Remoção de oocistos e de indicadores físicos de Cryptosporidium Parvum em águas de abastecimento por meio de decantação: estudo em escala piloto

Abstract

The presence of microorganisms, that present low infectious dosage and high resistance to the usual water treatment process, is a threat to public health. The contamination of surface water by Cryptosporidium has deserved special attention by researcher and public health authorities,because there is no doubt that, in greater or lesser degree, springs carries these microorganisms, as it has been demonstrated in some research projects. The Brazilian public health law nº 518/2004, recommends the research of Cryptosporidium in water destined forhuman consumption and considers that the reduction of turbidity to values inferior to 0,5 NTU is an important factor in the control of these microorganisms. However, it is necessary to make complementary studies to demonstrate the effectiveness of using turbidity as amicrobiological standard. Regarding the limitations of this detection method, it has been evaluated the usage of parameters that allow us to estimate the removal of protozoa in water treatment. The incorporation of biological parameters such as, aerobic esporogenic bacteria(Bacillus subtilis) and the physical parameters (turbidity and microsphere), admits the hypothesis that there may present similar removal standards as those registered for oocysts of Cryptosporidium. Considering the sanitary importance of the occurrence of outbreaks ofcriptosporidiosis, it the growing the awareness that it should be optimized the process of unitary operation that may guarantee the microbiological quality of water, which constitutes one of the objectives of this work. The present work evaluated, in a pilot scale, the efficiencyof two types of water clarifiers (conventional of vertical flow and high rate) regarding the removal physical indicators and of oocysts of Cryptosporidium. Two types of water were evaluated, simulating high and low turbidity situations (10 ± 0,5 NTU and 100 ± 5,0 NTU), utilizing two types of coagulants aluminium sulphate and ferric chloride. The experiments made in laboratory were done to determine the dosages of the coagulants and of the velocity gradients from the flocculaters used in the pilot-installation. Four levels of treatments were made and the efficiencies were compared to each sedimentation and the influence ofoperational conditions in the decanted water quality. It was concluded in this work that both decanters present similar behaviors regarding the removal of oocysts of Crysptosporidium, the turbidity and microspheres and that operations of treatment that used ferric chlorides in the process of coagulation had the best results. It was observed that microspheres can be used as indicators and that turbid waters present greater removal of oocysts of Cryptosporidium.