|M.Sc Student||Kadmon Avry|
|Subject||The Effect of Aeration, Circulation and Effluents Level on|
Removal of Organic Substrat from Domestic Sewage,
by Aquatic Plants
|Department||Department of Civil and Environmental Engineering||Supervisor||Mr. Yoram Zimmels (Deceased)|
|Full Thesis text - in Hebrew|
The research objectives were to determine the enhancement of organic matter removal from domestic sewage due to aeration and circulation applied at different rates in the presence of aquatic floating plants. Other objectives were to determine the optimal operational conditions and the kinetics of the organic substrate removal. The species of the floating plants utilized in this research were: Eichornia crassipes, Pistia strateotes, Hydrocotyl ranunculoides, Ludwigia stolonifera, Salvinia natans, Azolla californiana.
The research results showed improvement of the organic substrate removal in the presence of aquatic plants, circulation and aeration. Eichornia crassipes and Pistia strateotes were found to be the most efficient plants for COD, BOD and turbidity removal. The shortest retention time required to decrease the level of COD from 400 mg/l to 100 mg/l was 1.9 days with Eichornia crassipes and aeration of 0.4 liter/minute. In the control 7 days were required to this end. The shortest retention time to lower the level of BOD from 132 mg/l to 20 mg/l was 1.5 days with Pistia strateotes and 0.4 liter/minute aeration, as compared with 4.7 days in the control with plants, and 6 days in the control with no plants. The shortest retention time required to reduce the turbidity below 1 NTU was 5 days in the presence of Eichornia crassipes and circulation of 40 liter/hour. Without Eichornia crassipes more than 12 days were required to reach the same NTU level. Results of COD and BOD removal from sewage by aquatic plants at different effluents levels in the experimental containers provided no conclusive evidence that COD and BOD removal efficiency depend on these levels to any significant extent. The kinetics of BOD and COD removal were found to follow a second-order reaction model. This was verified at different circulation and aeration rates and for most plants tested.