|M.Sc Student||Bernadette Soudah Abou Atta|
|Subject||Use of Formaldehyde-Degrading Bacteria for|
Bioremediation of Industrial Wastewater and
|Department||Department of Biotechnology and Food Engineering||Supervisor||Professor Fishman Ayelet|
|Full Thesis text|
Formaldehyde is a volatile organic compound which is widely used in the chemical industry especially in the production of phenolic and urea resins. This toxic substance may become a reason of growth disorder, blindness, and respiratory diseases of living-organisms. Considering its high cytotoxicity with regards to human health and the environment, the removal of formaldehyde from soil, water, and air has become a necessity. Several formaldehyde degrading-microorganisms were isolated in our lab from soil, and identified as belonging to the genera Pseudomonas, Sinorhizobium, and Methylobacterium. The isolated strains were able to grow on agar plates containing 0.25% formalin as the sole carbon source and were able to fully degrade 500 ppm formaldehyde within a few hours. The aim of this work was to utilize these bacterial strains for bioremediation of formaldehyde contaminated-wastewater and industrial resin solutions. Initially, several methods were evaluated and optimized to quantify formaldehyde. A colorimetric assay (Hantzsch method) based on the reactivity with acetylacetone under alkaline conditions was found suitable for detecting formaldehyde at concentrations of 50-1000 ppm. A commercial kit based on a reaction with chromotropic-acid was found suitable for low concentrations of 0.02-8.00 ppm. An HPLC method was optimized for the range of 1-1000 ppm. The degradation ability of selected strains in a synthetic formaldehyde solution was evaluated, and two best performing strains (Pseudomonas sp. and Sinorhizobium meliloti) were further studied. These strains were then tested in resin solutions obtained from Carmel Chemicals Ltd., which contains 2500 ppm of formaldehyde, and could degrade 57-62% of the free formaldehyde under specific conditions which demanded to dilute the resin solution. However, in the wastewater, formaldehyde removal was not observed.
In order to improve the performance of the bacterial strains and protect them from the harsh environment, immobilization in calcium alginate was performed. The immobilization system improved the microorganisms' activity in the resin and maintained their activity in the synthetic formaldehyde solution but could not improve their activity in the wastewater. Both the immobilized and free microorganisms degraded 63% of the free formaldehyde in the resin, however, the immobilized cells could be reused with similar degradation activity for four consecutive cycles, while the free cells lost their activity after two cycles. Polyvinyl alcohol beads were also used for immobilization and exhibited similar activity to the cells immobilized in calcium alginate beads. These results indicate that formaldehyde-degrading microorganisms can be immobilized and protected from toxic materials and subsequently be utilized for bioremediation of industrial polluting solutions.