Transcript Trickling Filters_lecture

Attached Growth Biological WW
treatment Systems
Biofilm Systems
• Biofilm
– a biological slime layer
– bacteria in biofilm
degrade organics
– biofilm will develop
on almost anything
Types of Biofilm Systems
• Trickling filters
• Rotating biological contactors
• Fluidized bed reactors
• Biofilters
• Wetlands systems
• Sequencing batch biofilm reactors
(many of these can be aerobic or anaerobic)
Trickling
Filters
Flow Diagram for Trickling Filters
Recycle
Final
clarifier
Final
effluent
Influent
Primary
clarifier
Trickling
filter
Waste
sludge
Trickling Filters
• Not a true filtering or sieving process
• Material only provides surface on which
bacteria to grow
• Can use plastic media
–
–
–
–
–
lighter - can get deeper beds (up to 12 m)
reduced space requirement
larger surface area for growth
greater void ratios (better air flow)
less prone to plugging by accumulating slime
Trickling Filters
Filter Material
Typical Trickling Filter
Typical Modular and Random
Packed Plastic Media
Schematic diagrams of modular and random packed media used
in fixed-film treatment systems (Source: Bordacs and Young, 1998)
Leonard W. Casson, Ph.D., P.E., DEE
Random Packing
Leonard W. Casson, Ph.D., P.E., DEE
Structured Media
Bio-towers
Trickling Filter
• Tank is filled with solid media
– Rocks
– Plastic
• Bacteria grow on surface of media
• Wastewater is trickled over media, at top of tank
• As water trickles through media, bacteria degrade BOD
• Bacteria eventually die, fall off of media surface
• Filter is open to atmosphere, air flows naturally through media
• Treated water leaves bottom of tank, flows into secondary clarifier
• Bacterial cells settle, removed from clarifier as sludge
• Some water is recycled to the filter, to maintain moist conditions
Trickling Filter System
Trickling Filter Process
Bacteria Removal
Types of Trickling Filters
• 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
Types of Trickling Filters
• 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
Types of Trickling Filters
• 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
Design Criteria for Trickling Filters
Table 10.5
Typical Design Criteria for Trickling Filters
Item
Low-rate filter
High-rate filter
Super-rate filter
Hydraulic loading (m3/m2-d)
1-4
10 - 40
40 - 200
Organic loading (kg BOD5/m3-d)
0.08 - 0.32
0.32 - 1.0
0.8 - 6.0
Depth (m)
1.5 - 3.0
1.0 - 2.0
4.5 - 12.0
Recirculation ratio
0
1-3
1-4
Filter media
Rock, slag, etc.
Rock, slag,
synthetics
Filter flies
Many
Few, larvae are
washed away
Few or none
Sloughing
Intermittent
Continuous
Continuous
Dosing intervals
< 5 min
< 15 s
Continuous
Effluent
Usually fully
nitrified
Nitrified at low
loadings
Nitrified at low
loadings
Design Equation (NRC)
Single stage
E1 
1
 QC in 
1  4.12

VF


0.5
E1 = fraction of BOD5 removal for first stage at 20 oC, including recirculation
and sedimentation
Q = wastewater flow rate, m3/s
Cin = influent BOD5, mg/L
V = volume of filter media, m3
F = recirculation ratio
1 R
F
2
(
1

0
.
1
R
)
3
Qr = recirculation flow rate, m /s
R = Qr/Q
Design Equation (NRC)
Second stage
1
E2 
4.12  QC e 
1


1  E1  VF 
E2 = fraction of BOD5 removal for second stage filter at 20 oC, including
recirculation and sedimentation
Ce = effluent BOD5 concentration from first stage, mg/L
ET  E20
(T  20)
Study examples 9-2,9-3
and 9-4
Ex. 5-5
Given:
Single-stage, low rate trickling filter
Volume of filter = 1,443 m3
Hydraulic loading = 1,900 m3/d
F = 2.78; Cin = 150 mg/L
Question:
BOD5 of the effluent
Solutions:
1. Hydraulic loading: Q = (1,900 m3/d) (1d /86400 s) = 0.022 m3/s
2. Efficiency:
E1 
1
 (0.022)(150) 

1  4.12
 (1443)( 2.78) 
 0.8943
0.5
3. Concentration of BOD5: Ce = (1-0.8943)(150) = 15.8 mg/L
Rotating Biological Contactor
Rotating Biological Contactors,
commonly called RBC’s, are used in
wastewater treatment plants
(WWTPs). The primary function of
these bio-reactors at WWTPs is the
reduction organic matter.
RBC Schematic
Film of Microorganisms
Leonard W. Casson, Ph.D., P.E., DEE
Rotation
Wastewater
Rotating Biological Contactors
Rotating Biological Contactors
• RBCs constructed of plastic media on a long shaft
• Media is submerged in a tank
• Shaft rotates media through water
• Bacteria grow on media, degrade BOD in water
• Bacteria get air by exposure to atmosphere
• Bacteria eventually die, fall off media surface
• Dead bacteria and other solids are removed in the secondary clarifier
• Media up 12 feet in diameter
• Shafts as long as 25 feet
• Media areas up to 180,000 square feet per shaft
Rotating Biological Contactors
Primary
Settling
Sludge
Treatment
Secondary
Settling
Sludge Treatment
Flow Diagram for RBCs
Rotating Biological Contactor (RBC)
Single RBC
Rotating Biological Contactor (RBC)
Defective RBC’s at the Easton Wastewater Treatment Plant
Leonard W. Casson, Ph.D., P.E., DEE
Package RBC System