טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAmitai Ze-Li Sagiv
SubjectModification, Calibration and Verification of a Model
Depicting Hydrogen Sulfide Emission Rates in
Gravity Sewers
DepartmentDepartment of Agricultural Engineering
Supervisors Full Professor Lahav Ori
Full Professor Friedler Eran


Abstract

The detrimental effects of H2S(g) in gravity sewers includes its rotten-egg smell, its toxicity to humans, and its corrosive effect on concrete and metals. As all these relate to the presence of H2S in the gas phase, quantifying the rate of emission from the wastewater stream to the pipe’s atmosphere is essential. However, it appears that under conditions where stripping is the dominant process affecting H2S(aq) concentration, existing models seriously underestimate the stripping rate.


The present work proposes a new modeling approach to this phenomenon, in which the velocity gradient (G) is used to represent the mixing intensity, and then linked with H2S stripping rate. Two different equations were used for calculating G in a completely mixed tank and in a gravity sewer. The model was calibrated and verified both in a batch reactor and in a pilot-scale experimental sewer. The experimental work examined the affects of geometry, pH, temperature, and flow rate on the rate of stripping.

Results show a different dependency of the stripping rate on G in the batch experiments (rate proportional to G2) and for the experimental sewer (proportional to G1). The difference was associated with the different mixing patterns. Another series of experiments quantified the effect of local head losses in the sewer on the emission rate.

Minimal input requirements make the new model a useful tool for the prediction of H2S emission rates in municipal sewer systems. The model can be used as a design/operational and maintenance tool to predict H2S emission rate in gravity sewers.