Induced blanket reactor IBR

The IBR is an in-vessel high-rate (<6 day HRT) anaerobic digester developed at Utah State University (Fig. 23.2). An IBR tank has a height :

Fig. 23.1 UASB reactor schematic.

Influent

Fig. 23.1 UASB reactor schematic.

Table 23.3 Characteristics of the UASB reactor

Advantages

Disadvantages

High organic loading capacity Short HRTs

High COD removal efficiency No need for support media Simple reactor construction Low energy demand

Granulation process difficult to control Granulation depends on wastewater properties Granule floatation

Restriction on nearly solids-free wastewater Sensitive response to organic shock loads

Fig. 23.2 IBR anaerobic digester.

diameter ratio of 2.5 : 3.5, which can vary depending on waste type. The tanks are usually ~10 m tall to facilitate settling. There is a septum located near the top of the tank. Treated waste must pass through a relatively small orifice in the septum. An anti-plugging device fills the orifice and can be made to push solids back below the septum or can be reversed to pull solids through the hole, if necessary (Hansen and Hansen, 2005). IBRs are also equipped to break up foam or a floating layer that may otherwise form at the top. Waste enters the bottom of the tank and is treated as it moves vertically through the tank and is discharged at the top. The upward velocity is much less than that recommended for UASB reactors. Livestock waste has been successfully treated with short HRTs in an IBR that was about 10 m high by 4 m in diameter (Hansen and Hansen, 2002).

The IBR captures solids from the influent where they are kept in the reactor vessel so that SRT greatly exceeds HRT. These solids also become attachment media for bacteria. If the solids concentration becomes too great, a portion is removed to avoid plugging. The IBR thus forms a sludge blanket within the digester vessel and can help maintain the size of the blanket so as to avoid plugging. As previously stated, high-rate anaerobic digesters must have some means of retaining the slow-growing anaerobic bacteria. The blanket that is induced within the IBR retains bacteria. Media can be placed in the reactor vessel so that the bacteria attach to it, such as sand in a fluidized bed bioreactor. However, the attachment media tend to plug when trying to treat waste containing a high concentration of fibrous solids such as is found in animal manure.

An integral part of the IBR system is a modular approach. IBR tanks are usually not larger than 100 000-120 000 L. Very large agricultural production or processing facilities can be accommodated. A 1000-animal unit (1000 pounds (454 kg) of live weight per animal unit) farm would require three tanks. However, there are advantages in that an IBR system can easily be built to fit small or large facilities and can be easily expanded. If part of the system fails, it does not stop the entire process.

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