Motility-enhanced bioflocculation

Bacteria often rely on their ability to aggregate to survive in nature. They can form clusters among themselves or with suspended colloids, leading to biologically-enhanced flocculation (bioflocculation). We investigate the role of cell motility on bioflocculation by comparing two strains of~\textit{Escherichia coli,~}a wild type and a non-motile mutant.~We quantify settling rates from a suspension of bacteria and 1 $\mu $m polystyrene beads, by independently varying the concentration of bacteria and colloids. We find that motility enhances settling rates up to 6-fold\textbf{. }We~rationalize our findings in terms of an increase in encounter rates between bacteria and colloids. These results could contribute to improve the performance of wastewater treatment processes and provide a possible explanation for why motile bacteria are more successful biofilm formers.