Shielding immobilized biomass cryogel beads with powdered activated carbon for the simultaneous adsorption and biodegradation of 4-chlorophenol

Abstract

In order to retain a high concentration of activated sludge in the wastewater treatment plant, the dense activated sludge is entrapped into the polyvinyl alcohol (PVA) cryogel beads. For protecting the entrapped activated sludge biomass from the inhibitory effect exerted by recalcitrant pollutant, i.e., 4-chlorophenol (4-CP), the novel PVA cryogel beads with external surface covered by the powdered activated carbon (PAC) were successfully synthesized in this study. The synthesis was achieved by extruding the biomass-PVA polymeric matrix into the gelatin solution containing PAC. The maximum PAC density on the external surface of cryogel beads was calculated to be in the range of 938–978 mg/m2. The PAC distributed on the external surface of cryogel beads was found to possess a higher 4-CP adsorption capacity than the beads with homogenized PAC. These cryogel beads were also capable of shielding the activated sludge biomass entrapped within beads from being directly exposed to the inhibitory effect of 4-CP via adsorption by PAC distributed on the external surface. Thus, only low concentration of 4-CP was diffused into the beads and biodegraded to achieve a total removal of 4-CP. This beneficial effect was later confirmed could last for more than 20 cycles of uses in removing 4-CP via the simultaneous adsorption and biodegradation processes.