Abatement of gaseous VOCs using activated sludge systems: Technology feasibility and cost analysis

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1 Sustin Environ Res, 22(5), (2012) 295 Abtement of gseous VOCs using ctivted sludge systems: Technology fesibility nd cost nlysis 1, 2 Wen-Hsi Cheng nd Yi-Chin Fng 1 Deprtment of Occuptionl Sfety nd Hygiene Fooyin University Kohsiung 83102, Tiwn 2 Refinery Generl Affirs Tem Formos Petrochemicl Coopertion Yunlin 63801, Tiwn Key Words: Voltile orgnic compounds (VOCs), emission, wstewter tretment plnt (WWTP), VOC tx, Wter 9 ABSTRACT This study ssessed the ir exhustion control of corrugted plte interceptor (CPI) oil seprtors in refinery wstewter tretment plnt for biodegrdtion of voltile orgnic compounds (VOCs) by deep ctivted sludge ertion systems Three pproches were used to derive VOC emission fctors: Clculting using the ertion rte nd VOC gs-liquid equilibrium concentrtion (C g ), (b) Simultion using the Wter 9 model, nd (c) VOC mss blnce clcultion Bsed on field smpling nd lbortory nlysis, lipophilic lknes (900,200 ppm s totl hydrocrbons (THCs)) were removed by the ctivted sludge system nd only ppm THC VOCs were emitted, nd VOC emission fctors were g m wstewter using the different clcultion pproches We recommended using the C g nd instlled ir ertion rtes s more effective ccurte method for simulting VOC emissions rtes thn exmining individul queous VOC concentrtions for Wter 9 model simultion In compring with the cpitl costs of reconstructing pipelines from CPI oil seprtors to the ctivted sludge system s well s those of smpling nd nlysis, to py legl VOC txes, the former demonstrtes its economic efficcy of reducing the mount of VOC exhusts INTRODUCTION Wste is cost of industril production Mny polluters, including sources of voltile orgnic compound (VOC) emissions, must now py for their pollution [1] Imposing pollution txes my eventully reduce pollution Among ll pollution txes, the gsoline tx nd crbon dioxide tx re two useful tools becuse those cn induce drivers to lter their behviors nd reduce crbon dioxide emissions, respectively [2,3] Frnce strted chrging for VOC emitted into the tmosphere in 1985; this ws Europe's first VOC tx [4] However, pying tx bsed on rel emission rtes is problemtic, s one cnnot monitor ll emissions t their sources [5] Insted, governments impose pollution txes t different rtes for specific industries ccording to the chrcteristics of prticulr mnufcturing nd their pollution controlling processes Tiwn Environmentl Protection Administrtion (TEPA) begn imposing n ir pollution tx on VOC emissions from sttionry sources in 2007 As the imposed emission fctors vlues re uniform nd not prcticlly suitble for ech emission source; governmentl estimted VOC emission rtes generlly exceed ctul rtes of recovery systems for skimmed oil from wstewter, or devices controlling VOC emissions Thus, owners of fcilities emitting VOCs cn dopt lterntive VOC emission rtes; however, these rtes must be pproved by the TEPA s field VOC emission rtes In June 2009, TEPA revised its procedures for determining the VOC emission tx rtes Appliction nd exmintion of lterntive VOC emission fctors re divided into two stges First, polluter must submit proposl tht lists the procedures for obtining lterntive VOC emission fctors VOC emission rtes must be clculted using the ertion rtes of ertors, or simulted by the model Once the Corresponding uthor Emil: PL031@milfyedutw

