Adsorbing flocs in expanded/fluidised bed reactors: A new basis for pollutants removal

The present work describes studies concerning a new adsorption technique based on the use of adsorbent flocs in an expanded/fluidised bed reactor for the removal of pollutants from aqueous solutions. The technique, based on flocculation of aqueous suspensions of powdered adsorbent materials, when conducted in an expanded/fluidised bed reactor takes advantage of conducting adsorption and solid–liquid separation in one single stage. Studies were performed using flocculated powdered activated carbon and natural zeolites, alone and in mixtures, for phenol and ammonia adsorption. A reactor with cylindrical–conical geometry was used for the pollutants adsorption in flocs beds (pure and mixed), as well as the regeneration/recycle of the exhausted adsorbents. Results proved the high adsorption efficiency of powdered natural zeolites and activated carbon flocs for the uptake of ammonia (11 mg NH3–N g−1) and phenol (132 mg g−1), at 38 and 19 m h−1 loading rates, respectively. Regeneration/recycle of the pollutant-saturated beds was possible for the ammonia/natural zeolites adsorption case, using sodium sulphate as regenerator. Use of mixed flocs beds was efficient, showing advantages such as multiple-pollutants adsorption in one single stage, higher loading rates when using light materials (activated carbon) combined with heavier ones (natural zeolites) and use of small adsorbent concentrations (not possible otherwise). Economical and environmental issues regarding the technique are also discussed in the paper. The new technique shows great potential as an alternative physicochemical adsorption process for pollutant removal from aqueous solutions using low-cost and highly-available powdered adsorbent materials.