טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKurzbaum Eyal
SubjectThe Contribution of Plants, Microbial Activity and Porous
Bed, in Reduction of Dissolved Organic Carbon
Compounds in Constructed Wetland System
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Robert Armon
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Constructed wetland (CW) system is an artificial marsh or swamp created for anthropogenic discharge treatment (such as effluents from wastewater, agriculture, industry, and stormwater). The scope of this work was to investigate the relative contribution of each system component (plants, gravel, bacteria, abiotic processes) to the overall removal of phenol and to study the interactions between these system components.

The first part of the research work was focused on phenol degradation in a subsurface flow CW system with emphasis on the characterization of the relative contribution of plants, porous media, microorganisms and physico-chemical processes to the overall reduction process of phenol. In addition, the relative contribution of the different system components was studied under two feed water concentrations (435.8 and 31.8 mg/l COD).

It was found that phenol evaporation, photolysis and adsorption onto plants and gravel, were negligible. In addition, an in depth analysis revealed that plants contribution alone was minor. In lower strength feed water it was found that root attached bacteria in the CW pilot system played the most significant contributor to total phenol reduction, while gravel attached and planktonic bacteria played a minor contribution with a much slower phenol degradation rate.

On the other hand, higher strength feed water caused the gravel attached biofilm to be the major contributor to phenol reduction. The planktonic population showed a significant contribution to phenol removal. The results suggest that while in lower wastewater concentrations there is an advantage for root surface bacterial colonization in comparison to gravel surface and solution (planktonic), in higher wastewater concentrations this advantage is not expressed, probably as the result of the presence of high organics in the treated water.

In the second part of the study, a phenol degrader bacterium isolated from the CW pilot system which identified as Pseudomonas pseudoalcaligenes based on 16S rRNA analysis, was characterized for its phenol biodegradation capabilities in three the following forms: planktonic (as suspension), root attached (on sterile corn hydroponic grown seedlings) and gravel attached (as biofilm) in controlled experimental bioreactors.

Measuring specific phenol removal rates (mg phenol/CFU/h) it was found that planktonic cells were quantitatively 22 times higher in comparison with root and gravel biofilms. Denser biofilms showed lower specific phenol removal rates, probably as a result of reduced phenol and oxygen mass transfer through the thicker biofilms. In addition, the results show that root surface biofilm was equally efficient to gravel biofilm in phenol specific removal.