Removing nitrate and ammonium from drainage water by simulation of natural biological processes

Simultaneous denitrification and nitrification may exist in natural biological processes provided that there is an environment suitable for photosynthesis. To determine whether it is possible to remove both nitrate and ammonia from drainage water by natural biological processes, several batch experiments were conducted in some shallow plastic tanks simulating natural biological processes in laboratory. The experiments showed that simultaneous denitrification and nitrification was possible. A batch experiment in a dark environment confirmed the dependence of nitrification on photosynthesis, i.e., photosynthesis was a major oxygen source for nitrification. Nitrification could proceed even at very low dissolved oxygen concentrations (0.2-0.6 mg/l). Raw pig slurry was used as an external carbon source for denitrification, its high COD concentration led to complete denitrification. When fibrous carriers were packed into the tanks, biomass developed on them, improved the processes of both denitrification and nitrification. It is concluded that a water depth shallow enough for photosynthesis to occur is critical for nitrogen removal from drainage water by natural biological processes such as basins or ponds/lagoons. (C) 1998 Elsevier Science Ltd. All rights reserved.