Ultrasonics Sonochemistry 17 (2010) 990–1003

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Ultrasonics Sonochemistry

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Advanced oxidation processes (AOPs) involving ultrasound for waste watertreatment: A review with emphasis on cost estimation

Naresh N. Mahamuni, Yusuf G. Adewuyi *

Department of Chemical Engineering, North Carolina Agricultural and Technical State University, Greensboro, North Carolina 27411, United States

a r t i c l e i n f o a b s t r a c t

Article history:Received 5 January 2009Received in revised form 4 September 2009Accepted 21 September 2009Available online 29 September 2009

Keywords:Cost estimationAOPUltrasoundSonochemistryWaste water treatment

1350-4177/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.ultsonch.2009.09.005

* Corresponding author. Tel.: +1 336 334 7564x107E-mail address: adewuyi@ncat.edu (Y.G. Adewuyi)

Two things are needed for any technology to be suitable for use in the industry, viz. 1. Technical feasibil-ity and 2. Economical feasibility. The use of ultrasound for waste water treatment has been shown to betechnically feasible by numerous reports in the literature over the years. But there are hardly any exhaus-tive reports which address the issue of economical feasibility of the use of ultrasound for waste watertreatment on industrial scale.

Hence an attempt was made to estimate the cost for the waste water treatment using ultrasound. Thecosts have been calculated for 1000 L/min capacity treatment plant. The costs were calculated basedupon the rate constants for pollutant degradation. The pollutants considered were phenol, trichloroeth-ylene (TCE) and reactive azo dyes. Time required for ninety percent degradation of pollutant was taken asthe residence time. The amount of energy required to achieve the target degradation was calculated fromthe energy density (watt/ml) used in the treatability study. The cost of treatment was calculated by con-sidering capital cost and operating cost involved for the waste water treatment. Quotations were invitedfrom vendors to ascertain the capital cost of equipments involved and operating costs were calculatedbased on annual energy usage. The cost was expressed in dollars per 1000 gallons of waste water treated.These treatment costs were compared with other established Advanced Oxidation Process (AOP) technol-ogies. The cost of waste water treatment for phenol was in the range of $89 per 1000 gallons for UV/US/O3

to $15,536 per 1000 gallons for US alone. These costs for TCE were in the range of $25 per 1000 gallons to$91 for US + UV treatment and US alone, respectively. The cost of waste water treatment for reactive azodyes was in the range of $65 per 1000 gallon for US + UV + H2O2 to $14,203 per 1000 gallon for US alone.

This study should help in quantifying the economics of waste water treatment using ultrasound onindustrial scale. We strongly believe that this study will immensely help the researchers working inthe area of applications of ultrasound for waste water treatment in terms of where the technology standstoday as compared to other available commercial AOP technologies. This will also help them think for dif-ferent ways to improve the efficiency of using ultrasound or search for other ways of generating cavita-tion which may be more efficient and help reduce the cost of treatment in future.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

It has been many years since Richards and Loomis [1] first usedultrasound for producing cavitation, degassing of water and foraccelerating chemical reactions. Ultrasound has since been usedfor many applications such as cell disruption, crystallization,atomization, degassing, polymerization, emulsification, nanotech-nology, waste water treatment, chemical reactions, food preserva-tion, drug delivery, cleaning, drilling, cutting, welding, flowmeasurements, flaw detection, ultrasonic imaging, sonar detectionand many more [2]. There have been many reviews on the subjectof sonochemistry spanning from themes based on particular

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application to general in nature. Recently, Bruce and Nareddy [3]and Thompson and Doraiswamy [2] gave a very good review ofsonochemistry in general whereas Adewuyi [4–6] critically cov-ered the subject of waste water treatment using ultrasound.

In recent years, ultrasound has been extensively used as an ad-vanced oxidation process (AOP) for waste water treatment. This isowing to the production of OH� radicals in aqueous solutions andsubsequent oxidation of pollutants in the presence of ultrasound.

H2O !ÞÞÞÞÞ H� þ OH� ð1Þ

H� þ O2 !ÞÞÞÞÞ

HOO� ð2Þ

Pollutantsþ OH� !ÞÞÞÞÞ Degradation products ð3Þ

PollutantsþHOO� !ÞÞÞÞÞ Degradation products ð4Þ

Nomenclature

CA0 initial concentration in ppmCA final concentration in ppmk rate constant, in ppm min�1 for zero order and min�1

for first order reactionSf sampling frequencySt sampling time1.2S total capital cost (Table 4)

A amortized annual capital costr annual discount rate (assumption = 7%)n life of project (assumption = 30 years)

EE/O is kWh/m3/orderPelec is the input power (kW) to the AOP systemt is the irradiation time (min)V is the volume in liter of water in the reactor

N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003 991

The formation of OH� radicals by decomposition of water was firstproposed by Weiss [7] and later confirmed by Makino et al. [8].The formation of OH� radicals takes place inside the cavity in thepresence of ultrasound by pyrolysis. The pyrolysis takes place insidethe cavity and near the interface of the cavity and surroundingliquid at the time of collapse of the cavity in the presence of ultra-sound. Pyrolysis takes place because of the very high temperaturesreached during cavitation. Suslick et al. [9,10] have found that thesetemperatures are in the range of 5200 K and 1900 K in the cavityand interfacial region, respectively. The formation of hydrogen per-oxide was observed by Fitzgerald et al. [11]. This hydrogen peroxidealso helps in the degradation of pollutants in wastewater.

PollutantsþH2O2 !ÞÞÞÞÞ

Degradation products ð5Þ

Since then ultrasound has been studied for the waste water treat-ment of various pollutants such as aromatic compounds, chlori-nated aliphatic compounds, explosives, herbicides and pesticides,organic dyes, organic and inorganic gaseous pollutants, organic sul-fur compounds, oxygenates and alcohols, pharmaceuticals, personalcare products, pathogens and bacteria in water [4]. It has virtuallybeen proved beyond doubt that ultrasound can be used for thetreatment of any kind of wastewater. But due to the inefficient con-version of energy in producing ultrasonic cavitation and possibledifficulties in its scale up, no industrial installations for waste watertreatment have been reported in the literature. Researchers are try-ing to circumvent these difficulties by using hybrid techniques forwaste water treatment using ultrasound. Gogate [12] has reviewedsuch efforts in his recent paper in ultrasonic sonochemistry. Thereare other reports in the literature where efforts have been madeto use ultrasound in the presence of ozone [13], hydrogen peroxide[14], Fenton’s reagent [14], photocatalysts [15] and enzymes [16].The intensification of ultrasonic waste water treatment with suchhybrid techniques might help reduce the cost of waste watertreatment.

An attempt has been made to estimate the cost for the wastewater treatment using ultrasound. The cost has been calculatedfor 1000 L/min capacity treatment plant. The cost is expressed inUS dollars (USD) per 1000 gallons of waste water treated (1 US gal-lon = 3.79 L). These treatment costs are compared with otherestablished AOP technologies. Candidates from three types of pol-lutants were selected as model pollutants for cost estimation be-cause they are widely studied in the literature; they are the mostcommon organic pollutants in waste water; and are among themost recalcitrant and harmful in nature. The three candidates arephenol, trichloroethylene (TCE) and reactive azo dyes.

Phenol has been ranked 182 in the 2007 the ComprehensiveEnvironmental Response, Compensation, and Liability Act (CER-CLA) Priority List of Hazardous Substances. Phenol is released tothe air and water as a result of its manufacture and use in phenolicresins, organic synthesis, petroleum products such as coal tar andcreosote. It can also be released by combustion of wood and autoexhaust. Phenol is also produced by the natural degradation of or-ganic wastes including benzene. Phenol mainly enters the water

from industrial effluent discharges. Phenol has been measured ineffluents (up to 53 ppm), ambient water (1.5 P 100 ppb), drinkingwater (not quantified), groundwater (1.9 P 10 ppb), rain (0.075–1.2 ppb), sediment (>10 ppb) and ambient air (0.03–44 ppb). TheUnited States EPA lifetime health advisory for phenol in water istwo milligrams per liter (2 mg/L) [17].

Trichloroethylene (TCE) is reasonably anticipated as a human car-cinogen [18]. The largest releases of TCE generally come from met-alworking facilities, plastics and plastic products facilities, electrontubes facilities and aircraft facilities. Because TCE is pervasive inthe environment, most people are likely to be exposed to TCE bysimply eating, drinking and breathing in the nearby area of source.As per Safe Drinking Water Act, Maximum Contaminant Level(MCL) for TCE in water is 0.005 mg/L [19].

