Sewage Treatment Processes

The following is a brief description of treatment standards of effluent. It should be noted that the strict definition of treatment varies among water authorities. The specific standards of treatment is determined by an EPA licence. The more polluted the effluent and/or the higher the treatment desired, the more energy intensive and costly it is to treat effluent.

Primary Sewage Treatment is the lowest treatment standard where solids are removed from waste water. Disinfection is included if this is the only level of treatment. Wastewater often defined as 'Class D or E'.

Secondary Sewage Treatment is the next level of treatment where a large amount of oxygen demanding organisms and suspended solids are removed. Many bacteria and viruses such as strains of hepatitis meningitis are not removed by this treatment. This effluent has restricted levels of reuse. For example can not be sprayed on vegetables with leaves but can be drip filtered into the roots of vines. Wastewater often defines as 'Class C'.

Tertiary Sewage Treatment is the further removal of oxygen demanding organisms as well as removal of nutrients such as phosphorus and nitrogen. Many bacteria and viruses such as strains of hepatitis meningitis are not removed by this treatment. This effluent has unrestricted horticultural and agricultural use. Wastewater often defined as 'Class A'

Potable Water Treatment is classed as effluent that has been treated to a standard safe to drink according to drinking water guidelines. This may be achieved by Ultra Violet Irradiation, Chlorination, Membrane Treatment (Reverse Osmosis), Peroxyacetic Acid Addition (PAA) and Advanced Oxidation. UV irradiation, Oxidation andReverse Osmosis are recognised as the best techniques to remove bacteria and viruses from effluent. Defined as 'Potable'.