WATER RESOURCES ENGINEERING
10
Wastewater Treatment – Unit Processes
((Tertiary
y Treatment, Chemical Processes & Advance Treatment))
h Manuell B.Vergell
John
BS CE, MS
BS-CE, CE
MS-CE
Tertiaryy Treatment
y WasteWater Treatment Process:
Tertiaryy Treatment
y WasteWater Treatment Process:
Tertiaryy Treatment
y Tertiary
T ti y ttreatment
t t is often used as a sysnonym
y y for advanced
water treatment even though they have different meaning.
meaning
y Tertiary suggests a third step that is applied after primary and
secondary
d y pprocessing.
g
Tertiaryy Treatment
y Suspended Solids Removal
1
1. Tertiary granular filtration can be used to remove relatively
large solids and upgrade effluent quality
2
2. Membrane filtration removes particles by physical straining
and depending on media porosity, has the ability to remove
b
bacteria,
i , viruses
i andd dissolved
di l d solids.
lid
3. Microfiltration
c off t at o ca
can remove
e o eGGiardia
a d a aandd C
Cryptosporidium
yptospo d u cyst.
4
4. Reverse Osmosis can be used to remove viruses and reduce
di l d solids.
dissolved lid
Tertiaryy Treatment
Advance Treatment
Advance Treatment
Advance Treatment
y Advanced wastewater treatment is the application of a process or
system that follows secondary treatment or that includes
pphosphorus
h ph removall or nitrification
i ifi i iin conventional
i l
secondary treatment.
secondary treatment
y It
I is
i usedd to augment
g conventional
i l secondary
d y treatment
bbecause secondary
d y treatment
t t t typically
typi lly removes only
ly
between 85 and 95% of the BOD and TSS in raw sanitaryy
sewage.
sewage
y It is
i often
ft usedd to
t remove additional
dditi l pollutants
p ll t t ffrom
t t d wastewater.
treated t t
Advance Treatment
y Secondaryy treatment does not significantly
g y reduce the
effluent concentration of nitrogen (causes high ammonia
compounds which is toxic to aquatic life) and phosphorus
(important plant nutrients) (causes formation of algal
blooms) in sewage.
sewage
y Advanced
Adva ced wastewate
wastewater ttreatment
eat e t ca
can remove
e ove more
o e than
tha
99% off the
h pollutants
ll from
f raw sewage andd can produce
d
an effluent of almost potable (drinking) water quality.
Advance Treatment
y Advance Treatment includes:
1. Chemical
Ch i lTTreatment
2
2. Microscreening
3
3. Filtration
4
4. Bi l gi l Nitrification
Biological Nit ifi ti
5. Biological
l g l Denitrification
f
6
6. Carbon Adsorption
7
7. Land Application
8
8. Bi l gi l Nutrient
Biological N i Removal
R l
Advance Treatment
y Chemical Treatment:
• It is often accomplished as an “add
add-on
on” to existing treatment
systems or by means of separate facilities specifically designed
f chemical
for h l addition
dd
• The basic process are:
1 Chemicals are thoroughly mixed with the wastewater.
1. wastewater
2 The chemical reactions that occur form solids
2.
(coagulation)
(coagulation).
3 The solids are mixed to increase particle
3. p size
(flocculation).
(flocculation)
4 Settlingg and filtration ((separation)
4. p ) remove
remo e the solids.
solids
Advance Treatment
y Operational
p Problems in Chemical Treatment:
1. Poor
P floc
fl formation
f i andd settling
li g characteristics.
h i i
2 Good floc formation,
2. formation poor removal in settling tank
tank.
3 Settling
3. S ttli g tank
t k sludge
l dg is
i turning
t i g anaerobic.
bi
Advance Treatment
y Microscreening:
• It is an advanced treatment process used to reduce suspended
solids
• The steel wire cloth acts as a fine screen
screen, with openings as
smallll as 20 mm ((or millionths
ll h off a meter)) that
h are smallll
enough gh to
t remove microscopic
i pi organisms
g i andd ddebris.
bi
• The
Th rotating
i g ddrum iis partially
p i lly submerged
b g d iin the
h secondary
d y
effluent, which
effluent hich must flo
flow into the drum then out
outward
ard
through the microscreen.
microscreen
Advance Treatment
y Microscreening:
g
• Expected
E p d performance
p f for
f suspended
p d d solids
lid removall iis 95 to
99%,, but
99% b t the
th typical
typi l suspended
p d d solids
lid removall achieved
hi d with ith
th units
these it iis about
b t 55%.
