349 15 Remov al of Pharmaceuticals in Biological Wastewater Treatment Plants Sungpyo Kim, A. Scott Weber, Angela Batt, and Diana S. Aga 15.1 INTRODUCTION Providingsufcientlycleanwatertothepublichasbecomeachallengingissue worldwide as the quality of water sources increasingly deteriorates. 1 Asaconse- quence, treated wastewater has attracted attention as an alternative water resource, provided appropriate treatment can be applied. 2 Therefore, the removal of micro- contaminants,suchaspharmaceuticalsandpersonal-careproducts,inwastewateris critical because many of these compounds survive conventional treatment. 3 In gen- eral, these compounds are present at parts per billion (ppb) levels or less in wastewa- ter. 4,5 Although these concentrations are much lower than the levels of traditionally known organic pollutants (such as the persistent organic pollutants DDT, PCBs, and the like) the potential long-term effects of these compounds to humans and wildlife cannot be neglected. For example, several studies have shown that even parts per tril- lion(ppt)levelsofethinylestradiol(theactiveingredientsofbirthcontrolpills)and natural estrogens can disrupt the hormone system of aquatic species. 6,7 In addition, low levels of antibiotics from the efuents of wastewater treatment plants (WWTPs) can promote antibiotic resistance in microorganisms that are exposed constantly to these compounds. 8–10 Contents 15.1 Introduction 349 15.2 Fate of Pharmaceuticals in Biological Wastewater Treatment Process 350 15.3 Pharmaceutical Removal Mechanisms 350 15.3.1 Biodegradation and Biotransformations 351 15.3.2 Sorption 352 15.4 Inuence of Wastewater Treatment Plant (WWTP) Operating Conditions 354 15.5 Final Remarks 358 References 358 © 2008 by Taylor & Francis Group, LLC 350 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems Residues of human and veterinary pharmaceuticals are introduced into the envi- ronmentviaanumberofpathwaysbutprimarilyfromdischargesofwastewatertreat- ment plants or land application of sewage sludge and animal manure. Most active ingredientsinpharmaceuticalsaretransformedonlypartiallyinthebodyandthus areexcretedasamixtureofmetabolitesandbioactiveformsintosewagesystems. AlthoughWWTPsremovesomepharmaceuticalsduringtreatment, 4,11,12 removal efcienciesvaryfromplanttoplant.Despiterecentinvestigationsdocumentingthe occurrence of pharmaceuticals in the environment, important information on their fate and long-term effects is still lacking. 13 15.2 FATE OF PHARMACEUTICALS IN BIOLOGICAL WASTEWATER TREATMENT PROCESS Some antibiotics and other pharmaceutical compounds in wastewater can be reduced or eliminated in biological wastewater treatment systems using the activated sludge process, which is the most commonly used wastewater treatment process in the world.Wastewatertreatmentprocessgenerallyconsistsofaprimary,secondary, andsometimesanadvancedtreatmentstage,withdifferentbiological,physical,and chemicalprocessesavailableforeachstageoftreatment.Aschematicdiagramofa typical WWTP that employs the activated sludges for secondary treatment is shown in Figure1 5.1. The primary treatment stage generally utilizes physical treatment, such as screens and a gravity settling process, typically referred to as sedimenta- tion,toremovethesolidcontentsinwastewater.Secondarytreatment,whichtypi- cally relies on microorganisms to biodegrade organic matter and/or other nutrients, can differ substantially. In some wastewater treatment facilities, the efuent also is disinfectedbeforeitisreleasedintotheenvironment,typicallybychlorinationor ultraviolet(UV)radiation.Inaddition,advancedwastetreatmentprocessescanbe appliedtoremovenitrogen,phosphorus,andotherpollutantsorparticles. 14 RecentreportsdemonstratethatconventionalWWTPsarenotcapableofremov- ing pharmaceutical contaminants under typical operating conditions, which results in a discharge of these compounds into surface waters. 5,15–26 Accordingly, WWTPs areimportantpointsourcesforantibioticcontaminationofsurfacewaters. 