Effects of Ozone/Hydrogen PeroxidePretreatment on AerobicBiodegradability of NonionicSurfactants and PolypropyleneGlycolM E H M E T K I T I S , † C R A I G D . A D A M S , * , ‡

J O H N K U Z H I K A N N I L , ‡ A N DG L E N T . D A I G G E R §

Department of Environmental Engineering and Science,Clemson University, 342 Computer Court, Anderson,South Carolina 29625, Department of Civil Engineering,202 Butler-Carlton Hall, University of MissourisRolla,Rolla, Missouri 65409-0030, and CH2MHill,P.O. Box 241325, Denver, Colorado

Studies were conducted which used the ozone/hydrogenperoxide (O3/H2O2) advanced oxidation process to pretreatthree classes of compounds prior to aerobic biologicaltreatment. The study compounds included ethylene oxide/propylene oxide (EO/PO) block copolymers, polypropyleneglycols (PPGs), linear secondary alcoholethoxylates (LSAEs),and alkylphenolethoxylates (APEs). After preoxidationwith ozone and hydrogen peroxide (added at theirstoichiometric ratio), 300 mg/L as COD samples werebioassayed in aerobic batch bioassays with a mixed liquorsuspended solids concentration of 1500 mg/L. It wasfound that unoxidized polypropylated compounds (EO/POblock copolymers and PPGs) and LSAEs tended to bebiorecalcitrant, while alkylphenolethoxylates (APEs) werepartially biodegradable. Increasing oxidant dosages (i.e., ozoneplus stoichiometric hydrogen peroxide) consistentlyincreased both the rate and extent of biodegradation ofthese compounds with the exception of NP(EO)5, which initiallydecreased in biodegradability upon oxidation. Oxidantdosages required to enhance biodegradability variedsignificantly between and within classes of surfactant.For example, the average oxidant dosages required to reachan 85% DOC removal in the batch bioassays were 0.3mg O3/mg compound (plus H2O2) for LSAEs, 1.0 mg/mg for EO/PO and PPGs, and 5.0 mg/mg for APEs, respectively.

IntroductionNonionic surfactants are important due to their ability toretain surfactant properties in hard waters over a wide pHrange (1). The primary hydrophilic functionality in nonionicsurfactants is a poly(ethylene oxide) chain of varying lengths.The lipophilic functionalities may include polypropyleneoxide, alkylphenols, linear alcohols, and secondary alcohols.Ethylene oxide/propylene oxide (EO/PO) block copolymers,linear secondary alcoholethoxylates (LSAEs), and alkylphe-

nolethoxylates (APEs) represent major classes of nonionicsurfactants used worldwide (Figure 1). Unfortunately, theseclasses of surfactants are often biorecalcitrant in manyconventional aerobic biological treatment processes.

Polypropylene glycol (PPG) of varying lengths is animportant nonsurfactant component of many surfactantformulations. PPG alone or in EO/PO block copolymersimparts the biorefractory nature of these compounds due tosteric effects on the transport of the compounds through cellmembranes (2-4).

LSAEs are nonionic surfactants used extensively in a widerange of formulations and applications. In a generic alcoholethoxylate, the major factors affecting the rate and extent ofbiodegradability are as follows: (1) the degree of branchingin the alkyl chain (the hydrophobe) and (2) the length of theethylene oxide (EO) chain (the hydrophile) (2). The biode-gradability of LSAEs has been shown to decrease withincreasing EO chain length (5).

Biodegradation studies of partially biodegradable APEsindicate a complex metabolic behavior. Initial biodegradationproceeds via EO-chain cleavage of terminal EO units, therebydecreasing the aqueous solubility and hence biodegradability.This phenomenon results in the characteristic of partialbiodegradability often observed in APEs (6-8).

