Detailed Theory.ppt

7/30/2019 Detailed Theory.ppt

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May 2005 1

Bio-Sand FilterDesign & Key Operating

Parameters


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May 2005 2

Conventional Slow

Sand Filter Continuous flow Large volumes

BioSand Filter Intermittent flow

Small size


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May 2005 3

BioSand Filter

Description

Filter Regions

Removal Mechanisms

Design

Key Operating

Parameters

EQUIP NorthCarolina


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May 2005 4

Filter DescriptionFilter Lid

Prevents contaminants

from entering the filter

Fine Sand Layer

Traps organic and inorganicmaterial at the top of the

filter media

Diffuser Plate

Protects the schmutzdecke

from damage when water is

poured into the filter

Standing Water Layer

Keeps the schmutzdecke

alive during pause periods.

Course Sand

Prevent sand from

plugging gravel

Outlet Pipe

Conducts effluent from

filter base to outside

Gravel Underdrain

Promotes vertical flow of

water into collector pipe


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May 2005 5

Filter Regions

Sand Bed

Contains virtually no

living microbes

Schmutzdecke (biolayer)

Layer of slime, mud and

micro organisms which

develop at the sand

surface

Influent ReservoirAir Space above the filter

media which allows for

diffusion of oxygen to the

water.

Gravel Underdrain

No living microbes

present

Biological Zone

5 to 10 cm deep

Living layer of

microorganisms

SupernatantThe standing water layer

present during the pause

periods when the filter is

not in use.


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May 2005 6

Removal Mechanisms

Combination of biological and mechanical

Fine sand traps organic material at surfaceof sand and forms a layer where micro

organisms grow 4 main mechanisms

Mechanical trapping between sand grains

Adsorption/attraction onto each other, floatingmaterial and on to sand grains

Predation- bacterivore

Natural die-off


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May 2005 7

Sand Grains

ohioline.osu.edu/ b876/b876_1.html www.glg.msu.edu/research/ geophys/sand_grains.jpg

Biological film around

each sand grain

Pore spaces between

sand grains


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May 2005 8

Trapping between sand grains

Large pathogens (helminthes), silt and organicmaterial becomes trapped in the spaces betweenthe sand grains

Sand Grain

Water

Sand Grain

Pore

Space

Large Pathogens

Organic

material

Silt

Bacteria attached

to the silt


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May 2005 9

Adsorption - Attraction

Micro-organisms become attached to each other,to sediment and to the sand grains

Sand Grain

Water

Sand Grain

Silt

Silt


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May 2005 10

Predation Cycle of Life Survival ofthe Fittest

Micro-organisms consume carbon and nitrogensources

Sand Grain

Biofilm layer

of livingorganisms, carbon

and nitrogen

sources

Water


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May 2005 11

Natural Die-off Cycle of Life

Micro-organisms complete their life cycle and

become carbon and nitrogen sources

Sand Grain

Biofilm layer

of living and dyingorganisms, carbon

and nitrogen

sources

Water


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May 2005 12

THE RUNwater is pouredin the top and runs through the filter

Water providesoxygen, nutrients

and microbiology

Contaminant

removal

increases with

time

Flow rate

decreaseswith time

Larger

particlesplug pore

openings


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May 2005 13

Oxygen from

the air diffuses

through thesupernatant to

the biolayer

Organisms die off

Micro

organisms

consumepathogens Organic material oxidized

Degradable organic matter

gradually broken down

Partialunplugging

of pores

THE PAUSE PERIODno flow, water is sitting in the filter


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May 2005 14

Operation & Maintenance(Swirl and dump - filter cleaning)

Percentage Removal Efficiency with Time

Typical Curve


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May 2005 15

Key Operating Parameters

Flow rate controlled by sand size(Sieving and washing)

Pause period(Micro-organisms consume pathogens)

Water / Sand level Too shallow biolayer dries out

Too deep insufficient oxygen for biolayer

Supply water quality Consistent

Clean enough to prevent premature fouling (not greater than 50 -100 NTU)


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May 2005 16

Key Operating Parameters

Start up time establish biolayer

Maintenance Cleanliness

Swirl and dump

Filtered water quality > 95 % removal efficiency

Disinfection recommended for best quality water

Detailed Theory.ppt

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