4,27–30 15.3 PHARMACEUTICAL REMOVAL MECHANISMS Several laboratory studies have been conducted to assess the efciencies of vari- ous treatment technologies in removing antibiotics and other pharmaceuticals from ABC A: Primary Treatment — Screen Bar and First Settlement B: Secondary Treatment — Activated Sludge and Second Settlement C: Advanced Treatment — Chlorination FIGURE 15.1 Aschematicdiagramofbiologicalwastewatertreatmentprocess. © 2008 by Taylor & Francis Group, LLC Removal of Pharmaceuticals in Biological Wastewater Treatment Plants 351 wastewater. 31–33 The primary pollutant removal mechanisms in conventional biologi- cal wastewater treatment processes are biodegradation and sorption by microorgan- is ms.Therefore,itisreasonabletoassumethatthekeycomponentinbiological WWTPsresponsiblefortheremovalofpharmaceuticalpollutantsistheaeration basin containing the microorganisms (activated sludge). Biodegradation and sorption alsocouldtakeplaceinotherunitprocesses,suchasprimarysettling,butremoval efciencies at this stage are difcult to control. 14 Other removal mechanisms such as volatilization(duetoaeration)orphotodegradation(duetosunlight)areeithernegli- gi ble or nonexistent. 34 Disinfection processes, such as chlorination or UV treatment, which are intended to remove pathogens, not only reduce drug-resistant bacteria but may also contribute in the elimination of some pharmaceuticals in wastewater. However,notallWWTPsincludeadisinfectionstep,manyfacilitiesonlydisinfect treated efuents seasonally, and several studies reported that disinfection does not effectively remove a wide range of antibiotics. 18,35 Accordingly, in this chapter we will limit our discussion on the pharmaceutical removal by biodegradation and sorp- ti on. However, Chapters 10, 11, and 12 int his book examine the efciencies of vari- ous disinfection processes in the removal of pharmaceuticals in drinking water. 15.3.1 BIODEGRADATION AND BIOTRANSFORMATIONS DuringbiologicaldegradationinWWTPs,pharmaceuticalcontaminantscould undergo (1) mineralization; (2) transformation to more hydrophobic compounds, which partition onto the solid portion of the activated sludge; and (3) transformation to more hydrophilic compounds, which remain in the liquid phase and are eventually discharged into surface waters. 13,36 Despite the wide consortium of microorganisms present in the activated sludge, it is unlikely that pharmaceuticals present as microcontaminants in wastewater can be effectively removed by biodegradation alone. First, the relatively low concentra - ti on of pharmaceuticals relative to other pollutants in wastewater may be insufcient to induce enzymes that are capable of degrading pharmaceuticals. 3 Second,manyof these compounds are bioactive, which can inhibitgrowthormetabolismofmicroor- ga nisms. Thus, it is unlikely that pharmaceuticals will be favorable energy or carbon sources for microorganisms. Third, the degree of biodegradation will depend on the natureofeachcompoundandontheoperatingconditionsemployedinWWTPs. Joss et al. 34 provided a comprehensive and intensive study investigating the bio- degradationofpharmaceuticals,hormones,andpersonal-careproductsinmunicipal wastewater treatment. Target compounds included antibiotics, antidepressants, anti - ep ileptics, antiphlogistics, contrast agents, estrogens, lipid regulators, nootropics, andfragrances.Amongthem,only4(ibuprofen,paracetamol,17 C-estradiol, a nd estrone) of the 35 compounds studied were degraded by more than 90%, while 17 compounds (including macrolides and sulfonamides) were removed by less than 50% during biological wastewater treatment. The biodegradation of sulfonamides 31,33 and trimethoprim 33 has been evaluated in batch reactors, and they were found to be non- readilybiodegradableandhavethepotentialtopersistintheaquaticenvironments. Many biodegradation studies only report the disappearance of the parent com - po undsbutdonotelucidatetheformationofmetabolites,whichalsomaybepersistent © 2008 by Taylor & Francis Group, LLC 352 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems and may have similar ecotoxicological effects. Recent studies that attempted to identify the byproducts of biodegradation