Nonionic surfactants such as alkylphenol ethoxylates are known to be quite stable in the environment and poorly biodegradable. Advanced Oxidative Processes (AOPs) are considered as an alternative way to biodegradation.
The process of oxidative destruction of the nonionic surfactants by hydrogen peroxide in the presence of Fe3+ in aqueous solution has been investigated using surface tension and dynamic light scattering measurements. The effect of temperature and pH on the destruction of nonylphenol ethoxylates with different ethylene oxide chain length as well as with straight and branched alkyl radical has been studied. Initial concentrations of the surfactants in the experiments were either less or higher than their critical micelle concentrations.
The oxidative destruction is proved to take place both in micellar and nonmicellar solutions. As light scattering data evidence at pH>3 colloidal particles of iron hydroxocomplexes form in the process that is confirmed by measurements of their electrokinetic potential. The aggregates are seemed to be stabilized by molecules of the nonionics and intermediates of their oxidative destruction. Under more acidic conditions (pH=1) the destruction slows down and is not accompanied by the colloid-chemical effects described. As temperature rises the rate of the process increases significantly.
The obtained results demonstrate that colloid-chemical effects are of importance in mechanism of the oxidative destruction of ethoxylated nonionic surfactants by hydrogen peroxide in the presence of Fe3+.
The study has been financially supported by the state assignment (reg. number 3.853.2011).