Reclamation of an activated-sludge microbial consortium by selective biostimulation

Our previous study showed that an activated-sludge process broke down at th e phenol-loading rate of 1.5 g l(-1) day(-1), when non-flocculating bacteri a (called R6T and R10) overgrew the sludge, resulting in a sludge washout. In this study, we attempted to circumvent this breakdown problem by reclaim ing the consortium structure. Activated sludge was fed phenol, and the phen ol-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 ph enol-loading rate of 1.0 g l(-1) day(-1). Pure culture experiments have sug gested galactose to be a preferential substrate for a floc-forming bacteriu m (R6F) that predominantly degrades phenol under low phenol-loading conditi ons. Supplying galactose allowed sustainment of the R6F population and supp ression 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 brok e down at 2.0 g l(-1) day(-1). In contrast, supplying glucose reduced the R 6F 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 re clamation of the activated-sludge consortium by selective biostimulation of the hoc-forming population improved the phenol-treating ability of the pro cess.