55% The
Th normall range
g is
i from
f 10 tto
80%.
80%
Advance Treatment
y Microscreening:
g ((Operational
p Problems))
1. Decrease
D in
i throughput
h ghp rate (f
(from
( slime
li growth).
g h))
2 Decreased performance from leakage at ends of the
2.
drum
drum.
3
3. S
Screen capacity
p i y iis reduced
d d after
f shutdown
h d period.
p i d
4
4. Drive System is running hot or noisy.
noisy
5
5. E ti drum
Erratic d rotation.
t ti
6. Sudden increase in effluent solids.
7
7. Decreased screen capacityy after high-pressure
high
g pressure washing.
washingg
Advance Treatment
y Filtration
• Wastewater flows to a filter (gravity or pressurized).
pressurized)
• The filter contains single,
single
g dual,
dual or multimedia.
multimedia
• Wastewater
W t t flflows through
th gh ththe media,
di which
hi h removes solids.
lid
• The
Th solids
lid remain
i iin the
h fil
filter.
• Backwashing the filter as needed removes trapped solids.
• Backwash solids are returned to the plant for treatment.
treatment
Advance Treatment
y Filtration
• Processes
P typically
ypi lly remove 95 to 99% off the
h suspended
p d d
matter.
atte .
Advance Treatment
y Filtration ((Operation
p Problems))
1. High effluent turbidity.
2
2. High
g head loss through g the filter.
filter
3. High head
High h d loss
l through
h gh unit i right
igh after
f bbackwashing.
k hi g
4
4. Backwash water requirement exceeds 5%. 5%
5
5. Filt surface
Filter f clogging.
l ggi g
6
6. Short filter runs.
runs
7
7. Filter effluent turbidity
turbidity increases rapidl
rapidly.
p y
8. Mudd Ballll Formation.
Advance Treatment
y Filtration: ((Operation
p Problems))
9. Gravel
G l displacement.
di pl
10 Medium is lost during backwash cycle.
10. cycle
11 Filter
11. Filt bbackwash
k h cycle
y l nott effective
ff ti dduring
i g warm
weather.
h
12 Air binding causes premature head loss increase.
12. increase
Advance Treatment
y Biological Nitrification
• In
I nitrification,
it ifi ti the th ammonia
i nitrogen
it g is i converted
t d to
t nitrate
it t
nitrogen,
it g producing
p d i g a nitrified
it ifi d effluent.
ffl t
• In nitrification,
nitrification the secondary effluent is introduced into
another aeration tank, trickling filter, or biodisc.
• At thi
this point,
p i t the
th nitrogen
it g hash nott actually
t lly been
b removed,
d
only converted to a form that is nontoxic to aquatic life and
that does not cause an additional oxygen demand.
demand
Advance Treatment
y Biological
g Nitrification ((Opereational
p Problems))
1. p
pH
H ddecreases with
i h lloss off nitrification.
i ifi i
2 Incomplete nitrification
2.
3 SVI off nitrification
3. it ifi ti sludge
l dg is
i veryy high
high (>250).
(>250)
( )
Advance Treatment
y Biological Dentrification
• It removes nitrogen from the wastewater.
• When
Wh bacteria
b i come iin contact with
i h a nitrified
i ifi d element
l in
i
the absence of oxygen,
oxygen they reduce the nitrates to nitrogen
ggas,, which
h h escapes
p the
h wastewater.
y The
Th denitrification
d it ifi ti pprocess can bbe done
d iin either
ith an anoxic
i
activated sludge system (suspended growth) or in a column
system
y t (fi(fixed
( d growth).
g th))
y The denitrification process can remove up to 85% or more of
nitrogen.
Advance Treatment
y Biological Dentrification
• Suspended growth denitrification reactors are mixed
mechanically, but only enough to keep the biomass from
mechanically
settling
l g without
h adding
dd g unwantedd oxygen.
yg
y A fine media downflow filter is sometimes used to provide
b h denitrification
both d i ifi i andd effluent
ffl fil
filtration.
i
y A fluidized
flu d ed sa
sandd bbed
ed where
he e wastewater
aste ate flows
flo s upward
up a d
through
th gh a media
di off sandd or activated
ti t d carbon
b att a rate
t tto
fluidize the bed may also be used.
used
y Denitrification
D it ifi ti bacteria
b t i grow
g on the
th media.
di
Advance Treatment
y Biological
g Dentrification
• The
Th most common ddemandd source added
dd d is
i soluble
l bl BOD or
methanol.
h l
• Approximately 3 mg/L of methanol is added for every 1
mg/L of nitrate
nitrate-nitrogen
nitrogen.
