Bioresource Technology 72 (2000) 85ą93
Inactivation of indicator bacteria in wastewater by chlorine�a
kinetics study
a,* b b c
Abdennaceur Hassen , Abderrahim Heyouni , Hedi Shayeb , Mohamed Cherif ,
d
Abdellatif Boudabous
a
Institut National de Recherche Scienti�que et Technique, Laboratoire Environnement, B.P. 24-1082, Cite Mahrajene, Tunis, Tunisia
b
Ecole Nationale des Ingenieurs de Tunis, Campus Universitaire, B.P. 37-1002, Tunis Belvederes Tunis, Tunisia
c
Institut National Agronomique de Tunisie, 43 Avenue Charles Nicole, 1082, Cite Mahrajene, Tunis, Tunisia
d
Faculte des Sciences de Tunis, Laboratoire de Microbiologie, Campus Universitaire, 1060 Tunis, Tunisia
Received 28 February 1998; received in revised form 28 April 1999; accepted 25 May 1999
Abstract
The aim of this study was to characterise the kinetics of chlorine consumption and of inactivation of indicator bacteria in
secondary wastewater using a batch laboratory reactor. In this time-course study, di�erent concentrations of chlorine, used as
NaOCl, were injected into the reactor, the levels of the di�erent forms of residual chlorine were measured, and the numbers of faecal
coliforms and faecal streptococci were determined. The results of the kinetics of chlorine consumption showed that monochlor-
amines and trichloramines were the more important forms of residual chlorine as compared to free chlorine and dichloramines. The
high contents of trichloramines indicated that the reaction of chlorine with ammoniacal nitrogen was very fast and that the
transformation of chlorine into trichloramines was carried out in a time shorter than 1 min. Experimental results showed that the
application of the model of Chick-Watson in its original form was not representative of the kinetics of inactivation of faecal
coliforms and faecal streptococci. Modi�cation of this model, in considering an initial reduction just at the contact of water with
chlorine, improved the results of adjustment of the model. The same �ndings are valid for the model of Collins-Selleck in considering
a value m imposed to the concentration of residual chlorine, since it appeared clearly that the concentration of chlorine inŻuenced
the output of disinfection more than did the time of contact. Ó 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Wastewater; Disinfection; Chlorine; Modelling; Residual chlorine; Indicator bacteria
1. Introduction radiation (Moeller and Calkins, 1980; Come and Bariou,
1980, Anonymous, 1989). Disinfection by chlorine has
Disinfection is often a stage for the reusability of gained wide acceptance commercially, probably because
treated wastewater. The main objective of disinfection is of its simplicity and its moderate cost; despite the major
to reduce sanitary risks related to the presence of problem of secondary harmful products generated by
pathogens. Assessment of sanitary risks consists in in- this treatment (Pourmoghaddas and Stevens, 1995;
dexing and identifying pathogens that may be present in Racaud and Rawzy, 1994; Sanchez, 1993). Disinfection
such a water. Nevertheless, a serious analytical problem achieved by such a process is often accomplished in two
may be encountered, especially when the number of steps: a step of fast mixture and a step of contact be-
these pathogens is relatively low and their presence is tween chlorine and water, during a su�ciently long time
random. A growing body of evidence has indicated that to allow the product to play its disinfection role. The
the use of indicator bacteria, which have the advantage success of the operation of disinfection depends greatly
of being abundant and easily countable, is very useful in upon the conditions prevailing during the second step.
the assessment of sanitary risks related to the presence Besides the physico-chemical quality of the treated wa-
of pathogens (Wyer et al., 1997). ter, many other factors may a�ect this operation, among
Water disinfection can be achieved via di�erent which we �nd the hydraulic functioning of the cont-
means such as chlorination, ozonation and ultraviolet actor, the kinetics of chlorine reaction with the
components present in water and the kinetics of
*
Corresponding author. Tel.: [phone]; fax: [phone]. bacterial inactivation.
0960-8524/00/$ - see front matter Ó 1999 Elsevier Science Ltd. All rights reserved.
