Several industrial processes such as petroleum refinement, coal tar processing, petrochemicals and resins production release wastewaters containing both, ammonium and phenolic compounds. The presence of phenolic compounds in these industrial wastewaters could advise for expensive physic-chemical treatments due to the potential inhibitory or toxic effects over a biological treatment. Nevertheless, there is no doubt that biological nitrogen removal (BNR) via nitrite: (i) full nitritation plus heterotrophic denitritation and (ii) partial nitritation plus Anammox, could be regarded as the technologies with the cheapest costs and the lowest environmental foot-print available nowadays for treating ammonium-rich wastewaters. However, phenolics compounds are recognised as inhibitors of both, nitritation and anammox processes. Therefore, the development of a BNR via nitrite process with a high removal capacity for both nitrogen and phenolic compounds would be a significant improvement in the current state-of-the-art.
The possible technological options could be: (i) a two-sludge system composed by a first full nitritation reactor followed by a denitrifying reactor or (ii) a two-sludge system composed by a first partial nitritation reactor followed by an Anammox reactor. In both cases, the nitritation reactor should guarantee an effluent suitable for the subsequent denitrifying or Anammox stage, i.e. an effluent with 100% of nitrite or a nitrite/ammonium ratio around one and without phenolic compounds. Granular biomass reactors are considered a robust alternative for the treatment of wastewaters containing inhibitory or toxic organic compounds. The diffusion gradients existing in aerobic granules could contribute to reduce the inhibitory effect of these compounds protecting sensitive bacteria. The development of aerobic granules is commonly achieved through SBRs by applying short settling times and high shear stress. However, conventional batch operation is not advisable for the treatment of recalcitrant compounds, and alternative strategies like distributed feeding along the SBR cycle have been proposed to minimize substrate inhibition. Continuous reactor operation avoids this drawback since the bulk liquid concentration of the recalcitrant compound in the reactor is expected to be low if the removal efficiency is high, therefore, mitigating the toxic effects over the biomass.
Currently, we are developing aerobic granular reactors at bench scale able to perform simultaneously partial or full nitritation and removal of phenolic compounds (phenol, cresol, nitrophenol, quinoline) from high-strengh industrial wastewaters. Moreover, we are developing anoxic UASB reactors able to denitrify from nitrite with phenol as sole organic carbon source. In the future, we expect to develop Anammox reactors able to work with industrial influents containing low concentration of phenolic compounds.