Improving the effluent quality of facultative stabilization ponds by means of submerged aerated biofilters

This paper describes the use of a submerged aerated biofilter (BF) in the tertiary treatment of effluent from facultative stabilization ponds(FSP). The results, obtained over four months of tests, confirm the ability of the BF to remove algae and, principally, to achieve tertiary nitrification. For hydraulic loading rates of 2m3/m2.h, the mean efficiency of the process in the removal of algae (SS) and COD was 58% and 63% respectively. Concentrations above 70 mg SS/1 and 195 mg O2/1 (GOD) in the effluent from the ponds was reduced to 30 mg SS/1 and 70 mg O2/1 (GOD) in the effluent from the BF. In addition to the removal of organic forms of nitrogen and phosphorus, the biofilter also reaches the soluble COD and ammonia. Tertiary nitrification was achieved with a mean efficiency of 86% for volumetric loads of up to 0.7 kg N-NH4+/m3.day (27 degrees C). For concentrations above 20 mg n-NH4+/1 in the feed, the process can produce with safety effluents with less than 1 mg N-NH4+/1. The period of operation between the 2 successive washings of the bed filter was in the order of three days. Copyright (C) 1996 IAWQ.