Because it may not be feasible to use biologically labilesurfactants in all applications, there is a need to identify anddevelop economically viable treatment technologies to reduceorganic content and toxicity in wastewaters containingsurfactants. In this research, we studied the effect of O3/H2O2 pretreatment on the aerobic biodegradability of selectedEO/PO block copolymers, PPGs, LSAEs, and APEs. In theO3/H2O2 advanced oxidation process (AOP), the hydroper-oxide ion (i.e., the conjugate base of H2O2 or HO2

-) reactswith ozone to form radical species which further decomposeto hydroxyl radicals in an autodecomposition cycle (9).

AOPs have been shown to effectively modify the molecularstructures of a variety of surfactants and related compounds,resulting in dissolved organic carbon (DOC) and chemicaloxygen demand (COD) reductions, loss of surface activeproperties (e.g., foaming, hydrophobicity), and affectedbiodegradability (3, 10-13). The purpose of the researchdescribed in this paper was to examine the viability ofintegrating O3/H2O2 pretreatment of EO/PO block copoly-mers, PPGs, LSAEs, and APEs with subsequent biologicaltreatment in a conventional activated sludge (AS) process.

Materials and MethodsTest Chemicals. The four EO/PO block copolymers examinedwere Pluronic L31, L35, F38, and P85 (BASF Corp.). The LSAEsexamined included Tergitol 15-S-7, 15-S-12, 15-S-20, and15-S-40 (Union Carbide) where the trailing number indicatesthe nominal number of ethylene oxide (EO) units present.Three APEs (all nonylphenolethoxylates) were examined with5, 12, and 40 EO units (NP(EO)5, NP(EO)12, NP(EO)40,respectively) (Rhone-Poulenc). Additionally, two polypro-pylene glycols were examined, PPG 425 and PPG 725 (wherethe number corresponds to the nominal molecular weight)(Aldrich Chemical Co.). The generic chemical structure andstructural information of each class of compound studiedare provided in Figure 1 and Table 1, respectively. All otherchemicals used for experiments or analysis were at leastreagent grade and were purchased from VWR ScientificProducts or Aldrich Chemical Co.

Analytical Methods. The laboratory methods used forthis research were from either Standard Methods (14),methods developed in previous projects (3), or methods

* Corresponding author phone: (573)341-4041; fax: (573)341-4729;e-mail: adams@umr.edu.

† Clemson University.‡ University of MissourisRolla.§ CH2MHill.

Environ. Sci. Technol. 2000, 34, 2305-2310

10.1021/es981228d CCC: $19.00 2000 American Chemical Society VOL. 34, NO. 11, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 2305Published on Web 05/04/2000

specified by the manufacturer of an instrument. Chemicaloxygen demand (COD) measurements were made using low-and high-range COD ampules (Hach Chemical) with aspectrophotometer (Spectronic 20D, Milton Roy) accordingto published Hach methods. Dissolved Organic Carbon (DOC)was measured using a Shimadzu TOC-5000 TOC Analyzerwith ASI-5000. pH measurements were made using a CorningpH meter (Model 220) and probe (Model 476540). Hydrogenperoxide was measured using a Hach Model HYP-1 titrametrictest kit.

O3/H2O2 Oxidation Procedure. O3/H2O2-based advancedoxidation was conducted in a 1-L semibatch reactor withboth inlet and outlet ports for ozone, hydrogen peroxidefeed, temperature monitoring, reactor feed, and sampleremoval (Figure 2). Ozone was supplied with a Model GTC-1B (Griffin Technics Corp.) or a Model OZAT 0 (Ozonia Corp.)ozone generator fed pure oxygen. Gas-phase ozone con-centrations in the ozone feed and offgas streams weremonitored using a Model HC-12 ozone monitor (PCI Ozoneand Control Systems, Inc.). Using mass flow controller data(Tylan FC-280 MFC), the absorbed ozone concentrations werecalculated using a Camile 2000 Data Acquisition and ControlSystem (Dow Chemical). Hydrogen peroxide was added viaa peristaltic pump at a rate of 0.35 mg of H2O2 per mg ofabsorbed ozone (i.e, stoichiometric ratio). The solutions thatwere oxidized contained an average initial surfactant (or PPG)concentration of 1000 ((28 mg/L, R ) 0.05) mg/L as COD.An initial volume of 700 mL was used in the 1-L semibatchreactor to allow enough headspace for potential foaming.The solutions were buffered with 8 mM sodium phosphateto assist in maintaining the pH in the optimum region forthe effective hydroxyl radical production. pH was monitoredex situ but not controlled during the oxidation. In theseexperiments, the pH decreased from an initial pH of 8.8 ((0.5)to 7.3 ((0.2) during oxidation. The reactor temperature was22 °C ((1) for all the oxidation experiments.

