A pilot study was performed at the Fox River Fiber recovered paper processing company in DePere, Wisconsin, to determine theextent to which injection of oxygen and ozone could reduce the high chemical oxygen demand, COD, in the effluent and theeffectiveness of the ozone/oxygen stream in suppressing production of hydrogen sulfide gas in downstream sewage lines. AdaptiveOzone Solutions, LLC, supplied the oxygen/ozone generation and injection system. Samples were analyzed both before and afteroxygen/ozone injection. Hydrogen sulfide gas was continuously monitored at sewer stations downstream of Fox River Fiber. Resultsshowed that with a very short contact time, effluent COD was reduced by over 15%. A simple kinetic model predicts that a contacttime of fewer than 30 minutes could reduce COD by as much as 60%. In addition, downstream hydrogen sulfide gas productionin the sewage mains was also better controlled, such that costly Bioxide applications could be reduced.
1. Introduction and Literature Review
In a growing world, it is increasingly more necessary to treatmunicipal and industrial wastewaters using environmentallygreen technologies. Current technologies often employ man-made chemicals as the primary treatment agent, but there aregrowing concerns and problems associated with the residualeffects of putting more chemicals in wastewater. Displacingthese chemicals with economic, environmentally friendlyprocesses offers a significant market opportunity [1].
Among primary manufacturing industries, paper manu-facturing is the fourth largest user of energy and the largestgenerator of wastes, measured by weight. Water is the basicmedium of pulp and paper manufacturing; it carries fibersthrough each treatment step and separates spent pulpingchemicals and the complete mixture of organic residues fromthe pulp [2]. The process of pulp and paper processinginvolves production of effluent water streams with highchemical oxygen demand, COD, loads. COD is a measure ofthe oxygen requirement of the organic matter susceptible tooxidation by a strong chemical oxidant. It is used to define
the organic strength of industrial wastes and polluted waters.COD wastes usually are not readily biodegradable and oftencontain compounds that inhibit biological activity [3] inwastewater treatment facilities.
In addition, one of the challenges faced by wastewatertreatment facilities is hydrogen sulfide, H2S, gas productionin sewer lines, especially in warmer weather. High biologicaland chemical oxygen demand loads combined with lowdissolved oxygen content of sewage water and effluents frompaper processing facilities create anaerobic septic conditionsin sewage lines. Hydrogen sulfide gas, produced as a resultof these conditions, is the most common odorous gas foundin municipal wastewater collection and treatment systems. Itemits a characteristic smell of rotten eggs and is both toxic tohumans and corrosive to steel and concrete. Condensationmoisture on the side walls and crowns of sewer pipes absorbsH2S and oxygen from the atmosphere in the sewer andsulfur-oxidizing bacteria, Thiobacillus, then forms H2SO4.The sulfuric acid reacts with lime in concrete sewers causingcrown corrosion and compromising the structural integrityof sewer lines [3, 4].
2 International Journal of Chemical Engineering
The best protection for sanitary sewers is to use corrosionresistant pipe, such as vitrified clay or plastic, but thismay be economically prohibitive in large systems. In thesesystems crown corrosion can be retarded by ventilation tocontrol build-up of H2S gas. Another treatment option isBioxide, an aqueous solution of calcium nitrate, produced bySiemens Water Technologies, Inc. Bioxide creates a biologicalprocess that both removes dissolved H2S and prevents itsformation through the addition of nitrate oxygen. It reducessewage treatment biological oxygen demand (BOD) loadswhile preventing corrosion of concrete or metal collectionsystems. The biggest drawbacks to Bioxide is that it adds anew chemical, calcium nitrate, to a process. Because it is stillunder patent protection, the biggest drawback of Bioxide isits cost, which many facilities find to be prohibitive [5].
Fox River Fiber Company, FRF, is a small recovered fiberpaper manufacturing facility located in DePere, Wisconsin.The process of recovering recycled paper involves deinkingby either chemical or mechanical means and creating marketpulp ready for conversion to paper products. The paper-making process uses on average between 10 to 19 liters ofwater per kilogram of product, which includes deinking andpulping chemicals, inks, coatings, adhesives, and cellulosicand lignin paper fibers.