PII: S 0 9 6 0 - 8 5 2 4 ( 9 9 ) 0 0 086- 3
86 A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93
In order to characterize the functioning of such a 3. Results and discussion
process, we have undertaken an experimental study en-
abling modelling of the kinetics of chlorine consumption The goal of the present investigation was to charac-
and bacterial inactivation in secondary wastewater. terize the kinetics of chlorine consumption and bacterial
Once combined with an adequate hydrodynamic model, inactivation. The rates of reduction of faecal indicator
the obtained kinetics would allow the construction of a bacteria, as a function of time of contact, in the presence
simulation model of a chlorination reactor. The goal of of di�erent chlorine concentrations were determined.
this study was, therefore, to characterize the kinetics of The rate of inactivation was associated with a concen-
chlorine consumption and indicator bacterial inactiva- tration, C, of residual free chlorine and with a time of
tion in secondary wastewater. contact measured using as origin time t � 0 corre-
sponding to the moment of chlorine injection into the
water.
2. Methods
3.1. Reaction of chlorine consumption
2.1. Wastewater treatment
The wastewater, even when puri�ed and treated by
�ltration, contained relatively large quantities of organic
Chlorination assays were performed on samples of
and mineral matters with a BOD5 content varying from
secondary treated wastewater (trickling �ltrate) previ-
15 to 30 mg O2/l and a COD ranging from 20 to 30 mg
ously sand �ltered in a semi-industrial pilot plant. Sand
O2/l. The content in ammoniacal nitrogen Żuctuated
�ltration allowed an appreciable improvement of the
between 8 and 20 NH3ąN mg/l according to the exper-
quality of water and resulted in a considerable lowering
iments. After the initial mixture of chlorine and water,
of the initial demand for chlorine.
there was competition among two types of reactions:
� Oxido-reduction with some reducing compounds that
2.2. Experimental procedure consume a part of the injected chlorine rendering it
unavailable for the disinfection.
Disinfection assays: Experiments were performed in 3 � Substitution that forms some compounds of addition
l pyrex beakers each containing a magnetic stirrer ro- or of substitution mainly with ammonia to form
tating at 500 rpm. Wastewater (2 l) was mixed with 50 chloramines, which have a low bactericidal power.
ml of disinfectant (sodium hypochlorite) prepared at Fig. 1 shows chlorine consumption where only the
� 10 the required �nal dose. Wastewater chlorination results obtained for the concentrations of 6.5 and 13.6
was tested with concentrations varying from 6.5 to 25 mg/l have been represented. From Fig. 1, it appears that
mg/l. Samples (50 ml) were taken at regular intervals for all the studied concentrations and regardless of the
varying from 2 to 40 min, and the oxidative reaction was time of contact:
immediately stopped by addition of sodium thiosulphate � Monochloramines and trichloramines remained very
before residual chlorine measurement and faecal bacte- important as compared to free chlorine and dichlor-
ria enumeration. Each assay was carried out at least 4 amines.
times. In the control, 50 ml of sterile distilled water were � Dichloramines appeared as the lowest chlorine form,
mixed with wastewater samples instead of the disinfec- with a concentration usually less than 10% of the in-
tant. jected concentration.
Residual chlorine measurement: The di�erent forms of � Trichloramines appeared as the most important form
residual chlorine were determined by the sulphate di- of residual chlorine. Their levels decreased with the
ethyl-p-phenylenediamine (DPD) method according to time of contact, to reach their lowest levels by the
Nicholson (1965). Chlorine and derived compounds re- end of the experiment (20ą30 min).
act with DPD to give a red colour susceptible of tit- These results indicated that the reaction of chlorine
rimetric measuring with ammonium ferrous (II) with ammoniacal nitrogen of the water was very rapid
sulphate solution. Addition of potassium iodide (KI) as and that evolution of chlorine as trichloramines took
an oxidiser, at di�erent contact times, allowed di�eren- place in less than 1 min. This result appears to agree
tiation among free chlorine and di�erent combined with those mentioned in the literature by several authors
forms of chlorine such as mono-, di-, and trichlor- (Soulard, 1982; Saunier, 1979; Alouini et Seux, 1987;
amines. Adin et al., 1991). According to Adin et al. (1991), based
Enumeration of indicator bacteria: The number of on kinetic constants of these reactions, the formation of
indicator bacteria was determined based on the French monochloramines is the most rapid. Reactions of
standard methods of the most probable number MPN chloramines destruction are relatively slow and
(Rodier, 1978), and the corrected MPN tables proposed trichloramines are only gradually hydrolysed following
by Man (1983) were used. their appearance in the medium.