Samples were removed at predetermined absorbed ozonedosages over a period ranging from 20 to 40 min for bioassays,DOC, COD, and pH analysis. Immediately after removing asample, residual H2O2 was quenched by adding a slight excessof sodium sulfite. Foaming in the reactor during ozonationwas only a problem for the initial 1 to 3 min and was controlledusing a foam trap.

Bioassay Procedure. An aerobic sequencing batch reactor(SBR) with a 10-day solids retention time (SRT) and 1.5-dayhydraulic retention time (HRT) was continuously operated

throughout the experiments to generate biomass for batchaerobic bioassays of oxidized and unoxidized samples. Theinitial seed was obtained from two AS processes at industrialwastewater facilities. The SBR was fed nutrients (e.g., NH4

+,Ca2+, Fe3+, Co2+, Zn2+, Mg2+, Mn2+, Cu2+, and Mo3+) as wellas a mixture of synthetic organic chemicals including thefollowing: ethylene glycol, poly(ethylene glycol), Alkumuls0-14, catechol, resorcinol, hydroquinone, trihydroxybenzene,and butyl ether (15). The organic compounds in the feedwere selected based on their chemical functionalities po-tentially being similar to those of anticipated intermediatesor byproducts of the O3/H2O2 advanced oxidation. Therefore,the biomass in the SBR was acclimated to these certainchemical structures thereby reducing the associated lag timein the bioassays. The SBR also provided a uniform biomassfor the bioassays. The SBR was fed daily with a feed solution,macro- and micronutrients, and deionized water using aCartridge Pump (Cole-Parmer Inst. Co., Model 7519-00).Potassium phosphate monobasic (KH2PO4) and potassiumphosphate dibasic (K2HPO4) were provided in the nutrientsolution for buffering purposes as well as a nutrient. Mixingand aeration were provided using activated-carbon filteredlaboratory air.

The SBR system was automated using a controller(ChronTrol, Model XT). Just before each daily cycle ended(before aeration/mixing was turned off), 1.2 L of Mixed LiquorSuspended Solids (MLSS) was wasted from the reactor tomaintain the 10-day SRT and to provide the biomass to beused in the bioassays. After the air was turned off, biomasswas allowed to settle for 50 min. Then the treated supernatantwas removed using a submerged pump (Little Giant PumpComp., Model P-AAA-WG) leaving the biomass in the reactor,thus completing one cycle. The next cycle was then initiatedby refeeding the reactor. After an initial stabilization periodof approximately 20 days, the MLSS averaged 2500 (( 200)mg/L over the following 9 months (15). After the initial start-up period, 90-95% COD removals were achieved with 4 hin the SBR during each daily cycle.

