Joaquín Suárez

Storm tank against combined sewer overflow: Operation strategies to minimise discharges impact to receiving waters

The pollution reduction opportunities of a drainage basin, located in Barcelona (Spain), were analysed as a case study in order to assess strategies for optimised management of sewerage networks in the Mediterranean region. The analysis results show that the introduction of a large storm tank against combined sewer overflow significantly reduces the negative impacts associated with discharges during rainy weather. The total annual mass into the receiving waters is reduced by 45%, measured in terms of suspended solid and chemical oxygen demand. The performance of large storm tanks can be optimised taking advantage of the natural sedimentation of the retained rainwater. At optimum stratification conditions, the annual regulation capability can be increased by 15% compared to the traditional operating conditions. Apparently, the environmental impacts associated with the materials used in the construction of the tank will also be reduced per unit volume of regulated water with the increasing annual regulation capacity.

Global Sensitivity and GLUE-Based Uncertainty Analysis of a 2D-1D Dual Urban Drainage Model

AbstractThis paper presents a global sensitivity and uncertainty analysis of a dual drainage model applied to a 0.049 km2 (4.9-ha) urban catchment based on generalized likelihood uncertainty estimation (GLUE). The model solves the nonlinear bidimensional (2D) and one-dimensional (1D) Saint-Venant equations to compute respectively the surface runoff and the flow in the sewer network. The sensitivity of the outlet hydrograph to the input parameters of the model was determined by using variance-based Sobol sensitivity indices. These indices highlight the great effect of the overland flow parameters on the model output, in contrast with the limited effect of the sewer-network parameters. The Manning coefficient of the impervious terrains was identified as the most influential model parameter. The effect on model calibration of two subjective factors of the GLUE methodology (the acceptability threshold and the shaping factor of the likelihood function) was analyzed. From this analysis, a NSE acceptability thre...

A simplified method for determining potential heavy metal loads washed-off by stormwater runoff from road-deposited sediments

A simplified method is proposed for determining the potential load of heavy metals (HMs) derived from the wash-off caused by surface runoff on road-deposited sediment (RDS). The method consists of three phases: (i) characterization of RDS load wash-off, (ii) assessment of HM load in dry weather, and (iii) application of a wash-off equation. Two processes were included in the wash-off equation: HM transport (solid fraction) and HM leaching (dissolved fraction). The average wash-off of HMs ranges from 16.6 to 46.3%, relative to the total mass of HMs associated with dry-weather RDS (Pb, Zn, Cu, Cr, Ni, Cd, Fe, Mn, Co, and Ba). Cd, Mn, and Zn presented the highest wash-off in the areas studied. The size fraction below 250μm contributed an average of 86.7% of potential HM load washed-off from RDS. Based on the phenomena included in the wash-off equation, it was observed the following order of precedence: transport of RDS<250μm, leaching of RDS<250μm, and leaching of RDS≥250μm. Solid and dissolved fractions contributed 70.7 and 29.3% of the potential HM load washed-off by runoff from RDS, respectively. The proposed method serves as a management tool for road HM pollution during rain.

Simultaneous carbon and nitrogen removal from municipal wastewater in full-scale unaerated/aerated submerged filters

Characterization and evaluation of a biological submerged filter was carried out on a full-scale pilot plant performing removal of biochemical oxygen demand (BOD) and total nitrogen (TN) from pre-treated urban wastewater. The average influent values of BOD5, chemical oxygen demand (COD) and TN were 370, 1,015 and 60 mg/L, respectively. The pilot plant produced good discharge quality during steady-state operation. Average effluent BOD5, COD and TN values were 11, 58 and 15 mg/L, respectively. The reactor had been operating beyond its organic design capacity (200 population equivalent (PE)). At 480 PE the removal achieved for BOD, COD and TN were 98, 97 and 78%, respectively. This technology can absorb pollutant overloads while maintaining stable performance. Denitrification was performed by using sewage itself as carbon source. It was used as an intermittent aeration cycle in the unaerated cell to improve the denitrification process. The predenitrification with submerged unaerated filter has proved to be an efficient process for advanced removal of TN.

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.