Aerobic granulation with petrochemical wastewater in a sequencing batch reactor under different operating conditions

Abstract

The aim of this study was to define the best operating conditions for the successful start-up of a granular sludge sequencing batch reactor (GSBR) treating petrochemical wastewater (PW) produced by the integrated gasification combined cycle and characterized by high NH4+-N concentration (up to 630 mg/L). Two different start-up strategies were applied during Phases A and B, using different shear forces, inoculum source and pH. The GSBR was fed with a mixture of synthetic medium and real wastewater, and a readily degradable growth substrate (i.e. sodium acetate) was supplied in order to maintain the volumetric organic loading rate at 3 g COD/L d: the share of PW in the influent was gradually increased, depending on the observed reactor performance. In Phase A, aerobic granules irreversibly deteriorated when the share of PW in the influent was increased to 30%. Conversely, a faster and more stable granulation was observed during Phase B, likely due to the higher superficial gas velocity applied (i.e. harsher conditions) and the different sludge used as inoculum (already acclimated to toxic substances): under such conditions, the synthetic medium was completely replaced by the PW. The observed total organic carbon removal efficiencies were similar in Phases A and B (92 ± 6–94 ± 2%, respectively), while NH4+-N removal efficiency was higher during Phase B (up to 78% when PW% was 100%). The inoculum with acclimated sludge and the harsher selective pressure (Phase B) were proved to speed up the formation of compact and well settling granules, more resistant to the increase of PW share in the influent

Aerobic granular sludge formation in a sequencing batch reactor treating agro-industrial digestate

“…were comparable with those achieved in previous studies with simulated and real industrial wastewaters [17,[29][30][31], landfill leachates [11,32] and different anaerobic digestates: in particular, Cydzik-Kwiatkowska et al [14] reported SVI 5 values within the range of 25-30 mL g TSS −1 in a GSBR treating diluted and undiluted anaerobic digester supernatant at different cycle lengths (6, 8, 12 h); Świątczak et al [6] reported SVI of about 50 mL g MLSS −1…”

“…The highest FA concentration measured in our GSBR at the beginning of the cycle was approximately 5 mg N L −1 . However, no significant NOB inhibition was observed, likely due to the occurrence of different factors like prolonged biomass exposure to high ammonium (and FA) concentrations which may have favoured NOB acclimation; the granular layered structure, which may have preserved NOB from relatively high FA concentrations in the bulk liquid due to diffusion limitation, as previously observed with other toxic and inhibiting compounds [17,29,38]; a drop of initial FA concentration due to biomass activity and air stripping, which may have reduced its inhibiting potential.…”