|M.Sc Student||Levin Doron|
|Subject||Analysis of Primary-secondary Sludge Ratio and Influences on|
Wastewater Treatment Costs
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Noah Galil (Deceased)|
|Professor Avi Ostfeld|
In wastewater treatment plants which are based on activated sludge process, two types of sludges are being produced.
· Primary sludge which is produced by the primary sedimentation tanks with solid concentration of 5%-9%. This sludge constitutes usually 40%-60% from all sludge according to weight ratio, depending on the primary sedimentation type.
· Surplus secondary Sludge from the biological process with low solid concentration of 0.8%-2%. This sludge constitutes usually 40%-60% from all sludge according to weight ratio, depending on the primary sedimentation type.
The influences of ratio and quantity of primary - secondary sludges on wastewater treatment costs were examined by mathematical procedure that was developed for this purpose.
The mathematical model is based on a techno- economic algorithm which was built and calibrated according to international values and according to construction and operation data of wastewater treatment plants in Israel. The model is practical and enables to implement optimization of wastewater treatment plants with constant flow diagram (type and arrangement of treatment units is fixed). The optimization is carried out by the software What’s Best 7.0 produced by Lindo.
The main results were as follows:
· For enhanced primary sedimentation, reduction of 8% to 16% in the treatment costs is expected as depending on the removal efficiency.
· The ratio of sludge treatment cost from the total cost is expected to remain similar for regular and enhanced primary sedimentation.
· An increase of up to 1.44 times in the treatment costs is expected, for growth up to twice in the suspended solids and volatile suspended solids in raw wastewater.
In summary, these results show that using enhanced primary sedimentation by chemical means for planned wastewater treatment or for expanding existing wastewater treatment plants is an applicable and economical option.