Textile industries consume large volumes of water and chemi-cals for wet processing of textiles. The chemical reagents usedare very diverse in chemical composition, ranging from inorganiccompounds to polymers and organic products. The presence ofeven very low concentrations of dyes in the effluent is highly visi-ble and undesirable. There are more than 100,000 commerciallyavailable dyes with over a million ton of dye-stuff produced annu-ally [20]. Due to their chemical structure, dyes are resistant to fad-ing on exposure to light, water and many chemical treatments.Decoloration of textile dye effluent does not occur when treatedaerobically by municipal sewerage systems. Over 90% of some4000 dyes tested in the Ecological and Toxicological Associationof Dyes and Organic Pigments Manufacturers (ETAD) survey hadLD50 values greater than 2000 mg/kg [21]. Acute toxicity involvesoral ingestion and inhalation, skin and eye irritation and skin sen-sitization. There is evidence that some reactive azo dyes cause con-tact dermatitis, allergic conjunctivitis, rhinitis, occupationalasthma or other allergic reactions in plant workers [20]. Many dyesare difficult to decolorize due to their complex structure and syn-thetic origin. Brightly colored, water-soluble reactive azo and aciddyes are the most problematic, as they tend to pass through con-ventional treatment systems unaffected. Municipal aerobic treat-ment systems, dependent on biological activity, were found to beinefficient in the removal of these dyes [21]. Hence, advanced oxi-dation processes (AOPs) are needed for their treatment. Reactiveazo dyes are by far the most important class of dye, accountingfor over 50% of the world annual production. Hence we selectedreactive azo dyes as model candidate for the cost estimation study.

2. Theory of AOPs

Advanced oxidation processes (AOPs) are those processes whichare based on production and utilization of hydroxyl radicals. AOPshave considerable similarities due to the participation of hydroxylradicals in most mechanisms that are operative during the reac-tion. Hydroxyl radicals are extremely unstable and reactive be-cause of their high oxidation potential. Since the reactionsbetween hydroxyl radicals and organic species are extremely fastand nonspecific, these reactions are almost always controlled bythe mass transfer of hydroxyl radical to the organic species or

Table 1Various AOPs and their principle reactions.

Process Principle reactions Reference

O3 O3 þ OH� ! HO�2 þ O2 ð6ÞO3 þHO�2 ! HO�2 þ O��3 ð7Þ

Belran [50]

US/O3 O3þÞÞÞ ! O2ðgÞ þ Oð3PÞðgÞ ð8ÞOð3PÞðgÞ þH2OðgÞ ! 2�OH ð9Þ

Destaillats [51]

O3/H2O2 H2O2 þ 2O3 ! 2OH� þ 3O2 ð10Þ Glaze and Kang, [52]

UV/O3 O3 þH2O !hm 2OH� þ O2 ð11Þ Glaze et al. [53]; Peyton and Glaze, [54]

UV/H2O2 H2O2 !hm

2OH� ð12Þ Legrini et al. [55]

US/H2O2/CuO MþH2O! Mþ þ OH� þ OH ð13ÞH2Oþ OH! H2 þHO2 ð14ÞHO2 ! Hþ þ O�2 ð15ÞMþ þ O�2 !Mþ O2 ð16ÞMþHO2 ! Mþ þHO�2 ð17Þ

Drijvers et al. [56]; Weiss, [57]

O3/UV/H2O2 O3 þH2O2 þH2O !hm 4OH� þ O2 ð18Þ Mokrini et al. [58]; Beltran, [50]

Fenton’s reagent H2O2 þ Fe2þ ! Fe3þ þ OH� þ OH� ð19Þ Walling and Goosen, [59]

US/Fenton Fe2þ þH2O2 ! Fe3þ þ OH� þ OH� ð20ÞFe2þ þH2O2 ! Fe�OOH2þ ð21ÞFe�OOH2þþÞÞÞÞÞ ! Fe2þðisolatedÞ þHO�2 ð22ÞFe2þðisolatedÞ þH2O2 ! Fe3þ þ OH� þ OH� ð23Þ

Neppolian et al. [60]

PhotocatalysisTiO2 !

hme� þ hþ

TiO2ðhþÞ þH2Oad ! TiO2 þHO�ad þHþ ð24ÞTiO2ðhþÞ þHOad ! TiO2 þHO�ad ð25ÞTiO2ðhþÞ þ RXad ! TiO2 þ RX�þad ð26Þ

Legrini et al. [55], Adewuyi, [5,6]

992 N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003

production of hydroxyl radicals. The kinetics seems to be first orderwith respect to hydroxyl radical concentration and to the pollutant[22,23]. Kinetic constants are in the range of 108–1010 M�1 s�1,whereas radical concentration, even in steady state, in these pro-cesses is between 10�12 and 10�10 M. Therefore, the pseudo firstorder constant is in the range of 10�4–.1 s�1. Given that the hydro-xyl radical is such an unstable and reactive species, it must begenerated continuously ‘‘in situ” through chemical or photochem-ical or sonochemical reactions. The main processes and theirmechanisms to obtain these radicals are summarized in Table 1,Eq. (6-26). Andreozzi et al. [24] have made a survey of variousAOPs and described their general mechanisms.

3. Cost estimation methodology

A very simple methodology was developed to arrive at the treat-ment costs of the various AOPs studied. First of all, data werecollected from the published literature for all the AOPs involvingthe use of ultrasound and some standard commercial AOPs. Table2 shows the various studies considered for this investigation alongwith their operating conditions. From this data, the kinetics ofpollutant removal was found. If the kinetics is reported then itwas taken from the literature as such; otherwise it was calculatedfrom the data given in the literature using standard methods offinding kinetics [25]. By kinetics, we mean the order of degradationand the rate constant. Table 3 depicts the kinetic data collectedfrom these studies. These rate constants were then used to calculatethe time required for 90% degradation of the pollutant from itsinitial concentration. This time was assumed as the residence timefor the reactor for waste water treatment using the given AOP. Thecost estimation was done for the assumed flow rate of 1000 L/min.

The reactor capacity was calculated by multiplying the residencetime with the design flow rate (1000 L/min). From the treatabilitystudy in the literature, the energy consumption data was thencollected as energy dissipated per unit volume (watt/ml). The totalamount of energy required to treat the waste water at the designedflow rate for given residence time was then calculated. From thequotations, which we had invited from manufacturers, we knewthe amount of energy supplied by one commercial unit. Hencethe number of such commercial units required for dissipating therequired energy was calculated. From the number of commercialunits required, the capital cost of the waste water treatment unitwas calculated (AOP unit cost). This AOP unit cost was used tocalculate the total capital cost using certain standard assumptions.These assumptions are described in the next section. Similarly totalannual operating and maintenance cost was also calculated. Thetotal capital cost was amortized at a rate of 7% over a period of30 years to arrive at total amortized annual capital cost. Sum ofthe annual operating and maintenance cost and annual capital costgave the total annual operating cost. Dividing this cost with theamount of gallons of waste water treated in a year gave us the costof waste water treatment per 1000 gallons of water treated. It wasassumed that the plant is running throughout the year (52 weeks)continuously.

The cost estimation of various ultrasonic AOPs for the elimina-tion of phenol, reactive dyes and TCE was performed on the basis ofthe rate constants. Since the rate of degradation changes signifi-cantly with the experimental system, the reactor configurationand the operating conditions such as pH, UV intensity or US inten-sity etc., limited number of sources having similar operating condi-tions were considered. Kinetic data was collected from a limitednumber of sources in the literature (as shown in Table 3). Five

Table 2The operating conditions in treatability studies.

Process Reactionvolume

Initial concentration UV source US source Ozone SOURCE Oxidant Catalyst Reference

For phenolUV, US, O3, UV + US

US + O3, UV + O3,US + UV + O3

100 ml 2.5 mM (235.275 mg/L) 254 nm, ULTRAMAX STL 257,15 W

300 kHz, Undatimultrasonics, 25 W

Ozonelab OL-100 model,36 W at 0.75 L/min flow

O3 4.4 mg/L – Kidak and Ince,[38]

US + H2O2 + CuO 150 ml 0.6 mM (56.47 mg/L) – 520 kHz Undatim orthoreactor 18.2 W

– H2O2

100 mMCuO 1 mg/ml Drijvers et al.

[56]Fenton and US + Fenton 350 ml 0.67 mM (63.05 mg/L) – 35 kHz SODEVA 50 W – H2O2

60.5 mMCuSO4 2.39 mM Entezari et al.

