Water quality information is essential supporting decision making in water management processes. The lack of information restricts, at some point, the implementation of adequate sanitation, which is still scarce in developing countries. In this study, an ecosystemic water quality assessment was conducted in the Virilla river in Costa Rica, in a section of particular interest for future sanitation development. It included the monitoring of physical, chemical, microbiological and benthic macroinvertebrate parameters from 2014 to 2016. Mutivariate statistics and water quality indexes were used for data interpretation. Results indicated that water quality decreased downstream towards more urbanised areas. Particularly, extreme values of phosphorous, nitrogen and E. coli were found. Sample sites were grouped in two clusters, which were consistent with land use. Benthic macroinverterbrates diversity was predominantly represented by Baetidae, Chironomidae, Leptohyphidae, Hydropsychidae, Simuliidae and Physidae. They were mostly influenced by water temperature, nitrite, ammonium, soluble reactive phosphorous, total solids, alkalinity, nitrate and total suspended solids. Three water quality indexes consistently showed the poor condition of the water body. The overall results indicate that the main sources of pollution in the river are likely to be wastewater discharges. Thus, special efforts should be undertaken regarding its regulation in the country.

Introducción: La calidad del agua en una cuenca hidrográfica, y su uso potencial, se ven afectados por factores antrópicos y naturales. El río Tárcoles es el receptor final de aguas de la región central de Costa Rica, donde el tratamiento de aguas residuales es inadecuado o inexistente. Objetivo: Evaluar la contaminación del agua en el río y evaluar a los macroinvertebrados como bioindicadores del ecosistema. Métodos: Se realizaron evaluaciones fisicoquímicas, microbiológicas y de macroinvertebrados del agua superficial en cuatro sitios durante doce meses consecutivos, incluidos dos índices de calidad del agua (ICA-NSF y holandés). Hicimos visitas mensuales para la colocación y recolección de sustratos artificiales para macroinvertebrados acuáticos, y visitas bimensuales para la recolección de muestras de agua para análisis ex situ de los parámetros fisicoquímicos y microbiológicos. Además, se caracterizó el uso del suelo en la parte baja de Tárcoles a partir de archivos tipo “raster” de cobertura. Resultados: Algunas variables fisicoquímicas tuvieron concentraciones similares a las informadas para otros ríos costarricenses, mientras que el oxígeno fue inferior. Las variables microbiológicas indicaron altos niveles de contaminación, especialmente en la época de lluvias. En la estación seca, hubo más macroinvertebrados acuáticos, siendo Chironomidae, Oligochaeta e Hydrobiidae los más abundantes. La contaminación de los ríos se clasifica como "incipiente" según el índice holandés y como "calidad media" según el ICA-NSF. Conclusiones: la contaminación del río Tárcoles se debe principalmente a un uso inadecuado del suelo y actividades antrópicas. Recomendamos un plan de gestión de cuencas e investigación sobre la salud del ecosistema y la conservación de especies vulnerables.

Currently, nitrogen has become the main element of water pollution, causing riverine, lacustrine and coastal eutrophication. The continuous contamination of aquifers and the absence of planned water resource utilization, boost its scarcity, and has been the only way in which our societies become aware of the urgent need to process the generated wastewater. The objective of this research was to evaluate the nitrifying capacity of different autochthonous bacterial isolates from soils from nearby sources of domestic wastewater drainage. For this, bacteria were isolated from Pirro River, contaminated with nitrogen of domestic sewage. Nitrifying bacteria were counted by serial dilution and agar plates, and were isolated until obtaining axenic colonies. These were identified by biochemical batteries or genetic sequencing, and the quantification of their nitrifying capacity was obtained by the methods 4500- NH4 + -F and 4500-NO-2-B, all between September 26, 2011 and March 16, 2014. A total of seven strains of nitrifying microorganisms were isolated and purified, including four Streptomyces sp., one Pseudomonas putida, one Sphingomonas sp. and one Aeromonas sp. We found that there were 2.23 x 105 UFC/g of soil of ammonium oxidizing bacteria and 2.2 x 104 CFU/g of soil of nitrite oxidizing bacteria in the samples. The quantification of the nitrifying capacity of the strains by colorimetric methods, determined that the maximum ammonium removal capacity was 0.050 mg N/L/day and 0.903 mg N/L/day of nitrite. The collection of few strains of nitrifying organisms and a low CFU count, can be attributed to the technique used, since this only recovers 1 % of the microorganisms present in a sample, which, however, is acceptable for studies which main purpose is to obtain cultivable microorganisms. Future research should consider removal tests with higher ammonium and nitrite levels, to find the maximum capacity of the isolated microorganisms, and evaluate their potential use in wastewater treatment systems.

El objetivo de esta investigación fue determinar la relación entre la calidad del agua superficial en la parte alta de la microcuenca del río Poás y las principales presiones socioambientales que pueden alterar este factor. Para ello se realizó un estudio exploratorio, con enfoque cuantitativo, donde se identificaron las principales presiones socioambientales que experimenta el recurso hídrico en la zona. Además, se analizó la calidad del agua superficial a través de indicadores físicos, químicos y microbiólogos, para la aplicación de dos índices de calidad. Se encontraron seis presiones socioambientales de impacto negativo al recurso, materializadas a través de acciones puntuales ejecutadas desde el hogar y otras actividades de tipo socioeconómico. A pesar de que la evidencia mostró cumplimiento mayoritario de los parámetros analizados con los criterios de calidad sugeridos a nivel nacional e internacional, los índices revelaron niveles de contaminación incipiente, además de calidad buena y media. Estadísticamente, se encontró que la calidad del agua de la microcuenca no varía espacialmente; sin embargo, sí lo hace de manera temporal, debido a la incidencia de los patrones de lluvia en la zona. Este hallazgo, en conjunto con la determinación de correlaciones significativas entre los parámetros monitoreados, contribuyó a reconocer que los sitios analizados en época lluviosa mantienen mayor relación con parámetros asociados con contaminación orgánica debido a procesos de escorrentía y descarga de agua residual. Por tanto, se plantea la necesidad de coordinar esfuerzos que garanticen la sostenibilidad de la microcuenca, que mejoren la infraestructura sanitaria local, fortalezcan los procesos de gestión del agua y se dirijan al establecimiento de una red de monitoreo desde un marco de referencia con visión de cuenca.

Herein, we report the physical, chemical, and biological treatment of wastewater generated in the teaching laboratories at Universidad Nacional, Costa Rica. Initial physicochemical treatment included neutralization and coagulation-flocculation, followed by a biological treatment with fungi (Aspergillus sp. and Penicillium dipodomyicola) or bacterias, the latter were isolated from the sludge from the campus’ wastewater treatment plant and the greywater collection tank at the School of Chemistry. The samples’ pH prior to treatment was ≤ 2, while COD ranged between 3000 and 30 000 mg/L. Gas chromatography-mass spectra analysis indicated the presence of 55 organic compounds in the wastewater, some of which reached undetectable concentrations after treatment. The fungi and the bacterial strain removed up to 50% of the substances, while the toxicity decreased with respect to time of exposure to the treatment. Results support the potential use of these microorganisms as bioremediators. Although the organic compounds were partially removed, the treated wastewater exhibited high toxicity for Daphnia magna (water flea). Further experiments with longer treatment times or other strains might be needed for effective removal of pollutants.