Sludge settling prediction in sequencing batch reactor plants

Sequencing batch reactors are widely applied in domestic and industrial wastewater treatment facilities. Their use relies on the possibility of separating the sludges from the liquid phase by settling in an acceptable time. The aim of this work has been to develop a simple method for predicting the settling curve in pilot and industrial plants from the results obtained at laboratory scale. For this purpose, jar test settling experiments were carried out in a one-litre cylinder tube together with sludge volume index and volatile suspended solids determinations. For sludges with low content of filamentous microorganisms, a simple method consistent in obtaining settling velocities as a function of the relative height of the sludge blanket was developed. Additionally, a more general correlation between the sludge volume index and the ratio (settling velocities at pilot plant scale)/(settling velocities in the laboratory tests) was obtained. Having estimated the settling velocity, the necessary settling time may be calculated and the industrial equipment units can be dimensioned. The method yields good results for the values of sludge volume index between 30 and 240 mL/g.