Artificial beachrock, formed by coral sand solidification through microbially induced carbonate precipitation (MICP), could provide coastal protection instead of concrete structures, and would be eco-friendly as well as help minimize costs. The present study was conducted to solidify coral sand through the MICP method by using an ureolytic bacterium (Parahodobacter sp.) isolated from peripheral beachrock. The goal was to obtain a sample with an unconfined compressive strength (UCS) of 20 MPa or more. We also aimed to examine the growth characteristics of this bacterium in the culture medium ZoBell2216E, which is commonly used for marine bacteria. In order to determine the suitability of the MICP test, growth properties of the microbial strain were observed under various culture conditions. A sand solidification test with MICP was carried out in a syringe as well as a PET cylinder. The strength of the resulting specimens was measured with the needle penetration test. The specimen solidified up to 20 MPa of the estimated UCS after 21 days of curing. For optimum growth of the bacterium, 1.0 g of the culture was added to100 mL culture media and incubated with shaking at 160 rpm. The preferred final concentration in solidification promoting solution of both urea and CaCl 2 was 0.5 M, with bacterial cell densities of 10 9 CFU/mL. In order to efficiently induce solidification, the optimum pH was 7.0 or higher, and Ca 2+ concentration was maintained at 1.0 g/L. The results were enhanced by re-injecting the culture solution when the pH and Ca 2+ concentrations in the specimen were not in the ideal ranges indicated above.

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Erosion in the coastal area of Bangladesh is a big point of concern. The present study was conducted to find out the protective measure from coastal erosion in Bangladesh as well as evaluate the prospects of the formation of artificial beachrock. This study was conducted based on literature survey of related works. In the coast of Bangladesh, average recession through erosion will occur 0.87m due to per 1cm sea level rise. Beachrock as well as artificial beachrocks have the potentiality to prevent such coastal erosion. Beachrock is a type of sedimentary deposit that generally occurs on the tropical and subtropical beaches as a result of intertidal lithification of loose beach sands and gravels by carbonate cementation. Beachrock in the world differs by their chemical composition but it composed mainly of CaCO 3 , SiO 2 and Al 2 O 3. Usually, beachrocks are formed by the cementation of CaCO 3 precipitation with the influence of seawater and/or seawater evaporation as well as surface microorganisms. From the knowledge of natural beachrock formation as well as sand properties, in the future, it may possible to manufacture artificial beachrocks similar to beachrocks for erosion control purposes in Bangladesh.

ABSTRACT:The coastal erosion has been a problem in associate with manmade construction. The maintenance and management is expensive for repair and rebuild the coast. Compared to the concrete structure coral sand solidification would considered to minimize cost. The present experimental study was conducted to coral sand solidification through microbial carbonate precipitation (MCP) using Pararhodobacter sp. Ureolytic bacteria; Pararhodobacter sp. was isolated from the beachrock in Nago, Okinawa, Japan. ZoBell2216E as a medium for marine bacteria was used for the culture of the bacteria. Suitability for the use in MCP syringe test, growth properties of the bacteria were observed in various cultural conditions. MCP sand solidification test was carried in 30mL Terumo syringe injected bacterial culture fluid. Strength of the specimen was measured by needle penetration test. The maximum value of the absorbance at bacterial growth curve was constant if the added amount of the medium is 100mL. The correlation coefficient of determination for absorbance measurements and viable cell count measurements was obtained 0.5478. In MCP syringe test, pH of the specimen was decreased and Ca 2+ concentration was increase with time. The estimated value of unconfined comprehensive strength (UCS) also increased with time. The maximum value of UCS of the specimen was 12MPa. The estimated UCS values of the specimen produced by sand solidification test for 14 days curing time have been achieved.

Erosion is a great problem in the coast areas of Bangladesh. The present study was conducted through literature survey to evaluate the prospects of making artificial beachrock through sand solidification for the protection from coastal erosion in Bangladesh. On average, recession through erosion due to sea level rise (SLR) in the coast of Bangladesh will occur 0.87m per 1cm rise in sea level. Artificial beachrocks have the potentials to inhibit coastal erosion. Beachrock is a type of sedimentary deposit that generally occurs on tropical and subtropical beaches as a result of intertidal lithification of loose beach sands and gravels by carbonate cementation. Chemically, beachrock around the world differs in composition but mainly it composed of CaCO3 and SiO2. Beachrocks are cemented by high Mg calcite (HMC) with the influence on precipitation from seawater and/or seawater evaporation (PSW) and on surface microorganisms, bacterial ureolysis. On 30 0 C curing temperature which is similar to the average temperature in Bangladesh beach sand solidified 5 to 8 MPa unconfined comprehensive strength (UCS) in 28 curing days using the ureolytic bacteria (Pararhodobacter sp.). It is concluded that it may be possible to manufacture artificial rocks through sand solidification similar to beachrocks for erosion control purposes in Bangladesh.