14 Natural gas sweetening process will generate high concentration of amine in
wastewater and the concentration of amine may reach as high as 15 – 50 by weight
in practice [13]. Hence, the wastewater from the gas processing unit needs to be treated before discharging into the environment [26
– 27].
Figure 2. 3 Constituent of wastewater.
2.2.3 Wastewater Treatment Methods
Removal of contaminants in wastewater can be carried out by three methods i.e. physical, chemical, and biological. These methods are typically grouped as physical,
chemical, and biological unit operations [22]. However in actual wastewater treatment plants WWTP, several methods are used individually or in combination with each
other. Physical unit operations are commonly used to remove the suspended material in the wastewater and this process is to be used in the preliminary treatment. These
processes include: the screening, mixing, flocculation, sedimentation, floatation, filtration, and gas transfer volatilization and gas stripping [22]. Chemical unit
processes are used for the removal of contaminants inside the wastewater by chemical reaction. In this process, chemicals are added into the wastewater to form more stable
components or break down the contaminants into harmless components [22]. Biological unit processes are the removal of biodegradable contaminants present in
the wastewater by involving biological activity. In this process, the biodegradable
15 organic contaminants are changed into gases that can escape into atmosphere or into
the biological cell tissue, which can be removed by settling [22].
2.2.4 The Hybrid Process of Advanced Oxidation followed by Biological
Treatment
Effluentswastewater with high concentration of alkanolamine will be generated and leaving the natural gas processing unit and these effluents are often toxic to the
bacteria and hence can not be degraded by biological oxidation. Advanced oxidation process is recently chosen by many researchers to treat recalcitrant organic
contaminants in the effluent. Fenton’s treatment, UVH
2
O
2
treatment, and UVO
3
treatment are commonly used to degrade the recalcitrant organic contaminant into smaller fragments, which are biodegradable. In order to achieve a complete
degradation of recalcitrant organic contaminant, by coupling of chemical oxidation as pre-treatment and biological oxidation as post-treatment is conceptually
beneficial to increase the overall treatment efficiency [28 – 30], as illustrated in
Figure 2.4.
Figure 2. 4 The concept of coupling AOP-based pre-treatment with biological post-
treatment [28].
16
2.3 Advanced Oxidation Processes