Advance Treatment
y Biological
g Dentrification ((Operational
p Problems))
1. Process
P effluent:
ffl sudden
dd iincrease iin BOD
BOD.
2 Sudden increase in effluent nitrate concentration.
2.
3 High head loss (packed bed nitrification).
3. nitrification)
4 Out
4. O t off service
i packed
p k d bed
b d unit
it binds
bi d on start-up.
t t p
Advance Treatment
y Carbon Adsorption
• The main purpose of carbon adsorption used in advanced
treatment processes
p is the removal
remo al of refractor
refractoryy organic
g
compounds (non(non-BOD)
BOD) and soluble organic material that are
diffi lt tto eliminate
difficult li i t by by biological
bi l gi l or physical
phy i l or chemical
h i l
treatment.
treatment
• Organics
g adsorb
d b onto the
h carbon
b (i.e.,
( , organic
g molecules
l l are
attracted to the activated carbon surface and are held there)
with
w th su
sufficient
ff c e t contact
co tact time.
t e.
• Most
M contact chambers
h b are either
i h open
p concrete gravity-type
g y yp
systems or steel pressure containers applicable to either upflow or
d
downflow
fl operation.
p i
Advance Treatment
y Carbon Adsorption
p
• With
Wi h use, carbon
b loses
l iits adsorptive
d p i capacity.
p i y Th
The carbon
b must
then be regenerated or replaced with fresh carbon
carbon. Carbon used
for adsorption may be in granular or powdered form.
form
Advance Treatment
y Carbon Adsorption
p ((Operational
p Problem))
1
1. Excessive
E i hheadd loss.
l
2. Hydrogen
yd g sulfide
lf d is in carbon
b contactor.
3.. Large
g decrease in CO
COD removed or ppounds of carbon
regenerated.
g d
4. Corrosion off metall parts
p or ddamage
g to concrete in contactors.
Advance Treatment
y Land Application
pp
• The
Th application
ppli i off secondary
d y effluent
ffl onto a land
l d surface
f can
p id an effective
provide ff ti alternative
lt ti tto th
the expensive
p i andd
complicated
pli t d advanced
d d treatment
t t t methods
th d previously
p i ly
mentioned
• A high quality polished effluent can be obtained by the
natural processes that occur as the effluent flows over the
vegetated
g d ground
g d surface
f andd percolates
p l through
h gh the h soil.
l
Advance Treatment
y Types
yp of Land Application
pp
1
1. IIrrigation
ig i (slow
( l rate))
2. Overland
O l d Flow l
3.. Infiltration-percolation
p ((rapid
p rate))
Advance Treatment
y Types of Land Application
1 Irrigation (slow rate):
1.
• Wastewater is sprayed or applied (usually by ridge
ridge-and-
and
ffurrow surface
f spreading
p di g or bbyy sprinkler
p i kl systems)
y t ) tto th
the
surface of the land.
• Wastewater
W enters the
h soil.
l CCrops
p growing
g g on the
h irrigation
g
area utilize available nutrients.
nutrients
• Soil organisms stabilize organic content of the flow.
flow
• Wate
Water returns
etu s to the
the hhydrologic
yd olog c (water)
(wate ) cycle
cycle through
th ough
evaporation or by enteringg the surface water or ggroundwater.
groundwater
Advance Treatment
y Types of Land Application
1 Irrigation (slow rate):
1.
• Water returns to the hydrologic (water) cycle through
evaporation
p ti or by
by entering
t i g the
th surface
f water
t or groundwater.
g d t
• The irrigation land application method provides the best
results
l ((compared
p d withh the
h other
h two types
yp off llandd application
ppl
systems) with respect to advanced treatment levels of
ppollutant
ll removal.
l
• Not
N t only
ly are suspended
p d d solids
lid andd BOD significantly
ig ifi tly reduced
d d bbyy
filtration of the wastewater,
wastewater but also biological oxidation of the
organics
g i iin theh topp ffew iinches
h off soilil occurs.
Advance Treatment
y Types
yp of Land Application
pp
1. Irrigation
I g (slow
( l rate):
)
• Nitrogen is removed primarily by crop uptake, and
phosphorus is removed by adsorption within the soil
Irrigation
g expected
p
performance
p f levels
l l are:
1 BOD — 98%
1.
