disinfection efficiency, etc

8/3/2019 Disinfection Efficiency, Etc

1/14

Water Research 37 (2003) 45734586

Disinfection efficiency of peracetic acid, UV and ozone after

enhanced primary treatment of municipal wastewater

Ronald Gehra,*, Monika Wagnera, Priya Veerasubramaniana, Pierre Paymentb

aDepartment of Civil Engineering, McGill University, Montreal, Canada H3A 2K6b INRS-Institut Armand-Frappier, Universit!e du Qu !ebec, Laval, Canada H7V 1B7

Received 6 August 2002; received in revised form 3 April 2003; accepted 17 June 2003

Abstract

The City of Montreal Wastewater Treatment Plant uses enhanced physicochemical processes (ferric and/or alum

coagulation) for suspended solids and phosphorus removal. The objective of this study was to assess the ability of

peracetic acid (PAA), UV, or ozone to inactivate the indicator organisms fecal coliforms, Enterococci, MS-2 coliphage,

or Clostridium perfringens in the effluent from this plant.

PAA doses to reach the target fecal coliform level of 9000 CFU/100 mL exceeded 6 mg/L; similar results were

obtained for enterococci, and no inactivation of Clostridium perfringens was observed. However a 1-log reduction of

MS-2 occurred at PAA doses of 1.5 mg/L and higher. It was expected that this effluent would have a high ozone

demand, and would require relatively high UV fluences, because of relatively high effluent COD, iron and suspended

solids concentrations, and low UV transmittance. This was confirmed herein. For UV, the inactivation curve for fecal

coliforms showed the typical two-stage shape, with the target of 1000 CFU/100 mL (to account for photoreactivation)

occurring in the asymptote zone at fluences >20 mJ/cm2

. In contrast, inactivation curves for MS-2 and Clostridiumperfringens were linear. Clostridium perfringens was the most resistant organism. For ozone, inactivation was

already observed before any residuals could be measured. The transferred ozone doses to reach target fecal coliform

levels (B2-log reduction) were 3050 mg/L. MS-2 was less resistant, but Clostridium perfringens was more resistant than

fecal coliforms.

The different behaviour of the four indicator organisms studied, depending on the disinfectant, suggests that a single

indicator organism might not be appropriate. The required dose of any of the disinfectants is unlikely to be

economically viable, and upstream changes to the plant will be needed.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Enhanced primary treatment; Disinfection; Peracetic acid; UV; Ozone

1. Introduction

The City of Montreal Wastewater Treatment Plant

(CMWTP) uses physicochemical processes to treat up to

7.6 106m3/d of combined domestic and industrial

wastewater. These processes include screening, grit

removal, addition of ferric chloride and/or alum as well

as a polyelectrolyte to precipitate phosphorus and

improve solids settling, and sedimentation prior to

discharge into the St. Lawrence River. At present there

is no disinfection. Since the use of chlorine for waste-

water disinfection has been banned in the Province of

Quebec, the City of Montreal is exploring alternative

disinfectants in order to produce water which could be

suitable for contact aquatic sports, and as a raw potable

water source to communities downstream. The dis-

charge permit for this wastewater treatment plant would

allow for an effluent containing 9000 CFU (colony

ARTICLE IN PRESS

*Corresponding author. Tel.: +1-514-398-6861; fax: +1-

514-398-7361.

E-mail address:[email protected] (R. Gehr).

0043-1354/$- see front matterr 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0043-1354(03)00394-4


2/14

forming units) of fecal coliforms (FC) per 100 mL, and

1000 CFU/100 mL to allow for photoreactivation if

ultraviolet radiation (UV) is used [1]. However concerns

have been raised regarding the adequacy of indicator

organisms such as FC to predict the performance of

various disinfection processes against pathogens. Ac-

cordingly, the objectives of this study were (a) to assessthe doses required for three disinfection processes

peracetic acid (PAA), UV or ozoneto reach the

target FC standard, and (b) to compare the responses

of three other indicatorsEnterococci (EC), Clostridium

perfringens (CP) and MS-2 coliphageto these

disinfectants. The data will be used to determine the

level of disinfection required at this wastewater treat-

ment plant to attain a level of risk (using a model

proposed by Haas et al. [2]) that is acceptable to public

health and to the population, and is economically

feasible. The risks examined will be those associated

with recreational activities during which direct andindirect contact occurs with river water impacted by this

effluent.

2. Background

2.1. Peracetic acid (PAA)

Of the three disinfectants being studied, PAA is

the newest alternative for applications in North Amer-

ica, though it has been used in Europe for waste-

water disinfection for many years. Interest in the use

of PAA as a disinfectant for wastewaters began in

the late 1980s with publications by Baldry and cow-

orkers [3,4]. Grantham [5] presented results from

many internal studies of the National River Authority

(NRA) of England and Wales. He pointed out that

since PAA is an equilibrium mixture, the PAA dose

stated in terms of the initial concentration of the

mixture will actually underestimate the dose of

PAA delivered. The EPA [6] and Atasi et al. [7] have

suggested that PAA could be particularly suited to

disinfection of combined sewer overflows (CSOs), and

Gehr et al. [8] reported that PAA might be more

appropriate as a disinfectant for biologically treatedeffluents, rather than those from physicochemical

effluents.

Commercially available PAA (also known as ethane-

peroxoic acid or peroxyacetic acid) is available in a

quaternary equilibrium mixture containing acetic acid,

hydrogen peroxide, peracetic acid and water, as shown

in the equation below:

CH3CO2H H2O22CH3CO3H H2O: 1

The biocidal form is considered to be the undissociated

acid (i.e. CH3CO3H) which is predominant at pHo4:7

[9]. However the H2O2 may also contribute directly to

disinfection in a synergistic fashion (although Lubello

et al. [10], dispute this), and in the long term because it

persists longer than PAA.