in wastewater indicated that metabolites of many pharmaceuticals are not very different from their parent compounds. For example, Ingerslev and Halling-Sørensen 31 reported biodegradation of several sul- fonamide antibiotics in activated sludge, based on their disappearance over time, but quantities and identities of transformation product were not reported. In another study, the reported metabolites 37 of the antibiotic trimethoprim in activated sludge have structures that are only slightly modied compared to the parent compound (Figure 15.2). Whether these metabolites still exhibit the antibacterial activity of the parent compound or not remains to be tested. The lack of sensitive analytical tools able to detect low concentrations of unknown compounds in complex matrices has unfortunately limited the identication of pharmaceutical metabolites formed dur- ingbiodegradationinWWTPs.Thisisacriticalresearchneedbecauseriskassess- ments based only on the presence of parent compounds in wastewater could lead to underestimationoftheirriskstotheaquaticenvironment. 15.3.2 SORPTION Itisimportanttonotethatthemainremovalmechanismofsomerecalcitrantphar- maceuticals in biological WWTPs is sorption on activated sludge, rather than bio- degradation.SorptioninWWTPsismorelikelyanadsorptionprocess,whichis the physical adherence onto activated sludge or bonding of ions and molecules onto O N N N NH 2 NH 2 OCH 3 H 3 CO H 3 CO OH N N NH 2 NH 2 OCH 3 H 3 CO H 3 CO CH 3 N NH NH 2 NH 2 OCH 3 H 3 CO H 3 CO OH N NH 2 NH 2 OCH 3 H 3 CO H 3 CO Trimethoprim Trimethoprim Metabolites FIGURE 15.2 Trimethoprim and its biodegradation metabolites. © 2008 by Taylor & Francis Group, LLC Removal of Pharmaceuticals in Biological Wastewater Treatment Plants 353 the surface of microorganisms or microbial ocs. For example, ciprooxacin and tetracycline are removed mainly by sorption to sludge. 38,39 Astudywasconducted byKimetal. 39 to examine the relative importance of biodegradation and sorption in the removal of tetracycline in activated sludge. The similarity in the concentra- tion proles shown inFigure 15.3obtainedfromtwotypesofbioreactors,oneof which was amended with 0.1% sodium azide to suppress microbial activity, reveals that tetracycline concentration decreases over time even in the “activity-inhibited” control conditions. This suggests that the decrease in concentration was not due to biodegradation. In fact, chemical analysis of the aqueous phases from these bioreac- torsshowednobiodegradationproductsbeingformed.Fromthisbiodegradability test,thestrongsimilaritybetweeninhibited(spikedwithtetracycline+0.1%NaN 3 ) andnoninhibitedbiomass(spikedwithtetracyclineonly),andthelackoftetracy- cline metabolites, suggests that sorption is the primary mechanism for tetracycline removal in activated sludge. The sorption isotherm of tetracycline on activated sludge was determined and is presented in Figure 15.4. 39 The calculated K ads was8400±500mL/g(standard error of slope). This adsorption coefcient in activated sludge is approximately three times that reported for the more polar oxytetracycline (3020 mL/g) and much higher than that of ciprooxacin (K d =416.9mL/g), 40 whichwasfoundtobe95%associated with the sludge or biosolids. 38 Therefore, it is reasonable to assume that tetracycline is mostly adsorbed in the activated sludge. A study was conducted to compare the sorption kinetics of four selected antibi- oticsinactivatedsludge.Toinhibitmicrobialactivity,sodiumazidewasaddedinto the mixed liquor. Also, caffeine was spiked into the test system to serve as indicator of residual biological activity. (Caffeine is known to be readily biodegradable and hasnomeasurablesorptiontosludge.)Theexperimentwasconductedusing3600 mg/Lofmixedliquorsuspendedsolid(MLSS)obtainedfromalocalmunicipal 250 Spiked Spiked (+0.1% NaN 3 ) 200 Concentration (µg/L) 150 100 50 0 0510 Time (d) 15 FIGURE 15.3 Removal of tetracycline under batch-activated sludge conditions with active and “activity-inhibited” biomass. (Reactor spiked with 200 μg/L.) © 2008 by Taylor & Francis Group, LLC 354 