Evaluation de l’efficacité des désinfectants commercialisés sur les formes de résistances des protozoaires intestinaux en milieu aquatique

Abstract

Access to safe drinking water remains a major concern in sub-Saharan Africa, especially in urban areas where populations are confronted with pollution, poor hygiene, inadequate sanitation and lack of appropriate treatment methods at the household level. Therefore, the integration of chemical and biological water treatment processes could be a sustainable alternative in improving the quality of drinking water and water discharged into the environment after use. The present study conducted from March 2019 to September 2020 focuses on the evaluation of the efficaciency of several commonly used disinfectants (Moringa, Gypsum, Bleach, Calcium Chloride, Ammonia and Hydrogen Peroxide) on the resistance of intestinal protozoan dissemination forms in wastewater of various origins in a mesocosm at the Hydrobiology and Environment laboratory. Four sampling stations were selected corresponding to three types of effluent base on theies origin (student, mixed population, hospital) for this study: three in the city of Yaoundé (Cité Universitaire, Camp sic Messa and Hôpital Général) and one in the city of Douala (Bois de Singes). The first phase of this study which lasted 5 months (March to July 2019) consisted of a series of tests on several disinfectants to be used and the appropriate concentration range. The second phase, which took place from July 2019 to September 2020, consisted of taking wastewater samples in sterile bottles and transporting them to the laboratory in a refrigerated chamber for the quantification of protozoan cysts and oocysts using standard protocols. In the field, samples were pre-sieved to remove microparticles suspended in the water. In the laboratory, non-viable cysts and oocysts were removed by aspiration using the flotation power of n-butanol, and the resulting pellet was subjected to parasitological analysis (Faust, sedimentation, Ziehl Nielsen). In 07 different beakers (01 control and 06 tests) with 100mg/l, 200mg/l, 300mg/l, 400mg/l, 500mg/L and 600mg/l, 500mL of samples were introduced. The samples were then homogenised in order to bring the disinfectants and parasites into perfect contact. Then 5mL of the pellet was taken from each sample and washed twice with distilled water and sodium thiosulphate in order to neutralise the excess disinfectant in the sample. The monitoring of physicochemical and parasitological parameters at different decantation times made it possible to determine the optimal conditions and to evaluate the efficiency of the treatments. These tests showed that, depending on the abiotic characteristics of the water, settling times of between 24-36 h appeared to be sufficient to eliminate almost all the suspended matter and colloids. The physicochemical analysis showed that the wastewater studied is weakly basic (7.04±0.7 U.C), weakly oxygenated (32.4±14%), rich in suspended matter (1233.5±309.7 mg/L), colour (9211±8131.3PtCo) and turbidity (2350±1117.8 mg/L). The parasitological analysis identified 8 species (Cryptosporidium spp. 17%, Cyclospora spp. 5%, Isospora spp. 1%, Sarcocystis spp. 17%, Giardia spp. 5%, Entamoeba histolytica 6%, Entamoeba coli 47%, Balantidium coli 2%). During the treatment, the decrease of some physicochemical parameters such as biodegradable organic matter content expressed by oxidability and the increase of other parameters such as pH, electrical conductivity and Total Dissolved Solids facilitated the reduction of parasites during the treatment while the increase of other physicochemical parameters such as Suspended Solids, Total Dissolved Solids, turbidity and Colour had an antagonistic action. Parasitological removal was on average 95% for Isospora spp. 89% for Cryptosporidium spp. 88% for Cyclospora spp. and 90% for Sarcocystis spp. oocysts, 95% for Giardia spp., 96% for Entamoeba histolytica, 95.75% for Entamoeba coli and 98.5% for Balantidium coli cysts. The efficiency of each disinfectant varied according to its concentration and the nature of the effluent. Thus, oxygenated water acted by producing free radicals which interacted with membrane and cytoplasmic proteins facilitating the destruction of cysts and oocysts, bleach had similar effects, gypsum acted by producing Ca2+ ions allowing a drop in pH reducing contact with the cystic wall and weakening it, Calcium chloride acted on the membrane of cysts and oocysts by detrushing lipopolysaccharides which facilitated membrane permeability and rupture, and moringa acted by facilitating the precipitation and oxidation of the cystic wall, due to the double power of Quiercetin. Out of desinfectants , Calcium chloride and moringa showed more efficiency. These results showed on the one hand that cysts and oocysts of intestinal protozoa are more resistant to commonly used disinfectants (bleach, hydrogen peroxide, etc.) and on the other hand that the treatment of raw water with the aqueous extract of the leaves of Moringa oleifera, which is less toxic than other disinfectants, considerably improves the quality of the water.