The disinfecting mechanism of PAA is still subject to

some speculation. Lefevre et al. [11] and Liberti et al. [9]

suggested that the disinfectant property is due to the

release of active oxygen, which in turn disruptssulfhydryl (SH) and sulfur (SS) bonds within enzymes

contained in the cell membrane. Thus transport across

the cell membrane is affected, which impedes cellular

activity.

A second suggested disinfectant mechanism is the

release of hydroxyl radicals [10]. By varying the

proportion of PAA to H2O2, Lubello et al. [10] also

determined that it was the PAA, and not the H2O2,

which was responsible for the biocidal action.

Gehr et al. [8] presented results of batch screening

tests where PAA was assessed as a disinfectant for

physicochemical as well as biological effluents. For atarget FC level of 1000 CFU/100 mL, and contact times

of 30120 min, PAA doses for the physicochemical

effluents ranged between 2 mg/L and greater than

6 mg/L, whereas for biological effluents lower doses of

0.64 mg/L were required. Another recent study [10]

assessed the possibility of using PAA in conjunction

with UV as a type of advanced oxidation process. A UV

fluence of 120mJ/cm2 applied simultaneously with a

PAA dose of 8 mg/L (30 min contact time) was able to

achieve over 4-log reduction of total coliforms, or less

than 2 CFU total coliforms/100 mL, which is Italys

standard for unrestricted wastewater reuse in agricul-

ture. Such levels of inactivation were not possible with

PAA or UV used separately.

PAA reacts with organic matter in the sewage. If

there is little organic matter, the disinfection reaction

will be fast, and the additional disinfection after

30min contact will be insignificant. However, at

high concentration levels of organic matter, dis-

infection could also occur after this time, provided

that the initial PAA dose was high enough to satisfy

the PAA demand of the sewage, and to establish a

residual [8].

As with all disinfectants, PAA has varying effective-

ness depending on the organism. Baldry et al. [4] foundthat E. coli and MS-2 coliphages had similar (low)

resistance, but poliovirus, echovirus and coxsackievirus

were considerably more resistant. Studies by Lazarova

et al. [12] showed that different bacteriophages had

vastly different sensitivities to PAA: using the same

wastewater effluent and 120 min contact time, 10 mg/L

PAA was able to reduce f 174 bacteriophage by 7.5

logs, whereas 5 mg/L PAA was needed to reduce MS-2

coliphage by only 3.5 logs. Liberti et al. [9] determined

that although PAA was effective against total coliforms,

it was ineffective towards Giardia and Cryptosporidium

parasites.

ARTICLE IN PRESS

R. Gehr et al. / Water Research 37 (2003) 457345864574


3/14

2.2. Ultraviolet radiation (UV)

UV radiation is now the most common alternative to

chlorination for wastewater disinfection in North

America [13]. UV lamps emit significant radiation in

the range 240260 nm, exactly that range over which

nucleic acids (such as DNA and RNA) absorb energy.When exposed to UV light, adjacent thymine bases on

the nucleic acid strands dimerize. Thus accurate

transcription of this DNA strand cannot occur, and

the bacterial cell cannot divide [14]. Similar mechanisms

apply to inactivation of viruses.

UV doseresponse curves typically show an initial steep

decline (attributed to inactivation of the free-swimming

organisms), followed by a second stage with a much

shallower slope. This latter stage is generally accepted to

be due to the shielding effect of particulates [15], although

Blatchley et al. [16] suggest that it might also be due to

clumping of bacterial cells. If the target inactivation levelis in this region, much higher UV dosesnow referred to

as fluenceswill be required [17]. The critical particle

size is in the range of 910mm [15,18]; below this size

particles cannot shield or embed bacteria. Emerick et al.

[15] claimed that above this size there is no difference in

the particles in terms of their ability to harbour coliform

bacteria, but this result is disputed [19].

Early studies at the CMWTP [18] had established that

a UV fluence of 35 mJ/cm2 would be required to achieve

a 3-log or greater reduction in FC counts. This would be

sufficient to meet a target level of 2000 CFU/100 mL

before dilution and possible photoreactivation. At that

time the plant was operating suboptimally; suspended

solids (SS) was approximately 40 mg/L, unfiltered UV

transmittance at 254nm was 40%, and Fe concentrations

were frequently above 1 mg/L. More recent collimated

beam tests [8] determined that fluences of 812 mJ/cm2

could achieve target FC levels of 1000 CFU/100 mL for

SS of 2030mg/L, when the facility was operated with a

mixture of ferric chloride and alum as coagulants.

There have been many studies on the effect of UV on

different organisms (including Angehrn [14], Masschelein

[20], and Oppenheimer et al. [21]). The typical indicator

aerobic bacteria such as fecal coliforms show a relatively

low resistance (such as a 1-log inactivation requiringapproximately 2.53mJ/cm2), bacteriophages and many

viruses are slightly more resistant, and the anaerobic

spore-formers such as Clostridium perfringens are the

most resistant (over 10 mJ/cm2 per log inactivation).

However none of the studies that we are aware of have

commented on whether the presence of particles may

have different effects on different types of organisms.

2.3. Ozone (O3)

Although ozone has been a popular and successful

disinfectant for drinking water, it has not been widely

used for wastewater disinfection due to operation and

maintenance problems of first generation systems, as

well as the high ozone demand of many effluents [22,23].

Grantham [5] notes that water and wastewater utilities

in England and Wales do not use ozone due to the high

costs involved. We have not been able to find examples

of current usage of ozone for large scale wastewaterdisinfection in North America, but several smaller plants

exist in the US, Canada, Japan, Korea and Europe

[24,25].

