Experiments and modelling on biomass transport inside upflow sludge blanket reactors intermittently fed

The paper describes the experimental and theoretical acitivities developed to study the biomass transport phenomena occurring in upflow anaerobic reactors influencing the biomass washout. Particularly, the experimenatl investigations have been carried out on a full-scale ABR and on a pilot UASB intermittently fed with the aim to determine the extent to which washout is affected by: daily flow distribution; upflow velocity; concentration and sedimentation properties of the biomass. The thoeretical study focused on the proposal of a mathematical model able to simulate the sludge transport phenomena in the above cited reactors, in order to obtain a tool to estimate sludge washout in different influent flow conditions. The research has shown the considerable influence on the biomass behaviour of the time interval occurring between two successive feeds of the reactors. In fact, if this period is more than 1 h considerable losses of biomass into the effluent were found, independent of the upflow velocity. On the other hand, shorter periods give to a regular sludge expansion of the interface even with very high upflow velocities (up to 4 m/h), and consequently to limited sludge washout.