To assess the extent of biodegradability of the chemicallyoxidized and unoxidized samples, batch aerobic bioassayswere conducted on 200 mL volumes (in 300 mL flasks). Thesolutions had an initial surfactant concentration of 300 ((15)mg/L as COD. A MLSS concentration of 1500 mg/L was usedin the bioassays with the biomass provided from the wastesludge of the SBR. Flasks were shaken on shaker tables(Labline Orbit Shaker) at 180 rpm to provide mixing andaeration. Required micro- and macronutrients and buffering(phosphate) were also provided in the bioassays. All bioassayexperiments were conducted with an initial pH of ap-proximately 7.2 ((0.1) and at a temperature of 22 °C ((1).The biodegradable feed solution for the SBR was used aspositive control for every bioassay experiment to demonstratethat the bioculture was viable. A blank flask containing onlybiomass and nutrient solution was also bioassayed to measurethe relative DOC contribution of the biomass solution to theoriginal DOC concentrations of contaminant solutions.Samples were periodically removed from the flasks, centri-fuged to remove the biomass, and analyzed for DOC. Eachof the bioassays was analyzed by plotting the DOC concen-trations versus bioassay duration from which the maximumDOC removal could be estimated.

The potential for sorptive and volatilization loss of organicsin the bioassays was examined using mercuric nitrate (toinhibit biological activity) and found to be negligible (lessthan 5%). Low volatilization losses are due to low vaporpressures of the study compounds.

Results and DiscussionBiodegradability of the Unoxidized Compounds. As a firststep in this study, bioassays were conducted to determine

FIGURE 1. Representative structures of study compounds.

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the aerobic biodegradability of the unoxidized compounds.DOC removals were used to assess the extent of biodegrada-tion of the compounds. Table 1 shows the bioassay resultsfor the unoxidized compounds. Compounds with DOCremovals equal to or less than 40%, between 40 and 90%,and equal to or greater than 90% were considered biore-calcitrant, partially biodegradable, and readily biodegradable,respectively.

Examination of the results from the bioassays of unoxi-dized PPGs showed that both PPG 425 and PPG 725 werehighly biorecalcitrant with DOC removals of only 17 and2.4%, respectively. This result can be due either to thepresence of a methyl side chain, which can interfere with thetransport of the molecule across the cell envelope, or to thefolding of the molecule that can make the ends of the chaininaccessible to the biodegradation (4). In any event, it isapparent that high molecular weight may decrease thebiodegradability of the unoxidized PPGs.

Each member of the Pluronic 30-series (EO/POs) had thesame number (16 units) of biorecalcitrant PO units. Exami-nation of the biodegradability results for the EO/PO polymerswith 3, 24, and 96 EO units for L31, L35, and F38, respectively,showed that increasing the EO-chain length significantlydecreases the biodegradability of the unoxidized surfactantsfrom 61 to 12 to 8.6% DOC removal, respectively (Figure 4).This trend suggests that while PPG may impart biorecalci-trance to specific compounds, the molecular weight of the

EO/POs may also play an important role in biorecalcitranceeven if the additional structure is simply an EO polymer (Table1).

TABLE 1. Molecular Weight and Structural Information for Each Study Compounda

class av mol wtno. of

EO unitsno. of

PO units CAS no. trade name

maximumDOC

removal (%) biodegradability

EO/PO block copolymer 1100 3 16 586770 Pluronic L31 61 partialEO/PO block copolymer 1900 24 16 13390 Pluronic L35 12 biorecalcitrantEO/PO block copolymer 4700 96 16 583095 Pluronic F38 8.6 biorecalcitrantEO/PO block copolymer 4600 58 39 588850 Pluronic P85 14 biorecalcitrantPPG 425 424 7 20,230-4 polypropylene glycol 17 biorecalcitrantPPG 725 714 12 20,231-2 polypropylene glycol 2.4 biorecalcitrantLSAE (15-S-7) 509 7 84133-50-6 Tergitol (15-S-7) 47 partialLSAE (15-S-12) 729 12 84133-50-6 Tergitol (15-S-12) 59 partialLSAE (15-S-20) 1081 20 84133-50-6 Tergitol (15-S-20) 50 partialLSAE (15-S-40) 1961 40 84133-50-6 Tergitol (15-S-20) 21 biorecalcitrantAPE/NP(EO)5 422 5 9016-45-9 IGEPAL CO-520 52 partialAPE/NP(EO)12 730 12 9016-45-9 IGEPAL CO-720 61 partialAPE/NP(EO)40 1962 40 9016-45-9 IGEPAL CO-890 76 partial

a Identified by class, CAS number, and trade name. Maximum DOC removal (percent) and biodegradability assessment achieved in batchactivated sludge bioassays for each compound. “Biorecalcitrant”: ∆DOC < 40%; “partial”: 40 < ∆DOC < 90%.

