Udymovych V. Development of technology for the production and application of biomement biosafe for the environment

A new area of biotechnology - the use of microorganisms for the needs of construction has been successfully developing in the world over the past 15 years. The production of biomement occupies a special place among new building materials by and soil enhancers based on the use of urease-producing bacteria, which, in the presence of urea and calcium ions in an alkaline medium, form insoluble calcite crystals. The advantage of biomement over traditional cement is its low viscosity (30–300 times less than the viscosity of a cement suspension), which ensures its ability to penetrate deeply into the pores and cracks of soil, concrete or stone (Ivanov and Stabnikov, 2017). The use of biomement is proposed for a wide range of civil engineering applications and may be a new cost-effective solution in environmental and construction engineering, especially in the field of geotechnical engineering. The disadvantages of biocementation are the use of live urease-producing bacteria that are introduced into the environment (and some biotechnologies suggest using opportunistic bacteria), the release of toxic ammonia into the atmosphere and the possible release of ammonium ions into the ground and surface waters. It has been shown that one of the possible ways to increase the biosafety of biocementation can be the application of acid urease when bone meal containing calcium in the form of hydroxyapatite is used as a source of calcium. A selection of a bacterial strain that synthesized acid urease was carried out among bacteria isolated from acidic soil. The strain with the highest urease activity was identified by amplification and 16 rRNA gene sequencing as Staphylococcus saprophyticus AU1. The maximum growth rate of the AU1 strain was 0.15 h-1, the maximum biomass accumulation was 6.9 g/L dry biomass, and the maximum urease activity was 8.1 mM hydrolysed urea/min. The highest urease activity in the Staphylococcus saprophyticus AU1 strain was observed in the pH range from 4.5 to 5.5, gradually decreasing with pH increasing. To ensure the biosafety of the environment, it was proposed to use for biocementation inactivated urease-active bacterial cells after their treatment with a 0.5% solution of sodium dodecyl sulfate for 120 minutes. When carrying out biocementation, where bone meal containing calcium in the form of hydroxyapatite was used as a source of calcium with a reduced amount of urea using inactivated bacterial cells, the water permeability of biocemented sand was 2×10-5 m/s, which makes it possible to apply this type of biocementation to strengthen the soil . in order to reduce its liquefaction, for example after an earthquake or to control dust erosion to reduce atmospheric pollution. The main advantage of this method is the ability to reduce the consumption of urea by 75% and thereby reduce the release of ammonium and ammonia into the environment. In addition, the problem of bone waste disposal is solved and the cost of materials for biocementation is reduced. Lactic acid bacteria can be completely biosafe producers of acid urease. The ability of lactic acid bacteria Lactobacillus reuteri and Streptococcus thermophilus to synthesize urease has been shown, which makes them promising microbial agents in biocementation processes. Lactobacillus reuteri was cultivated on cabbage broth. The maximum urease activity of Lactobacillus reuteri bacteria was observed at pH 5.0. When carrying out biocementation using Lactobacillus reuteri, sand after 8 biotreatments with lactic acid bacteria had a water permeability of 6×10-5 m/s. Therefore, this method of biocementation can only be used to strengthen the soil or to prevent dust erosion. It is possible to replace bacterial urease with plant-derived urease. Screening of seeds of agricultural crops grown in Ukraine showed that soybeans can be used as a source of urease for biocementation in the form of a crude aqueous extract from the crushed mass of seeds or germinated within 24-48 hours. The use of a crude extract from soybean seeds showed its effectiveness for the precipitation of calcium carbonate from a mixture of solutions of calcium chloride and urea, and its use in the biocementation of sand made it possible to reduce its water permeability by 6000 times and obtain values corresponding to the seepage rates of sand biocemented with traditionally used urease-producing bacteria. Key words: biocementation; biotechnology; biosafety; bacteria; agro-industrial waste; biosynthesis; metabolites; environmental technology; plant urease; environmental protection; soil biogrouting; physical, chemical and biological methods; pure cultures; biologically active substances; liquid culture media; рН; sources of carbon and nitrogen nutrition; Lactobacillus; lactic acid bacteria; enzymes; producer; microorganisms; microbial synthesis; Bacillus; probiotic microorganisms; nutrient medium; growth medium; screening; Streptococcus thermophilus