Determination of variables influencing the effectiveness of disinfection of surface water used for human consumption in Costa Rica

Disinfection of water for human consumption is a challenge to ensure that water is free of pathogens and pollutants while avoiding the formation of potentially harmful undesirable products. The establishment of disinfection facilities must take into account the local context as well as technical and economic feasibility to ensure their sustainability. Chlorination is a disinfection technique that is widely used throughout the world and can take several forms. However, this technique can lead to the formation of disinfection by-products, some of which are harmful to human health and are a source of growing concern. This present report focuses on chlorination using tablets that release chlorine when eroded by contact with water. This study aimed at improving the understanding of the effect of various parameters on the efficiency of water chlorination in the Cartago region (Costa Rica). First a chlorination facility located in a village near Cartago was studied. The purpose of this assessment was to diagnose the current situation, determine the changes needed to improve it and implement them. It was showed that the chlorine concentration delivered by this facility was too low and variable. A new chlorinator and a tank allowing a better mixing of the chlorinated solution have been installed. These modifications have resulted in a higher and more homogeneous chlorine concentration in the storage tanks and an improvement in some water quality parameters. On the basis of the results, recommendations were made to ensure the proper functioning of the facility and the continuation of measurements during future campaigns. It should be noted that this was a short-term study, measurements over a longer period would allow more precise conclusions to be drawn. The second part of the project concerned 10 chlorination facilities in the Cartago region. The purpose was to compare the results of various parameters of surface and groundwater samples collected in the rainy/transition season in 2018 with those of the 2019 dry season. For the moment there were thus only two series of data but this has nevertheless allowed us to observe an improvement in certain parameters during the dry season. Future measurements campaigns will consolidate these results.