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems WWTP. While more than 80% of ciprooxacin and tetracycline were removed in thedissolvedphaseaftera5-hequilibration,onlylessthan20%ofthemorehydro- phi lic sulfamethoxazole and trimethoprim were removed (Figure 15.5). Removal o f caffeine was not observed, indicating that the biological activity of the sludge was inhibitedbytheadditionofazide.Itcanbeinferredfromtheseresultsthatsorption is an important removal mechanism for both ciprooxacin and tetracycline but not for sulfamethoxazole and trimethoprim. Sorption of antibiotics on activated sludge that is eventually land applied poses a special concern because these antibiotics may remain biologically active and thus have the potential to inuence selection of anti - bi otic-resistant bacteria in the terrestrial environment. 15.4 INFLUENCE OF WASTEWATER TREATMENT PLANT (WWTP) OPERATING CONDITIONS The performance efciency of a biological WWTP depends highly on the operating conditionsanddesignandmaybeaffectedbydisturbances,suchashighconcentra- ti ons of pharmaceuticals or potentially toxic chemicals in inuent wastewater. Usu- al ly the ow rate and pollutant concentrations of wastewater are time dependent and hard to control. For example, the antibiotic concentrations in a composite sample and in grab samples were compared in two different WWTPs (Amherst, New York, and Holland,NewYork).ThepopulationsservedbyAmherstandHollandWWTPsare 115,000and1,750,respectively.Grabandcompositesampleswereobtainedtwice during the day (8 A.M.and4P.M.).Bothgrabandcompositesampleswereanalyzed for four selected antibiotics (ciprooxacin, sulfamethoxazole, tetracycline, trim- et hoprim). Figure 15.6 shows t he difference in concentration (% variation) for each antibiotic in the grab samples relative to the concentrations obtained in composite Amount of Tetracycline Sorbed/ Mass of Sorbent (mg/g) 0.5 0.4 K des = 22600 ± 2,200 R 2 = 0.850 K ads = 8400 ± 500 R 2 = 0.943 0.3 0.2 0.1 0.0 0.0 1.0 × 10 –5 2.0 × 10 –5 3.0 × 10 –5 Concentration of Tetracycline in Solution (mg/mL) 4.0 × 10 –5 5.0 × 10 –5 6.0 × 10 –5 FIGURE 15.4 Adsorption and desorption isotherms for tetracycline on activated sludge.K ads :sorp- tion coefcient, K des : desorption coefcient. (Error bars correspond to one standard deviation.) © 2008 by Taylor & Francis Group, LLC Removal of Pharmaceuticals in Biological Wastewater Treatment Plants 355 samples. There is high variability in the antibiotic concentrations during the two sampling times in the smaller WWTP (Holland), showing up to 70% difference in concentrations between the grab samples and the composite samples. Joss et al. 41 also reported higher pharmaceutical loads in daytime composite samples (8:00 to 16:00) as compared with other sampling times. This trend is similar to the characteristics of conventionalpollutantindicatorssuchassuspendedsolid(SS)orbiologicaloxygen demand (BOD). 14 This observation suggests that these conventional parameters may be good indicators for predicting the load of antibiotics in WWTPs. Some degree of biological WWTP removal efciency can be controlled by oper - ati ng parameters such as solid retention time (SRT) and hydraulic retention time (HRT). Several studies reported that biological wastewater treatment processes with highersolidsretentiontime(SRT)(>10days)tendtohavebetterremovalefciencies for pharmaceutical compounds compared to lower SRT processes. 35,42,43 This obser- vation implies that there is an enhanced biodegradation ability or different sorption capacityformicrocontaminantsinsludgewithahigherSRT. Kimetal. 39 reported the inuence of HRT and SRT on the removal of tetra- cyclineintheactivatedsludgeprocesses,usingasequencingbatchreactor(SBR) spikedwith250μg/Loftetracycline.Threedifferentoperatingconditionswere appliedduringthestudy(Phase1—HRT:24h,SRT:10d;Phase2—HRT:7.4h, SRT: 10 d; Phase 3—HRT: 7.4 h, SRT: 3 d). The removal efciency of tetracycline in Phase3(78.4±7.1%)wassignicantlylowerthanthatobservedinPhase1(86.4± 8.7%)andPhase2(85.1±5.4%)atthe95%condencelevel.ThereductionofSRT inPhase3whilemaintainingaconstantHRTdecreasedtetracyclinesorption,result - in gindecreasedremoval.Todate,thereislittleevidenceintheliteraturetosuggest biodegradationasalikelyremovalmechanismfortetracycline.Becauseofthehigh sorption of tetracycline in sludge, the inuence of SRT on the sorption behavior of           # $   " !    