INVESTIGATION OF THE SIMULTANEOUS UREA HYDROLYSIS AND DENITRIFICATION ACTIVITY OF BIOGRANULES UNDER VARIOUS ENVIRONMENTAL CONDITIONS AND THEIR COMPARISON WITH THE INHERENTLY PRESENT PURE CULTURES

Abstract

In microbially induced calcium carbonate precipitation (MICP) related studies, urea hydrolysis and denitrification metabolisms have been prevalently investigated. Furthermore, studies were mostly conducted by using axenic cultures, and biomineralization performances were determined only through a single metabolic pathway. Several constraints were detected in MICP applications due to the limits of the exploited metabolic pathway and the axenic cultures. Recently, researchers presented a way to overcome the reported limitations in MICP applications by combining the aforementioned metabolic pathways in non-axenic granulated cultures. Yet, MICP performance of these non-axenic granulated cultures and their advantages over axenic cultures under different environmental conditions still remain unknown. Therefore, the objective of this thesis study was to investigate granular cultures, capable of conducting simultaneous urea hydrolysis and nitrate reduction, under various environmental conditions and compare its biomineralization performance with the axenic cultures. Biogranules were compared with ureolytic Sporosarcina pasteurii DSM 33 and denitrifying Pseudomonas aeruginosa as well as with the axenic cultures isolated from the biogranules. The study compared how MICP performance of axenic and non-axenic cultures depended on changes in the following parameters: (i) yeast extract concentration (0.05-5.00 g.L-1), (ii) dehydration stress (wet/dry), (iii) salinity (35 g.L-1, 1 g.L-1 and 0.02 g.L-1 NaCl), (iv) temperature (10oC, 22oC, 45oC), and (v) dissolved oxygen concentration (<0.2 mg.L-1, 1.3 mg.L-1, 4.8 mg.L-1). Results indicated that wet biogranules had higher biomineralization performance than axenic cultures in all tests. Biogranules’ MICP performance appeared to be less dependent on the presence of yeast extract, and biogranules could be dried and resuscitated without any problem. Wet biogranules and S. pasteurii totally precipitated dissolved calcium as CaCO3 (0.65 g CaCO3) in the environment under three different oxygenic conditions and three different temperatures. Moreover, wet biogranules and S. pasteurii totally precipitated dissolved calcium as CaCO3 (0.65 g CaCO3) in the environment under fresh water and rainwater conditions except for marine water conditions. In marine water conditions, wet biogranules were superior to S. pasteurii in terms of biomineralization performance. Wet biogranules precipitated 0.62±0.01 g CaCO3, while S. pasteurii precipitated 0.57±0.03 g CaCO3.

According to these results, it was revealed that wet biogranules could simply adapt to changes in environmental conditions. Dried biogranules could resuscitate under all tested conditions and induced calcium carbonate precipitation. Consequently, this thesis study revealed that the non-axenic biogranules capable of urea hydrolysis and denitrification were superior to axenic cultures for MICP applications, and they were more resilient to the changes in environmental conditions making them more suitable for MICP applications.