The effect of different additives on bacteria adsorption, compressive strength and ammonia removal for MICP

Microbial induced calcite precipitation is a commonly used technique for the application of biocementation. The metabolism of urea by ureolytic active bacteria leads, among other metabolic products such as ammonium, to carbonate ions. In the presence of calcium ions, calcium carbonate formation occurs. It was investigated whether the addition of different additives (Ca-bentonite, Na-bentonite, clinoptilolite, natrolite, limestone, marl clay, concresol, secursol, and activated carbon powder) can optimize this process. First, the influence of these additives on the adsorption rates and distribution of the ureolytic active organism Sporosarcina pasteurii in quartz sand columns was tested. Moreover, an investigation was conducted on the impact of various additives on ammonium immobilization to mitigate its leaching from soils subjected to the biocementation process. For eight additives uniaxial compressive strength tests in quartz sand columns and a storage method according to DIN EN 12390–2 were carried out. Each additive showed a characteristic adsorption and localisation progression. Furthermore, each additive was able to enhance the immobilization behavior of the present ammonium, with a maximum immobilization capacity of 10.76 \(\frac{mg (NH^+_4)}{g (additive)}\). The uniaxial compressive strength of biocemented columns out of quartz sand could sectionally be increased by the addition of each additive. However, the storage methodology shows a much greater influence on column strength. Overall, the best results were achieved with the two additives, Ca-bentonite and clinoptilolite, resulting in strength increases in sand columns of up to 4.64 and 3.22 \(\frac{N}{mm^2}\), respectively.