Optimizing the Photo-Fenton Process to Reduce the Effluent Organic Matter of Pulp and Paper Mill Wastewater Using the Response Surface Method

The pulp and paper industry has historically been one of the world‘s largest consumers of freshwater resources and producers of wastewater, which, can cause serious damage to the water and soil ecosystem if directly discharged into the environment. On the other hand, the use of traditional treatment techniques including biological treatment and coagulation is restricted by the presence of non-biodegradable organic compounds with high molecular masses. The photo-Fenton process is an environmentally friendly, simple, and fast method with low operational cost which could oxidize polluting substances by producing powerful hydroxyl radicals. The most important variables in the effectiveness of this process are the concentration of the oxidant agent, the concentration of Ferro ions, and pH. With three variables; the dimensionless concentration of hydrogen peroxide, the concentration of Ferro ions, and the pH, the experiment's design was carried out by the central composite method based on the response surface method in 18 experiments. pH was adjusted, Ferro ion and hydrogen peroxide were added, and the solution was then immediately exposed to UV light in order to apply the Photo Fenton treatment procedure to the sample. COD was defined as an indicator of wastewater pollution, and sodium sulfite was used to eliminate the effect of hydrogen peroxide on COD test. Effective factors were also optimized for the best performance at the most economical cost. The maximum value of COD removal = 71.51% was obtained experimentally. In the economic optimal state with the initial concentration of dimensionless oxidant dose = 0.369, ferro ion concentration = 98.99 mg/L, and pH = 3.28, 65.21% of COD removal was achieved and 1.37 riyals for removal of 1 COD unit were obtained.