2 296 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) proposl is pproved, n ssessment report bsed on field smpling, lbortory nlysis, nd simultion of emission rtes from trget sources must be verified by government The vlid period for ech pproved lterntive VOC emission fctor is 5 yr [6] The min chemicl/odor emissions from industril wstewter tretment plnts (WWTPs) re from the mnufcturing processes [7] For instnce, voltile solvents/hydrocrbons, including lknes, oxygencontining hydrocrbons (ketones nd lcohols), romtic hydrocrbons, nd chlorinted romtic compounds, re emitted from petroleum refineries nd chemicl production process Bio-oxidtion of gseous pollutnts in n ctivted sludge ertion tnk hs been developed in the pilot experiment [8] The trget ctivted sludge ertion systems re t the WWTP in petroleum refinery (Fig 1) locted on Tiwn's southwest cost The open-bsin ctivted sludge system is the VOC exhust tretment unit for the seled oil seprtor TEPA clculted the VOC tx for corrugted plte interceptor (CPI) type oil seprtor using the emission fctor of 06 kg VOC m wstewter, nd permitted VOC reduction efficiency of 085 for collection nd bio-oxidtion by n ctivted sludge 3 system During 2009, n verge of 212,560 m wstewter/seson ws treted by the oil seprtor Tht is, the clculted mount of VOC emissions, ws 1913 t seson during 2009 nd the VOC tx ws NT$ 229,600 bsed on the rte of NT$ 12,000 t VOCs According to the current exchnge rte of NT$ 30 for 1 USD, the nnul VOC tx ws roughly USD 30,600 This study collected field smples tht were subject to lbortory nlyses to clculte rel VOC emission rtes (kg VOC m wstewter) nd emission fctor (kg VOC seson ) Bsed on nlyticl results, the WWTP mngers cn ssess the rtionlity of cost investment in equipment to reduce VOC emissions from the CPI oil seprtors Thus, the technologicl fesibility of biologicl oxidtion of VOCs from the oil seprtors cn be determined METHODS 1 Trget Fcility nd its VOC Emissions The oil-contining wstewter flowing into the WWTP from the light oil refinery is combined with lkline wter from other production processes (Fig 1) The wstewter tretment procedures re s follows: the primry physicl-chemicl tretment stge includes oil seprtion nd ir flottion; during the secondry biologicl tretment stge, ctivted sludge ertion tnks B, C nd D decompose orgnic compounds; the tertiry membrne bio-rector (MBR) further oxidizes queous chemicl oxygen demnd (COD) concentrtions; nd the thickened bio-sludge is then returned to the ctivted sludge ertion tnks Typiclly, the concentrtions of suspended solids (SS) in the effluent were = 5 mg L Notbly, ertion tnk A ws used seprtely to remove orgnic pollutnts from wstewter from deslting nd cidic wshing processes; the effluent ws lso dischrged into the MBR system The min VOC emission source t this WWTP is the seled CPI oil seprtor The ir strems contining VOCs were exhusted into the suction of ertors in ctivted sludge ertion tnks A, B, C nd D Tble 1 shows the design specifictions nd wstewter tretment chrcteristics of the ctivted sludge ertion tnks 2 Assessments of VOC Emission Rtes According to Tiwn's regultions for VOC emissions, VOC emission rtes must be clculted using both, the totl ertion rte of ertors nd the gs- liquid equilibrium concentrtion (C g ), or by simultion using the Wter 9 model [9] Additionlly, third ssessment procedure for VOC emission rtes is to clculte the mss blnce of VOCs within ctivted sludge systems Mss blnce results re then com- Exhust ir for ertion Wstewter influent (non-oil contined) M Wstewter influent (oil contined) Air blower Recycle sludge Effluent CPI oil seprtor Neutrliztion tnk DAF Deep ctivted sludge ertion (b) Tnks A/B/C/D MBR Effluent pit Note: CPI: Corrugted plte interceptor; DAF: Dissolved ir flottion tnk; MBR: Membrne bio-rector b Tnk A ws used seprtely for polishing deslting wstewter Fig 1 Process digrm of the wstewter tretment plnt