FIGURE 15.5 Antibiotic removal by adsorption in activated sludge. (Caffeine was used as marker for residual biological activity.) © 2008 by Taylor & Francis Group, LLC 356 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems pharmaceuticals is of interest, as sorption characteristics of the biomass may change withSRT.Severalresearchershaveobservedincreasedbiomasshydrophobicityat higher SRTs. 44,45 Infact,recentworkbyHarperandYi 46 has shown that bioreactor conguration can have a signicant inuence on biomass hydrophobicity and parti- cl esize,whichcanaffectthebioavailabilityandfateofpharmaceuticalsinWWTPs because of their impact on particle oc characteristics. Even though tetracycline has a low n-octanol/water partition coefcient, at certain pH values, hydrophobic inter - act ionsstillplayaroleforthesorptionoftetracyclineonsoilorclay. 47 Batt et al. 48 explored the occurrence of ciprooxacin, sulfamethoxazole, tetracy- cline, and trimethoprim antibiotics in four full-scale WWTPs. The WWTPs chosen utilized a variety of secondary removal processes, such as a two-stage activated sludge process with nitrication, extended aeration, rotating biological contactors, andpureoxygenactivatedsludge.InallfourWWTPs,thehighestreductioninanti - bi otic concentrations was observed after the secondary treatment processes, which is where the majority of the organic matter is eliminated and therefore is the most important processes for antibiotic removal. The extended aeration combined with 100 80 60 40 20 0 –20 Concentration Variation (%) –40 –60 Amherst Influent 8- AM 4-PM –80 –100 Trimethoprim Tetracycline Ciprofloxacin Sulfamethoxazole 80 60 40 20 0 Concentration Variation (%) Holland Influent 8- AM 4-PM 100 –20 –40 –60 –80 –100 Trimethoprim Tetracycline Ciprofloxacin Sulfamethoxazole FIGURE 15.6 Variation of antibiotic concentrations during the day. (Error bars correspond to one standard deviation.) © 2008 by Taylor & Francis Group, LLC Removal of Pharmaceuticals in Biological Wastewater Treatment Plants 357 ferrous chloride precipitation utilized at the East Aurora, New York, plant proved to bethemosteffectiveoftheWWTPdesignsexaminedintermsoftheoverallremoval ofthefourantibiotics.ExtendedaerationoperateswiththelongestHRTamongall theprocessesinvestigated(28to31hoursasopposedto1to4hours).Higherover - al l removal was observed at the Amherst, New York, plant than the remaining two (Holland,NewYork,andLackawana,NewYork),withthesecond-stageactivated sludge process at the Amherst operating with the longest SRT of the investigated WWTPs. The enhanced nitrication activity under long SRT has been suggested to play an important role in the increased removal of micropollutants, such as pharmaceuticals, in WWTPs. 33,37,43 It was noted that ammonia oxidizing bacteria (AOB) can come- tabolize various polyhalogenated ethanes 49 andmonocyclicaromaticcompounds. 50 It also has been reported that trimethoprim antibiotic can be removed more effec- ti vely in nitrifying activated sludge (high SRT) compared with that in conventional activated sludge (short SRT). 33,37,51 Batt et al. 51 investigated the fate of iopromide and trimethoprim under lab-scale nitrifying activated sludge. A signicantly higher biodegradation of both iopromide and trimethoprim was observed in the bioreac- to r where the activity of nitrifying bacteria was not inhibited (Batch-1), relative to the bioreactor where nitrication was inhibited by addition of allylthiourea (Batch- 2) (Figure15.7).The se results provide strong evidence that nitrifying bacteria play a key role in enhancing the biodegradation of pharmaceuticals in WWTPs. 