טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentJacob Lila
SubjectComparative Study of Biosolids from Membrane Bioreactor
versus Activated Sludge
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Emeritus Noah Galil (Deceased)
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Membrane BioReactor (MBR) is a conventional biological wastewater treatment process, combines with membrane separation. The membrane enables to concentrate the biomass, for reducing hydraulic retention time and wasted sludge volume. However, the high biomass concentration means working at higher sludge age and higher dissolved oxygen requirements compared with conventional Activated-Sludge.


The objectives of this research are to study the changes of biomass and sludge characteristics due to the high biomass concentrations in the MBR reactor and biosolids separation by membrane, compared with biomass formed in Activated-Sludge system.


The MBR system in this research was a submerged Hollow-Fibers Ultra-Filtration membrane. The comparable Activated-Sludge systems included: (a) aerated reactor with a secondary sedimentation tank, (b) Sequencing Batch Reactor (SBR). Both systems were operated in parallel at three sludge ages: 10, 25, 45-65 days. At each sludge age the systems were fed with synthetic and domestic wastewater. At sludge age of 10 and 25 days with domestic wastewater, the functioning of biomass with the addition of external hydrophobic contaminant was examined.


The results show that MBR effluent solids concentration is almost zero, the turbidity is less than 0.4 NTU. Compared to Activated-Sludge effluent in which the turbidity was 3-10 times higher. The BOD concentrations of MBR effluent were 0.2-3.6 mg/L, and 2.2-14 mg/L in Activated-Sludge effluent.


In most of the MBR systems the biomass oxygen uptake rate (OUR) was higher than the rate of Activated-Sludge systems. The protein/carbohydrate ratio released from the biomass of MBR systems was smaller than the ratio of Activated-Sludge biomass.

The bio-flocculation of biomass from most MBR systems was worse than bio-flocculation of Activated-Sludge biomass. The SVI values of MBR systems were 1.5-5 times higher than those of Activated-Sludge.

The filterability was quantified in terms of Capillary Suction Time (CST) and Sludge Resistance to Filtration (SRF). The MBR SRF and CST values were at least 20% higher than that of Activated-Sludge systems. The affinity of the solids to water in MBR sludges was higher than the sludges from Activated-Sludge, hence the dewaterability of MBR sludges was more difficult. The MBR sludges contain only small volume of free water. Most of the water in the MBR sludge was interstitial or vicinal water, which could not be released by simple gravitational separation.