Optimization of the combined Fenton and ozonation processes for efficient COD removal in rubber wastewater treatment

This study investigates the characteristics of rubber wastewater and identifies optimal conditions for its treatment using a combination of Fenton and ozonation processes. Initial analyses revealed that the wastewater had a pH of 4.68±0.01 and chemical oxygen demand (COD) of 43,919.89±0.34 mg/L. The experimental design, statistical analysis, and optimization were conducted using the Central Composite Design (CCD) within the Response Surface Methodology (RSM) implemented through the Design Expert. Under the optimal conditions using only the Fenton process, the results indicated that the maximum COD removal efficiency of 78.46±0.17% was achieved with 5:1 of H 2 O 2 :FeSO 4 •7H 2 O and 90 minutes of contact time. The study found that ozone dosage rate and contact time noticeably affect COD removal efficiency using the combined Fenton and ozonation processes. The maximum value of COD removal efficiency received from the combination process was 98.02±0.07 at 800 mg/hr of ozone dosage rate and 30 minutes of contact time. The experimental results were further statistically analyzed. The quadratic model was found to be the most suitable model to describe COD removal efficiency through the combined processes. The obtained mathematical model for predicting COD removal efficiency is: y = -50.67977 + 0.034142A + 0.389243B -0.000176AB + 0.000592A 2 - 0.000251B 2 . Optimal conditions for COD removal efficiency via the combined processes were determined utilizing the Response Optimizer. Results indicate that the optimal conditions were an ozone dosage rate of 764 mg/hr and a contact time of 30 minutes, leading to a COD removal efficiency of 97.62% with a desirability of 0.928.