The document discusses biological wastewater treatment processes. It defines key terms, describes treatment objectives like BOD removal and nutrient reduction, and outlines common treatment unit processes. These include suspended growth processes like activated sludge and attached growth processes like trickling filters, which use microorganisms attached to a solid media to treat wastewater as it flows past. Typical process flows are shown for activated sludge systems and other biological wastewater treatment approaches.

3. • Objectives of biological treatment
• Some useful definitions
• Role of microorganisms in wastewater treatment
• Type of biological process for wastewater treatment
– Suspended growth processes
– Attached growth processes

4. • To transform dissolved and particulate biodegradable
constituents into acceptable end products.
• To capture and incorporate suspended and nonsettleable
colloidal solids into a biological floc or biofilm.
• To transform or remove nutrients.
(such as nitrogen and phosphorus)
• To remove specific trace organic constituents and
compounds.

5. Influent
Bar rack
Screenings
Grit
chamber
Grit
Primary
clarifier
Sludge
Aeration
tanks
Waste sludge
(optional)
Secondary
clarifier
Disinfection
Effluent
Sludge
Return activated sludge
Waste
sludge
(optional)
a
b
Influent
Bar rack
Screenings
Disinfection
Effluent
Aerated
lagoon
Settling pond
Sludge
Return sludge (optional)
Figure 1. Typical (simplified) flow diagrams for biological used for wastewater treatment
(a) activated-sludge process, (b) aerated lagoons

6. Figure 1. Typical (simplified) flow diagrams for biological used for wastewater treatment
(c) trickling filter, (d) rotating biological contactors.
Influent
Bar rack
Screenings
Grit
chamber
Grit
Primary
clarifier
Sludge
Trickling
filter
Waste sludge
(optional)
Secondary
clarifier
Disinfection
Effluent
Sludge
c
Recycle
Influent
Bar rack
Screenings
Grit
chamber
Grit
Primary
clarifier
Sludge
Aeration
tanks
Secondary
clarifier
Disinfection
Effluent
d
Sludge

7. • Some useful terms.
– Metabolic function
• Aerobic process
• Anaerobic process
• Anoxic process
• Facultative process
• Combined process
– Treatment process
• Suspended growth process
• Attached growth process
• Combined process
• Lagoon process
– Treatment functions
• Biological nutrient
removal(BNR)
• Stabilization
• Nitrification
• Biological phosphorus
removal
• Denitrification
• Carbonaceous BOD
removal
• Substrate

8. Term Definition
Metabolic function
Aerobic (oxic) process Biological treatment process that occur in the presence of
oxygen
Anaerobic process The process that occur in the absence of oxygen
Anoxic process Nitrate nitrogen is converted biologically to nitrogen gas in
the absence of oxygen, Known as denitrification
Facultative process Process in which the organisms can function in the presence
or absence of molecular oxygen
Combined aerobic/
Anoxic/Anaerobic
process
Various combinations of aerobic, anoxic, and anaerobic
processes grouped together to achieve a specific treatment
objective
Table 1. definition of common terminology used for biological wastewater treatment

9. Term Definition
Treatment processes
Suspended-growth
processes
Biological treatment processes in which the microorganisms
responsible for the conversion of the organic matter or other
constituents in the wastewater to gases and cell tissue are
maintained suspension within the liquid
Attached-growth
processes
Biological treatment processes in which the microorganisms
responsible for the conversion of the organic matter or other
constituents in the wastewater to gases and cell tissue are
attached to some inert medium, such as rock, slag, or
specially designed ceramic or plastic materials. Also known as
fixed-film processes
Combined processes Term used to describe combined processes (combined
suspended and attached growth processes)
Lagoon processes A generic term applied to treatment processes that take place
in pond or lagoons
Table 1. definition of common terminology used for biological wastewater treatment

10. Term Definition
Treatment functions
The term applied to the removal of nitrogen and phosphorus in
biological treatment
Biological phosphorus
removal
Removal of phosphorus by accumulation in biomass and
subsequent solids separation
Carbonaceous BOD removal Conversion of the carbonaceous organic matter to cell tissue and
various gaseous end product.
Assumed – Nitrogen converted to ammonia
Nitrification Ammonia is converted first to nitrite and then to nitrate
Denitrification Nitrate is reduced to nitrogen and other gaseous
Stabilization The biological process by sludge from primary settling and
wastewater is stabilized. The process is known as aerobic or
anaerobic digestion.
Substrate The organic matter or nutrients that are converted during biological
treatment or that may be limiting in biological treatment
Table 1. definition of common terminology used for biological wastewater treatment

11. • Removal of dissolved and particulate BOD and the
stablization of organic matter found in wastewater.
• Conversion of simple end product and additional
biomass
v1(organic material) + v2O2 + v3NH3 + v4PO4
3- → v5(new cells) + v6CO2
+ v7H2O
v : the stoichometric coefficient
O2, NH3, PO4
3- : Nutrients needs for the conversion of the organic matter to simple end
products(CO2)

12. • Nitrogen removal in the wastewater treatment process.
– Nitrification
– Denitrification
• Phosphorus removal in the wastewater treatment
process.
– Excess inorganic phosphorus ingestion and storage of
microorganisms.

13. • Types of biological process.
– Suspended growth process.
– Attached growth process.
• Typical process applications are given in table 2

14. Type Common name Use
Aerobic processes
Suspended growth Activated-sludge process
Aerated lagoons
Aerobic digestion
C - BOD removal, nitrification
C - BOD removal, nitrification
C - BOD removal, stabilization
Attached growth Trickling filters
Rotating biological contactors
Packed-bed reactors
C - BOD removal, nitrification
C - BOD removal, nitrification
C - BOD removal, nitrification
hybrid (combined)
suspended and
attached growth
processes
Trickling filter / activated sludge C - BOD removal, nitrification
Table 2. major biological treatment processes used for wastewater treatment

15. Type Common name Use
Anoxic processes
Suspended growth Suspended growth denitrification denitrification
Attached growth Attached growth denitrification denitrification
Anaerobic processes
suspended growth Anaerobic contact processes
Anaerobic digestion
C – BOD removal
Stabilization, solids destruction,
pathogen kill
Attached growth Anaerobic packed and fluidized bed C – BOD removal, waste
stabilization, denitrification
sludge blanket Up flow anaerobic sludge blanket C – BOD removal, especially
high strength wastes
hybrid Up flow sludge blanket / attached growth C – BOD removal
Table 2. major biological treatment processes used for wastewater treatment

16. Suspended growth process
Influent Effluent
Return activated
sludge
Air
Plug flow aeration
tank
Clarifier
Sludge
Influent Effluent
Return activated
sludge
Clarifier
Complete mix
aeration tank
Sludge
 The microorganisms are maintained by appropriate mixing method.
 The most common suspended growth process is the activated sludge
process.
Figure 2. Suspended growth biological treatment process

17. • The microorganisms are attached to an inert packing
material.
– Packing material
• Rock · Gravel
• Slag · Sand
• Redwood · Plastic
• Synthetic materials
• The organic materials and nutrients are removed from the
wastewater flowing past the attached growth also known as
a biofilm.
• The most aerobic attached growth process : trickling filter.

18. Effluent
Clarifier
Sludge
Influent
Recycle
(optional)
Trickling filter
with rock
packing
Effluent
Clarifier
Sludge
Recycle
(optional)
Tower
trickling filter
with plastic
packing
Influent
Recycle
Figure 3. Attached growth biological treatment process