Correlation between nitrous oxide (N2O) emission and carbon to nitrogen (COD/N) ratio in denitrification process: a mitigation strategy to decrease greenhouse gas emission and cost of operation

Abstract

The reliability and accuracy of in-situ ion selective electrode and ultraviolet (NO) probes have been investigated at four different treatment plants with different operational conditions. This study shows that the mentioned probes tend to compromise their accuracy and trending stability at lower NO of <1.0 mg N/L, which if used as a measuring variable for PI feedback controller for denitrification (biological reduction of nitrate to nitrogen gas), would cause overfeeding the external carbon source. In-situ Clark-type NO sensors, recently introduced for industrial scale use (Unisense Environment) could potentially open a new horizon in the automation of biological processes and particularly denitrification. To demonstrate the applicability of such probes for automation, two in-situ NO probes were used in two treatment plants in parallel with NO-N probes. The effects of operational conditions such as COD/N ratios and the correlation between NO and NO were investigated at those plants. NO production at non-detect dissolved oxygen concentrations and pH of 7-7.2 were found to be a function of influent nitrogen load or the ratio of COD/N. Finally, using an NO probe as a proxy sensor for nitrates is proposed as a measured variable in the PI feedback in the automation of the denitrification process with a NO set point of <1.2 mg N/L).

Enhancing Nitrate Removal from Waters with Low Organic Carbon Concentration Using a Bioelectrochemical System—A Pilot-Scale Study

“…This means that lower N2O fluxes from the MES could have been caused by the electric enhancement and most of the NO3‾ was completely denitrified to nitrogen gas. Previous work has also shown that less N2O is emitted during denitrification when more electron donors are present [25]. The rise in NH 4 + concentration was presumably caused by the DNRA and ammonification, as stated previously, and was most probably used in the anammox process until the 22nd day, when the concentration dropped below the detection range in both reactors [44].…”

“…This means that lower N 2 O fluxes from the MES could have been caused by the electric enhancement and most of the NO 3 − was completely denitrified to nitrogen gas. Previous work has also shown that less N 2 O is emitted during denitrification when more electron donors are present [25].…”

“…As O2 can inhibit the denitrification process above concentrations of 0.5 mg O2 L −1 , the DO concentration was monitored [10]. The MES showed significantly lower DO concentrations compared During the experiment, the DOC was measured to ensure that the MES did not have a higher DOC/N ratio than the control reactor, as organic carbon compounds are used for heterotrophic denitrification [25,35]. As shown in Figure 6A, the MES had a significantly lower DOC concentration compared to the control reactor at 15.2 and 19.9 mg C L −1 , which indicates that the organic carbon concentration could not have been the reason why nitrogen removal efficiency was better in the MES.…”

“…Inorganic carbon, such as carbonate or carbon dioxide (CO 2 ), is used as a carbon source [23,24]. Depending on the availability of electron donors, the intermediate compounds such as nitrite (NO 2 − ) or nitrous oxide (N 2 O) can start to accumulate, causing the inhibition of denitrification or increased release of GHGs respectively [25].…”

Effects of partially saturated conditions on the metabolically active microbiome and on nitrogen removal in vertical subsurface flow constructed wetlands

“…emissions have not been monitored in the present study, combining data from online N2O sensors with the functional expression of NDN-based genes could contribute to the implementation of more sustainable nitrogen removal technologies in urban wastewater treatment (Andalib et al, 2018).…”