Nitrogen removal from wastewaters at low C/N ratios with ammonium and acetate as electron donors

A denitrifying upflow anaerobic sludge blanket (UASB) reactor was operated at different nitrate loading rates at a C/N ratio of 1.2, with acetate as a n electron donor. This resulted in an increase in the accumulation of nitri te. After this, the UASB reactor was supplemented with 100 mg NH4+-N l(-1) d(-1), while acetate was gradually limited in the medium. This prevented ni trite accumulation at a CM ratio of 0.6 due to an enhanced nitrite reductio n rate achieved in the reactor. An increasing amount of ammonium was consum ed when the CIN ratio was lowered in the medium. This suggested that ammoni um was used as an alternative electron donor during denitrification, which is supported by nitrogen balances. Nitrite was shown to be toxic for the ni trogen removal process at 200-400 mg NO2--N l(-1) when the CM ratio was dec reased to 0.4 leading to formation of ammonium. The present study showed th at addition of ammonium as an alternative electron donor for denitrificatio n achieved a nitrogen removal process with negligible accumulation of undes irable intermediates. (C) 2001 Elsevier Science Ltd. All rights reserved.