The hydraulic model EPANET was applied and calibrated for the water distribution system (WDS) of La Sirena, Colombia. The Parameter ESTimator (PEST) was used for parameter optimization and sensitivity analysis. Observation data included levels at water storage tanks and pressures at monitoring nodes. Adjustable parameters were grouped into different classes according to two different scenarios identified as constrained and unconstrained. These scenarios were established to evaluate the effect of parameter space size and compensating errors over the calibration process. Results from the unconstrained scenario, where 723 adjustable parameters were declared, showed that considerable compensating errors are introduced into the optimization process if all parameters were open to adjustment. The constrained scenario on the other hand, represented a more properly discretized scheme as parameters were grouped into classes of similar characteristics and insensitive parameters were fixed. This had a profound impact on the parameter space as adjustable parameters were reduced to 24. The constrained solution, even when it is valid only for the system's normal operating conditions, clearly demonstrates that Parallel PEST (PPEST) has the potential to be used in the calibration of WDS models. Nevertheless, further investigation is needed to determine PPEST's performance in complex WDS models.

This study presents the behavior of residual chlorine using computer modeling for a small water supply system located in La Sirena, Cali, Colombia. The study included field work to calibrate and validate the model together with lab determinations. Results show that the kinetics of first and second order together with the kinetics of mixed order can adequately describe the behavior of residual chlorine in this type of network. The research showed the variables that influence the behavior of residual chlorine in the network are: the quality of the input water, chlorine dosing, the effect of storage that increases the water age, and the presence of dead zones in the tanks. The study revealed that 95% of the reaction occurs in the storage tanks due to the small variation in the water level and the negligible reactions at the pipe walls. This study proved that the residual chlorine modeling in this small network in particular is a valuable tool for monitoring the water quality in the distribution network, which is useful to comply with water quality guidelines.

This work aims to examine the effect of bias correction (BC) methods on the development of Intensity–Duration–Frequency (IDF) curves under climate change at multiple temporal scales. Daily outputs from a 9-member CORDEX-CA GCM-RCM multi-model ensemble (MME) under RCP 8.5 were used to represent future precipitation. Two stationary BC methods, empirical quantile mapping (EQM) and gamma-pareto quantile mapping (GPM), along with three non-stationary BC methods, detrended quantile mapping (DQM), quantile delta mapping (QDM), and robust quantile mapping (RQM), were selected to adjust daily biases between MME members and observations from the SJO weather station located in Costa Rica. The equidistant quantile-matching (EDQM) temporal disaggregation method was applied to obtain future sub-daily annual maximum precipitation series (AMPs) based on daily projections from the bias-corrected ensemble members. Both historical and future IDF curves were developed based on 5 min temporal resolution AMP series using the Generalized Extreme Value (GEV) distribution. The results indicate that projected future precipitation intensities (2020–2100) vary significantly from historical IDF curves (1970–2020), depending on individual GCM-RCMs, BC methods, durations, and return periods. Regardless of stationarity, the ensemble spread increases steadily with the return period, as uncertainties are further amplified with increasing return periods. Stationary BC methods show a wide variety of trends depending on individual GCM-RCM models, many of which are unrealistic and physically improbable. In contrast, non-stationary BC methods generally show a tendency towards higher precipitation intensities as the return period increases for individual GCM-RCMs, despite differences in the magnitude of changes. Precipitation intensities based on ensemble means are found to increase with the change factor (CF), ranging between 2 and 25% depending on the temporal scale, return period, and non-stationary BC method, with moderately smaller increases for short-durations and long-durations, and slightly higher for mid-durations. In summary, it can be concluded that stationary BC methods underperform compared to non-stationary BC methods. DQM and RQM are the most suitable BC methods for generating future IDF curves, recommending the use of ensemble means over ensemble medians or individual GCM-RCM outcomes.

