Surface-active substances or surfactants are molecules having amphiphilic characteristics, i.e. both hydrophilic and hydrophobic properties (Hutchinson et al., 1967; Van Dyke et al., 1991). Because of the presence of hydrophilic and hydrophobic groups within the same molecule, surfactants partition preferentially at the interface between fluid phases of different degrees of polarity and hydrogen bonding. The formation of an ordered molecular film at the interface lowers the interfacial tension and is responsible for the unique properties of surfactant molecules (Georgiou lat al., 1992). The hydrophilic part of a surfactant may be anionic, cationic or neutral, while the hydrophobic portion normally consists of hydrocarbon chains. Depending on the type of charge present, there are four possible kinds of surfactants, i.e. anionic (negatively charged), cationic (positively charged), nonionic (no charge) and amphoteric (positive and negative charges within the same molecule) (Georgiou et al., 1992).