Implementing Hydrocyclones in Mainstream Process for Enhancing Biological Phosphorus Removal and Increasing Settleability through Aerobic Granulation.

Coupling physical selection with biological selection for the startup of a pilot-scale, continuous flow, aerobic granular sludge reactor without treatment interruption

“…If this more conventionally applied bioflocs-to-AGS transition setup were applied, the external physical selector would be the only driving force to transform flocculent sludge to AGS, and thus a much more radical biofloc washout type of short SRT would have to be employed ( Sun et al., 2019 ). Even with the sidestream hydrocyclone installation, only 5–7% of the RAS can be subjective to physical selection ( Avila et al., 2021 ; Partin, 2019 ; Regmi et al., 2022 ), leaving majority of the bioflocs and AGS unseparated in the RAS returned to the feast zone where bioflocs gain more growth advantage over AGS, which explains the slow startup period, e.g., one year, needed to observe sludge settleability improvement ( Ford et al., 2016 ; Kent et al., 2018 ; Roche et al., 2022 ; Welling et al., 2015 ; Wett et al., 2015 ).…”

“…Hydrocyclones have been employed to provide such a selection pressure; however, their relatively low hydraulic capacity (e.g., 120–3360 m 3 d − 1 ) limits their application in large systems to sidestream return activated sludge (RAS) where only a small portion, e.g., 5–7%, of the RAS flow can be processed for physical selection ( Avila et al., 2021 ; Partin, 2019 ; Regmi et al., 2022 ). This low strength selection pressure plus the high suspended solids content in RAS, e.g., 5000 mg L − 1 , compromised the physical selection efficiency of hydrocyclones for AGS ( Ford et al., 2016 ). As a result, a prolonged startup phase perhaps as long as a year was required to observe significant sludge settleability improvements in full-scale continuous flow reactors in which AGS formation is still a challenge ( Ford et al., 2016 ; Kent et al., 2018 ; Roche et al., 2022 ; Welling et al., 2015 ; Wett et al., 2015 ).…”

“…This low strength selection pressure plus the high suspended solids content in RAS, e.g., 5000 mg L − 1 , compromised the physical selection efficiency of hydrocyclones for AGS ( Ford et al., 2016 ). As a result, a prolonged startup phase perhaps as long as a year was required to observe significant sludge settleability improvements in full-scale continuous flow reactors in which AGS formation is still a challenge ( Ford et al., 2016 ; Kent et al., 2018 ; Roche et al., 2022 ; Welling et al., 2015 ; Wett et al., 2015 ). For this reason, an alternative strategy should be developed to provide sufficient selection strength to promote successful continuous flow AGS formation while maintaining the startup treatment performance required for large full-scale applications.…”

Enhancing bioflocculation in high-rate activated sludge improves effluent quality yet increases sensitivity to surface overflow rate

“…Physical selectors, like a screen or cyclone used for deammonification, could artificially increase the selection pressure on the sludge without jeopardizing effluent quality (Wett et al, 2015). There are indications that this holds true for selective retention of phosphate accumulating bacteria (Ford et al, 2016). However, further research will have to show the design and effectiveness of a physical selector for continuous HRAS applications.…”

Biological process architecture in continuous‐flow activated sludge by gravimetry: Controlling densified biomass form and function in a hybrid granule–floc process at Dijon WRRF, France

“…The first facility to implement the technology using hydrocyclones in continuous‐flow configuration was Strass in Austria in 2012 in an oxidation ditch process, with over 25 installations in the past 9 years in various other formats of continuous‐flow configurations, including continuous‐flow anaerobic‐anoxic‐oxic (A 2 O) configuration (Avila et al, 2021), anaerobic‐oxic (AO) simultaneous nitrification/denitrification (SND) configuration (Regmi et al, 2019), modified Ludzack‐Ettinger (MLE) configuration (An et al, 2021; Partin, 2019) integrated fixed‐film activated sludge (IFAS) four‐stage Bardenpho configuration (Ford et al, 2016; Partin, 2019), and membrane bioreactors (Noguchi et al, 2018; Zhuzbay et al, 2021). Despite this large diversity of installations, a detailed morphological transition of hydrocyclone based densification is missing, and opportunities for its control are needed.…”