Application of Hybrid Process of Coagulation/Flocculation and Membrane Filtration for the Removal of Protozoan Parasites from Water

Abstract

Among the waterborne diseases, enteric diseases are most frequent. Approximately 19% of waterborne gastroenteritis outbreaks in the United States are attributed to parasitic protozoans, particularly Giardia and Cryptosporidium species, due to their wide distribution in the environment, high incidence in the population, and resistance to conventional water treatment. These microorganisms and impurities present in water do not approach each other, it is necessary to add a coagulant. Chemical coagulants are the most used and among them the most common is aluminum sulfate, since it is cheap and easily obtained. However, chemical coagulants have certain disadvantages, as they require tight control over their residual concentration in treated water for human consumption as well as in industrial food production. Then, the objective of the present work was to evaluate the efficiency of Moringa oleifera seeds as natural coagulant in removing apparent color, turbidity, Giardia spp. cysts and Cryptosporidium spp. oocysts from water in association with microfiltration. The surface water used in the tests was collected at the Pirapó river basin, which supplies the city of Maringá, Paraná, Brazil. Samples of high and low turbidity were mixed to obtain water with different initial turbidities. Water samples with initial turbidity of 50, 150, 250, 350, and 450 NTU were used in this study. Prepared samples were artificially contaminated with 106 cysts/L of Giardia and 106 oocysts/L of Cryptosporidium obtained from the positive control (suspension of cysts and oocysts) present in the commercial kit Merifluor (Meridian Bioscience, Cincinnati, OH, USA). After being prepared, these samples were subjected to the processes of (1) coagulation/flocculation with moringa seeds (CFM), (2) coagulation/flocculation with aluminum sulfate; (3) microfiltration (MF), and (4) combined coagulation/flocculation with moringa seeds or aluminum sulfate followed by microfiltration (CFM-MF or CFM-MF). Coagulation/flocculation tests with moringa were performed in a jar test device. Each sample, with initial turbidity from 50 to 450 NTU, was subjected to 12 different concentrations.of moringa coagulant solution, ranging from 25 to 350 mg/L. Polyimide membrane with porosity of 0.40 μm was used for the MF process with an operating pressure of 1 bar. Moringa solution concentrations above 150 mg/L showed the best removal efficiency of turbidity – which varied from 3% to 97% – and color, ranging from 6.7% to 73.5%. The CFM process achieved 1.2 log removal for Giardia and 1.0 log removal for Cryptosporidium. To membrane process, color and turbidity removal ranged from 80 to 100%, and the best results were obtained with the combined CFM-MF. It was also observed that the pretreatment with moringa reduced membrane fouling (which was between 7.48 and 40.9%) and increased permeate flux (between 157 and 226 L/hm) when compared with the MF (membrane fouling from 6.13 to 56.32% and permeate flow from 157 to 187 L/hm2). It can be concluded that coagulation with moringa showed satisfactory results, reducing the number of (oo)cysts of protozoan parasites in accordance with WHO recommendations for the process of coagulation/flocculation, as well as reducing color and turbidity. Combined with MF, the proposed process removed nearly 100% of Giardia and Cryptosporidium (oo)cysts and achieved high levels of color and turbidity removal from water samples, presenting the advantage of improving the quality of filtered water and the characteristics of the MF process (reduction of fouling and increase of permeate flux).