3 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) 297 Tble 1 Specifiction nd opertion performnce of deep ctivted sludge ertion system Equipment specifiction Construction Shpe Number of tnks in prllel Inner dimeter (m) Side wter depth (m) Aertion pipeline depth (m) Aertion system Type of ertors Number of ertors 2 Diffuser re (m tnk ) Instlltion power (kw ertor ) Dimeter of pddle of ertor (m) Rottion speed of motor of ertor (rpm) Dischrge pressure of ertor (kp) 3 Dischrge ir flowrte of ertor (Nm h ) Circle Screw compressors 4/ , ,500 (b) Opertion performnce (c) 3 Wstewter tretment flowrte (m h ) (c) 3 Recycle sludge flowrte (m h ) (d) Influent COD (mg L ) (d) Effluent COD (mg L ) (d) MLSS in ertion tnk (mg L ) (d) ph vlue in the ctivted liquor 537 ± 76 1,985 ± ± ± 15 5,618 ± Six ertors were instlled: two ertors were on duty nd four for spre, nd took turns for opertion b Dt were vergely collected per month from November 2009 to October 2010, nd displyed s men vlue ± stndrd devition c Sum vlues of ech influent strems d Averge vlues for tnks B, C nd D pred with those by the other two pproches The VOC emission rtes, q, from the deep ctivted sludge ertion tnks cn be clculted using the C : g (1) where Q is the ir blowing rte of ertors nd obtined using design specifictions or estimted by Eq 2 using motor power of the ertors (P) nd wter depth t outlets of submerged ertion pipes In this study, C g is treted s n equivlent totl orgnic hydrocrbon (THC) concentrtion (mg THC m ir) (2) 3 where the ertion rte of 05 m ir min t wter depth of 5 m typiclly requires 075 kw power for the motor of n ertor The Wter 9 model [9] ws designed to simulte q of specific VOCs from wstewter collection nd tretment units In this study, the Wter 9 model is pplied to clculte emission rtes from open bsins of deep ctivted sludge ertion tnks The Wter 9 model uses the following prmeters: Wter content prmeters, including cpcity of wstewter 3 tretment (m h ), wter temperture, totl dissolved solids (TDS), nd totl SS (TSS) Surfce wind nd mbient temperture re lso utilized for open bsins Aqueous VOC components nd concentrtions must be identified exctly nd input for simultion (b) Equipment specifictions, including tnk dimensions (length x width x side wter depth (SWD)), horsepower of the gittor nd blower motors, gittor impeller dimeter The tnk is open or closed must be lso identified (c) Properties of VOCs in wstewter, nd biologicl oxidtion coefficients in the model dtbse The rnge of biologicl oxidtion coeffi- -6 cients x 10 g VOCs g MLSS s in this study The pplictions of these coefficients hve been proven fesible in the erlier ssessments of VOC emissions from WWTPs [102] Finlly, VOC emission rtes re clculted s g s, nd the fte of queous VOCs is simulted s percentge emitted into the tmosphere, degrded by the biomss, nd dissolved in wter Additionlly, the VOC mss blnce for the sludge ertion system is clculted The VOC emission rtes (g THC h ) re derived by summing ll VOC feeding mss rtes (in influent wter, recycle sludge liquor nd erting ir) nd then subtrcting out-flows of effluent s well s the frction of VOCs degrded by the ctivted sludge system The vlues of VOC biologicl degrdtion coefficients re obtined from the Wter 9 dtbse 3 Smpling nd Anlysis Field smples were obtined five times over 3-d period in lte September 2010 Ech smpling intervl ws 10 h Liquid smpling, following the method by Cheng