[61]Photocatalysis and

US + Photocatalysis100 ml 1 mM (94.11 mg/L) MP-UV mercury vapor quartz

lamp 450 W20 kHz UWR ultrasonic75 W

– O2 500 ml/min

HOMBIKAT TiO2

UV-100 0.25 g/LChen andSmirniotis, [15]

For reactive azo dyeUV, US, O3, UV + US,

US + O3, UV + O3,US + UV + O3

1200 ml 57 lM (19.95 mg/L) 254 nm, Philips, PL-L 18 W TUVtwo lamps

520 kHz, UndatimUltrasonics, 600 W

Ozonelab OL-100 model,36 W at 0.25 L/min flow

O3 40 mg/L – Tezcanli-Guyerand Ince, [62]

US + H2O2, UV + H2O2,US + UV + H2O2

4500 ml 0.1 g/L (100 mg/L) 254 nm, Philips, PL-L 11 W TUVsix lamps

Specifications not given(20 kHz, 120 W assumed)

– H2O2

6.53 mMCuO 1 mg/ml Fung et al. [63]

Photocatalysis andUS + Photocatalysis

700 ml 0.5 mM (393.75 mg/L) MP-UV U-mercury vaporquartz lamp 500 W

47 kHz Branson 1200model 30 W

– Air 0.1 m3/h Degussa P-25TiO2 0.75 g/L

Taicheng et al.[64]

For TCEUV, UV + H2O2 5000 ml 12.6 lM for UV(1.66 mg/L)

16.7 lM for UV + H2O2

(2.194 mg/L)

254 nm, OSRAM, HNS 20 W/U20 W LP mercury vapor lamp

– – H2O2 5 mM – Hirvonen et al.[65]

US 600 ml 250 lM (32.85 mg/L) – 520 kHz, Undatimultrasonics, 50 W

– H2O2

6.53 mMCuO 1 mg/ml Distaillates

et al. [28]O3 150 ml 2.5 mg/L – – Equipment not given flow

rate 500 ml/minO3 20 mg/L – Nakano et al.

[66]US + UV 4100 ml 0.102 mM (13.40 mg/L) 254 nm, 100 W MP-UV

mercury vapor lamp20 kHz, Model XL2020Misonix 330 W

– – – Sato et al. [67]

Photocatalysis 7200 ml 15 mg/L 450 W HANOVIA MP-UVmercury vapor quartz lamp

– – Dissolvedoxygen9 mg/L

1% Pt on TiO2

from Aldrich0.5 g/L

Crittendenet al. [68]

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Table 3Rate constants of various AOPs for degradation.

Process k Reference

For phenolUV (254 nm) 0.0021 min�1 Kidak and Ince [38]US (300 kHz) 0.0008 min�1 Kidak and Ince [38]O3 (2 mg/L) 0.0279 min�1 Kidak and Ince [38]US + UV 0.005 min�1 Kidak and Ince [38]US + O3 0.0326 min�1 Kidak and Ince [38]UV + O3 0.0869 min�1 Kidak and Ince [38]US/UV/O3 0.1793 min�1 Kidak and Ince [38]US/H2O2/CuO 0.0149 min�1 Drijvers et al. [56]Fenton 0.0106 min�1 Entezari et al. [61]SonoFenton 0.058 min�1 Entezari et al. [61]UV/H2O2 0.0524 min�1 Primo et al. [69]Photocatalysis 0.433 ppm min�1 Chen and

Smirniotis [15]Sonophotocatalysis 0.712 ppm min�1 Chen and

Smirniotis [15]

For reactive azo dyeUV (254 nm) No degradation

observedTezcanli-Guyer andInce [62]

US (300 kHz) 0.00175 min�1 Tezcanli-Guyer andInce [62]

O3 (12.4 mg/L) 0.01108 min�1 Tezcanli-Guyer andInce [62]

US + UV 0.0055 min�1 Tezcanli-Guyer andInce [62]

US + O3 0.01674 min�1 Tezcanli-Guyer andInce [62]

UV + O3 0.02064 min�1 Tezcanli-Guyer andInce [62]

US/UV/O3 0.02171 min�1 Tezcanli-Guyer andInce [62]

US/H2O2 0.0032 min�1 Fung et al. [63]UV/H2O2 0.0124 min�1 Fung et al. [63]US/UV/H2O2 0.0357 min�1 Fung et al. [63]Photocatalysis 0.0207 ppm min�1 Taicheng et al. [64]Sonophotocatalysis 0.0757 ppm min�1 Taicheng et al. [64]

For TCEUV (254 nm) 0.0589 min�1 Hirvonen et al. [65]US (500 kHz) 0.0457 min�1 Destaillats et al.

[28]O3 (6 mg/L) 0.0209 min�1 Nakano et al. [66]US + UV 0.181 min�1 Sato et al. [67]UV/H2O2 0.4418 min�1 Hirvonen et al. [65]Photocatalysis Apparent rate

constant = 49.57 lg/L s�1

adsorption equilibriumconstant = 0.000466 l/lg

Crittenden et al.[68]

Table 4General calculation of capital costa.

Item Cost (USD)

AOP reactor PPiping, valves, electrical (30%) 0.3 PSite work (10%) 0.1 PSubtotal 1.4 P = QContractor O&P (15%) 0.15 QSubtotal 1.15 Q = REngineering (15%) 0.15 RSubtotal 1.15 R = SContingency (20%) 0.2 STotal capital 1.2 S

a The % values are taken from vendor data in the MTBE report from NWRI(National Water Research Institute, USA) Melin, [33].

994 N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003

sources were considered for phenol and TCE whereas three sourceswere considered for reactive dyes. The collected data was thencompared with the kinetic data available for a number of othersimilar treatability studies in the literature to make sure that it iscomparable with the reported values.

Adewuyi [4] has summarized results of a number of studies ofwaste water treatment using ultrasonic processes. They have re-ported the rates of degradation for phenol, TCE, reactive dyes anda number of other hazardous compounds. Kidak and Ince [26] haverecently reviewed the subject of phenol degradation using ultra-sonic processes. Beckett et al. [27] have described the degradationof phenols and chlorinated compounds and their mixtures usingultrasonic cavitation. They have reported that TCE has the degrada-tion rate in the range of 0.0197–0.0617 min�1. Destaillats et al.[28,29] have reported the scale up of sonochemical reactors forwaste water treatment. They have reported the rates of degrada-tion of TCE in a number of sonochemical reactors and the rate ofTCE degradation was in the range of 0.033–0.203 min�1. They havealso reported the rates of degradation for reactive dyes. It lies inthe range of 0.002–0.045 min�1. Lesko [30] have reported the ratesof degradation of phenol using a pilot station sonochemical reactor.The authors found that the rate of phenol degradation was in therange of 0.0011–0.063 min�1. Zheng et al. [31] have reported therates of sonochemical degradation of phenol in the range of0.014–0.061 min�1. Lesko et al. [13] have reported the rate of phe-nol degradation in the presence of ozone and ultrasound to be inthe range of 0.137 min�1. One can observe from Table 3 that the re-ported rates of degradation of phenol, TCE and reactive dyes are inthe same range as are considered in this study. Hence it can safelybe said that the results of cost estimation of this study can at leastprovide an order of magnitude glimpse of the economics involvedin the waste water treatment using ultrasonic processes.

3.1. General procedure for calculation of capital cost

Most investigators have observed the kinetics of sonodegrada-tion of pollutants to be either first order or zero order [4]. A generalprocedure is given below to calculate the capital cost for a givenAOP. Using k to denote the rate constant for degradation and t90

for time required for 90% degradation of the pollutant, the first-or-der degradation of pollutants is given by [25]

lnCA0

CA¼ kt ð27Þ

For 90% degradation, this equation is converted to

t90 ¼2:3025851

kð28Þ

For zero order degradation of pollutants [25],

CA ¼ CA0 � kt ð29Þ

For 90% degradation, this equation is converted to

t90 ¼0:9CA0

kð30Þ

From the design flow rate of 1000 L/min, the capacity of the wastewater treatment reactor (AOP reactor) is given by = 1000 * t90 = Xliters.

From the referred publications or calculations from the data inthe publications (energy density, e), the total energy requirementin the AOP reactor is given by X e watt.

From the manufacturer quotations, the energy supplied by sin-gle unit of AOP = E watt.

The number of such standard commercial units required,N = X e/E.

Cost of each unit from the manufacturer = C USD.Total cost of N units = cost of AOP reactor = P = N C.From this the capital cost of the equipment was calculated. The

general calculation of capital cost is presented in Table 4. The cap-ital cost is amortized over a span of years at given amortizationrate. Amortized capital cost (A) is given by following formula [32]:

Table 5Summary of cost estimation of various AOPs for degradation.

