Biological Wastwwater Treatment

8/6/2019 Biological Wastwwater Treatment

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Freshwater systems, resources and society

A different water cycle

Biological Waste Water Treatment

Prof. Helmut KroissInstitute for Water Quality, Resource and Waste

Management Vienna University of Technology

Paris, 21. 11. 2008


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Materials and Water cyclePrecipitation

Drinkingwater

water forindustry

Nutritionmaterialsenergychemicals

N, P Soil

Sludge

nutrientshazardous comp . RiverslakesSea

Waste WaterTreatment

non biodegradablesubstancesmicro-pollutants

Our needsdemands

evapo(transpi)ration


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Conventional waste water treatmentplant configuration

Screen Grit chamber Primary Settling

AT SST

Biological treatment

Excess SludgeSludge

return flowsfrom sludge

treatment

DewateringIncineration

Disposallandfill

agricultural use,landscaping

Thickening

Stabilisation

Sludge treatment

Mechanical treatment

Sludge disposal


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Biological treatment processes

Bacteria and other microorganisms use waste waterpollution as their nutrition and grow as this happens innatural waters or soils:

in/on free floating flocs, separation from the treated

effluent by sedimentation or membranes (activatedsludge process, MBR)on a support medium (slag, stones, clay and plasticmaterial, soil particles); only excess sludge separatedfrom treated effluent by sedimentation or filtration(trickling filters, biofilters, rotating disks, constructedwetlands, etc.)


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Schematic View of Bacterial Cells

N (degradable) substrates(-ions, e.g. CH 3COO -)

E Enzymes for breakdown andtransport of substrates

A excrements(e.g. CO 2)

amplification ~100.000 times

Bacteria have only direct access to dissolved material. Solid pollution and manycomplex org. compounds have to be pre-treated by enzymes emitted by the bacteria.

Pili (hairs)

Cell-wall

Cell-membrane

Cytoplasm

flagella

DNA(geneticinformation)

metabolism(strongly

simplified)

N

N+E E

N

A

A

N + -N

N


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Five Laws of Applied Microbiologyin Biotechnology

The micro organism is always right, your friend anda sensitive partner.

There are no stupid micro organisms.

Micro organisms can and will do everything.

Micro organisms are smarter, wiser, more energetic

than chemists, engineers and others. If you take care of your microbial friends they

will take care of your future.D. Perlman, 1980


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Monod-equation

How metabolism of bacteria is controlled?

concentration of limiting substrate0


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SK

Svv:MentenMichaelis

M

max+

=

V substrate utilisation rate [g/g/d]

vmax

vmax

limiting substrate concentration

Vmax , KM are characteristic for bacterial strain

[mg/l]


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Concentration of limiting substrateK S [ng/l]

vmax

[g/g.h]

v2 v = vmax

S

K + S

0

Conversion rate, growth rate,

Monod / Michaelis Menten

2

Biological Substrate Removal Equilibrium

S [ng/l]0

No experimentalresults!

?

v


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In clean environmentsco-operation and frugalitydetermine competition

In polluted environments (nutrients donot limit growth) competition iscontrolled by genetically determined

maximum growth rate

high

biodiversity

low

biodiversity

10

conc.0

survival of the fittest

depends on substrate availability


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Adsorption Equilibrium

a , k c : Constants depending onadsorbents and adsorbing compound

aa

a = a ckc+ c

kc effluent concentration


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pollution + air

endproducts

+org. C + oxygen (O 2)energy requirement

aerobic

sludge

biologically inertsolids

decay

heterotrophic bacteria

Removal of organiccarbonaceous pollution


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org. N strict aerobic

nitriteNH4-N + oxygen (O 2)Ammonia + air

nitrate

sludge(org. C)

autotrophic nitrifying bacteria

Nitrificationfrom Ammonia to Nitrate


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anoxic

Nitrification

heterotrophic,C-consuming bacteria

sludge(biomass)

N2 (gas), CO 2H2O

Nitrogen removal bydenitrification


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actually applied for sludge liquors

~50%

aerobic denitrification

2

ANAMMOXDAEMON

aerobic

nitrite

NH 4-NNH4-N

NO 2-N

C X

biofilm

anoxicO 2

De-ammonificationRemoval of ammonia from wastewaters

poor in carbon source


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Can be characterised by:

Prevailing environmental conditions- aerobic processes (with oxygen)

- anaerobic processes (without oxygen )

Bacterial growth pattern- attached to support material (fixed film)

- suspended flocksArea requirements for plant construction

- high (>>1m/PE)- low (


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natural technological bacterial growthconstructedwetlands (1)

waste water ponds (3)

trickling filter, bio-discs,bio-filters (1)

Activated sludge (2)

attached

suspended flocks

All these processes are derived from natural, so called self purificationprocesses:

in soils (especially agricultural soils) (1) in rivers (especially in large rivers) (2) in polluted (shallow) lakes (3)

Anaerobic processes (in hot climates):only C-removal, energy production?

