Performance Evaluation of Microbial Cementation in Soil Improvement Using Different Ureolytic Bacteria Species

Abstract

The process of using microorganisms to improve the strength of residual soil is referred to as biocementation process. This technique utilizes the concept of microbial calcite precipitation to precipitates calcium carbonate into the soil matrix structure leading to the cementation of the soil particles and subsequent improvement in the strength and reduction of hydraulic conductivity. This research studied the performance of two bacteria species in the stabilization of residual soil via urea hydrolysis. The bacteria species used were Sporosarcina pasteurii and Klebsiella pneumoniae UM123 at concentrations of 1.20×106 cfu/ml and 1.80×106 cfu/ml and 1.5×105 cfu/ml and 2.9×106 cfu/ml respectively to evaluate the strength improvement of the residual soil. Similarly, cementation reagents used consists of urea and calcium chloride at 0.5M concentration. The study also employed treatment durations of 24, 36, 48, and 60 hours. The findings obtained demonstrated that higher concentrations of bacteria of 1.80×106 cfu/ml and 2.9×106 cfu/ml provided better strength improvement compared to lower concentrations of 1.20×106 cfu/ml and 1.5×105 cfu/ml for Sporosarcina pasteurii and Klebsiella pneumoniae UM123 species respectively. Thus, it was also found that as the bacteria cells concentrations are increased during biocementation process more calcite are precipitated leading to higher strength improvement with 2.2% being the highest strength improvement ratio obtained at 48 hours treatment duration for Sporosarcina pasteurii specie. Similar observations were made with Klebsiella pneumoniae UM123 with 2.1% being the highest strength improvement ratio recorded at 48 hours treatment duration.  Hence, the higher the amount of calcite precipitated the more the strength improvement up to 48 hours treatment duration for the two bacteria species. Therefore, at 48-hours of biocementation process, the strength of the soil had improved by 120% and 110% for Sporosarcina pasteurii and Klebsiella pneumoniae UM123 species respectively; compared to the untreated sample, representing the highest recorded strength improvement. Consequently, Sporosarcina pasteurii was found to performed better than Klebsiella pneumoniae UM123 in urea hydrolysis reaction and subsequent biocementation.