Process k Pelec (kW) t (min) V (liter) C0 C Energy density usedin treatability study(watt/ml)

EE/O orEE/M

Cost $/1000 gallon

For phenolUV (254 nm) 0.0021 min�1 0.015 1096.47 0.1 235.28 23.528 0.15 2741.2 1520.86US (300 kHz) 0.0008 min�1 0.025 2878.23 0.1 235.28 23.528 0.25 11993 15536.59O3 (2 mg/L) 0.0279 min�1 0.036 82.53 0.1 235.28 23.528 0.36 495.18 1.2023US + UV 0.005 min�1 0.04 460.52 0.1 235.28 23.528 0.4 3070.1 3127.51US + O3 0.0326 min�1 0.061 70.63 0.1 235.28 23.528 0.61 718.07 384.431UV + O3 0.0869 min�1 0.051 26.5 0.1 235.28 23.528 0.51 225.25 38.648US/UV/O3 0.1793 min�1 0.076 12.842 0.1 235.28 23.528 0.76 162.67 89.7851US/H2O2/CuO 0.0149 min�1 0.0182 136 0.15 58.1 8.82 0.182 335.92 429.185Fenton 0.0106 min�1

** 218 0.35 63 6.3 ** ** 14.2829SonoFenton 0.058 min�1 0.05 39.69 0.35 63 6.3 0.5 94.5 137.626UV/H2O2 0.0524 min�1 0.15 90 0.75 1100 5.53 0.15 130.51 308.482Photocatalysis 0.433 ppm min�1 0.45 180 0.1 100 2.36 0.45 138263 8648.79Sonophotocatalysis 0.712 ppm min�1 0.52 145.18 0.1 100 3.02 0.52 129741 7337.33

For reactive azo dyeUV (254 nm) No degradation observed 0.036 60 1.2 20 20 0.03 1.38E+09 –US (300 kHz) 0.00175 min�1 0.6 1315.76 1.2 20 2 0.5 10964.69 14203.7O3 (12.4 mg/L) 0.01108 min�1 0.036 207.814 1.2 20 2 0.03 103.91 4.0839US + UV 0.0055 min�1 0.636 418.65 1.2 20 2 0.53 3698.09 4639.155US + O3 0.01674 min�1 0.636 137.55 1.2 20 2 0.53 1215.02 1492.066UV + O3 0.02064 min�1 0.072 111.56 1.2 20 2 0.06 111.56 34.02462US/UV/O3 0.02171 min�1 0.672 106.06 1.2 20 2 0.56 989.9 1187.477US/H2O2 0.0032 min�1 0.066 60 4.5 100 45.65 0.027 43.07 416.491UV/H2O2 0.0124 min�1 0.186 60 4.5 100 84.35 0.0147 559.2 74.613US/UV/H2O2 0.0357 min�1 0.186 60 4.5 100 9.13 0.0413 39.76 65.172Photocatalysis 0.0207 ppm min�1 0.5 111.24 0.7 402.6 40.26 0.7143 3654.68 739.8451Sonophotocatalysis 0.0757 ppm min�1 0.53 30.41 0.7 402.6 40.26 0.7571 1059.08 234.2085

For TCEUV(254 nm) 0.0589 min�1 0.02 30 5 1.66 0.291 0.004 2.64 4.668US (500 kHz) 0.0457 min�1 0.05 90.61 0.6 32.85 0.4376 0.0833 67.1 91.14O3 (6 mg/L) 0.0209 min�1 0.036 25 0.1 2.2 1.3 0.36 656.51 2.3549US + UV 0.181 min�1 0.43 29.9 4.1 13.4 1.49 0.1049 54.78 25.8247UV/H2O2 0.4418 min�1 0.02 14.84 5 2.194 0.003 0.004 0.35 3.3266Photocatalysis Apparent rate

constant = 49.57 lg/L s�1

Adsorption equilibriumconstant = 0.000466 l/lg

0.45 30 7.2 15 0.21 0.0625 2112914 15.0993

N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003 995

A ¼ 1:2S � r

1� 11þr

� �n ð31Þ

3.2. General procedure for calculation of O&M cost

The O&M (operating and maintenance cost) consists of partreplacement costs, labor costs, analytical costs, chemical costsand electrical costs.

(1) Part replacement cost: Part replacement cost may includebulb replacements for UV systems, ozone generator partsfor ozone system, catalyst holder replacements for catalyticsystems, tip replacements or electronic circuit replacementsor transducer element replacements for ultrasound systems.For ultrasonic systems, the part replacement costs wereassumed to be 0.5% of the capital cost. This assumptionwas made based upon the vendor data in the MTBE reportfrom NWRI (National Water Research Institute, USA) [33].For UV systems, the part replacement costs were assumedto be 45% of the annual electrical power consumption costs[34,35]. For ozone systems, the annual part replacement costwas assumed to be 1.5% of the capital cost [33].

(2) Labor cost: The labor costs consisted of water sampling cost,general and specific system O&M costs. System specificoperation and maintenance consisted of inspection, replace-ment and repair based on hours of service life. General O&Mannual labor consists of general system oversight and

maintenance such as pressure gauges, control panels, leak-ages etc. General O&M labor was assumed to be 312 h/yearfor all the systems. The labor rate was assumed to be $80/h [33].

For ultrasonic systems, it was assumed that (based on ven-dor data in [33]) sampling frequency (Sf) = 3 samples/week;sampling time (St) = 1 h per sample or 3 h/week and timerequired for O&M = 128 h/year. Operation and maintenanceconsisted of inspection, replacement and repair based on1000 h of service life.For UV systems, it was assumed that (based on vendor datain [33]) Sf = 3 samples/week; St = 1 h per sample or 3 h/week; and time required for O&M = 18 h/year. Operationand maintenance consisted of change outs of lamps every3000 h of service.For ozone systems, it was assumed that (based on vendordata in [33]) Sf = 4 samples/week; St = 1 h per sample or4 h/week; time required for O&M = 48 h/year. Operationand maintenance consisted of change outs of damaged parts,repairing of electrodes etc. during the year and ozone gener-ator replacement every year. For H2O2 systems, no laborcosts were considered as we believe that it involves justthe use of a metering pump and a reservoir for H2O2 storage.For catalyst systems, no labor costs were considered.

(3) Analytical costs: Analytical costs were based upon samplingfrequency, the labor required to do the analysis of the sam-ples and the cost of chemicals required for analysis. Thesecosts were considered at a rate of $200/h [33].

Table 6Capital cost estimation ($) of various AOPs for degradation.

Item AOPreactor

Piping,valves,electrical(30%)

Sitework(10%)

Subtotal ContractorO&P (15%)

Subtotal Engineering(15%)

Subtotal Contingency(20%)

Totalcapital

Amortizedannualcapitalcost

For phenolUV 2.47E+08 7.40E+07 2.47E+07 3.46E+08 5.18E+07 3.97E+08 5.96E+07 4.57E+08 9.14E+07 5.48E+08 4.42E+07US 9.00E+09 2.70E+09 9.00E+08 1.26E+10 1.89E+09 1.45E+10 2.17E+09 1.67E+10 3.33E+09 2.00E+10 1.61E+09O3 3.40E+04 1.02E+04 3.40E+03 4.76E+04 7.14E+03 5.47E+04 8.21E+03 6.30E+04 1.26E+04 7.55E+04 a7.55E+04US + UV 1.54E+09 4.63E+08 1.54E+08 2.16E+09 3.24E+08 2.49E+09 3.73E+08 2.86E+09 5.72E+08 3.43E+09 2.77E+08US + O3 2.22E+08 6.66E+07 2.22E+07 3.11E+08 4.66E+07 3.58E+08 5.36E+07 4.11E+08 8.22E+07 4.93E+08 b3.98E+07UV + O3 6.08E+06 1.82E+06 6.08E+05 8.51E+06 1.28E+06 9.78E+06 1.47E+06 1.12E+07 2.25E+06 1.35E+07 b1.12E+06US + UV + O3 4.36E+07 1.31E+07 4.36E+06 6.10E+07 9.15E+06 7.01E+07 1.05E+07 8.06E+07 1.61E+07 9.68E+07 b7.83E+06US + H2O2 + CuO 2.35E+08 7.05E+07 2.35E+07 3.29E+08 4.94E+07 3.78E+08 5.68E+07 4.35E+08 8.71E+07 5.22E+08 4.21E+07Fenton *** *** *** *** *** *** *** *** *** *** ***US + Fenton 7.14E+07 2.14E+07 7.14E+06 1.00E+08 1.50E+07 1.15E+08 1.72E+07 1.32E+08 2.64E+07 1.59E+08 1.28E+07UV + H2O2 1.32E+07 3.96E+06 1.32E+06 1.85E+07 2.77E+06 2.13E+07 3.19E+06 2.44E+07 4.89E+06 2.93E+07 2.36E+06Photocatalysis 1.40E+09 4.21E+08 1.40E+08 1.97E+09 2.95E+08 2.26E+09 3.39E+08 2.60E+09 5.20E+08 3.12E+09 2.51E+08US + photocatalysis 2.05E+09 6.14E+08 2.05E+08 2.87E+09 4.30E+08 3.30E+09 4.95E+08 3.79E+09 7.58E+08 4.55E+09 3.67E+08

