Fe(III)/Fe(II) forwarding a new anammox-like process to remove high-concentration ammonium using nitrate as terminal electron acceptor.

The study demonstrated a novel anammox-like process to remove high-concentration ammonium using nitrate as terminal electron acceptor under Fe(III)/Fe(II) cycle. Compared with NO in common anammox, NO used here is more available in practice, suitable for in-situ removal of high-concentration NH in a single anaerobic system. The NO and Fe(II) produced from Feammox [Fe(III) reduction coupled to anaerobic ammonium oxidation] subsequently react together via NO-dependent Fe(II) oxidation to regenerate Fe(III) that potentially stimulates next round of Feammox. However, these processes couldn't be lasting due to inadequate Fe(III) regeneration because NO is non-dominant product during Feammox. In this study NO was added to supplement the insufficient NO to enhance Fe(III) regeneration and remove nitrogen successively. Results showed that periodically adding nitrate caused oscillations between Fe(III) and Fe(II) in the sludge, implying Fe(III) regeneration and consumption. Consequently, nitrogen removal of the digester with an initial total nitrogen of 1036.7 mg/L reached 90.1% after 98-day operation, much higher than that of control (41.6%) without NO addition. Adding NO in the digester to trigger Fe(III)/Fe(II) cycle for removing ammonium is just equivalent to an anammox-like process using NO as terminal electron acceptor to oxidize NH.