33,37 It appearsthatprolongingSRTtoachievestablenitricationintheactivatedsludge has an added benet of increasing the removal efciencies of microcontaminants. A similar observation relating SRT and percent removal was reported recently for 100 Removal Percentage (%) 90 80 70 60 50 40 30 20 10 0 Batch-1 Reactor Type Batch-2 Iopromide Trimethoprim FIGURE 15.7 Iopromide and trimethoprim removal in nitrifying activated sludge: without amonia oxidizing material (AOB) inhibition (Batch-1), and with AOB inhibition (Batch-2). (Error bars correspond to one standard deviation.) © 2008 by Taylor & Francis Group, LLC 358 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems other pharmaceuticals and personal-care products in full-scale WWTPs with vary- ing SRTs. 43 15.5 FINAL REMARKS It is clear from the existing knowledge that attention is needed on optimizing WWTP operation to achieve maximum removal efciencies of pharmaceuticals in waste- wat er.ItisknownthatcurrentWTTPdesignsdonoteliminatemanymicropollut- an tscompletely.Whilevarioustreatmentprocessesindrinkingwaterproduction (such as activated carbon, ozonation, and membrane technologies) are effective in reducing concentration of micropollutant, 32 these technologies are not easily afford- able at many municipal WWTP facilities. Therefore, prolonging SRT in WWTPs maybeasimplesolutiontoreducetheconcentrationsofpharmaceuticalsintreated wastewater. Knowledge of the identities of metabolites, particularly those that are similar in structures to the parent pharmaceuticals and are persistent in the environment, iscritical.Foracompleteriskassessmentofpharmaceuticalsintheenvironment, itwillbenecessarytoconsiderpersistenttransformationproductsintheequation becausethesecompoundsmayposetheirownecologicalrisks.Todate,ecotoxicity data on metabolites and mixtures of pharmaceuticals are scarce. In a study that aimed at removing organic contaminants from an industrial wastewater treatment, it was found that despite the complete removal of the only known toxic contaminant (diethanolamine) in the wastewater, the toxicity of the bio - lo gically treated efuents was higher than what was calculated based on the removal efciency of the total organic carbon. 52 This implies that the majority of the observed effectsafterbiologicaltreatmentmustbeduetotheformationofmetabolites,which werenotidentiedinthestudy.Inanotherstudyexample,thephotodegradation product of the diuretic drug furosemide was found to be more mutagenic than its parent compound, 53 further demonstrating the importance of considering byproducts in toxicity testing and risk assessment. Basedonamorerealisticecologicalandhumanhealthriskassessment,current water quality standards can be updated to set acceptable levels of micropollutants thatdeterminehow“clean”watershouldbebeforeitcanbedischargedintothe environment. This is particularly critical for recycled wastewater that will be used asapotablewaterresource.Reductionofpharmaceuticalcontaminantsatthesource (efuent of WWTP) is obviously needed if recycled water is to become a signicant part of our domestic water supply. REFERENCES 1. Saeijs,H.L.andVanBerkel,M.J.,Globalwatercrisis:themajorissueofthe21stcen- tury, a growing and explosive problem, Eur. Water Poll.Cont.,5,26,1995. 2. Papaiacovou, I., Case study—Wastewater reuse in limassol as an alternative water source, Desalination, 138, 55, 2001. 3.Sedlak,D.L.,Gray,J.L.,andPinkston,K.E.,Understandingmicrocontaminantsin recycled water, Environ. Sci. Technol., 34, 509A, 2000. © 2008 by Taylor & Francis Group, LLC [...]... 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However, Chapters 10, 11, and 12 int his book examine the efciencies of vari- ous disinfection processes in the removal of pharmaceuticals in drinking water. 15. 3.1 BIODEGRADATION AND BIOTRANSFORMATIONS DuringbiologicaldegradationinWWTPs,pharmaceuticalcontaminantscould undergo. Group, LLC 354 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems WWTP. While more than 80% of ciprooxacin and tetracycline were removed in thedissolvedphaseaftera5-hequilibration,onlylessthan20%ofthemorehydro- phi lic. standard deviation.) © 2008 by Taylor & Francis Group, LLC 358 Fate of Pharmaceuticals in the Environment and in Water Treatment Systems other pharmaceuticals and personal-care products in