But PSB are difficult to be collected fromwastewater because of their
small size and resistance to flocculation [14–17]. The typical diameter of PSB is 0.5–3.0 μm [16,17], and each PSB cell as a single individual disperses in water, so PSB cannot form flocs like activated sludge. Their resistance to flocculation leads to poor settling efficiency and poor biomass recovery efficiency in traditional PSB wastewater treatment systems.