Environmental Engineering Reference
In-Depth Information
taBle 32.11
applicable hrt for treatment of raw domestic Wastewater
in a uasB reactor
maximum hrt
for 4- to 6-h Peak (h)
temperature (°c)
average hrt (h)
16-19
10-14
7-9
22-26
7-9
5-7
>26
6-8
4-5
Source:
Lettinga, G. and Hulshoff, L.W., UASB-process design for various types of
wastewaters.
Water Sci Technol
, 24, 87-107, 1991.
taBle 32.12
upflow velocities and reactor heights recommended for uasB reactors
upflow velocity [m/h]
reactor height [m]
Wastewater type
range
typical
range
typical
COD nearly 100% soluble
1.0-3.0
1.5
6-10
8
COD partly soluble
1.0-1.25
1.0
3-7
6
Domestic wastewater
0.8-1.0
0.7
3-5
5
32.4.3 S
EquEncing
B
atch
r
Eactor
Sequencing or sequential batch reactors (SBR) are industrial processing tanks for the treatment of
wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or
mechanical biological treatment facilities in batches. Oxygen is bubbled through the wastewater to
reduce biochemical oxygen demand (BOD) and chemical oxygen demand (COD) to make it suitable
for discharge into sewers or for use on land.
A sequencing batch reactor in the system with activated sludge (Orhon 1994) operates on the
basis fill-and-draw. In recent years, the modification of the fill-and-draw process is intensifying as
an SBR system. SBR offers various advantages in comparison with a conventional activated sludge
system.
All wastewater treatment plants that were in operation between 1914 and 1920 were designed as
fill-and-draw systems. When continuous flow activated sludge systems were developed, interest for
sequencing batch reactors extremely declined. In the early 1960s, SBR systems began to reappear
with the development of new technology and equipment (Dennis 1979; Hoepker et al. 1979; Irvine
et al. 1979; Ketchum 1979; Irvine and Moe 2001).
The SBR process is composed of one reactor or by a series of parallel reactors where complete
treatment procedures occur: wastewater treatment and separation of sludge from treated
wastewater. The operating principles of the SBR are characterized by five discrete periods:
fill, react, settle, decant, and idle. When the SBR is subjected to sequential redox environments
(anaerobic/anoxic/aerobic conditions) during the react period, it provides the removal of
organic substrate and nutrients simultaneously. Ammonium is oxidized to nitrite and nitrate
(nitrification) in the aerobic phase and nitrate is reduced to N
2
(denitrification) in the anoxic
phase of the react period. Organic substrate from the wastewater is oxidized in the anoxic phase
in the denitrification process.
Although the SBR process looks like the classical
fill-and-draw
process with activated sludge,
the development of SBR is most recent (Irvine et al. 1979; Chambers 1993; Wilderer 2001).
