Model-based evaluation of mechanisms and benefits of mainstream shortcut nitrogen removal processes

Self Cite

Despite the increased research efforts, full-scale implementation of shortcut nitrogen removal strategies has been challenged by the lack of consistent nitrite-oxidizing bacteria out-selection. This paper proposes an alternative path using partial denitrification (PdN) selection coupled with anaerobic ammonium-oxidizing bacteria (AnAOB). A nitrate residual concentration (>2 mg N/L) was identified as the crucial factor for metabolic PdN selection using acetate as a carbon source, unlike the COD/N ratio which was often suggested. Therefore, a novel and simple acetate dosing control strategy based on maintaining a nitrate concentration was tested in the absence and presence of AnAOB, achieving PdN efficiencies above 80%. The metabolic-based PdN selection allowed for flexibility to move between PdN and full denitrification when required to meet effluent nitrate levels. Due to the independence of this strategy on species selection and management of nitrite competition, this novel approach will guarantee nitrite availability for AnAOB under mainstream conditions unlike shortcut nitrogen removal approaches based on NOB out-selection. Overall, a COD addition of only 2.2 g COD/g TIN removed was needed for the PdN-AnAOB concept showing its potential for significant savings in external carbon source needs to meet low TIN effluent concentrations making this concept a competitive alternative. • Practitioner points• Nitrate residual is the key control parameter for partial denitrification selection. • Metabolic selection allowed for flexibility of moving from partial to full denitrification. • 2.2 g COD/g TIN removed was needed for partial denitrification-anammox process.

Section: Discussionmentioning

confidence: 99%

Nitrate residual as a key parameter to efficiently control partial denitrification coupling with anammox

Peng

et al. 2019

Self Cite

“…Additional SRT control might be needed when working with glycerol to better manage the denitrifier population while separately managing the AnAOB mass. AnAOB can be selectively enhanced and retained within systems through daily bioaugmentation from sidestream deammonification systems (Al‐Omari et al., ) or proper retention mechanism such as cyclones (Wett et al., ) or screens (Han, Vlaeminck et al., ). In our study, the retention of AnAOB might not have been high enough to allow for lower nitrite levels in the glycerol reactor.…”

Section: Discussionmentioning

confidence: 99%

“…Despite a remarkable success of sidestream shortcut nitrogen processes treating high ammonia strength water, mainstream implementation is currently under development and facing several challenges. One of these challenges is out‐selecting nitrite‐oxidizing bacteria (NOB), which requires maintaining NH4 + ‐N residual concentration of 1–2 mg N/L (Al‐Omari et al., ; Han et al., ; Regmi et al., ). As a result, implementation of either of these two processes can be problematic to WWTPs which practice stringent limits on NH4 + ‐N of <1 mg N/L or total inorganic nitrogen (TIN) discharge limit of 3–5 mg TIN/L.…”

Section: Introductionmentioning

confidence: 99%

Impact of carbon source and COD/N on the concurrent operation of partial denitrification and anammox

Peng

et al. 2019

Self Cite

In this study, concurrent operation of anammox and partial denitrification within a nonacclimated mixed culture system was proposed. The impact of carbon sources (acetate, glycerol, methanol, and ethanol) and COD/NO3 − -N ratio on partial denitrification selection under both short-and long-term operations were investigated. Results from short-term testing showed that all carbon sources supported partial denitrification. However, acetate and glycerol were preferred due to their display of efficient partial denitrification selection, which may be related to their different electron transport pathways in comparison with methanol. Long-term operation confirmed results of batch tests by showing the contribution of partial denitrification to nitrate removal above 90% after acclimation in both acetate and glycerol reactors. In contrast, methanol showed challenges of maintaining efficient partial denitrification. COD/NO3 − -N ratio mainly controlled the rate of nitrate reduction and not directly partial denitrification selection; thus, it should be used to balance between denitrification rate and anammox rate. © 2018 Water Environment Federation • Practitioner points• The authors aimed to investigate the impact of carbon sources and COD/NO3 − -N ratio on partial denitrification selection. • All the carbon sources supported partial denitrification as long as the nitrite sink was available. • 90% partial denitrification could be achieved with both acetate and glycerol in long-term operations. • COD/NO3 − -N ratio did not directly control partial denitrification but can be used to balance between denitrification rate and anammox rate.

“…The secondary treatment was a high-rate activated sludge system (1 to 2 days of sludge retention time) focused on the removal of organics; (2) Biological-Nitrogen Removal (BNR) sludge was obtained from the Blue Plains tertiary treatment process operated at an aerobic SRT of 10 to 15 days, which received methanol as external carbon source. This flocculant system has shown good settling properties over the years, resulting in reliable effluent quality (Table 1); (3) Mainstream sludge was obtained from a mainstream deammonification pilot plant at Blue Plains (Al-Omari et al, 2015). This pilot simulated the BNR system at Blue Plains with the difference that an aggressive aerobic SRT (1 to 5 days) was used under transient anoxia and anammox granules were bioaugmented.…”

Section: Methodsmentioning

confidence: 99%

Novel Stokesian Metrics that Quantify Collision Efficiency, Floc Strength, and Discrete Settling Behavior

Mancell-Egala

Clippeleir

et al. 2017

Self Cite

Novel parameters were developed to predict the effluent quality and settling behavior in clarifiers that cannot conventionally be achieved using either the conventional flux theory or overflow rates. Simple batch experiments based on the critical settling velocity (CSV) selection were used as the basis for the development of three novel parameters: intrinsic settling classes (ISC), threshold of flocculation/flocculation limitation (TOF/α), and floc strength. ISC was proven to accurately (±2%) determine the granule fraction and discrete particle distribution. TOF quantified the minimum solids concentration needed to form large flocs and was directly linked to collision efficiency. In hybrid systems, an exponential fitting on a CSV matrix was proposed to quantify the collision efficiency of flocs (α). Shear studies were conducted to quantify floc strength. The methods were applied to a wide spectrum of sludge types to show the broad applicability and sensitivity of the novel methods.