Advanced phosphorus removal from membrane filtrates by adsorption on activated aluminium oxide and granulated ferric hydroxide

The advanced phosphorus (P) removal by adsorption was studied for its suitability as a post-treatment step for membrane bioreactor (MBR) effluents low in P concentration and particle content. Two commercial adsorbents, granulated ferric hydroxide (GFH) and activated aluminium oxide (AA), were studied in batch tests and lab-scale filter tests for P adsorption in MBR filtrates. GFH showed a higher maximum capacity for phosphate and a higher affinity at low P concentrations compared to AA. Competition by inorganic ions was negligible for both adsorbents at the original pH (8.2). When equilibrium P concentrations exceeded 2 mg L−1 in the spiked MBR filtrates, a precipitation of calcium phosphates occurred additionally to adsorption. During column studies the effluent criteria of 50 μg L−1 P was reached after a throughput of 8000 bed volumes for GFH and 4000 for AA. Dissolved organic carbon appears to be the strongest competitor for adsorption sites. A partial regeneration and reloading of both adsorbents could be achieved by the use of sodium hydroxide.