For reactive azo dyeUV – – – – – – – – – – –US 8.23E+09 2.47E+09 8.23E+08 1.15E+10 1.73E+09 1.32E+10 1.99E+09 1.52E+10 3.05E+09 1.83E+10 1.47E+09O3 2.04E+05 6.12E+04 2.04E+04 2.86E+05 4.28E+04 3.28E+05 4.93E+04 3.78E+05 7.55E+04 4.53E+05 a4.53E+05US + UV 2.64E+09 7.91E+08 2.64E+08 3.69E+09 5.54E+08 4.25E+09 6.37E+08 4.88E+09 9.77E+08 5.86E+09 4.72E+08US + O3 8.63E+08 2.59E+08 8.63E+07 1.21E+09 1.81E+08 1.39E+09 2.08E+08 1.60E+09 3.19E+08 1.92E+09 b1.55E+08UV + O3 5.04E+06 1.51E+06 5.04E+05 7.06E+06 1.06E+06 8.11E+06 1.22E+06 9.33E+06 1.87E+06 1.12E+07 b1.16E+06US + UV + O3 6.74E+08 2.02E+08 6.74E+07 9.43E+08 1.41E+08 1.08E+09 1.63E+08 1.25E+09 2.49E+08 1.50E+09 b1.21E+08US + H2O2 2.40E+08 7.20E+07 2.40E+07 3.36E+08 5.04E+07 3.86E+08 5.80E+07 4.44E+08 8.89E+07 5.33E+08 4.30E+07UV + H2O2 4.09E+07 1.23E+07 4.09E+06 5.73E+07 8.59E+06 6.59E+07 9.88E+06 7.58E+07 1.52E+07 9.09E+07 7.33E+06US + UV + H2O2 3.60E+07 1.08E+07 3.60E+06 5.04E+07 7.55E+06 5.79E+07 8.69E+06 6.66E+07 1.33E+07 7.99E+07 6.44E+06Photocatalysis 1.20E+08 3.60E+07 1.20E+07 1.68E+08 2.52E+07 1.93E+08 2.90E+07 2.22E+08 4.44E+07 2.67E+08 2.15E+07US + photocatalysis 4.98E+07 1.49E+07 4.98E+06 6.98E+07 1.05E+07 8.02E+07 1.20E+07 9.22E+07 1.84E+07 1.11E+08 8.92E+06

For TCEUV 2.35E+06 7.04E+05 2.35E+05 3.28E+06 4.93E+05 3.78E+06 5.67E+05 4.34E+06 8.69E+05 5.21E+06 4.20E+05US 5.24E+07 1.57E+07 5.24E+06 7.34E+07 1.10E+07 8.44E++07 1.27E+07 9.71E+07 1.94E+07 1.17E+08 9.39E+06O3 1.02E+05 3.06E+04 1.02E+04 1.43E+05 2.14E+04 1.64E+05 2.46E+04 1.89E+05 3.78E+04 2.27E+05 a226623.6US + UV 1.34E+07 4.03E+06 1.34E+06 1.88E+07 2.82E+06 2.16E+07 3.25E+06 2.49E+07 4.98E+06 2.99E+07 2.41E+06UV + H2O2 3.13E+05 9.40E+04 3.13E+04 4.38E+05 6.58E+04 5.04E+05 7.56E+04 5.80E+05 1.16E+05 6.96E+05 5.61E+04Photocatalysis 2.34E+06 7.03E+05 2.34E+05 3.28E+06 4.92E+05 3.77E+06 5.66E+05 4.34E+06 8.68E+05 5.21E+06 4.20E+05

a Since ozone generator is assumed to be replaced every year, amortized cost is taken as the same as that of the capital cost.b Cost of ozone generator is added to the amortized cost of UV and US system amortized over 30 years at 7% rate.

996 N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003

(4) Chemical costs: The chemical costs include the costs of con-sumables such as hydrogen peroxide and chemicals involvedwith the AOP such as catalysts like CuSO4, CuO and TiO2 etc.The price of hydrogen peroxide (50%) was considered to be$4 per gallon. The price of CuO was considered to be $3.42per kg. The price of TiO2 was assumed to be $300 per kg.The price of CuSO4 was considered to be $2.2 per kg. Theseprices were obtained from standard industrial supplierssuch as ICIS Pricing and Inframat Advanced Materials [36].

(5) Electrical costs: Electrical costs were based on the powerconsumption by a given AOP. The electricity cost was calcu-lated at a rate of $0.08/kWh. Power consumption was calcu-lated for each AOP based upon the power consumed in ayear multiplied by the electricity rate.

3.3. General procedure for calculation of EE/O or EE/M

Electric energy per order (EE/O) is the electric energy in kilo-watt hours [kWh] required to degrade a contaminant by one orderof magnitude in a unit volume [e.g., 1 m3 (1000 L)] of contaminatedwater or air [37]. This figure-of-merit is best used for situationswhere [CA] is low (i.e., cases that are overall first-order in concen-tration of pollutant) because the amount of electric energy re-quired to bring about a reduction by one order of magnitude inconcentration is independent of [CA]. Thus, it would take the sameamount of electric energy to reduce the contaminant concentrationfrom 10 mg/L to 1 mg/L in a given volume as it would to reduce itfrom 10 lg/L to 1 lg/L. EE/O is, in general, a measure of operating

cost. It allows for easy and accurate scale up to a full scale designand costs. EE/O is defined as:

EE=O ¼ Pelec � t � 1000V � 60 � logðCA0=CAÞ

ð32aÞ

For zero order degradations, EE/M (electrical energy per unit mass)is used instead of EE/O. EE/M is defined as:

EE=M ¼ Pelec � t � 1000V �M � 60 � ðCA0 � CAÞ

ð32bÞ

4. Sample calculations

4.1. Sample calculations (O3 + US + UV treatment) for phenoldegradation

A sample calculation for the hybrid process of O3 + US + UV forthe degradation of phenol is shown below. Cost estimations forall other processes were done similarly. Table 5 summarizes the re-sults of these calculations. All the calculations done for the estima-tion of cost of waste water treatment using ultrasound for phenol,reactive azo dye and TCE are tabulated in Table 6–12.

4.1.1. Capital cost calculationsThe work of Kidak and Ince [38] was used as the treatability

study for phenol. From their published data, the first-order degra-dation rate constant for phenol was 0.1793 min�1. One can easily

Table 7Annual O&M cost estimation ($) of various AOPs for degradation.

Item Part replacement cost Labor cost Analytical cost Chemical cost Electrical cost Total annual O&M cost

For phenolUV 5.19E+07 3.89E+04 3.12E+04 0.00E+00 1.15E+08 1.67E+08US 4.50E+07 4.77E+04 3.12E+04 0.00E+00 5.04E+08 5.49E+08O3 5.10E+02 4.54E+04 4.16E+04 0.00E+00 4.09E+03 9.16E+04US + UV 2.90E+07 6.16E+04 6.24E+04 0.00E+00 1.29E+08 1.58E+08US + O3 1.11E+06 6.82E+04 7.28E+04 0.00E+00 1.24E+07 1.37E+07UV + O3 1.28E+06 5.94E+04 7.28E+04 0.00E+00 2.84E+06 4.25E+06US + UV + O3 8.19E+05 8.21E+04 1.04E+05 0.00E+00 3.65E+06 4.65E+06US + H2O2 + CuO 1.18E+06 4.77E+04 3.12E+04 3.15E+06 1.32E+07 1.76E+07Fenton 0.00E+00 4.77E+04 3.12E+04 1.91E+06 0.00E+00 1.99E+06US + Fenton 3.57E+05 4.77E+04 3.12E+04 1.91E+06 4.00E+06 6.35E+06UV + H2O2 2.78E+06 3.89E+04 3.12E+04 3.15E+07 6.17E+06 4.05E+07Photocatalysis 2.95E+08 3.89E+04 3.12E+04 1.56E+04 6.56E+08 9.51E+08US + photocatalysis 1.86E+08 6.16E+04 6.24E+04 9.53E+03 4.67E+08 6.54E+08

For reactive azo dyeUV – – – – – –US 4.11E+07 4.77E+04 3.12E+04 0.00E+00 4.61E+08 5.02E+08O3 3.06E+03 4.54E+04 4.16E+04 0.00E+00 2.45E+04 1.15E+05US + UV 1.71E+07 6.16E+04 6.24E+04 0.00E+00 1.56E+08 1.73E+08US + O3 4.32E+06 6.82E+04 7.28E+04 0.00E+00 4.84E+07 5.28E+07UV + O3 1.06E+06 5.94E+04 7.28E+04 0.00E+00 2.38E+06 3.57E+06US + UV + O3 4.36E+06 8.21E+04 1.04E+05 0.00E+00 3.98E+07 4.43E+07US + H2O2 1.20E+06 4.77E+04 3.12E+04 2.06E+05 1.35E+07 1.49E+07UV + H2O2 8.60E+05 3.89Ev04 3.12E+04 2.06E+05 1.91E+06 3.05E+06US + UV + H2O2 4.09E+05 6.16E+04 6.24E+04 2.06E+05 1.88E+06 2.62E+06Photocatalysis 2.52E+07 3.89E+04 3.12E+04 2.52E+04 5.61E+07 8.14E+07US + photocatalysis 7.07E+06 6.16E+04 6.24E+04 6.98E+03 1.64E+07 2.36E+07

For TCEUV 4.93E+04 3.89E+04 3.12E+04 0.00E+00 1.10E+05 2.29E+05US 2.62E+05 4.77E+04 3.12E+04 0.00E+00 2.94E+06 3.28E+06O3 1.53E+03 4.54E+04 4.16E+04 0.00E+00 1.23E+04 1.01E+05US + UV 1.47E+05 6.16E+04 6.24E+04 0.00E+00 9.14E+05 1.18E+06UV + H2O2 6.58E+03 3.89E+04 3.12E+04 3.15E+05 1.46E+04 4.06E+05Photocatalysis 4.93E+05 4.30E+04 4.16E+04 7.50E+03 1.10E+06 1.68E+06

N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003 997

calculate the time required for 90% degradation of phenol using Eq.(28) as t90 = 12.84–13 min.

