Investigation of partial and full nitrification characteristics of fertilizer wastewaters in a submerged biofilm reactor

Abstract

Nitrification characteristics of a high-strength fertilizer wastewater were studied in an upflow submerged biofilm reactor. The aim was the investigation of nitrogen removal rates with regard to ammonium removal and the determination of NOx-N production rates in terms of nitrile build-up and nitrate production. For this purpose the biofilm reactor was operated at various loading rates and DO levels. The system could reach high ammonium removal rates up to about 0.6 kgNH4-Nm−3d−1 (13.2 gNH4-Nm−2d−1). In a number of runs nitrification was incomplete and nitrite reached a considerable level. One of the most important factors for nitrite build-up was the relative ratio of bulk oxygen to bulk ammonium. More important than this was the ratio of bulk oxygen to bulk free ammonia. When this ratio was lower than 10, nitrite was the dominant species in the produced NOx-N. Also the increase in volumetric loading rate generally led to an increase in nitrite production. Thus, in order to achieve partial nitrification, free ammonia inhibition can be enhanced by operating at relatively low DO, high bulk ammonium and high bulk pH values. The main inhibition in the treatment of these wastes was substrate inhibition at indicated operating conditions. Since the concentration of free nitrous acid was very low, product inhibition could be disregarded.