4 298 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) nd Chou [10], ws conducted by submerging 300- ml glss bottle in wter Ech open bsin of the ertion tnks ws divided into eight equl sections, nd liquors were smpled t 1 m wy from the bsin sides of ech section The smpled liquid bottles were stored t < 4 C in portble refrigertor Other liquid smples from pipelines were gthered vi drining holes The liquid smples were djusted by sulfuric cid to keep ph < 20, nd were then nlyzed fter removing solids in liquid smples The specific queous voltile compounds nd their concentrtion were nlyzed using the nlyticl method, developed by the US EPA [13]; procedures included the purge nd trp procedure with Teledyne Tekmr XPT smple concentrtor (Series 3100, Mson, OH), followed by gs chromtogrph (GC, Agilent 6890N, Wilmington, DE), nd mss spectrometry (MS, Agilent 5973N, Wilmington, DE) Tble 2 lists the 58 hydrocrbons to be identified by GC-MS nd their method detection limits Additionlly, the nlyticl procedures of C, g described s the concentrtion of mg THC m wter, re presented in Fig 2 The THC in liquid wter ws nlyzed by GC with flme lioniztion detector (Agilent 6890N, Wilmington, DE), following US EPA procedures [14] Other wter contents, including COD, TDS, mixed liquor SS (MLSS) nd ph were determined using the Stndrd Methods [15] Design specifictions nd opertion prmeters of deep ctivted sludge ertion systems were provided by the opertion center Gs smpling ws vi suction pump (Dwyer, Smpling using gstight syringe Michign City, IN) nd Teflon smpling tube locted 10 cm bove the wter surfce in open tnks [102] Gs smples were collected in 10-L Teflon smpling bg (SKC, Eighty Four, PA) Bgs were stored t low temperture of 15 C nd tken to the lbortory for nlysis within 24 h Specific gseous hydrocrbons were nlyzed using the sme experimentl procedures s tht for queous VOCs Tempertures nd wind speed t 10 cm bove the wter surfce were determined using portble thermonemometer [102] Ambient tempertures nd wind speeds during field smpling were C nd 162 m s, respectively Ambient wind speeds nd tempertures re prmeters when simulting VOC emission rtes using the Wter 9 model 4 Cost Anlysis According to procedures outlined in the hndbook: Control Technologies for Hzrdous Air Pollutnts [16], cost nlysis for controlling gseous emissions from WWTPs ws ssessed herein The control costs include cpitl costs (eg, equipment, piping, construction, instrumenttion, nd electricl engineering costs) nd operting costs (eg, electricl power, fuel nd mintennce costs) for given tretment system The cpitl cost (USD) for therml incinertors ws clculted using Eqs 3-5, which were developed by the US EPA [16] 0250 Cost 1 = 54,286Q i (3) (For n incinertor with 70% recupertive het recovery) (For ctlytic incinertor with 70% recupertive het recovery) 0553 Cost 2= 10,800Q i (4) Plstic closure with PTFE sept Tke wter bth more thn 1 h t the temperture followed the field dt A glss vil contins 40 ml VOC-contining wter smple nd the inside hed spce is 2 ml Cost 3 = 123,429Exp(00019Q i) (5) (Incinertor with 93% regenertive het recovery) 3 where Q i represents the tretment cpcity (Nm min ) of therml incinertor The WWTP provided its cpitl cost for sending collected gseous exhust from the CPI oil seprtors to the ctivted sludge ertion system Finlly, operting cost ws clculted bsed on current locl prices for electricl power nd fuel in Tiwn The cost for treting VOC (USD t THC) ws derived by dividing totl cpitl nd operting costs by the treted mss of VOC 5 Qulity Control Fig 2 Experimentl setup for exmining gs-liquid equilibrium concentrtion, C g Clibrtion curves for exmining queous nd gseous VOCs were checked before ech nlyticl run nd the error percentge ws confirmed s < 5% Stndrd concentrtion VOC smples were dded into nlyticl smples nd the error must be < 5%