We assume that the residence time for the proposed wastewater treatment plant = 13 min. With a design flow rate of1000 L/min and ultrasonic power density of 250 watt/L, theamount of ultrasonic energy needed for the plant = 3250 kW.

From the quotation received from a leading ultrasonic devicemanufacturer (Hielscher USA, Inc., Ringwood, NJ 07456, USA), theamount of energy supplied by the ultrasonic device is 16 kW. Thedevice is claimed to be by far the most powerful ultrasonic proces-sor world-wide providing a continuous power of 16,000 watts atan efficiency of more than 80%. The frequency of ultrasonic deviceis 20 kHz. As there are no industrial ultrasonic devices to the bestof our knowledge which work at 300 kHz, it was assumed that theavailable ultrasonic device will produce the same results as in thetreatability study. This assumption may be valid as the amount ofultrasonic energy provided by both devices is the same (although itis generally known that effect of high frequency is slightly betterthan low frequency ultrasound). The quoted cost of this device is200,000 USD. The number of such standard device needed for theplant will be 204.

The cost of ultrasonic devices required = 204 * 200,000 =4.08 � 107 USD.

The power density used for UV energy in the treatabilitystudy = 150 watt/L.

The amount of energy needed in the form of UV energy for theplant = 13000 * 150 = 1950 kW. From the quotation received froma leading LP-UV Lamp provider (Emperor Aquatics, Inc., Pottstown,PA 19464, USA) the amount of energy supplied by the LP-UV Lampis 200 W. The quoted cost of this device is 300 USD.

The number of such standard device needed for theplant = 1950000/200 = 9750.

The cost of UV device required = 9750 * 300 = 2.925 � 106 USD.The dissolved concentration of ozone used in the treatability

study = 2 mg/L.We have to continuously maintain similar concentration in the

plant reactor of 13,000 L capacity. Hence the amount of dissolvedozone needed = 13000 * 2 = 26 g.

This is the amount of ozone needed during start up. Once thedissolved concentration reaches a steady state of 2 mg/L, the de-mand for dissolved ozone is only for 1000 L/min waste water.Hence, at steady state, the demand for ozone = 2000 mg/min = 6.3648 lb/day. The solubility coefficient of ozone at 20 �C is0.31 mg/L in water per 1 mg/L in gas [39].

Hence, to obtain a dissolved concentration of 2 mg/L in the reac-tor, the concentration of ozone required in the ozone/air mixture at20 �C = 2/0.31 = 6.45 mg/L. From the quotation received from aleading Ozone Generator manufacturer (Spartan EnvironmentalTechnologies, L.L.C. Mentor, OH 44060, USA), the capacity of ozonegenerator was 7.5 lb/day. The concentration of ozone in the ozone–air mixture was 5% by weight. This comes out to be 70 mg/L ozonein the ozone–air mixture. Thus one unit of ozone generator is suf-ficient to meet our ozone demand in this case. The quoted cost ofthis device is 34000 USD. Since it was assumed that ozone gener-ator is replaced every year, its cost was not amortized. The energyconsumption of this device (including other accessories such as aircompressor etc.) was 5.83 kW.

Thus the cost of ozone system required = 34000 USD.Hence, the total capital cost of the AOP unit for (O3 + US + UV)

treatment = P = cost of ultrasonic system + cost of UV system =40625000 + 2925000 = 4.3550E+07.

From Table 4, total capital cost of waste water system = 1.2S = 9.68E+07 USD.

Using Eq. (31), amortized capital cost, A = 7797491 USD.

Table 8Breakdown of labor costs ($) of various AOPs for degradation.

Item Sampling frequency(Samples/Week)

Sampling annuallabor (h)a

AOP system O&M(h/year)

General O&M wholetreatment plant (h/year)

Total annuallabor (h)

Total annuallabor cost ($)b

For phenolUV 3 156 18 312 486 38880US 3 156 128 312 596 47680O3 4 208 48 312 568 45440US + UV 6 312 146 312 770 61600US + O3 7 364 176 312 852 68160UV + O3 7 364 66 312 742 59360US + UV + O3 10 520 194 312 1026 82080US + H2O2 + CuO 3 156 128 312 596 47680Fenton 3 156 128 312 596 47680US + Fenton 3 156 128 312 596 47680UV + H2O2 3 156 18 312 486 38880Photocatalysis 3 156 18 312 486 38880US + photocatalysis 6 312 146 312 770 61600

For reactive azo dyeUV – – – – – –US 3 156 128 312 596 47680O3 4 208 48 312 568 45440US + UV 6 312 146 312 770 61600US + O3 7 364 176 312 852 68160UV + O3 7 364 66 312 742 59360US + UV + O3 10 520 194 312 1026 82080US + H2O2 3 156 128 312 596 47680UV + H2O2 3 156 18 312 486 38880US + UV + H2O2 6 312 146 312 770 61600Photocatalysis 3 156 18 312 486 38880US + photocatalysis 6 312 146 312 770 61600

For TCEUV 3 156 18 312 486 38880US 3 156 128 312 596 47680O3 4 208 48 312 568 45440US + UV 6 312 146 312 770 61600UV + H2O2 3 156 18 312 486 38880Photocatalysis 4 208 18 312 538 43040

a It is assumed that the plant is working the whole year. Also there are 52 weeks in a year.b Labor rate is assumed to be $80 per hour.

998 N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003

Total amortized capital cost = A + cost of ozone generator =7797491 + 34000 = 7831491 USD.

4.1.2. Operating and maintenance cost calculations

(1) Labor cost: For US systems and UV systems, the samplingfrequency was taking 3 samples per week. For ozone sys-tems, it was 4 samples per week. It was assumed to be52 weeks in a year. It was assumed that sampling labor takes1 h per sample.a) For UV system: Annual sampling labor = 3 * 52 = 156 h;

UV system O&M = 18 h/year; total annual labor hours =156 + 18 = 174.

b) For US system: Annual sampling labor = 3 * 52 = 156 h;UV system O&M = 128 h/year; total annual labor hours =156 + 128 = 284 h.

c) For OZONE system: Sampling labor = 4 * 1 = 4 h/week;Annual sampling labor = 4 * 52 = 208 h;ozone system O&M = 48 h/year;Total annual labor hours = 208 + 48 = 256.

d) For General O&M of the waste water treatmentplant = 312 h per year.Thus, the total annual labor hours = 174 + 284 + 256 +312 = 1026.Total annual labor cost = 1026 * 80 = 82080 USD

(2) Analytical cost:a) For UV system: Annual analysis labor = 3 * 52 = 156 h;

total annual labor hours = 156 h.

b) For US system: Annual analysis labor = 3 * 52 = 156 h;total annual labor hours = 156 h.

c) For OZONE system: Annual analysis labor = 4 * 52 =208 h; total annual labor hours = 208 h.Total annual analysis labor hours = 156 + 156 + 208 =520.Total annual analysis cost = 520 * 200 = 104000 USD.

(3) Chemical cost: Since there is no other chemical consumption(as per treatability studies) in O3 + US + UV process. This costis considered as zero.

(4) Electrical cost: Power consumption in the O3 + US + UVsystem = sum of power consumed by each system = 5.83 +3250 + 1950 = 5205.83 kW. Total energy consumed in ayear = 31536000 * 5205.83 = 164171054880 kJ = 45603070.8/kWh. Rate of electricity = $0.08/kWh.So, the total annual electrical cost = 0.08 * 45603070.8 =3.648245664 � 106 USD.

(5) Part replacement cost:a) For UV system: Part replacement cost = 45% of electrical

cost = (0.45 * 1950 * 31536000 * 0.08)/3600 = 614952USD.

b) For US system: Part replacement cost = 0.5% of capitalcost of ultrasonic system = 0.005 * 40625000 = 203125USD.

c) For ozone system: Part replacement cost = 1.5% of capitalcost of ultrasonic system = 0.015 * 34000 = 510 USD.

So, total part replacement cost = 614952 + 203125 + 510 =818587 USD.

Table 9Breakdown of analytical costs ($) of various AOPs for degradation.