The kinetics of ozone reactions have received the

attention of many researchers. The kinetics are complex

because of the different reaction rates with different

chemicals in solution, speciation of the ozone and its

decomposition products, and the interaction of these

with the microorganisms. According to the literature,

ozone decomposes in three phases, although there is

disagreement as to the exact pathways [13]. The type and

kinetics of ozone decomposition has implications on themechanism of disinfection. If ozone decomposition is

slow, then chemicals (and microorganisms) will undergo

direct ozone attack. These reactions are selective and

slow. On the other hand, if ozone decomposition is

rapid, which occurs when the alkalinity is low, and/or

organics concentration is high, then oxidation will occur

by means of the OH radical, which is very reactive and

non-selective. Studies with E. coli and G. muris have

suggested that these organisms undergo greater inacti-

vation when ozone residuals persist, rather than when

ozone is rapidly decomposed.

Hermanowicz et al. [26] showed that the reaction rates

for individual batch tests could be roughly described by

first-order kinetics, but that both the rate constant and

the reaction order decreased with increasing ozone dose

transferred. Rates of ozone consumption were much

higher in the continuous-flow experiments than in the

batch tests. For their batch tests, Oke et al. [27] mixed a

saturated ozone solution with the test sample, and found

that first-order kinetics were appropriate for clean

waters, but for natural lake waters there was a gradually

decreasing rate constant. Comparison of batch contact

reactors (where the ozone gas is added at the start of the

reaction) with continuous-flow reactors is made more

difficult because of the simultaneous increase ofdissolved ozone and decrease of oxidizable species as

well as microorganisms. If Ct values are used, the

assumption is that C will be constant throughout the

contact time t, and that the kinetics (order and rate

constant) are also constant. In the present work, C was

not constant, but the kinetics were assumed to be

constant, and the Ct values were calculated as the area

under the Ct curve.

There is a need to satisfy the ozone demand before

disinfection can proceed. Ozone demand can be caused

by certain inorganics, organics, and suspended solids.

This may lead to unrealistically high doses, especially for

ARTICLE IN PRESS

R. Gehr et al. / Water Research 37 (2003) 45734586 4575


4/14

the CMWTP, which uses only physicochemical treat-

ment [28]. However Gehr and Nicell [28], Lazarova et al.

[12] and Xu et al. [23] show that up to 3-logs of

inactivation of E. coli or fecal coliforms could be

obtained even before the ozone demand was met. This

calls into question the concept of the product of residual

concentration and contact time (Ct) as a governingparameter for wastewater disinfection performance.

The actual mode of action of ozone disinfection is

poorly understood, with various researchers suggesting

that ozone alters proteins and the unsaturated bonds of

fatty acids in the cell membrane, or that it affects cell

DNA. Hunt and Marin as [29] showed that noticeable

changes in the interior of E. coli cells did not take place

until most of the cells in the sample were non-viable.

This confirms the hypothesis that in most cases

inactivation was due to damage of the cell membrane,

and that DNA damage might occur, but only if ozone

dosages were very high.Absi et al. [30] and Gehr and Nicell [28] reported on

continuous-flow pilot studies of ozone disinfection at the

CMWTP. Disinfection could not be well correlated with

wastewater quality parameters, although it was clear

that higher COD levels resulted in higher required ozone

doses. The target FC level in that study was 5000 CFU/

100 mL. When FeCl3 was used as the upstream

coagulant, the required ozone dose to achieve the target

90% of the time was 17 mg/L; when alum was used, a

limited number of tests indicated that this could be

reduced to perhaps as low as 10 mg/L.

It is well accepted that ozone is effective against all

organisms likely to be encountered in wastewaters,

including viruses and protozoan cysts. Even organisms

resistant to chlorination, such as poliovirus Type 3, as

well as Cryptosporidium and Giardia protozoa, can be

inactivated by ozone at residual concentrations of 1 mg/

L or even less, and sufficient contact time (severalminutes) [12,13]. Xu et al. [23] found that at

a transferred ozone dose (TOD) of 15.2mg/L, the

order of resistance of the microorganisms tested was

F-coliphage (>2.09 log reduction), FC and EC (2.48

log), and CP (0.31 log). To reach the WHO standard

for irrigation FC 1000 CFU=100 mL; TODs of215 mg/L were needed, depending on the quality of

the wastewater.

3. Materials and methods

3.1. Materials for disinfection

Materials for disinfection and analysis of disinfectants

are shown in Table 1.

3.2. Analytical procedures for disinfection

3.2.1. PAA

Residual concentrations of peroxycompounds (sum of

H2O2 and PAA) were measured in terms of the

absorbance of the radical cation of ABTS, formed when

ARTICLE IN PRESS

Table 1

Materials for disinfection and analysis of disinfectants

Disinfectant Reagent/apparatus Source

PAA (12% w/w) Solvay Interox, Houston, TX

Peracetic acid Horseradish peroxidase (EC 1.11.1.7, RZ 1.1) Sigma Chemical Co, St. Louis, MO

Catalase (EC 1.11.1.6) Sigma Chemical Co, St. Louis, MO

ABTS (98%) Sigma Chemical Co, St. Louis, MO

Dibasic sodium phosphate Fisher Scientific Co., Montreal, QC

Monobasic potassium phosphate Fisher Scientific Co., Montreal, QC

Sodium thiosulfate Fisher Scientific Co., Montreal, QC

Spectrophotometer Beckman DU-65

UV Low pressure mercury lamp collimator

Radiometer International Light, Newsburyport, MA

Ozone OzoTitanTM ozone generator Hankin Ozone Systems Ltd., Scarborough, ON

Oxygen feed gas MEGS Inc., Ville St. Laurent, QC

Magnehelics differential pressure gauge Dwyer Instruments, Inc., Michigan City, IN

