Production and compatibility assessment of denitrifying biogranules tailored for self-healing concrete applications
Abstract
Microbial granules have been mostly used for wastewater treatment. Recently, biogranules consisting nitratereducing microorganisms have appeared as a unique healing agent providing simultaneous self-healing of
cracks and corrosion inhibition of rebar in concrete. Yet, information about the production process and microbial
activity of these biogranules as well as their compatibility with cementitious materials remains unknown. This
study presents the biogranule production procedure in detail and evaluates the compatibility of the produced
biogranules with the cementitious composites. In the form of biogranules, bacteria doses varying between 0.25%
and 3.00% w/w cement were incorporated into mortar and the variations in fresh and hardened properties of
mortars were evaluated with respect to abiotic mortars. Biogranules were also tested for their compatibility with
concrete at minimum and the defined maximum tolerable doses. Biogranules with a NOx-N reduction activity of
0.10 g NOx-N.g− 1 bacteria.d− 1 and organic carbon oxidation activity of 1.50 g HCOO⁻.g− 1 bacteria.d− 1 were
produced successfully by using minimal medium. It was found out that biogranules enable bacteria incorporation
into mortar up to a dose of 2.50% w/w cement without compromising fresh and hardened properties of
cementitious composites. It was revealed that the compatibility of the biogranules was due to the mineral layer
surrounding the biogranules which prevented interaction between the cement matrix and the microbial content.
The thickness of the protective mineral layer around the granules was varying between 50 and 300 μm depending
on the granule size. Net yield for concrete compatible biogranule production was determined as 0.05 g biogranule.g− 1 HCOO⁻.
