Biological treatment processes

1. BBiioollooggiiccaall TTrreeaattmmeenntt PPrroocceesssseess
» By
Mrs. A.K.Khembete
Lecturer, CED,SVNIT, Surat
E Mail: akk@ced.svnit.ac.in

2. AAccttiivvaatteedd SSlluuddggee SSyysstteemmss
• Activated sludge systems are designed to
maintain intimate contact between the
wastewater, a large population of bacteria
and oxygen
• The microorganisms are “activated” for
rapid uptake of new substrate, thus the term
activated sludge

3. SScchheemmaattiicc DDiiaaggrraamm ooff aann
AAccttiivvaatteedd SSlluuddggee SSyysstteemm
Influent
wastewater
Air
Aeration
basin
Waste
activated
sludge
Effluent
wastewater
Final
clarifier
Return activated sludge

4. VVaarriiaattiioonnss ooff tthhee
AAccttiivvaatteedd SSlluuddggee PPrroocceessss
• Step aeration
– wastewater is introduced at intermediate points
in a plug-flow aeration basin
• provides more uniform BOD loading
• Contact stabilization
– biosorption of organics and their subsequent
biodegradation are carried out in separate tanks
• Oxidation ditch
– closed-loop channel through which the
wastewater flows

5. AAccttiivvaatteedd SSlluuddggee VVaarriiaattiioonnss
((ccoonnttdd..))
• High-rate process
– high food-to-microorganism ratio
– short detention time
• Extended aeration process
– long aeration times and a low F/M ratio to
minimize sludge production
• Pure oxygen
– good, but very expensive

6. AAccttiivvaatteedd SSlluuddggee VVaarriiaattiioonnss
((ccoonnttdd..))
• Powdered activated carbon (PAC) Process
– PAC is added to aeration tank
– PAC becomes enmeshed in the activated sludge
floc
• adsorbs recalcitrant organics from the wastewater
that might otherwise pass untreated through a
conventional activated sludge process
• In some cases, these adsorbed organics are
eventually biodegraded by bacteria growing on the
activated carbon surfaces.

7. DDeessiiggnn PPaarraammeetteerrss ffoorr
AAccttiivvaatteedd SSlluuddggee SSyysstteemmss T a b l e 1 0 . 4
D e s i g n p a r a m e t e r s f o r a c t i v a t e d s l u d g e t r e a t m e n t p r o c e s s e s
T y p e o f
p r o c e s s
M e a n c e l l
r e s i d e n c e
t i m e ( d a y s )
F / M
( k g B O D 5 /
k g M L S S )
L o a d i n g
( k g / B O D 5 /
m 3 - d )
H y d r a u l i c
r e t e n t i o n
t i m e ( h r )
M L S S
( m g / L ) R e c y c l e r a t i o
C o n v e n t i o n a l 5 - 1 5 0 . 2 - 0 . 4 0 . 3 - 0 . 6 4 - 8 1 5 0 0 - 3 0 0 0 0 . 2 5 - 1 . 0
S t e p a e r a t i o n 5 - 1 5 0 . 2 - 0 . 4 0 . 6 - 1 . 0 3 - 5 2 0 0 0 - 3 5 0 0 0 . 2 5 - 0 . 7 5
C o m p l e t e l y
5 - 3 0 0 . 1 - 0 . 6 0 . 8 - 2 . 0 3 - 6 2 5 0 0 - 4 0 0 0 0 . 2 5 - 1 . 5
m i x e d
C o n t a c t
s t a b i l i z a t i o n
5 - 1 5 0 . 2 - 0 . 6 1 . 0 - 1 . 2 0 . 5 ( c o n t a c t )
3 - 6 ( s t a b i l . )
1 0 0 0 - 3 0 0 0
4 0 0 0 - 1 0 0 0 0
0 . 5 0 - 1 . 5
H i g h - r a t e 5 - 1 0 0 . 4 - 1 . 5 1 . 6 - 1 6 2 - 4 4 0 0 0 - 1 0 0 0 0 1 . 0 - 5 . 0
E x t e n d e d
a e r a t i o n
2 0 - 3 0 0 . 0 5 - 0 . 1 5 0 . 1 6 - 0 . 4 1 8 - 3 6 3 0 0 0 - 6 0 0 0 0 . 7 5 - 1 . 5
P u r e o x y g e n 8 - 2 0 0 . 2 5 - 1 . 0 1 . 6 - 3 . 2 1 - 3 3 0 0 0 - 8 0 0 0 0 . 2 5 - 0 . 5

8. BBiiooffiillmm SSyysstteemmss
• Biofilm
– a biological slime layer
– bacteria in biofilm
degrade organics
– biofilm will develop
on almost anything