5 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) 299 Tble 2 Method detection limits (MDL) of 58 queous VOCs in wstewter CAS number / / VOCs Chloromethne Vinyl Chloride Chloroethne Trichlorofluoromethne 1,1-Dichloroethene Methyl bromide Dichloromethne Nphthlene trns,2-dichloroethene 1,1-Dichloroethne 1,3-Dichloropropene cis,2-dichloroethene 2,2-Dichloropropne Bromochloromethne Chloroform 1,1,1-Trichloroethne 1,1-Dichloropropene Crbon Tetrchloride Benzene 1,2-Dichloroethne 1,1,2-Trichloroethylene 1,2-Dichloropropne Dibromomethne 1,2-dibromo-chloropropne cis,3-dichloropropene Dibromochloromethne Toluene Dichlorodifluoromethne Trichloroethylene 1,3-Dichloropropne Tetrchloroethylene Dibromochloromethne 1,2-Dibromoethne Chlorobenzene 1,1,1,2-Tetrchloroethne Ethylbenzene (m + p + o) Xylenes Hexchlorobutdiene Styrene Bromoform iso-propylbenzene 1,1,2,2-Tetrchloroethne Bromobenzene 1,2,3-Trichloropropne n-propylbenzene 2-Chlorotoluene 1,3,5-Trimethylbenzene 4-Chlorotoluene Isobutylbenzene 1,2,4-Trimethylbenzene tert-butylbenzene 1,3-Dichlorobenzene p-isopropyltoluene 1,4-Dichlorobenzene n-butylbenzene 1,2-Dichlorobenzene 1,2,4-Trichlorobenzene 1,2,3-Trichlorobenzene MDL (mg L ) CAS number mens the registry number for ech chemicl, ssigned by the Chemicl Abstrcts Service, division of the Americn Chemicl Society

6 300 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) RESULTS AND DISCUSSION 1 Opertion Performnces nd VOC Emission Chrcteristics of the Deep Activted Sludge Aertion System According to experimentl nlysis, the min VOCs in the refinery wstewter were romtic hydrocrbons (eg, benzene, toluene, ethylbenzene, nd xylenes) nd chlorinted hydrocrbons (eg, chloroform, vinyl chloride, nd 1,2,3-trichlorobutne) Tble 3 lists the rnges of queous concentrtions The VOCs in ir strems exhusted from oil seprtors nd input into deep ctivted sludge tnks were minly composed of 900,200 ppm (s THC) lipophilic lknes (eg, iso-butne, 1-butene/butne, t-2-butene, 2-methylbutne, 1-pentene, pentne, hexne/1-hexene, nd methylcyclopentne) In dditionl to these orgnic compounds, severl highly hydrophobic hydrocrbons in deslting wstewter flowed individully into ertion tnk A, including isopntne, n-hexne, methylethylbenzene, 1,2,4,5- tetrmethylbenzene, 1-methylnphthlene, nd 2- methylnphthlene According to Chou nd Chng [17], mixture of VOCs composed of benzene, xylenes nd dichloromethne t 250,000 ppm were decomposed t degrdtion rte of 93-99% under n ertion rte of m m h, ph of 6-8 nd MLSS 1,600-2,800 mg L in 11-m ctivted sludge bsin Furthermore, bio-dsorption between the bio-sludge cell surfce nd hydrophobic orgnic compounds is stronger thn tht Tble 3 Concentrtion nlysis of gseous nd queous VOCs, wter contents nd flow rtes for the deep ctivted sludge ertion systems The vlues of dt re displyed s the men of nlysis vlues in series of smples nd its stndrd devition in the prentheses b The concentrtion of THC ws presented bsed on the sum of concentrtion of chloroform, chloroethne nd 1,2,3-trichloropropne, s well s the verge trnsfer fctor 151, which ws pplied to the formul s [(mg THC m ) = (mg VOCs m )/151] c Six hydrocrbon components in the liquor contents of Tnk A, including iso-pntne, n-hexne, methylethylbenzene, 1,2,4,5- tetrmethylbenzene, 1-methylnphthlene nd 2-methylnphthlene were not individully quntified in the mss spectrogrm d Four effluent strems were drined together in n effluent pit, nd only one smple ws tken nd nlyzed