The Green Bay Metropolitan Sewerage District(GBMSD) wastewater treatment plant recently beganaccepting effluent wastewater from FRF to its DePere, WI,facility. In order to control the introduction of pollutantsinto the sewerage system and, ultimately, its facility, GBMSDhas implemented an industrial pretreatment program toregulate certain industries called Significant IndustrialUsers (SIUs). SIUs must comply with federal, state, andlocal requirements through a permit system that includesself monitoring and compliance. GBMSD also inspectsSIUs annually to review operations and promote pollutionprevention. FRF because of its high effluent COD levels hasbeen designated as an SIU.
Unlike larger paper manufacturers, Fox River FiberCompany does not pretreat its effluent water prior todischarge to the GBMSD system and, hence, must pay thesewerage district to compensate for the load associated withsuch high COD levels. Fox River Fiber’s effluent water streamhas between 5000 to 6000 mg/L CODs depending on thevariety of recovered paper being processed. At its currentCOD release level, Fox River Fiber pays GBMSD $1.4 millionper year, $200,000 of which is fixed and $1.2 million of whichis a linear function of the plant’s effluent COD level.
In addition to high COD loads, to suppress production ofhydrogen sulfide gas in sewage mains, Fox River Fiber appliesas much as 1710 liters per day of Bioxide to their effluentduring warm summer months when H2S production is at itsworst. Lower quantities are applied during colder months.GBMSD requires that effluent from Fox River Fiber does notlead to H2S gas levels in the air space of the downstreamsewage system that exceed a maximum peak of 40 ppm andan average of 20 ppm over a twenty-four hour period. Theplant’s normal operating temperature is about 40◦ Celcius,which contributes to H2S gas production and makes CODreduction more difficult.
Previous studies have considered applications of ozoneto water treatment, but primarily as a disinfectant, whereozone’s effectiveness is well documented [1, 3]. Ozone isshown to reduce cryptosporidium and control taste and odorproblems in surface water treatment systems [6]. Recentstudies [7, 8] investigated ozonation to increase the biodegra-dation of resistant textile wastewaters containing dyes anddetergents. Many commercial laundering systems have usedozone successfully and its microbiological benefits have beenobserved [9]. Another recent study [10] summarized poten-tial options for improvement of wastewater treatment planteffluents using ozone and integration of ozone technology toexisting and conventional plants. Preozonation has also beenconsidered to enhance the biodegradability of recalcitrantcompounds prior to biological treatment of wastewater [11].In addition, the applicability of ozone to treatment and massreduction of wastewater sludge has been studied [12].
A pilot study was performed on the Fox River Fibereffluent to determine to what extent COD reduction couldbe achieved through addition of high pressure oxygen andozone. In addition, suppression of H2S gas production insewage lines was monitored. The study included reductionof Bioxide application during oxygen/ozone injection. Todetermine the project’s success, COD was monitored inthe FRF’s effluent before and after oxygen/ozone injectionas well as dissolved oxygen (DO), pH, and temperature.Due to the pilot study’s limitation that the ozone injectionsystem be completely with Fox River Fiber’s plant and thatpre- and postinjection samples be drawn from within FoxRiver Fiber’s facility, the contact time between injected ozoneand wastewater stream was considerably less than optimal.Experiments were performed to model the kinetics of theoxygen COD degradation reaction and estimate the overallpotential of the process for a longer contact time that wouldbe included in a permanent system. A third oxygen/ozoneexperiment was conducted to quantify the effect of increasingozone levels on COD removal. In addition, H2S gas wasmonitored at several gravity sewage mains downstreamof Fox River Fiber. While other effluent streams join thewater flow to GBMSD, the temperature and COD loadassociated with Fox River Fiber’s effluent make it the greatestcontributor to low DO levels and H2S gas production insewage lines.
One potential concern with the use of high pressureozone is that it is known to be corrosive to some gasketmaterials that are prevalent in water collection systems. Uni-Bell PVC Pipe Association [13] has published information onresistance of natural and synthetic rubber gasket materials toozone exposure. A number of factors must be present beforeozone degradation of synthetic rubbers forms cracks thatgrow and lead to material failure. First, elongation must bepresent for crack formation. Unstretched rubber reacts withozone until all of the surface double bonds are consumed,and then the reaction ceases. In the process, a gray film, orfrosting, appears on the surface of the rubber, but no cracksform. Ozone will continue to react with rubber only if thesurface of ozonized products is moved aside to expose under-lying unsaturation. Consequently, cracks only form and growif the rubber is stretched to expose underlying unsaturation.
