Characteristics of Biological Nitrogen Removal in a Multiple Anoxic and Aerobic Biological Nutrient Removal Process

Abstract

Two sequencing batch reactors, one with the conventional anoxic and aerobic (AO) process and the other with the multiple AO process, were operated to examine characteristics of biological nitrogen removal, especially of the multiple AO process. The long-term operation showed that the total nitrogen removal percentage of the multiple AO reactor was 38.7% higher than that of the AO reactor. In the multiple AO reactor, at the initial SBR cycle stage, due to the occurrence of simultaneous nitrification and denitrification, no nitrite and/or nitrate were accumulated. In the multiple AO reactor, activities of nitrite oxidizing bacteria were inhibited due to the multiple AO operating mode applied, resulting in the partial nitrification. Denitrifiers in the multiple AO reactor mainly utilized internal organic carbon for denitrification, and their activities were lower than those of denitrifiers in the AO reactor utilizing external organic carbon.

Nitrogen removal, nitrous oxide emission and microbial community in sequencing batch and continuous-flow intermittent aeration processes

“…Furthermore, the suppression of NOB in SBR systems was more remarkable (with relatively low r NOB /r AOB ratio) in comparison with CMR systems, especially in the presence of organics. The result was consistent with Wang et al [2], who demonstrated that the r NOB /r AOB ratio was 0.32 in the multiple AO SBR process, which was lower than 0.98 of the AO SBR process [2]. In the presence of organics, AOB activity was inhibited in sequencing batch biofilm reactors, where the r NOB /r AOB ratio was 0.21-1.08 without and 0.25-1.25 with the addition of organics [23].…”

“…The r NOB /r AOB ratio markedly reduced from 1.06-1.37 to 0.47-1.21 under DO of 1 mg/L and from 0.74-1.08 to 0.52-0.98 under DO of 2 mg/L. The balance between AOB and NOB could be destroyed in the presence of organic carbon, which might result in NO 2 -N accumulation in the intermittent aeration process [2]. With organics, competition for oxygen between heterotrophs and nitrifiers would be promoted, with the suppressed nitrifying activity [22].…”

“…The PHAs-type denitrification (with NO 2 -N) caused more N 2 O emission, likely due to the slow degradation rate of PHAs inducing the competition for electrons between denitrifying enzymes [23,31]. Denitrifiers of IASBR preferred to utilize PHAs for denitrification [2]. As a result, more N 2 O emission was observed for denitrifiers in SBR.…”

“…Alternative anoxic and aerobic (AO) conditions can be realized timely within one sequencing batch reactor (SBR) as the intermittent aeration SBR (IASBR) or spatially in sequential reactors as the multiple anoxic and aerobic process [1]. For examples, total inorganic nitrogen (TIN) removal percent-age in IASBR was 38.7% higher than in the AO SBR system [2]. In the intermittent aeration process, simultaneous nitrification and denitrification (SND) and denitrification with internal organic carbon could be enhanced [2].…”

“…For examples, total inorganic nitrogen (TIN) removal percent-age in IASBR was 38.7% higher than in the AO SBR system [2]. In the intermittent aeration process, simultaneous nitrification and denitrification (SND) and denitrification with internal organic carbon could be enhanced [2]. In addition, AOB stimulation and NOB inhibition were observed under transition from anoxic to aerobic conditions, inducing partial nitrification [3].…”