Item Samplingfrequency(samples/week)

Samplingannuallabor (h)

Total annuallabor cost ($)a

For phenolUV 3 156 31200US 3 156 31200O3 4 208 41600US + UV 6 312 62400US + O3 7 364 72800UV + O3 7 364 72800US + UV + O3 10 520 104000US + H2O2 + CuO 3 156 31200Fenton 3 156 31200US + Fenton 3 156 31200UV + H2O2 3 156 31200Photocatalysis 3 156 31200US + photocatalysis 6 312 62400

For reactive azo dyeUV – – –US 3 156 31200O3 4 208 41600US + UV 6 312 62400US + O3 7 364 72800UV + O3 7 364 72800US + UV + O3 10 520 104000US + H2O2 3 156 31200UV + H2O2 3 156 31200US + UV + H2O2 6 312 62400Photocatalysis 3 156 31200US + photocatalysis 6 312 62400

For TCEUV 3 156 31200US 3 156 31200O3 4 208 41600US + UV 6 312 62400UV + H2O2 3 156 31200Photocatalysis 3 156 31200

a Analytical labor rate was assumed to be $200 per hour.

Table 10Breakdown of chemical costs ($) of various AOPs for degradation.

Item Chemicals Amount ofchemicalsconsumed (g)

Cost ofchemicals(USD)

Total costof chemicals($)

UV NAUS NAO3 NAUS + UV NAUS + O3 NAUV + O3 NAUS + UV + O3 NAUS + H2O2 + CuO H2O2 3.57E+09 3.15E+06 3.15E+06

CuO 1.55E+05 5.30E+02Fenton CuSO4 1.31E+05 2.88E+02 1.91E+06

H2O2 2.16E+09 1.91E+06US + Fenton CuSO4 2.40E+04 5.28E+01 1.91E+06

H2O2 2.16E+09 1.91E+06UV + H2O2 H2O2 3.57E+10 3.15E+07 3.15E+07Photocatalysis TiO2 5.20E+04 1.56E+04 1.56E+04US + photocatalysis TiO2 3.18E+04 9.53E+03 9.53E+03

For reactive azo dyeUV NAUS NAO3 NAUS + UV NAUS + O3 NAUV + O3 NAUS + UV + O3 NAUS + H2O2 H2O2 2.33E+08 2.06E+05 2.06E+05UV + H2O2 H2O2 2.33E+08 2.06E+05 2.06E+05US + UV + H2O2 H2O2 2.33E+08 2.06E+05 2.06E+05Photocatalysis TiO2 8.40E+04 2.52E+04 2.52E+04US + photocatalysis TiO2 2.33E+04 6.98E+03 6.98E+03

For TCEUV NAUS NAO3 NAUS + UV NAUV + H2O2 H2O2 3.57E+08 315179.9 315179.9Photocatalysis TiO2 25000 7500 7500

N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003 999

Total O&M cost = part replacement cost + labor cost + analyticalcost + chemical cost + electrical cost. Thus, total O&M cost =818587 + 82080 + 104000 + 0 + 3648245.664 = 4652912.664 USD.

Total annual operating cost for O3 + US + UV system = totalamortized annual capital cost + annual O&M cost = 7831491 +4652912.664 = 12484403.664 USD.

Total amount of water treated in a year = 1000 * 60 * 24 *365 = 525600000 liter = 139047.619 thousand US gallons. Hence,cost of waste water treatment = 12484403.664/139047.619 =89.78509661 USD per thousand gallon.

4.2. Sample EE/O calculation

For O3 + US + UV process the total electrical energy utilized inthe treatability study [38] was 76 watts. The amount of treatmentvolume was 100 ml. The treatment time was 12.84 min. The initialconcentration was 235.28 ppm and final concentration was23.528 ppm in this much treatment time. The EE/O is calculatedusing Eq. (32).

Thus, EE/O = (0.076 * 12.84 * 1000)/(0.1 * 60 * log (235/23.5)) =162.67 kWh/m3/order.

5. Results and discussion

All the costs are expressed in terms of amount in dollars neededto treat 1000 gallons of phenolic waste water for 90% degradation.These costs are calculated for the conditions described in the treat-ability studies. Pilot plant studies can give much closer conditions

to estimate accurate costs. But still, the costs estimated in thisstudy using the lab scale treatability studies can be used as a usefulguide as to what may be the order of magnitude of the treatmentcost for ultrasonic waste water treatment systems.

Table 5 shows the summary of the cost estimation of variousAOPs along with EE/O values for phenol, reactive azo dye andTCE. It can be seen from Table 5 that the cost of phenolic wastewater treatment using ultrasound is $15536.6 for US process alone.It is $3127.51 for combinative US + UV process. The cost of combi-native US + O3 process is $384.43. It is $89.79 for US + UV + O3

combinative process, $429.19 for US + H2O2 + CuO, $137.63 forUS + Fenton and $7337.33 for US + photocatalysis combinativeprocesses. These costs are plotted in Fig. 1. At the first glance ofthe Fig. 1, one can observe that the cost of treatment for ultrasoundalone is very high ($15536.6). But the cost of ultrasonic wastewater treatment reduces when it is combined with other sourcesof producing oxidizing species such as photocatalysis ($7337.33),UV ($3127.51), H2O2/CuO ($429.19), O3 ($384.431), Fenton($137.63) and UV + O3 ($89.79). The lowest cost ($89.79) isachieved when ultrasound is used in combination of UV and ozonefor phenol degradation. A similar trend is observed for the reactiveazo dyes and TCE degradation in the presence of ultrasonic pro-cesses. Table 5, Figs. 2 and 3 show how the costs of waste watertreatment for reactive azo dyes and TCE have decreased whencombination of AOPs was used instead of single AOP. The lowestcost for ultrasonic reactive azo dye degradation was $65.17 forUS/UV/H2O2 process and it was $25.82 for TCE degradation usingUS + UV process. But still the cost of treatment is not practicallyimplementable.

Table 11Breakdown of part replacement cost ($) of various AOPs for degradation.

Item Part replacement cost ($)

For phenolUV (45% of electrical cost) 5.19E+07US (0.5% of capital cost) 4.50E+07O3 (1.5% of capital cost) 5.10E+02US + UV US 7.20E+06 2.90E+07

UV 2.18E+07US + O3 US 1.11E+06 1.11E+06

O3 5.10E+02UV + O3 UV 1.28E+06 1.28E+06

O3 5.10E+02US + UV + O3 UV 6.15E+05 8.19E+05

US 2.03E+05O3 5.10E+02

US + H2O2 + CuO 1.18E+06Fenton NAUS + Fenton 3.57E+05UV + H2O2 2.78E+06Photocatalysis 2.95E+08US + photocatalysis US 5.95E+06 1.86E+08

UV 1.80E+08

For reactive azo dyeUV (45% of electrical cost) –US (0.5% of capital cost) 4.11E+07O3 (1.5% of capital cost) 3.06E+03US + UV US 1.31E+07 1.71E+07

UV 3.96E+06US + O3 US 4.31E+06 4.32E+06

O3 3.06E+03UV + O3 UV 1.06E+06 1.06E+06

O3 3.81E+03US + UV + O3 UV 1.01E+06 4.36E+06

US 3.34E+06O3 3.06E+03

US + H2O2 1.20E+06UV + H2O2 8.60E+05US + UV + H2O2 US 1.08E+05 4.09E+05

UV 3.01E+05Photocatalysis 2.52E+07US + photocatalysis US 8.30E+04 7.07E+06

UV 6.98E+06

For TCEUV (45% of electrical cost) 4.93E+04US (0.5% of capital cost) 2.62E+05O3 (1.5% of capital cost) 1.53E+03US + UV US 6.52E+04 1.47E+05

UV 8.20E+04UV + H2O2 6.58E+03Photocatalysis 4.93E+05

Table 12Breakdown of electrical costs ($) of various AOPs for degradation.

Item Powerconsumed (kW)

Total annualpower consumed(kWh)

Powercost ($)a

For phenolUV 1.65E+05 1.44E+09 1.15E+08US 7.20E+05 6.31E+09 5.04E+08O3 5.83E+00 5.11E+04 4.09E+03US + UV UV 6.92E+04 1.62E+09 1.29E+08

US 1.15E+05US + O3 US 1.78E+04 1.56E+08 1.24E+07

O3 5.83E+00UV + O3 UV 4.05E+03 3.55E+07 2.84E+06

O3 5.83E+00US + UV + O3 US 3.25E+03 4.56E+07 3.65E+06

UV 1.95E+03O3 5.83E+00

US + H2O2 + CuO 1.88E+04 1.65E+08 1.32E+07Fenton NA NA NAUS + Fenton 5.71E+03 5.01E+07 4.00E+06UV + H2O2 8.80E+03 7.71E+07 6.17E+06Photocatalysis 9.36E+05 8.20E+09 6.56E+08US + photocatalysis UV 5.72E+05 5.84E+09 4.67E+08

US 9.53E+04

For reactive azo dyeUV – – –US 6.58E+05 5.76E+09 4.61E+08O3 34.98 3.06E+05 2.45E+04US + UV UV 1.26E+04 1.95E+09 1.56E+08

US 2.10E+05US + O3 US 6.90E+04 6.05E+08 4.84E+07

O3 34.98UV + O3 UV 3.36E+03 2.97E+07 2.38E+06

O3 34.98US + UV + O3 US 5.35E+04 4.97E+08 3.98E+07

UV 3.21E+03O3 34.98

US + H2O2 1.92E+04 1.68E+08 1.35E+07UV + H2O2 2.73E+03 2.39E+07 1.91E+06US + UV + H2O2 US 1.73E+03 2.35E+07 1.88E+06

UV 9.53E+02Photocatalysis 8.00E+04 7.01E+08 5.61E+07US + photocatalysis UV 2.21E+04 2.06E+08 1.64E+07

US 1.33E+03

For TCEUV 156.4 1370064 109605.12US 4195.831 36755485 2940438.8O3 17.49 153212.4 12256.992US + UV UV 260 11421253 913700.24

US 1043.796UV + H2O2 20.88 182908.8 14632.704Photocatalysis 1562.5 13687500 1095000

a Electricity rate was assumed to be $0.08 per kWh.