International Journal of Chemical Engineering 3
Because rubber gaskets in service are under a compressiveload, they do not experience elongation and, hence, it isnot likely that they will degrade via ozone attack past theinitial inner surface of the gasket that contacts the ozonatedwater. The gray film, or frosting, associated with surfaceattack should appear, but the compressive forces holdingthe gasket in place should prevent the critical elongationrequired to expose underlying saturation. Selection of anEPDM, neoprene or Viton gasket material will also protectagainst loss of service due to gasket failure [14–16].
2. Experimental Methods and Results
Adaptive Ozone Solutions, AO3, LLC, designed and installedthe ozone system used in all pilot studies and experiments.The company, located in Lenexa, Kansas, manufactures andsells oxygen and ozone systems for municipal and industrialapplications. Their patented technology uses electrochemicalcells to generate ozone and supplies concentrated oxygen andozone feed streams to wastewaters via aerosol diffusers.
Dissolved oxygen, pH, and temperature were mea-sured using a Hach HQ40d IntellicalTM portable field kit.COD was measured using Hach standard method 8000photometric analysis with a Hach DRD200 reactor, HachDR890 colorimeter, and Hach high range (0 to 15,000 ppm)plus reagent tubes. All tests were performed in triplicatewith averages presented. Dissolved ozone concentration wasmeasured with a model Q45H portable dissolved ozoneanalyzer from Analytical Technology, Inc. The analyzer hascapability to measure dissolved ozone in the low range of0–200 ppb and also the range of 0–2 ppm, typical of waterbottling or municipal water treatment applications.
2.1. Ozone Corrosivity. Because of the potentially corrosivenature of ozone to synthetic rubber gasket materials, testswere performed to determine how long after injectioninto a pipe system ozone maintains a residual. A modelexperimental apparatus was constructed at the Green BayMetropolitan Sewerage District, Green Bay, Wisconsin, tomeasure ozone residual following injection into a streamof incoming wastewater. The system consisted of an ozonegenerator, ozone diffuser, and four inch PVC piping systemdesigned by Adaptive Ozone Solutions, LLC. The generatorfed ozone in an oxygen stream into the system at a rate of18 grams/hour ozone. To measure ozone residual, nine testports were installed into the piping system. Each of these wasconnected to a dissolved ozone monitor and cell.The sampleports were located at 1.5, 4.5, 10.7, 16.8, 22.9, 29.0, 50.3, 53.3,and 59.4 meters, respectively, from the diffuser.
Wastewater flow through the system was 76 liters/minute.Ozone measurements taken at the first sample port, 1.5meters from injection, showed no residual ozone. Tests wereperformed multiple times to verify the zero reading. Thesame was the case for all downstream sample ports. For9-centimeter outer diameter PVC pipe, a 76 liter/minuteflow gives a water velocity of about 17.7 cm/second and aresidence time of 8.6 seconds to reach the 1.5 meter sampleport. Therefore, the ozone residual in the water was less
Table 1: Pre- and post-O2/O3 injection measurements (O3
loading rate of 0.053 g/min/liter water and O2 loading rate of0.53 g/min/liter water).
TemperaturepH
DO COD Standarddeviation(◦C) (mg/L) (mg/L)
Pre injection 40.6 7.47 0.12 5244 352
Postinjection 40.8 7.31 18.56 4422 256
than 8.6 seconds. This is similar to a result found by astudy of ozone disinfection of water [1] who measured ozoneresiduals following disinfection with contact times of 10, 18,50, and 93 seconds and found that, in some cases, ozoneresidual decayed too rapidly to be measurable.
2.2. Effect of Ozone and Oxygen on COD Effluent fromFox River Fiber. For seven weeks during June throughJuly 2009, an AO3 installed ozone generator injected 4grams/minute of ozone, in addition to high pressure oxygen,into the approximately 76 liters/min effluent water streamof Fox River Fiber Paper Company. The ozone loadingrate was 0.053 grams/min/liter water and that for oxygenwas 0.53 grams/min/liter water. During this time, Bioxideaddition was reduced incrementally from its peak applicationrate of 1520 liters per day to 1330 liters per day, 950 litersper day, and finally 570 liters per day. Dissolved oxygen,pH, temperature, and COD were measured both at a samplepoint upstream of the injection point and one downstreamof the injection point, but prior to entering the GBMSDsewage lines. Process limitations required that the postozoneinjection sampling point be located within the plant, suchthat the contact time of the oxygen/ozone stream in thesystem prior to the second sample point was limited toapproximately two minutes. Table 1 shows the pre- andpostinjection point averages for triplicate samples collectedbi-weekly during the nine week pilot run.
