BIOCEMENTATION OF SRI LANKAN BEACH SAND USING LOCALLY ISOLATED BACTERIA: A BASELINE STUDY ON THE EFFECT OF SEGREGATED CULTURE MEDIA

Abstract

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.