Granulation of activated sludge in a laboratory upflow sludge blanket reactor

The creation of anoxic granulated biomass has been monitored in a laboratory USB (Upflow Sludge Blanket) reactor with the volume of 3.6 L. The objective of this research was to verify the possibilities of post-denitrification of residual NO3-N concentrations in treated wastewater (denitrification of 10-20 mg L−1 NO3-N) and to determine the maximum hydraulic and mass loading of the granulated biomass reactor. G-phase from biodiesel production and methanol were both tested as external organic denitrification substrates. The ratio of the organic substrate COD to NO3-N was 6. Only methanol was proven as a suitable organic substrate for this kind of reactor. However, the biomass adaptation to the substrate took over a week. The cultivation of anoxic granulated biomass was reached at hydraulic loading of over 0.35 m h−1. The size of granules was smaller when compared with results found and described in literary reports (granules up to 1 mm); however, settling properties were excellent and denitrification was deemed suitable for the USB reactor. Sludge volume indexes of granules ranged from 35-50 mL g−1 and settling rates reached 11 m h−1. Maximum hydraulic and mass loadings in the USB reactor were 0.95 m3 m−2 h−1 and 6.6 kg m−3 d−1. At higher loading levels, a wash-out of the biomass occurred.