|Ph.D Student||Klein Shiri|
|Subject||Microencapsulation of Pseudomonas sp. ADP Cells for|
Application in Bioreactor for Atrazine Removal
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Michal Green|
|Full Thesis text|
Encapsulation of whole cells in novel insoluble electrospun polymeric microtubes for water treatment, with atrazine degradation by Pseudomonas sp. ADP as the case study, was the main objective of this research. The encapsulation process was found to negatively affect cells as enzymatic assays of phosphatase in P. ADP and β-galactosidase in Escherichia coli KT4/RP4 exhibited only ca. 10% and ca. 23% activity, respectively, immediately after encapsulation in comparison to that of the free cells prior to electrospinning. The atrazine degradation rate of encapsulated P. ADP cells tested immediately after encapsulation was also found to decrease more than a magnitude relative to that of an equivalent free cell suspension (0.15±0.05mg atrazine/l/h vs. 6.95±1.1mg atrazine/l/h, respectively) and 79% of the degraded atrazine was found to be in the form of hydroxyatrazine. However, respiration under denitrifying conditions showed that encapsulated P. ADP cell membrane and functionality of certain regulation systems remained intact and viable. It was subsequently shown that cells could grow inside the microtubes by subjecting them to suitable growth media. After this growth period, high enzymatic activity, such as phosphatase, nitrite reductase and atrazine degradation was regained.
Encapsulated cells subjected to growth period directly after electrospinning were able to degrade significant amounts of atrazine without the addition of carbon (non-growth conditions). Successful recovery of atrazine enzymatic activity after loss under non growth conditions was also demonstrated when the encapsulated cells were subjected to a revitalization period in atrazine growth medium.
The use of microtube encapsulated P.ADP cells as an artificial biofilm was demonstrated in a continuous fixed bed bioreactor for atrazine removal under non sterile conditions with and without the addition of an external carbon source. Plastic carriers were prepared by wrapping them with a layer of encapsulated microtubes directly from the electrospinning apparatus and placed in a reactor. Results showed the under conditions of continuous flow and aerobic growth (with carbon source), the atrazine removal rate in the reactor reached 93mg/l reactor/day, similar to the performance of previously operated biofilm reactors. During operation under non growth conditions, the total amount of atrazine removed was ca. 1.4g atrazine/l reactor and no significant deterioration in the efficiency of atrazine removal was observed. Reactor operation was terminated due to significant microtube covering detachment throughout the experimental period. Development of a more durable and non-biodegradable microtube as well as improving microtube adhesion to the surface of the carrier is required for further experimentation.