Mainstream partial denitrification‐anammox in sand and expanded clay deep‐bed polishing filters under practical loading rates and backwashing conditions

Abstract

This study focused on evaluating the feasibility of expanded clay and sand as media types for mainstream partial denitrification‐anammox (PdNA) in deep‐bed single‐media polishing filters under nitrogen and solids loading rates as well as backwash conditions similar to conventional denitrification filters. The surface roughness and iron content of the expanded clay were hypothesized to allow for enhanced anammox retention, nitrogen removal rates, and runtimes. However, under the tested loading rates and backwash conditions, no clear benefit of expanded clay was observed compared with conventional sand. This study showed the feasibility of PdNA in filters with both sand and expanded clay with PdN efficiencies of 76% and 77%, PdNA rates of 840 and 843 g N/m3/d and TIN removal rates of 960 and 964 g N/m3/d, respectively. Glycerol demands were 1.5–1.6 g COD added per g TIN removed, thus indicating potential carbon savings up to 75% compared with conventional denitrification. Overall, this study showed for the first time PdNA filters performing at nitrogen removal rates double that of previous PdNA studies under realistic conditions while providing insights into the media choice and backwashing conditions. Future research on expanded clay backwash conditions is needed to provide its full potential in PdNA filters. Practitioner Points Hydraulic and TSS loading rates similar to conventional denitrification can be applied in PdNA filters. Conventional sand can be used when retrofitting conventional denitrification filters into PdNA filters. Carbon savings up to 75% can be achieved with glycerol when retrofitting conventional filters into PdNA filters

Partial denitrification–anammox (PdNA) application in mainstream IFAS configuration using raw fermentate as carbon source

“…In mainstream shortcut nitrogen removal systems, a recent study by Van Winckel et al (2019) emphasized the importance of anammox retention for success. One‐stage PdNA applications have been tested so far in MBBRs (Campolong et al, 2019; Gu et al, 2020; Ma et al, 2017) and downflow filters (Fofana, Chen, et al, 2021; Klaus, 2020; Ma et al, 2020; Young et al, 2021), but studies with an IFAS application under real wastewater conditions are limited or missing to the best of our knowledge. One of the benefits offered by an IFAS configuration is the ease and flexibility of implementation into new and existing systems.…”

Full‐scale transition from denitrification to partial denitrification–anammox (PdNA) in deep‐bed filters: Operational strategies for and benefits of PdNA implementation

“…Only one genus of AnAOB was found in the filters, Candidatus Brocadia, which has been frequently identified in PdNA systems (Cui et al, 2020; Du et al, 2019; Fofana, Huynh et al, 2022; Lu et al, 2021; Schoepflin et al, 2022; Wang et al, 2020; Wang, Xu et al, 2020; Zhan et al, 2020; Zheng, et al, 2020). The relative abundance of Candidatu s Brocadia (2–5%) obtained in the filters was significantly higher than other one‐stage PdNA filters (0.7–1.0%) (Cao et al, 2020; Lu et al, 2021), most likely due to the higher loading rates at full‐scale.…”

“…To maintain AnAOB activity during normal operation right after a backwash, sufficient methanol needs to be provided to decrease the DO and ensure that the top of the filters is fully anoxic while at the same time avoid methanol overdose. While there are early reports that methanol can be inhibitory to AnAOB (Güven et al, 2005;Isaka et al, 2008), recent experiences in methanol PdNA process has shown no anammox inhibition (Bachmann et al, 2021;Campolong et al, 2019;Fofana et al, 2021;Macmanus et al, under review) even under temporal methanol concentration of 200 mg COD/L (Campolong et al, 2019). However, avoiding methanol overdose is also important in order to maintain a consistent NO 3 À -N residual to encourage PdN.…”

“…Integrated refers to PdNA occurring within the mixed liquor in either a pre‐ or post‐anoxic zone of the biological nutrient removal (BNR) process with some mechanism for AnAOB retention (e.g., screens, hydrocyclones, or integrated fixed film activated sludge [IFAS]) (Ali et al, 2020; Bachmann et al, 2021; Cui et al, 2021; Ladipo‐Obasa et al, 2022; Le et al, 2019a). Polishing refers to PdNA occurring in a separate reactor downstream of secondary clarification such as in moving bed biofilm reactors (MBBRs) (Bachmann et al, 2021; Campolong et al, 2019; Schoepflin et al, 2022; Wang et al, 2020), sequencing batch reactors (Du et al, 2019; Sharp et al, 2017; Zhang et al, 2019), upflow anaerobic sludge blanket reactors (Du et al, 2019; Zhang et al, 2019), and deep‐bed filters (Cao et al, 2019; Cui et al, 2020; Fofana, Huynh et al, 2022; Lu et al, 2021; Ma et al, 2020).…”

“…PdN selection, often expressed as PdN efficiency or how efficiently NO 3 − ‐N reduction is halted at NO 2 − ‐N, is also dependent on the carbon source used. Carbon sources such as acetate or glycerol are very effective with PdN efficiencies in range of 75–95% (Campolong et al, 2019; Fofana, Huynh et al, 2022; Le et al, 2019b), while PdN efficiency decreases to 38–49% for fermentate (Ali et al, 2020; Ladipo‐Obasa et al, 2022) and about 49–71% for methanol (Campolong et al, 2019; Le et al, 2019b; Macmanus et al, under review). For the latter carbon sources, it was hypothesized that having a good NO 2 − ‐N sink by efficient AnAOB retention is critical to provide efficient PdNA (Ladipo‐Obasa et al, 2020; Riffat et al, 2021).…”