7 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) 301 between the bio-sludge cell surfce nd hydrophilic compounds [18] Tht is, mixtures of romtic nd chlorinted orgnic pollutnts cn be degrded effectively by biologicl sludge in ctivted sludge systems The opertors t the WWTP exmined VOC emission concentrtions t 10 cm bove the wter surfce of the deep ctivted sludge ertion tnks; this method is in ccordnce the VOC emission nlyticl methods recommended by others [10,11] The VOC concentrtions were roughly ppm s THC Additionlly, verge nnul queous COD removl efficiencies exceeded 98% (Tble 1), indicting stedy degrdtion efficiencies of orgnic compounds in the ctivted sludge ertion system over 1 yr According to these concentrtion dt, ll VOC mixtures (eg, romtic hydrocrbons, chlorinted hydrocrbons, nd lipophilic lknes) were removed vi biodegrdtion by ctivted sludge, nd only smll mounts of gseous VOCs were emitted into the tmosphere 2 Aqueous VOCs Distributions in the Sludge Aertion System Tble 3 shows smpled nd nlyzed VOC concentrtions in the sludge ertion systems Typiclly, men queous VOC concentrtions in tnks B, C nd D were mg THC m wter, nd minly composed of chloroform, chloroethne nd 1,2,3- trichloropropne The MLSS were 1,500-2,700 mg L, mrkedly higher thn those (men 250 mg L nd stndrd devition of 110 mg L ) in Tnk A The extremely low concentrtion of MLSS in Tnk A resulted from neutrliztion of deslting wstewter t low ph of 45 Six hydrocrbon components in the liquor of Tnk A, including iso-pntne, n-hexne, methylethylbenzene, 1,2,4,5-tetrmethylbenzene, 1-methylnphthlene nd 2-methylnphthlene were not identified due to lck of VOC mss spectrogrms in this study, resulting in reltively low THC concentrtions in Tnk A However, individul VOCs must be input when simulting VOC emission rtes using the Wter 9 model Therefore, using the C g concentrtion (Fig 2), nd directly nlyzing mixed VOCs s THC in the hedspce under gseous-liquid concentrtion equilibrium is recommended s better method for ssessing the totl VOC emission rte thn exmining individul VOC concentrtions 3 VOC Emission Rtes from the Sludge Aertion System TEPA [6] imposes pollution tx bsed on 600 g THC m wter with minimum VOC reduction efficiency of 85% for VOC emissions from n oil seprtor Nmely, the net emission fctor is 90 g m (600 g m (1-085)) However, reltively lower VOC emission fctors ( g m wter (Tble 4)) exist for this deep ertion biologicl tretment system, indicting tht the biologicl tretment process is n effective pproch for reducing emissions contining hevy VOCs from seled CPI bsins Additionlly, gseous VOCs of lipophilic lknes exhusted from oil seprtors, except for chloroform, chloroethne, nd 1,2,3-trichloropropne, were < 002 mg L in the deep ertion ctivted sludge system This finding demonstrtes tht bio-dsorption combined with biodegrdtion by ctivted sludge is n effective btement pproch for VOC emissions Figure 3 shows tht the distributions of q re generlly similr to those of VOC emission fctors in Tble 4; in other words, ssessment of VOC emissions vi ertion flow rtes generted highest vlues for emission fctors nd emission rtes thn those by Wter 9 simultion Differences in VOC emission rtes nd emission fctors for different clcultion pproches (Fig 3 nd Tble 4) minly resulted from the use of individul VOC concentrtions for Wter 9 simultion, or THC of C g for other pproches Be- cuse six hydrocrbon components (ie, iso-pntne, n-hexne, methylethylbenzene, 1,2,4,5- tetrmethylbenzene, 1-methylnphthlene nd 2- methylnphthlene) could not be quntified nd then input into the Wter 9 model, simulted VOC emission rtes were underestimted VOC emission rte (g THC h ) Aertion rte clcultion 24 Model Simultion vi wter Mss blnce Fig 3 VOC emission rtes from deep ctivted sludge ertion tnks using different clculting pproches Tble 4 Comprison of VOC emission fctors from the deep ctivted sludge ertion system nd the legl vlue Aertion rte clcultion 055 VOC emission rte per cubic meter wstewter (g THC m wstewter) Different VOC emission clcultion pproches Model Simultion vi Wter Mss blnce 044 The net VOC emission rte 90 g THC m wstewter is clculted s the formul 600 g m (1-085) Legl vlue 90

