|M.Sc Student||Ben-David Keren|
|Subject||Removal of Nitrogen and Phosphours Compounds by Biological|
Process with Membrane Separation
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Noah Galil (Deceased)|
|Dr. Haim Sheindorf|
|Full Thesis text - in Hebrew|
The necessity and obligation to protect surface water bodies against eutrophication phenomena has prompted world-wide stringent water quality standards for phosphorus and nitrogen compounds. Biological nitrogen and phosphorus removal from wastewater is widely accepted. Nitrogen removal requires aerobic-anoxic stages, while phosphorus removal requires alternating anaerobic-aerobic stages. Typical conventional biological nutrient removal (BNR) systems include three separated stages: anaerobic/anoxic/aerobic concluding with a secondary clarifier. The membrane bioreactor (MBR) technology has been gaining great attention in wastewater treatment as membrane filtration allows significant process intensification and better effluent quality due to very efficient separation of biosolids, high biomass concentrations, and long biosolids residence time.
The objective of this project was to adapt and test the enhanced biological nutrient removal process (EBNR) in MBR technology and to investigate EBNR performance under high mixed liquor suspended solids (MLSS) and long solid retention time (SRT).
The experiments included a bench scale pilot plant continuously fed with 500 liter/day of municipal wastewater from the sewerage network of Haifa, Israel. Raw wastewater was characterized by COD, nitrogen and phosphorous concentrations of 760, 60 and 15 mg/L, accordingly. The aerobic zone (190 L), equipped with immersed UF membrane, was constantly aerated. The MLSS from the aerobic tank, was pumped to the anoxic tank (80 L) for denitrification with a recycle ratio of 400%. MLSS was pumped from the anoxic tank to the anaerobic tank (30 L) with a recycle ratio of 100%. The bioreactors were operated under MLSS concentrations of 8,000 to 12,000 mg/L and cell residence times of 16 to 29 days.
The results indicate excellent removals of phosphorus (96%) with less than 1 mg/L in the effluent, COD (95%), with less than 40 mg/L and nitrogen (90%) with less than 7.5 mg/L. The aeration tank served primarily for nitrification and thus the use of membrane is advantageous over clarification in retaining nitrifiers and prolonging their SRT. Therefore complete nitrification occurred during the research (99.8%) with ammonia residual concentrations of less than 0.1 mg/L
The performances of the pilot plant show a clear advantage to the combination of the MBR technology in the EBNR process. High quality effluent, free of particles was achieved in the MBR system, therefore, no contribution of phosphorus and nitrogen from volatile suspended solids (VSS) was observed. This achievement is particularly crucial to BNR systems, since the effluent VSS from the EBPR is characterized by high content of phosphorus.