2 Suspended solids — 98%
2.
3 Nitrogen — 85%
3.
4 Phosphorus — 95%
4.
5.. Metals — 95%
Advance Treatment
y Types
yp of Land Application
pp
1. Irrigation
I g (slow
( l rate):
)
Advance Treatment
y Types of Land Application
2 Overland flow:
2.
• It is used for water purification is accomplished by physical,
chemical,
h i l andd biological
bi l gi l processes
p as the
th wastewater
t t flowsfl in
i
a thin film down the relatively impermeable surface.
• In
I the
h process,
p , wastewater sprayed
p y d over sloped
l p d terraces flflows
slowly over the surface.
surface
• Soil and vegetation remove suspended solids,
solids nutrients,
nutrients and
organics.
g i
• A small portion of the wastewater evaporates.
evaporates
Advance Treatment
y Types
yp of Land Application
pp
2. Overland
O l d flflow:
f
y The remainder flows to collection channels. Collected
effluent is discharged to surfacewaters.
Overflow
O fl flflow expected
p d performance
p f llevels
l are:
1 BOD — 92%
1. 4 Phosphorus
4. Ph ph — 40 to 80%
2 2.
2. 2 Suspended
S p d d solids
lid — 92% 5 Metals
5. M t l — 50%
3 Nitrogen — 70 to 90%
3.
Advance Treatment
y Types
yp of Land Application
pp
2. O l d flflow:
Overland f
Advance Treatment
y Types of Land Application
3 Infiltration
3. Infiltration-percolation
percolation (rapid rate):
• Wastewater is sprayed/pumped to spreading basins (a.k.a.
recharge
h g basins
b i or llarge
g ponds).
p d)
• Some wastewater evaporates
evaporates. The remainder
ppercolates/infiltrates
l / fl into soil.
l
• Solids
S lid are removedd by
by filtration.
filt ti Water
W t recharges
h g th the
groundwater system.
system
• Most
ost of
of tthe
he eeffluent
fflue t percolates
pe colates to the
the groundwater;
g ou dwate ; very
ve y
little of it is absorbed by vegetation.
vegetation
g
Advance Treatment
y Types
yp of Land Application
pp
3. IInfiltration-percolation
fl p l ((rapid
p d rate):
)
• The filtering and adsorption action of the soil removes most
of the BOD, TSS, and phosphorous from the effluent;
h
however, , nitrogen
g removall is relatively
l ly poor.
p
Infiltration-percolation expected performance levels are:
1 BOD — 85 to 99%
1. 4 Phosphorus — 60 to 95%
4.
2.. Suspe
Suspended
e solids
so s — 98% 5. Metals
eta s — 50 to 95%
3 Nitrogen
3. Ni g — 0 to 50%
Advance Treatment
y Types
yp of Land Application
pp
3. I fl
Infiltration-percolation
p l ((rapid
p d rate):
)
Advance Treatment
y Land Application (Operation Problem)
1. In irrigated areas, water is ponding.
2. Deterioration off ddistribution
b piping.
pp g
3. N flow
No fl from
f source sprinkler
p i kl nozzles.
l
4
4. W t are running
Wastes i g off
ff irrigation
i ig ti area.
5
5. I ig t d cropp is
Irrigated i ddead.
d
6
6. Poor crop growth.
growth
7
7. Irrigation pump has normal pressure
pressure, but above average
flflow rate.
8. Irrigation
I ig i pump p p hhas above
b average g pressure,
p , but
b bbelow
l
average flow.
flow
Advance Treatment
y Land Application
pp ((Operation
p Problem))
9. Irrigation
I ig i pumpp p hhas below
b l average
g pressure
p andd flow
fl
rate
ate
10
10. Excessive erosion occurring.
occurring
11
11. Od complaints.
Odor pl i
12
12. Center pivot irrigation rigs stuck in mud.
mud
13
13. Nit t in
Nitrate i groundwater
g d t near iirrigation
ig ti site
it iis
i
increasing.
i g
Advance Treatment
y Biological Nutrient Removal
• BNR systems are reliable and effective in removing nitrogen
and phosphorus.
phosphorus
p p
• The process is based upon the principle that under specific
conditions,
d , microorganisms
g willll remove more phosphorus
ph ph
and nitrogen than is required for biological activity.
activity
• Several patented processes are available for this purpose.
purpose
• Performance
e fo a ce depends
depe ds on
o tthe
he biological
b olog cal activity
act ty aandd tthe
he
process employed.
employed
