1. Chapter 7 - Fundamentals of Biological Treatment

2. 7-1. Overview of Biological wastewater Treatment

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

6. Objectives of Biological Treatment
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 c
Recycle
chamber
Primary
clarifier
Aeration
tanks
Secondary d

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

8. Biological Treatment Metabolic function Term Definition
Table 1. definition of common terminology used for biological wastewater treatment
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

9. Biological Treatment Treatment processes Term Definition
Table 1. definition of common terminology used for biological wastewater treatment
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
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

10. Biological Treatment Treatment functions Term Definition
Table 1. definition of common terminology used for biological wastewater treatment
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

11. Role of microorganism in wastewater treatment
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 + v4PO43- → v5(new cells) + v6CO2 + v7H2O
v : the stoichometric coefficient
O2, NH3, PO43- : Nutrients needs for the conversion of the organic matter to simple end products(CO2)

12. Role of microorganism in wastewater treatment
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 for wastewater treatment
Suspended growth process.
Attached growth process.
Typical process applications are given in table 2

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

15. Wastewater Treatment
Table 2. major biological treatment processes used for wastewater treatment
Type
Common name
Use
Anoxic processes
Suspended growth
Suspended growth denitrification
denitrification
Attached growth
Attached growth denitrification
Anaerobic processes
suspended growth
Anaerobic contact processes
Anaerobic digestion
C – BOD removal
Stabilization, solids destruction, pathogen kill
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

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

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