According to Costa and Morais (2010), algal biomass can be converted into biofuel, yielding a CO2-neutral energy carrier comparable to biofuels produced from other biomass sources. There are many advantages of using bioethanol compared to gaso­line. Bioethanol has a higher octane number (i. e. 107), broader flammability limits, higher flame speeds and higher heats of vaporisation. Octane number is a measure of the gasoline quality and can be used for prevention of early ignition which leads to cylinder knocks. Higher octane numbers were preferred in internal combustion engines. An oxygenate fuel such as bioethanol provides a reasonable anti-knock value. Ethanol contains 35% oxygen, which reduces particulate and NOx emissions from combustion. Also, as it contains oxygen, fuel combustion is more efficient, reducing hydrocarbons and particulates in exhaust gases. The complete combustion of a fuel requires the right amount of stoichiometric oxygen in existence and the amount of stoichiometric oxygen. Oxygen content of a fuel increases its combustion efficiency. Because of this, the combustion efficiency and octane number of bio­ethanol are higher than those of gasoline (Balat et al. 2008). With these properties, bioethanol is higher in compression ratio, shorter in burning time and leaner in burn engine, which leads to theoretical efficiency advantages over gasoline in an internal combustion engine (Balat and Balat 2009). Some properties of alcohol fuels are shown in Table 13.2.

Several papers have been published on macroalgae fermentation to produce bio­ethanol. Among them, they were Horn et al. (2000a, b) who reported the fermenta­tion process from extraction of Laminaria hyperborea pretreated with water at pH 2 and 65% for 1 h and fermentation using Zymobacter palmae instead of yeast to produce bioethanol. This was in contrast with Adams et al. (2009) who found that the pretreatments were not required for the fermentations with Saccharina latis — sima. It was found that higher ethanol yields were achieved in untreated fermenta­tions than in those with altered pH or temperature pretreatments. Besides that, Lin et al. (2000) also report that acid hydrolysis could be performed at 0.4 M, at 100% for 3 h after extraction of carrageenan from seaweeds Eucheuma serra. The work by

Lin and coworkers was used as the pretreatment of E. cottonii as this raw material belonged to the same species.

The present work explores the suitability of macroalgae E. cottonii as fermenta­tion feedstock for bioethanol production via yeast fermentation. The effect of differ­ent acid hydrolysis conditions, such as the temperature and acid molarity on the concentration of bioethanol, was investigated.