Abstract
ABSTRACT This study aimed to verify if coal ash, a residue from thermal power plants, could act as a granulation nucleus, cations source, and abrasive element to favor granules formation and stability in aerobic granular sludge (AGS) systems. Two simultaneous fill/draw sequencing batch reactors (SBRs) (R1 and R2) were operated with 6-h cycles, i.e., the filling and drawing phases occurred simultaneously, followed by the reaction and settling phases. R1 was maintained as control, while R2 was supplemented with coal ash (1 g·L-1) on the first day of operation. Granulation was achieved in both reactors, and no significant differences were observed in terms of settleability, biomass retention, morphology, resistance to shear, and composition of the EPS matrix. However, the ash addition did not change the settleability, biomass retention, granule morphology, shear resistance, and extracellular polymeric substances (EPS) content significantly. COD removal was high (≥ 90%), while nitrogen (~50%) and phosphorus (~40%) removals were low, possibly due to the presence of nitrate during the anaerobic phase. With granulation, microbial population profile was altered, mainly at the genus level. In general, the operational conditions had a more considerable influence over granulation than the ash addition. The possible reasons are because the ash supplementation was performed in a single step, the low sedimentation rate of this particular residue, and the weak interaction between the ash and the EPS formed in the granular sludge. These factors appear to have decreased or prevented the action of the ash as granulation nucleus, source of cations, and abrasive element.
Highlights
Aerobic granulation is a process through which microorganisms self-immobilize due to the influence of several selection pressures, such as short settling times and high aeration intensity (ROLLEMBERG et al, 2018)
The mature granules showed sludge volume index at 30 min (SVI30) between 30 and 80 mL·g-1, which corresponds to the variation reported in aerobic granular sludge (AGS) literature for both conventional and simultaneous fill/draw sequencing batch reactors (SBRs)
Granulation was achieved in simultaneous fill/draw SBR operated with low upflow velocity
Summary
Aerobic granulation is a process through which microorganisms (mainly bacteria) self-immobilize due to the influence of several selection pressures, such as short settling times and high aeration intensity (ROLLEMBERG et al, 2018). Researches have been conducted on simultaneous fill/draw SBR, known as constant-volume SBR (DERLON et al, 2016; WANG, Q. et al, 2018). These studies are still incipient, even though the majority of full-scale AGS systems are operated in such a manner, e.g., the Nereda® technology (NEREDA, 2017)
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