COD in Fox River Fiber’s effluent averaged 5244 mg/L,while that postoxygen/ozone injection averaged 4422 mg/Lfor an average reduction of 15.7%. The water pH was notsignificantly affected by addition of oxygen/ozone. WhileBioxide addition rates were reduced during this period, CODmeasurements were not affected by these changes. Becauseof the chemicals used in the recovered paper manufacturingprocess, plant effluent DO was very low, but Adaptive OzoneSolution, LLC’s, generator raised values to approximately25 mg/L at the injection point and almost 20 mg/L asmeasured at the second sample point. Based on an average15.7% reduction in COD and a linear relationship betweenthe $1.2 million per year payment made to GBMSD forexcessive COD, AO3’s system could save Fox River Fiber$188,400 per year.
2.3. Kinetic Study. Because of the limitations associated withthe existing piping system at Fox River Fiber, the previousCOD and DO measurements were taken after a contacttime of only approximately two minutes. Given an almost16% reduction in COD for such a short reaction time,
Table 2: Kinetics of first-order reaction with k = 0.12/min.
Time (min) C/Co % Unreacted O2
1 0.89 89%
2 0.79 79%
5 0.55 55%
10 0.30 30%
20 0.09 9%
experiments were performed to estimate the kinetics of thereaction of oxygen with COD waste and, hence, estimate theeffectiveness of oxygen and ozone to continue to reduce CODin Fox River Fiber’s effluent. Dissolved oxygen was measuredas a function of time in postinjection samples to estimatehow rapidly oxygen is consumed by COD waste. First-orderkinetics
ln(C
Co
)= −kt, (1)
with respect to oxygen degradation, were assumed for thereaction
O2 + COD ⇐⇒ CO2 + H2O, (2)
where Co is initial recorded DO at the postinjection samplepoint, C is DO remaining in water after time t, t is reaction,or contact time of oxygen with COD waste, and k is reactionrate constant (min−1).
The first-order reaction rate constant was conservatively0.12/min. Based upon this and a reaction time between injec-tion and the postinjection sample point of approximately twominutes, only 21% of injected oxygen was consumed priorto sampling. The COD was reduced 15.7% based upon this.Table 2 shows the percent of oxygen that would be consumedas a function of time, which would lead to lower COD
Figure 2: Close-up of aerosol bubble mass transfer.
Table 3: DO and COD as a function of Ozone/Oxygen injectionrate.
O3 loading rate DO COD% COD reduced
(g/min/liter) (mg/L) (mg/L)
No O2 or O3 0.14 5907
0.53 O2 67.1 5440 7.9
0.053 O3 61.6 4970 15.8
0.105 O3 58.5 5043 14.6
0.158 O3 59.9 5040 14.7
0.212 O3 62.0 5053 14.5
0.318 O3 68.4 5033 14.8
levels if the sampling point was further downstream of theinjection point. While the exact reduction cannot be exactlyquantified without more information about the nature of theCOD waste, it is clear that actual reduction in COD sentto GBMSD would be considerably lower than that recordedfrom the postinjection sample point at Fox River Fiber. If aconstant stoichiometric ratio of O2 to COD was assumed,a reaction time adequate to deplete 80% of injected oxygencould potentially remove up to 60% of COD with a reactiontime of less than 20 minutes. At a linear rate of reductionin the fee paid to GBMet for excessive COD, Fox River Fibercould save $720,000 per year.
2.4. COD as a Function of O3. A final experiment wasperformed to quantify the effect of increasing the ozoneinjection rate on effluent COD. A 9.5 liter/min side streamof Fox River Fiber’s effluent stream was diverted and dosedwith increasing quantities of ozone under the same waterflow velocity and contact time as tests performed on thetotal effluent stream. Ozone was generated and injected withoxygen as aerosol bubbles using an AO3 system as shown inFigures 1 and 2. Initially just oxygen was added, after whichboth oxygen and ozone were added with the oxygen amountapproximately constant at 0.53 grams/min/liter water. At
International Journal of Chemical Engineering 5
Table 4: Peak hydrogen sulfide gas as a function of Bioxide addition at sample sites downstream of Fox River Fiber.
Sample sitePeak H2S : no O3 Peak H2S (ppm) for each bioxide application rate with O3
each ozone level, samples were drawn and analyzed for DOand COD. Table 3 summarizes the results.
The average percent reduction in COD due to ozoneaddition was 14.9%, but increasing ozone above a loadingrate of 0.053 grams/min/liter water did not improve CODreduction. Addition of both oxygen and ozone did improveCOD removal compared to just oxygen addition.
