Abstract
A database was built with the results of the physicochemical analysis of 23,435 samples of wastewater discharges obtained from the operational reports presented and the cross-checks carried out by the Ministry of Health to the operating entities, in accordance with the provisions of Decree 30661-MINAE-S, for the period 2016–2020. Using Bayesian networks, the probabilities of compliance with current regulations were estimated by preparing an acyclic directed graph for three alternative scenarios. At the national level, the BOD and the COD are the variables that record the lowest values, showing important differences between the results obtained for the central region of the country with respect to the other regions. Another determining variable turned out to be the type of final disposal, wherein the reuse of wastewater presents important compliance deficiencies for all regions except for Chorotega. In the case of BOD, COD and TSS, the lowest probabilities are recorded for ISIC codes 3821 (treatment of non-hazardous waste), 1040 (manufacture of animal and vegetable fats) and 145 (pig farming). Additionally, the integrated environmental risk was calculated as a product of the discharges, obtaining that for the evaluated parameters, the BOD and COD represent the highest risk values given their probability of occurrence rate, as well as the magnitude of the environmental impact. The Pacifico Central and Brunca regions recorded the highest integrated environmental risk value for BOD, COD and TSS compared to the other areas of the country. Based on the results obtained, proposals for improvement were generated for the control of wastewater discharges carried out by the environmental authorities in search of achieving a better comprehensive management of the water resource.
Highlights
Most countries worldwide have seen an accelerating pattern of economic growth coupled with a strong trend of unplanned urbanization, leading to a series of impacts associated with the discharge of pollutants across several environmental matrices that include the aquatic environment [1]
To study the variability of the data obtained, an ANOVA analysis of the biological oxygen demand (BOD), oil and grease (OG), chemical oxygen demand (COD) and total suspended solids (TSS) was performed for every planning region, considering the mechanism of final disposal and the wastewater sample type where the subclassification of both the mechanism of disposal and sample type comes from Decree 33601-MINAE-S, which regulates the disposal and reuse of wastewaters in Costa Rica
Regarding BOD and COD, the Central and Brunca regions record the highest mean concentrations with no significant differences between them, while the Huetar Norte and Chorotega regions show the lowest concentrations. When it comes to disposal type, the lowest values for BOD and COD are for wastewater discharged into receiver bodies, which are statistically different from the means for reuse and sewerage
Summary
Most countries worldwide have seen an accelerating pattern of economic growth coupled with a strong trend of unplanned urbanization, leading to a series of impacts associated with the discharge of pollutants across several environmental matrices that include the aquatic environment [1]. Most of the residual water treatment systems in developed countries focus on removing suspended solids and organic matter; some nutrients such as nitrogen, phosphorous, trace metals and emerging contaminants may still be present in the discharge, contributing to the eutrophication process and posing various environmental risks [3]. Lack of proper sanitation infrastructure to treat wastewater contaminates the environment and increases the burden on human health, leading to economic activity loss and a decrease in potential general growth.
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