All biological wastewater treatment systems remove mainly "fast food," i.e. readily biodegradable soluble organics (including some organic nitrogen compounds), but (very) little "slow food," i.e. recalcitrant organic carbon compounds (COD) and organic nitrogen (TKN) such as colloids, organic color compounds (e.g. lignin, dyes), and various synthetic organic chemicals (e.g. pharmaceuticals).
Key reasons why biological wastewater treatment systems remove (very) little "slow food" are insufficient reaction time in bulk liquid, mass transfer limitations (e.g. biofilm systems, enzyme contact), micropopulation issues (e.g. adaptation, selection, regeneration, activity, diversity), and suboptimal operating conditions (e.g. temperature, nutrients).
Over the last 40 years, Model Engineering stepwise improved the well-known activated sludge (AS) process which is the standard biological treatment in over 90% of sewage and wastewater treatment plants worldwide. In the early 1990s, they achieved a breakthrough to boost AS process performance by removing most of the "slow food," in addition to the "fast food." They do this by capturing this "slow food" from the bulk liquid and putting it in direct contact with microbial enzymes resulting from their proprietary selection and regeneration integrated into new and existing AS systems. Since then, they have applied their advanced activated sludge (AAS) process at full scale, mainly on industrial wastewaters, albeit with low salt concentrations. A next step is treating wastewater with higher salt levels.