Application of Diauxic Growth for Treatment of Total Nitrogen and Free Cyanide in Wastewater Treatment

Abstract

Treatment of Nitrogen containing wastewater have gained more attention in the previous years ever since it was shown to poses severe complications to aquatic life (Ge et al., 2015; Duan et al., 2015). Thus, there are standard in place to ensure that this type of water is treated before it is disposed. The conventional methods used for removing total nitrogenous compounds in wastewater treatment plants (WWTP) is biological treatment which is highly efficient and cost effective compared to other methods. Biological processes consist of nitrification followed by denitrification (Shoda & Ishikawa, 2014). Nitrification is known to be a sensitive method to organic matter (Joo et al., 2005), being inhibited by spent caustic soda, cyanides (CN- ), heavy metals, sulphides, sodium chloride and other substances, with free cyanide (FCN- ) being reported to possess highest toxicity effect towards nitrification and denitrification (Wild et al., 1994). It affects respiratory system of the microbial population, however, it is biodegradable and some microorganisms are able to use it as nitrogen source (Inglezakis et al., 2017). The inhibition effect of FCNtowards nitrification and denitrification have been eradicated by addition of activated carbon which absorb FCN- , nevertheless, this method does not have significant effect on FCNdue to low absorption ability of activated carbon to FCN - , furthermore, this results in additional cost (Han et al., 2013). Hence, WWTP evolved from sole COD removal to simultaneous COD removal (Leyva-Díaz et al., 2015). Simultaneous COD removal is as the result of microbial ability to grow on multiple substrates, these phenomena is known as dauxic growth, and this is an important phenomena in biological wastewater treatment since biological oxygen demand may be composed of different carbon sources. However diauxic growth have only been studied in multiple carbon sources and have never been explored in multiple nitrogenous source, thus this study investigate application of diauxic growth phenomena into total removal of nitrogen in cyanide containing samples in order to mitigate the inhibitory effect of cyanide towards nitrification and denitrification.