Attached Growth Biological WW treatment Systems

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Attached Growth Biological WW treatment Systems
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Biofilm Systems

• Biofilm
• a biological slime layer
• bacteria in biofilm
• degrade organics
• biofilm will develop
• on almost anything

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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)

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TricklingFilters
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Flow Diagram for Trickling Filters
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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

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Trickling Filters
Filter Material
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Typical Trickling Filter
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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)
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Random Packing
Leonard W. Casson, Ph.D., P.E., DEE
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Structured Media
Leonard W. Casson, Ph.D., P.E., DEE
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Bio-towers
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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

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Trickling Filter System
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Trickling Filter Process
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Bacteria Removal
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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

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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

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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

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Design Criteria for Trickling Filters
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Design Equation (NRC)
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Design Equation (NRC)
Second stage
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
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Ex. 5-5
Study examples 9-2,9-3 and 9-4
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
3. Concentration of BOD5 Ce (1-0.8943)(150)
15.8 mg/L
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Rotating Biological Contactor

• Rotating Biological Contactors, commonly called
  RBCs, are used in wastewater treatment plants
  (WWTPs). The primary function of these
  bio-reactors at WWTPs is the reduction organic
  matter.

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(No Transcript)
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RBC Schematic
Film of Microorganisms
Rotation
Leonard W. Casson, Ph.D., P.E., DEE
Wastewater
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Rotating Biological Contactors
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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

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Rotating Biological Contactors
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Flow Diagram for RBCs
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Rotating Biological Contactor (RBC)
Single RBC
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Rotating Biological Contactor (RBC)
Defective RBCs at the Easton Wastewater
Treatment Plant
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Package RBC System
Leonard W. Casson, Ph.D., P.E., DEE