Effect Of Effluent Organic Matter On Ozonation For PPCPs Degradation

Secondary effluents discharged from wastewater treatment plants(WWTPs)have been identified as hotspots for the release of pharmaceutical and personal care products(PPCPs)into the aquatic environment.Due to the inefficiency of conventional biological treatment processes,a great variety of PPCPs entering WWTPs can still be detected in secondary effluents and discharged into the aquatic environment directly.Ozonation is capable of removing most PPCPs present in secondary effluents.Secondary effluent organic matter(EfOM)plays a vital role in ozonation for PPCPs degradation because it will react with ozone to affect the formation of OH and chain reaction.Therefore,in this study,ozonation was used as a high efficient technology to remove PPCPs.The objectives are to investigate the influence of various factors on PPCPs ozonation efficiency,and establish the ozonation kinetics models in synthetic secondary effluent and real secondary effluent,to investigate the influence of initial pH,ozone dose and EfOM concentration of solution on ozonation,as well as the mechanisms.The main results were summarized as follows:(1)Humic acid(HA),bovine serum albumin(BSA),sodium alginate(AGS)and dextran were selected as model EfOM,and several pharmaceuticals of different reactivity with O3(kO3 ranging from<0.1 to 6.8×105M-ls-1)were selected as target contaminants to investigate the effect of different EfOM on the PPCPs degradation.The results indicate that ozone can effectively remove PPCPs(DCF,BZF,IBP and CA),and PPCPs removal followed the pseudo-first-order kinetic equation.The rate constants for ozone-reactive PPCPs(e.g.,DCF and BZF)decreased rapidly in presence of different EfOM,but ozonation efficiency for ozone-resistant PPCPs(e.g.,CA and IBP)removal with 10 mg/L TOC EfOM addition showed the following order:HA>Dextran≈DW(deionized water)≈AGS>BSA.HA can facilitate·OH formation and thus accelerate the degradation efficiency of ozone-resistant PPCPs.The reaction rate constant is three times higher and the removal rate increased 17.5%compared with those without HA addition.BSA significantly inhibited the formation of OH and reduced the rate of ozone-resistant PPCPs degradation.(2)The degradation efficiency of PPCPs and the formation of·OH always increased with the increase of initial pH with different EfOM addition.pH would influence the effect of HA on ozone-resistant PPCPs degradation as well.With the initial pH of 4,the addition of HA can facilitate·OH formation and ozone-resistant PPCPs degradation,but with the increase of initial pH,HA shows inhibition effect due to the structure change.The concentration of HA has a complicated effect on the degradation of ozone-resistant PPCPs.It was found that HA can facilitate the formation of OH and the degradation of ozone-resistant PPCPs with the concentration of 1 mg/L TOC,while it shows inhibition effect when the concentration was increased.(3)The water qualities of the secondary effluent from a WWTP in Taixing were analyzed.TOC,pH,Cl-concentration NO3" concentration and SO42-concentration of the effluent were below 16 mg/L,7.89-8.65,14.44-62.23 mM,0.30-0.96 mM and 7.6316.15 mM,respectively.The three dimensional fluorescence spectra show that in the secondary effluent,the peak at Ex/Em 250-270/350-380 nm corresponds to SMPs-like structures and the peak at Ex/Em 220-240/370-390 nm corresponds to aromatic proteinlike structures.EfOM was fractionated into hydrophobic acid(HO A),hydrophobic base(HOB),hydrophobic neutral(HON)and hydrophilic fraction(HI)by XAD-8 resin.The results indicated that HO A constituted the major part of the EfOM.The HO A fractions in this study contained humic-like substances according to EEM spectra,while other fractions only comprised SMPs-like and aromatic protein-like materials.(4)The secondary effluent from a WWTP in Taixing was treated by ozonation,and the removal of TOC,UV254 and SUVA reached 24.55%,90.63%and 87.58%,respectively after 60 min.The removal of TOC is better with initial pH of 8.After ozonation,an obvious fluorescence decrease was observed in the regions of SMPs-like structures,and aromatic protein-like peak showed a blue shift.These results indicated that ozonation was able to completely remove the SMPs-like substances,and changed the type of proteins in the EfOM.(5)EfOM in secondary effluent of a WWTP has significant effect on the degradation efficiencies of CA,and the concentration of EfOM and O3 would influence the laws and efficiencies of ozonation for CA degradation.The rate constants for CA removal reached a maximum at EfOM concentration of 12.52 mg/L(TOC)and gO3/gDOC of 0.67.