Wastewater
Treatment
ENGR. DANIEL G. SIERRA
Wastewater Treatment
A process to convert wastewater - which is water
no longer needed or suitable for its most recent
use - into an effluent that can be either returned
to the water cycle with minimal environmental
issues or reused.
Main water pollutants
Pollutant Main representative parameters Possible effect of the pollutant
Suspended solids Total suspended solids Aesthetic problems
Sludge deposits
Pollutants adsorption
Protection of pathogens
Biodegradable Biochemical oxygen demand Oxygen consumption
organic matter Death of fish
Septic condition
Nutrients Nitrogen Excessive algae growth
Phosphorus Toxicity to fish (ammonia)
Illness in new-born infants (nitrate)
Pollution of groundwater
Pathogens Coliforms Water-borne diseases
Main water pollutants
Pollutant Main representative parameters Possible effect of the pollutant
Non-biodegradable Pesticides Toxicity (various)
organic matter Some detergents Foam (detergents)
Others Reduction of oxygen transfer (detergents)
Non-biodegradability
Bad odors (e.g. phenols)
Metals Specific elements Toxicity
(As,Cd,Cr,Cu,Hg,Ni,Pb,Zn,etc.) Inhibition of biological sewage treatment
Problems of agricultural use of sludge
Contamination of groundwater
Inorganic Total dissolved solids Excessive salinity – harm to plants
dissolved solids Conductivity Toxicity to plants (some ions)
Problems with soil permeability (sodium)
Sources of wastewater
• Residences
◦ human and animal excreta and waters used for washing,
bathing, and cooking.
• Commercial institution
• Dairy and industrial establishment
◦ slaughterhouse waste, dairy waste, tannery wastewater,
etc.
Types of wastewater treatment
Physical water treatment – physical methods are
used for cleaning the wastewater. No chemicals are
involved in this process such as screening, and
sedimentation. Aeration is also a physical
treatment process.
Types of wastewater treatment
Biological water treatment – This uses various biological
processes to break down the organic matter present in
wastewater, such as soap, human waste, oils and food.
Microorganisms metabolize organic matter in the
wastewater in biological treatment.
Types of wastewater treatment
Three categories of biological waste treatment
◦ Aerobic processes: Bacteria decomposes the organic matter
and converts it into carbon dioxide that can be used by plants.
Oxygen is used in this process.
◦ Anaerobic processes: Here, fermentation is used for
fermenting the waste at a specific temperature. Oxygen is not
used in anaerobic process.
◦ Composting: A type of aerobic process where wastewater is
treated by mixing it with sawdust or other carbon sources.
Types of wastewater treatment
Chemical water treatment - this treatment involves the use of
chemicals in water.
Chlorine, an oxidizing chemical, is commonly used to kill bacteria
which decomposes water by adding contaminants to it.
Another oxidizing agent used for purifying the wastewater is
ozone.
Neutralization is a technique where an acid or base is added to
bring the water to its natural pH of 7. Chemicals prevent the
bacteria from reproducing in water, thus making the water pure.
Wastewater Treatment
◦Pre-treatment
◦Preliminary treatment
◦Primary treatment
◦Secondary treatment
◦Tertiary treatment
◦Sludge (biosolids) disposal
Pre-treatment
◦Pre-treatment
waste water moves towards the plant by means of gravity. Lift
station pump water are used from low lying areas.
removes large objects and non-degradable materials.
bar screen and grit chamber
Pre-treatment
Bar Screen
- catches large objects
that have gotten into
sewer system such as
bricks, bottles, pieces of
wood, etc.
Pre-treatment
Grit Chamber – removes rocks, gravel, broken glass, etc.
Mesh Screen – removes diapers, combs, towels, plastic
bags, syringes, etc.
Pre-treatment
Suspended Solids – the quantity of solid materials floating in the water
column
B.O.D. = Biochemical Oxygen Demand – a measure of the amount of
oxygen required to aerobically decompose organic matter in the water
Measurements of Suspended Solids and B.O.D. indicate the
effectiveness of treatment processes
Both Suspended Solids and B.O.D. decrease as water moves through the
wastewater treatment processes
Primary Treatment
Primary Treatment
It involves sedimentation of solid waste within the water.
This is done after filtering out larger contaminants within the water.
Wastewater is passed through several tanks and filters that separate water
from contaminants.
The resulting “sludge” is then fed into a digester, in which further
processing takes place.
