Aerobic Granulation in a Sequencing Batch Reactor Using Real Domestic Wastewater

Aerobic granulation has been extensively investigated in recent decades but most researchers have focused their studies on granule formation in laboratory-scale reactors using synthetic wastewaters at high organic loading rates (OLR) ($\mathrm{OLR}>2.5\mathrm{kg}\mathrm{COD}·{\mathrm{m}}^{-3}·{\mathrm{d}}^{-1}$). This research studied the aerobic granulation in a sequencing batch reactor (SBR) using real domestic wastewater with an OLR at or lower than $2\mathrm{kg}\mathrm{COD}·{\mathrm{m}}^{-3}·{\mathrm{d}}^{-1}$. The reactor was operated in three different stages (Stage I, II, and III), according to the applied OLR (1.4, 1.0, and $2.0\mathrm{kg}\mathrm{COD}·{\mathrm{m}}^{-3}·{\mathrm{d}}^{-1}$, respectively). After 140 days of operation (Stage II), the reactor biomass consisted mainly of compact mature granules (average diameter of 0.7 mm) with a good settling ability ($\mathrm{SV}{\mathrm{I}}_{30}$ approximately $53\mathrm{mL}·{\mathrm{g}}^{-1}$). The OLR increase caused a partial disintegration of the mature granules during the beginning of Stage III. However, the granules were able to quickly recover after the disturbance caused by the higher OLR. The reactor was effective at removing carbon and nitrogen compounds, especially when operated with an OLR of $2\mathrm{kg}\mathrm{COD}·{\mathrm{m}}^{-3}·{\mathrm{d}}^{-1}$, providing an average removal efficiency of 92% for $\mathrm{CO}{\mathrm{D}}_{\mathrm{D}}$ and 96% for $\mathrm{N}{\mathrm{H}}_4^{+}–\mathrm{N}$. The results demonstrated that aerobic granules can be formed, using real domestic wastewater, with an effective carbon and nitrogen removal.