Abstract:
Simultaneous nitrification and aerobic denitrification (SNaD) is a preferred method for single
stage total nitrogen (TN) removal, which was recently proposed to improve wastewater treatment
plant design. However, SNaD processes are prone to inhibition by toxicant loading with free cyanide
(FCN) possessing the highest inhibitory effect on such processes, rendering these processes ineffective.
Despite the best efforts of regulators to limit toxicant disposal into municipal wastewater sewage
systems (MWSSs), FCN still enters MWSSs through various pathways; hence, it has been suggested
that FCN resistant or tolerant microorganisms be utilized for processes such as SNaD. To mitigate
toxicant loading, organisms in SNaD have been observed to adopt a diauxic growth strategy to
sequentially degrade FCN during primary growth and subsequently degrade TN during the secondary
growth phase. However, FCN degrading microorganisms are not widely used for SNaD in MWSSs
due to inadequate application of suitable microorganisms (Chromobacterium violaceum, Pseudomonas
aeruginosa, Thiobacillus denitrificans, Rhodospirillum palustris, Klebsiella pneumoniae, and Alcaligenes
faecalis) commonly used in single-stage SNaD. This review expatiates the biological remedial strategy
to limit the inhibition of SNaD by FCN through the use of FCN degrading or resistant microorganisms.
The use of FCN degrading or resistant microorganisms for SNaD is a cost-effective method compared
to the use of other methods of FCN removal prior to TN removal, as they involve multi-stage systems
(as currently observed in MWSSs). The use of FCN degrading microorganisms, particularly when
used as a consortium, presents a promising and sustainable resolution to mitigate inhibitory effects of
FCN in SNaD.
