Investigation On The Treatment Of Biologically-treated Pharmaceutical Wastewater By Coagulation-UV/H₂O₂

In recent years,with the strengthening of environmental consciousness and the improvement of environmental standards worldwide,disposal of pharmaceutical wastewater gains more and more attention.In this paper,the goal is to propose an enhanced treatment process to treat the bio-treated pharmaceutical wastewater.Finally,coagulation-UV/H₂O₂ process was applied to treat the wastewater based on the analysis of wastewater characteristics.In the coagulation process,polyaluminium chloride?PAC?,polymeric ferric sulfate?PFS?and polyaluminium ferric chloride?PAFC?were applied to treat the effluent of pharmaceutical wastewater.The effects of coagulate dosage and pH were investigated.The results showed that coagulation was effective to remove contaminants from the wastewater,and PFS was more effective than the other coagulants.The optimum coagulant dosage was 0.4 g/L,where the removal efficiency of TOC,UV254,turbidity and NH4+-N reached 44.2%,35.8%,88.5%and 20.0%,respectively.Three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis?EEMs-PARAFAC?was used to investigate the fluorescent characteristics of dissolved organic matter?DOM?of the pharmaceutical wastewater.Five fluorescence components were identified,including one fulvic-like component?Cl?,one xenobitic-like component?C2?,two humic-like components?C3 and C5?and one protein-like component?C4?.It shows that hydrophobic substances with larger molecular weight like C5 were much easier to remove.Further study showed that in the investigation of coagulant dosage the correlation of DOM components?C3,C4,C5?with TOC and UV254 removal efficiencies were significant?R2>0.9?.In the UV/H₂O₂ process,sole UV irradiation,UV/H₂O₂ and coagulation-UV/H₂O₂ were compared,the effects of H₂O₂ dosage,pH and UV power on the reduction of pharmaceutical wastewater were investigated.The results demonstrated that the removal efficiencies increased with the increase of the H₂O₂ dosage and UV power,while excessive H₂O₂ would reduce its utilization.The removal efficiencies increased with the pH and then decreased.The maximum removal efficiencies of TOC and UV254 were 77%and 91.5%,respectively,under the optimum operating conditions of 500 mg/L of H₂O₂,pH of 7.0 and the ultraviolet lamp power of 15W,where the ratio of BOD5/COD was increased from 0.11 to 0.56.According to the fluorescence spectrum,fluorescent substances were degraded rapidly in the UV/H₂O₂ process after coagulation.Four fluorescence components were identified by EEMs-PARAFAC,including one protein-like component?Cl?,one fulvic-like component?C2?and two humic-like components?C3 and C4?.Hydroxyl radicals have an effective degradation on these four fluorescent components.Four different DOM fractions fractionated using XAD-8 and XAD-4 resins.The UV/H₂O₂ process was more effective for removing the non-acid hydrophobic substances.Choosing acetaminophen?AAP?and sulfadiazine?SD?as the typical pollutants,the effects of H₂O₂ dosage,initial pH value and UV power were investigated.And the degradation mechanism of the main intermediates was analyzed.The results showed that the UV/H₂O₂ was effective for these two substances,AAP was oxidized by hydroxyl radical?OH?while SD was oxidized by the combine of OH and photon;the reduction of degradation fit well with the pseudo-first-order kinetics model.The degradation rate constant increased with the increase of the H₂O₂ dosage and UV power.The degradation rate increased when the pH value increased from 3.0 to 7.0,and then decreased from 7.0 to 11.0.The results of gas chromatography-mass spectrometry?GC/MS?suggested that the firstly formed degradation products were hydroquinone,p-aminophenol and acetamide during UV/H₂O₂ of AAP.Then,the intermediate products were further oxidized.The results of liquid chromatography-mass spectrometry?LC/MS?suggested that three intermediate degradation-products,such as 4-aminobenzenesulfonic acid,were formed with a mass-to-charge ratio?m/z?of 173,186 and 200,respectively.It is proposed that S—N bonds and N—N bonds were broken,and the intermediate products might be further degraded.