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It can be seen that even the lowest cost of waste water treat-ment containing phenol using ultrasonic processes is one or twoorder of magnitudes higher than the cost of phenol degradationusing other AOPs. Esplugas et al. [22] have shown that these costsrange from $1.09 per kg of phenol removed for ozonation to $293.1for UV for 75% degradation of phenol. The lowest cost of phenoltreatment using an ultrasonic process (O3 + US + UV) is $89.79 for1000 gallons. This converts to 263.56 dollars/kg of phenol. Also ifone looks at the cost of treatment of commercial processes suchas ozonation, UV + H2O2 or H2O2 + O3 for ground water treatmentcontaining volatile organic compounds such as TCE, the cost ofultrasonic treatment is at least one order of magnitude higher.Amiri [40] from Hydroxyl Systems Inc. (9800 McDonald Park Rd.,Sidney, BC, CanadaV8L5W5) has shown that the cost of wastewater treatment for volatile compounds in ground water is in therange of $0.68–1.14/1000 gallons for H2O2 + O3 and UV + H2O2,respectively. James and Kovalick [41] have shown that the cost ofwaste water treatment containing chlorinated VOCs such as TCE,PCE and DCA range from $7 to $11 per 1000 gallons for a commer-cial process called Perox-pureTM from Calgon Carbon Oxidation

Technologies (500 Calgon Carbon Drive, Pitttsburgh, PA 15205,USA). The lowest cost for such treatment using ultrasonic processin our study was $25.82 for US + UV. The costs of ultrasonic treat-ment of waste water containing reactive azo dyes are comparableor an order of magnitude less than the commercial H2O2/UV andozonation processes. The costs of waste water treatment for reac-tive azo dyes are of the order of €52/m3 and €45/m3, respectively[42]. This converts to $283.02/1000 gallon and $244.92/1000 gal-lon for H2O2/UV and ozonation processes, respectively. The lowestcost of ultrasonic process for waste water treatment containing azodyes was $65.172/1000 gallons for US + UV + H2O2.

The higher costs of ultrasonic treatment processes are becauseof the very high operating costs involved in the use of ultrasoundsystems in terms of electrical costs and very high capital costs.One reason for this is that the conversion of electrical energy intocavitation energy is very inefficient. About 34% of the electrical en-ergy supplied is actually used for producing desired final effect[43]. The second reason, we observe, is the use of large amount

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1002 N.N. Mahamuni, Y.G. Adewuyi / Ultrasonics Sonochemistry 17 (2010) 990–1003

of energy for treating very small reaction volumes. One can observefrom the Table 5, that the power densities used for the treatabilitystudies are very high. It ranges from a low of 0.027 watt/ml to ahigh of 0.76 watt/ml. This when scaled up to industrial scale, be-comes huge amount of energy requirement which needs very highenergy capacity equipment .This results in very high capital cost ofequipment and higher O&M costs. Hence there is an urgent need touse the minimum possible energy density to produce the optimumresults while carrying out treatability studies. This can be doneusing larger treatment volumes in the laboratory with given equip-ment. We feel that the energy density to be used for ultrasonic pro-cesses should not be more than 0.05 watt/ml in order to make theprocess economically viable at industrial scale. Also all treatabilitystudies should weigh the relative increase in EE/O values with re-spect to the observed improvements in the rates when one addsmore amount of energy to increase the rates of degradation. Thiswill help keep tab on the amount of energy usage in the treatabilitystudies. Also one should look for alternative ways of producing thesame cavitational effects as observed in ultrasound with high en-ergy density but at lower energy costs. One of these ways maybe the use of hydrodynamic cavitation [44,45], the use of additives[46] or the hybrid methods [47].

It can be observed that the cost of treatment for hydrophilic pol-lutants such as reactive azo dyes and phenol are relatively higherthan that of hydrophobic contaminants such as TCE (Table 5).Whereas the cost of phenol treatment was $15536 using ultra-sound alone, it was only $91 for TCE degradation. This has to dowith the mechanism of degradation of these two kinds of pollu-tants. TCE is degraded inside the cavitation bubbles whereas phe-nol and reactive azo dyes are degraded outside the cavitationbubbles. Hence the mass transport of OH� radicals to the contami-nant becomes the controlling step of the degradation mechanism.Most of the OH� radicals recombine to produce less reactive speciessuch as H2O2 before they can come in contact with the contami-nant molecules. Destaillats et al. [48] and Adewuyi [4] have de-scribed the detailed mechanism of these processes. One can alsoobserve that the cost of treatment of reactive azo dyes is compara-ble to that of phenol but more than that of TCE. This is because ofthe fact that these reactive azo dyes remain in bulk and are verycomplex high molecular weight chemicals.

One should also understand that, this is a new technology and isin developmental stage. As it matures, the cost of treatment willcome down. Also there are known detrimental health effects ofother low cost waste water treatment technologies such as ozona-tion and UV processes which make ultrasonic and hydrodynamiccavitation processes even more attractive. Breathing ozone cantrigger a variety of health problems including chest pain, coughing,throat irritation, and congestion. It can worsen bronchitis, emphy-sema, and asthma. Ground-level ozone can reduce lung functionand inflame the linings of the lungs. Repeated exposure may per-manently scar lung tissue. Ground-level ozone can also have detri-mental effects on plants and ecosystems. These effects include: (1)interfering with the ability of sensitive plants to produce and storefood, making them more susceptible to certain diseases, insects,other pollutants, competition and harsh weather; (2) damagingthe leaves of trees and other plants, negatively impacting theappearance of urban vegetation, as well as vegetation in nationalparks and recreation areas; and (3) reducing forest growth andcrop yields, potentially impacting species diversity in ecosystems[35]. UV processes are ineffective when the waste water is opaqueto UV or the particle content of the waste water increase as in rainyseason. Hence pretreatments of the waste water to be treated arerequired before it can be passed onto UV process. These limitationscan be overcome with the use of ultrasonic technology which doesnot need any pretreatment of the wastewater. Also current use ofDesign of Experiment (DOE) optimization techniques such as Tagu-

chi method to understand the effects of multiple parameters on theoverall sonication effectiveness and establish optimal conditionsfor sonochemical and combinative advanced oxidation processeswill aid cost effectiveness and commercialization of ultrasonic pro-cesses for water and wastewater treatments [49]. Hence this canbe an economically viable alternative technology for waste watertreatment in the future.

6. Conclusion

The following are the main conclusions of this cost estimationstudy.

(1) Combination of ultrasound with different AOPs was eco-nomically more attractive than the use of ultrasound alonefor waste water treatment.

(2) US + UV + O3 process was found to be the most economicalultrasonic process for phenol treatment in this study.The cost of the phenolic waste water degradation usingthis process was $89.78/1000 gallon. This is at least oneorder of magnitude higher than available commercialprocesses.

(3) US + UV + H2O2 was found to be the most economical ultra-sonic process for waste water treatment containing reactiveazo dye. The cost of the waste water treatment containingreactive azo dyes using this process was $65.17/1000 gallon.This is an order of magnitude less than available commercialprocesses.

(4) US + UV was found to be the most economical ultrasonicprocess for TCE degradation. The cost of the waste watertreatment containing reactive azo dyes using this processwas $25.82/1000 gallon. This is one order of magnitudehigher than available commercial processes.

(5) The cost of ultrasonic waste water treatment containinghydrophobic contaminants is found to be an order of magni-tude less than that of waste water containing hydrophiliccontaminants.

(6) As of today, the cost of waste water treatment using hybridultrasonic processes is one to two orders of magnitude morethan currently established AOPs such as ozonation, O3/H2O2

and UV/H2O2.(7) The high cost of ultrasonic waste water treatment is due to

the very high energy densities used in the treatabilitystudies.

Acknowledgement

The authors acknowledge the funding received from NationalScience Foundation (NSF) for the financial assistance via AwardNo. Grant CBET-0651811.

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