טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentTzfati Eran
SubjectStudy of the De-ammonification Process for Nitrogen Removal
from Reject Streams to Reduce Municipal WWTP Load
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Noah Galil (Deceased)
Dr. Haim Sheindorf
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract


Municipal Wastewater Treatment Plants (MWWTP) must comply with increasingly stringent requirements for organic and nitrogen levels in the discharged effluent. The main processes for organic and nitrogen removal are taking place in the secondary treatment, namely the biological process. Conventional biological nitrogen removal includes Nitrification and De-nitrification processes. Applying these processes considerably contribute to the energy consumption of these plants. Reduction in the nitrogen load introduced to the bio-reactors is expected to reduce the amount of air required to supply the oxygen needed for the nitrification process, following substantial saving in the total energy of the plant.


In most MWWTP the primary and secondary excess sludge are treated for stabilization by anaerobic digesters and further dewatered for volume and mass reduction. The water from the dewatering units is returned to the main process (called "reject water"). This stream have no hydraulic influence on the main process, since it consist no more than 2% of the main wastewater stream. However, 20-30% of the nitrogen load on the WWTP comes from the recycled reject water. Efficient treatment processes to remove nitrogen from reject streams will considerably reduce the nitrogen load on the secondary treatment bio-reactors, and will reduce the overall energy consumption at the MWWTP.


The De-ammonification combines two of the following stages:  Nitritation and Anammox.

Nitritation refers to oxidation of 50% of the ammonia nitrogen into nitrite. The produced nitrite and the remaining 50% of the ammonia nitrogen are reacting in the Anammox process which produced elementary nitrogen (N2)


In this study the De-ammonification process was implemented in a single SBR technology for reject water treatment in the MWWTP (known as “Demon?”). To study and demonstrate the process, a pilot plant was built in the "Sorek" MWWTP. The one 10 lit reactor includes both of the main biomass: AOB's and Anammox. The Anammox biomass is growing in a granulated form, while the AOB's biomass appears in a suspended form. These features enable to separate the two types of sludge and remove different amount of sludge within the same reactor. In this way different sludge ages, for the two biomass population can be maintained.

The results obtained from the pilot studies indicated the feasibility of the De-ammonification process to efficiently remove nitrogen from the reject water stream at the "Sorek" MWWTP. The nitrogen loading rate (NLR) in the pilot was maintained at 0.75 kg N/m3/day, with 85-95% ammonia nitrogen removal.


In addition, kinetics bench experiments were showed a good correlation with 1st order reaction for the ammonia nitrogen in the Nitritation process with K1=0.3733 hr-1. Zero order reaction for ammonia and nitrite nitrogen in the Anammox process with K equal to 23.04 mg/l/hr and 15.63 mg/l/hr respectively, and pseudo-zero or pseudo-1st order reaction for the combined Nitritation/Anammox reactions with K=0.044hr-1.


Potential energy saving was calculated in the "Sorek" MWWTP with De-ammonification as a separated process for the reject water. The Net air savings for the MWWTP is only 10% compared to a plant without separated treatment for the reject water.