A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93 87
Fig. 1. Evolution of the content of residual chlorine as a function of the time of contact. Clustred error bar graphs and bars represent standard error
of mean with at least n � 4.
� The quantity of free chlorine, the main cause of of water for chlorine, conditioned by the presence
disinfection, was variable according to the injected of reducing compounds as well as compounds of
concentration. In contrast, it showed, on average, addition or substitution, the free residual chlorine
a low variation in the course of time for the same remained more or less at the same level until the
concentration of total chlorine. For instance, with end of the experiment. It appears particularly that
the high chlorine concentration of 20 mg/l, the level the content of residual free chlorine in the second-
of free chlorine was nearly constant and of the or- ary wastewater always exceeded the value of 10%
der of 3.5 mg/l (Result not shown). This result of the quantity of chlorine injected at the beginning
clearly indicated that after the immediate demand of the experiment. This result was valid at any time
88 A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93
of contact studied and regardless of the chlorine and the number of faecal bacteria. For each chlorine
concentration applied. concentration applied, tests were conducted at progres-
Based on all these results, it may be concluded that sive contact times ranging from 2 to 40 min. The three
the consumption of chlorine during the process of retained chlorine concentrations (6.5, 8.6 and 13.6 mg/l)
wastewater disinfection undergoes two steps: were tested on wastewater with MPN of 6.02 � 104 to
� A �rst rapid step corresponding to the consumption 6.02 � 105 of faecal coliforms per 100 ml and 3.16 � 104
of chlorine following its reaction with the reducing to 5.62 � 105 of faecal streptococci per 100 ml. All results
compounds in water. This step, called `the immediate are reported in Table 1.
satisfaction demand', seemed to be instantaneous. The initial contents of faecal bacteria (N0) in waste-
� A second step, during which residual chlorine was water di�ered from one experiment to another (results
transformed rapidly into the free and combined chlo- not shown), which was related to the quality of water
rine forms. This step concerns particularly the pro- used in each experiment. The speed of faecal bacteria
cess of disinfection since residual chlorine will be reduction varied from one concentration to the other.
available to exert its antiseptic power. It is clear that The higher the initial concentration of chlorine was, the
the modelling of the kinetics of chlorine consumption higher was the reduction of bacteria. For instance, dur-
or disinfection would concern only the second step of ing the same contact time of 10 min, a reduction in faecal
the reaction, which is amenable to measurement. streptococci of 1.63 and 3.36 logarithmic units was ob-
On the other hand, as has previously been mentioned, tained with the respective initial chlorine concentrations
combined chlorine (mono-, di- and trichloramines) ap- of 6.5 and 13.6 mg/l. In order to ensure a su�cient safety
peared as the most important form of residual chlorine. during wastewater reuse or rejection, the number of
So, the role of this form of residual chlorine could not be faecal coliforms or streptococci must be less than 103
disregarded compared with free chlorine. In fact, free bacteria per 100 ml (White, 1976). In this study, this
chlorine is considered as the best disinfectant, but the objective was reached after contact times of 30, 20 and 10
role of combined chlorine in the bacterial reduction is min following the injection of a concentration of sodium
not negligible (Anonymous, 1989). hypochlorite of, respectively, 6.5, 8.6 and 13.6 mg/l.
