ADAPTING DATA FROM AERATED BIOLOGICAL FILTERS TO DESIGN UNAERATED RECIRCULATING SAND FILTERS FOR CARBON AND NITROGEN REMOVAL FOR WASTEWATER TREATMENT IN DEVELOPING ECONOMIES Thor Young and John Brinkley – Stearns & Wheler, LLC * Dipankar Sen – Santa Clara Valley Water Authority Marty Johnson and Chip Yaniga – Anne Arundel County, Maryland Redouane Choukr-Allah, Institut Agronomique et Vétérinaire Hassan II Ramzi Sabella – United States Agency for International Development Mohammed Mansour – Water Authority of Jordan Joseph Karam – ECODIT, Inc. * Stearns & Wheler, LLC 16701 Melford Boulevard, Suite 330 Bowie, MD 20715 ABSTRACT In developing economies such as Morocco, nearly 70% of all of the wastewater treatment plants are not functioning due to lack of spare parts and poor cost recovery (USEPA, September 2004). Intermittent and recirculating sand filters offer a treatment technology with minimal electro- mechanical components and low operating costs, which is advantageous to sustainable wastewater treatment for developing economies. When properly designed with the correct nitrification kinetics and operated to prevent accumulation of excess biofilm biomass within the filters, such systems can achieve a high degree of nitrification. The use of recirculating sand filters in conjunction with low-maintenance, low-cost technologies provide an affordable treatment system for nitrogen removal with beneficial opportunities. Chemical Oxygen Demand (COD) removal and nitrification rates were determined from converting unaerated recirculating sand filter (U-RSF) to an aerated recirculating sand filter (A- RSF) for full-scale installations in the U.S. and abroad. These rates were adapted to design U- RSFs for carbon removal and nitrification at additional wastewater treatment facilities in developing economies. The COD removal and nitrification rates achieved in an U-RSF filter which was overloaded were successfully increased with aeration to reduce effluent ammonium-N levels from a range of 10 to 20 mg/L to less than 1 mg/L. The differences in COD removal and nitrification kinetics observed during unaerated and aerated conditions were studied and applied to the design of U-RSFs for nitrogen removal in Morocco and Jordan. Upflow biological aerated filters (BAFs) with periodic backwashing, such as Infilco Degremont’s Biofor ® and Kruger’s Biostyr ® , can achieve simultaneous carbon removal and nitrification, with rates of 1 kg/m 3 /d at liquid temperatures of 12 to 15 o C, when the influent soluble biodegradable COD is less than 20 mg/L. These conditions typically exist downstream of a first-stage COD removal system, such as an activated sludge or fixed-film biological treatment system. The nitrification rate achieved in an A-RSF operating without backwash was lower, averaging 0.5 kg/m 3 /d at temperatures of 10 to 22 C. For U-RSFs installed without aeration systems in developing economies, the only means of aerating the biofilm is by raking the filter 1052 Nutrient Removal 2007 Copyright ©2007 Water Environment Federation. All Rights Reserved