Microbial Induced Carbonate Precipitation (MICP) via urea hydrolysis is an emerging sustainable technology that provides solutions for numerous environmental and engineering problems in a vast range of disciplines. Attention has now been given to the implementation of this technique to reinforce loose sand bodies in-situ in nearshore areas and improve their resistance against erosion from wave action without interfering with its hydraulics. A current study has focused on isolating a local ureolytic bacterium and assessed its feasibility for MICP as a preliminary step towards stabilizing loose beach sand in Sri Lanka. The results indicated that a strain belonging to Sporosarcina sp. isolated from inland soil demonstrated a satisfactory level of enzymatic activity at 25 °C and moderately alkaline conditions, making it a suitable candidate for target application. Elementary scale sand solidification test results showed that treated sand achieved an approximate strength of 15 MPa as determined by needle penetration device after a period of 14 days under optimum conditions. Further, Scanning Electron Microscopy (SEM) imagery revealed that variables such as grain size distribution, bacteria population, reactant concentrations and presence of other cations like Mg2+ has serious implications on the size and morphology of precipitated crystals and thus the homogeneity of the strength improvement.

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Beachrocks are sedimentary structures where gravelly or sandy beaches have been transformed into rock outcrops formed through precipitation of connective cements amid their interstices. They are well-noted coastal features along the coastal belt of Sri Lanka due to the prevalent tropical climate. This study was aimed at gathering data on surface nature and cementation characteristics of beachrock occurrences along a part of Sri Lankan shoreline through field observations and a series of analyses including X-ray diffraction, X-ray fluorescence, scanning electron microscopy (SEM) techniques and petrographic thin-section analysis. The combined research findings from different techniques are also employed as a preliminary step to determine the formation mechanism of the studied beachrocks. The seaward-inclined low-angle beds running parallel to present shoreline are composed mostly of sandstone with occasional conglomerate. Almost all the beachrocks are made of quartz grains amalgamated by cement. One remarkable feature of Sri Lankan beachrocks is the presence of heavy minerals generally in thin lamina form. The cementing agents are predominantly composed of metastable carbonate phases, high magnesium calcite (HMC) and aragonite (Ar) with varying microfabrics and textures. From SEM examinations and thin-section images, main morphologies identified are acicular Ar, scalenohedral magnesium calcites along with bridge cements and micritic coatings which are typical of a marine-phreatic precipitation with the exception of occasional meniscus cements. Further, the presence of evidences of living organisms may be an indication of influence from the biological aspects which can be confirmed by more detailed analyses.

Bioengineering has paved the way into multidiscipline as a more sustainable and eco-friendly solution to numerous problems. Among them, microbial induced carbonate precipitation (MICP) is a newly emerging microbiological soil/sand stabilization method, where microbial urease is employed for calcium carbonate precipitation throughout the soil matrix by urea hydrolysis which leads to soil strength and stiffness enhancement. This paper investigates avenues for strengthening loose beach sand from Sri Lanka by MICP through a series of laboratory experiments. A bacterial strain belonging to Sporosarcina sp., a native ureolytic bacterium was isolated from Sri Lankan soil, and urease activity and induction of calcium carbonate precipitation were quantified. The isolated bacteria showed a stable growth over the test period of 7 days and a maximum urease activity of 2.1 µmol of hydrolyzed urea/min.mL after 48 hours of cultivation. A major part of the study was focused on determining the effect of centrifuged cell pellets resuspended in distilled water and fresh culture medium (NH4-YE medium) on the effectiveness of MICP. The small-scale column solidification tests revealed that although urease activity is considerably higher for cell pellets suspended in distilled water, the strength improvement on column top by intact cell culture injection is about 5 times higher than that from cell pellets. Further, different size and types of calcium carbonate crystals were examined in MICP tests done for intact culture liquid and centrifuged cell suspensions. However, detailed analysis of biocementation by the selected isolate is highly recommended as future work.