Nitrogen transformations in an aerated lagoon treating piggery wastes

Effluents from anaerobic lagoons were treated in two parallel aerated lagoons, at variable organic load and hydraulic residence time. The removal of total Kjeldahl nitrogen (TKN) was found to increase rapidly at higher TKN food to microorganisms (F/M) ratios. At BOD F/M ratios below 0·6 kg kg⁻¹ day⁻¹ nitrification manifested itself through accumulation of oxidised forms of nitrogen. The apparent decrease in denitrification, evidenced by nitrites and nitrates present at these loads, can be attributed to an inadequate supply of easily available carbon as electron donor. Accumulation of nitrites at lower loads (higher residence times) might have been due to free nitrous acid toxicity to the Nitrobacter species. A maximum TKN removal of 50% was achieved at TKN F/M = 0·5, which corresponded to a BOD/TKN ratio of 3·4.