). The analytical quality test of the detection method revealed an overall recovery percentage of 69.19 ±5.02. Thus, the mean percentage recoveries ranged from 55.56% to 73.74% and precision values ranged from 0 to 25.71 for the GAC bed height evaluated. These values are within the quality control acceptance criteria for detection methods of Cryptosporidium in water established by the USEPA [29]. One of the first studies including GAC to remove C. parvum oocysts from drinking water was a water purifier mounted in a faucet and consisting of a cartridge composed of a hollow fibre membrane filter with 0.1 µm multi-layer pores and a layer of GAC [20]. While the water was running, C. parvum oocysts (3 ×10 7 ) were injected into the tube connected to the water purifier and the faucet. The proposed water purifier effectively removed C. parvum oocysts from drinking water, as oocysts were not detected in the purified water collected from all the cartridges [20]. In a previous study using river water, it was observed that the capability of GAC filters to eliminate C. parvum oocysts is higher in comparison with viruses and bacteria [19]. However, the reductions obtained were lower than those achieved in this work. Thus, at the pilot scale, two columns (ø =0.15 m; height 1.35 m) filled with 1 m of GAC (median grain size 1 mm) were supplied with pre-treated river water at a constant flow rate of 5 m/h (contact time of 12 min), raising 1.2 and 2.7 LR for C. parvum in loaded and fresh GAC, respectively [19]. Another study assessed the efficacy of the GAC biofilter to reduce five pathogen surrogates using synthetic greywater (SGW), which is composed of chemical products to simulate organic and inorganic pollution of greywater from bathrooms [31]. The experiments were performed in a cylindrical column reactor (ø =9 cm; effective height of 60 cm). The reactor’s effective depth was packed with commercial GAC (mesh particle size of 4–12). In the study, the highest reduction (3.4 LR) was achieved with Saccharomyces cerevisiae, used as surrogate for Cryptosporidium and Giardia oo/cysts, obtaining different removal efficiencies against the other four surrogates: 1.1 LR for Staphylococcus epidermidis; 0.9 LR for Enterococcus faecalis; 0.3 LR for E. coli and no reduction was observed for MS2 bacteriophage [31]. The LR value raised with SGW was very similar to the corresponding obtained in our work (3.4 vs. 3.5, respectively), although the mesh size of the GAC employed was different. In the present work, the mesh size of the GAC was 12–40, while Sharaf et al. [31] used GAC with a smaller mesh size, specifically 4–12, which could increase the removal capability. The information regarding the mechanisms involved in the oocysts removal by GAC particles is limited. Hijnen et al. [19] evaluated the GAC adsorption filters as barriers for Cryptosporidium oocysts, among other pathogens, in water treatment and explained the removal of the oocysts by straining and attachment. Based on the experiments and the mathematical models applied, they reported a minor contribution of straining in removing Cryptosporidium oocysts. They attributed the removal to a strong attachment of these parasitic forms to the GAC. However, they concluded that there needs to be more information about several factors, such as the influence of GAC characteristics (shape and size), the column features (diameter and height) and the adhesion efficiency [19]. Although in the present work, the experiments were carried out with fresh GAC and well water, which prevents the formation of biofilms, previous studies suggested that the saturation and age of the GAC filter should be considered in the elimination of waterborne protozoan parasites because of these parameters can improve the removal of Cryptosporidium oocysts. Thus, polyvinyl chloride (PVC) columns (ø =3.2 cm; effective height of 74 cm) were loaded with GAC and fed during 18 weeks with river water amended with a nutrient solution (flow 5 m/h) to promote biofilm growth in the filter. Then, transport experiments were performed with river water spiked with C. parvum oocysts to a concentration of 6 ×10 5 oocysts/mL. The best removal performance was observed with aged GAC (71 ±2% or 0.54 LR) which supported the highest amount of biomass [21]. Moreover, Sharaf et al. [31] demonstrated 2.7 and 0.7 LR for S. cerevisiae (used as surrogate of Cryptosporidium oocysts) in saturated and unsaturated zones of a GAC biofilter, being the degree of biofilm development well correlated with high efficiencies of removal. Furthermore, eukaryotic organisms present in surface waters can grow in GAC filters of water treatment plants, proliferating along the distribution systems [32]. In addition, some waterborne pathogens can survival inside