3.2. Kinetic study of water disinfection by chlorine 3.3. Modelling of the kinetics of disinfection
The experimental methodology adopted consisted in It is important to note that the approach to the ki-
measuring simultaneously residual chlorine contents netics of microorganism inactivation is generally em-
Table 1
Log reductions of faecal coliforms and faecal streptococci as a function of time and chlorine concentration
Faecal coliforms Faecal streptococci
Chlorine Time Free Monochlor- Dichlor- Trichlor-
(mg/l) (min) chlorine amines (mg/l) amines (mg/l) amines (mg/l)
(mg/l)
(N/N0) Reductiona (N/N0) Reduction
6.5 2 0.0339 1.47 0.1185 0.92 1.62 � 0.37 3.45 � 0.38 0.97 � 0.20 4.10 � 0.88
5 0.0324 1.49 0.0372 1.43 1.22 � 0.26 1.77 � 0.32 1.07 � 0.48 1.90 � 0.54
10 0.0234 1.63 0.0234 1.63 1.25 � 0.15 2.52 � 0.24 0.47 � 0.05 2.10 � 0.40
20 0.0100 2.00 0.0135 1.87 1.35 � 0.15 2.47 � 0.85 0.52 � 0.12 2.40 � 1.20
30 0.0018 2.75 0.0020 2.69 1.40 � 0.12 1.92 � 0.42 0.67 � 0.14 0.93 � 0.22
40 0.0009 3.04 0.0005 3.27 1.40 � 0.12 ND ND ND
8.6 2 0.0170 1.76 0.1632 0.78 2.68 � 0.69 5.62 � 0.99 1.55 � 0.60 9.60 � 0.70
5 0.0174 1.75 0.0724 1.32 1.72 � 0.28 4.70 � 1.14 1.78 � 0.58 6.40 � 2.50
10 0.0022 2.65 0.0100 2.00 3.30 � 0.97 4.45 � 1.02 0.95 � 0.52 6.46 � 0.60
20 0.0018 2.74 0.0052 2.28 1.52 � 0.22 4.87 � 0.28 0.72 � 0.23 4.00 � 1.86
30 0.0005 3.28 0.0007 3.12 2.97 � 0.70 2.32 � 1.16 0.60 � 0.18 0.35 � 0.04
40 0.0005 3.28 0.0007 4.12 2.52 � 0.42 ND ND ND
13.6 2 0.01000 2.00 0.0575 1.24 2.48 � 0.34 10.15 � 0.30 0.60 � 0.17 12.00 � 3.20
5 0.00120 2.92 0.0087 2.06 3.15 � 0.25 7.65 � 1.04 1.88 � 1.04 18.00 � 1.97
10 0.00091 3.04 0.0004 3.36 4.62 � 1.04 5.80 � 1.20 0.68 � 0.35 8.60 � 1.80
20 0.00038 3.41 0.00004 4.36 3.50 � 0.28 6.35 � 0.28 1.62 � 0.36 8.20 � 2.30
30 0.00034 3.45 0.00014 3.84 1.22 � 0.05 7.48 � 0.58 1.08 � 0.32 10.30 � 1.00
40 0.00019 3.70 0.00004 4.36 1.72 � 0.24 ND ND ND
a
Logarithmic units � log (N/N0); N: Number of micro-organisms at the instant t; N0: Number of micro-organisms at the instant t � 0; �: Standard
error.
A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93 89
pirical, based on laboratory studies, and consequently a In this way, expressions obtained for the rate of
model is only valid in conditions similar to those of its inactivation were
establishment. So, concentration-time (CT) values ex-
N
for faecal coliforms: � exp 0:1046 C1:1T
pressed in mg.min/l were calculated by mathematical
N0
integration of the concentration of residual free chlorine
with a coe�cient of determination R2 of 0.12.
in water versus time. In this paper only results of the
models of Chick-Watson and Collins-Selleck will be N
for faecal streptococci: � exp 0:1635 C0:7T
considered as a reference and the whole results obtained
N0
with the di�erent concentrations of chlorine will be
with a coe�cient of determination R2 of 0.42.
combined in order to establish an expression for the
An illustration of these adjustments is given in Fig. 2.
kinetics of disinfection.
Fig. 2 shows an important variation between the
measured and the calculated values. Consequently, the
3.4. Chick-Watson model
model of Chick-Watson was not representative of the
kinetics of disinfection. Therefore, a second approach to
The expression of the kinetics of disinfection ac-
modelling was adopted and an initial microbial reduc-
cording to the model of Chick-Watson is given as fol-
tion, just at the moment of contact of water with chlo-
lows: dN=dt � KCnN with N is the number of
rine, was considered. The model becomes in this case:
microorganisms, C the concentration of residual free
N=N0ą � A exp KCnT ą with A is the initial reduction
chlorine, n the coe�cient of dilution, which is a function
just at the moment of contact of water with chlorine,
of the quality of water, and K is the coe�cient trans-
The expressions obtained for the rate of reduction
lating the disinfecting power.
were:
Parameters to identify are K and n. By using the in-
N
tegrated form of the model and by changing to the
for faecal coliforms: � 0:011 exp 0:0369 C1:1T
N0
logarithm:
with a coe�cient of determination R2 of 0.63.
N
ln ln � ln Ką � n ln Cą � ln T ą;
N
N0
for faecal streptococci:
N0
and with the help of a linear regression, we can deter-
� 0:0727 exp 0:1065 C0:7T
mine the values of K and n.
