Investigation of a basic nitrification-denitrification biofiltration system for primary wastewater treatment

The study aimed to eliminate the nitrogen and its main residual forms from municipal wastewater by using a biofilter system adapted for a small community. The biological nitrification/denitrification system used involved two successive PVC columns; a first gravel column (C1) loaded with primary wastewater followed by a second sandy column (C2). A complex biofilm development on the gravel and sand materials has been confirmed by scanning electron microscope. The efficiency of chemical oxygen demand (COD), BOD5, TSS, and NH4+-N removal from primary wastewater reached 75.3, 88.4, 83.5, and 88.1%, respectively, at the exit of the sandy column (C2). Inoculation with activated sludge as an external carbon source allowed an improvement in the nitrate removal, from 80 to 28 mg/l N-NO3. However, sludge inoculation showed non-significant fecal coliforms and Streptococcus contamination, and the biofilter appeared as effective for total nitrogen removal and a bacterial abatement of over 3.2 U-log10. The average bacterial removal seemed directly related to the applied load of about 50 cm/day and a tertiary disinfection treatment, such as UV-C254 irradiation, is needed as a preventive step to ensure the removal of pathogens.