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Table 2.1 Malaysian effluent standard regulation for sewage and industrial effluents,
environmental quality act 1974 [Laws of Malaysia; act 127. 1999]
Parameters Unit
Standard A Standard B
Temperature ˚C
40 40
pH value -
6.0 – 9.0
5.5 – 9.0
BOD5 at 20˚C mgL
20 50
COD mgL
50 100
Suspended Solids mgL
50 100
Phenol mgL
0.001 1.0
Free chlorine mgL
1.0 2.0
Sulphide mgL
0.50 0.05
Oil and grease mgL
Non detectable 10.0
2.1.3 Wastewater treatment Methods
Essentially, contaminants in the waste water are removed by three major methods
–physical, chemical and biological–. The removal methods are usually classified as physical unit operations, chemical unit operations, and biological unit
operations Metcalf and Eddy, 1991. However, wastewater treatment in a centralized wastewater plant WWTP, rarely uses any individual treatment method in isolation.
The WWTP consists of several treatment techniques in combination:
a. Physical Unit Operations: The physical unit operations include screening,
mixing, flocculation, sedimentation, flotation, filtration, and gas transfer. These methods are generally first to be utilized in the wastewater
treatment. Physical treatment is predominantly used to remove the suspended materials Metcalf and Eddy, 1991.
b. Chemical Unit Processes: Removal of contaminants from wastewater by
addition of chemicals or by other chemical reactions is known as chemical
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unit processes. Precipitation, adsorption, and disinfections are the common examples used in the wastewater treatment. The chemicals that are added
to the wastewater directly react with the pollutants to form more stable chemical or act as flocculants or coagulant that change the configuration
of pollutant. In other instances the chemical reagents break down or decompose the pollutant compounds to harmless end products.
c. Biological Unit Processes: These constitute removal processes of
contaminants from wastewater by biological activity. Biological unit processes is used primarily to remove the biodegradable organic
substances colloidal or dissolved in wastewater.
In industrial applications, treatment units involve several steps depending on the characteristic of wastewater and specific treated wastewater objectives. Since
each method is effective in a particular situation, the process of selection is very important to obtain the best performance and to reduce operational cost as well as
investment cost.
As mentioned above, unit operations and processes are grouped together to provide various levels of treatment. Historically, the term “preliminary” andor
“primary” referred to physical unit operation; “secondary” referred to chemical and biological unit processes; and “advanced” or “tertiary“ referred to combination of all
three unit processes. However, a more rational approach is first to establish the level of contaminant removal treatment required before the wastewater can be made fit
for reuse or discharge to the environment. The required unit operations and processes necessary to achieve that required level of treatment can then grouped on the basic
fundamental consideration Metcalf and Eddy, 1991.
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2.2 Natural Gas Sweetening Process Waste