Top-Trak digital gas flow meter Sierra Instruments Inc., Monterey, CA

AFXTM model H1 high concentration UV-ozone analyser IN USA, Inc., Needham, MA

Potassium iodide (ACS reagent) Fisher Scientific, Nepean, ON

Concentrated sulfuric acid Anachemia Canada Inc., Montreal, QC

Starch indicator (1%) Lab Chem Inc., Pittsburgh, PA

Potassium indigo trisulfonate for indigo Sigma Chemical Co, St. Louis, MO

Reagents I and II



5/14


6/14

meter, which was calculated according to

OPR CO3Pstandard

Pactual F; 4

where OPR is the ozone production rate (mg/min); CO3is the ozone concentration in the gas stream according to

the UV-ozone analyser g=m3

mg=L; Pstandard is thestandard pressure used by the UV-ozone analyser to

calculate the ozone concentration Pstandard 101:3 kPa;Pactual is the actual pressure in the gas stream (kPa); F is

the gas flow rate (L/min).

The differential pressure in the ozone reactor

Pactual Pstandard was 3.2 kPa when one trapping bottle

was used and approximately 5.7 kPa when both trapping

bottles were connected in line. Thus, the value of the

pressure correction factor was 0.97 and 0.95, respec-

tively. Despite pressure correction, the ozone production

rate based on the iodometric method yielded a value that

was 10% lower than the one obtained based on the UV-ozone analyser and the gas flow rate.

Determination of the ozone mass flow rate leaving the

reactor: During ozonation experiments the concentra-

tion of ozone in the gas leaving the reactor bottle was

monitored using the UV-ozone analyser. These values

were corrected by a factor of 0.9 and multiplied by the

gas flow rate in order to obtain the mass flow rate of

ozone leaving the reactor over the course of the

ozonation experiment.

Determination of the ozone transfer rate and the

quantity of ozone transferred: The ozone transfer rate

into the ozonated sample was calculated according to

Ozone transfer rate mg=L min

OPR F CO3outPstandard

Pactual 0:9

Vreactor; 5

where CO3out is the ozone concentration in the gas stream

leaving the ozone reactor according to the UV-ozone

analyser g=m3 mg=L; Vreactor is the volume ofozonated sample in the ozone reactor bottle

Vreactor 2:3 L: The quantity of ozone transferredwithin a specified time period (in mg/L) was calculated

by multiplying the ozone transfer rate by the ozonation

time.Determination of dissolved ozone concentrations (ozone

residuals) [indigo colorimetric method]: The determina-

tion of dissolved ozone concentrations was essentially

carried out according to Standard Method # 4500-ozone

[34]. Before the onset of ozonation 12.5 mL of sample

were withdrawn through a septum installed into the side

wall of the reactor bottle (see Fig. 1) using a syringe and

mixed with 1.4 mL of indigo reagent I or reagent II

(depending on the ozone concentration). The absor-

bances of these solutions were immediately recorded as

the absorbance blank values. After ozonation was

initiated, samples (12.5 mL or less depending on the

expected ozone concentration) were withdrawn through

the septum at regular intervals, mixed with the appro-

priate ozone reagent and the absorbances were imme-

diately recorded. The concentration of dissolved ozone

in an ozonated wastewater sample CO3 was calculated

according to

CO3 Vtotal Asample Ablank

f c Vsample; 6

where Asample is the absorbance of the indigo assay

solution containing the ozonated wastewater sample at

600nm; Ablank is the absorbance of the indigo assay

solution containing the wastewater before the start of

the ozonation at 600 nm; f is the proportionality

constant [f 0:42 (cm mg/L)1]; l is the path length ofthe cell l 5 cm; Vsample is the sample volume in the

indigo assay solution (mL); Vtotal is the total volume of

the indigo assay solution Vtotal 14 mL:

3.3. Experimental procedure for disinfection

3.3.1. PAA

Sample aliquots were added to 250 mL dark glass

bottles, and stirred using magnetic stirring bars during

disinfection. The experiment was started by adding the

PAA disinfectant to yield PAA doses of 1.5, 3, 4.5 and

6.0 mg/L. After 1 h incubation, samples were withdrawn

from the bottles for residual peroxycompound measure-

ments and added to the ABTS-HRP assay solution.

Immediately after this, catalase was added at 50 mg/L to

quickly decompose the residual H2

O2

following the

addition of sodium thiosulfate (Na2S2O3) at 100 mg/L to

eliminate residual PAA. Two control bottles were

included in the experiment: one bottle was supplied

with 6.0 mg/L PAA, but the disinfectant was quenched

immediately by the addition of catalase and sodium

thiosulfate (quench control); the other bottle contained

the raw sample (0-sample).

3.3.2. UV

UV fluenceresponse curves were obtained according

to standard procedures for collimated beam tests (see,

for example, Masschelein [20]). Ultraviolet light irradia-

tion was carried out with a mercury low vapour pressure

lamp emitting light mainly at 253.7 nm, which was

mounted over a collimating tube. The incident light

intensity (I0) was recorded using a radiometer IL 1400A

with cosine diffuser lens (International Light, New-

buryport, MA). Fifty millilitres of wastewater sample

were poured into a crystallization dish containing a

magnetic stirring bar and placed on a magnetic stirrer

under the collimated beam lamp. The irradiation time

required to obtain the predetermined fluence was

calculated according to

tir fluence=Iavg; 7

ARTICLE IN PRESS



7/14

where tir is the irradiation time (s); fluence is the intended

UV fluence (mJ/cm2); Iavg is the average radiation

intensity inside an irradiated sample (mW/cm2).

