|M.Sc Student||Bruker Yehuda|
|Subject||Study of External and Internal Factors Affecting Water|
Separation from Biological Sludge
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Noah Galil (Deceased)|
Wastewater treatment processes produce large quantities of biosolids (sludge). Sludge treatment comprises around 60% of the total expense for sewage treatment.
Major part of the sludge treatment process is reduction of sludge volume by water separation, combined with organic matter and pathogenic decrease.
The water in sludge consists of three types:
Free water - not associated with the solids particles and includes void water.
Interstitial water - trapped inside crevices and interstitials spaces of flocs.
Bound water - held on the surface of solid particles, and intercellular water.
Regards to the solids contents, it is impossible to accurately predict the sludge treatment process performance.
This study was requested by the Karmiel WWTP. The complex nature of the sewage and sludge required the need for quick method to match dewatering polymer - type and dosage.
This study focused on two major aspects:
1. Develop method to match sludge dewatering polymer.
2. Examine the influence of anaerobic sludge digestion temperature on the dewatering polymer requirements, and the water distribution in the sludge.
A sequence of tests was made:
1. Regular "Safety Test" method of sludge and polymer limited mixture.
2. Slow mixing of sludge and polymer.
3. Gravity drainage - for free water separation.
4. Vacuum filtration, while monitoring time and filtrate volume - for interstitial water separation, and calculation of the SRF (specific resistance to filtration).
5. Dehydration of the filtration cake, to determine the bound water amount.
The criteria on choosing the most suitable polymer is based on the amount of free and interstitials water.
Three simulators were built in order to examine the influence of anaerobic sludge digestion temperature on the requirements of the dewatering polymer, and the water distribution in the sludge. These simulators were operated at temperatures in the mezophilic range 320c, 350c, 380c, and constantly fed, in order to best simulate the full scale conditions. Samples were periodically taken to perform the above sequence of tests.
In parallel digestion efficiency was monitored.
The small 20 liter simulators volume posed a problem. The system was very sensitive to any change in feeding patterns and temperature. This regularly damaged the process and required to restart the system
This study resulted in method for separating water from sludge and matching sludge dewatering polymer.
The anaerobic simulation results did not conclusively point out correlation between digestion temperature, polymer requirement or water distribution. Furthermore, no correlation was found between SRF and water distribution in sludge.