Fig. 2. Determination of the kinetic of disinfection of faecal coliforms and faecal streptococci according to the model of Chick-Watson. N: Number
of micro-organisms at the instant t; N0: Number of micro-organisms at the instant t � 0; C: Free chlorine concentration; n � parameter n of the
model; T: Time; x � CnT ; Symbols, measured; lines, calculated.
90 A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93
with a coe�cient of determination R2 of 0.78. An il- N
� 1 for CT 6 s;
lustration of these adjustments are given in Fig. 3.
N0
Considering, n
N s
� for CT P s:
N0 CT
v�������������������������������������������������������������
" #2
u
u
By exploiting all experimental points, and by changing
tX N N ;
�
to the logarithmic form (ln N=N0ą � n ln są n
N0 cal N0 exp
ln CT ą), the values of s and n were determined using a
linear adjustment.
which is a parameter representative of the deviation
The obtained expressions were:
among calculated and measured values, the couples of
For faecal coliforms:
values of before ( ) and after ( ) modi�cation of the
0 m
N
model ( � 1.2250; � 0:0393) and ( � 0.9200;
0 m 0 � 1 for CT 6 0:2028;
N0
� 0:1319), obtained, respectively for faecal coliforms
m
1:2664
and faecal streptococci, indicated that the modi�ed N 0:2028
� for CT P 0:2028 with r2 � 0:69:
model of Chick-Watson �N=N0ą � A exp KCnT ą�
N0 CT
better described the kinetics of bacterial disinfection
For faecal streptococci:
than did the original form of the model
N
�N=N0ą � exp KCnT ą�.
� 1 for CT 6 1:9068;
This �nding is also con�rmed by Fig. 3 which indi- N0
2:276
cates that the modi�ed model of Chick-Watson de-
N 1:9068
� for CT P 1:9068 with r2 � 0:80:
scribes the kinetics of bacterial disinfection when an
N0 CT
initial reduction was considered.
The model of Collins-Selleck has been used by Qualls
and Johnson (1985) and Montgommery (1985) for dif-
3.5. Model of Collins-Selleck ferent kinds of wastewater. In those studies, chlorine
and dioxide of chlorine were used as disinfectants. These
The same procedure was applied for the model of authors reported s � 4:06 and n � 2.82 for faecal coli-
Collins-Selleck. Parameters of identi�cation of this forms. These values are very di�erent from those ob-
model are s and n with tained in our study (s � 0:2028 and n � 1.266), which
Fig. 3. Determination of the kinetic of inactivation of faecal coliforms and faecal streptococci according to the model of Chick-Watson with an
initial reduction just at the moment of contact of water with chlorine. N: Number of micro-organisms at the instant t; N0: Number of micro-or-
ganisms at the instant t � 0; C: Free chlorine concentration; n � parameter n of the model; T: Time; x � CnT. Symbols, measured; lines, calculated.
A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93 91
Fig. 4. Determination of the kinetic of disinfection of faecal coliforms and faecal streptococci according to the model of Collins-Selleck. N: Number
of micro-organisms at the instant t; N0: Number of micro-organisms at the instant t � 0; C: Free chlorine concentration; m � parameter m of the
model; T: Time. Symbols, measured; lines, calculated.
may be explained by the quality of the water and the For faecal coliforms:
operating conditions.
N
Fig. 4 shows rather large discrepancy between the
� 1 for C1:8T 6 0:2484;
N0
measured and the theoretical values for faecal coliforms,
1:1775
indicating that the model of Collins-Selleck was not N 0:2484
� for C1:8T P 0:2484 with r2 � 0:74:
representative of the obtained experimental results.
N0 C1:8T
In order to improve the representativeness of this
For faecal streptococci:
model, a value m was imposed on the concentration of
residual chlorine, since it appeared clearly from the Figs.
N
� 1 for CT 6 1:5783;
2ą4 that the concentration of chlorine inŻuenced the
N0
output of disinfection more than did the time of contact.
