Reclamation of an activated-sludge microbial consortium by selective biostimulation

Abstract

Our previous study showed that an activated-sludge process broke down at the phenol-loading rate of 1.5 g l(-1) day(-1), when non-flocculating bacteria (called R6T and R10) overgrew the sludge, resulting in a sludge washout. In this study, we attempted to circumvent this breakdown problem by reclaiming the consortium structure. Activated sludge was fed phenol, and the phenol-loading rate was increased stepwise from 0.5 g l(-1) day(-1) to 1.0 g l(-1) day(-1) and then to 1.5 g l(-1) day(-1). Either galactose or glucose (at 0.5 g l(-1) day(-1)) was also supplied to the activated sludge from the phenol-loading rate of 1.0 g l(-1) day(-1). Pure culture experiments have suggested galactose to be a preferential substrate for a floc-forming bacterium (R6F) that predominantly degrades phenol under low phenol-loading conditions. Supplying galactose allowed sustainment of the R6F population and suppression of the overgrowth of R6T and R10 at the phenol-loading rate of 1.5 g l(-1) day(-1). This measure allowed the activated-sludge process to treat phenol at a phenol-loading rate up to 1.5 g l(-1) day(-1), although it broke down at 2.0 g l(-1) day(-1). In contrast, supplying glucose reduced the R6F population and allowed the activated-sludge process to break down at the phenol-loading rate of 1.0 g l(-1) day(-1). This study demonstrated that reclamation of the activated-sludge consortium by selective biostimulation of the floc-forming population improved the phenol-treating ability of the process.

Stable augmentation of activated sludge with foreign catabolic genes harboured by an indigenous dominant bacterium

“…On day 35, 20 days after inoculation, the activated sludge was subjected to a shock loading with phenol at 2.0 g l −1 day −1 . Our previous study (Watanabe et al ., 2000) has shown that phenol was discharged from the activ‐ated sludge unit immediately after the loading rate was increased to 2.0 g l −1 day −1 , even after the sludge had been sufficiently acclimatized to phenol. Figure 2B shows that phenol was promptly discharged from the non‐inoculated control, rN7‐inoculated and R5‐inoculated units after the shock loading at 2.0 g l −1 day −1 , whereas the rN7(R503)‐inoculated unit could cope with this shock loading.…”