Isolation, Characterization and Application of Calcite Producing Bacteria from Urea Rich Soils

Abstract

Calcium carbonate is one of the most common minerals widespread on earth (4% by weight of the earth's crust). Bacteria are incredibly diverse and abundant and many bacterial species contribute to the precipitation of mineral carbonates in various natural environments. Alkaline pH is the primary means by which microbes promote calcite precipitation which results from the hydrolysis of urea.
The study used selective enrichment culture technique to isolate urease-producing bacteria from local urea rich soil and others materials. All isolates were identified using conventional biochemical tests. In addition, all isolates were tested for their ability to enhance the consolidation of sand and compressive strength of mortar as well as absorption reduction properties. One isolate with promising results was selected and optimization of environmental and nutritional conditions was performed. The growth curve of the selected strain with optimized condition was investigated.
Thirty three isolates were obtained from the enrichment culture technique. Among them 13 isolates showed increased consolidation of sand. The isolate that showed the highest performance was identified as Bacillus mycoides. The optimum pH of the isolate was shown to be 7.0 and an optimum temperature of 35 oC was found. The growth curve was constructed with a stationary phase starting after 10 hours. The test results indicated that inclusion of Bacillus mycoides isolate in cement mortar enhanced the compressive strength, with a maximum increase of 17% in compressive strength and 32% reduction in water absorption was observed with a 28-day mortar sample.
In conclusion, locally isolated strain identified as Bacillus mycoides enhanced the properties of the cement mortar. It is recommended that a larger scale application of this isolate be implemented.