1 CHAPTER 1
INTRODUCTION
1.1. Background of Research
Methyldiethanolamine MDEA is one of the common alkanolamines used in the petrochemical industries such as natural gas processing plant, refineries, and ammonia
gas plant. MDEA in water solution is used as a solvent for the absorption of acidic gases such as CO
2
and H
2
S, which are present in natural gas. Petrochemical industries discharge large amount of alkanolamine in wastewater during the cleaning,
maintaining and scheduled inspection of the plant. The presence of this contaminant generates toxic and often non biodegradable substances into the aqueous phase,
resulting in severe environmental pollution problem. The toxicity of this wastewater is due to its high content of nitrogen and dissolved organic compounds i.e. chemical
oxygen demand COD concentration is approximately 500000 ppm. Toxicity and non biodegradability of alkanolamine have been reported by Sandin et al. [1], Duran-
Moreno et al. [2] and Fürhaker et al. [3], respectively. In the recent two decades, advanced oxidation processes AO
P’s are underlined by significant number of investigations for their application in wastewater treatment,
especially for the treatment of recalcitrant organic contaminant which are difficult to degrade using conventional biological oxidation unit. The AOP
’s can reduce the concentration and toxicity of contaminant to certain limits and could not achieve
complete degradation of contaminant present in wastewater even though the modification of the experimental conditions has been reported. In addition, the widely
used biological treatment in the removal process of organic and inorganic contaminant in the wastewater could not completely degrade the toxic contaminant
2 since the toxic contaminant often inhibited or even eliminated the bacteria populations
in the conventional wastewater treatment plants. Therefore, a hybrid process i.e. AOP’s prior to biological treatment is required to achieve a complete degradation of
contaminant. In other words, the toxic wastewater should be pre-treated using AOP’s
before biological treatment. In terms of refinery wastewater, the wastewater is commonly generated with high
concentration of alkanolamine and often difficult to degrade using the conventional biological degradation. This issue is becoming an interesting research topic for the
degradation study of wastewater containing alkanolamine. Therefore, during the recent decade many researchers started to look for developing alternative
methodstechniques for refinery wastewater treatment. Ali et al. [4] used the ZnOSnO
2
coupled photocatalysts in the presence of UV light 356 nm to degrade MDEA in water solution. They successfully reduced the MDEA and total organic
carbon TOC as much as 39.18 and 23.15 respectively using the photocatalysts for 5 hours of treatment and the initial concentration of MDEA was 1000 ppm. Even
though this treatment could partially remove MDEA and TOC, however a better performance method with high efficiency for the complete degradation of refinery
wastewater may still be required. One of the considerably demonstrated techniques from AOP’s namely, Fenton’s treatment has been well studied to degrade the organic
contaminant that are commonly present in the refinery wastewater. Fenton’s reagent,
a mixture of ferrous sulfate and hydrogen peroxide [5] has been used to treat MEA [6], DEA [7], DIPA [8], and real Qilu refinery wastewater in China [λ]. The Fenton’s
process was found to be more effective due to its rapid oxidation process, but the formation of sludge and their applicability at particular pH condition i.e. acidic pH,
have created a necessity for an alternative technique for the treatment of refinery wastewater. Due to the limitation of photocatalysis low performance for MDEA
degradation and Fenton’s treatment formation of slugde during the process and
applicable only in the low pH, Arrif et al. in 2010 [10] used UVH
2
O
2
process to treat monoethanolamine MEA in water solution, and a successful degradation was
reported. The UVH
2
O
2
has many advantages such as no formation of sludge during the process, high capability of hydroxyl radical production, and applicable for a wide
range of pH.
3 Based on these advantages, in this present research the UVH
2
O
2
technique is proposed to treat MDEA in water solution. MDEA is commonly chosen as the
scrubbing agent since this alkanolamine can be used for the absorption and stripping of hydrogen sulfide H
2
S and carbon dioxide CO
2
and also can be used to remove carbonyl sulfide COS [2]. Even though MDEA is widely used as the scrubbing
agent during sweetening process of acidic gas from natural gas, the study pertaining to the degradation of MDEA present in effluents are highly limited.
1.2 Problem Statement
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