The average radiation intensity inside an irradiated

volume of a stirred wastewater medium was calculated

according to Morowitz [35]:

Iavg I01 edln 1=T

d ln 1=T

; 8

where I0 is the incident radiation intensity (mW/cm2); d

is the depth of wastewater sample under UV irradiation

d 2:2 cm; Tis the transmittance at 254 nm [with a cellpath length of 1 cm] (as a decimal fraction of 1).

The sample was irradiated for the specified time and

kept in the dark and cold until microbiological analysis

was performed.

3.3.3. Ozone

The wastewater sample (2.3 L) was added to a gaswashing bottle equipped with a glass-fritted diffuser

(ozone reactor bottle) and placed on a magnetic stirrer

(Fig. 1). During ozonation the gas flow rate, the

pressure, the concentration of ozone in the outgoing

gas and the ozone residuals were monitored. Samples for

microbiological analysis were withdrawn at 5, 10, 15, 30

and 45min. Residual ozone was eliminated using

sodium thiosulfate at a concentration of 50 mg/L. The

temperature of the wastewater was 2021C throughout

the experiments.

3.4. Wastewater analysis

Most wastewater analyses were performed according

to Standard Methods [34]. Particle size distribution was

analysed using a Lasentec M100 F Particle System

Characterization Monitor (Lasentec, Redmond, WA).

3.5. Microbial analyses

Samples of wastewater effluent, following disinfec-

tion, were assayed for three groups of bacteria. Samples

were also spiked with MS-2 coliphage stock solution so

as to obtain a final titre ofB105 plaque forming units

(PFU)/mL, then disinfected. Procedures performed aresummarized in Table 2. Medium for selective culture of

C. perfringens was prepared according to a method

described by Armon and Payment [36]. Briefly, it

contained 71.14g/L media mCP (Difco, QC), 0.4g/L

d-cycloserine, 0.025 g/L polymyxin-B-sulphate, 0.06 g/L

indoxyl B-d-glucoside, 0.1 g/L phenolphthalene dipho-

sphate and 0.9 g/L ferric chloride (all from Sigma

Chemical Co, St. Louis, MO) in distilled water. Strainsof E. coli F+ and MS-2 coliphage were obtained from

Payment (Armand Frappier Institute, Laval, QC) and

stored at 80C.

4. Results and discussion

4.1. Wastewater characteristics

Due to the wide variability in the quality of the

effluent samples from the wastewater treatment plant,

the data are presented in Fig. 2 on a log scale showingthe mean as well as the range. An attempt was made to

correlate these data with disinfection performance, but

this was largely unsuccessful. It is clear, however, that

this wastewater would not be easy to disinfect, and

this is typical of wastewaters from purely physicochem-

ical treatment plants [17]. In particular, the high

concentrations of COD (123240 mg/L), SS (1645 mg/

L), turbidity (1631 NTU), and total iron (0.27.5 mg/

L), and low UV transmittance (4.629.5%) are noted. It

is known from previous work that high COD will

compromise the performance of ozone and PAA ([8,28],

respectively), whereas high SS, turbidity and iron, as

well as low UV transmittance will compromise UV

performance [15,17].

4.2. PAA disinfection efficiency

Fig. 3 shows the inactivation of fecal coliforms vs.

PAA dose for a contact time of 1 h. Due to the high day-

to-day variability of the wastewater quality, hence the

disinfection efficiency of the PAA, results from all five

test days are shown. Fig. 4 shows the residuals measured

after 1 h for various doses. Although a contact time of

approximately 2 h would be available in the outfall

tunnel at average flow, earlier studies had shown that theadditional contact time was not beneficial [8] and this is

ARTICLE IN PRESS

Table 2

Microbiological analytical procedures

Microorganisms Analytical procedures

Fecal coliforms Membrane filtration (Method 9222D, [34])

Enterococci Membrane filtration (Method 1600, [37])

Clostridium perfringens Membrane filtration and m-CP medium [36] incubated in BBLsGasPak (Fisher Co., Mtl, QC) at

44.5C for 1824 h

MS-2 coliphage Single-agar layer procedure with E. coli F+ as host strain: Method 1602 [38]



8/14

understandable in light of the low residual concentra-

tions of peroxycompounds remaining after 1 h. The

target FC level (9000 CFU/100mL) was reached on

only 2 days (August 21 and September 12) at a

PAA dose of 4.56 mg/L. No significant disinfection

was observed on the other days. The samples from

August 21 and September 12 had higher than

average UV transmittance, lower COD, BOD and

turbidity, and were more dilute than the other

samples. It appears therefore that the high level of

organics in most samples was responsible for the poor

effectiveness of PAA.

For a 1-log removal of EC, 4.5 mg/L PAA were

required, and there was no inactivation of CP (results not

shown). Only two dose curves were obtained for MS-2,

and up to 1-log inactivation was achieved at relatively

low doses of 1.53 mg/L PAA (Fig. 5), but this did not

improve at higher doses. It is possible that the mechan-

ism of inactivation for the bacteriophages is different to

that for bacteria. Given that a dose ofB1mg/L was

considered to be economically viable, and that there was

large variability in the resultspointing to high sensi-

tivity of PAA to variable effluent qualitythe use of

PAA would have to be ruled out for this application.

ARTICLE IN PRESS

0

1

10

100

1,000

COD(mg/L)

BOD5(mg/L)

Medianparticle

size(m)

Kurtosis

Calciumtotal

(mg/L)

COTnon-

purgeable(mg/L)

SS(mg/L)

Turbidity(NTU)

UVT@

254nm

(%/cm)

Mgtotal(mg/L)

Fetotal(mg/L)

Fefiltrable

20 mJ/cm2), but there were instances where

even at 60 mJ/cm2 the FC count was above 1000 CFU/

100 mL. As with PAA, similar results were obtained for

EC inactivation.