9. TTyyppeess ooff BBiiooffiillmm SSyysstteemmss
• Trickling filters
• Rotating biological contactors
• Fluidized bed reactors
• Biofilters
• Wetlands systems
• Sequencing batch biofilm reactors
(many of these can be aerobic or anaerobic)

10. FFllooww DDiiaaggrraamm ffoorr TTrriicckklliinngg FFiilltteerrss
Recycle
Primary
clarifier Trickling
filter
Final
clarifier
Waste
sludge
Final
Influent effluent

11. TTyyppiiccaall TTrriicckklliinngg FFiilltteerr

12. TTyyppeess ooff TTrriicckklliinngg FFiilltteerrss
• Standard or low rate
– single stage rock media units
– loading rates of 1-4 m3 wastewater/m2 filter
cross-sectional area-day
– large area required

13. TTyyppeess ooff TTrriicckklliinngg FFiilltteerrss
• High rate
– single stage or two-stage rock media units
– loading rates of 10-40 m3 wastewater/m2 filter
cross-sectional area-day
– re-circulation ratio 1-3

14. TTyyppeess ooff TTrriicckklliinngg FFiilltteerrss
• Super rate
– synthetic plastic media units
• modules or random packed
• specific surface areas 2-5 times greater than rock
• much lighter than rocks
• can be stacked higher than rocks
– loading rates of 40-200 m3 wastewater/m2 filter
cross-sectional area-day
– plastic media depths of 5-10 m

15. Design CCrriitteerriiaa ffoorr TTrriicckklliinngg FFiilltteerrss
T a b l e 1 0 . 5
T y p i c a l D e s i g n C r i t e r i a f o r T r i c k l i n g F i l t e r s
I t e m L o w - r a t e f i l t e r H i g h - r a t e f i l t e r S u p e r - r a t e f i l t e r
H y d r a u l i c l o a d i n g ( m 3 / m 2 - d ) 1 - 4 1 0 - 4 0 4 0 - 2 0 0
O r g a n i c l o a d i n g ( k g B O D 5 / m 3 - d ) 0 . 0 8 - 0 . 3 2 0 . 3 2 - 1 . 0 0 . 8 - 6 . 0
D e p t h ( m ) 1 . 5 - 3 . 0 1 . 0 - 2 . 0 4 . 5 - 1 2 . 0
R e c i r c u l a t i o n r a t i o 0 1 - 3 1 - 4
F i l t e r m e d i a R o c k , s l a g , e t c . R o c k , s l a g ,
s y n t h e t i c s
F i l t e r f l i e s M a n y F e w , l a r v a e a r e
w a s h e d a w a y
F e w o r n o n e
S l o u g h i n g I n t e r m i t t e n t C o n t i n u o u s C o n t i n u o u s
D o s i n g i n t e r v a l s < 5 m i n < 1 5 s C o n t i n u o u s
E f f l u e n t U s u a l l y f u l l y
n i t r i f i e d
N it r i f i e d a t l o w
l o a d i n g s
N it r i f i e d a t l o w
l o a d i n g s

16. TTyyppiiccaall MMoodduullaarr aanndd RRaannddoomm
PPaacckkeedd PPllaassttiicc MMeeddiiaa
Schematic diagrams of modular and random packed media used
in fixed-film treatment systems (Source: Bordacs and Young, 1998)

17. RRoottaattiinngg BBiioollooggiiccaall CCoonnttaaccttoorr
• Consists of 2-4 m diameter disks, closely
spaced on a rotating horizontal shaft
• Disks are covered with biofilm that rotates
in and out of the wastewater to repeatedly
wet the biofilm with wastewater and aerate
the biofilm
• Shaft rotates at 1-2 rpm

18. FFllooww DDiiaaggrraamm ffoorr RRBBCCss

19. SSttaabbiilliizzaattiioonn PPoonnddss && LLaaggoooonnss
• commonly used to treat industrial wastes
• inexpensive to construct and to operate
• can handle a wide variety of wastes
• usually an earthen basin
• may or may not have a liner

20. TTyyppeess ooff SSttaabbiilliizzaattiioonn PPoonnddss
• Aerobic ponds
– shallow ponds (less than 1 m deep) where
dissolved oxygen, mainly due to the action of
photosynthesis, is present throughout the depth
of the pond.
• Facultative ponds
– 1 to 2.5 m deep, which have an aerobic upper
layer due to photosynthesis or surface re-aeration,
a facultative middle zone, and an
anaerobic lower zone.

