Ammonium removal using a novel unsaturated flow biological filter with passive aeration

A novel vertical bed process for the removal of ammonium from secondary eff luents, using a "passive air pump", has been developed. The process is base d on convective aeration caused by a fill and draw operational sequence, an d combines the advantages of the vertical wetlands concept with the high lo ading rates typically associated with trickling filters. Experiments were c arried out in a 500-l reactor using simulative effluents and actual municip al secondary effluents. A maximal ammonium removal rate of 1100 g N/m(2) re actor/d was achieved using simulative effluents and an effective gravel siz e of 0.96 mm. At all hydraulic loads applied, the nitrification rate was fo und to be limited by the oxygen transfer rate. The small-size medium used w ith simulative effluents clogged when using actual municipal secondary effl uents. Two other media (2.46mm and 4.31mm) did not clog during the entire e xperimental period and a maximum removal load of 300 g N/m(2) reactor/d was achieved. This value is still much higher than typical rates reported for conventional vertical beds. (C) 2000 Elsevier Science Ltd. All rights reser ved.