Internal Circulation Reactor IC

In industrial practice, one major limitation of UASB reactors is the washout of seed sludge during the start-up period. In order to overcome the washout-related operation problem in conventional UASB system, Pereboom and Vereijken (1994) presented a modified design of two-stage UASB reactor, namely the internal circulation (IC) reactor. The IC reactor consists of two inter-connected UASB compartments on top of each other. In the first stage located in the bottom part of the IC reactor, most biogas will be produced, and it will be trapped in the first section of gas-hoods and then rise through the riser section to a gas-liquid separator placed on top of the reactor. The biogas production thus drives an internal circulation flow, which results in excellent mixing in the bottom section. In the second stage in top biomass retention and effluent polishing takes place. It seems that the high turbulence and adequate mixing characteristics make the IC reactor more attractive for reducing clogging and handling high strength organic wastewater. Comparison of results is listed in Table 3.4. Obviously, the performance of IC reactor is comparable with or even better than that of UASB for high strength industrial wastewater treatment.

Table 3.4. The performance of internal circulation (IC) and conventional UASB reactors (extracted from Pereboom and Vereijken, 1994)

UASB

IC

IC

UASB

IC

Wastewater type

Brewery Brewery Brewery

Potato

Potato

Reactor volume (m3)

1400

50

162 x 6 units

1700 x 2 units

100

VLR (kg COD/m3 -d)

6.8

20

24

10

48

OLR (kg COD/kg VSS-d)

0.2

0.7

0.96

0.35

1.3

Biogas production (m3/m3-d)

2.0

5.5

3.0

COD removal efficiency (%)

80

85

80

95

85

Average diameter of

0.6

0.84

0.66

0.51

granules (mm)

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