1.1 ENVIRONMENTAL POLLUTION BY TEXTILE WASTEWATER
It is well known that the earth’s surface and the environment surrounding are the most crucial to human health. In recent years, the environmental crisis is a major problem all around the world and it had adversely affect the lives of millions of people and caused many death and health disorders. Nowadays, toxic organics in wastewater had become a major problem to the earth creatures. These toxic organic occurs mainly from industrial sector especially from the effluent of textile industries. With the increased demand for textile products, the textile industry and its wastewaters have been increasing proportionally, making it one of the main sources of severe pollution problems worldwide .
Dye is one of the most common organics in wastewaters discharged from textile industries. The effluents from textile dyeing industry contain many organic pollutants and cause serious environmental problems due to their color, high chemical oxygen demand and nonbiodegradability. Reactive dyes from textile and dyeing industries pose grave environmental problem as it gives toxicity that can be harmful to the living organism. Reactive dyes are highly water soluble, nondegradable under the typical aerobic conditions (biological treatment systems), and adsorb very poorly to biological solids, resulting in residual color in discharged effluents.
Thus, a proper treatment must be employed to the textile wastewater effluent before discharged into the water sources. Some conventional treatment of dye production wastewater for instance, adsorption, coagulation,oxidation and precipitation were commonly used to treat dyes in wastewater effluent. Among these treatments, advanced oxidation processes (AOPs) had been widely investigated by researchers around the world and it considered as a promising treatment method to destroy these organic pollutions in wastewater. One of the AOPs so called wet air oxidation (WAO), is used primarily for the treatment of high strength industrial effluent using oxygen or air to oxidize organics in aqueous solution. However, WAO usually acts under extremely operating condition for instace, high temperatures and pressure, which consequently increase the capital cost of the process. To overcome the drawbacks, catalytic peroxide oxidation (CWPO) processes has been developed in recent years.
CWPO is a green technology that meets the characteristics required to perform efficiently in the treatment of such highly contaminant streams. By adding catalyst and oxidant, CWPO process can work well under mild condition without too much energy consumption as the •OH radicals generated in the reaction are highly oxidative, non-selective, and able to decompose many organic compounds including dyes and pesticides (Arun Kumar Kondru et al., 2009). The hydroxyl peroxide being oxidizing reagent can be activated to form even more powerful hydroxyl radicals by using inexpensive solid catalyst under very mild conditions of temperature and pressure. Noble metal oxides had been used as catalyst in WAO and the reaction usually carried out with higher pressure and temperatures (Lin & Ho, 1997). The cost of catalyst and deactivation problems limited the application of noble metal catalyst in WAO process. Thus, transition metals usually used as a catalyst for various reactions in the industries as it is interesting and cheaper alternative instead of more noble metals which are considered to be very expensive (Farooq et al., 2012).
Although CWPO has been widely used for the oxidation of wastewater streams with high total organic (TOC) content, the utility of this system is also limited because of the restricted viable pH range and the need for the recovery of the homogeneous catalyst. The use of heterogeneous catalysts based on low-valence transition metals appears as a promising option to overcome these problems since oxidation efficiencies are...