TU Berlin

Urban Water InterfacesS1 - Interfaces in sewer systems – corrosion and odour

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S1 - Interfaces in sewer systems – corrosion and odour

Doctoral candidate: Micaela Pacheco Fernandez

Supervisors: Prof. Dietmar Stephan, Prof. Matthias Barjenbruch, Prof. Ulrich Szewzyk, Regina Gnirss

Introduction/Background

Some of the main problems associated with sewer networks are odour nuisances and corrosion. These conditions commonly arise due to the ageing of the sewer network (old systems), weather variations (dry and wet periods) and the reduction of the water consumption in cities. These events lead to high retention times of wastewater in sewer pipes and to the development of anaerobic conditions. In this case, hydrogen sulphide (H2S) is produced in the wastewater due to biological processes and then further released into the sewer atmosphere, producing the unpleasant smell of rotten eggs, health risks to sewer workers as well as corrosion and in the worst case structural failures of the sewer pipe system due to biogenic sulphuric acid corrosion.

Aims

The main objective of project S1 is the study of physical and chemical interactions across the air-water interface in sewer systems. With this aim, a two-step strategy has been planned.

First, the project focuses on the monitoring prediction and formation of sulphurous species in the water phase with a UV/Vis spectral analyser.

Second, once the first step is completed, the project will study the hydrogen sulphide mass transport across the air-water interface under turbulent waterflow conditions. The UV/Vis analyser employed in step one will be implemented at this stage to continuously monitor the liquid phase.

After completion of step two, the experimental results can be used for validation of the model (project S2, Abhinav Dixit) developed by Katharina Teuber (project T3).

Methods

The research activities related to this project are carried out at the sewer pilot plant of the Berlin Waterworks (Berliner Wasserbetriebe).  A schematic layout of the plant is shown in Figure 1.

Figure 1: Schematic layout of the sewer pilot plant of the Berlin Waterworks
Lupe

 

Results

Before implementing the UV/Vis spectral analyser, the device was calibrated according to the wastewater matrix of the sewer pilot plant. The working principle of the spectral analyser is shown in Figure 2.

Figure 2: Principle of a UV/Vis Spectral analyser
Lupe

After a first calibration, the spectral analyser was tested for predicting the sulphate concentration in several wastewater samples. Results show that in all tested samples the sulphate concentration ranges between 100 and 200 mg/L (Figure 3), which is in good agreement with the measurement range of Berlin. Furthermore, the spectral analyser is currently being calibrated for monitoring the total dissolved sulphide concentration (S2-, HS- and H2S) in wastewater. The aim of this calibration is to predict the concentration of the individual sulphide species based on their chemical equilibrium.

Figure 3: Sulphate concentration of several wastewater samples predicted by spectral analyser
Lupe

Preliminary experiments for step two have been carried out with oxygen in a test reactor. The mass transfer has been studied under various turbulent conditions and results have been quantified by calculation of the mass transfer coefficient KLa. The oxygen experiments were performed using the absorption method, where the oxygen transfer is computed by increasing the concentration (Figure 4, left) of the initially artificially lowered oxygen concentration. The KLa value was calculated using the log deficit parameter estimation (Figure 4, right). The experiments related to the hydrogen sulphide mass transport are currently being carried out in the test reactor. After completion of the reactor experiments, these studies will be performed at a larger scale in the sewer pilot plant.

Figure 4: Left: oxygen absorption in the liquid phase under turbulent conditions. Right: Log deficit parameter estimation method.
Lupe

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