Anaerobic Rotating Disc Reactor

Anaerobic rotating disc reactors (RDR) are characterized by a horizontal wheel that, on a technical scale, can have a diameter of up to 2 m and a length of about 5 m (Fig. 8.9). With a plate spacing of 5 cm, about 100 plates can be installed, giving a total surface area of about 630 m2.

An anaerobic RDR has a double wall for heating and temperature control, has a closed top and is combined with a gas collection system. The plates are completely submerged in the wastewater. Surplus sludge is collected at the bottom and must be removed periodically. The discs rotate with a speed of 0.5-2.0 min-1.

Several authors have published results obtained by laboratory-, pilot- and large-scale studies (Tait and Friedman 1980; Laquidara et al. 1986; Ware and Pescod 1989; Ware et al. 1990; Breithaupt 1997; Breithaupt and Wiesmann 1998).

Breithaupt (1997) used plates with a covering made from a synthetic structural material which made it possible to form biofilms with a higher area and thickness. In these anaerobic RDR both a high total COD removal and a high COD removal rate could be realized for wastewater with high acetate concentrations.

The reactor is not completely mixed: the concentration of immobilized bacteria increases in the first 25% of the total length up to 10 g L-1 MLSS and decreases in the last 75% down to 2.5 g L-1 MLSS. The pH increases due to the methanization of acetate. Using an acetate balance and considering axial dispersion, Haldane kinetics and the influence of locally changing pH, mathematical models were used to calculate the acetate concentration profile (Breithaupt 1997).

Anaerobic RDRs are particularly suitable for moderate amounts of highly loaded wastewater. Low amounts of <10 m3 d-1 wastewater are more appropriate for aero

Hn..hia iuqn À Plates with textile I effluent double wall structure material ▼

heating water heating water

Fig. 8.9 Anaerobic rotating disc reactor (Breithaupt 1997).

bic treatment; and high amounts of >103 m3 d-1 should be treated by using one of the other anaerobic processes described above.

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