21. TTyyppeess ooff SSttaabbiilliizzaattiioonn PPoonnddss ((ccoonntt..))
• Anaerobic lagoons
– deep ponds that receive high organic loadings
and which are anaerobic throughout their depth.
• Aerated lagoons
– ponds that are oxygenated through the use of
surface aerators or diffused aeration systems

22. DDeessiiggnn DDaattaa ffoorr LLaaggoooonn SSyysstteemmss
T a b l e 1 0 . 6
T y p i c a l d e s i g n d a t a f o r i n d u s t r i a l w a s t e w a t e r l a g o o n s y s te m s
I n d u s t r y
A e r o b i c a n d f a c u l t a t i v e l a g o o n s A n a e r o b i c l a g o o n s
A v e . a r e a
D e t e n t i o n
( m 2 )
t i m e
( d )
L o a d i n g
( g / m 2 - d )
B O D
r e m o v a l
( % )
A v e . a r e a
( m 2 )
D e t e n t i o n
t i m e
( d )
L o a d i n g
( g / m 2 - d )
B O D
r e m o v a l
( % )
M e a t a n d
p o u l t r y
5 , 2 6 0 7 8 . 1 8 0 4 , 0 5 0 1 6 1 4 1 . 2 8 0
C a n n i n g 2 7 , 9 0 0 3 8 1 5 . 6 9 8 1 0 , 1 2 0 1 5 4 4 . 0 5 1
C h e m i c a l 1 2 5 , 4 6 0 1 0 1 7 . 6 8 7 5 7 0 6 5 6 . 1 8 9
P a p e r 3 3 9 , 9 5 0 3 0 1 1 . 8 8 0 2 8 7 , 3 4 0 1 8 3 8 . 9 5 0
T e x t i l e 1 2 , 5 5 0 1 4 1 8 . 5 4 5 8 , 9 0 0 4 1 6 0 . 6 4 4
S u g a r 8 0 , 9 4 0 2 9 . 6 6 7 1 4 1 , 6 5 0 5 0 2 6 . 9 6 1

23. LLaanndd AApppplliiccaattiioonn
• Land treatment involves applying the
wastewater to land by one of several
conventional irrigation techniques
• Treatment is provided by natural processes
as the wastewater moves through the plant
and soil system

24. TTyyppeess ooff LLaanndd AApppplliiccaattiioonn
• Slow-rate process
– wastewater is applied to vegetated land as
irrigation water for the crops
– wastewater can be applied by sprinklers or by
flooding the land using ridge-and-furrow
techniques
– wastewater is evapo-transpirated
• used by the plants
• percolates through the soil
• system is designed to minimize surface runoff

25. TTyyppeess ooff LLaanndd AApppplliiccaattiioonn
• Rapid-infiltration systems
– Wastewater is applied to relatively permeable
soil within a basin at a much higher rate than in
the slow-rate system
• Plants may be present in the basin, but play only a
minor role in wastewater renovation.
– Treatment is accomplished by natural processes
in the soil.
– Requires much smaller land areas
• higher application rates
• recharges groundwater table

26. TTyyppeess ooff LLaanndd AApppplliiccaattiioonn
• Overland flow
method
– Minimizes percolation
into the soil
– The renovated
wastewater is collected at
the bottom of the slope
and discharged into a
surface water body
Treatment is provided by the
plants and the microbial
biomass at the soil surface as
the wastewater flows down a
sloping field

27. TTyyppeess ooff LLaanndd AApppplliiccaattiioonn
• Wetland treatment
– Also known as aquatic
treatment.
– Consist of natural or
artificial wetlands to
which wastewater is
applied Renovation is accomplished by
sedimentation and biological
activity by the plants and
microorganisms present

28. DDeessiiggnn CChhaarraacctteerriissttiiccss
T a b l e 1 0 . 7
C o m p a r a t i v e c h a r a c t e r i s t i c s o f l a n d t r e a t m e n t s y s te m s
F e a t u r e S l o w - r a t e i r r i g a t i o n R a p i d i n f i l t r a t i o n O v e r l a n d f l o w
H y d r a u l i c l o a d i n g r a t e ( c m / d ) 0 . 2 - 1 . 5 1 . 5 - 3 0 0 . 6 - 3 . 6
L a n d r e q u i r e d f o r 1 , 0 0 0 m 3 / d
6 3 . 4 - 3 9 6 3 . 2 - 6 3 . 4 2 6 . 4 - 1 5 9
( 1 , 0 0 0 x m 2 )
S o i l t y p e L o a m y s a n d t o c l a y S a n d s C l a y t o c l a y l o a m
S o i l p e r m e a b i l i t y M o d e r a t e l y s l o w t o
m o d e r a t e l y r a p i d
R a p i d S l o w

29. SSlluuddggee MMaannaaggeemmeenntt
• Sludge is 90-99%
water
• Biodegradable
organic content can
be reduced by use of
aerobic or anaerobic
treatment systems or
by composting
•Dewatering is a
difficult and expensive
process
•vacuum filtration
•filter presses
•drying beds
•centrifugation
•lagooning
•thermal processing

30. • THANK YOU