14-Trattamenti acque reflue - DICCISM

Università di Pisa
Wastewater treatment objecives
Removal of suspended and floatable materials
Degradation of biodegradable organics
Removal of nutrients
Elimination of priority pollutants
Elimination of pathogenic organisms
Untreated wastewater
Contaminants
Solids, total
BOD5
COD
Nitrogen
Phosphorous
Total coliforms
Units
mg L-1
mg L-1
mg L-1
mg L-1
mg L-1
No L-1
Concentration
350-1200
110-400
250-1000
20-85
4-15
107-1010
Treated wastewater
Contaminants
Solids, total
BOD5
COD
Nitrogen
Phosphorous
Total coliforms
Units
mg L-1
mg L-1
mg L-1
mg L-1
mg L-1
No L-1
Concentration
30
30
60
5
2
103
1
Università di Pisa
Unit operations and processes for ww treatment
Suspended solids
Screening
Sedimentation
Filtration
Flotation
Coagulation
Biodegradable organics
Activated sludge
Trickling filters
Nitrogen
Biological nitrogen removal
Ammonia stripping
Phosporous
Chemical precipitation
Lime coagulation
Biological phosphorous
removal
Volatile organic compounds
Air stripping
Carbon adsorption
Refractory organics
Carbon adsorption
Advanced oxidation
Heavy metals
Chemical precipitation
Ion exchange
Dissolved inorganic compounds
Ion exchange
Reverse osmosis
Pathogens
Chlorination
Ozonation
UV radiation
2
Università di Pisa
Methods of wastewater treatment - 1
Preliminary wastewater treatment: removal of those constituents
that may cause maintenance or operational problems with the
treatment operations, processes and ancillary systems.
Screening and comminution for the removal of debris
Grit removal for the elimination of coarse suspended solids
Floatation for the removal of oil and grease
Primary wastewater treatment: removal of a portion of the
suspended solids and organic matter.
Primary sedimentation
Secondary wastewater treatment: removal of biodegradable
organics and suspended solids.
Activated sludge
Trickling filters
Lagoons
3
Università di Pisa
Methods of wastewater treatment - 2
Nutrient removal: Removal of nitrogen and posphorous, required for
i) discharge to confined bodies where cultural eutrophication may occur;
ii)discharge to flowing streams where nitrification can tax oxygen resources.
Biological processes (coupled with secondary treatment)
Chemical processes
Combination of biological and chemical processes.
Advanced wastewater treatment: the level of treatment required
beyond conventional secondary treatment and nutrient removal to
remove:
i) increased amounts of organic material, suspended solids and nutrients (for water
reuse)
ii)constituents of concern, including toxic compounds
Chemical coagulation, flocculation and sedimentation
Filtration
Activated carbon
Ion exchange
Reverse osmosis
4
Università di Pisa
Methods of wastewater treatment - 3
Sludge processing: unit operations and processes or systems used to process the
sludge removed from the liquid portion of the wastewater (partcularly in primary and
secondary treatment).
Thickening (concentration): a procedure used to increase the solids content of
sludge by removing a portion of liquid.
Gravity thickening
Floatation thickening
Centrifugation thickening
Stabilisation: sludges are stabilised to:
i) reduce pathogens;
ii) eliminate offensive odors;
iii) Reduce or eliminate potentials for putrefaction.
Biological reduction of the volatile matter
Chemical oxidation of the volatile matter
Chemical inhibition of microbial growth
Thermal disisnfection
Conditioning: to increase the sludge dewatering characteristics.
Chemical
Thermal
Dewatering: mechanical unit operation used to reduce the moisture content of
sludge.
Press filtration
centrifugation
5
Università di Pisa
Process flow diagram
bar
screen
grit
chamber
primary
clarifier
aeration
tank
secondary
clarifier
contact
tank
effluent
influent
chlorine
debris
O2
grit
return
sludge
supernatant
return
digested
sludge
dewatered
sludge
belt
press
anaerobic
digester
gravity
thickener
6
Wastewater treatment plant
Università di Pisa
7
Università di Pisa
Screens
8
Università di Pisa
Grit chambers
9
Università di Pisa
Dissolved air floatation system
10
Università di Pisa
Primary clarifiers - 1
11
Università di Pisa
Primary clarifiers - 2
12
Università di Pisa
Primary clarifier with flocculator
13
Università di Pisa
Aeration tanks
14
Università di Pisa
Air diffusers
Fine bubble diffuser
Jet aerator
Surface turbine aerator
15
Università di Pisa
Secondary clarifiers
16
Università di Pisa
Chlorine contact tanks
17
Università di Pisa
Sludge thickener -1
Gravity sludge thickener
18
Università di Pisa
Sludge thickener - 2
Centrifugal sludge thickener
19
Università di Pisa
Sludge digestor - 1
Microbiological pathways of anaerobic digestion
20
Università di Pisa
Sludge digestor - 2
Low-rate anaerobic disgestor
21
Università di Pisa
Sludge digestor - 3
Low-rate anaerobic disgestor
22
Università di Pisa
Belt filter
23
Università di Pisa
Adsorption on activated carbon
24
Università di Pisa
Trickling filters
25
Università di Pisa
Membrane bioreactors
26
Università di Pisa
Particulate biofilm reactors
27