other microscopical organisms, which act as carriers through water systems [32–36]. The role of zooplankton, such as rotifers, copepods and cladocerans, as a temporary vehicle of pathogens through drinking water is still not well known. However, the impact of the predation by zooplankton on the transport and destination of Cryptosporidium oocysts in GAC filters was studied [37,38]. Thus, Bichai et al. [37] performed a study with two parallel GAC filter columns (ø = 15 cm; bed height of 1 m) in a pilot plant, which operated under full-scale conditions (filtration rate 5 m/h; contact time of 12 min; and no backwashing). After two weeks, they observed a mean mass reduction of C. parvum oocysts of 32.1% and 66.2% in the lower (50–95 cm) Fig. 2. Logarithmic reductions for each granular activated carbon (GAC) bed height obtained during the experiments carried out to evaluate the capability of GAC on the removal of Cryptosporidium parvum oocysts from well water (WW). S. Couso-P´ erez et al. Journal of Environmental Chemical Engineering 11 (2023) 111185 5 and the upper (0–30 cm) zones of the GAC filter beds, respectively [37]. Then, the zooplankton was isolated from the GAC filter bed and effluent water, identifying mainly rotifers, which are predators of oocysts [36, 37]. The authors concluded that the remobilisation of Cryptosporidium oocysts retained on GAC filters and the transmission of these parasitic forms to drinking water may be influenced by zooplankton [37]. Finally, C. parvum is considered by the WHO as the reference pathogen for waterborne protozoan parasites [3]. The International Scheme to Evaluate Household Water Treatment Technologies establishes a minimum required LR of ≥2 for protective methods (2-star) and ≥4 for highly protective methods (3-star) when C. parvum oocysts concentrations of ≥5×10 4 oocysts/mL are subjected with an acceptable reduction deviation of 1 logarithmic variance [13,30]. In the present work, >2 LR were achieved with a bed height of 35 cm, specifically, 2.93 ±0.53 LR. Therefore, the reductions raised by GAC filtration are consistent with a 2-star protection method according to the WHO, offering comprehensive protection against cryptosporidiosis. 4. Conclusions Studies evaluating the efficacy of GAC filters for the removal of the infectious forms of the waterborne protozoan parasite Cryptosporidium are scarce. Considering the results obtained in the present work and the filtration conditions, the oocysts of C. parvum were removed significantly from WW. Therefore, unlike bacteria and viruses, GAC filters can represent important additional barriers for Cryptosporidium oocysts in household water treatments in middle and low-income countries or poor resource environments, providing extra protection against cryptosporidiosis. 5. Recommendations for future studies Further studies are needed to evaluate the effects of GAC filters in the oocyst survival and the influence of GAC type and backwashing on the removal capability at full-scale. Moreover, it is well known that Cryptosporidium oocysts are sensitive to UV radiation and solar water disinfection (SODIS) method improves the microbiological quality of drinking water in medium and low-income countries, although Cryptosporidium oocysts are resistant to this procedure. In this way, the use of GAC filters may constitute one important barrier for protozoan parasites from drinking water, even can reduce its turbidity. Therefore, the implementation of these filters as previous step to SODIS would increase the protection against waterborne protozoan parasites. CRediT authorship contribution statement Seila Couso-P´ erez: Investigation, Formal analysis, Writing – original draft, Writing – review & editing. María Jesus Abeledo-Lameiro: Investigation, Writing – review & editing. Ana Isabel Vidal-Varela: Investigation. Hip´ olito G´ omez-Couso: Investigation, Formal analysis, Supervision, Writing – review & editing, Project administration, Funding acquisition. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data Availability Data will be made available on request. Acknowledgements This study is part of the research project entitled “Photo-irradiation and Adsorption based Novel Innovations for Water-treatment (PANIWATER)” (grant number 820718), which was jointly funded by the European Union’s Horizon 2020 Research and Innovation Programme of the European Commission and the Department of Science and Technology of India. SC-P is the beneficiary of a Margarita Salas contract funded by the Programme for requalification, international mobility, and talent attraction in the Spanish university system, Ministry of Universities (grant UP2021–042). References [1] U. Ryan, A. Zahedi, Y. Feng, L. 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