10. Biocoating of Surfaces

Biocoating of concrete with a layer of calcium carbonate crystals can be performed using urease-producing bacteria, calcium salt, and urea. The calcium carbonate biocoating of the concrete surface could protect the concrete constructions in marine environment from reactions of magnesium and bicarbonate ions with the calcium silicate hydrate gel of concrete. Additionally, it promotes colonization of the calcium carbonate-coated surface with epibiota, so calcium carbonate biocoating can be used for the construction of artificial coral reefs or water purifying epiphytic biosystems. Biocoating changed surface properties of recycled concrete aggregates, so they can be bound with asphalt mixture. Biocoating of concrete and stone surfaces is significantly affected by the gravitational precipitation of bacterial cells and carbonate crystals. The content of adhered calcite crystals on the vertical concrete surface was about 3 % of those on the horizontal surface of concrete. Similarly, the contents of adhered calcium carbonate crystals on the polished surfaces of the horizontal granite plates after flow of biocoating solution between them were 113 and 17 mg CaCO₃/cm² for the floor and ceiling plates, respectively. So, to coat the surface of concrete object by even layer of calcium carbonate crystals on all sides the object must be slowly rotated in the treatment tank. Different calcium carbonate crystals—prisms of calcite, spheres of vaterite, needles of aragonite, rose-shaped or other shapes of minerals—are formed in the coating layer depending on the conditions of treatment. Gravitational precipitation of both bacterial cells and calcium carbonate crystals, that ensured some contact time between particles and coated surface, is an essential step in their adhesion to this surface and formation of biocoating layer. Calcium carbonate biocoating could be cheaper, more sustainable, environment friendly, and more aesthetical than any other types of the concrete surface coating. Biocoating could be used for decoration of the concrete surface, for the manufacturing of the artificial coral reefs as well as the frames for shellfish aquaculture. Other materials such as wood, plastic, glass, clay can be also coated with the calcium carbonate layer using biotechnology. It is possible to coat the surface of concrete, rocks, wood, stems and leaves of the terrestrial plants, and the plastic materials with the layer of calcite using microbially induced calcium carbonate precipitation (MICP) to enhance colonization of these surfaces with larvae of corals and shells as well as with microscopic algae and photosynthetic bacteria.