removal in down-flow hanging sponge reactors: insights from laboratory reactor studies.

Down-flow hanging sponge (DHS) reactors, employed in domestic wastewater treatment, have demonstrated efficacy in eliminating and other potentially pathogenic bacteria. The aim of this study was to elucidate the mechanism of removal of by employing a cube-shaped polyurethane sponge carrier within a compact hanging reactor. An removal experiment was conducted on this prepared sponge. level was found to decrease by more than 2 logs after passing through five nutrient-restricted DHS sponges. Conversely, a newly introduced sponge did not exhibit a comparable reduction in level. Furthermore, under conditions of optimal nutritional status, the reduction in level was limited to 0.5 logs, underscoring the crucial role of nutrient restriction in achieving effective elimination. Analysis of the sponge-associated bacterial community revealed the presence of a type VI secretion system (T6SS), a competitive mechanism observed in bacteria. This finding suggests that T6SS might play a pivotal role in contributing to the observed decline in level.