Biological nitrogen removal of high-strength ammonium industrial wastewater with two-sludge system

The biological nitrogen removal (BNR) process is the most common method for removing low quantities of ammonium from wastewater, but this is not the usual treatment for high-strength ammonium wastewater. The capacity to biologically remove the nitrogen content of a real industrial wastewater with a concentration of 5000 mg N-NH4+ L^-1 is demonstrated in this work. The experimental system used is based on a two-sludge system, with a nitrifying activated sludge and a denitrifying activated sludge. This system treated real industrial wastewater for 450 days, and during this period, it showed the capacity for oxidizing all the ammonium at average nitrification rates between 0.11 and 0.18 g N-NH4+ g VSS^-1 d^-1. Two key process parameters were evaluated: the maximum nitrification rate (MNR) and the maximum denitrification rate (MDR). MNR was determined in continuous operation at three different temperatures: 15°C, 20°C and 25°C, obtaining values of 0.10, 0.21 and 0.37 g N-NH4+ g VSS^-1 d^-1, respectively. Complete denitrification was achieved using two different industrial carbon sources, one containing mainly ethanol and the other one methanol. The MDR reached with ethanol (0.64 g N-NOx- g VSS^-1 d^-1) was about 6 times higher than the MDR reached with methanol (0.11 g N-NOx- g VSS^-1 d^-1).