## 4 Conclusions and Implications for the Target Application  
This paper intends to report the results of a preliminary study carried out to investigate the potential of implementing microbial induced carbonate precipitation (MICP) as a novel approach towards stabilizing loose beach sand in Sri Lanka to minimize coastal erosion. This is the first study to address this aspect in the aforementioned region. After conducting a series of laboratory tests, the following conclusions were drawn. Although ureolytic bacteria are ubiquitous in nature, not all have the required potential for MICP applications. The isolated native bacterium belonging to _Sporoscrina_ sp. showed sufficient feasibility for the intended application. It is a moderately alkalo-tolerant bacterium, showing maximum growth and urease activity at an ambient temperature of 25 \({}^{\circ}\)C which is compatible with the tropical climate prevailing in the target region. Laboratory scale (syringe) sand solidification test results depicted that a batch treatment of bacterial culture injected twice (in the beginning and after 7 days) with a daily injection of 0.5 M cementation solution yielded sufficiently homogeneous strength improvement after a treatment period of 14 days under saturated conditions. The residual Ca\({}^{2+}\) and pH measurements of the effluent draining out from the bottom provided substantial information about the rate of urea hydrolysis and eventual calcium carbonate precipitation and can be used as good indication of the state of MICP. Local strength analysis of two types of natural beach sand solidified by MICP exhibited that particle size and gradation, bacterial cell concentration, and the concentration of reactants have a great deal of importance on the degree and homogeneity of the strength enhancement. A precipitation pattern of uniformly distributed crystals cladding grain surfaces along with agglomerated crystal clusters at the particle contact points showed high efficiency in improving the compressive strength of biocemented sands than randomly distributed larger crystals which may result under high reactant concentrations. Introducing magnesium into the MICP process deemed to negatively affect the desired engineering properties of the treated specimens. At the extreme, excessively high concentrations of magnesium where the Mg\({}^{2+}\)/Ca\({}^{2}\) molar ratio was 1.0, resulted in a significant reduction in the UCS. It is clearly deduced that the strength decline is mainly due to the change in crystal morphology (rather than the quantity of precipitate) to a needle shaped crystal form with lower bonding capacity than that of the well-interweaved and cross-linked rhombohedral crystals produced in the absence of magnesium. However, the effect will be negligible in the target environment where naturally available Mg\({}^{2+}\) is considerably lower compared to the concentration of Ca\({}^{2+}\) supplied with the cementation solution. On the other hand, the sand columns in this study were cemented under one-dimensional vertical flow of solutions where opted pathway of solutions were confined by syringe walls. In a real field application, the flow will be three-dimensional where flow dynamics will be dependent on numerous factors including the characteristics of the solution, sand matrix and the groundwater level. Finally, there is still need for further experiments, under laboratory and natural conditions, in order to scale up the process and bring them to practical use. The ultimate goal of this part of the current research study was to evaluate the initial feasibility for MICP as an ecofriendly alternative approach towards beach sand stabilization and to determine the preliminary optimum conditions, making this technique one step closer to in-situ application.