71
3.3.10 Measurement of UV Intensity
During the study of effect of UV intensity in the mineralization process of MDEA using combination of UV and H
2
O
2
, the UV intensity used was varied. Variation of UV intensity was made by connecting the UV lamp to adjustable dimmer. The
different UV intensities produced were measured using UV radiometer Cole-Parmer model: 97651-10 with sensor UV at 254 nm model: 97651-20.
The factors affecting the optimization process of the degradation of wastewater containing MDEA using UVH
2
O
2
process are the intensity of UV, initial concentration of waste organic contaminant, initial concentration of H
2
O
2
, initial pH and temperature. Based on the preliminary study, the factor of UV intensity and initial
concentration of waste were found to have no optimum value. Hence for the optimization of UVH
2
O
2
process, these two factors were always kept constant at 12.06 mWcm
2
and 1000 ppm of total organic carbon. The UV intensity was chosen at this value due to the limitation of UV lamp available in the laboratory. This UV
intensity of 12.06 mWcm
2
was the highest intensity that could be provided by the available facilities in the laboratory. Increasing UV intensity would increase the
degradation rate, thus the highest UV intensity can be used for better efficiency. Similar trend without optimum value was found for the initial concentration of waste.
In this case, increasing initial concentration of waste would decrease the degradation rate. Hence, 1000 ppm of total organic carbon was chosen as the initial concentration
of waste since the degradation process was easier to monitor.
3.4 Statistical Design of Experiments DOE for Optimization of Degradation
Process by Using UVH
2
O
2
Optimization process was carried out using response surface methodology RSM. Portable Statgraphics Centurion 15.2.11.0 was used for RSM analysis. RSM is a
method used in modeling and analysis of problem in which a response of importance get influenced by several factors. The objective of this method is to optimize this
72 response. Response surface is normally represented graphically where the contour
plot are often drawn to visualize the shape of the response surface [80]. Determination of the optimum conditions for the degradation process was carried
out according to the Box-Behnken design. This design was chosen since for three factors evaluated, the Box-Behnken design offers some advantage in requiring a fewer
number of runs compared to other design such as central composite circumscribed CCC design and central composite inscribed CCI. Three level factorial designs
which consist of a 2
2
full factorial with 3 center points were created. The three level factors chosen based on the preliminary experiment and coded as low -1, middle 0,
and high +1. The factors included initial concentration of H
2
O
2
range 0.12 M to 0.24 M, pH range 7 to 11, and temperature range 30ºC to 50ºC. Percentage of
TOC removal was measured as influence response. The levels indicated the presence of a curvature which wished-for that the experimental ranges were relatively close to
the optimum. When the process is close to optimum, the second order model that incorporates curvature is represented in Equation 3.6.
j i
j i
ij i
k i
ii i
k i
i o
x x
x x
y
2
1 1
3.6
where y is the predicted response, is the intercept,
i
is the linear effect,
ii
is the squared effect,
ij
represents the interaction effect , and ε is the error term. After
conducting the screening of factors by the factorial design, a response surface analysis was employed to optimize the highest TOC removal of the waste. The results of
experimental design was analyzed using Portable Statgraphics Centurion 15.2.11.0 statistical software to estimate the dependent response variable and to find the effects,
coefficients, standard deviation of coefficients as well as other parameters of the model. Optimized condition was obtained from contour plot graphically and also by
solving the polynomial regression equation. Quality of fit was expressed by the coefficient of determination R
2
. Statistical significance was analyzed using the analysis of variance ANOVA, with 5 probability level [108].
73 CHAPTER 4
RESULTS AND DISCUSSION
The present chapter deals with the details of the results obtained in the present research and the interpretation of the same. Accordingly the discussion includes the
details of the preliminary studies conducted, proposal of degradation mechanism of MDEA, kinetic study, UVH
2
O
2
treatment of a real effluent obtained from a refinery plant PPMSB, biodegradability test of partially degraded simulated wastewater and
real effluent and then the estimation of electrical energy efficiency of the UVH
2
O
2
process. The detailed discussion follows:
4.1 Preliminary Studies
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