Nitrous oxide generation in denitrifying phosphorus removal process: main causes and control measures

Abstract

Despite the many benefits of denitrifying phosphorus removal process, the significant generation of nitrous oxide (N2O), a potent greenhouse gas, remains a problem for this innovative and promising process. To better understand and more effectively control N2O generation in denitrifying phosphorus removal process, batch experiments were carried out to investigate the main causes of N2O generation, based on which the control measures were subsequently proposed. The results showed that N2O generation accounted for 0.41 % of the total nitrogen removal in denitrifying phosphorus removal process, whereas, in contrast, almost no N2O was generated in conventional denitrification process. It was further demonstrated that the weak competition of N2O reductase for electrons and the high nitrite accumulation were the two main causes for N2O generation, evidenced by N2O production and reduction rates under different conditions. Accordingly, the reduction of N2O generation was successfully achieved via two control measures: (1) the use of continuous nitrate addition reducing N2O generation by around 91.4 % and (2) the use of propionate as the carbon source reducing N2O generation by around 69.8 %.

Nitrous oxide emission depending on the type of electron acceptor by a denitrifying phosphorus removal sludge

“…In the study of Oehmen et al (2010), similar phenomenon was also reported but was not emphasized. However, the phenomenon was different from other previous studies in DNPAO systems, where during the anoxic phase, denitrification of nitrate was accompanied with the nitrite accumulation (such as Li et al, 2013b andWang et al, 2011a). , while the NOx-N reduction rate was around 6.0 mg g VSS -1 h -1 under all conditions.…”

“…The last reason could be due to the competetion among the denitrifying reductases. Li et al (2013b) obtained that N2O generation accounted for 0.41% of the total nitrogen removal in denitrifying phosphorus removal process and the weak competition of N2O reductase for electrons and the high nitrite accumulation were the two main reasons causing N2O generation. The same group also obtained that N2O emission increased with increasing the organic carbon concentrations, which could be due to that a high concentration of organic carbon induced a high production of PHA and consequently a high concentration of accumulated nitrite (Li et al 2013a).…”

“…The reason could be due to that the utilization rate of PHB was slow, which might cause a carbon limitation condition and induce a high N2O emission (Meyer et al, 2005;Wang et al, 2011b;Zhou et al, 2013). In addition, during denitrification, a high accumulation of nitrite may also induce N2O emission, especially when denitrifying activities were inhibited (Li et al, 2013b;Zhou et al, 2008;Wang et al, 2011a). Wu et al (2013) obtained that when PHB was used as the organic carbon for denitrification, a high N2O emission occurred when nitrite was coexisted.…”

Influence of organic shock loads on the production of N2O in denitrifying phosphorus removal process

“…The main reason for the high N 2 O production during this period was that DPAOs use PHA as a carbon source for denitrification. Compared with the external carbon source, the rate of PHA degradation is slow, which cannot provide enough electrons for the requirement of denitrifying enzymes, and N 2 O reductase has a weak competition for electrons (Kampschreur et al, 2009;Li et al, 2013a). As a result, N 2 O reduction will be inhibited.…”

Nutrients removal and nitrous oxide emission during simultaneous nitrification, denitrification, and phosphorus removal process: effect of iron

“…Moreover, it was reported that iron could induce N 2 O emission by enhancing the chemical denitrification pathway (Kampschreur et al 2011). Under lowoxygen condition of SNDPR system, N 2 O can be produced by many biochemical processes, such as heterotrophic denitrification, nitrifier denitrification, and denitrifying phosphorus removal processes (Jia et al 2013;Li et al 2013). The interactions of iron cycle and nutrient cycle are different to soil ecosystem.…”