Removal of high phenol concentrations with adapted activated sludge in suspended form and entrapped in calcium alginate/cross-linked poly(N-vinyl pyrrolidone) hydrogels

The present work evaluates the aerobic removal of 0.25-2 g/L of phenol by adapted activated sludge in batch and continuous reactors, in suspended form and trapped in polymeric hydrogel beads of calcium alginate(1%) and cross-linked poly(N-vinyl pyrrolidone), x-PVP (4%). The mechanical and chemical resistance of the entrapping hydrogel was also evaluated in three different media: (I) rich in phosphate and ammonium ions; (II) using alternate P and N sources, and (III) without nutrients. The adapted consortium removed phenol concentrations up to 2 g/L more efficiently in the immobilized systems. A decrease in phenol removal rate was observed as the food/microorganisms (F/M) ratio increased. A zero-order kinetics was observed with phenol concentrations > 1 g/L and a first-order kinetics at concentrations < 1 g/L. The best response (100% removal) was in the continuous reactors using type II medium, with a hydraulic residence time (HRT) of 12.5 h, an influent pH = 5, and an F/M ratio below 0.25. The immobilizing matrix deteriorated after 170 h of use in continuous reactors, especially with media I and II, probably due to the attrition forces, to chemical weakness of the material, and to the pressure of the bacterial growth inside the bead.