8 302 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) 4 Cost Anlysis of Pying the VOC Tx nd Investing in Equipment for Pollution Control Tble 5 compres the cost for controlling gseous VOC emissions from CPI oil seprtors for therml incinertion nd injection of VOC into the biologicl oxidtion tnk Typiclly, therml incinertion is not recommended for 1000 ppm THC s CH 4 Injection of VOC exhusts into the ctivted sludge bsin vi existing blowers is the most economicl pproch The VOC emission rte ws 052 t THC seson using ertion rte the dt (Fig 3) (ie, (241 g h ) -6 (24 h d ) (90 d seson ) (10 g t )) However, in Tiwn, the minimum limit for VOC emission txtion is 1 t THC per seson; thus, this compny, due to its ir pollution control systems, does not need to py VOC emission txes Bsed on NT$ 12,000 t VOCs, verge tx pyment per seson ws NT$ 229,600 in 2009 Bsed on cost nlysis (Tble 5), this study demonstrtes tht the compny is only required to py cpitl cost of NT$ 4,000,000, provided by the mnger of the WWTP, to reconstruct the exhust pipelines from oil seprtors tht re connected the sludge ertion systems, exclusive of existing ertors nd operting costs Additionlly, the cost of VOC field smpling nd lbortory nlysis to verify the VOC emission fctor for Tiwn's EPA ws roughly NT$ 800,000 for ech 5-yr period (verge of NT$ 160,000 yr ) The cost recovery period is [(4,000, ,000) ( /4)]/229,600 = 183 sesons (ie, 46 yr) t n nnul interest rte of 5% The cost recovery period is close to the vlidity period of 5 yr for the VOC emission fctor by TEPA Tble 6 compres the tretment costs of VOCs collected from WWTPs in Tiwn using the ctivted sludge systems The costs typiclly rnged from USD 49 to 57 t VOCs (s CH 4) for WWTPs of petroleum refinery, petrochemicl nd science-bsed industry WWTPs, which contin semiconductors, photoelectronics, electronic products nd biologicl technol- ogy industries The tretment costs for t VOC re close mong min WWTPs in Tiwn CONCLUSIONS The trget open-bsin ctivted sludge system is used s the tretment system for VOCs exhusted from the seled oil seprtor According to smpling nd nlyticl dt, ll queous nd gseous VOC mixtures (eg, romtic hydrocrbons, chlorinted hydrocrbons, nd lipophilic lknes) in the ctivted sludge liquor were confirmed to be removed, nd only limited mounts of gseous VOCs (04-06 ppm s THC) were emitted into the tmosphere The VOC emission rte ws 052 t THC per seson, lower thn the VOC emission tx minimum vlue of 1 t THC per seson The VOC emission fctors for imposing tx in Tiwn were drfted using the US EPA dtbse, Fctor Informtion REtrievl Softwre [19] Generlly, Tble 5 Cost nlysis for controlling VOC emissions from WWTPs Methods of control Therml incinertion Incinertor with 70% recupertive het recovery Ctlytic incinertor with 70% recupertive het recovery Incinertor with 93% regenertive het recovery Injection into the biologicl oxidtion tnk New blowers Existing blowers Cost per t VOC (USD t CH ) 2,980 2,530 2, Recommended rnking Not recommendble Not recommendble Not recommendble clcultion is bsed on inlet concentrtion 1000 ppm (s THC) using the rtio of 1 USD = 30 NT$ (new Tiwnese dollr), 8000 working h yr, nd deprecition period of 10 yr 2 1 Tble 6 Cost comprisons for controlling VOC emissions by ctivted sludge systems WWTP descriptions petroleum refinery petrochemicl science-bsed industry (contining primrilysemiconductors, photo-electronics, electronic products nd biologicl technology) petroleum refinery Totl 10 WWTPs were collected herein Cost per t VOC (USD t CH ) Types of ctivted sludge systems conventionl ctivted sludge conventionl ctivted sludge conventionl ctivted sludge deep ctivted sludge Reference [11] [12] [12] this study

