**6. Design of experiments**

66 Multivariate Analysis in Management, Engineering and the Sciences

(Gabardo Filho, 2005; Domènech et al., 2001):

Full Mineralization of pollutants;

(Domenech et al., 2001; Moral, 2005):

**5. Heterogeneous photocatalysis** 

such as the biologic;

biological process; Allow *in situ* treatment;

mineralized;

or color.

**4.1. Advantages of advanced oxidation processes** 

Able to assimilate large variety of organic compounds;

Improve organoleptic properties of treated water;

Present high power with high oxidizing reaction kinetics.

**4.2. Disadvantages of advanced oxidation processes** 

Some processes are not available at appropriate scales;

the chemical structure of the semiconductor (Custo et al., 2006).

According to Nogueira and Jardim (1998), a semiconductor is characterized by:

Costs can be high due to energy consumption;

 Valence bands, where vacancies are generated; Driving Bands that are generating electrons; A region between bands called bandgap;

from the valence band to the conduction band;

schematically the behavior described above.

Can be integrated with other processes such as pre or post treatment;

AOPs have a number of advantages when compared to conventional oxidation processes

Employed in the destruction of refractory compounds resistant to other treatments,

Used in high toxicity wastewater that can cause some difficulty in the treatment of

Develop byproducts reaction intermediates that submitted to a post treatment may be

AOPs can be applied to certain types of waste under some restrictions, as follows

Some types do not apply to wastewater with high organic capability, turbidity, optical

The heterogeneous photocatalysis is a process based on the absorption of UV-visible by a solid semiconductor. In the interface area between the solution and the electrically excited solid, a degradation reaction or transformation of pollutants may occur, without changing

Semiconductor particles, when irradiated, absorb photons that may excite electrons

This generates vacancy electrons. The electron / vacancy pair migrates to the surface of the particle resulting in oxidation and reduction sites (Carp et al. 2004). Figure 1 illustrates Design of Experiments (DOE) has been widely used in the optimization of process parameters and improving of quality products by the application of engineering concepts and Statistics (Wang, Huang, 2007).

Design of Experiments is defined as a set of statistical techniques applied to planning, conduction, analysis and interpretation of controlled tests, in order to find define factors that influence the values of a parameter or group of parameters (Bruns; Neto; Scarmínio, 2010).

According to Franceschini and Macchietto (2008), DOE is a statistical tool used to maximize the value of variable responses obtained on each experiment and also to minimize cost and time by reducing the number of experimental conditions.

Interactions between variables are considered in the experimental design and can be used for optimizing the operating parameters in multivariable systems (Ay; Catalkaya; Kargi, 2009).

According to Salazar (2009), the experimental has been studied as an important mathematical tool in the area of Advanced Oxidation Processes (Heterogeneous Photocatalysis). In this study, fractionated schedules for the degradation of organic matter and COD percentage of dairy effluent were used to obtain 93.70% of the treatment.