FIGURE 2. Reactor system used for O3/H2O2 advanced oxidation of surfactant solutions (MFC ) mass flow controller).

FIGURE 3. Normalized DOC removal in batch activated sludgebioassay of EO/PO polymer P85 unoxidized and after O3/H2O2

oxidation (H2O2 dose ) 0.35 mg H2O2/mg O3). (Error bars indicate the95% confidence intervals.)

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The unoxidized LSAEs with 7, 12, and 20 EO units exhibitedpartial biodegradability with DOC removals between ap-proximately 47 and 59% (Table 1). The higher molecularweight LSAE with 40 EO units (M Wt 1961) was considerablyless biodegradable, with a DOC removal of only 21%, duepossibly to its larger size inhibiting transport across thebacterial cell membrane. Nonionic surfactants with longerEO chains (i.e., 40) may exhibit lower biodegradabilities thanthose with moderate EO chain length due to folding of themolecule inhibiting transcellular transport (2). On the otherhand, nonionic surfactants with relatively short EO chains(i.e., 7 units) may exhibit biorecalcitrance due to reducedaqueous solubility (2).

Unoxidized NP(EO)5, (NP(EO)12, and (NP(EO)40 demon-strated 52, 61, and 76% DOC removals during biodegradation,respectively. Partial biodegradation of APEs can be due tothe formation of APEs with shorter EO units, which areresistant to further microbial degradation (6-8). The observedeffect of long EO chains (12 and 40 units) on the nonylphenolswas to increase biodegradability.

Effects of Advanced Oxidation on Biodegradability. EO/PO Block Copolymers and PPGs. The results for the advancedoxidation of the EO/PO block copolymers showed thatadvanced oxidation was effective at enhancing the biode-gradability (represented by DOC removal) for each studycompound. For example, the DOC removal curve during theshaker table bioassays is presented in Figure 3 for EO/POP85. These data show that increasing oxidant dosagessignificantly increased biodegradability (i.e, the DOC re-moval) in the shaker table bioassays. In fact, greater oxidantdosages resulted in greater DOC removals for all of the EO/POs (Figure 4). Oxidant dosages of 1 mg O3/mg compound(plus H2O2) resulted in DOC removals of greater than 85%during biodegradation for the EO/PO block copolymers.

Similarly, the advanced oxidation was highly effective atenhancing the biodegradability for both PPGs examined.Specifically, Figure 5 shows the normalized DOC results fromthe shaker table bioassays for the unoxidized and oxidizedPPG 425. A slight increase in DOC for the unoxidized PPG425 is hypothesized to be due to cell lysis and release ofintracellular material into solution. Overall, greater oxidantdosages resulted in enhanced biodegradability for bothcompounds with DOC removals of approximately 92%achieved during biodegradation for both PPGs after ap-plication of 1 mg O3/mg compound (plus H2O2) (Figure 6).

Hydroxyl radicals react with both EO and PO polymersthrough hydrogen abstraction mechanisms at any carbonalong a chain or terminus (16). Oxidation of the carbon chainleads to polymer cleavage and lower molecular weightbyproducts that are much easier for bacteria to metabolize.Hydroxyl radical rate constants for both ethylene oxide (EO)

and propylene oxide (PO) monomers are both approximately1.7(109) L/mol‚s (17). Therefore, it is likely that hydroxylradicals would have relatively equal propensity towardoxidizing either the EO or PO portions of the EO/PO blockstructure. EO/PO L31, L35, and F38 have the same numberof PO units (sixteen) but different numbers of EO units (i.e.,3, 24, and 96, respectively). Therefore, a randomly cleavedL31 will result in a much higher PO to EO ratio (e.g.,approximately 5) than for F38 (e.g., approximately 0.2).Because of decreased solubility and greater branching, POsare less biodegradable than EO monomers or polymers (2).Therefore, a greater DOC removal for the oxidized EO/POF38 may result than for the L31 at 0.75 to 1.5 mg O3/mgcompound (plus H2O2) (Figure 4).