2:3091
N 1:5783
Indeed, for a �xed contact time, the reduction of faecal
� for CT P 1:5783 with r2 � 0:80:
N0 C0:68T
coliforms and faecal streptococci was as great as the
concentration of applied chlorine was high. By contrast,
Fig. 5 indicates, particularly for faecal coliforms, that
for a �xed chlorine concentration, bacterial reduction
the model of Collins-Selleck in the modi�ed form:
progressed relatively slowly as a function of the time of
N=N0 � s=CmT ąn allows a better description of the ki-
contact.
netics of decontamination than does its original form:
The model becomes in this case:
N=N0 � s=CT ąn:
N
Indeed, when we calculated the deviation
� 1 for CT 6 s;
N0
r�������������������������������������������������������������
h i2
X
n
N s
� for CT P s: � N=N0ącal N=N0ąexp
N0 CmT
and the parameters to be identi�ed are s, n and m.
for the two models, the values obtained according to the
By changing to the logarithm:
modi�ed form of the model of Collins-Selleck were
lower than those corresponding to the original form of
N
ln � n ln są nm ln Cą n ln T ą;
the same model (Table 2). Also, the di�erent expressions
N0
obtained according to the kinetic approaches of both
the values of n, m and s were determined using a linear Chick-Watson and Collins-Selleck are reported in
regression. The expressions obtained were: Table 2.
92 A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93
Table 2
Expressions obtained according to the kinetic models studieda
Bacteria Model Expression R2
N
FC Chick-Watson � exp 0:1046C T ą 0.12 1.2250
N0
N
Chick-Watson modi�ed � 0:011 exp 0:0269C1:1 T ą 0.63 0.0393
N0 1:2664
N 0:2028
Collins-Selleck � 0.69 0.0327
N0 C T
1:1775
N 0:2484
Collins-Selleck modi�ed � 0.74 0.0248
N0 C1:8 T
N
FS Chick-Watson � exp 0:1635C0:7 T ą 0.42 0.9200
N0
N
Chick-Watson modi�ed � 0:0727 exp 0:106C0:7T ą 0.78 0.1319
N0 2:276
N 1:9068
Collins-Selleck � 0.80 0.2227
N0 C T
2:3091
N 1:5738
Collins-Selleck modi�ed � 0.80 0.1900
N0 C0:68 T
a
FC: Faecal coliforms, FS: Faecal streptococci, R2: Coe�cient of determination, : Deviation among calculated and measured values, N: Number of
micro-organisms at the instant t; N0: Number of micro-organisms at the instant t � 0; C: Free chlorine concentration; T: Time.
Fig. 5. Determination of the kinetic of disinfection of faecal coliforms and faecal streptococci according to the modi�ed model of Collins-Selleck. N:
Number of micro-organisms at the instant t; N0: Number of micro-organisms at the instant t � 0; C: Free chlorine concentration; m � parameter m of
the model; T: Time; x � CmT . Symbols, measured; lines, calculated.
4. Conclusions tact of water with chlorine ln N=N0ą �
A exp KCnT ą, described very well the kinetics of
The following conclusions may be drawn from the disinfection of faecal coliforms and faecal strep-
present kinetics study: tococci.
� Monochloramines and trichloramines appeared as � The same remarks were valid for the model of Col-
the most important residual chlorine forms as com- lins-Selleck, which, in modi�ed form, N=N0 �
pared to free chlorine and dichloramines. s=CmT ąn described the kinetics of disinfection better
� The high levels of trichloramines showed clearly that than did the original form.
the reaction of chlorine with ammoniacal nitrogen is
very fast and that evolution of chlorine into trichlor-
amines is carried out in a time shorter than 1 min. Acknowledgements
� The original model of Chick-Watson ln N=N0ą �
KCnT was not able to describe the inactivation ki- This investigation was supported by grants from the
netics of indicator bacteria. Therefore, a modi�ca- International Foundation for Science (H-2327, IFS,
tion, based on the same model but after taking into Sweden) and from the CEE (Avicenne No. 93 AVI 054).
consideration an initial inactivation during the con- We thank Professor Jean J. Damelincourt, Centre de
A. Hassen et al. / Bioresource Technology 72 (2000) 85ą93 93
Pourmoghaddas, H., Stevens, A., 1995. Relationship between Triha-
Physique des Plasmas et Applications de Toulouse,
lomethane and Halocetic acids with total organic halogen during
University Paul Sabatier, France, for his help.
chlorination. Water Res. 29, 63ą66.
Qualls, R.G., Johnson, J.D., 1985. Modelling and e�ciency of
ultraviolet disinfection systems. Water Res. 19, 1039ą1046.
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