The presence of manganese (Mn) in drinking water causes aesthetic, operational, and health problems. Removal of Mn(II) by the use of Mn oxidizing microorganisms in biofiltration processes has been studied leading to a more economical and environmentally friendly process than conventional treatments with chemical products. There are multiple reports in temperate regions, but little information under tropical conditions, concerning Mn(II) removal by microorganisms. In this study, 13 autochthonous culturable manganese oxidizing bacteria isolated from water of two wells with ∼0.6 mg L⁻¹ and ∼0.2 mg L⁻¹ Mn(II), respectively, were evaluated in vitro to determine their potential as inoculums for application in biofiltration processes. The oxidation capacity of Mn(II) was evaluated by a qualitative test with Leucoberbelin blue I and the Mn(II) removal was quantified by measurements of the residual Mn(II) in a culture broth with an initial concentration of 5.9 mg L⁻¹. The biofilm formation capacity of the strains was also determined by crystal violet staining and by quantification of polysaccharides of extracellular polymeric substances. Three strains showed the highest percentage of Mn(II) removal in the culture in broth, two belonging to the genus Aeromonas (HAC-12 and RUE-1), with removal values of 42.5% and 40.1%, respectively, and one belonging to the genus Stenotrophomonas (S-3), with 40.3% removal. Besides, HAC-3B and RUE-6A showed the highest production of exopolysaccharides. These results allowed the selection of an Aeromonas strain (HAC-12) and one Stenotrophomonas strain (S-3) as possible candidates to be used as inoculums in biofilters for the removal of Mn(II) from groundwater.

Resumen El arsénico presente en agua puede llegar a causar serios problemas en la salud de los consumidores. En Costa Rica, se han identificado aguas de consumo humano con concentraciones mayores al límite permitido (10 µg/L). La adsorción del arsénico por un material adsorbente ha sido utilizada en otros países con éxito. Para ello, se han utilizado gran variedad de materiales adsorbentes sintéticos, naturales o subproductos de procesos industriales o agrícolas. Los adsorbentes sintéticos, por lo general, presentan alta capacidad de adsorción pero representan altos costos adquisitivos, contrariamente a los materiales naturales y de residuos de procesos que aunque tienen capacidades de adsorción menores, son más baratos y se encuentran más fácilmente. En el marco del contexto en mención, se presenta un análisis de las opciones de materiales naturales de origen local y de bajo costo adquisitivo, con un contenido relativamente alto de óxidos de hierro, aluminio y titanio, que podrían ser utilizados para remover arsénico del agua. Los materiales identificados son biotita, piedra caliza, diatomita, arenas ricas en magnetita y rocas piroclásticas de composición basáltica. Todos esos materiales son originarios de la zona de Guanacaste, afectada por la presencia de arsénico en agua.

Biofiltration for Mn removal has not been proven in the tropics (18–29 °C). Also, the use of pumice as an alternative filter medium for Mn removal is still poorly known. In this study, a bench-scale biofiltration experiment, using virgin pumice, silica sand, and anthracite, was conducted for 107 days using tropical groundwater at 22 °C. Characterization of manganese oxide (MnO_x) on filter media was carried out by Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The ability of culturable bacteria to oxidize Mn was verified by the leucoberbelin blue dye assay (LBB). The microbial activity on filter media was studied by ATP analyses. Identification of the MOB was performed by 16S rRNA sequencing. Results showed that the ripening time in each column was similar (∼80 days); therefore, the filter media and water temperature do not seem to accelerate the start-up period. The MnO_x present on all ripened media was of the birnessite type. The MnO_x morphology, influent water parameters, and microbiological activity suggest a start-up period likely assisted by biological oxidation. Therefore, biofiltration for manganese removal is feasible under tropical conditions. The similarity in the performance of pumice with the other media confirmed its suitability for biotic Mn removal. All materials presented similar known MOB at the genus level; however, different closest related species colonized selectively the filter media. Two strains of Pseudoxanthomonas sp., a not recognized genus on matured biofilters, look promising as inoculums in pumice and sand. Proper application of biofiltration in the tropics needs operational and bioaugmentation strategies.