1Department Environment, Water and Earth Sciences, Tshwane University of Technology, Nelson Mandela Drive 175, Arcadia, South Africa
2Department of Biotechnology and Food Technology, Tshwane University of Technology, Nelson Mandela Drive 175, Arcadia, South Africa
Abstract
No on-site sanitation system treats both urine and faecal matter in one process. A laboratory scale biological filter was fed with high concentration of urea (4 g N/L) and 17.1 g COD/L to determine if it will be possible to treat liquid that leach from a ventilated improved pit latrine. The HLR in the proposed biological filter system was calculated to be ca 36 L/m2/d, significantly lower than the rates that are typical applied in standard rate biological filters (in the range of 1000 – 4000 L/m2/d) used to treat domestic wastewater. However, the TKN and COD concentrations in standard rate biological filters are significantly lower, namely ca 60 mg N/L and 500 mg COD/L, compared to the typical nitrogen and COD concentrations of faecal sludge, namely 3 - 5 g N/L and 20 – 50 g COD/L, respectively. The biological filter was operated at 13.0, 23.9, 35.7 and 62.3 L/m2/d, until stable state conditions were obtained. It was possible to remove most of the nitrogen and COD at the applied hydraulic loading rates by a combination of volatilization, nitrification and de-nitrification processes. However, at 62.3 L/m2/d the column efficiency (1.5 m long column) decreased and ammonia concentration in the effluent increased again. The best performance was achieved at a hydraulic loading rate of 35.7 L/m2/d, with an average ammonia concentration of 285.5 (± 9.1) mg N/L.
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