Efficient aeration – oxygen transfer

34 Pages·2017·2.44 MB·English

by  Justus Behnisch

Efficient aeration –
oxygen transfer
Prof. Dr.-Ing. habil. Martin Wagner
Justus Behnisch, M.Sc.
Anja Ganzauge, M.Sc.
07.06.2017 | Institut IWAR | Prof. Dr.-Ing. habil. Martin Wagner | 1
Structure
 Introduction
 Oxygen transfer in wastewater
 SOTR
 General requirement
 α-value
 Dimensioning an energy efficient aeration system
 New design approach and the EXPOVAL project
 Conclusions
 References
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Energy demand for aeration/mixing
 WWTP consume large
POWER REQUIREMENT WWTP
amounts of energy
Consumer:
5% Aeration
5%
 Aeration Recirculation
15%
 Mixing
Sludge treatment
 Pumps
60% Mechanical
…
15%
cleaning
Other
 Optimization of
the energy efficiency of a
WWTP
[DWA(2008)]
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Objectives of Aeration
 provide oxygen for carbon and nitrogen oxidation
 maintaining minimum oxygen concentration:
 without nitrification > 0 – 0.5 mg/l
 nitrification 1.5 – 2.0 mg/l
Disc Tube Plate
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Objectives of Aeration
Mixing of aeration tanks
 avoid settling of activated sludge
 provide nutrient transfer (BOD, N, P, O )
2
to bacteria (-flocs)
 provide transport of metabolism
products from bacteria (-flocs)
 provide stripping of gases
 CO  from BOD degradation (pH-value)
2
 N  denitrification
2
source: Ruhrverband
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Aeration systems
1. Mechanical/Surface
aeration
 Water drops in the air
 O Diffusion from air into water
2
source: biogest.de
2. Fine bubble Aeration
 Gas-bubbles in the water
 O Diffusion from gas bubble into
2
water
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Dimensioning an aeration system
Standard Oxygen Transfer Rate SOTR [kg O /h]
2
 “SOTR is the mass [kg] of oxygen transferred by an aeration
installation in one hour in a tank of certain size filled with clean water
at DO of C = 0 mg/L, a water temperature of 20 °C and normal
atmospheric pressure (1,013 mbar).”
(ATV-M209E)
 Oxygen Transfer at Standard Conditions
 atmospheric normal air pressure (1,013 mbar -> C )
S
 TW = 20 °C -> c und k a
S L
 oxygen concentration C = 0 mg/l
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Dimensioning an aeration system
 calculation of Standard Clean Water Oxygen Transfer Rate
(SOTR) according to the DWA-M 229-1 (2013):
𝑓 ∙ 𝛽 ∙ 𝐶
𝑑 𝑆,20
𝑆𝑂𝑇𝑅 = ∙ 𝑂𝑉
𝑝 ℎ
𝛼 ∙ 𝑓 ∙ 𝛽 ∙ 𝐶 ∙ 𝑎𝑡𝑚 − 𝐶 ∙ 𝜃 𝑇 −20
𝑊
𝑑 𝑆,𝑇 1,013 𝑋
SOTR: Standard Oxygen Transfer Rate [kgO /h]
2
OV : Oxygen demand (OUR) [kgO /h]
h 2
f : depth factor [-]
d
c : O saturation concentration [mg/l]
S 2
β: salt factor [-]
f : salt factor for α-value [-]
S
α: alpha-value [-]
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General requirements
source: www.stol.it www.merkur.de www.shutterstock.com
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General requirements
Influence of salt:
Salt reduce O saturation concentration:
2
c = β · c
S,wastewater S
β: salt factor = 0,95 to 1,0 = 1 – 0,01 · TDS [-]
TDS: Total Dissolved Solids [g/L]
e.g. North Sea: β  0,8
Other effects by salt, where investigated in the EXPOVAL Project (later
in this presentation)
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