BIOLOGICAL TREATMENT
Objective
remove or reduce the concentration of organic and inorganic compounds
transform (i.e., oxidize) dissolved and particulate
biodegradable constituents into acceptable end products capture and incorporate suspended and nonsettleble colloids to a biological floc or biofilm
Role of microorganisms
Convert the colloidal and dissolved carbonaceous organic matters into various gas and cell tissue
>>> The resulting cells can be removed by settling
Microbial metabolisms require :
• source of energy : Light, chemical oxidation rxn. • carbon for the synthesis of new cellular
material : organic matter, CO2
“Heterotrophs” : organisms that use organic C “Autotrophs” : organisms that use CO2
Classification Energy source Heterotrophic :
- Photoheterotrophic Light
- Chemoheterotrophic org. Ox. - Red rxn.**
Autotrophic :
- Photoautotrophic Light
- Chemoautotrophic inorg.Ox.– Red. Rxn**
Type of microbial metabolism
- Emphasize on chemoheterotrophic organisms 1) . Respiratory metabolism
- organisms generate energy by enzyme mediated e
-transfer from an e- donor to an external e- acceptor
2) Fermentative metabolism
Environment e- acceptor Process
Aerobic O2 Aerobic metabolism
Anaerobic NO3- Denitrification
(Anoxic process)
SO42- Sulfate reduction
Types of biological treatment processes
5 major groups
1. Aerobic process
2. Anoxic processes
3. Anaerobic processes
4. Combined processes
Individual process is further subdevided : - Depends on method of use
• Suspended-growth processes • Attached-growth processes
Suspended growth processes:
The microorganisms responsible for treatment are maintained suspension by appropriate
mixing methods.
Attached – growth processes :
The microorganisms are attached to some inert medium, such as rock, slag or specially designed ceramic or plastic materials.
A. Suspended – growth
- Activated sludge process
- Aerated lagoon
- Aerobic digestion
B. Attached growth
- Trickling filters
- Rotating biological Reactors
- Packed-bed reactors
C. Combination suspended / attached growth
Important feature :
convert soluble and insoluble organic and inorganic compounds
flocculent settable microbial suspension
Remove the biomass by gravity settling (solid – liquid separation)
into 1.
2.
A. SUSPENDED GROWTH PROCESS
Process description
1. Org. Matters Reactor (suspension of bacteria) (oxidation and synthesis)
Organic matters (C,O,H,N,S) + O2 + nutrients
bacteria
CO2 + NH3 + C5H7NO2 + other end products (new cells)
5 O2 + C5H7NO2 5CO2 + 2H2O + NH3 +energy
bacteria
2.
After a specific period of time
Mixture of
new + old cells Settling tank Treated water Cells (sludge)
Reactor waste
3 Basic components
1. A reactor
- the microorganisms are kept in suspension and aerated
2. Liquid – solid separation
- usually in sedimentation tank
Types of reactors
i. Plug flow activated sludge
ii. Complete-mix activated-sludge reactor
i. Plug flow activated sludge
- Uses long and narrow aeration basins - Mixing regime approaches plug flow
flow
influent
Recycled sludge
clarifier
Beginning of aeration basin
- High rate of O2 Utilization
- Oxidation of org. - synthesis of cells
End of basin
- O2 utilization rate approaches the endogenous level - Oxidation of new
ii. Complete mix activated sludge
Influent + recycled sludge are introduced to the aeration basin
Contents are mixed completely
iii. Sequencing batch reactor
Single vessel is used to accommodate All of the unit processes
Processes are timed sequences 1. Fill
- An aerated lagoon is a basin of significant Depth e.g. 8-16 ft (2.4 – 4.9 m) deep
- Oxygenation mechanical aeration diffused aeration
induced surface aeration - 2 types Aerobic lagoon
Facultative lagoon
(Aerobic-Anaerobic lagoon)
- Aerated lagoon systems can be multiple basins i.e. Aerobic Facultative settling
• Aerobic lagoon
- dissolved O2 and suspended solid are maintained uniformly throughout the basin
- no solid recycle
• Facultative lagoon
- O2 is maintained in the upper liquid layer - only a portion of solids is maintained in
-The processes’ design depends on
o equipment
o Available area
B. ATTACHED GROWTH PROCESSES
a). Trickling filter
- A bed of a highly permeable medium to which microorganisms are attached
Lakeside Equipment Corporation
b). Rotating biological contractors
- A series of closely spaced circular disk of polystyrene or polyvinyl chloride
- Biological growths is attached and grown on the surface for 1-4 mm.
-The disks are submerged in wastewater (40% submerged) and rotated slowly through it
Process description
As the contractor rotates
When exposed to air the attached biomass absorbs air
and when immersed the microorganisms absorb the organic load.
Selection of aerobic treatments
Several factors affecting the choice of processes
1. OPERATING CHARACTERISTICS
System Resistance to
shock loads of organics or toxics
Sensitivity to intermittent operations Degree of skill needed
Lagoons Maximum Minimum Minimum
Trickling filters
Moderate Moderate Moderate
(b) COST CONSIDERATIONS
System Land needed Initial costs Operating
costs
Lagoons Maximum Minimum Minimum
Trickling filters
Moderate Moderate Moderate
Activated Minimum Maximum Maximum
Adapted from Rich, 1980.
ANAEROBIC PROCESSES
The anaerobic treatment
- degradation of the organic load to gaseous products (mainly CH4 and CO2)
Reactions occur in anaerobic treatment
Organic load soluble organic material
acid producing bacteria
volatile fatty acid, CO2, H2
methane producing bacteria
Insoluble org. (protiens, lipid) Hydrolytic and Fermentative bacteria Org. Material (soluble) cells
Acid producing bac.
cells
Volatile fatty acids,
CO2, H2
cells
CO2, H2
CH4
Endogenous met. Cell lysis