Complete autotrophic process for nitrogen removal from inkjet printing wastewater

Lab-scale results on the treatability of ammonium-rich wastewater from textile digital printing highlight the feasibility of an innovative biological process, based on purely autotrophic bacterial populations: ammonium oxidising bacteria (AOB) and anaerobic ammonium oxidisers (AAO). Activity of AOB has been measured through pH/DO-stat titration and that of AAO has been assessed through manometric tests, on raw mixed wastewater coming from textile-print factories (0.5 to 0-6 gN/L as ammonium nitrogen). AOB activity showed a reduction of 20-40% if compared with maximum activity on a synthetic medium. AAO activity tests showed a residual specific maximum anammox activity (SAA) of 0.1-0.4 gN2-N/gVSS/d, 40-60% of the control values obtained with synthetic wastewater. Activity tests confirmed treatability of the textile wastewater by AAO. Tests have been performed also on concentrated wastewater (2 to 3 gN/L as ammonium nitrogen) from the first rinsing bath. In this case, strong inhibition (between 80 and 100%) of anammox activity was observed. Careful operation of a continuous-flow completely mixed bioreactor can overcome this drawback, as pH and effluent ammonium concentration in the reactor are controlled.