LSAEs. For the LSAEs studied, advanced oxidation withvery low oxidant dosages was effective at enhancing bio-degradability. For example, ozone dosages of 0.25 mg O3/mgcompound resulted in percent DOC removal increases of 85,53, 78, and 370% for LSAEs with 7, 12, 20, and 40 EO units,respectively (Figure 7). While the highest molecular weightLSAE (15-S-40) had the lowest biodegradability for theunoxidized compounds 15-S-40 had the highest biodegrad-ability of any of the LSAEs after the advanced oxidation.Brambilla et al. (10) showed that hydroxyl radical attack ofthe EO chain was more rapid than for the alkyl chain of thealcohol moiety leading to EO chain cleavage. All four of the

FIGURE 4. Maximum DOC removal (percent) achieved in batchactivated sludge bioassays for ethylene oxide/propylene oxide (EO/PO) block copolymers as a function of ozone dose (H2O2 dose ) 0.35mg H2O2/mg O3).

FIGURE 5. Normalized DOC removal in batch activated sludgebioassay of PPG 425 unoxidized and after O3/H2O2 oxidation (H2O2

dose ) 0.35 mg H2O2/mg O3). (Error bars indicate the 95% confidenceintervals.)

FIGURE 6. Maximum DOC removal (percent) achieved in batchactivated sludge bioassays for polypropylene glycols (PPGs) as afunction of ozone dose (H2O2 dose ) 0.35 mg H2O2/mg O3).

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LSAEs examined had the same linear alkyl group. However,the EO-carbon to alkyl carbon ranged from approximately1.5 for 15-S-7 to 9 for 15-S-40. Therefore, for the highermolecular weight 15-S-40, the vast majority of its carbon isin the form of EO groups that may be readily biodegradedonce cleaved via oxidation as seen in Figure 7. On the otherhand, 15-S-7 has approximately 35% of its carbon as a morerecalcitrant secondary alcohol, leading to lower overallbiodegradability even after oxidation (Figure 7).

Alkylphenolethoxylates. The bioassay results for unoxi-dized and oxidized APEs showed advanced oxidation in-creased the biodegradability of APEs but not nearly asefficiently as with the EO/PO and PPG compounds. Thebioassay results for NP(EO)12 is presented in Figure 8 whichshow that advanced oxidation increased the biodegradationextent, albeit with relatively high oxidant dosages. Thebiodegradability enhancement achieved for each of the APEsexamined are presented as a function of ozone dosage inFigure 9. For example, an oxidant dosage of 7 mg O3/mgcompound (plus H2O2) resulted in DOC removals of 85, 81,95% of APEs with 5, 12, and 40 EO units, respectively.

The DOC removals of NP(EO)5 decreased from 52 to 33%after application of 1 mg O3/mg compound (plus stoichio-metric H2O2), a result consistent with findings of previous

studies (3). It is thought that the cause of the decreasedbiodegradability is that primary ozone- and hydroxyl-radical-based oxidation pathways for the APEs is EO chain shortening,thereby decreasing an APE’s solubility. Higher oxidantdosages than required to cleave all EO units would result ina variety of other reactions dominating, such as ring andalkyl chain hydroxylation and cleavage, resulting in morelabile compounds.

In summary, this research examined the viability ofenhancing the biodegradability of EO/PO block copolymers,LSAEs, APEs, and PPGs, using an integrated advancedoxidation/biological treatment process. Unoxidized polypro-pylated surfactants and PPGs were found to be biorecalci-trant, while unoxidized APEs and LSAEs were generallypartially biodegradable. The effectiveness of advancedoxidation for biodegradability enhancement of the studycompounds appears to be related hydroxyl radical cleavage.Those compounds that cleave to predominantly easilydegradable byproducts (e.g., EO units) are most efficientlysoftened by advanced oxidation pretreatment.

