Journal of Environmental Treatment Techniques
2020, Volume 8, Issue 3, Pages: 900-907
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.2 Nanofiltration membrane
The NF270 membrane (Dow-Filmtec, Minneapolis, MN) was
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Materials and methods
2
.1 Background of statistical analysis
selected for this study. According to the manufacturer, it is a thin-
film composite polyamide membrane that is widely used for water
and wastewater treatment application. This is a loose NF
membrane with a relatively high permeability (of approximately
1
Statistical analysis is useful for exploring and examining the
basic features of the data prior to applying statistical tests and
fitting statistical models. Because the fact that many factors
influence some phenomena, it is necessary to calculate the
interaction among phenomena. In order to attain this, multiple
regression methods can be used. Multiple regression has taken a
very significant place in statistical science. It is a method of
analysis for assessing the strength of the relationship between a
set of explanatory variables known as independent variables, and
a single response or dependent variable. Applying multiple
regression analysis to a set of data results in what are known as
regression coefficients, one for each explanatory variable [20,21].
Regression analysis is a mathematical measure of the average
relationship between two or more variables in terms of the
original units of the data. The concept of regression analysis
involves finding the best relationship between variables.
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1 L/bar m h). At pH 4 and above, this membrane is negatively
charged [23]. The flat sheet membrane samples were stored dry
before use.
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.3 Trace organic contaminants, analytical chemicals and
reagents
The target TrOCs for this research have been chosen from the
major classes of EDCs, PhACs and DBPs. They have diverse
physicochemical properties such as hydrophobicity, charge,
solubility, and molecular size. A stock solution was prepared at a
concentration of 1 mg/mL in pure methanol. A working solution
of these TrOCs was also prepared in pure methanol. Both these
solutions were stored in a freezer at -18 ºC prior to use.
Chemical solutions and feed waters were prepared with Milli-
Q water. Both the solvents used for solid phase extraction and
analysis of samples including methanol and dichloromethane,
purchased from Sigma-Aldrich (Sydney, Australia). Internal
standard of bisphenol A-d16 and N,O-bis (trimethylsilyl)
In case of researching relationship between two phenomena
and in case of prediction of the value of dependent variable, first
to identify variables and then to find out random sample n size for
the chosen values of dependent variables. Suppose that k
phenomenon is identified as independent variable (predictor), or
x
i
, i = 1, 2,…, k, and Y as dependent random variable. The whole
multiple linear model can be presented as one equation for
dependent variable Y
trifluoroacetamide
(BSTFA)
containing
1
%
of
trimethylchlorosilane (TMCS). Pyridine used in the derivatization
process. All reagents and chemicals were purchased from Sigma-
Aldrich (Sydney, Australia).
i
:
Y
i
= β
0
+ β
1
x
1
+ β
2
x
2
+ …+ β
k
x
k
+ ε
i
(1)
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.4 Experimental protocol
A laboratory scale cross flow NF/RO system consisted of a
where Y
of independent variable, β
regression coefficient), and ε
random error which has normal distribution, zero mean and
constant variance. The whole regression model can be estimated
by the sample regression model using least squares fitted
i
is dependent random variable, x
1
, x
2
, …, x
k
are values
0
, β
1
, …, β
k
are model parameters
stainless steel NF/RO membrane cell with an effective surface
area of 40 cm and channel height of 2 mm, a stainless steel feed
(
i
is a supporting element, or a
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reservoir, and a high pressure pump (Hydra-Cell, Wanner
Engineering Inc., Minneapolis, MN) was used. The temperature
of the feed solution was controlled by a chiller/heater (Neslab
RTE 7, Thermo Scientific Inc., Waltham, MA, USA) equipped
with a stainless steel heat exchanger coil which was submerged
directly into the feed reservoir. A digital flow meter (Optiflow
(prediction) equation (obtained by minimizing Error Sum of
Squares, SSE):
y
i
= b
0
+ b
1
x
1
+ b
2
x
2
+ …+ b
k
x
k
(2)
1
000, Agilent Technologies, Palo Alto, CA) connected to a PC
was utilized to measure permeate flow, and the cross flow was
monitored with a rotameter.
where y
i
is adjustable or foreseen value of dependent variable Y
, …, x are values of independent variables, and b , b , …,
are estimations of unknown parameters β , β , …, β . Once a
i
,
x
b
1
, x
k
2
k
0
1
The rejection of TrOCs was performed in a background
0
1
k
electrolyte solution containing 10 mM of NaCl, 1 mM of CaCl
2
,
regression model has been constructed, it may be important to
confirm the goodness of fit of the model and the statistical
significance of the estimated parameters. Commonly used
techniques to verify the goodness of fit include the R square,
Adjusted R square, Multiple R, and hypothesis testing. Statistical
significance can be verified by a Fisher distribution (F-test) of the
overall model, followed by tests of the individual parameters
using Student's t-distribution (t-test) [22].
The fit of a multiple regression model can be judged with
calculation of the multiple correlation coefficient, Multiple R,
defined as the correlation between the observed values of the
response variable and the values predicted by the model. The
and 1 mM of NaH PO (pH 7) and conducted over 24 hours. Prior
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4
to each experiment, the NF270 membrane samples were gently
washed with copious Milli-Q water to remove any preservatives.
They were then compacted using Milli-Q water at 1,000 kPa for
at least one hour until a stable permeate flux had been obtained.
The background electrolyte solution was then added to the feed
reservoir, and made up to the total feed volume of 10 litres.
During the experiment, the feed reservoir temperature and cross
flow velocity were kept constant at 20 ± 0.1 °C and 42 cm/s,
respectively. The permeate flux was set to the manufacturer’s
2
quoted nominal membrane flux of 42 L/m h throughout the
2
experiment. Both permeate and retentate were recirculated to the
feed reservoir. A mixture of 25 target TrOCs was then added to
the feed reservoir to obtain a concentration of 25 μg/L of each.
The feed solution pH was kept constant during the experiments
by periodically adding a small amount of 1 M of NaOH or 1 M
HCl. Approximately 100 mL of feed and permeate samples were
taken at specific times. Samples were stored in clean glass bottles,
squared value of R (R ) gives the proportion of the variability of
the response variable accounted for by the explanatory variables.
Adjusted R square used to compare models with different sets of
independent variables in terms of predictive capabilities. Analysis
of variance (ANOVA) will provide an F-test of the null
hypothesis that each of b
words that R is zero [21].
0
1 k
, b , b2,… b , is equal to zero, or in other
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