The curves for CP and MS-2 did not show the 2 stage

behaviour. The CP counts showed a steady decline with

increasing fluence (Fig. 7), with an approximate 1-log

reduction for an increment of 30 mJ/cm

2

. For the MS-2,

a 1-log reduction was achieved for each 10 mJ/cm2

(Fig. 8). Several interesting points emerge from these

results. First, as already noted, there was no tailing

effect (as is also evident in results obtained by Shin et al.

[39]). Hence, it must be surmised that neither CP nor

MS-2 were incorporated into flocs. Nieuwstad andHavelaar [40] did find tailing effects with bacterio-

phages, but they suggested that since all phages are

supposed to be identical, the tailing was due to

clustering.

Shielding (in the sense of an umbrella effect) appears

not to have taken place either, which is understandable

given the relatively long exposure times (1015 min),

hence the fact that a solids shield would not likely

remain in place so long. Confirmation of this hypothesis

(i.e. organisms not incorporated into solids or flocs) was

given in the case of the MS-2 by the fact that there was

no difference in the results for seeds which were added

ARTICLE IN PRESS

Fig. 4. PAA residuals.

1

10

100

1,000

10,000

100,000

0 1 2 3 4 5 6

PAA dose (mg/L)

MS-2(PFU/mL)

30-Aug

12-Sep

Fig. 5. MS-2 inactivation by PAA.



10/14

1 h (7 tests) or 16h (3 tests) before exposure to UV. This

fundamental difference in behaviour between the two

sets of organisms (FC and EC vs. CP and MS-2)

deserves further exploration, as it could have implica-

tions in interpreting them as indicators of inactivation of

pathogens (bacterial, protozoan or viral). In the former

ARTICLE IN PRESS

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

0 10 20 30 40 50 60

UV fluence (mJ/cm2)

Fecalcoliforms(CFU/100mL)

Bars are 95% c.I; n = 13

Fig. 6. Fecal coliform inactivation by UV.

1

10

100

1,000

10,000

0 10 20 30 40 50 60

Clostridium

perfringens(CFU/100mL)


UV fluence ( mJ/cm2)

Fig. 7. Clostridium perfringens inactivation by UV.

1

10

100

1,000

10,000

100,000

0 10 20 30 40 50 60

UV fluence (mJ/cm2

)

M

S-2(PFU/mL)


Fig. 8. MS-2 coliphage inactivation by UV.



11/14

case (FC and EC), nothing would be gained by

increasing UV fluences substantially, whereas in the

latter case (CP and MS-2) there would be a benefit

shown at higher fluences.

The second point to emerge is that CP is by far the

most resistant to UV light of the four organisms tested.

Thus it could be considered to be a conservativeindicator of UV performance.

4.4. Ozone disinfection efficiency

Fig. 9 shows a typical curve for ozone residual vs. time

in the batch test, and each successive point in Figs. 10

and 11 occurs at contact times of 5, 10, 15, 30 and

45 min, respectively. Pertinent data for ozone residuals,

etc., are shown in Table 3 below. The Ct values were

calculated using the area under the residual vs. time

curve (such as Fig. 9).

These values are within the same range as those givenby the EPA [41] for drinking water, viz. 1.0 for 4-log

inactivation of viruses (at 10C), 1.2 for 2.5-log

inactivation of Giardia cysts, and 2.410 for 2-log

inactivation of Cryptosporidium oocysts. However the

implication of Ct being equivalent to a dose in this

case is false, since it took close to 20 min to develop a

residual (hence any Ct value), yet inactivation did occur

during this period. It follows that reaction products of

ozone (notably the radicals) are implicated in the

inactivation process.

Results of inactivation of FC and CP by ozone are

shown in Fig. 10. Inactivation of EC was very similar to

that of FC. Although ozone effectiveness was approxi-

mately linear over the entire dose range tested, the target

FC level (equivalent to approximately 2-log inactiva-

tion) was reached only at a transferred ozone dose of

between 30 and 50 mg/L, and at these doses the CP

count had decreased by as little as 1-log. For practical

purposes (mainly economic), an ozone dose of 20 mg/L

or less was considered reasonable. Based on Figs. 9 and

10, the ozone demand of this wastewater (being the

transferred ozone dose when a residual first appears) is

approximately 25 mg/L. Therefore for the CMWTP

effluent in its current state, ozone is inappropriate.Although not tested explicitly, this very high ozone dose

requirement was assumed to be due to the presence of

organics in the wastewater, as shown by earlier studies

using a continuous-flow system [30].

Interestingly, the inactivation of MS-2 by ozone was

very successful, as indicated in Fig. 11. For a transferred

ozone dose of approximately 17 mg/L, counts had

decreased by over 3-logs. Hence it could be expected

that, notwithstanding the high ozone demand of the

wastewater, ozone would be an effective disinfectant for

viruses in this wastewater. This would suggest that the

inactivation mechanism of the bacteriophage was muchdifferent to that of the bacteria, as it had to be almost

instantaneous. The tailing effect is likely an artifact of

the MS-2 enumeration procedure, since MS-2 numbers

cannot be accurately measured below 1 PFU/mL, but it

could also be due to clustering.

5. Summary and conclusions

PAA was not a suitable disinfectant for the City of

Montreals Wastewater Treatment Plant. Based on a

fecal coliform (FC) target level of 9000 CFU/100 mL,

over 6 mg/L would be required, whereas 1.52 mg/L is

considered economically viable. For ozone, the required

dose exceeded 30 mg/L; this was also considered exces-

sive. On the other hand, for a more stringent FC target

of 1000 CFU/100 mL to account for photoreactivation,

ARTICLE IN PRESS

Sample - 14-Nov

0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50

Ozonation time (min)

Ozoneresidual(mg/L

)

Bac-Ozonation

MS2-Ozonation

Fig. 9. Development of ozone residuals.



