Amount and nature of soluble refractory organics produced by activated sludge micro-organisms in sequencing batch and continuous flow reactors

Comparative experiments with a Sequencing Batch Reactor (SBR) and a continuous flow activated sludge system have been conducted in bench-scale to study factors affecting molecular composition and concentration of residual Soluble Microbial Products (SMP). It was experimentally confirmed that the amount of SMP in secondary effluents depends on applied process conditions, in particular on sludge age, hydraulic detention time distribution and concentration gradients within the bioreactor. The residual SMP consist of both low and high molecular organic compounds. The former prevail. The continuous flow system with a completely mixed aeration tank produced consistently higher concentrations of SMP than the SBR. The lowest SMP concentration was found at sludge ages between 5 and 15 days.