Evaluation of Sulfide Control by Air-Injection in Sewer Force Mains: Field and Laboratory Study

Abstract

Chemical and biological processes consume dissolved oxygen (DO) in urban wastewater during transportation along sewer systems. Anaerobic conditions (DO < 0.2 mg/L) are easily reached, leading to sulfide (S 2− ) generation. Release of free sulfide, hydrogen sulfide gas (H 2 S), from the liquid to the gaseous phase, causes odor, corrosion of pipes and supposes a risk for health of people working in sewers. These issues get worse in force mains, due to inability to take oxygen from the gaseous phase of pipe. Air injection is a suggested practice to control H 2 S emission in force mains. That technique aims to keep aerobic conditions in wastewater in order to avoid sulfide generation and favor a decrease of Biochemical Organic Demand (BOD). However, several force mains with air injection are not achieving their goals due to a limited oxygen transfer. Field measurements of dissolved oxygen in urban wastewater are presented in an existing force main with air injection during the summer of 2014 in the southeast of Spain. A laboratory scale model is constructed to quantify two-phase flow conditions in pipe due to air injection for different incoming flows rates of water and air. Particularly, for the case of plug flow, also known as elongated bubble flow. Velocity field measurement of water phase in laboratory allows estimating turbulent diffusivity of oxygen in the water, E m , and inter-phase mass transfer coefficient K L (T). In the laboratory, flow and air depth, bubble length, water velocity field, pressure inside force main and water and airflow rates are determined experimentally. These variables are used to assess DO in water phase of force main by comparison with those obtained from field measurements. This work allows assessing air injection efficiency in wastewater, and, therefore, to predict DO in wastewater in force mains.

Analysis and interpretation of radiometric signals in a liquid-gas bubble flow

“…In presented experiments, the air was injected to the pipeline test section through a special nozzle generating a dispersed bubble flow. In contrast to the slug flow [10,15,16], in the bubble flow the bubbles do not have a free surface and are very small, in the order of a few mm. In the further section of the pipeline, bubbles forms clusters, as shown in Fig.…”

Odours in Sewerage—A Description of Emissions and of Technical Abatement Measures

“…Pumping may also be necessary along sections just prior to treatment plants. Gravity systems operating in conjunction with pressure conduits are particularly unsuited to maintaining wastewater in a state of appropriate quality [22]. This reflects the retention volume of wastewater [23], as adjusted in line with flow conditions.…”

An analysis and interpretation of the signals in gamma-absorption measurements of liquid–gas intermittent flow

“…• Square of Froude number (Morgado et al 2016;García et al 2017): • Characteristic dimension for liquid phase:…”

“…Although the technology of tomographic measurements is a familiar phenomenon, research in the development of such methods continues because the measurement systems usually constitute complex multi-sensor systems. As far as environment protection and hydrogeology is concerned, radiotracer methods are applied (Witczak et al 2009;García et al 2017;Biswal et al 2018). The development of the aforementioned measurement methods is also facilitated by the progress in the analysis of signals which uses advanced mathematical methods.…”