AcknowledgmentsThis research was sponsored by the Hoechst CelaneseCorporation and the National Science Foundation (ProjectBCS-9257625). At the time of this study, Mr. Kitis and Mr.Kuzhikannil were master’s students at Clemson Universityand the University of MissourisRolla, respectively. Dr. GlenDaigger is Sr. Vice-President of Wastewater Process Engi-neering at CH2MHill, Corp.

Literature Cited(1) Hellsten, M. In Industrial Applications of Surfactants: Industrial

Applications of Nonionic Surfactants; Karsa, D. R., Eds.; TheRoyal Society of Chemistry: Burlington House, London, 1986;pp 179-194.

(2) Swisher, R. D. Surfactant Biodegradation, 2nd ed.; Marcel DekkerInc.: New York, 1987.

(3) Adams, C. D.; Spitzer, S.; Cowan, R. L. J. Environ. Eng. 1996,122, 477-483.

(4) Alexander, M. Biodegradation and Bioremediation; AcademicPress: New York, 1994.

(5) Gebril, B. A.; Naim, H. M. Ind. J. Technol. 1969, 7, 365-369.(6) Reinhard, M.; Goodman, N.; Mortelmans, K. E. Environ. Sci.

Technol. 1982, 16, 351-362.(7) Giger, W.; Brunner, P. H.; Schaffner, C. Science 1984, 225, 623-

625.(8) Ahel, M.; Conrad, T.; Giger, W. Environ. Sci. Toxicol. 1987, 21,

697-703.(9) Glaze, W. H.; Kang, J. W. J.-Am. Water Works Assoc. 1988, 80:5,

57-63.(10) Brambilla, A. M.; Calvosa, L.; Monteverdi, A.; Polesello, S.;

Rindone, B. Water Res. 1993, 27, 1313-1322.(11) Delanghe, B.; Mekras, C. I.; Graham, N. J. D. Ozone Sci. Eng.

1991, 13, 639-673.

FIGURE 7. Maximum DOC removal (percent) achieved in batchactivated sludge bioassays for linear secondary alcohol ethoxylates(LSAEs) as a function of ozone dose (H2O2 dose ) 0.35 mg H2O2/mgO3).

FIGURE 8. Normalized DOC removal in batch activated sludgebioassay of NP(EO)12 unoxidized and after O3/H2O2 oxidation (H2O2

dose ) 0.35 mg H2O2/mg O3). (Error bars indicate the 95% confidenceintervals.)

FIGURE 9. Maximum DOC removal (percent) achieved in batchactivated sludge bioassays for alkylphenolethoxylates (APEs) as afunction of ozone dose (H2O2 dose ) 0.35 mg H2O2/mg O3).

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(12) Adams, C. D.; Cozzens, R.; Kim, B. Water Res. 1997, 31, 2655-2663.

(13) Cline, J. E.; Sullivan, P. F.; Fowler, R.; Lovejoy, M. A.; Collier, J.;Adams, C. D. 89th Annual Meeting of the Air and WasteManagement Association, Nashville, TN, March 1996.

(14) Standard Methods for the Examination of Water and Wastewater,18th ed.; American Public Health Assoc.: Washington, DC, 1992.

(15) Kitis, M. Master’s Thesis, Clemson University, Clemson, SC,1996.

(16) Alexander, M. Biotechnol. Bioeng. 1973, 15, 611-647.(17) Adams, G. E.; Boag, J. W.; Michael, B. D. Trans. Faraday Soc.

1965, 61, 1417-1424.

Received for review November 30, 1998. Revised manuscriptreceived February 11, 2000. Accepted March 14, 2000.

ES981228D

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