12/14

the required UV fluence was 20 mJ/cm2, which may be

economically acceptable. Based on previous studies as

well as on the current effluent quality, the high dose

requirements are likely due to the high COD, suspended

solids, and/or ferric concentrations in the effluent.

Lower concentrations of these parameters as a result

of changes to upstream processes or operations may

alter the picture and render PAA or ozone more viable.

ARTICLE IN PRESS

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

0 10 20 30 40 50 60 70

Transferred ozone (mg/L)

Fecalcoliforms(C

FU/100mL)

6-Nov

8-Nov

14-Nov

1

10

100

1,000

10,000

0 10 20 30 40 50 60 70


Clostridium

perfringens(CFU/100mL)

6-Nov

8-Nov

14-Nov

(a)

(b)

Fig. 10. (a) Inactivation of fecal coliforms by ozone and (b) inactivation of C. perfringens by ozone.

0.10

1.00

10.00

100.00

1,000.00

10,000.00

100,000.00

0 10 20 30 40 50 60 70 80


MS-2(CFU/mL)

6-Nov

8-Nov

14-Nov

Fig. 11. Inactivation of MS-2 coliphage by ozone.



13/14

When other organisms were assessed, the picture

changed considerably. At a dose of only 1.5 mg/L, PAA

was able to reduce MS-2 coliphage counts by 1-log, butthere was no effect on C. perfringens (CP). Compared to

FC, CP and MS-2 were much more resistant to UV.

Their inactivation curves did not show the classic two-

stage shape, hence their inactivation was not signifi-

cantly affected by the presence of solids. In contrast,

ozone was highly effective against MS-2, achieving a

reduction of over 3-logs for a dose of 17 mg/L. Thus it

would likely be considered the most appropriate

disinfectant if viruses were the target organisms.

Further research on the mechanisms of disinfection as

well as on the interaction between certain organisms and

suspended solids (chemical flocs) in the effluent is

warranted to explain the varying behaviour of these

organisms when subject to different disinfectants. A risk

management approach is being undertaken to determine

whether some forms of recreational activities could be

permitted in the area impacted by a disinfected effluent.

References

[1] MEQ. Crit"eres de qualit!e de leau de surface au Qu!ebec.

Minist"ere de lenvironnement du Qu!ebec (Canada),

1998.

[2] Haas CN, Rose JB, Gerba CP. Quantitative microbial risk

management. New York: Wiley; 1999.

[3] Baldry MGC, French MS. Disinfection of sewage effluent

with peracetic acid. Water Sci Technol 1989;21(3):2036.

[4] Baldry MGC, French MS, Slater D. The activity of

peracetic acid on sewage indicator bacteria and viruses.

Water Sci Technol 1991;24(2):3537.

[5] Grantham R. Research by the National Rivers Authority

(NRA) in England and Wales in the efficacy and side

effects of a variety of techniques for the disinfection of

sewage effluents. Proceedings of the conference Disin-

fecting Wastewater for Discharge and Reuse. Water

Environment Federation, Portland, OR, March 1720,

1996. p. 6-16-12.

[6] EPA. Combined sewer overflow technology fact sheet.

Alternative disinfection methods. 1999a, EPA 832-F-99-033.

[7] Atasi K, Rabbaig M, Chen C. Alternative disinfectantsevaluation for combined sewage overflow (CSO): Detroit

Baby Creek CSO case study. Proceedings of the 74th

Annual Conference, Water Environment Federation,

Atlanta, GA, 2001.

[8] Gehr R, Cochrane D, French M. Peracetic acid (PAA) as a

disinfectant for municipal wastewaters: encouraging per-

formance results from physicochemical as well as biologi-

cal effluents. Proceedings of the Disinfection 2002

Conference, Water Environment Federation, St. Peters-

burg, FL, February 1720, 2002.

[9] Liberti L, Lopez A, Notarnicola M. Disinfection with

peracetic acid for domestic sewage reuse in agriculture.

CIWEM J 1999;13:2629.

[10] Lubello C, Caretti C, Gori R. Comparison between PAA/

UV and H2O2/UV disinfection for wastewater reuse.

Water Sci Technol: Water Suppl 2002;2(1):20512.

[11] Lefevre F, Audic JM, Ferrand F. Peracetic acid disinfec-

tion of secondary effluents discharged off coastal seawater.

Water Sci Technol 1992;25(12):15564.

[12] Lazarova V, Janex ML, Fiksdal L, Oberg C, Barcina I,

Pommepuy M. Advanced wastewater disinfection technol-

ogies: short and long term efficiency. Water Sci Technol

1998;38(12):10917.

[13] WEF Wastewater disinfection. Manual of Practice FD-10.

Alexandra, VA: Water Environment Federation, 1996.

[14] Angehrn M. Ultraviolet disinfection of water. Aqua

1984;2:10915.[15] Emerick RW, Loge FJ, Ginn T, Darby JL. Modeling the

inactivation of particle-associated coliform bacteria. Water

Environ Res 2000;72(4):4328.

[16] Blatchley III ER, Dumoutier N, Halaby TN, Levi Y, La#n!e

JM. Bacterial responses to ultraviolet radiation. Water Sci

Technol 2001;43(10):17986.

[17] Gehr R, Wright H. UV disinfection of wastewater

coagulated with ferric chloride: recalcitrance and fouling

problems. Water Sci Technol 1998;38(3):1523.