2.5. Hydrogen Sulfide Suppression. In addition to CODreduction, another concern of GBMSD with the high CODreleased by Fox River Fiber is the production of H2S gasin gravity sewer lines between GBMSD and FRF. Bothprior to and following installation of the oxygen/ozonesystem, continuous measurements of H2S gas at a numberof sample locations in the air space of the sewage lines wereperformed using Odalog gas loggers, Detection InstrumentsCorporation, in the 0 to 200 ppm range. The first set ofdata was collected between 6/2/2009 to 6/25/2009. Duringthe first week of June, 2009, Green Bay experienced recordhigh temperatures which would increase H2S gas production.Table 4 summarizes the results. Dissolved sulfides in theliquid phase were also measured and varied between 0 and0.5 ppm.
At the beginning of the study Bioxide was added tothe system by FRF at a rate of 1520 liters per day. Almostimmediately Bioxide was reduced to 1330 liters per day.Within 24 hours, it was reduced to 950 liters per day. Aftereight days Bioxide was further reduced to 570 liters per day.For all tests, the O3 loading rate was 0.053 grams/min/literwater, and the O2 loading rate was 0.53 grams/min/literwater.
A comparison of peak H2S data in Table 4 for thecases of just 1520 liters/day Bioxide and 1520 liters/dayBioxide with ozone/oxygen generation shows that additionalof ozone/oxygen to the FRF effluent did reduce the peakH2S. Reducing the Bioxide addition to 1330 liters/day and950 liters/day did not result in increased H2S peak values,and average values were consistently below 20 ppm. Forall sample sites, peak H2S remained below the maximumacceptable upper limit of 40 ppm. In addition, average H2Sremained below the required 20 ppm for all but one mea-surement. Further reducing Bioxide to 150 gal/day resultedin two H2S peaks that exceeded the acceptable upper limitand many averages above 20 ppm. The optimal Bioxide dosecould be as low as 780 liters/day, which would save FRF up
to 780 liters/day during warmer summer months. Even at areduced dose of 950 liters/day, 150 gal/day of Bioxide couldbe saved. At a cost of $0.695 per liter, $396/day could besaved.
3. Conclusions
Addition of a high pressure oxygen/ozone stream to theeffluent discharged by Fox River Fiber Company to theGBMSD system reduced COD sent to GBMSD by FRF byover 15% despite a very small contact time. A first-orderkinetic model of the degradation reaction between oxygenand COD predicts as great as a 60% COD reduction if thecontact time was increased via additional piping to as fewas 30 minutes. Dissolved oxygen in the system was greatlyincreased by the Adaptive Ozone Solutions process. FRFcurrently pays a fee of $1.2 million per year to GBMSDto handle their high COD stream, but this fee is linearlyproportional to average COD. A 15.7% reduction, therefore,could save FRF $188,400 annually. A 60% reduction ineffluent COD could save the plant as much as $720,000annually. While this analysis did not include the electricalcost of the ozone generator, this amount would be small (onthe order of several hundred dollars per month) compared tothe potential savings.
Hydrogen sulfide gas monitoring during the studyshowed that the Adaptive Ozone Solutions, LLC, processcould suppress H2S gas production in the air space of thesewage mains to below peaks of 40 ppm, the maximumacceptable value, under reduced Bioxide applications. Datashowed that reducing Bioxide to 950 liters per day main-tained sufficiently low hydrogen sulfide production, but thatfurther decreasing the Bioxide addition rate to 570 litersper day caused two peaks above 40 ppm. Additional exper-imentation would be required to determine the exact pointbetween 570 and 950 liters per day at which hydrogen sulfidepeaks would become unacceptably high. This particularsewage system used gravity mains, which allows dischargeof residual injected oxygen. It is anticipated that hydrogensulfide production would be even more effectively suppressedin a force main, which operates under pressure. A reductionof 150 gallons per day would save FRF $144,540 per yearbased on 365 days per year operation. A reduction to as littleas 780 liters per day could save $192,720 annually. Hence, atthe experimental conditions employed during the summer
6 International Journal of Chemical Engineering
trial, FRF could save as much as $332,940 in cost of highCODs and reduced Bioxide. If the contact time betweeninjected oxygen and COD was increased prior to the effluentleaving the plant Bioxide could be reduced by as much as 950gallons per day, a maximum potential savings of $960,900annually.
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