Research On The Degradation Mechanism And Treatment Of Typical PPCPs In Water By Advanced Oxidation Processes

Pharmaceuticals and personal care products (PPCPs) are a group of compounds whichinclude prescription and over-the-counter (OTC) drugs, such as antibiotic, antineoplastic,antianxiety and anticonvulsion, harmonic, retardant, sympathomimetic, anti-inflammatory andantiobesity drugs, etc. These PPCPs are discharged into aquatic environment in the form ofintact and metabolites during the process of the production and usage, which are characterizedby wide distribution, low residual level, complicated chemical composition, high toxicity andrefractory. PPCPs are considered as emerging contaminants, with potential risks to waterecological system and human health. The low efficiency in the removal of PPCPs bytraditional wastewater treatment technology has resulted in the recent emergence of concernsabout the development of new technique for PPCPs removal, which become an importanttopic in the field of water treatment technology all over the world.Advanced oxidation processes (AOPs) have been considered as effective methods for thedegradation of refractory pollutant within aquatic environments. Due to their high detectionrate and high damage in discharging of urban sewage plant, sulfamonomethoxine (SMM) andOfloxacin (OFL) were chosen as the typical target pollutants in this study. A series of study onthe performance, operating condition and reaction kinetics of SMM-contained simulatedwastewater by UV/Oxone oxidation system, OFL-contained simulated wastewater by Fentonand UV/Oxone/Co2+oxidation system were carried out. The degradation mechanisms ofSMM and OFL were proposed based on the identification of transformation products duringthe oxidation processes. This work could offer a fundamental understanding towards thedegradation of SMM and OFL by AOPs. The main conclusions in the paper are as follows:1. Research on the degradation efficiency and reaction mechanism of SMM-contained simulated wastewater by UV/Oxone oxidation system. The results showed that UV urges theproduction of SO4-from Oxone, which could degrade SMM efficiently. The optimaloperating parameters for degradation of SMM by UV/Oxone oxidation system were:[SMM]=5mg L-1, UV irradiation throughout the experiment, neutral pH, reaction temperature=20°C, SMM:Oxone=0.0107and reaction time=90min. Under the optimal conditions, thedegradation efficiency of SMM and removal efficiency of TOC achieved96.78%and89.01%,respectively. The degradation reaction followed the pseudo-first-order kinetics and theapparent rate constant was0.038min-1. Six transformation products were detected with theaid of high performance liquid chromatography combined with mass spectroscopy (LC-MS).Based on this, the reaction mechanism of SMM by UV/Oxone was proposed. The resultsindicated that SMM could ultimately be mineralized to CO2and H2O by SO4-.2. Research on the degradation efficiency and reaction mechanism of OFL-containedsimulated wastewater by Fenton oxidation system. The results showed that the optimaloperating parameters for degradation of OFL by Fenton oxidation system were: pH=4.0,[OFL]=9mg L-1,[H2O2]=1.5mmol L-1,[Fe2+]=0.03mmol L-1,[H2O2]:[Fe2+]=50:1,reaction temperature=25°C and reaction time=80min. The degradation efficiency andTOC removal of OFL were achieved98.84%and73.7%under the optimal condition,respectively. The degradation reaction was obeyed the pseudo-first-order kinetics and theapparent rate constant was0.65min-1. Eight transformation products were detected with theaid of high performance liquid chromatography combined with mass spectroscopy (LC-MS)and the reaction mechanism of OFL-contained simulated wastewater by Fenton oxidationsystem were proposed. Results from infrared spectrum confirmed that the degradation of OFLwas initiated from the decarboxylation by OH radicals. The F ions which were detected withIon Chromatography could be released from Ofloxacin with the assistance OH radicals.3. Research on the degradation efficiency and reaction mechanism of OFL-contained simulated wastewater by UV/Oxone/Co2+oxidation system. The results showed that theoptimal operating parameters for degradation of OFL by UV/Oxone/Co2+oxidation systemwere:[OFL]=9mg L-1, UV light irradiation, pH=5.0,[Oxone]:[Co2+]=1000:1,[Oxone]=0.6mmol L-1, reaction temperature=25°C, and reaction time=60min. OFL could bedegrade completely and the TOC removal was achieved87%under the optimal condition.The degradation reaction was obeyed the pseudo-first-order kinetics and the apparent rateconstant was0.67min-1. The degradation efficiency and TOC removal of Ofloxacin byOxone/Co2+oxidation system achieved91.3%and65.8%under the identical condition,respectively. The results indicated that UV/Oxone/Co2+oxidation system which possessed UVlight displayed stronger oxidizing ability than Oxone/Co2+oxidation system.13kinds oftransformation products were detected with the aid of high performance liquidchromatography combined with mass spectroscopy (LC-MS), where the reaction mechanismof OFL-contained simulated wastewater by SO4-radicals were proposed based on theidentification. The results indicated that the pH value had important effect on the attack sitesof OFL by SO4-radicals, the destruction of the carboxyl of the quinolone moiety wasdominant under the neutral pH conditions, while the SO4-attack at the piperazinyl substituentwas preferable near pH=3.4. The degradation efficiency of OFL-contained simulated wastewater between Fentonand UV/Oxone/Co2+oxidation system was compared. It could be found that UV/Oxone/Co2+oxidation system displayed stronger oxidizing ability than Fenton oxidation system. The SO4-radicals could degrade OFL in multipath at the same time.