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Effluent Standards

Domestic sewage treatment is mainly designed to produce an effluent low in solids and organic. However, other treatments, which remove the nutrients alter the pH or disinfect the effluent may be added depending on the receiving environment for the effluent.

Standards have been established for the quality of effluent discharged from treatment plants to receiving waters. These take the form of acceptable upper limits for various effluent contaminants. Effluents from treatment plants are regularly sampled and tested in laboratories to ensure that these standards are being met and that treatment plants are being operated correctly.

Parameter Unit Standards
Temperature C 40 40
pH Value - 6.0-9.0 5.5-9.0
BOD5 at 20C mg/l 20 50
COD mg/l 50 100
Suspended Solids mg/l 50 100
Mercury mg/l 0.005 0.05
Cadmium mg/l 0.01 0.02
Chromium, Hexavalent mg/l 0.05 0.05
Arsenic mg/l 0.05 0.10
Cyanide mg/l 0.05 0.10
Lead mg/l 0.10 0.5
Chromium, Trivalent mg/l 0.20 1.0
Copper mg/l 0.20 1.0
Manganese mg/l 0.20 1.0
Nickel mg/l 0.20 1.0
Tin mg/l 0.20 1.0
Zinc mg/l 1.0 1.0
Boron mg/l 1.0 4.0
Iron (Fe) mg/l 1.0 5.0
Phenol mg/l 0.001 1.0
Free Chlorine mg/l 1.0 2.0
Sulphide mg/l 0.50 0.5
Oil and Grease mg/l Not Detectable 10.0

The pollutants in sewage are measured in order to better understand and thus facilitate the treatment of sewage as well as to examine the effects of effluent or treated sewage on the environment.

Effluent from all public sewage treatment plants is sampled at regular intervals and tested in modern laboratories to ensure that it meets the required standards. Tests are carried out as part of a monitoring programme in keeping with Indah Water's operational license conditions and to ensure the efficient operation of treatment processes.

This provides for a cleaner and safer environment that improves the living conditions of Malaysians. The two most important parameters measured are Biochemical Oxygen Demand (BOD) and Suspended Solids (SS).

BOD is a measure of the amount of oxygen that sewage consumes over a given time. High BOD is significant because it means that sewage will rapidly consume all the naturally-dissolved oxygen in streams, rivers and lakes, thus killing off all aquatic life, and rendering the water septic and foul-smelling. SS is a measure of the undissolved material in sewage. High SS leads to sludge deposits in the waterways, thus causing significant environmental deterioration.

Effluent that is discharged upstream of a water supply intake should meet Standard A, while effluent that is discharged downstream has to meet Standard B. These standards are set by the Environmental Quality Act 1974.

Standard BOD (mg/L) SS (mg/L)
A 20 50
B 50 100