This primary batch of sludge contains nearly 50% of suspended solids within
wastewater.
Primary Treatment
Primary Treatment
Pre-settling basin, primary sedimentation tanks or primary
clarifiers wherein two hours of detention takes place for
sewage for gravity settling. The tanks are used to settle
sludge while grease and oils rise to the surface and are
skimmed off.
Primary Treatment
Rapid mixing is a process of applying turbulence on the tank
adding chemicals that encourages coagulation to water
streams.
Primary coagulants
◦ aluminum coagulants (aluminum sulfate, aluminum chloride
and sodium aluminate)
◦ iron coagulants (ferric sulfate, ferrous sulfate, ferric chloride
and ferric chloride sulfate)
◦ other chemicals (hydrated lime and magnesium carbonate)
Primary Treatment
Flocculation - a gentle mixing stage, increases the particle
size from submicroscopic microfloc to visible suspended
particles. Microfloc particles collide, causing them to bond
to produce larger, visible
flocs called pinflocs.
Secondary Treatment
Secondary treatment removes the soluble organic matter that
escapes primary treatment.
It also removes more of the suspended solids.
Removal is usually accomplished by biological processes in
which microbes consume the organic impurities as food,
converting them into carbon dioxide, water, and energy for their
own growth and reproduction.
Secondary Treatment
Trickling filter – tank filled with a deep bed of stones. Settled
sewage is sprayed continuously over the top of the stones and
trickles to the bottom, where it is collected for further
treatment. As the wastewater trickles down, bacteria gather
and multiply on the stones.
Secondary Treatment
Secondary Treatment
Activated sludge – consists of an aeration tank followed by a
secondary clarifier. Settled sewage, mixed with fresh sludge that
is recirculated from the secondary clarifier, is introduced into
the aeration tank. The mixture then flows from the aeration
tank into the secondary clarifier, where activated sludge settles
out by gravity.
Secondary Treatment
Secondary Treatment
Oxidation pond – also called lagoons or stabilization ponds, are
large, shallow ponds designed to treat wastewater through the
interaction of sunlight, bacteria, and algae. Mechanical aerators
are sometimes installed to supply yet more oxygen. Sludge
deposits in the pond must eventually be removed by dredging.
Algae remaining in the pond effluent can be removed by
filtration or by a combination of chemical treatment and
settling.
Secondary Treatment
Tertiary Treatment
The aim of tertiary wastewater treatment is to raise the quality of
the water to domestic and industrial standards, or to meet
specific requirements around the safe discharge of water.
More than one tertiary treatment process may be used at any
treatment plant. If disinfection is practiced, it is always the final
process. It is also called "effluent polishing".
The treatment process is chemic/physical process to remove
remaining inorganic compounds, and substances, such as the
nitrogen and phosphorus.
Tertiary Treatment
Filtration is a process that removes particles and other
media of a certain size and larger from liquids. Removing
these particles and debris from a wastewater system allows
the water to be reused within that system.
Sand filtration removes much of the residual suspended
matter. Filtration over activated carbon, also called carbon
adsorption, removes residual toxins
Tertiary Treatment
Carbon filter Tubular membrane filter
Tertiary Treatment
Biological nutrient removal (BNR) is regarded by some as a type of
secondary treatment process, and by others as a tertiary (or
"advanced") treatment process .
Wastewater may contain high levels of the nutrients nitrogen and
phosphorus. Excessive release to the environment can lead to a buildup
of nutrients, called eutrophication.
Nitrogen is removed through the biological oxidation of nitrogen from
ammonia to nitrate (nitrification), followed by denitrification.
Tertiary Treatment
Phosphorus can be removed biologically in a process called enhanced
biological phosphorus removal. In this process, specific bacteria, called
polyphosphate-accumulating organisms (PAOs).
Phosphorus removal can also be achieved by chemical precipitation,
usually with salts of iron (e.g. ferric chloride), aluminum (e.g. alum), or
lime.
Once removed, phosphorus, in the form of a phosphate-rich sewage
sludge, may be dumped in a landfill or used as fertilizer.
Tertiary Treatment
Disinfection. The purpose of disinfection in the treatment of
waste water is to substantially reduce the number of
microorganisms in the water to be discharged back into the
environment for the later use of drinking, bathing, irrigation,
etc.
Common methods of disinfection include ozone, chlorine,
ultraviolet light, or sodium hypochlorite
Energy and nutrient recovery for municipal wastewater treatment
