Mass balance-based plant-wide wastewater treatment plant models -: Part 3:: Biodegradability of activated sludge organics under anaerobic conditions

From an experimental and theoretical investigation of the continuity of activated sludge organic (COD), inorganic and N compounds along the link between the fully aerobic or N removal activated sludge (AS) and anaerobic digestion unit operations, it was found that the unbiodegradable particulate organics originating from the influent wastewater and generated by the activated sludge endogenous process, as determined from the response of the activated sludge system, are also unbiodegradable under anaerobic digestion conditions. This means that the activated sludge biodegradable organics that can be anaerobically digested can be calculated from the active fraction of the waste activated sludge with the well-established stoichiometric and kinetic constants in steady state and dynamic simulation models. This research shows that the mass balance-based steady state activated sludge, aerobic digestion and anaerobic digestion models provide internally consistent and externally compatible elements that can be coupled to produce plant-wide steady state and dynamic simulation WWTP models.