Wastewater Treatment
                     WASTEWATER TREATMENT
Introduction
• Wastewater treatment is the process of converting 
wastewater into water that can be discharged back 
into the environment. The purpose of wastewater 
treatment is to speed up the natural processes by 
which water is purified.  
Source: www.wwdmag.com 2
Purpose of wastewater 
treatment
• The aim of wastewater treatment is to remove as 
much of the suspended solids as possible before the 
effluent is discharged back to the environment.
Source: www.wwdmag.com 3
How is wastewater 
formed?
• Wastewater is formed by several activities such as 
bathing, washing, using the toilet, and rainwater 
runoff. Wastewater is essentially used water that has 
been affected by domestic, industrial and commercial 
use.
Source: www.wwdmag.com 4
Pollution problems
• There are a number of ways in which wastewater can 
cause pollution problems, considering not all waste 
makes it to wastewater treatment plants. 
• Many cities, particularly older ones, have combined 
sewer systems (CSS), which collect domestic sewage 
in the same pipes as storm water runoff. 
Source: www.wwdmag.com 5
Effects of wastewater 
pollutants
• Decaying organic matter and debris can use up the 
dissolved oxygen in a lake so fish and other aquatic 
biota cannot survive
• Excessive nutrients, such as phosphorus and nitrogen 
(including ammonia), can cause eutrophication, or 
over-fertilization of receiving waters, which can be 
toxic to aquatic organisms
Source: www.usgs.gov 6
Effects of wastewater 
pollutants cont.
• Chlorine compounds and inorganic chloramines can 
be toxic to aquatic invertebrates, algae and fish
• Bacteria, viruses and disease-causing pathogens can 
pollute beaches and contaminate shellfish 
populations, leading to restrictions on human 
recreation, drinking water consumption and shellfish 
consumption
Source: www.usgs.gov 7
What is the process of 
wastewater treatment? 
• There are two main levels of wastewater treatment: 
primary and secondary treatment. 
• In the primary stage, solids are allowed to settle and 
be removed from wastewater. 
• The secondary stage uses biological processes to 
further purify wastewater. Sometimes these stages 
are combined, and in some cases additional 
treatment such as tertiary treatment and advanced 
wastewater treatment are used.
Source: www.wwdmag.com 8
Primary Treatment
• Primary treatment removes material that will either 
float or readily settle out by gravity. 
• This treatment includes the physical processes of 
screening, comminution the act of reducing a 
material to minute particles or fragments grit removal 
and sedimentation. 
Source: www.wwdmag.com 9
Secondary Treatment
• Secondary treatment removes the soluble organic 
matter that escapes primary treatment.
• Secondary treatment also removes more of the 
suspended solids, usually by biological processes in 
which microbes consume the organic impurities as 
food and then convert them into carbon dioxide, 
water and energy. 
Source: www.wwdmag.com 1
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Are there any “natural” 
ways to treat wastewater?
• If nature itself can cleanse water, then imitating 
nature’s processes may be the most effective and 
sustainable ways of treating wastewater. 
• A natural method is called rapid infiltration, which is a 
process where a basin is filled with wastewater, which 
has already gone through a pre-treatment. The 
ground acts as a filter and removes the pollutants 
from the water. 
Source: www.safewater.org 1
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