טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLifshitz Adi
SubjectCombining Nitrification with Storage Driven Denitrification
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Emeritus Michal Green
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

A combination of nitrification and storage driven denitrification was examined as a method for nitrogen compounds removal. The hypothesis of this research project is that combining nitrification reactor with a storage driven denitrification reactor will result in an efficient inorganic nitrogen compounds removal with low COD to N ratio, with the corresponding potential saving in operational costs. The objective is to investigate the combined system with an emphasis on the effect of ammonia concentration on the combined process.

In storage driven denitrification, bacteria first store intracellular carbon (PHA) in the presence of an electron donor and the absence of the electron acceptor nitrate. When the conditions of the system change and nitrate is present without an electron donor, the bacteria will use the stored carbon to perform denitrification. System integration is not trivial due to the specific conditions required by each process.

The experimental system was built using two biofilm sequential batch reactors: the first performed anaerobic storage and denitrification while the second performed aerobic nitrification. In the first reactor, wastewater undergoes anaerobic storage where organics are transformed by bacteria and accumulated in the form of PHA under feast conditions. After storage, the effluent continues to the second reactor where ammonium is converted to nitrate and the remaining COD is oxidized. The effluent from nitrification then returns to the first reactor for final denitrification while utilizing the carbon that was stored in the first stage. Throughout the experiments, the system was fed with actual wastewater after primary sedimentation.

The results showed that COD concentrations decreased throughout the storage and nitrification phases. Ammonia was fully oxidized to nitrate during nitrification, although nitrate was not fully reduced during the denitrification phase of the first reactor due to a deficiency in COD. It was found that the C/N ratio required for nitrogen removal in the system was slightly lower (5 mg COD/mg N) than that reported in the literature (5.8 mg COD/mg N) regarding similar systems. In addition the C/N ratio in the storage/denitrification reactor was found to be very close to the theoretical value, probably due to cell death that also contributed COD throughout denitrification.
In summarizing the conclusions, in order to have effective storage driven denitrification the following conditions should be met:
1) A relatively high concentration of ammonia.
2) Soluble COD that can be converted and stored in bacteria.
3) A relatively low concentration of particulate COD.