Biological treatment processes use microorganisms like bacteria and fungi to remove organic matter from wastewater. The most common type is activated sludge, which uses air bubbles in one basin to provide oxygen and mix wastewater and microbes, then a settling basin to remove microbial solids. Trickling filters and biological contactors grow microbial slime on solid surfaces that contact wastewater. Imhoff tanks separate wastewater into an upper settling chamber and lower anaerobic digestion chamber. Anaerobic lagoons treat manure wastewater through microbial breakdown that produces methane and other gases.

1. Biological Processes
Biological treatment methods for
controlling water pollution

2. Water treatment
• Water treatment describes those processes used to make water
more acceptable for a desired end-use.
• These can include use as drinking water, industrial
processes, medical and many other uses.
• The goal of all water treatment process is to remove existing
contaminants in the water, or reduce the concentration of such
contaminants so the water becomes fit for its desired end-use.
• One such use is returning water that has been used back into
the natural environment without adverse ecological impact.
• The processes involved in treating water for drinking purpose
may be solids separation using physical processes such as
settling and filtration, and chemical processes such as
disinfection and coagulation.

3. The Ringsend WWTP in Ireland

4. The Adana West WWTP in Turkey

5. Types of Secondary or Biological
treatment processes
• Aerobic
– Activated sludge
– Trickling filter
– Biological Contactor
• Anaerobic
– Imhoff tanks
– Anaerobic Lagoon

6. Activated sludge
• This is the most common type. It consists in a set
of two basins.
• In the first, air is pumped through perforated
pipes at the bottom of the basin, air rises through
the water in the form of many small bubbles.
• These bubbles accomplish two things.
– provide oxygen form the air to the water
– create highly turbulent conditions that favor intimate
contact between cells, the organic material in the
water and oxygen.

7. • The second basin is a settling tank, where water
flow is made to be very quiet so that the cellular
material may be removed by gravitational
settling.
• Some of the cell material collected at the bottom
is captured and fed back into the first basin to
seed the process.
• The rest is treated anaerobically (= without
oxygen) until it is transformed into a compost-
type material (like soil).

8. • The cost of an activated-sludge system is
chiefly due to the energy required to pump air
at high pressure at the bottom of the aerator
tank (to overcome the hydrostatic pressure of
the water).
• Another disadvantage is that the operation is
accomplished in two separate basins, thereby
occupying a substantial amount of real estate.

10. Trickling filter
• A trickling filter consists in a bed of fist-size
rocks over which the wastewater is gently
sprayed by a rotating arm.
• Slime (fungi, algae) develops on the rock
surface, growing by intercepting organic
material from the water as it trickles down.
• Since the water layer passing over the rocks
makes thin sheets, there is good contact with
air and cells are effectively oxygenated.

11. • Worms and insects living in this “ecosystem”
also contribute to removal of organic material
from the water.
• The slime periodically slides off the rocks and
is collected at the bottom of the
system, where it is removed.
• Water needs to be trickled several times over
the rocks before it is sufficiently cleaned.

12. • Multiple spraying also provides a way to keep
the biological slimes from drying out in hours
of low-flow conditions (ex. at night).
• Plastic nets are gradually replacing rocks in
newer versions of this system, providing more
surface area per volume, thereby reducing the
size of the equipment.

13. Trickling Filter

14. Biological Contactor
• This is essentially a variation on the trickling
filter, with the difference being that solid
material on which slime grows is brought to
the water rather than water being brought to
it.
• Rotating disks alternate exposure between air
and water.

15. Rotating Biological Contactor

16. Imhoff tanks
• The Imhoff tank, named for German engineer Karl
Imhoff (1876–1965), is a chamber suitable for the
reception and processing of sewage.
• It may be used for the clarification of sewage by simple
settling and sedimentation, along with anaerobic
digestion of the extracted sludge.
• It consists of an upper chamber in which sedimentation
takes place, from which collected solids slide down
inclined bottom slopes to an entrance into a lower
chamber in which the sludge is collected and digested.
• The two chambers are otherwise unconnected, with
sewage flowing only through the upper sedimentation
chamber and no flow of sewage in the lower digestion
chamber.

17. Imhoff tanks in the Bochum-Langendreer
sewage treatment in Germany

18. Anaerobic Lagoon
• Anaerobic Lagoon or Manure Lagoon is a man-made
outdoor earthen basin filled with animal waste that
undergoes anaerobic respiration as part of a system
designed to manage and treat refuse created by
Concentrated Animal Feeding Operations (CAFOs).
• Anaerobic lagoons are created from a manure
slurry, which is washed out from underneath the
animal pens and then piped into the lagoon.
• Sometimes the slurry is placed in an intermediary
holding tank under or next to the barns before it is
deposited in a lagoon.

19. • Once in the lagoon, the manure settles into two
layers: solid or sludge layer and the liquid layer.
• The manure then undergoes the process of
anaerobic respiration, whereby the volatile
organic compounds are converted into carbon
dioxide and methane.
• Anaerobic lagoons have been shown to harbor
and emit substances which can cause adverse
environmental and health affects.
• These substances are emitted through two main
pathways: gas emissions and lagoon overflow.

20. • Gas emissions are continuous (though the
amount may vary based on the season) and are a
product of the manure slurry itself.
• The most prevalent toxic gasses emitted by the
lagoon are
– ammonia, hydrogen sulfide, methane, and carbon
dioxide.
• Lagoon overflow is caused by faulty lagoons, such
as cracks or improper construction, or adverse
weather conditions, such as increased rainfall or
strong winds.

22. Thank you