Análise da demanda química de oxigênio em águas subterrâneas de municípios do estado do Ceará

Abstract

Because it has an irregular rainy block during the year, the surface water reservoirs of the State of Ceará have low levels, thus increasing the risk of water crisis in the state. An alternative to enable the obtaining of water for the municipalities of the state is the use of groundwater, accessed through the drilling of deep wells. Although they are waters less susceptible to pollution risks because of their geolocation, groundwater can be polluted by anthropic actions, such as irregular sewage dumping, making a characterization of its quality an indispensable study. Thus, the present work aims to analyze the quality of groundwater, focusing on the Chemical Oxygen Demand (COD) and relate this variable with the amount of organic matter present in the samples. The COD analyses were performed, using the colorimetric technique as described in APHA (2017), in 15 samples collected, following the procedures described in the National Guide for The Collection and Preservation of Water, Sediments and Effluents of the National Water Agency (ANA, 2011), in the second half of 2021, from three municipalities located in the interior of the State of Ceará. Based on the analyses performed and taking into account the mean values of COD and its relationship with the presence of organic matter, the municipalities 1 and 2 presented values of related to areas that have an anthropic and industrial activity (79.10 and 55.43 mg〖 O〗_2/L, respectively). Municipality 3 presented values corresponding to areas with low anthropic activity (31.30 mg〖 O〗_2/L) thus, with less load of organic matter, thus being able to relate groundwater to the pollution of organic matter present. A deviation was observed in only two samples from municipality 2, with COD of 218.49 mg〖 O〗_2/L and 329.49 mg〖 O〗_2/L, and the same ones were related to the presence of chlorides, considered one of the main interferences in the analysis of COD (APHA, 2017).