Aerobic treatmentprocesses


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biofilm

wastewater

supportmaterial

diffusion limited

supportmaterial

bacteria

wastewater

organicpollution

biomass + water(excess sludge)

anaerobic

aerobic

Fixed Film Reactor Technology


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Suspended flocks

O 2

O 2O 2

O2

filamentous bacteria

pollution(dissolved, suspended)

waterprotozoa

sludge flock


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WWTP Area Requirements

Natural processes: 2 to 10 m/PE

Conventional mechanical/biological treatmentplants including sludge treatment:0,13 to 0,25 m/PE

Biofilters, Membrane Bioreactors including sludgetreatment:0,1 to 0,15 m/PE

further reductions in space requirement by plantswith several floors (< 0,05 m/PE)

Criterion: costs for land ( 10 to 5000 /m)


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21

1001 10 1000 10000

constructioncosts

/m

total costs= Construction + Land/PE

0

100200300400

500600700800900

100011001200

Influence of area costson investment costs of large WWTPs

[Kroiss 2002]


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For the design of waste water treatment plants thefollowing information has to be fixed:

Design load (kg/d, m/h)(pollution loads expressed as PE or kg COD/d, the maximumhourly design flow m/h)

treatment efficiency requirement(effluent concentrations mg/l, or removal efficiency % for COD, NH 4-N, NO 3-N, TP, TN, etc.,

maximum input to the treatment plant and allowableoutput to the receiving water have to be defined for design with statistical definition and samplingprocedure (e.g.; EU-UWWD)

Design basis forwaste water treatment plants


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Scheme of a Trickling Filter Planttrickling filter

air

clarifier

primarysedimentationinfluent

effluent

primarysludge

excesssludge

air


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Biofilter technologylow space requirements, especially suitable for nitrificatione.g following chemically enhanced primary sedimentation


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1 3

2

influent effluent

aeration

4

Most important waste water treatment process worldwide

Activated sludge process

aeration tank secondarysedimentation tank

return sludge excess sludge


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MembraneBioreactor

Zul.

effluent

no suspended solids

nitrification,denitrification

P-precipitation

excess sludge

hollow fibre membranes

vacuum

vacuum

flat sheet membranes

effluent

membrane


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Activated sludge process

with phosphorus precipitation

chemicaladdition

Q [m/h]

TS BB [kg/m]

2Q

Q [m/h]TS RS = 2 TS RS

aeration

effluent

Q [m/h]

aerationtank

secondarysedimentation tank

or or

influent

return sludge excess sludge,

contains P-removed


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ASP with

N-Removal by Denitrification

denitrification(anoxic)

C-removalnitrification(aerobic)

aerationinfluent effluent

recirculation

aeration tank

secondarysedimentation tank

return sludge excess sludge


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ASP with biological

nitrogen and phosphorus removal

anaerobic anoxic aerobic secondarysedimentation tank

aeration tank

recirculation

return sludge

influent effluent

aeration

excess sludge,contains P-removed


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Technological limits for effluent quality andremoval efficiencies (municipal WW)

Effluent concentrations (95%ile daily composite

sample):C: 10 mg BOD 5/lN: 1 mg NH 4-N/lP: 0,5 mg P/l (with simultaneous precipitation)

With MBR even lower concentrations can be achievedRemoval efficiencies (depend on influent

concentrations and WW composition):BOD: 97-99%COD: 90-94%N: 80 -90 %

P: 80 95%


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Technological limits for effluent quality andremoval efficiencies (municipal WW)

Low ammonia effluent concentrations are the best

indicator for high and reliable biological treatmentefficiency for organic carbonaceous material(Monitoring!)

Low energy requirements (together with low ammoniaconcentrations) are the best indicator for optimumnitrogen removal and plant efficiency

Enhanced biological P-removal and chemicalprecipitation are compatible if properly controlled

MBR application is mainly relevant for hygienic quality

(bathing waters) and for reuse of WWTP-effluent


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Removal of micro-pollutants

high MCRT C and changing redox conditions (aerobic,

anoxic, anaerobic) are decisive factors for effluentquality and reliability.

Biodegradable micro-pollutants follow the same

dependencyAdsorbable micro-pollutants follow the adsorption

characteristics of the compounds and the

adsorption capacity of bacteria ( Sludge)Non biodegradable and adsorbable compounds can

be stripped to the air or will not be reduced

Zero effluent concentrations can never be achieved!


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Octylphenol (OP) and octylphenolethoxylates(OP 1,2 EO)

Higher removal up to >95% with increasing SRT

Bisphenol-A A nearly complete removal isobserved at SRT 10C >10 days

Bisphenol-A

SRT 10C [d]0,5 1 2 5 10 20 50 100 200

r e m o v a

l [ % ]

0

20

40

60

80

100

120

[Clara et.al. 2005]


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Natural hormones (E 1, E 2 and E 3)Removal dependent on the SRTHigh removal rates (>95%) at

SRT10C higher than 10 days

17a-ethinylestradiole (EE 2)More persistent than natural hormonesEffluent concentrations between 1 and 5 ng/lEnhanced removal with increasing SRT

E1+E 2+E 3

SRT 10C [d]

0,5 1 2 5 10 20 50 100 200

r e m o v a

l [ % ]

0

20

40

60

80

100

120

LPWWTP 1WWTP 4WWTP 2

WWTP 3MBR

[Clara et. al. 2005]

C l i


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Conclusions

Biological waste water treatment with full nitrification represents a verycost efficient tool for achieving sustainable river protectionReasonable requirements for nitrogen removal (70 to 80 % as a yearly

mean) reduce energy consumption and contribute to abateeutrophication

Reasonable requirements for P-removal are an efficient tool to preventeutrophication of lakes and coastal areas and is a prerequisite toreduce losses of this valuable resource to the seas

The EU-UWWD requirements for sensitive areas, wisely interpreted,represent an economically sound tool to achieve a low andacceptable risk for water quality management in most areas of Europe

For waste water discharge to bathing waters or other very sensitivereceiving waters as well as in the case of direct reuse of the treatedeffluent Membrane technology (MBR) can be an advantageoussolution.

Many micro-pollutants are efficiently reduced by biological treatmentwith long SRTs but others are not or only little affected.

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Biological Wastwwater Treatment