[18] Cairns WL, Sakamoto G, Comair CB, Gehr R. Assessing

UV disinfection of a physico-chemical effluent by medium

pressure lamps using a collimated beam and pilot plant.

Proceedings of the Water Environment Federation

ARTICLE IN PRESS

Table 3

Ozone residual kinetics data and Ct

Date Test org. Time to

first appearance

of a residual

(min)

Slope after first

appearance

(mg/Lmin)

Ct (mg-min/L) after

given contact time (min)

Log inactivation after

given contact time (min)

515 30 45 5 10 15 30 45

Nov. 6 FC 21 0.0173 0.6 4.8 0 1 1 2 3

Nov. 7 MS-2 20 0.0037 0.2 1.3 1 NA NA NA 3

Nov. 8 FC 16 0.0157 1.6 7 1 2 2 2 3

Nov. 9 MS-2 17 0.0103 1 4.4 1 3 4 4 5

Nov. 14 FC 18 0.02 1.4 7.3 0.3 1.1 1.2 2.1 2.8

Nov. 15 MS-2 NA NA NA NA 1.2 4.0 3.8 3.9 4.1

NA = not available.



14/14

Specialty Conference: Planning, Design and Operation

of Effluent Disinfection Systems, Whippany, NJ, 1993.

p. 43344.

[19] Madge BA, Jensen JN. Discussion of: modelling the

inactivation of particle-associated coliform bacteria. Water

Environ Res 2001;73(4):5045.

[20] Masschelein WJ. Ultraviolet light in water and wastewatersanitation. Boca Raton: Lewis Publishers; 2002.

[21] Oppenheimer JA, La#n!e J-M, Jacangelo JG, Bhamrah A,

Hoagland JE. Chlorine and UV disinfection of tertiary

effluent: a comparative study of bacterial and viral

inactivation and effluent by-products. Proceedings of the

66th Annual Conference, Water Environment Federation,

Anaheim, CA, 1993. p. 55768.

[22] Robson CM, Rice RG. Wastewater ozonation in the

USAhistory and current status1989. Ozone Sci Eng

1991;13:2340.

[23] Xu P, Janex M-L, Savoye P, Cockx A, Lazarova V.

Wastewater disinfection by ozone: main parameters for

process design. Water Res 2002;36:104355.

[24] Paraskeva P, Graham NJD. Ozonation of municipalwastewater effluents. Water Environ Res 2002;74(6):

56981.

[25] Larocque R. Ozone applications in Canadaa state of the

art review. Ozone Sci Eng 1999;21(2):11926.

[26] Hermanowicz SW, Bellamy WD, Fung LC. Variability of

ozone reaction kinetics in batch and continuous flow

reactors. Water Res 1999;33(9):21308.

[27] Oke NJ, Smith DW, Zhou H. An empirical analysis of

ozone decay kinetics in natural waters. Ozone Sci Eng

1998;2:36179.

[28] Gehr R, Nicell J. Pilot studies and assessment of down-

stream effects of UV and ozone disinfection of a

physicochemical wastewater. Water Qual Res J Can 1996;

31(2):26381.

[29] Hunt NK, Marin as BJ. Kinetics of Eschericia coli

inactivation with ozone. Water Res 1997;31(6):135562.

[30] Absi F, Gamache F, Gehr R, Liechti P, Nicell J. Pilot

plant investigation of ozone disinfection of a physico-

chemically treated municipal wastewater. Proceedings of

the 11th World Ozone Congress, San Francisco,

Aug 29Sept 3, 1993. p. S-7-33-42.

[31] Wagner M, Brumelis D, Gehr R. Disinfection of waste-

water by H2O2 or PAA: development of procedures for

measurement of residual disinfectant, and application to

a physico-chemically treated municipal effluent. Water

Environ Res 2002;74(1):3350.[32] P.utter J, Becker R. Peroxidases. In: Bergmeyer J, GraXl M,

editors. Methods of enzymatic analysis., vol. 3. Weinheim:

Verlag Chemie; 1983. p. 28693.

[33] IOA (International Ozone Association). Iodometric meth-

od for the determination of ozone in a process gas, 1998.

[34] APHA, AWWA, WEF. Standard methods for the

examination of water and wastewater, 20th ed. Washing-

ton, DC: APHA; 1998.

[35] Morowitz HJ. Absorption effects in volume irradiation of

microorganisms. Science 1950;111:22930.

[36] Armon R, Payment P. A modified m-CP medium for

enumerating Clostridium perfringens from water samples.

Can J Microbiol 1988;34:789.

[37] EPA. Method 1600: membrane filter test method forenterococci in water. US Environmental Protection

Agency, Office of Water, Washington DC, 1997, EPA-

821-R-97-004.

[38] EPA. Method 1602: Male-specific (F+) and somatic

coliphage in water by single agar layer (SAL) procedure.

US Environmental Protection Agency, Office of Water,

Washington, DC, 2001, EPA 821-R-01-029.

[39] Shin G-A, Linden K, Handzel T, Sobsey MD. Low-

pressure UV inactivation ofCryptosporidium parvum based

on cell culture infectivity. Proceedings, American Water

Works Association Water Quality and Technology Con-

ference, Tampa, FL, 1999, October 31November 3.

[40] Nieuwstad ThJ, Havelaar AH. The kinetics of batch

ultraviolet inactivation of bacteriophage MS2 and

microbiological calibration of an ultraviolet pilot plant.

J Environ Sci Health A 1994;29(9):19932007.

[41] EPA. Alternative disinfectants and oxidants guidance

manual. US Environmental Protection Agency, Office of

Water, Washington, 1999b, EPA 815-R-99-014.

ARTICLE IN PRESS


disinfection efficiency, etc

Documents