Measuring biomass specific ammonium, nitrite and phosphate uptake rates in aerobic granular sludge

Aerobic granular sludge (AGS) technology offers the possibility to remove organic carbon, nitrogen and phosphorus in a single reactor system. The granular structure is stratified in such a way that both aerobic and anaerobic/anoxic layers are present. Since most of the biological processes in AGS systems occur simultaneously, the measurement and estimation of the capacity of specific conversions is complicated compared to suspended biomass. The determination of the activities of different functional groups in aerobic granular sludge allows for identification of the potential metabolic capacity of the sludge and aids to analyze bioreactor performance. It allows for comparison of different sludges and enables improved understanding of the interaction and competition between different metabolic groups of microorganisms. The most appropriate experimental conditions and methods to determine specific ammonium, nitrite and phosphate uptake rates under normal operation of AGS reactors were evaluated and described in this study. Extra biomass characterization experiments determining the maximum uptake rate of these compounds on optimized conditions were performed as well to see how much spare capacity was available. The methodologies proposed may serve as an experimental frame of reference for investigating the metabolic capacities of microbial functional groups in biofilm processes.

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► Methods to measure specific rates of NH4+,NO2- and PO43- in aerobic granular sludge are provided.
► Optimized conditions for widely used methods to determine specific activities are suggested.
► Gradual electron acceptor dosage is the most appropriate method to determine the maximum anoxic P-uptake.
► The maximum NH4+ and NO2- oxidation rate can be obtained in aerobic tests with crushed granules.
► Biological oxygen monitor tests should be conducted with pre-aerated (3h) crushed granules.