A two-stage biological treatment system for ammonium-nitrate-laden wastewater

A two-stage non-conventional bench scale biological treatment system was in vestigated for the treatment of the wastewater laden with ammonium nitrate. The first stage which consisted of a fixed film anoxic reactor effected de nitrification of nitrate ion, while the second stage consisting of a pond e ffected ammonia removal. Dissimilatory denitrification requires external ca rbon source as an electron donor. Methanol was used as electron donor in th is system. The system exhibited substantial nitrate and ammonia removal. Th e influent nitrate-N concentration which was on average 193.87 +/- 12.68 mg /l was reduced to 5.86 +/- 4.86 mg/l in the denitrification unit. There was only a marginal reduction of ammonia in the denitrification unit and most of the ammonia-N was removed in the pond. The ammonia-N was reduced from an average value of 104.87 +/- 3.49 mg/l at denitrification unit inlet to 33. 37 +/- 8.12 mg/l at the pond outlet. There was no corresponding increase in the nitrite or nitrate concentration in proportion to ammonia reduction in the pond. The average nitrate concentration in the pond outlet was 2.4 +/- 0.93 mg/l. Microbiological investigation of the system revealed the presen ce of significant populations of denitrifying organisms in the first stage, and denitrifying, nitrifying and algal populations in the second stage. Th e system also sustained wastewater of pH as low as 3.87 and appears to be v ery promising for larger scale industrial wastewater treatment.