Investigation and visualization of internal flow through particle aggregates and microbial flocs using particle image velocimetry

► Use of particle image velocimetry for flow visualization around large aggregates. ► PIV streamlines as direct experimental proof of internal flow through aggregates. ► Permeable and fractal feature of particle aggregates and bio-flocs. ► PIV images for determining fluid collection efficiency of falling aggregates. ► Lower permeability of bio-flocs than particle aggregates due to EPS production.