9 Cheng nd Fng, Sustin Environ Res, 22(5), (2012) 303 the difference between rel nd regulted emission fctors is enormous, prticulrly when improvements to VOC emission fcilities hve been mde This cse study demonstrtes the technologicl nd economic fesibility of VOC emission btement Investment in equipment for pollution control is worthwhile voiding pollution txes for lrge refinery WWTPs ACKNOWLEDGEMENT The uthors would like to thnk the opertors in the WWTP of Formos Petrochemicl Coopertion, Yunlin, Tiwn, for providing vluble opertion prmeters nd records REFERENCES Grsso, D nd D Riley, All polluters must py Environ Eng Sci, 19(3), 131 (2002) Sipes, KN nd R Mendelsohn, The effectiveness of gsoline txtion to mnge ir pollution Ecol Econ, 36(2), (2001) Felder, S nd R Schleiniger, Environmentl tx reform: Efficiency nd politicl fesibility Ecol Econ, 42(1-2), (2002) Ekins, P, Europen environmentl txes nd chrges: Recent experience, issues nd trends Ecol Econ, 31(1), (1999) O'she, L, An economic pproch to reducing wter pollution: Point nd diffuse sources Sci Totl Environ, 282/283, (2002) Tiwn EPA, VOC Emission Fctors of Air Pollution Txtion for Specific Industril Mnufcturing Processes nd Opertion Units nd Their Controlling Efficiencies Tiwn Environmentl Protection Administrtion, Tipei, Tiwn (2007) Lebrero, R, L Bouchy, R Stuetz nd R Muñoz, Odor ssessment nd mngement in wstewter tretment plnts: A review Crit Rev Env Sci Tec, 41(10), (2011) Chou, MS, CH Perng, TH Li nd JY Chen, Biooxidtion of gseous hydrogen sulfide in n ctivted sludge ertion tnk J Environ Eng Mnge, 20(1), (2010) US EPA, Wter 9-Air Emission Model for Wstewter Tretment, Version 100 US Environmentl Protection Agency, Wshington, DC (2001) 10 Cheng, WH nd MS Chou, VOC emission chrcteristics of petrochemicl wstewter tretment fcilities in southern Tiwn J Environ Sci Hel A, 38(11), (2003) 11 Chou, MS nd WH Cheng, Gseous emissions nd control in wstewter tretment plnts Environ Eng Sci, 22(5), (2005) 12 Cheng, WH, SK Hsu nd MS Chou, Voltile orgnic compound emissions from wstewter tretment plnts in Tiwn: Legl regultions nd costs of control J Environ Mnge, 88(4), (2008) 13 US EPA, Voltile Orgnic Compounds by Gs Chromtogrphy/Mss Spectrometry-Test Methods for Evluting Solid Wste, Method 8240B US Environmentl Protection Agency, Wshington, DC (1994) 14 US EPA, Determintion of Totl Gseous Orgnic Concentrtion Using Flme Ioniztion Anlyzer 40 CFR Method 25A US Environmentl Protection Agency, Wshington, DC (2000) 15 APHA, Stndrd Methods for the Exmintion of Wter nd Wstewter 21st ed Americn Public Helth Assocition, Wshington, DC (2005) 16 US EPA, Hndbook: Control Technologies for Hzrdous Air Pollutnts EPA/625/6-91/014 US Environmentl Protection Agency, Wshington, DC (1991) 17 Chou, MS nd HY Chng, Bio-oxidtion of irborne voltile orgnic compounds in n ctivted sludge ertion tnk J Air Wste Mnge, 55(5), (2005) 18 Lin, JH nd MS Chou, Temperture effects on Henry's lw constnts for four VOCs in irctivted sludge systems Atmos Environ, 40(14), (2006) 19 US EPA, Fctor Informtion Retrievl Dt System US Environmentl Protection Agency, Wshington, DC (2011) Discussions of this pper my pper in the discussion section of future issue All discussions should be submitted to the Editor-in-Chief within six months of publiction Mnuscript Received: My 23, 2012 Revision Received: July 3, 2012 nd Accepted: July 16, 2012