Abstract
The aerobic granular sludge (AGS) process is an effective wastewater treatment technology for organic matter and nutrient removal that has been introduced in the market rapidly. Until now, limited information is available on AGS regarding the removal of bacterial and viral pathogenic organisms present in sewage. This study focussed on determining the relation between reactor operational conditions (plug flow feeding, turbulent aeration and settling) and physical and biological mechanisms on removing two faecal surrogates, Escherichia coli and MS2 bacteriophages. Two AGS laboratory-scale systems were separately fed with influent spiked with 1.0 × 106 CFU/100 mL of E. coli and 1.3 × 108 PFU/100 mL of MS2 bacteriophages and followed during the different operational phases. The reactors contained only granular sludge and no flocculent sludge. Both systems showed reductions in the liquid phase of 0.3 Log10 during anaerobic feeding caused by a dilution factor and attachment of the organisms on the granules. Higher removal efficiencies were achieved during aeration, approximately 1 Log10 for E. coli and 0.6 Log10 for the MS2 bacteriophages caused mainly by predation. The 18S sequencing analysis revealed high operational taxonomic units (OTUs) of free-living protozoa genera Rhogostoma and Telotrochidium concerning the whole eukaryotic community. Attached ciliates propagated after the addition of the E. coli, an active contribution of the genera Epistylis, Vorticella, and Pseudovorticella was found when the reactor reached stability. In contrast, no significant growth of predators occurred when spiking the system with MS2 bacteriophages, indicating a low contribution of protozoa on the phage removal. Settling did not contribute to the removal of the studied bacterial and viral surrogates.
Highlights
The aerobic granular sludge (AGS) process has been shown to be an effective technology for wastewater treatment (Bengtsson et al, 2018; Nancharaiah and Kiran Kumar Reddy, 2018)
For the AGS_MS2 reactor average concentrations of 8 ± 9 mg NH4-N /L, 2 ± 2 mg NO2-N /L, and 0.6 ± 0.5 mg NO3-N /L were measured (Figure 2d and Figure 2f). It seems that copper from the feeding valve negatively affected the ammonia-oxidising bacteria community in the AGS_E. coli reactor
Since the behaviour of the N-conversion process was assumed not be influencing the removal of E. coli and MS2 bacteriophage the nitrification was not optimised
Summary
The aerobic granular sludge (AGS) process has been shown to be an effective technology for wastewater treatment (Bengtsson et al, 2018; Nancharaiah and Kiran Kumar Reddy, 2018). The biomass in the AGS system consists of agglomerated bacteria that simultaneously remove organic matter and nutrients (de Kreuk et al, 2007). The bacterial community in the granule consists of phosphate accumulating organisms (PAOs), ammonia-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB) (Winkler et al, 2013; Szabó et al, 2017). These bacterial groups are responsible for organic matter and nutrient removal. Full-scale AGS systems contain a large granular sludge and smaller flocculent sludge fraction (Ali et al, 2019)
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