Application of biofilms and biofilm support materials as a temporary sink and source

Wastewater treatment plants are typically subjected to variable influent loading conditions. Extreme variations of flow, composition and substrate concentration may occur in the influent of industrial wastewater treatment plants, but also at plants serving tourist areas. High rate reactors of low hydraulic buffer capacity are particularly affected. Exploitation of internal equalization capacities are proposed to dampen the fluctuations of biomass loading. In this context, the biomass itself and - in case of biofilm reactors - the biofilm support media may be considered as a sink during peak loading situations, and as a source of substrate as soon as the influent loading drops. Sequencing Batch Biofilm Reactors (SBBR) studies in laboratory and pilot scale were conducted to investigate the capacity of these internal sink and source terms. The reactors were packed with four types of biofilm carrier materials, blasted clay granules, granular activated carbon, zeolite and small size plastic rings (Kaldnes). Temporary storage of substrates was achieved by means of adsorption, ion exchange and absorption processes. As the react phase proceeded, the bulk liquid concentration dropped and desorption processes followed by metabolic reactions became dominant. From the results achieved it can be concluded that thick biofilms, and biofilm support media with sorptive capacities are favorable to counteract peak loading fluctuations, and to keep the effluent concentration from exceeding set discharge levels.