Jose Anta

Assessing Wastewater Micropollutant Loads with Approximate Bayesian Computations

Wastewater production, like many other engineered and environmental processes, is inherent stochastic in nature and requires the use of complex stochastic models, for example, to predict realistic patterns of down-the-drain chemicals or pharmaceuticals and personal care products. Up until now, a formal method of statistical inference has been lacking for many of those models, where explicit likelihood functions were intractable. In this Article, we investigate Approximate Bayesian Computation (ABC) methods to infer important parameters of stochastic environmental models. ABC methods have been recently suggested to perform model-based inference in a Bayesian setting when model likelihoods are analytically or computationally intractable and have not been applied to environmental systems analysis or water quality modeling before. In a case study, we investigate the performance of three different algorithms to infer the number of wastewater pulses contained in three high-resolution data series of benzotriazole and total nitrogen loads in sewers. We find that all algorithms perform well and that the uncertainty in the inferred number of corresponding wastewater pulses varies between 6% and 28%. In our case, the results are more sensitive to substance characteristics than to catchment properties. Although the application of ABC methods requires careful tuning and attention to detail, they have a great general potential to update stochastic model parameters with monitoring data and improve their predictive capabilities.

Estimation of Drag Coefficient and Settling Velocity of the Cockle Cerastoderma edule Using Particle Image Velocimetry (PIV)

Abstract This paper presents the results of a hydrodynamic study of a cockle population from the Ullas estuary in Galicia (Spain). An analysis of the parameters has made it possible to determine the hydraulic characteristics of whole cockles during their threshold of movement and suspension. Dynamic analysis of the forces exerted on the submerged cockles led to a detailed characterization of a final population of 11 cockles, including their characteristic dimensions in addition to shell and body density. The friction angle between the existing sediment in the Ullas estuary and the cockle shells was also recorded. The particle image velocimetry (PIV) laser technique was successfully applied to obtain an accurate calculation of the threshold velocity fields. This experimental tool provides the means to experiment with various approaches of the velocity governing the onset of motion and to obtain a more detailed definition of the parameters involved. Applying the PIV technique, three drag entrainment coefficients were obtained with different velocity profiles. Using the depth-averaged velocity profile, a constant entrainment drag coefficient value of 0.43 was obtained for this cockle family, whereas the use of the upper tangential velocity on the cockle resulted in a value of 0.56 with a wider range of variation. This velocity may be considered a more intrinsic parameter of the movement of the cockle. The process of cockle sedimentation was also monitored, enabling us to ascertain the settling velocity and to calculate the settling drag coefficient. Both parameters present constant values in the group of cockles analyzed, with mean values of 0.36 m s−1 and 1.08, respectively. The settling drag coefficient was also calculated. A comparison of these two experimental values with other existing reports exhibited similar results, thus validating both the procedures used and the effect of the shape factor on the settling drag coefficient value.

Two-layer exchange flows over a dune: effect of large-scale bottom roughness

Graphical Abstract

Monitoring accumulation sediment characteristics in full scale sewer physical model with urban wastewater

A series of experiments were carried out with real wastewater in a pilot flume located at A Coruña wastewater treatment plant (WWTP) (Spain). A full scale model was developed to test a circular (300 mm inner diameter) and an equivalent area egg-shaped plastic pipe under controlled experimental conditions (pipe slope 2-5‰, averaged discharge Q = 4 L/s). Velocity profiles and sediment accumulation in the pipe invert was daily measured. Within the 7-11 days, the average sediment accumulation rate found in the circular pipe was between 1.4 and 3.8 mm/d. The sediment height depended on the input wastewater sediment distribution and organic content. The egg-shaped pipe presented no sediment deposit for the same downstream boundary conditions, although biofilms were attached to the walls of both pipes. Besides, wastewater quality was monitored continuously and sediment composition was studied at the end of experiments. Two types of sediment were recorded: a granular bed deposit (ρ = 1,460 kg/m3, d50 = 202 μm) and wall biofilms (ρ = 1,190 kg/m3, d50 = 76 μm).

Development of a Smart System for the Operation of a Complex Sanitation System

The urban runoff contains a significant amount of pollutants. Due to CSO limitations and WWTP’s biological processes, wastewater discharge must be regulated not only in quantity but also in quality. In this regard, Canal de Isabel II is working on the Manzanares Sanitation System project to characterise pollution in different rainfall scenarios by profiling the collected rainwater pollutants. The results will be used to develop an integrated management protocol for the stormwater tanks during rain events focused on minimising not only the discharged volume, but mainly the environmental impact produced by the discharge into the receiving water bodies. After a storage period, the effluent pollution is noticeably reduced for the mere reason to be stored into the stormwater tank. As a conclusion, the sewer system’s dimensioning idea based on characterisation of sewage is gaining straight over first flush or dilution concept. The project, headed by Canal de Isabel II, takes place in the city of Madrid and studies the CSS that belongs to Manzanares river’s catchment.

Characterisation of sediments during transport of solids in circular sewer pipes

This research is focused in the monitoring of sediments in circular sewer pipes with different diameters at a flume facility fed with urban wastewater. For this purpose, sediment physical and chemical characteristics, and sediment mobility were recorded. The Structure from Motion photogrammetric technique was used for the measurement of sediment bed evolution. In addition, sediment properties were determined in order to study the cohesiveness of the bed deposits. In particular, the chemical oxygen demand and the oxygen uptake rate of the sediment samples were analysed after different accumulation periods on the pipe inverts, resulting in a relation between these parameters and the mobility processes of solids.

Experimental study of pollutant washoff on a full-scale street section physical model

This study analyses the mobilization of total suspended solids (TSS) for different spatial distributions of sediment load located over the roadway surface of a full-scale street section physical model. At the sewer network outlet, flow discharges were measured and TSS pollutographs were determined with manual grab samples and inferred from turbidity records. In all the tests, the rain duration was 5 min and its averaged intensity was 101 mm/h. In addition, solids that were not washed off at the end of the experiments were collected from the street surface, gully pots and pipes and the mass balance error was checked. The experiments were configured to assess the influence of the initial load, spatial distribution method, distance from gully pot and distribution area dimensions on the TSS washoff. The study showed that sediment initial load and distribution cannot explain completely pollutant washoff processes because other variables such as the spatial rainfall distribution or the runoff depth also affect to the outlet pollutographs and system mass balances.