Role of Hydrodynamic Shear in the Oxygenic Photogranule (OPG) Wastewater Treatment Process

Abstract

The role of hydrodynamic shear in the oxygenic photogranule (OPG) wastewater treatment process was investigated in three sequencing batch reactors (SBRs) operated under different shear conditions for 250 days. Mixing in Reactor 1, Reactor 2, and Reactor 3 was set at 50, 100, and 250 rpm, which induced theoretical shear stresses (τ) of 0.015, 0.04, and 0.14 N/m2, respectively. As shear increased, we observed significant increases in the relative abundance of filamentous cyanobacteria, the key microbial group for OPG granulation. Additionally, increasing hydrodynamic shear force in OPG reactors stimulated linearly increased production of extracellular polymeric substances (EPSs). Compared to high shear, photogranules produced at low shear were more spherical and much larger in size and, thus, contributed to higher total nitrogen removal through denitrification, a potential legacy of limited oxygen transfer in their structure. On the contrary, the smaller photogranules produced under high shear promoted better oxidation processes and, thus, higher removal of tCOD and NH4 + due to their higher oxygen production capabilities compared to the larger photogranules. Hydrodynamic shear can be manipulated to drive photogranulation toward desired size distribution and, thus, achieve specific treatment goals in the OPG wastewater treatment process.

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“…The low DO concentration, increasing granular size (Fig. S2), and short oxic time may favor denitrification in the AGS systems (Abouhend et al, 2023;He et al, 2018b;Mosquera-Corral et al, 2005) probably accounting for simultaneous nitrification and denitrification in the present system. On the other hand, the DOC concentrations during the illumination phase were statistically (p < 0.05) higher than those under the mechanical aeration condition (Fig.…”

Water quality indicators influencing the formation and morphology of hydrostatically-formed photogranules

“…The scale parameter, l, represents the characteristic strength at which 63.2% of the material will have failed. Eqn (6) illustrates the regression line between ln(−ln(1 − F(x))) and ln(x i ), but the corresponding Fi for each independent variable x i is yet to be determined. To address this, the mean rank method, which considers the relationship between the rank of experimental data point i and the total number of all data points n, is employed using the following equation: 26…”

“…[1][2][3][4] OPGs offer a unique approach to wastewater treatment by functioning without the need for mechanical aeration, which is currently the most energyintensive process in wastewater treatment operations. 2,[5][6][7] OPGs achieve wastewater treatment through a synergistic combination of biological and physical processes facilitated by their diverse microbial community. 1,2,6 The phototrophic microorganisms with OPGs, such as cyanobacteria and green algae, utilize sunlight in photosynthesis to produce oxygen as a byproduct, improving dissolved oxygen levels in the wastewater.…”

“…2,[5][6][7] OPGs achieve wastewater treatment through a synergistic combination of biological and physical processes facilitated by their diverse microbial community. 1,2,6 The phototrophic microorganisms with OPGs, such as cyanobacteria and green algae, utilize sunlight in photosynthesis to produce oxygen as a byproduct, improving dissolved oxygen levels in the wastewater. 8 This oxygenation supports aerobic microbial activities, including organic matter degradation and pollutant transformation.…”

“…1,2,14 The primary distinguishing factor between these granule types is their size. 1,2,6,14 The production of hydrostatic photogranules involves the transformation of activated sludge batches into photogranules under hydrostatic batch conditions with the presence of light. [1][2][3][4]15 This transformation occurs through the enrichment of the phototrophic community within the sludge biomass, resulting in approximately 50% phototrophic content.…”