Up-scaling application of microbial carbonate precipitation: optimization of urease production using response surface methodology and injection modification

Abstract

In order to reduce the cost of the microbial-induced carbonate precipitation, mixotrophic growth of Sporosarcina pasteurii was carried out at different yeast extract/sodium acetate concentrations and constant chemical oxygen demand for optimal production of urease enzyme. Optimization of cultivation conditions was also investigated using a 3-level central composite design approach based on the response surface methodology. A good agreement between predicted values of enzyme activity and experimental results was observed (R2 value of 0.973). All three chosen independent variables had statistically great effects on the efficiency of urease activity. The maximum activity of 2.98 mM urea min−1 was achieved at yeast extract concentration of 5 g L−1, NH4 concentration of 9.69 g L−1, and incubation time of 60 h as the optimal conditions. Thereafter, a novel injection procedure as sequencing batch mode injection has been proposed for bacteria and cementation fluid injection at obtained optimal urease activity. After fourth injection of bacteria and cementation fluid, uniform CaCO3 distribution with unconfined compression strength of 795 kPa was obtained even for poorly graded sand. The presented experimental approach for optimizing urease activity and strength production in porous media can be used to design the treatment protocol for practical engineering applications.