Degradation characteristics of four major pollutants in chemical pharmaceutical wastewater by Fenton process.

• Degradation characteristics of 4 organics in pharmaceutical wastewater was studied • SCPW exhibited good biodegradability when H 2 O 2 dosage reached 0.6 Q • The biodegradability of SCPW was improved due to oxidation intermediate of organics • The removal of organics and COD was in line with the second-order kinetic model • The greater the E RB3LYP of the organic, the more difficult it was to be removed Present study deals with the treatment of simulated chemical pharmaceutical wastewater (SCPW) using Fenton oxidation process for the degradation of typical pollutants containing n-butanol, ethyl p-nitrobenzoate, 4, 7-dichloroquinoline and ethyl acetoacetate. The effects of operational parameters like the initial pH, H 2 O 2 /Fe²⁺ molar ratio, H 2 O 2 dosage and reaction time on the degradation efficiency of pollutants and biodegradability of SCPW were investigated. The Fenton reaction steps and the removal kinetics of SCPW were analyzed. Finally, the effects of the molecular structure on the degradation efficiency of organics were investigated. The degradation ratio of n-butanol, ethyl acetoacetate, 4, 7-dichloroquinoline, ethyl p-nitrobenzoate and chemical oxygen demand (COD) in SCPW is 56%, 75%, 100%, 78% and 38%, respectively, for conditions of initial pH of 2.5, H 2 O 2 /Fe²⁺ molar ratio of 20, H 2 O 2 dosage of 0.6 Q (Q is the theoretical dosage of Fenton reagent) and reaction time of 30 min. The reaction steps analysis indicated that the biodegradability of SCPW was improved mainly by the oxidation intermediate of pollutants. The kinetics study showed that the removal processes of pollutants and COD were consistent with the second-order kinetic model. Quantum chemical analysis showed that the correlation between the total energy E RB3LYP and removal kinetic constant K [RH] was most significant, and E RB3LYP was negatively correlated with K [RH]. The results indicated that the higher the total energy of the organics, the more difficult it was to be removed. The findings reported herein are significant to predict the treatment efficiency of pollutants in real pharmaceutical wastewater. [ABSTRACT FROM AUTHOR]