Photographs of aggregates following a 72-hour aggregation period in the roller tanks. Set-up 1 (a, b) included high concentrations of microbeads only, estimated at 24000 and 16000 L^–1 (treatments 1 and 2, respectively); set-up 2 (c, d), same high concentrations of microbeads, aggregated with 10⁶ cells L^–1 of T. weissflogii (treatments 4 and 5, respectively); set-up 3 (e, f), moderate concentrations of microbeads, estimated at 4000 and 2000 L^–1 (treatments 8 and 9, respectively), aggregated with 10⁶ cells L^–1 of T. weissflogii; and set-up 4 (g, h), same moderate concentrations of microbeads, aggregated with 10⁶ cells L^–1 of T. weissflogii, and 130 mg sediments (treatment 12). Images in panels a–f were taken in aggregation tanks for treatments 1, 2, 4, 5, and 8, 9, respectively (Table 1). Images in panels g and h were taken in the settling columns from treatment 12. A fishing line of 250 μm in diameter (as in panels g and h) was used to calibrate image size. DOI: https://doi.org/10.1525/elementa.317.f2