Wastewater Discharge and Reuse Regulation in Costa Rica: An Opportunity for Improvement

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.