The ultrasound method is used to improve mass transfer between incompressible reactants which increases their chemical reaction and reduces reaction time as well as energy consumption. In this research, transesterification process variables of rice bran oil were optimized using response surface methodology (RSM). Three process parameters were investigated, namely methanol to oil molar ratio, catalyst concentration, and time. The optimum conditions of the transesterification process based on RSM were: (1) methanol to oil molar ratio: 1:6; (2) catalyst concentration: 0.5% wt.; and (3) time: 48 min, with methyl ester yield of 94.12 %. The optimum rice bran methyl ester yield predicted by RSM was validated by replicating three independent parameters with showed average rice bran methyl ester yield of 93.98%. The properties of the rice bran biodiesel properties were measured and the values met the requirements of the ASTM D6751 and EN 14214 standards.

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Lightweight foamed concrete is a concrete made by cement slurry mixed with foam so that foamed concrete that is much lighter than conventional concrete can be produced. The objectives of this study is to develop optimal pre-foamed lightweight foamed concrete and to achieve desired density of lightweight concrete that is below 2400 kg/m3. Three samples of concrete were batching with 0%, 25% and 50% of foam respectively under mixing ratio of 1:1:2 and foam dilution ratio 1:5 to obtain optimum result. Based on the result attained, the samples achieved the bulk density ranged from 1943 kg/m3 to 2305 kg/m3. In addition, other physical characteristics of this mixture of materials show that its water absorption for all the samples was increased from 6.508% to 11.889%. This trend of results was obtained if the volume of foam presented in the concrete were increased. Furthermore, the samples achieved compression strength ranged from 22.418 MPa to 32.229 MPa with presence of foam. In summary, with additional of fly ash and concrete sludge as aggregate it can help to produce comparable concrete composites with lighter density.

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