Degradation of Partially Soluble Wastewater in an Anaerobic Sequencing Batch Biofilm Reactor Role of Impeller Type

This work reports on the role of the impeller type and agitation rates on the performance of an anaerobic sequencing batch biofilm reactor treating a partially soluble wastewater. Different types of impellers (propeller, flat-blade, pitched-blade, and curved-blade turbines), operating at different agitation rates, were tested for the treatment of soymilk-based synthetic wastewater. The substrate contained a concentration of suspended solids corresponding to about 45% of the total (1,000 mg·L^–1) chemical oxygen demand (COD). The reactor, with 6.5 liters of working volume, was filled with an inert support consisting of 3-cm cubic polyurethane foam particles for attachment of the biomass. The startup period was rapid, and an average COD removal of about 70% was achieved with each type of impeller. After the acclimatization period, temporal COD profiles were obtained for each impeller and agitation rate. The effect of the agitation rate on the kinetics was evaluated based on an analysis of the parameters derived from adjusting a modified first-order expression to the temporal COD profiles. The apparent kinetic constants of the two groups of impellers differed: mixed- (propeller and pitched-blade) and radial-flow (flat and curvedblade). Different values of residual COD were also obtained. An analysis of organic matter consumption rates indicated that the reactor equipped with radial-flow impellers provided the best overall performance, whereas the mixed-flow would be more suitable for higher agitation rates. It was concluded that mechanical stirring can improve the performance of anaerobic reactors treating wastewaters containing particulate organic matter.