IV. Wastewater Treatment technologies
Topic IV. 9. Wastewater Treatment Facilities with
Suspended Biomass - Aerated Tanks: Kinds,
Structures, Basic Technological Parameters
Kinds of Aerated Tanks
I. According to the hydrodynamic conditions
 Completely mixed reactors
 Plug flow reactors
 Diffusion reactors
 Cell reactors
II. According to the aeration system
 With pneumatic aeration
 With surface (mechanical) aeration
 With combine aeration
 With pure oxygen supply (oxytanks)
1
Kinds of Aerated Tanks
III. According to the activated sludge regeneration
 Conventional (without activated sludge regeneration)
 Contact stabilisation (with activated sludge regeneration)
IV. According to activated sludge separation
 With separate secondary settling tanks
 With combined aerated tanks/settling compartments
 With membrane activated sludge separation
V. According to the stages
 One stage
 Two stages
VI. According to the structures and distribution
 Conventional (corridor)
 Carousel
 Stepwise wastewater (or air) distribution
2
Kinds of Aerated Tanks
Schemes
a - without regenerator
б - with regenerator
1 - wastewater influent; 2 - aerated tank; 3 - secondary clarifier; 4 - regenerator; 5 - mixed
liquor; 6 - wastewater effluent; 7 - recirculating activated sludge; 8 - waste activated sludge
3
Aerated Tanks Structures
Conventional Aerated Tank with Pneumatic Aeration
4
Aerated Tanks Structures
Fine Bubbles Pneumatic Aeration System with
Distributing Channels and Filtering Plates
5
Aerated Tanks Structures
Fine Bubbles Dome-wise
Aerator
Fine Bubbles Disk- wise
Aerator
6
Aerated Tanks Structures
Surface (mechanical) Aerator
7
Basic Technological Parameters
X - activated sludge concentration (SS) in
the aerated tank, g/m3
Rw - aerated tank volume hydraulic load, m3/m2.d
RL - aerated tank organic load, gBOD5/m3.d
RFM - food to micro-organisms ratio (F/M ratio),
gBOD5/gSS.d
U - substrate utilisation rate, gBOD5/gVSS.h
x - activated sludge age, d
I - activated sludge index, cm3
r - activated sludge recirculation ratio
EO - specific oxygen demand, gO2/Rw
t - hydraulic retention time, h
Q - wastewater flowrate, m3/h
W - aerated tank volume, m3
Qr - recirculating activated sludge flowrate, m3/h
Xr - recirculating activated sludge concentration, g/m3
QWAS - waste activated sludge flowrate, m3/h
QO2 - oxygen mass rate, g/h
Rw  Q / W
RL  Q.L0 / W
RFM  Q.L0 / W . X
 x  W . X / X r .QWAS
r  Qr / Q  ( X r  X ) / X r
QO2  E o .Rw
8