The key principle is to grow a mixed biomass of algae (and phototrophic cyanobacteria) and selected bacteria. The latter could be ordinary heterotrophs, nitrifiers or in special cases anammox bacteria. PAS technology is different from regular pond systems, in that it optimises the mixed culture and the observed volumetric removal rates are much higher, because of higher biomass concentration and gentle mixing.
- Natural system with better effluent quality
- Significantly less complicated than activated sludge
- Under tropical conditions <0.5 m² per population equivalent
- Net energy producer, no mechanical aeration, algae biomass production and anaerobic biomass digestion
- Nutrient recovery (P)
- Good disinfection