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This study removes two technical constraints for transitioning full-scale activated sludge infrastructure to continuous flow, aerobic granular sludge (AGS) facilities. The first of these is the loss of treatment capacity as a result of the rapid washout of flocculent sludge inventory and in turn the potential loss of nitrification during initial AGS reactor startup. The second is the physical selector design which currently is limited to either the complex sequencing batch reactor selection or sidestream hydrocyclones. Briefly, real wastewater data collected from this study suggested that by increasing the surface overflow rate (SOR) of an upflow clarifier to 10 m h - 1, the clarifier can be taken advantage of as a physical selector to separate flocculant sludge from AGS. Redirecting the physical selector underflow and overflow sludge to the feast and famine zones of a treatment train, respectively, can create a biological selection that not only promotes AGS formation but also safeguards the effluent quality throughout the AGS reactor startup period. This study provides a novel concept for economically implementing continuous flow AGS within existing full-scale, continuous flow treatment trains.

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Plug flow reactors (PFRs) made of multiple completely stirred tank reactors (CSTRs) in series were used to cultivate aerobic granules in real domestic wastewater. Theoretically, changing the number of CSTR chambers in series will change the nature of plug flow, and thus alter the pattern of the feast/famine condition and impact the aerobic granulation progress. Therefore, PFRs were operated in 4-, 6-, and 8-chamber mode under the same gravity selection pressure (a critical settling velocity of 9.75 m h-1) and hydraulic retention time (6.5 h) until steady states were reached to evaluate the effect of the feast/famine condition on continuous flow aerobic granulation. The sludge particle size, circularity, settleability, specific gravity, zone settling velocity, and extracellular polymeric substance contents were analyzed to evaluate the role that a feast/famine regime plays in aerobic granulation. It was found that aerobic granulation failed whenever the feast/famine ratio was greater than 0.5. The results support a conclusion that the feast/famine condition is likely a prerequisite for continuous flow aerobic granulation.

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Plug flow reactors (PFRs) approximated by the connection of multiple completely stirred tank reactors (CSTRs) in series were used to achieve continuous flow aerobic granulation in real domestic wastewater. This study revealed, possibly for the first time, that the morphology and characteristics of aerobic granular sludge transformed in the course of a mixed liquor flow through a PFR. The feast zone, located at the front end of the PFR, can quickly develop filamentous structure on the surface of aerobic granular sludge which later disappeared in the famine zone at the back end of the PFR. Detention time from the front to the back end of the PFR was only 6.5 h. During this period the observed sludge morphological change led to sludge settleability fluctuation as much as 66% in zone settling velocity, 16% in specific gravity, and 40% in settled sludge volume. Further analysis revealed these types of sludge morphologies and characteristics were closely related to the specific substrate removal rate profiles of the PFR, i.e., the feast zone might have encouraged filamentous bacteria to extend outward into the bulk solution for soluble substrate, and the famine zone appeared to play an essential role in solidifying the structure of granular sludge structure prior to subjecting it to the gravity selection pressure. It can be inferred from this study that the lack of a famine zone in aerobic granulation reactors can loosen the granule structure and in turn deteriorate granule settleability. For a PFR, a famine zone following the feast zone is essential for maintaining the structural integrity of aerobic granular sludge in a continuous flow wastewater treatment system.

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Although granular activated carbon (GAC) has been broadly applied in ozone-biologically activated carbon filtration (O3/BAC) systems for potable reuse of municipal wastewater, the mechanisms of various pollutant removal remain largely unknown as the regenerated GAC develops microbial populations resulting in biofiltration but loses significant adsorption capacity as it becomes spent GAC. Therefore, pilot-scale parallel performance comparisons of spent and regenerated GAC, along with a range of pre-oxidant ozone doses, were used to shed light on the mechanisms responsible for the removal of various types of treatment byproduct precursors and trace organic compounds. It was confirmed from this pilot-study that ozone alone can effectively degrade chlorinated trihalomethane (THM) and haloacetic acid (HAA) precursors, chloramine-reactive N-nitrosodimethylamine (NDMA) precursors, and 29 PPCPs. In contrast, biodegradation by microbial population on spent or regenerated GAC can remove NDMA and 22 PPCPs, while the adsorption by regenerated GAC can remove chlorinated THM and HAA precursors, PFAS, flame retardants, and 27 PPCPs. The results of this pilot study are intended to provide those interested in potable reuse with an example of the simultaneous removal capabilities and mechanisms that can be anticipated for treating a complex mixture of organics present in real municipal wastewater effluent.

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