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

A two-stage non-conventional bench scale biological treatment system was investigated for the treatment of the wastewater laden with ammonium nitrate. The first stage which consisted of a fixed film anoxic reactor effected denitrification of nitrate ion, while the second stage consisting of a pond effected ammonia removal. Dissimilatory denitrification requires external carbon source as an electron donor. Methanol was used as electron donor in this system. The system exhibited substantial nitrate and ammonia removal. The 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 presence of significant populations of denitrifying organisms in the first stage, and denitrifying, nitrifying and algal populations in the second stage. The system also sustained wastewater of pH as low as 3.87 and appears to be very promising for larger scale industrial wastewater treatment.[PUBLICATION ABSTRACT]